Cells

 

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  1. Cells 2.1. Signs of Life

Humans, animals and plants are similar in that they consist of microscopically small building blocks called cells. Every living thing consists of cells. The bigger it is, the more cells it has. The cells are actually not bigger per se, the being simply consists of more cells – or multiple cells.

The body of an adult human consists roughly of 10, 000, 000, 000, 000 - 100, 000, 000, 000, 000 cells, whereby each second many millions of those cells die and are replaced via the process of cell division.

The size of human cells lies between 1 and 150 μm. 150 μm is the size of a woman’s egg cell, which can be recognised by the naked eye. μ is a Greek letter and stands for micro or small, fine, etc. In mathematics μ stands for the factor of 10-6. So 1 μm is one millionth of a metre or one thousandth of a millimetre.

Cells can merge with one another. The length of a muscle cell in the musculoskeletal structure can be up to 15-20 centimetres long. Nerve cells can build cellular projections, which can reach up to one metre in length. Cells have different shapes and forms. They can be round, spindle form, smooth, cubic or cylindrical. The most common cell type is the red blood cell.

Even though cells can have different sizes and appearances, the basic structure is always the same: they consist of a cell body and a cell nucleus.

There are living beings that consist out of only one cell.

The body is made up of not only cells but more specifically out of cells and bodily fluids, such as blood plasma, lymph, gall, spinal and intercellular fluid as well as mucous and secretions.

The body is therefore made up of:

Cells Bodily Fluids Blood plasma Lymphatic fluid Gall fluid Intercellular fluid Brain and spinal cord Secretions Mucous

One can imagine that an organism is just a sequential package of single cells, which are bathed in interstitial fluid. Interstitial fluid originates out of the blood and has the task of caring for the cell.

As you can see in the image below, nutrients exit the blood capillaries and float in the intercellular space, which is filled with intercellular fluid. They then make their way over to the cell, give it a service. In response the cell excretes any waste into the intercellular fluid , which is drawn back into the blood capillary and transported away.

2.1.1 Cell Composition

When you investigate out of what chemical elements a cell is made, you will find that there is no difference between animate and inanimate matter.

The following percentages of chemical elements are found in a cell:

O – Oxygen – 65% C – Carbon – 18% H – Hydrogen – 10% N – Nitrogen – 3% Ca – Calcium – 2% P – Phosphorus – 1%

In addition, small amounts of the following are also found: Potassium (K), Sulphur (S), Chlorine (Cl), Sodium (Na), Magnesium (Mg) and Iron (Fe).

Chlorine is often called Chloride. But this is incorrect according to the world of chemistry. Chloride is the salt of hydrochloric acid (Hcl). The most well known of these salts is household salt or NaCl.

Most of these elements are found in compound form in the body. For example, the element Chloride is a yellowish-green, corrosive gas, which is unfortunately used as a weapon. To have something such as this in its purest form in the body would be terrible.

2.1.2 Signs of Life

Even though living organisms and inanimate matter share the same chemical elements, there are certain phenomena that differentiate the living from the dead. These are the so-called Signs of Life. They include:

Metabolism – is a collection of all of the chemical reactions in the body. There are two different processes recognisable under Metabolism: catabolic and anabolic. Catabolic metabolism is the breaking down of substances, whereas anabolic metabolism is the building up of substances. This is where crude raw materials are used to create complex physical building blocks. Regeneration and Reproduction – these are achieved via cell division, out of which two identical daughter cells are created. Growth – is achieved via cell enlargement and cell multiplication. Arousal – by this we mean that the human body is ready to communicate with its environment. For this to be possible the body must possess receptor cells, which react according to specific arousal thresholds. The eye has receptor cells for receiving light impulses, the ear has receptor cells to receive sound waves. Once the receptor threshold has been met, an electrical impulse is let loose which follows the nerve fibres to the brain. This is where consciousness of sensory arousal takes place. Conductivity – Rub two stones together and a reaction is instantly released from the point of friction. In a similar case, the human body would react as a whole. Movement – Movement can show that a cell can move forwards as a whole, as in the case of phagocytes that move towards a site of infection. But also some kinds of bacteria, which consist of only a single cell, can move forward as cilia. On the other hand there are also immovable bacteria which do not possess locomotion, but which still represent movement as currents in the inner cell body. Adaptibility – the living being is able to (within limits) blend in with its surroundings. The ability of bacteria to encapsulate itself when it senses danger is just one example. The colour changes of chameleons is also an example, as well as heart enlargement (hypertrophy). This takes place when the heart must take on an increased amount of work. Acclimatisation is also a part of this process, and is otherwise known as evolutionary selection or survival of the fittest. Those who adapt, survive.

Paramecium are living organisms which consist of a single cell. However, there are living organisms which consist of more cells, such as humans, plants and animals.

