Gene regulation Flashcards
Name the four ways which genes can be regulated
Transcriptional - genes can be turned on or off
Post-transriptional - mRNA can be modified which regulates translation and the types of proteins involved
Translational - translation can be stopped or started
Post-translational - proteins can be modified after synthesis which changes their functions
Give an example of transcriptional control
Chromatin remodelling
Heterochromatin - tightly wound DNA causing chromosomes to be visible during replication
-Transcription of genes isn’t possible because RNA polymerase cannot access the genes
Euchromatin - loosely wound DNA present during interphase
Give two other examples of transcriptional control
Lac operon
Histone modification
Explain histone modification
DNA coils around histones because DNA is negatively charged and histones are positively charged
The addition of acetyl groups or phosphate groups, reduces the positive charge on the histones
-This causes DNA to coil less tightly
The addition of methyl groups makes the histones more hydrophobic so the DNA coils around them more tightly
Give two examples of post transcriptional control
RNA processing
RNA editing
Explain RNA processing
The product of transcription is a precursor molecule, pre-mRNA
-This is modified forming mature mRNA before it can bind to a ribosome and code for the production of a protein
A cap is added to the 5’ end
- A tail is added to the 3’ end
- These both help to stabilise the molecule and delay degradation in the cytoplasm
Splicing also occurs
Explain RNA editing
The nucleotide sequence of some mRNA molecules can be changed through the addition, deletion or substitution
List four examples of translational control
1) Degradation of mRNA - the more resistant the molecule, the longer it will last in the cytoplasm, therefore a greater amount of protein synthesised
2) Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins
3) Activation of initiation factors which aid the binding of mRNA to ribosomes
4) Protein kinases - Enzymes that catalyse the addition of phosphate groups to proteins
- This changes the tertiary structure and so the function of the protein
List four examples of post-translational control
1) Addition of non-protein groups such as carbohydrate chains, lipids or phosphates
2) Modifying amino acids and the formation of bonds such as disulfide bridges
3) Folding or shortening proteins
4) Modification by cAMP - e.g. in the lac operon - cAMP binds to cAMP receptor protein, increasing the rate of transcription of the structural genes
