Embryonalen Stammzellen Und Deutschland (Teil 1)

Ich möchte gern Fortschritte in der Medizin diskustieren, inbesondere embryonalen Stammzellenforschung und die Benutzung davon in Deutschland. Einerseits können sie der erste Schritt zur Heilung von Volkskrankenheiten sein und deswegen sind sie als der Zukunft der Medizin gefeiert, aber andereseits ist es ein sehr umstrittenes Thema, indem einigen es für ein ethisches Verbrechen halten.

Was sind Stammzellen und warum sind sie so wichtig im medizinischen Bereich?

Stammzellen sind zellen, die pluripotent sind. Die asymetrische Teilung ermöglicht den Aufbau und die Reparatur von Organen, indem sie neue Gewebzellen produzieren. Sie sind voteilhaft, da Genetische Defekte auf ein Mindestmaβ begrenzt sind– zellen sammeln sich Mutationen an, die langfristig Krebs verursachen können, aber es gebe kleinere Riskio mit jüngeren Zellen, weil sie die wenigsten geschädigte DNA haben. Es ist wichtig, dass wir solche Variablen in Forschung oder Versuche kontrolieren, so dass die Werte nicht beeinträchtigt oder voreingenommen werden.

Von dem medizinischen Standpunkt aus seien die mögliche Anwendungen wirklich endlos. Zum Beispiel ist Antibiotikaresistenz etwas, was in den letzten Jahren immer problematischer geworden ist. 2011 gab es 100,000 Todesfälle wegen MRSA in Europa, und deswegen brauchen wir alternative Heilbehandlung, und mittels des neues Wissens und den neuen Technologien von Stammzellforschung können wir solche Probleme lösen.

Dass Deutschland immer älter wird, zeigt, wie wichtig die regenerative Medizin worden wird. Es ist etwas, was in den letzten Jahren immer erfolgreicher geworden ist, etwa bei der Behandlung von Parkinson und Alzheimer. Stammzellen können Gedächtnisprobleme heilen, da die Mehrheit aller Gedächtnisprobleme auf einem Mangel an Anschlüssen in Gehirn beruhen, aber neue Nerven erlauben die unterschiedliche Hirnregionen noch einmal miteinander zu kommunizieren.

Jedoch handelt es sich dabei um nur eine sozialökonomische Vorteil. Man sollte ihnen auch aus wirtschaftspolitischen Gründen benutzen – Deutschland ist die viertgrößte Wirtschaft der Welt nach dem USA, Japan und China, und um sowohl diese Lage der Kraft zu behalten als auch das Wirtschaftswachstum zu unterstützen, muss Deutschland in einträglichen Bereichen wie Stammzellenforschung anlagen.

Was ist das Gesetz in Deutschland, was Stammzellen im Moment betrifft?

Laut dem Embryonenschutzgesetz 1991 (und auch zum Teil dem Grundgesetz) sind Embryonen geschützt, indem die Erzeugung eine Stammzelllinie eine strafbare Handlung ist. Jedoch hat das Stammzellgesetz 2002 zur Folge, dass man Stammzelllinien benutzen kann, die bevor 1. Mai 2007 erzeugt waren, aber nur wenn es unbedingt lebensnotwendig sei und nach man Erluabnis von der Zentrale Ethik-Kommission für Stammzellenforschung bekommen hat.

(Für diejenigen, die nicht schon wissen, was eine Stammzelllinie betrifft, sind sie Stammzellen, die alle auf den selben Ursprung zurückgehen und in-vitro vermehrt worden sind.)

Also was sollte mit embryonalen Stammzellen gemacht werden, wenn man das Gesetz verändern könnte?

Ich bin der Meinung, dass Embryonen, die nicht während künstliche Befruchtung eingenistet sind, sollen Stammzellen für Forschung oder Stammzellentherapie abgeben. Es ist verschwenderisch, ihnen aus der Welt zu schaffen – hauptsächlich denn für jede erfolgreiche IVF-Geburt muss man 30 embryonen shaffen und dann zerstören.

 

Was halten Sie von Stammzellen? Halt die Augen offen für Teil 2!

