Flashcards in JUNE 2015 Deck (16):
One form of muscle disease is caused by a mutated allele of a gene. This leads to the production of myosin molecules that are unable to bind to other myosin molecules.
If myosin molecules are unable to bind to other myosin molecules, this prevents muscle contraction.
Use your knowledge of muscle contraction and figure 1 to suggest why. (3 marks)
1. Can't form thick filaments
2. Myosin molecules have to be joined to pull actin
3. Myosin moves
4. Can't move actin filaments towards each other/ Can't shorten the sarcomere
What is an oncogene? (2 marks)
1. Tumour suppressor gene inactivated
2. Rate of cell division too fast
How does a tumour suppressor gene prevent, or slow, the growth of a tumour? (1 mark)
1. Genetic code is degenerate
Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour. (3 marks)
1. Antibody has a specific tertiary structure
2. Complementary to the receptor protein
3. Prevents growth factor binding to the receptor protein
Suggest two ways in which the use of a questionnaire may have affected the reliability of these data (2 marks)
1. Parents/students may lie
2. May be unsure abut whether their parents smoke
3. Don't know what parents smoke
4. Don't know the strength of what the parents smoke
For each student, the scientists also determined how much methylation was present within the specific gene. DNA methylation is the attachment of substances called methyl groups to adenine or cytosine. This prevents transcription.
Suggest how methylation of DNA can prevent expression of a gene (3 marks)
1. Prevents the binding of transcription factors
2. Prevents RNA Polymerase binding
3. Prevents complementary base pairings
4. Transcription doesn't occur so pre-mRNA is not produced
5. No mRNA produced so translation cannot occur
Damage to the myelin sheaths of neurones can lead to problems controlling the contraction of muscles.
Suggest one reason why. (2 marks)
1. Action potentials travel more slowly
2. So delay in muscle contraction
Cannabinoids are hydrophobic molecules. In the body, they easily pass into neurones.
Explain why (1 mark)
1. They are lipid soluble and can pass throught the phospholipid bilayer
Cannabionoid receptors are found in the pre-synaptic membrane of neuromuscular junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction (4 marks)
1. Prevents the influx of calcium ions (into the pre-synaptic neurone)
2. Synaptic vesicles do not fuse with the membrane of the presynaptic neurone
3. Neurotransmitter does not diffuse across the synpase
4. No depolarisation of post-synaptic membrane
Cannabinoids include substances found in cannabis that can enter brain tissue.
Scientists are developing artificial cannabinoids that can enter neuromuscular junctions but cannot enter brain tissue.
Suggest why these artifical cannabinoids would be better to use than cannabis when treating someone with MS. (2 marks)
1. Won't affect synapses in the brain
2. Won't cause problems with the brains functions
3. Only neuromuscular junctions treated
Give one similarity and one difference between a taxis and a tropism (2 marks)
1. SIMILARITY - Both a directional response towards a stimulus
2. DIFFERENCE - taxis : whole organism moves
tropism: growth is response
Explain how the normal mice prevented their blood glucose concentrations falling when they had not eaten for 48 hours (3 marks)
1. Release glucagon
2. Leads to formation of glucose in the liver cells
3. From non-carbohydrates
Explain why the scientists used the same restriction endonuclease enzymes on each DNA sample (2 marks)
1. Cut the DNA at the same base sequence (recognition sequence)
2. So get fragments with gene R
Explain why primer A3 and primer A4 only bind to specific DNA fragments (2 marks)
1. Each has a specific base sequence
2. Complementary to allele R
The scientists wanted to know on which chromosome the gene with alleles R and r was located. From the flies with the genotype RR, they obtained cells that were in mitosis and added a labelled DNA probe specific to alle R. They then looked at the cells under a optical microscope.
Explain why they used cells that were in mitosis (2 marks)
1. The chromsomes are visable with cells in mitosis
2. So can see which chromosome the DNA probe is attached to