The Regulation Of Gene Expression Flashcards
Describe the 4 different ways in which genes are regulated
- Transcriptional= genes can be turned on or off
- Post- transcriptional= mRNA can be modified which regulates translation and the types of proteins produced
- Translational= translation can be stopped or started
- Post translational= proteins can be modified after synthesis which changes their functions
What is a promoter?
A section of DNA ahead of a gene which allows RNA polymerase to attach, allowing transcription of the gene to occur
What happens if RNA polymerase can attach or can’t attach to the gene?
If it can attach the gene is transcribed, if it can’t attach the gene is not transcribed
What structure is chromatin when transcription can not occur?
When the DNA is tightly wrapped around the histones (heterochromatin)
What structure is chromatin when transcription can occur?
During interphase, when lots of protein synthesis is needed, the DNA is more loosely wrapped around the histones (Euchromatin). In this state the DNA can be transcribed because the enzyme can access the DNA to make mRNA
Explain how histones can be modified and why this is important for the wrapping of the DNA
-histones are positively charged, DNA is negatively charged therefore it can coil around.
-the histones can be modified, controlling how tightly the DNA wraps around
-the addition of phosphate groups reduces the positive charge on the histone, so the DNA wraps less tightly, allowing transcription to occur
-the addition of methyl groups makes the histones more hydrophobic so they bind together more tightly, so the DNA coils more tightly, preventing transcription
-epigenetics is often used to describe this control of gene expression
Explain the process of the second stage post transcriptional control
-genes in eukaryotic DNA contain sections of introns and exons.
-introns are areas that do not code for amino acids (non-coding)
-exons are areas that do code for amino acids
-during transcription, both introns and exons are copied into mRNA, so are called primary mRNA transcripts
-the introns are removed from primary mRNA strands by a process called splicing. Introns are removed and exons are joined, forming mature mRNA strands. This takes place in the nucleus
-a cap is added to the 5’ end, and a tail added to the 3’ end to help stabilise the mRNA so that it doesn’t break down before it reaches the ribosomes
-the mature mRNA leaves the nucleus for the next stage of protein synthesis
Explain what Spliceosomes are and what there function is during post transcriptional control
-these are the enzymes involved in joining the exons together, giving functional mRNA
-the spliceosomes could join the same exons in a variety of different ways, therefore 1 gene could produce several different versions of functional mRNA
-This would result in different arrangements of a.a
Explain the 3rd process of translational control
-these are factors which can regulate when translation starts and stops
-all mRNA breaks down in the cytoplasm eventually, but some mRNA strands can persist for longer than others, so more translation occurs, so more of that protein is made
What are inhibitory proteins and initiation factors in process 3?
-inhibitory proteins= can bind to the mRNA and stop it attaching to the ribosome, so inhibit translation
-initiation factors= help the binding of mRNA to ribosomes, so promote translation and protein synthesis
Explain the final process of post-translational control
-involves the final modifications to the proteins that have been made and include:
-the addition of non-protein groups, such as carbohydrates/lipid/etc
-the folding and shortening of the protein into its final shape
-activation of proteins by cAMP
Explain what cAMP and how it activates or changes the shape of the protein?
-an inactive protein is made up of regulatory subunits and inactive catalytic subunits
-cAMP binds to the inactive protein, causing it to change shape in the enzymes 3D structure, releasing the active subunits
-once the protein is activated, it can then activate other proteins/ enzymes within the cell
What is the method of transcriptional control used in prokaryotes?
-operons
-these are structural genes that code for proteins
-this determine whether transcription occurs or not
-they are very effective way to save resources as if certain gene products are not needed by the cell, then all of the genes involved in making that product can be switched off
Why is glucose the preferred respiratory substrate rather then lactose?
-glucose in a monosaccharide, but lactose is a disaccharide
-lactose would have to be hydrolysed first into glucose and galactose before being respired
-it is smaller so can enter bacterial cells more easily across the cell surface membrane
What is lac operon?
-an operon which regulates the genes needed to utilise lactose in E-coil, it is found within circular bacterial chromosome
-this operon means that if lactose becomes available to the bacteria, they will switch on the genes coding for the enzymes to make use of the lactose