Paramecium are micro-organisms which can be found in great supply in pools. As you can see in the image, the paramecium consists of a mouth, with cilia that assist in the collection of nutrients. Nutrients are then ingested and metabolised. Substances that are critical to the regeneration and growth of the paramecium are carefully selected and valued. Whatever is invaluable is excreted out of its behind. A paramecium can be divided into anterior and posterior parts. The anterior part is extremely sensitive. Defense rods live here, which in emergency cases can be rolled out.

You can also see that even though the paramecium is a single cell organism it shows multi-cellular behaviour. It can take over specific tasks that affect the entire body.

2.2 Cell Composition and Function

Composition A cell consists of two main parts: a body and a nucleus.

The cell nucleus or core is separated from the body by a nucleus membrane (Nucleolemma). The cell body is surrounded by its own cell membrane (Plasmalemma) which keeps it separate to the outside world. These kinds of membrane construction are analogue in nature.

Cell body = cytoplasma Cell core = nucleus Cell membrane = plasmalemma Core membrane = nucleolemma

Even though human cells basically consist of a cell body and cell nucleus, cells can manifest in a number of different forms and sizes.

Muscle cells (fasciated) Sperm cells Bone cells Cartilage cells Nerve cells

Most cells in the body are only a few millimetres long. But there are of course larger cells available, such as the cells of fasciated musculature (15-20 cm) and nerve cells e.g. nervus ischiadicus (ischias nerve) which is over one metre long. Some cell nuclei are also different. There are human cells which multiple cell nuclei, such as fasciated muscle cells, bone resorption (break down) cells e.g. oestoclasts. Liver cells also comprise multiple cell nuclei (most 2), as these cells have a wide variety of tasks to perform.

In contrast, there are also cells which possess no cell nucleus. Red blood cells do not possess a core which is why they are not able to reproduce or divide and have a lifespan of 120 days, after which they are decomposed in the spleen, liver or medulla.

Basic Structure of a Cell The contents of a cell (protoplasma) can be divided into a cell body (cytoplasma) and a cell nucleus (nucleoplasma).

Cytoplasma / Cell plasma – work and storage area Nucleoplasma / Core plasma – command central consisting of genetic information encrypted into chromosomes

Plasma is the liquid in which cell organelles as well as the cell nucleus are found. In the cytoplasma substances are dissolved e.g. calcium, magnesium, chlorine; and also stored e.g. glycogen (storage form of glucose).

Cell Plasma: This is the work and storage area of the cell, in which cell organelles are found. Cell organelles are mini organs. They each have a specific task in the cell, comparable to the function of the organs in the human body. Work area means that tasks such as the production of protein is done. Storage area means that substances that the cell needs to perform its duties are stored. For example amino acids are stored for the production of protein, small fat droplets and glycogen are stored for energy production. Cell Nucleus: Is the command central of the cell. Genetic information is saved and stored in the chromosomes. This is otherwise known as the blueprint of life. Not only is information about appearance and design of the body saved here, but also the blueprint of every single required protein, such as the composition of hormones and enzymes. 2.2.1 Cell Membrane (Plasmalemma)

The cell and nucleus membranes have a similar structure. They consist of a double layer of lipids. The individual fat molecules have a water loving head (outer position) and water fearing tail (inner position). As you can see in the image, the tails are surrounded by the heads.

Between these fat molecules are so-called carriers, which transport much needed substances through the cell membrane. Carriers brings the required substance from the outside of the cell, through the fat layer and deposits it in the inside of the cell. Waste, which the cell no longer requires, follows the reverse route.

Basically, there are two different possibilities as to how substances are transported through the cell membrane:

Active Transport – needs energy which is supplied by the carrier Passive Transport – uses no energy but instead filtration, diffusion and osmotic processes to transport substances through the cellular membrane. 2.2.2 Cell Body

The cell body is the so-called work and storage area, where hormones and enzymes are produced and released. To perform this task the cell requires specific cell organelles. These will now be explained.

Mitochondria – the energy supply of the cell. Energy is stocked up and released so that the work of the cell can be done. Ribosomes – consist of RNA (ribonucleic acid) and makes protein production possible. Smooth Endoplasmic Reticulum – transports substances inside the cell. This can be found in fasciated musculature and in cells that produce the steroid hormone. Rough Endoplasmic Reticulum – is populated by ribosomes on its exterior and therefore serves in the production of substance transport and protein production. Golgi Apparatus – involved in the production of secretions, the storage of protein and the transport of these in vesicles through the cell membrane. It protects the cell from aggressive substances that it may build itself and which could damage the cell e.g. decomposing protein enzyme. Lysosomes – consist of a decomposing protein enzyme. They are found in phagocytes or scavanger cells. Centriole – responsible for the building of the spindle apparatus and cell division. Microtubules – a scaffolding system that supports the building of the cell skeleton. They play an important role in intracellular transport inside nerve cells. 2.2.3 Cell Nucleus

The cell nucleus is the command central of the cell and it alone decides who does and what work needs to be done inside the cell body. Apart from this it is here that genetic information is imprinted into the chromosomes and therefore each cell nucleus contains the complete genetic information (DNA code) about the individual.

