This page contains the AQA A2 Biology B20 Recombinant DNA Technology Questions and kerboodle answers for revision and understanding.This page also contains the link to the notes and video for the revision of this topic.
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C20.1 Gene mutations AQA A2 Biology Recombinant DNA Technology Kerboodle Answers: Page No. 238
1 Deletion and addition because the bases arc deleted from one chromosome and added to a different one. 2 a Deletion b Inversion c Substitution d Addition 3 a It will cause a frame shift causing triplets (codons) in a sequence r.o be read differently because each has been shifted r.o the right by one base. H the addi tional base is inserted early in the sequence most codons will be changed. so will the amino acids they code for. The resultant polypeptide will be very different from normal. b lf the additional base is inserted at the end of the sequence few, if any codons will be changed. Few, if any, amino acids they code for will differ and the resultant polypeptide will be normal or near normal. 4 Where the duplicated bases are consecutive, the frame shift is three bases long and so the subsequent codons are not affected. The polypeptide will have an additional amino acid but otherwise be unchanged. If the bases are separate, the frame shift will initially be one base long becoming two bases long after the second duplicate base is added. Codons after both the duplications will be changed and the polypeptide will have many different amino acids (but not necessarily all -degenerate code). After the third duplicate base the codons will be unchanged. 5 Some codons will be changed co ones that code for the same amino acid (degenerate code). The frame shift might not alter some codons because the replacement bases arc the same as the originals.(e.g. GCT TTT CGA -a single base frame shift to the right does not alter the TTT codon).20.2 Stem cells and totipotency AQA A2 Biology Recombinant DNA Technology Kerboodle Answers : Page No. 242
1 Totipotent cells arc cells with the ability to develop into any other cell of the organism. 2 Totipotent -can differentiate into any type or cell in the body and comprise the first few cells that form from 1he zygote. Pluripotent -can differentiate into almost any type of cell (but not all) and are round in the embryo and young foetus. Multipotent -can differentiate into a limited number of cells and found in the umbilical cord and some adult tissues e.g. bone marrow. Unipotent -can only differentiate into a single type of cell and are found in adult tissue such as the skin. 3 ln skin cells the gene that codes for keratin is expressed but not the gene for myosin. The genetic code for keratin is translated into the protein keratin, which the cell therefore produces, but the genetic code for myosin is not translated. ln muscle cells, the gene for myosin is expressed but nor the gene for keratin. In the same way, the genetic code for myosin rather than keratin is translated and so only myosin is produced. 4 Skin cells, being on the outside or the body, are subjected 10 much wear and tear and so need replacing frequently. Many other organs are less prone LO damage and need liule cell replacement.20.3 Regulation of transcription and translation AQA A2 Biology Recombinant DNA Technology Kerboodle Answers : Page No. 247
1 Transcriptional factors stimulate transcription of a gene. 2 Oestrogen diffuses through the phospholipid portion of a cell-surface membrane into the cytoplasm of a cell, where it binds with a site on a receptor portion of the transcriptional factor. Oestrogen changes the shape of the DNA binding site on the 1ranscription factor so it can now bind with DNA. The transcriptional factor now enters the nucleus through a nuclear pore and binds with DNA, scimula1ing transcription of the gene that makes up that portion of DNA, i.e. it stimulates gene expression.20.4 Epigenetic control of gene expression AQA A2 Biology Recombinant DNA Technology Kerboodle Answers : Page No. 253
1 Epigenetics is the process by which environmental factors can cause heritable changes in gene function without changing the base sequence of DNA. 2 Decreased histone acetylation and increased DNA methylation. 3 The other strand would have complementary bases (i.e. GCUA instead of CGAU respectively). It is unlikely chat these opposite base pairings would complement a sequence on the mRNA. The siRNA, with enzyme attached, would therefore not bind to the mRNA and so would be unaffected. 4 a Some siRNA 1hat blocks a particular gene could be added 10 cells. By observing the effects (or lack of them) we could determine what the role of the blocked gene is. b siRNA could be used to prevent the disease by blocking the gene that causes it. 5 a Chromatin would be more condensed (tightly packed). b Transcription would cease.20.5 Gene expression and cancer AQA A2 Biology Recombinant DNA Technology Kerboodle Answers : Page No. 258
1 Fat cells of the breasts tend to produce more oestrogens after the menopause. These locally produced oestrogens release an inhibitor molecule that prevents transcription causing proto-oncogenes of breast tissue to develop into oncogenes. These oncogenes increase the rate of cell division leading to the development of a tumour (breast cancer). 2 Proto-oncogenes increase the rate of cell division and so their activation produces a mass of cells (tumour) but tumour suppressor genes decrease the rate of cell division and so their deactivation produces tumour. 3 Cells of a benign tumour produce adhesion molecules that make them stick together and are surrounded by a capsule of dense tissue. The tumour therefore remains as a compact structure and so surgical removal is likely to remove all tumour cells. 4 Malignant tumours spread to other regions of the body and so even though surgery can remove the more obvious larger ones, tiny ones will require other therapies to prevent these re-growing into new tumour~. 5 HADC removes acetyl groups from histones, inhibiting transcription and switching off the gene. Some cancers are the result of genes (e.g. tumour suppressor genes) that normally help repair DNA (and so prevent cancers) being switched off. By inhibiting HADC. phenylbutyric acid could prevent the removal of acetyl groups from histones and switch the ‘protective’ gene back on.20.6 Genome project AQA A2 Biology Recombinant DNA Technology Kerboodle Answers : Page No. 263
1 A genome is all the genetic material in an organism. A proteome is all the proteins produced by the genome. 2 Simple organisms generally have just one, circular piece of DNA tha1 is not associated with histones and there is little, if any, non-coding DNA. Complex organisms have considerably more DNA and the majority of this does not code for proteins. 3 lt allows identification of those proteins that act as antigens on the surfaces of the pathogens. These antigens can then be used to produce effective vaccines against the disease. Banner 2Practice questions : Page No. 264-265
1 (a) Will replace themselves/keep dividing/replicate. Undifferentiated/can differentiate/develop into other cells/ totipotent/ multipotent/ pluripotent. (b) Reverse transcriptase. (c) (i) Alters base/nucleotide sequence/causes frame shift; Different sequence of amino acids in polypeptide/protein/primary structure; Alters tertiary structure; (ii) Affects tumour suppressor gene; Inactivates (tumour suppressor) gene; Rate of cell division increased/tumour cells continue to divide; (d) Yes SCID patients unlikely to survive/quality of life poor unless treated; Cancer that develops is treatable/only affects 25%/five children; No Risk of developing cancer is high/25%; Cancer may recur/may not be treated successfully in future/only short time scale so more may develop cancer; 2 (a) RNA polymerase; (b) (i) (Receptor/transcription factor) binds to promote. Stimulates RNA polymerase/enzyme X. Transcribes gene/increase transcription. (ii) Other cells do not have the/oestrogen/ ERα receptors; (c) Similar shape to oestrogen. Binds receptor/prevents oestrogen binding. Receptor not activated/will not attach to promoter/no transcription. 3 (a) 1. Methylation prevents transcription of gene.- Protein not produced that prevents cell division/ causes cell death/apoptosis.
- No control of mitosis.
- Fat on x axis and death rate on y axis;
- (Because) looking at relationship between two discrete/independent variables;