Regulation Of Transcription And Translation Flashcards
(11 cards)
How is transcription of target genes stimulated or inhibited?
Transcription of genes is controlled by protein molecules known as transcription factors which move from the cytoplasm to the nucleus.
In nucleus they bind to a specific DNA site known as promoter regions which are usually found near the start of the target genes associated.
Control the expression of a gene by controlling the rate of transcription.
Describe the two types of transcription factors
Activators simulate / increase rate of transcription by helping RNA polymerase to bind to the start of the target gene.
Repressors inhibit/ decrease rate of transcription by binding to the start of the target gene preventing RNA polymerase from binding.
Describe the role of oestrogen in initiating transcription.
Oestrogen is a steroid hormone which affects transcription by binding to a transcription factor called an oestrogen receptor.
Binding for oestrogen - oestrogen receptor complex which moves from the cytoplasm into the nucleus where it binds to specific DNA sites ( promoter reigons ) near the start of the target genes.
Acts as an activator of transcription, allows RNA polymerase to bind to the start of the target gene.
What is RNAi
RNAi affects gene expression where small double stranded RNA molecules are produced which stop mRNA from target genes from being translated.
Molecules involved include small interfereing RNA, siRNA and micro RNA, miRNA
How does RNAi work ?
siRNA associated with several proteins and unwinds, one strand is selected the other is degraded.
Single siRNA strand binds to the target mRNA as base sequence is complementary to some section of the target mRNA, complementary base pairing.
Proteins associated with the siRNA cuts the mRNA into fragments to it can no longer be translated.
Fragments move into a processing body containing tools to degrade them.
Similar process occurs with miRNA instead in plants.
How does miRNA affect translation in mammals?
In mammals miRNA usually isn’t fully complementary to the target mRNA making it less specific so can target more that one mRNA molecule.
When first transcribes exists as long folded strand which is the processed into a double strand then two single strands by enzymes.
One strand associates with proteins forming miRNA - protein complex which binds to target mRNA in the cytoplasm physically blocking the translation of the target mRNA
Moved to a processing body where it can be stored or degraded - if stored it can be returned and translated at another time.
What is epigenetic control of gene expression.
Epigenetic control determines whether a gene is switched on or off through the attachment or removal of chemical groups known as epigenetic marks to or from DNA/ histone proteins.
How does epigenetics cause heritable changes in gene function?
Epigenetic marks alter how easily enzymes and other proteins required for transcription interact with and transcribe DNA.
Most epigenetic marks on DNA are removed between generations however some escape the removal process and are passed onto the offspring.
- means that the expression of some genes in the offspring are affected by environmental changes with affected parents previously
How does increased methylation affect transcription of DNA ?
Methyl groups always attach to the CpG site ( guanine and cytosine adjacent linked by phosphodiester bond ).
Increased methylation causes DNA structure to be more condensed so transcriptional machinery cannot interact with the gene, gene is switched off.
How does increased acetylation affect transcription of DNA?
Histones are proteins which wrap around DNA to form chromatin which makes up chromosomes.
Chromatin can be highly condensed or less which affects the accessibility of DNA and whether it can be transcribed.
Histones can be epigenetically modified by the attachment or removal of acetyl groups known
Increased acetylation means chromatin is less condensed so transcriptional machinery cannot factors and enzymes can access the DNA and transcribe it
Which enzyme is responsible for removing acetyl groups from histone proteins
Histone deacetylase