Also imprinted into the chromosomes is the information about the assembly of each individual protein, hormone and enzyme. It is here that one can find out if the genetic code is for a flea, crocodile or human being. Or whether the code is for a blond-haired, blue-eyed woman or a dark-haired, brown-eyed man. If the above mentioned genetic information is to be built, then the commands given by the cell nucleus to the cell body must be error-free. Finally, if new cells are created, the exact same genetic information must be copied and saved on every new cell.

2.2.3.1 Composition of the Cell Nucleus

Inside each cell nucleus is a viscous liquid (caryolymph) in which nucleoli and chromosomes are found. The whole contents of the cell nucleus are called caryoplasma.

Nucleus plasma – comprises of a protein rich liquid. Chromsomes live here. It maintains and holds the form of the nucleus with a reverse pressure against the cell body. Nucleoli – have the task of building and storing RNA. In human cells there are at least 1-3 (up to 10) nucleoli. Chromosomes – are the carriers of genetic information. As soon as the cell goes into work mode, the chromosomes change into chromatin, which is its uncoiled DNA form. During cell division DNA and chromosomes typically take on their clothes peg form.

For a certain time, a specific form of DNA exists inside the nucleus either as coiled chromosomes or uncoiled chromatin.

2.2.3.2 Chromosomes (Genetic Information)

Chromosomes are actually the carriers of genes. In every human cell there are 46 chromosomes or 23 pairs, of which 22 pairs are autosome (identical pairs) and 1 sex chromosome (the so-called gonosome). The autosome pairs correspond in regards to their size, form and necking (centromere) and are numbered according to their size.

As far as the sex chromosomes go, men have a combination of XY and women have a combination of XX. A mature egg and sperm cell consist however of only half of the genome. They consist of only 23 chromosomes (hapolid set) and not of 46 chromosomes (diploid set). But when the egg and sperm cells merge, the fertilised cell will consist of a complete set of 46 chromosomes.

Every chromosome consists of two identical halves of chromatin. These are connected by a centromere, a kind of binding cord. The chromosomes are the carrier of genes.

DNA and Genes Genes lie linearly in rows on chromosomes. Genes essentially consist of DNA (deoxyribonucleic acid).

Composition of DNA

Nucleic bases

C = Cytosine G = Guanine A = Adenine T = Thymine

As you can see in the image, DNA looks a bit like a ladder (Watson-Crick Model). This ladder formation, better said a double helix, is wound into a spiral. When the cell is in work mode, the spiral unfolds, opening the genetic information up so that RNA can copy it.

As soon as the cell starts to divide, the double helix starts to spiral intensively. The advantage here is that less room is required but the disadvantage is that genetic information is harder to access thereby closing off the possibility for the cell to perform its work. This means that upon cell division, any special tasks, such as the production of hormones, can no longer be performed.

The sides of the ladder consist of a sugar and phosphate group. The rungs are each composed of two nucleic bases, which are connected by a hydrogen bond. Added to this are the pairs of Cytosin and Guanine, and Adenine with Thymine. The sequence of the nucleic bases represent the genetic code alphabet. Their sequence determine the composition of proteins. The letters of the genetic code alphabet are built by so-called triplets. These are a sequence of nucleic bases which represent a specific amino acid.

RNA serves as a copy of DNA (m-RNA = messenger RNA). The nucleic base Thymine is here replaced by Uracil. Other than this, RNA is an important transport medium (t-RNA = transfer-RNA) for amino acids, which are delivered to ribosomes.

Below is a comparison of the special features of RNA and DNA:

DNA	RNA Sugar	Deoxyribose	Ribose Nucleic base	Adenine, cytosine, guanine, thymine	Adenine, cytosine, guanine, uracil Task	Carrier of genetic information	Copy of DNA (m-RNA)


Transport medium of amino acids (t-RNA) 2.2.3.3 Protein Production (Protein Synthesis)

A protein is an assembly of amino acids, very small building blocks. So when someone talks about a protein, they mean at least 100 amino acids placed tightly together.

To make protein synthesis possible, the appropriate DNA location on the chromosome is activated and opened so that building instructions for a specific protein are made available. This is where RNA arrives and offers itself as messenger and go-between, copying the necessary information. The RNA copy leaves the nucleus and enters the cell body, where it attaches itself to a ribosome. The t-RNA which was attached to the m-RNA delivers the required building info. This is possible because nucleic bases only fit together as pairs. As you can see in the diagram the t-RNA consists of triplets. The corresponding amino acid is attached to the t-RNA. As soon as the protein is built, it detaches itself from the RNA and transports over to its required location. Normally, the different t-RNA triplets are found ready to go in the cell plasma. They are stocked up here so that the production of amino acids can be quickly done.

