3.8.2.2 Regulation of translation and transcription Flashcards
Steroid hormone feature
example
It is derived from the lipid cholesterol.
It is lipophilic & hydrophobic - it is able to cross the cell-surface membrane (phospholipid bilayer) by simple diffusion.
Receptors for oestrogen are located in the cytoplasm of target cells.
e.g. oestrogen , testosterone
how oestrogen affects gene transcription?
Oestrogen binds to a receptor protein located in the cytoplasm.
The receptor is complementary to oestrogen.
The oestrogen receptor is also a transcriptional factor.
Binding of oestrogen changes the shape of the DNA binding site on the transcriptional factor, so that it can now bind to a specific base sequence on the DNA.
The activated transcriptional factor moves into the nucleus and binds to promoter region of a gene, stimulating binding of RNA polymerase and transcription of the gene (increase)
Epigenetics
Epigenetics involves heritable changes in gene function that occur without changing the base sequence of DNA.
It explains how changes in an organism’s environment (due to factors such as diet and stress) can alter the genetic inheritance of its offspring.
epigenome
chemical tags on DNA & histones, which affects the packing of chromatin, and therefore the expression of genes.
How Acetyl and Methyl affect histone packing therefore transcription
Histone packing is determined by:
the extent of acetylation of histones
the extent of methylation of DNA
Acetyl : affect histone — loosely packed — more transcription
Methyl : affect DNA (cytosine) — affect DNA packing : relaxing / pack
Closer DNA packing — less gene expression — less chance TF binding to promotor –lesson transcription
What type of chromatin is easier to transcribe
Loosely-packed chromatin can be easily transcribed.
Densely-packed chromatin has low levels of transcription.
How exactly methylation inhibit transcription
This inhibits the transcription of genes in two ways:
Prevents the binding of transcriptional factors to DNA
Promotes the condensing of DNA, making it less accessible to transcription factors.
How exactly acetylation inhibit transcription
Histone tails have a positive charge and hence associate tightly with the negatively charged DNA.
Decreased acetylation leads to the histones packing more tightly, inhibiting transcription.
Adding an acetyl group to the tail (acetylation) neutralises the charge, making DNA less tightly coiled and increasing transcription
explain how small interfering RNA affects gene expression?
One si RNA strand binds to an enzyme
hybridizes to its complementary mRNA sequence (hybridisation)
The enzyme hydrolyses the targeted mRNA, preventing translation of the associated gene