DNA Probes, Electrophoresis and PCR

Locating a desired DNA sequence

A DNA probe is a short single-stranded section of DNA that is complementary to the section of DNA being investigated. The probe is labelled in one of two ways:

1. Using a radioactive marker so that the location can be revealed by exposure to photographic film
2. Using a fluorescent marker that emits a colour on exposure to UV light
Copies of the probe are added to a sample of DNA fragments and will anneal to any fragment where a complementary base strand is present:
DNA probe
Isolating a desired DNA sequence
  1. DNA samples are treated with restriction enzymes to cut them into fragments
  2. The DNA samples are placed into wells cut into the negative electrode end of an agarose gel
  3. A DNA standard is added to one well – the fragments are of known length so can be used to estimate the size of the fragments in the samples
  4. The gel is immersed in a tank of buffer solution and an electric current is passed through the solution for around 2 hours
  5. DNA is negatively charged because of its phosphate groups so is attracted to the positive electrode
  6. Shorter lengths of DNA move faster than longer lengths so move further in the time the current is run
  7. The position of the fragments can be shown by using a dye that stains DNA molecules (see above)

electrophoresis

You could try carrrying out this procedure in a virtual lab by clicking here!

Amplifying a DNA sequence

PCR stands for the polymerase chain reaction. It is used to make lots of copies of DNA and is even used by the police to give a large enough quantity of DNA for testing from the smallest blood or other sample.

  1. The DNA sample is mixed with a supply of DNA nucleotides and DNA polymerase
  2. The mixture is heated to 95°C. This breaks the hydrogen bonds holding the strands together, so the samples are now single stranded
  3. Primers (short lengths of single stranded DNA) are added
  4. The temperature is reduced to 55°C to allow the primers to bind and form small sections of double stranded sections;
  5. DNA polymerase can bind to these double-stranded sections;
  6. The temperature is raised to 72°C. The enzyme extends the double stranded section by adding nucleotides to the unwound DNA;
  7. When the DNA polymerase reaches the other end of the DNA, a new, double stranded DNA molecule is generated;
  8. The whole process can be repeated many times so the amount of DNA increases exponentially.

PCR

You can watch this procedure being carried out by clicking here and going to ‘techniques – amplifying’ or you could carry out the procedure for yourself in a virtual lab here!

Cloning In Plants And Animals

identical_triplets

Clones are abundant in nature – when a zygote splits in two identical twins are formed, when bacteria divideasexually by binary fission the resulting bacteria are clones of the original bacterium, when plants reproduce asexually by producing runners the resulting plants are clones and when a singles cell divides during mitosis the two daughter cells are clones. These clones produced by asecual reproduction are advantageous as the process is quick, can be carried out when sexual reproduction cannot and all of the offspring have the genetic information to allow them to survive in their environment. However, asexual reprodcution generates no genetic variation, unless a mutation occurs, and so all of the offspring are equally suscebtible to envorinomental changes such as the introduction of a new disease-causing pathogen.

There are two main types of cloning – reproductive and non-reproductive. Reproductive cloning is the production of offspring which are genetically identical to either their mother, if created by nuclear transfer, or the other offspring, if created by splitting embryos. Non-reproductive cloning is the use of stem cells in order to generate replacement cells, tissues or organs which may be used to treat particular diseases or conditions in humans.

Splitting embryos is the process of seperating out cells from a developing embryo and so producing separate, genetically identical organisms:

splitting embryos

Nuclear transfer is when the nucleus of a differentiated adult cell is placed in an enucleated egg cell:

nuclear transfer

Advantages of artficially cloning aniamls:

  • High value animals, such as cows with a high milk yield, can be cloned in large numbers.
  • Rare animals can be cloned in order to preserve the species.
  • Genetically modified animals, such as goats which produce spider silk in their milk, can be quickly produced.

Disadvantages of artifically cloning animals:

  • As with asexual reproduction, the genetic unformity of cloning means that all of the offspring will be susceptible to environmental changes.
  • Animal welfare is not always taken into account, for example chickens with a high meat yield, yet are unable to walk, have been produced.
  • It is not yet known if animals cloned using nuclear material from adult cells will develop any long term health problems.