2.3 Cell Division and Gender Determination

Cell division is a process that can take several hours to perform. The cell body divides itself via the process of fragmentation. The cell divides itself in two. Each new cell is only half the size of the original. The division of the cells organelles is random. After the completion of cell division, each new cell produces the cell organelles that it needs and requires during the growth phase. Parallel to the fragmentation of the cell is the division of the cell nucleus (mitosis). Mitosis follows a specific schema so that it can assure that the genetic information is stored error-free in the daughter cell. There are five different stages in cell division.

2.3.1 Mitosis

Interphase Chromosomes change into chromatin. This means the chromosomes are uncoiled and the cell is at work. Even hormones can be made at this time.

Prophase The chromosome spirals progressively and it is possible to see this as fine fibres. The nucleus membrane dissolves. The centriole builds a spindel apparatus. The focus here is protein structure, which is built on both ends of the cell. The RNA-rich nucleoli also dissolve.

Metaphase The spindle apparatus is now complete and the chromosomes attach together with the centromere to the equator of the cell.

Anaphase Every chromatid moves to the opposite pole.

Telophase The spindle apparatus dissolves and a new cell nucleus is built. The chromosomes uncoil so that they can start work in the new cell. This is when the interphase restarts and the genetic information is doubled in anticipation of the next division.

An easy way of remembering these phases is to use the following:

I – Interphase (start engine) P – Prophase (scaffolding/dissolution) M – Metaphase (equator) A – Anaphase (polarisation) T – Telophase (new nucleus) 2.3.2 Meiosis

During meiosis the diploid chromosome set from 46 chromosomes is reduced to haploid set of 23 chromosomes. This takes place in the female egg and the male sperm. The process is reversed when the egg and sperm merge.

2.3.3 Gender Determination

Every male cell consists of the sex chromosome combination of XY and every female cell the XX combination. As a result of maturation (meiosis) each female egg cell has 22 autosomes and only one X chromosome. In contrast, each male sperm cell has 22 autosomes and either one X or one Y chromosome. Depending on which sperm fertilises the egg, there will be a gonosome combination of XX or XY. The combination XX produces a girl and the combination XY produces a boy. As you can see it is the man who decides the gender of the baby.

2.4. Chromosome Abnormality

Sometimes not everything goes well. Chromosome abnormalities focus on the abnormality of a chromosomes number or form. The cause of this abnormality can be traced back to an error during maturation. It can happen that a newly built cell either has too many chromosomes or too few. For example, Trisomy (Down Syndrome) occurs when there are three instances of chromosome 21 instead of two. Cells with missing chromosomes as a rule do not survive. Chromosomes with a missing X chromosome do have a chance of survival and this is known as Turner Syndrome.

2.4.1 Trisomy 21

Trisomy 21 is also called Down Syndrome. The chances of it affecting a child increases with the age of the mother. The following is true for Down Syndrome:

Defective organs Organs and tissue grow slower and age faster Growth deficit of the inner organs, 51% of Down Syndrome patients suffer from a heart problem Intellectually challenged/disabled Increased infantilism

Other Characteristics

Small head Back of the skull is flattened Almond-shaped eyes with epicanthal eyelid folds Increased spacing between the eyes Widened bridge of the nose Base of the nose sunken Ears quite deep on the head (smaller) Mouth is usually open, tongue is quite large due to diminished muscle tonus Increased saliva Hands are small and wide, with folds Fingers are shorter, pinky finger curves in Distance between first and second toe is increased 2.4.2 Klinefelter Syndrome

Only men are affected by this abnormality. The cause is an oversupply of X chromosomes, so that there exists an XXY sex chromosome combination instead of XY. Sometimes this can be XXXY, XXXXY, or XXXYY.

The following symptoms are possible:

Testicular Hypoplasia (hypoplasia). Hypoplasia is the underdevelopment of organs. Here the testicles are underdeveloped. This results in a lessened or absent sperm production. Most sufferers are infertile because of this. Excessive tallness is caused by the delayed closure of the long bone growth plates. Gynecomastia (enlargement of the breast glands) Osteoporosis

The therapy that is most applied and used in the treatment of Klinefelter Syndrome is testosterone replacement. This helps the patient to control their outer appearance so that it does not cause concern.

2.4.3 Turner Syndrome

Turner Syndrome affects women. The X chromosome is missing. Sex chromosome combinations of X0 occur instead of XX. Turner Syndrome is the only case where even though a chromosome is missing the chances of survival are good. However most fetuses die (98%) in the first three months of pregnancy.

