Translation and Post-translation 2C part 2

Question 1

ribosomes are composed of

Answer 1

2 subunits made of a complex of protein and rRNA

Question 2

Large subunit 50S (2)

+general sum up

Answer 2

made of 5S and 23S rRNA+34 proteins and contains the peptidyl-transferase centre for the formation of peptide bonds

peptide bond formation catalytic activity

Question 3

small subunit 30S (2)

+general sum up

Answer 3

made of 16 S rRNA +21 proteins and contains decoding centre where charged tRNA read and decode the codon of mRNA

Reads codon and see which tRNA is comming

Question 4

each subunit of the ribosome

Answer 4

exist separately in the cytoplasm but join tgt on the mRNA molecule during translation

Question 5

charged tRNA

Answer 5

tRNA to which its cognate amino acid is chemically bonded (charged).

Question 6

P site (peptidyl) binds to….

Answer 6

binds to the tRNA attached to the growing peptide chain

Question 7

A site (aminoacyl) (3)

+ relative location of ribosome and end chain number

Answer 7

binds to the tRNA carrying the next amino acid to be added

most 3’ area

front of ribosome

Question 8

E site (exit) (2)

+ relative location of ribosome

Answer 8

binds to the tRNA that carried the previous amino acid added

back of ribosome

Question 9

Initiator complex in translation (3)

Answer 9

ribosome+mRNA+ initiator tRNA bound to meyhionine

Question 10

translation initation in eukaryotes: (4)

Answer 10

First, the tRNA carrying methionine attaches to the small ribosomal subunit.

Together, they bind to the 5’ end of the mRNA by recognizing the 5’ GTP cap (added during processing in the nucleus).

Then, they “walk” along the mRNA in the 3’ direction, stopping when they reach the start codon (often, but not always, the first AUG).

Binds there an large subunits come and and bind onto to form initiation complex. It is now ready to accept the first tRNA in the A site

GTP is hydrolyzed to GDP and translation begins

Question 11

Translation initation in prokaryotes

Answer 11

the small ribosomal subunit doesn’t start at the 5’ end of the mRNA and travel toward the 3’ end. Instead, it attaches directly to certain sequences in the mRNA. These Shine-Dalgarno sequences come just before start codons and “point them out” to the ribosome.

Question 12

GTP elongation

Answer 12

During the elongation stage of translation, ENlongation factor-GTP is used as an energy source for the binding of a new amino bound tRNA to the A-site of the ribosome.
It is also used as an energy source for the translocation of the ribosome towards the 3’ end of the mRNA.

Question 13

GTP in initation

Answer 13

The large subunit binds to form initiator complex and GTP is hydrolyzed into GDP completinng initiation.

Question 14

tell me what happens after inititation complex loaded (4)

Answer 14

correct aminoacy tRNA (amino acid+trna aka charged) is loaded to the A site by Elongation factor GTP

Peptide transferease in large subuit forms peptide bonds between the carboxyl group of the growing polypeptide and the amino agroup of the amino acid in the A site. As the peptide bond is transfered to the amino acid in A site, P site trna is uncharged

Ribosome translocate in which the tRNA with the polypeptde shifts from A-P site and the uncharged tRNA shift from P to E site where it is ejected.

The next codon of mRNA is now in the A site and the next amino actyl tRNA can be loaded by Elongation factor GTP

Question 15

Tell me about stop codons (3)

Answer 15

They are not reocgnized by tRNAs but by proteins called release factors

When ribosomes reaches the stop codon the release factor binds the A site and stimulates peptidyl transferease to cleave the polypeptide from the P site tRNA

Ribosome subunits seperate and detach from mRNA and the mpty tRNA and release factor also seperate

Question 16

translation rate determining step

Answer 16

how fast ribosome find start codon

Question 17

Phosphorylation+ ex (2)

Answer 17

Phosphorylation can either activate a protein or inactivate it. Kinase is an enzyme that phosphorylates proteins.

CDK undergos dephosphorlation and loses phosphate group to become activated. It then phosphorlates MAP (gives phosphate group) to promote spindle assembly and mitotic entry.

Question 18

Unbiquitination

Answer 18

addition of ubiquitin molecules to proteins target them for deconstruction by the proteasome marks proteins needed to be degraded

Question 19

proteolysis +ex (2)

Answer 19

specific cleavage of the protein can induce activity

ex: HIV enzyme pretease cleaves viral protein to mature

Question 20

Epigenectics

Answer 20

changes in gene transcription occurs without changes in DNA sequence

Question 21

lysines on histone tail
What is it and modification on it….. (2)

Answer 21

Histone tails contain a large number of positively charged lysine and arginine residues, and thus preferentially contact DNA via electrostatic interactions.

modification on it affect yranscription of genes/ whether a gene is tirned on or off

Question 22

Histone acetylation

Answer 22

add acetyl groups (Ch3OO-) to histone tails which makes histones more negative and DNA will repulse away. This would mean DNA is winded around less tight and gene expression will increase.

Question 23

methylation of histone tails

Answer 23

2 or 3 methyl group are added to lysine of the histones can activate and repress transcritption of gen3s

Question 24

DNA methylation at CpG

Answer 24

methyl group added to CPG means cystosin-phophodiester bond-Guanine
These CpG islands are usually located in the promoter region, and methylation suppresses the activity of transcription. This is because it blocks general transcritption factors to bind to promotor

Question 25

Chromatin remodeling complex (3)

+general more profesion sum up about the states before and after

Answer 25

displaces nucelosomes from promotor regions activating transcription. Slides nucleosome to create spacing.

ATP dependent

rearrangement of chromatin from a condensed state to a transcriptionally accessible state, allowing transcription factors or other DNA binding proteins to access DNA and control gene expression.

Question 26

Translation regulation (2)

Answer 26

control of protein synthesis

rate of translation inititation or formation of the inititation complex

Question 27

Posttranslational regulation

Answer 27

Control of protein abundance and activity (avaliable of functional proteins)

Question 28

Abundance of protein depends on its

Answer 28

rate of synthesis (translation inititation) and degradation (posttranslational)

Question 29

Activity of protein depends on (2)

Answer 29

Post translational modifications

phosphorlation and processing (cleavage)

Question 30

The expression level of a specific gene depends on the (2)

Answer 30

Abundance of protein and its activity