Translation and Post-translation 2C part 2 Flashcards
ribosomes are composed of
2 subunits made of a complex of protein and rRNA
Large subunit 50S (2)
+general sum up
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
small subunit 30S (2)
+general sum up
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
each subunit of the ribosome
exist separately in the cytoplasm but join tgt on the mRNA molecule during translation
charged tRNA
tRNA to which its cognate amino acid is chemically bonded (charged).
P site (peptidyl) binds to….
binds to the tRNA attached to the growing peptide chain
A site (aminoacyl) (3)
+ relative location of ribosome and end chain number
binds to the tRNA carrying the next amino acid to be added
most 3’ area
front of ribosome
E site (exit) (2)
+ relative location of ribosome
binds to the tRNA that carried the previous amino acid added
back of ribosome
Initiator complex in translation (3)
ribosome+mRNA+ initiator tRNA bound to meyhionine
translation initation in eukaryotes: (4)
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
Translation initation in prokaryotes
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.
GTP elongation
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.
GTP in initation
The large subunit binds to form initiator complex and GTP is hydrolyzed into GDP completinng initiation.
tell me what happens after inititation complex loaded (4)
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
Tell me about stop codons (3)
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
translation rate determining step
how fast ribosome find start codon
Phosphorylation+ ex (2)
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.
Unbiquitination
addition of ubiquitin molecules to proteins target them for deconstruction by the proteasome marks proteins needed to be degraded
proteolysis +ex (2)
specific cleavage of the protein can induce activity
ex: HIV enzyme pretease cleaves viral protein to mature
Epigenectics
changes in gene transcription occurs without changes in DNA sequence
lysines on histone tail
What is it and modification on it….. (2)
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
Histone acetylation
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.
methylation of histone tails
2 or 3 methyl group are added to lysine of the histones can activate and repress transcritption of gen3s
DNA methylation at CpG
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
Chromatin remodeling complex (3)
+general more profesion sum up about the states before and after
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.
Translation regulation (2)
control of protein synthesis
rate of translation inititation or formation of the inititation complex
Posttranslational regulation
Control of protein abundance and activity (avaliable of functional proteins)
Abundance of protein depends on its
rate of synthesis (translation inititation) and degradation (posttranslational)
Activity of protein depends on (2)
Post translational modifications
phosphorlation and processing (cleavage)
The expression level of a specific gene depends on the (2)
Abundance of protein and its activity