Symptoms of untreated Turner Syndrome:

Sexual Infantilism. This is where the secondary female gender characteristics are absent. This is due to a lack of estrogen, which is caused by missing ovaries. These often only appear as connective tissue strands. However with estrogen replacement it is possible to develop the secondary female gender characteristics. Absent Menstruation. Caused by lack of hormones. Hormone replacement leads to the regulation of menstruation, however, infertility remains as a result of absent folicles in the ovaries. Underdevelopment. Quite often the body height is only 1.45 cm. Abnormal Inner Organs. Especially the heart and aorta, kidneys, skeleton and urether.

A possible therapy is after the fourth year, growth hormones are administered to help undergrowth. However, despite this, a normal height cannot be achieved. Normally around the 12th year estrogen is given so that the secondary gender characteristics can develop, especially breasts. Later, progesteron is given so that a regular menstruation can start. This is needed to keep the uterus healthy.

2.4.4 Filtration, Diffusion, Osmosis 2.4.4.1 Filtration

Filtration means the release of solid particles of a particular size through a filter. A good example of this is a coffee filter: larger particles stay in the filter, whereas water and dissolved particles pass through the filter. The human body also has its own examples of filtration. An example was already given in the first book about the Fundamentals of health science: substance exchange through capillary walls.

Dissolved substances such as nutrients and blood cells flow through the blood stream. Blood vessels branch out into smaller vessels down to the smallest capillaries. This is where substances are exchanged. Nutrients flow through the capillary walls, which act as a filter, into the inter cellular zone. Meanwhile blood proteins and blood cells remain in the capillaries as they are too big to pass through the filter.

Analogously this also takes place at the cell membrane. Small water molecules pass through the cell membrane, while larger particles remain behind. Recall that water molecules can pass through the cell membrane one of two ways:

Semi permeable: The cell wall is half permeable. Small substances can pass through the cell membrane via filtration. No energy is required for this to happen. Selective permeability: The cell decides which substance it will allow through the wall and assigns a specific carrier to do the job. Energy is required for this to happen.

Now we have seen how small substances can pass through the capillary walls. The same scenario plays out at the cell membrane. Small substances can also pass through the cell membrane, but not too large substances. If the cell wants to have larger particles pass through into the inner cell, then carrier molecules will bring these into the cell via active transport.

2.4.4.2 Diffusion

Diffusion is a physical equalising process, where exchange and movement occurs (mixing of two substances of different concentrations) based on the goal of equalisation. For example, where particles of a high concentration move to an area of low concentration. Particles (liquid, gases) have a certain ego-motion which are influenced by temperature, pressure and concentration of the corresponding particle. This ego-motion ensures that the particles are thrown together and through this bounce off one another to move away from each other. If the concentration is high, then they continue bouncing off one another until they find a place where the concentration is balanced.

Example: Thermic influence of migration velocity Imagine that you place an ice cube made of milk into a glass of lukewarm water. As long as the ice cube remains frozen, the two substances water and milk remain separate (high concentration difference). As soon as the ice cube melts, the two substances start to mix. This continues until the two become one (no concentration difference anymore).

Diffusion is the driving force behind mass distribution between the cell – the between cell space – capillaries. This results in the passive distribution of nutrient and waste substances in this area.

Another example: Put some sugar into a glass and fill it with tea. Now leave the glass alone for a while (without stirring it). After a while the sugar dissolves and becomes equally distributed with the tea. This happens faster the hotter the tea is. This means that the ego-motion is dependent on the temperature: the higher the temperature, the bigger the ego-motion.

2.4.4.3 Osmosis

Note: remember that when substance passes through a wall of some sort, filtration, osmosis and diffusion all play an equal role. These three processes cannot be separated. Osmosis is a kind of diffusion through a semi permeable wall. A semi permeable wall is like a filter, it allows small particles to pass through and large particles to stay behind.

Example 1: Place a plunger with a semi permeable membrane in a tub of water. The filter will allow small water molecules to pass through. How high does the water rise in the plunger? Naturally as high as the water is in the tub, as there is no substance concentration difference between the tub and the plunger.

Example 2: In this example, the water and protein molecules in the tub and plunger are equally distributed. How high does the water in the plunger rise? Once again, it rises as high as the water in the tub, as the same phenomenon is experienced here.

Example 3: In this example the plunger has a semi permeable wall on the bottom only, which allows the water molecules to pass through but not the protein molecules. How high does the water rise in the plunger? The water will rise much higher in the plunger as seen in the previous examples.

Why? The water molecules in the tub diffuse in the plunger as a way of producing a concentration equalisation. The driving force of osmosis is therefore the concentration discrepancy. Water will fill in the plunger until a concentration equalisation is achieved, e.g. until both contain the same amount of protein molecules.

