central dogma- protein synthesis

Question 1

4 ways to regulate protein synthesis

Answer 1

1. amount of transcription that occurs
2. stability of mRNA transcript
3. location of protein
4. destruction of protein

Question 2

what complexes help with transcription regulation and what do they do? what histone modifications can be done for transcription regulation?

Answer 2

histones: regulated by host of nuclear proteins

-chromatin remodelling complexes: reposition nucleosomes on DNA to either expose or obscure gene regulatory elements (i.e. promoters)

-chromatin writer complexes: carry out histone modification (i.e methylation, acetylation, phosphorylation)

histone modifications:

-histone acetylation: open chromatin and increase transcription via histone acetyltransferases
–> deacetylation reverse these changes and promotes chromatin condensation

–> methylate histones and DNA
-histone methylation: transcriptional activation or repression (depends on the histone residue)
-DNA methylation: transcriptional silencing

Question 3

mRNA stability (regulate protein synthesis)

Answer 3

-the longer mRNA lasts in cytosol= more protein made via translation
-non-coding RNA (i.e. miRNA or siRNA) could promote destruction of mRNA transcript
-specific proteins can bind mRNA and prevent degradation= more protein synthesis
–> i.e. transferrin: protein receptor that brings iron into the cell (no transferrin receptor made in high iron, receptor made in low iron to bring iron into cell)

Question 4

targeting of cellular location (protein synthesis regulation)

Answer 4

-cells limit protein to particular location
-proteins needed for intracellular cytosolic use are translated on free ribosomes in the cytosol

-if destined for nucleus mitochondria or peroxisomes:
–> once translated in cytosol, specific amino acid signal in the polypeptide will target the protein for its intracellular location

-proteins destined fro lysosomes, ER, cell membrane or section need to be directed to the rough ER for translation in a process called co-translational transfer
a) translation begins of a free ribosome in the cytosol
b) signal peptide sequence is translated, which binds a single recognition particle (SRP)
-binding of SRP strops translation and directs the ribosome to the rough ER when it binds to a SRP receptor
-translation re-starts with the growing polypeptide moving through a channel into the lumen of the rough ER
-once in the rough ER, the signal peptide sequence is removed

-if a protein needs to be inserted into a cell membrane, it will contain a stop transfer sequence
-when the stop transfer sequence comes into contact with the translocator, translation is paused
-translocator will discharge the polypeptide into the phospholipid bilayer of the ER membrane
-translation resumes until polypeptide is complete

Question 5

what are the types of histone modification and what complex are they done by?

Answer 5

done by chromatin writer complexes

-histone acetylation
-histone methylation
-DNA methylation

Question 6

when is co-translational transfer needed? and when is it not needed?

Answer 6

for proteins destine for the lysosomes, ER, cell membrane

not needed for proteins destined to nucleus, mitochondria, or peroxisomes

Question 7

what particle is used in co-translational transfer to get a protein into the rough ER

Answer 7

signal recognition particle

Question 8

what sequence is necessary if a protein needs to be inserted into a cell membrane?

Answer 8

stop transfer sequence