AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011

hey, does anyone know if there was a jan 2011 BIOL5 paper??

Hi, i'm really confused with a chapter 15 exam style question in the nelson thornes text book. Its question 4a

It asks about how oestrogen stimulates some breast cancers, and how tamoxifen is a drug to treat it by binding to oestrogen receptors, and therefore prevents the cancer from dividing.

But i thought cancer was caused by uncontrolled cell division, and is completely unrelated to protein synthesis, but the mark scheme talks about protein synthesis by saying:

less / no oestrogen binds to receptor;
less / no receptors change shape;
fewer / no transcriptional factors;
less protein synthesis;

so obviously cancer is related to protein synthesis, but how????

well you know there are sequences of bases coding for oncogenes and tumour suppressor genes, basically if protein synthesis does not occur OR something goes wrong during transcription/translation, a tumour supressor gene may not be coded for. this means tumour supressor genes will either not function properly or not be made at all, therefore cancer can occur as cells will divide uncontrollably without these tumour supressor genes.
hope that helps, thats all i could think of for cancer caused by protein synthesis.. i probably would have said caused by mutagens or something :/

Physics 5 is my last exam, both that and biology 5 are an utter pain.

Questions:

Describe what a vector is in terms of DNA technology.

Describe the process of translation of DNA into a polypeptide in full, and adaptations that can increase the rate of synthesis of polypeptides.

Vector: A carrier.The term may refer to something such as a plasmid, which carries DNA into a cell, or to an organism that carries that carries a parasite to its host.
Plasmids are circular circular lengths of DNA, found in bacteria. An example of there use is with the synthesis of insulin. The desired gene/DNA fragment is cut out using a specific restriction endonuclease, a plasmid is also cut with the same restriction endonuclease to ensure that the 'sticky ends' are complimentary to each other. The DNA fragments are mixed with the plasmids and become incorporated into them, the join is made permenant by DNA ligase. These plasmids are then transferred into bacteria and the insulin is cultured.

Translation of DNA occurs outside the nuclear membrane, a mRNA starting codon attaches to a ribosome and tRNA molecules carry complimentary anticodons to the ribosome to bind with the mRNA. Each triplet base corrosponds to a specific amino acid, as the triplet bases bond, so a polypeptide is synthesised. The amino acids form peptide bonds by condensation reactions.
The rate of synthesis can be increased through the increase in presence of related enzymes and corresponding tRNA molecules. The alteration of temperature, pressure, water potential and pH to optimum levels.

Gd Questions-Hope thats covered it.

QS: Explain the transmission of an action potential across a neuromuscular junction.

QS: Explain how a muscle contracts.

Rod cells and cone cells are the photosensitive cells in the retina of the eye. Cone cells can perceive colour by having pigments for red, blue and green, whereas rod cells can not perceive colour. Both types of cell are connected to bipolar neurones. However 3 rod cells are connected to every bipolar neurone compared to only one cone cell per bipolar neurone. This allows rod cells to perceive very low intensity light, as when photons of light cause the breakdown of pigment in the rod(and cone cells) a generator potential is created. In low intensity light a smaller generator potential is created but with multiple rod cells per bipolar neurone the generator potential accumulates. This means a smaller generator potential per light sensitive cell is required to reach the threshhold frequency in the bipolar neurone and cause an action potential to the brain. The disadvantage of this however is that rod cells have a lower resolution and visual acuity as a result.

Also, the distribution of rod cells puts the majority of them at the edges of the retina, whereas the highest concentration of cone cells are at the fovea of the retina.

So much prep needed for BIOL5, it's almost driving me insane. And boy, do genetics suck