Osmosis diffuses the small molecules in the solution which have a stronger concentration of large molecules and will be watered down. Osmotic pressure is the prevailing elevated pressure of the intensively concentrated solution.

Wikipedia: The osmotic pressure is defined to be the pressure required to maintain an equilibrium, with no net movement of solvent. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity.

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  1. Was ist eine Zelle?

Eine Zelle ist die kleinste Einheit des Lebendigens.

  1. Woraus besteht eine Zelle?

Ein Organismus besteht aus Zellen und Körperflüssigkeiten.

Die Flüssigkeiten sind Blut, Lymphe, Hirn- und Rückenmarkflüssigkeiten, Sekrete, Schleim, Intrazellularflüssigkeiten und Galleflüssigkeit.

Die Zellen nehmen Nährstoffe von und geben Abbauprodukte (Abwehrstoffe) ab zu den Blutkapillaren. Nährstoffe springen raus aus die Blutkapillaren und sorgen die Zellen. Die Zellen geben Abbaustoffe zurück zur Blutkapillaren zu.

Blut besteht aus Blutzellen und Blutplasma. Lymphe besteht aus Lymphplasma und Lymphozyten.

2.3 Zusammensetzung der Zelle

Eine Zelle besteht aus verschiedene chemische Hauptelemente. Die Hauptelemente sind Sauerstoff, Kohlenstoff, Wasserstoff, Stickstoff, Kalzium und Phosphor. Sauerstoff macht 65%.

2.4 Kennzeichen des Lebendigen

Die sieben Kennzeichen des Lebendigens sind Stoffwechsel, Neubildung und Fortpflanzung, Wachstum, Reizbarkeit, Leitfähigkeit, Beweglichkeit, und Anpassungsfähigkeit.

Unter Stoffwechsel unterscheidet man Katabolismus und Anabolismus. Katabolismus ist der Abbau von Stoffen (Abbaustoffwechsel). Anabolismus ist der Aufbau von Stoffen (Aufbaustoffwechsel). Unter Neubildung und Fortpflanzung versteht man die Zellteilung von Zellen. Unter Wachstum versteht man die Vergrössung und Vermehrung von Zellen. Unter Reizbarkeit versteht man die Kommunikation der Zelle (durch Rezeptoren). Ein Reiz musst passend sein, damit ein elektrischer Impuls ausgelöst werden kann. Unter Leitfähigkeit versteht man die komplett Reagierung des Lebewesens. Unter Beweglichkeit versteht man die Mobilität und Flexibilität des Lebewesens. Unter Anpassungsfähigkeit versteht man die Anpassung des Lebewesens zu seiner Umwelt. 2.5 Aufbau und Arbeitsweise der Zelle

Jede Zelle hat ein Zellkern und Zellleib. Der Zellkern ist das Nukleus und der Zellleib ist die Zytoplasma.

Die Zelle ist von der Zellmembran umgegeben. In der Mitte der Zelle ist der Zellkern. Der Zellkern ist von der Kernmembran umgegeben.

Die Zellen können unterschiedliche Formen haben, z.B. Knorpelzellen, Nervenzellen, Muskelzellen und Knochenzellen.

Quergestreifte Muskelzellen sind 15-20 cm gross. Nervenzellen mit ihre Axone und Dendriten sind bis 1 metre lang.

Leberzellen besitzen zwei Zellkerne. Blutkörperchen besitzen keinen Zellkern.

2.6 Grundstruktur der Zelle

Der Zellinhalt heisst Protoplasma. Plasma ist eine Flüssigkeit.

Es gibt ein Zellplasma (Zytoplasma) und ein Kernplasma (Karyoplasma). Das Kernplasma ist die Kommandozentrale und beinhaltet die Erbinformation und die Chromosomen. Das Zellplasma ist das Arbeits- und Speichergebiet und beinhaltet die Zellorganellen.

Zellorganellen sind kleine Organe. Sie haben bestimmte Funktionen und Aufgaben. Das Arbeitsgebiet ist da, wo Eiweiss gespeichert wird. Das Speichergebiet ist da, wo Stoffe, die wichtig für die Zellarbeit sind, eingelagert werden (Glycogen zur Energiegewinnung).

Die Erbinformation ist der Bauplan des Lebens. Ihre Informationen sind auf den Chromosomen gespeichert. Es geht auch um den Bauplan für das Eiweiss, die Hormone und Enzyme.

2.7 Zellmembran

Die Membran besteht aus einer lipidische Doppelschicht. Die Fettmoleküle haben ein wasserverträgliches Köpfchen und Schwänzchen. Bei der äußeren Schicht liegen die Köpfchen nach aussen und die Schwänzchen nach innen. Bei der inneren Schicht liegen die Schwänzchen nach aussen und die Köpfchen nach innen.