An example of natural vegetative propogation is the English Elm tree. After damage to the parent plant, such as disease or burning, root suckers (basal sprouts) begin to grow from the meristem tissue in the trunk close to the ground, as this is where the lest damage is likely to have occured. This response to stress or trunk death helps the elm to spread, for example, when an elm is felled during copicing, the root suckers grow into a circle of new elms, called a clonal patch, around the old trunk. These new elms produce their own root suckers, and so the clonal patch continues to expand where resources permit it. However, this adaptation can also be disadvantageous, in particular when it is in response to Dutch elm disease. The roots of an elm infected with dutch elm disease will produce many root suckers, but as these suckers are clones of the original plant they have no resistance to the fungal attack and so as they continue to grow they also begin to show symptoms of the disease. Many plants we take for granted also use vegetative propogation as a survival mechanism – potatoes form tubers which are underground stems swollen with nutrients from which new plants grow, onions and daffodils form bulbs which are condensed shoots containing nutrients and from which new bulbs can fom and strawberries have specialised stems, called runners (see below), which grow along the ground, forming new roots and shoots at the tips. These adaptations all mean the plant can reproduce even if it becomes isolated and there is no reliance on wind, insects or other pollinating agents, but the tubers and bulbs are also a disadvantage as they are an attractive foood source for certain animal including us humans.

natural_vegetative_propogation

Plants can also be propogated aritifically. Traditionally there were two methods of doing this; taking cuttings and grafting:

Taking cuttings is where a stem is cut between nodes and its lower leaves are removed. The cut end is then treated with plant hormones to encourage root growth  before planting. The cuttingss are clones of the parent plant. Commercially this techniques is used to quickly produce large numbers of plants such as geraniums.

cuttings

Grafting is where a shoot section of a woody plant, such as a rosebush or fruit tree, is joined to a rootstock (a root and stem already growing). The graft then grows and is a clone of the original plant, but the rootstock is genetically different.

grafting

Although these methods are useful they cannot easily produce high numbers of plants and some plants struggle to reproduce successfully in these ways. The more mordern method of artificial vegetative propogation is micropropogation by callus tissue culture. This method can quickly produce very large stocks of a plant from a small amount of plant tissue, and it has an added advantage that the stock is disease free. Many household plant, such as orchids, are produced using the following method:

  1. A small piece of tissue (an explant) is taken from the shoot tip of a plant.
  2. The explant is placed on a nutrient growth medium and cells in the tissue divide to form a callus (a mass of undifferentiated cells).
  3. Single callus cells are seperated from the mass and placed on a growing medium with plant hormones that encourage shoot growth.
  4. These growing shoots are then transferred to another medium with hormones encouraging root growth.
  5. Growing plants are then transferred to a greenhouse to acclimatise and grow further, before being planted outside.

micropropogation

Plant cloning in agriculture has both advantages and disadvantages. Lots of genetically identical plants can be produced from one plant – you know what the plants will be like and the process is faster than selective breeding. Also, costs are reduced as the crop is all ready at the same time and plants can be produced at any time of the year instead of having to wait until their natural growing season. However, the process is arguably more labour intensive as it’s harder to replant small plants than sow seed. Most importantly, environmental change such as the arrival of a new disease could damage the whole crop as their identical genetics means that they would all be equally susceptible.

Meiosis

Meiosis 1

Prophase 1:

prophase1

  • Chromatin condenses and supercoils so chromosomes shorten and thicken.
  • Chromosomes come together in their homologous pairs to form a bivalent.
  • The non-sister chromatids wrap around each other and attach at chiasmata. Sections may be swapped in crossing over.
  • Nucleolus disappears and nuclear envelope disintegrates.
  • A spindle (made of microtubules) forms.

Metaphase 1

  • Bivalents line up across equator of spindle, attached to spindle fibres at the centromeres.
  • They are arranged randomly with each member of a homologous pair facing opposite poles.

Anaphase 1

anaphase1

  • The homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles. The centromeres do not divide. The chiasmata separate (and swapped sections stay swapped).

Telophase 1

telophase1

  • In animals two new nuclear envelopes form and the cell divides by cytokinesis.

Meiosis 2 (division is in a plane at right angles to meiosis 1)

Prophase 2:

  • Reformed nuclear envelopes break down, the nucleolus disappears, chromosomes condense and spindles form.

Metaphase 2:

  • Chromosomes line up on equator of spindle and are attached to the spindle fibres at centromeres.
  • The chromatids of each chromosome are randomly assorted.

Anaphase 2:

  • The centromeres dvide and the chromatids are pulled to opposite poles by the spindle fibres. The chromatids randomly segregate.

Telophase 2

  • Nuclear envelopes reform around the haploid daughter nuclei
  • In animals the two cells now divide to give four haploid cells
  • In plants a tetrad of four haploid cells is formed.

