mutations, gene expression and cancer Flashcards

Question

what are transcription factors

Answer 1

protiens which when activated bind to the promotor region of a gene stimulating RNA polymerase to transcribe the target gene

Answer 2

1) the transcription factors bind to promotor region upstream of the gene 2) this stimulates RNA polymerase to bind to the gene 3) to make mRNA / transcription

Answer 3

1) oestrogen is lipid soluble and passes through the cell membrane and nuclear membrane into the nucleus of the cell 2) oestrogen binds to a complementary receptor ( ER alpha ) - inactive transcription factor 3) ER alpha oestrogen receptor changes shape and is released from the protien complex which its inhibited its action 4) oestrogen binds to promotor region of target gene and stimulates RNA polymerase to transcribe the target gene

Answer 4

- microRNA ( miRNA ) - small interfering RNA ( siRNA )

Answer 5

a single strand of miRNA and siRNA can bind to a protien in the cytoplams to form a complex, called an RNA induced silenceing complex ( RISC ). The miRNA / siRNA has a complementary base sequence to part of a specific mRNA molecule. the RISC blocks gene expression by binding to the mRNA with the following outcomes : - siRNA binds to the target mRNA and the mRNA is hydrolysed into fragments by an enzyme - RNA hydrolyse - miRNA binds to the target mRNA and prevents ribosomes from attatching to the mRNA, blocking translation translation does not take place, polypeptide is not produced and the expression of the gene has been blocked

Answer 6

inheritable changes in gene function without changes to the DNA base sequences these inheritable changes are caused by changes in the genes environment that inhibit transcription by increased methylation of DNA or decreased acyetylation of histones

Answer 7

a methyl group is added to carbon atom 5 of a ctyosine residue happens most commonly where there is a high proportion of cytosine followed by guanine residues ( CpG islands ) methyltransferase catalyses the reaction repeated CpG sequences are common at the 5 end of many genes e.g near the promotor region during development methylation of these islands silences the affected genes by preventing activation of RNA polymerase, as RNA polymerase cant bind, the gene does not get transcribed

Answer 8

the chromosomal DNA of eukaryotes is wrapped around molecules of the protien histone, forming bead-like nucleosomes. The winding may be tight or loose. Histones molecules have side branches or " tails " these " tails " contain the amino acid leucine. Leucine can be acytlated e.g. an aceytl group is transferred to from acetyl - coA when acetylated, the histones become more loosely packed and the promotor and target genes are accessible by transcription factors and RNA polymerase and the target genes can be transcribed.

Answer 9

M switches off genes and prevents transcription by inhibiting RNA polymerase from binding, whereas A switches genes on and allows transcroiption M adds a methyl group to cytosine residues of DNA whereas A causes DNA to be looselt packed around histones, target genes and become accessible to transcription factors and RNA polymerase

Answer 10

begnin are capsulated by connective tissue, slower growing and do not metastaisse wherease malignant tumours are fast grwoing, non capsulated and they do not metastasise.

Answer 11

stimulates cell division

Answer 12

code for protiens which inhibit cell division

Answer 13

if a DNA mutation occurs in a proto - oncogene, it alters to become an oncogene. This results in an over stimulation of a cell division, so that cell division is permanently switched on, resulting in a tumour. If DNA mutation occurs in a tumour supressor gene, the gene becomes inactived, so the protiens coded for stop inhibiting cell division, so rate of cell division increases.

Answer 14

if the tumour supressor gene is over methylated, the gene becomes inactivated, so the protiens coded for stop inhibiting cell division, so the rate of cell division increases if an oncogene is under methylated the gene becomes more activated, so that cell division is switched on, so the rate of cell division increases.