Stoffe werden mit zwei Möglichkeiten durch die Zellmembran transportiert: aktiver und passiver Transport. Der aktive Transport braucht Energie und ein Träger. Der passive Transport braucht keine Energie. Hier wird die Osmose, Diffusion und die Filtration genutzt.

2.8 Zellkern

Der Zellkern ist die Kommandozentrale der Zelle. Er entscheidet die Arbeitsschritte des Zellleibs.

Die Chromosomen enthalten die Erbinformation für die Zusammensetzung alle Eiweiße, Hormone und Enzyme.

Kernsaft, Chromosomen und Kernkörperchen befinden sich im Zellkern.

Der Kernsaft (Karyolymphe) ist eine eiweißhaltige Flüssigkeit. Die Chromosomen sind hier eingebettet.

Kernkörperchen (Nucleolus) bilden RNS (Ribonukleinsäure). Es gibt 1-3 Kernkörperchen in jeder menschlichen Zelle.

Chromosomen sind Erbinformationsträger. Wenn die Zelle in der Arbeitsphase ist liegen die Chromosomen als Chromatin vor. Die DNS ist entspiralisiert. Während der Zellteilung, spiralisiert sich die DNS und die Chromosomen nehmen ihre normale Form an.

2.9 Chromosomen

Sie sind Träger der Erbanlage. Es gibt 23 Chromosomenpaare oder 46 Chromosomen. Die 23 Chromosomenpaare bestehen aus 22 identischen Paaren und einem Gonosomen Paar.

Jeder Mann hat die Kombination XY (Gonosome) und jede Frau hat die Kombination XX (Gonosome).

Jedes Chromosom besteht aus zwei identischen Chromatiden Hälften. Sie sind durch ein Zentromer (Einschnürung) verbunden. Die Gene liegen auf den Chromosomen. Die Gene bestehen aus DNS (Desoxyribonukleinsäure).

DNS ist wie eine Doppelhelix aufgebaut und ist der Träger der Erbanlage. Wenn die Zelle arbeitet, entspiralisiert sich die Doppelhelix. Die Erbinformation liegt offen und RNS kann alles kopieren.

Die RNS kopiert die DNS und transportiert die Aminosäuren (Transportmedium) zu den Ribosomen.

Während der Zellteilung, spiralisiert sich die DNS und die Erbinformation ist abgeschlossen und gesperrt.

DNS besteht aus Desoxyribose-Zucker, Adenin, Cytosin, Guanin und Thymin Nukleinbasen.

RNS besteht aus Ribose-Zucker, Adenin, Cytosin, Guanin und Uracil Nukleinbasen.

3.0 Eiweissproduktion

Eiweiß ist aus 100 Aminosäuren aufgebaut. Die Aminosäuren sind aneinander gereiht. Chromosomen enthalten den Bauplan von jedem Eiweiß. Das Chromosom öffnet sich an der Stelle an der die richtige Eiweißinformation gespeichert ist. Die RNS kommt und kopiert den Bauplan und wandert in den Zellleib und gibt die Information zu den Ribosomen ab. Eigentlich liefern die Transfer-RNS die richtigen Bauteile als Tripletts oder Triple Nukleinbasen zu den Ribosomen.

3.1 Zellteilung

Die Zellteilung dauert Stunden. Der Zellleib teilt sich durch einfache Durchschnürung. Gleichzeitig läuft der Prozess der Teilung des Zellkerns ab. Diese Teilung heisst Mitose. Die Mitose sichert den fehlerfreien Übergang der Erbinformation zu der Tochterzelle.

Es gibt fünf Stadien:

Interphase Prophase Metaphase Anaphase Telophase 3.2 Mitose

Interphase (Zwischenphase) bedeutet die Chromosomen liegen entspiralisert und offen. Die Zelle arbeitet.

Prophase (Vorphase) bedeutet die Kernmembran löst sich auf, so dass der Spindelapparat aufgebaut werden kann. Es geht um die Eiweißstruktur. Die Kernköperchen lösen sich auch auf.

Metaphase (Mittelphase) bedeutet der Spindelapparat ist völlig aufgebaut. Die Chromosomen binden sich zusammen mit ihrem Zentromen an die Äquatorialebene.

Anaphase (Nachphase) bedeutet jede Chromatid Hälfte wandert zu einem Spindelpol.

Telophase (Endphase) bedeutet der Spindelapparat löst sich auf, und eine neue Kernmembran wird aufgebaut. Die Chromosomen entspiralisieren sich nochmals und der Zyklus beginnen wieder. Die nächste Mitose kommt gleich im Anschluss.

3.2 Meiose

Hier wird eine Reduktionsteilung in Gang gesetzt. Es geht um die Reduzierung des Chromosomensatzes von 46 Chromosomen zu 23 Chromosomen. Diese Reduzierung findet im Ei und im Samen statt.

