Topic 7 Flashcards
translation is carried out on…
ribosomes
mRNA read ….
5’ to 3’
tRNA
allow for change in “language” (between mRNA and amino acids)
how many possible amino acid encoding codons?
61 (+3 STOP)
tRNA read….
3’ to 5’ (anticodon)
aminoacyl tRNA
special tRNA with a specific amino acid covalently bound at 3’ end
rRNA
serves both a structural and functional role; RNA components of ribosomal subunit
anticodon is located on…
the tRNA
______ ribosomes are more complex than_________ ribosomes.
eukaryotic, prokaryotic
prokaryotic ribosomes
70S; 50S large, 30S small
eukaryotic ribosomes
80S; 60S large, 40S small
what makes up ribosomes?
protein and rRNA
ribosomes are assembled where
nucleolus of nucleus
describe ribosome assemble
- ribosomal proteins are imported to nucleolus
- they attach to pre-rRNA
- pre-rRNA splits to two (large and small subunit)
tRNAs are synthesized by…
RNA pol III
__-shaped structure is critical for proper anticodon function
L
3 steps of tRNA processing
produced through RNA processing
- RNA cleavage
- covalent addition of CCA
- base modification (RNA editing)
There are _____ different aminoacyl tRNA synthetase
20
Each aminoacyl tRNA synthetase recognizes
- correct amino acid
- correct codon on mRNA
Three steps to “charge” a tRNA
- activation of amino acid
- addition of amino acid to tRNA
- proper folding of tRNA which can bring amino acid to the ribosome
What are the first 2 controls for specificity of amino acid incorporation into a protein?
- matching correct amino acid to correct tRNA (specificity of enzyme)
- correct base-pairing of codon and anticodon (specificity of base pairing)
wobble hypothesis
some tRNAs can recognize more than one mRNA codon
monocistronic
- one gene codes for one protein
- eukaryotic genome
plycistronic
- one gene codes for more than one protein
- prokaryotic genome
3 stages of translation
- initiation
- elongation
- termination
signals for translation initiation in prokaryotes
-Shine-Dalgarno sequence
signals for translation initiation in eukaryotes
small ribosomal unit binds to 5’ cap of mRNA and slide along until it finds start codon
initiation of translation in euk. part 1
40S ribosomal subunit + eIFs (eukaryote Initiation Factors) + charged tRNAmet assemble
initiation of translation in euk. part 2
- assembly from Step 1 meets up with a mature mRNA (poly AA tail + PABP and 5’ cap)
- and binds to its 5’m7G cap
initiation of translation in euk. part 3
Step 2 assembly starts at 5’m7G cap and scans mRNA for AUG start codon
initiation of translation in euk. part 4
- Entire complex dissociates from start site (except the 40S subunit and tRNAmet ),
- 60S ribosomal subunit attaches
elongation stage involves which 3 tRNA binding sites?
- A (aminoacyl) site
- P (peptidyl) site
- E (exit) site
A (aminoacyl) site
arrival
P (peptidyl) site
pause
decoding centre
within small subunit; ensures proper aminoacyl tRNA pairs with codon
third step in specificity
decoding centre
elongation of translation step 1
tRNAmet is at start site from the cap
elongation of translation step 2
the next tRNA comes to A site
elongation of translation step 3
a peptide bond forms between the first two amino acids
elongation of translation step 4
ribosome moves downstream (A site to P site); translocation
elongation of translation step 5
repeat steps 2-4
termination of translation step 1
stop codon ends up in A site
termination of translation step 2
a releasing factor moves into A site
termination of translation step 3
poly-peptide chain released
termination of translation step 4
release factor causes ribosome to disassemble from mRNA
post-translational modification
chemical modification of a polypeptide chain after translation
chaperones
protein that keeps protein unfolded until completely synthesized and facilitates folding, but does not incorporate into complex
proteolysis or cleavage
important for maturation of several proteins
signal sequences
mature proteins that target proteins to specific cellular compartments
some enzymes and hormones require……. to create a functionally active protein
cleavage
types of post-translational modification
- phosphorylation
- glycosylation
- lipid addition
- ubiquitylation
phosphorylation
small molecules such as phosphate added to regulate protein activity
glycosylation
carbohydrate addition to form glycoproteins
lipid addition
lipid addition to form lipoproteins
ubiquitylation
addition of ubiquitin polypeptide to target proteins for degradation
unlike protein cleavage, PTMs are….
reversible
What processes can ultimately regulate the level of a protein in the cell?
regulation of degradation
autpophagy
protein degradation by lysosomes