The Lac Operon

Explain genetic control of protein production in a prokaryote using the lac operon

Ecoli

E-coli grown without lactose are placed in a medium with lactose. At first they cannot metabolise the lactose as they only have tiny amounts of the enzymes needed to metabolise it. After a few minutes the rate of synthesis of these enzymes increases. Lactose triggers the production of these enzymes and so is the inducer.

the lac operonStructural genes code for the enzyme, the operator region can switch them on and off, and the promoter region is where RNA polymerase binds to begin transcription. The regulatory gene is not part of the operon and may be some distance away.

 lactose absent

When lactose is absent:

  1. The regulator gene is expressed and the repressor protein is synthesised. It has binding sites for lactose and the operator region.
  2. he repressor protein binds to the operator region, covering part of the promoter region where RNA polymerase attaches.
  3. RNA polymerase cannot bind to the promoter region so the structural genes are not transcribed to mRNA, so the genes cannot be translated into the two enzymes.

lactose present

When lactose ispresent:

  1. Lactose (inducer) molecules bind to the other site on the repressor protein, causing the repressor protein to change shape and dissociate from the operator region.
  2. The promoter region is now unblocked so RNA polymerase can bind to it and initiate transcription.
  3. The operator-repressor-inducer system is a molecular switch.
  4. The E. coli can now make lactose permease to take up lactose and β-galactosidase to convert it into glucose for respiration.

Here is an animation which summarises the above:

10 things you’ve always wondered about humans, explained.

 

I_Wonder

1. Why do women test perfume on their wrists?

In order to smell perfume it has to be vapourised using heat, and as there are lots of blood vessels just under the skin surface of the wrist it is a warm part of the body where the perfume will vapourise quickly.

2. Cocaine can enter the bloodstream by being sniffed, so why can’t diabetics inhale Insulin instesd of having to inject it?

To pass into the blood vessels in the nose drugs must pass through the thin epithelium lining the nasal passages, but drugs which are not fat soluble cannot pass through the phospholipid bilayer of cells, and as Insulin is not fat soluble (whereas cocaine is) it wouldn’t be able to pass through the nasal cells to enter the bloodstream.

3. Why have we not selected against and eradicated genes from the human genomw which cause ageing?

In order for genes to be passed on, the orgnism must reach reproductive age, so any characteristics, and therefore genes, which help the organism to survive so it can breed will mean the organism is more lkely to survive and pass those genes on. However, genes which cause ageing have no affect upon the survival of the species as these characteristics are only expressed after reproduction.

4. Why does one year seem longer to a child?

Time is relative. A child of 10 will think a year is very long as it is 10% of all the time they’ve lived so far, but to a 50-year-old one year is only 2% of  all the time they’ve lived, so as one year is a much larger proportion of a child’s life it appears much longer to them, and this is also why time appears to speed up as we get older.

5. If humans are so sophisticated why to we only have 46 chromosones when some plants such as ferns have around 1320?

Numbers of chromosones have nothing to do with sophistication, rather they are indicator of the age of the species. As ferns have been evolving for millions of years they have experienced more mutations in their chromosones which has led to an increase overall in the number of chromosones.

6. Why is milk white when tears and sweat are colourless?

It is simply down to the fact that milk contains fat forming a white-coloured emulsion whereas sweat and tears only contain mainly water and salts.

7. Why do our shins, which often suffer when we walk into something, have so little protection?

Our ancestors walked on all fours and so their shins would be on their hind legs and were rarely banged into so there was no need to protect them.

8. Why do females of other species, such as dogs, have much less painful pregnancies?

Animals who walk on four legs havethe weight of their offspring shared equally between four legs instead of two, and their backbone provides a horizontal support. As we walk on two legs the weight of the baby pulls forward, which is why many pregnant women experience severe backache.

9. Why do we have two sets of teeth?  

If we only had one set, as the jaw continued to grow during childhood, gaps would appear between our teeth as teeth cannot grow sideways, so we need a second set for when our jaw has stopped growing.

10. Why are more people dying each year from cancer nowadays, depsite huge advances in medical treatment and improving survival rates?

Vaccination has meant that very few people each year die from diseases such TB, polio, pneumonia etc and so as this has greatly increased our life expectancy, and our population is continually increasing,  more people are reaching the older age groups where cell mutations, i.e. cancer, occurs more frequently.