3.3 Geschlechtsbestimmung

Die Kombination XX ergibt ein Mädchen und die Kombination XY ein Jungen. Es ist der Mann der das Geschlecht des Kindes bestimmt.

22 Autosomen und ein X Chromosom befinden sich in der reifen Eizelle. 22 Autosomen und entweder ein Y oder X Chromosom befinden sich in der reifen Samenzelle. 3.4 Chromosomenabweichungen

Bei einer Chromosomenaberation handelt sich um eine Abweichung von Chromosomen entweder in ihrer Anzahl oder Form. Das Problem passiert während der Reduktionsteilung, z.B. ein Chromosom zu viel oder zu wenig. Dann ist die Überlebenschance höher als wenn das X Chromosom fehlt.

Es gibt 3 Abweichungen:

Trisomie 21 (Down Syndrom) Turner Syndrom Klinefelter Syndrom Trisomie 21

Trisomie 21 bedeutet, daß das Chromosom 21 dreifach vorliegt. Die Menschen leiden unter einem Organfehler, wie z.B. einem Herzfehler, und einer Behinderung der geistigen Entwicklung.

Andere Merkmale sind: Mund steht offen, kleiner Kopf, schräge Augenstellung, vergrößerter Abstand zwischen dem 1. und 2. Zehen, erhöhte Speichelproduktion, tiefsitzende Ohren.

Klinefelter Syndrom

Hier sind nur Männer betroffen. Sie haben zu viele X Chromosomen. Es liegen XXY, XXXY, XXXXY, oder XXXYY - Kombinationen vor.

Symptome sind: Hodenhypoplasie (Unterentwicklung der Hoden), Unfruchtbarkeit, Hochwuchs, Vergrößung der Brustdrüsen, und Osteoporose.

Therapie: Sie müssen Testosteron einnehmen.

Turner Syndrom

Es sind nur Frauen betroffen. Ihnen fehlt ein X Chromosom. Es liegt die X0-Kombination vor.

Symptome sind: Sexueller Infantalismus, Östrogenmangel, das Fehlen der Eierstöcke, (check what is this JM) Bindegewebestränge, fehlende Menstruation, Unfruchtbarkeit, Minderwuchs, Herz-, Niere- und Aorta-Fehlbildungen.

Therapie: Wachstumshormon (STH) im 4. Lebensjahr; Östrogen und Progesteron im 12. Lebensjahr.

3.5. Filtration, Diffusion, Osmose Filtration

Das ist der Durchtritt von festen Teilchen durch einen Filter. Diese Bewegung braucht eine physikalische Gewalt, z.B. die Pumpfunktion des Herzens. Ein Beispiel ist der Stoffaustausch durch die Kapillarwand. Bestimmte Stoffe können für der Filter zu groß werden.

Es gibt zwei Wege zu der Zellmembran:

  • Semipermeabel - Die Zellwand ist halbdurchlässig. Es wird keine Energie verbraucht.
  • Selektiv permeabel - Die Zelle wählt aus welche Stoffe durch die Zellwand kommen können und die Stoffe werden auf einem Träger transportiert. Energie wird verbraucht.

Diffusion

Das ist ein physikalischer Ausgleichsprozess wobei zwei Stoffe unterschiedlicher Konzentration gleichemäßig verteilt werden.

Teilchen sind von Temperatur, Druckverhältnissen und Konzentration beeinflusst. Die Eigenbewegung (Brownische Bewegung) sichert, daß sich die Teilchen von einander weg bewegen können.

Wenn die Konzentration zu hoch ist, dann bewegen sich die Teilchen vom Ort der höchsten Konzentration zum Ort der niedrigsten Konzentration.

Osmose

Bei der Osmose handelt es sich um die Wasserkonzentration der Zelleumgebung im Vergleich mit der Wasserkonzentration der Zelle. Das Wasser geht durch eine semipermeable Membran in eine stärker konzentrierte Lösung über.

Wenn die konzentrierte Lösung zu niedrig ist, dann bewegt sich das Wasser vom Ort der niedrigt konzentrierten Lösung zum Ort der höher konzentrierten Lösung.

Die NaCl Konzentration der Zellumgebung ist gleich der NaCl Konzentration der Zelle selbst.

Hypertonisch bedeutet, dass die NaCl Konzentration der Zellumgebung größer ist als die NaCl Konzentration der Zelle. In diesem Fall, fliesst Wasser aus der Zelle, welches zur eine Zelleschrumpfung führen kann.

Hypotonisch bedeutet, dass die NaCl Konzentration der Zellumgebung niedriger ist als die NaCl Konzentration der Zelle. In diesem Fall, fliesst Wasser in der Zelle, welches zur Zellezerplatzung führen kann.

Osmose braucht Energieaufwand und Wasser.