Regulation of transcription and translation Flashcards
How can transcription of target genes be inhibited or stimulated
when molecules called transcription factors move from the cytoplasm into the nucleus
How do transcription factors affect transcription
they move into the nucleus from the cytoplasm and bind to the promoter or the operator region of DNA, either initiating or inhibiting transcription and therefore translation of the protein
OPERONS ARE ON INTRONS
What happens when transcription factors aren’t present at all
the gene is ‘turned off’ so the protein is not made
How can oestrogen initiate transcription
oestrogen can pass through bilayer of the cell as it is LIPID SOLUBLE
it will bind to a receptor site on a transcription factor (not all cells contain oestrogen receptor sites on their transcription factors)
this changes the tertiary structure of the TF as an inhibitor molecule is released, therefore the TF is now complementary and can bind to promoter region of DNA, initiating transcription
What are epigenetics
environmental changes that cause heritable changes in gene function without changing the DNA base sequence
What is the epigenome
Collective term for the ‘chemical tags’ that mediate epigenetic control
2 epigenetic tags that inhibit transcription
Increased methylation of DNA + decreases acetylation of associated histones
What is methylation of DNA and how does it affect transcription
Methyl groups are added to DNA at cytosine bases
this attracts proteins that condense chromatin which prevents transcription factors from binding to promoter region of DNA, also RNA polymerase cant bind
this inhibits transcription as gene is turned off
What is acetylation of histones and how does it affect translation
If acetyl groups are removed from histones, histones become more positively charged, attracting phosphate groups on DNA as they have negative charge
this causes chromatin to condense, so TFs and RNA polymerase cannot bind and gene is switched off
How can epigenetic control be used to treat cancer
increased methylation or decreased acetylation of oncogenes will inhibit their transcription so less protein is not translated which prevents stimulation of cell division, inhibiting tumour formation
increased acetylation or decreased methylation of tumour suppressor genes will promote their transcription, so more proteins are produced that stimulate apoptosis, so removes tumours
What is RNA interference and the two types of RNAi
where translation of mRNA of target genes is inhibited by RNAi
mRNA is destroyed before translation, so polypeptide chain is not formed
Either siRNA or miRNA
How do siRNA and miRNA work
enzyme cuts mRNA into double stranded siRNA and one strand of siRNA binds with an enzyme
the siRNA enzyme complex binds to complementary base on mRNA
(siRNA is specific so can only bind to one type of mRNA)
therefore the cell cannot recognise double stranded mRNA, so enzyme degrades mRNA before translation
miRNA does the same, but is less specific so can bind to many mRNA types