Diet and Food Production

Balanced Diet: a diet which contains all the nutrients required for health in the appropriate proportions.

Balanced

  • Obesity is when a person is 20% or heavier than the recommended weight for their height. Obesity is caused through malnutrition, which is where a person’s diet is unbalanced. In this case of malnutrition, the person consumes too much energy and the excess is deposited as fat in the adipose tissues which can impair health. The conditions most commonly associated with obesity are cancer, cardiovascular disease, type 2 diabetes, gallstones, osteoarthritis and high blood pressure (hypertension).

HDL and LDL

  • High blood cholesterol is linked with coronary heart disease. Although it’s found in cell membranes, the skin and is used to make steroid sex hormones and bile, above 5.2mmol/dm3 is harmful. Cholesterol is insoluble but is carried by HDL’S and LDL’s. Lipoproteins are a combination of lipid, cholesterol and protein.
    •  HDL’s contain unsaturated fat and tend to carry cholesterol from the body tissues back to the liver where it’s used in cell metabolism to make bile or is broken down, meaning high levels of HDL’s are associated with reducing blood cholesterol levels. They reduce deposition of cholesterol in the artery walls (called atherosclerosis) and may help to remove the depositions already there.
    • LDL’s contain saturated fats. They tend to carry cholesterol to body tissue from the liver. The concentration of LDL’s in the blood increases when a diet contains too much saturated fat and cholesterol. High LDL levels result in deposition in the artery walls.
      • Saturated fats decrease the activity of LDL receptors in body tissue so as the concentration of blood LDL’s rises; less is removed resulting in higher LDL concentrations and more deposition. Polyunsaturated and monounsaturated fats increase the activity of LDL receptors so more is removed from the blood.
    • Coronary heart disease: a condition in which the coronary arteries narrow from an accumulation of plaque (atherosclerosis) and cause a decrease in blood flow.
  • Humans depend on plants for all food as they are the basis of all food chains. This is because humans eat both plants directly, and herbivores who eat plants.
  • Making food production more efficient:
    • Plants:
      • Improve growth rate, increase yield, reduce crop loss due to diseases/pests, easier harvest by standardising crop size, and improve response to fertilisers.
    • Animals:
      • Improve growth rate, increase productivity, and increase resistance to disease
    • Selective breeding:
      • Isolation → artificial selection → inbreeding/line breeding
      • A pair of animals displaying desirable characteristics is allowed to reproduce. The offspring are sorted and those with the best combinations of characteristics are allowed to reproduce. Over many generations this exaggerated the desired characteristic.
      • Selecting which animals can breed or which seeds to be sown is known as applying selection pressure.
    • Pesticides, fungicides and fertilisers increase plant yield as they are less likely to die from insects eating them or a fungal disease, and the fertilisers provide all the minerals the plant needs to grow so it can grow faster. Antibiotics can increase food production of animals as fewer animals die from disease so a higher yield is achieved.

bacteria2

  • Methods of preventing food spoilage;
    • Cooking – denatures enzymes and other proteins killing microorganisms
    • Pasteurising – heat then rapid cooling kills microorganisms
    • Drying/salting/coating in sugar all dehydrate microorganisms as water will leave their cells by osmosis
    • Smoking – smoke contains antibacterial chemicals and the food develops a hardened, dry outer surface.
    • Pickling – an acidic pH kills microorganisms by denaturing enzymes and other proteins.
    • Irradiation – ionising radiation disrupts the DNA structure of microorganisms so they are killed.
    • Cooling/freezing – although microorganisms aren’t killed, the activity of their enzymes is slowed so their metabolism/growth/reproduction is also slow.
  • Using microorganisms to make food (e.g. cheese/yoghurt/bread/alcohol/single cell protein (Quorn – a mycoprotein)
    • Advantages:
      • Can be much faster than animal/plant production
      • Production can be increased/decreased according to demand
      • No animal welfare issues
      • Good source of protein for vegetarians
      • Protein contains no animal fat or cholesterol
      • SCP could be combined with removal of waste products, as they grow on almost any organic substrate e.g. paper or whey
    • Disadvantages:
      • People might not want to eat fungi or food grown on waste
      • Need to isolate protein from the microorganisms in the fermenter
      • Protein needs purification so it’s not contaminated
      • Need to control infection – the microorganisms grow at the same temperatures as harmful pathogens
      • Palatability – the protein has a different taste/texture to meat