translation Flashcards
what is the start codon. what A.A. does it code for
- AUG= Met
broadly, what does translation do (2)
synthesis of polypeptide directed by mRNA
1 codon= how many nucleotides = how many A.A.
3 nucleotides =1 A.A.
each codon specifies what
an A.A.
What is redundancy in translation
most amino acids are specified by more than one mRNA codon
What is no ambiguity in translation
each codon specifies one A.A.
in ribosome, what does P site do
tRNA holding growing PP bound here
in ribosome, what does A site do
tRNA holding next A.A.
in ribosome, what does E site do
empty tRNA goes there
what is in the large subunit of ribosome
- P site
- A site
- E site
what is in the small subunit of ribosome
mRNA binding site
wobble theory
when tRNA goes to bind to codon, only 1st 2 need to match. If 3rd doesn’t, will wobble
what does rRNA do
associates w protein to form ribosome
what does mRNA do (3)
- generated from DNA
- serves as template for prot. synthesis
- contains info in form of codons
what does tRNA do ?
- attaches to specific A.A. at 3’ end
- brings A.A. to ribosome via its anticodon
what is an anticodon
sequence of 3 bases that are complimentary to the bases on mRNA
of tRNA identical
no
what enzyme catalyzes attachment of A.A. to tRNA
aminoacyl-tRNA synthetase (each A.A. has specific one)
is the catalysis of attachment of A.A. to tRNA endo or exo
endergonic
how does aminoacyl-tRNA synthetase get its energy
AMP from ATP
what are the 3 steps of translation
initiation, elongation, termination
what do all steps of translation require
protein factors and energy (GTP hydrolysis)
what does initiation require
initiation factors
what are the 3 components of initiation
- binding of small ribosomal subunit to mRNA
- binding of initiator tRNA to mRNA
- attachment of large ribosomal subunit to small subunit
what does iniatiator tRNA contain
anti-codon (3’-UAC-5’) + A.A. Met
what does initiator tRNA base pair with on mRNA
AUG start codon
what does the attachment of the 2 ribosomal subunits require
- GTP
- initiator tRNA in P-site
what does elongation require
elongation factors
what are the 3 components of elongation
- codon recognition
- peptide bond formation
- translocation
what is codon recognition
in A site, mRNA codon forms H-bond with anticodon of incoming tRNA, requires GTP
what is peptide bond formation
- growing polypeptide transferred from tRNA in P site to tRNA in A site
- peptide bond formed b/n NH2 terminus of new A.A. and the COOH end of growing PP
what is translocation
- tRNA w/ growing polypeptide in A-site is moved to P-site
- empty tRNA in P-site moved to E-site & exits ribosome
- codon in A site now ready to receive next aminoacyl tRNA
- requires GTP
what happens during termination
- stop codon reaches A-site
release factor binds to the codon (NOT tRNA) - hydrolysis of bond b/n tRNA in P-site and polypeptide chain occurs
- polypeptide released
- ribosome dissociates and leaves mRNA
- breakdown of the translation assembly complex requires E (2GTP))
are polyribosomes found in prokaryotes or eukaryotes
both
what are polyribosomes
several ribosomes that can translate the same mRNA at once
when can a second ribosome assemble
when the first ribosome passes the AUG codon
what is the result of polyribosomes
mRNA makes many copies of same polypeptide
what are the two types of ribosomes found in cell
- free (cytosolic proteins)
- bound to rough endoplasmic reticulum (membrane and secreted proteins)
synthesis of ALL proteins starts where
free ribosomes
what directs the ribosome to become attached to ER
signal peptides (tell ribosome it needs to attach to RER)
where are signal peptides found
N-terminus of growing polypeptide
what does signal peptide consist of
20 hydrophobic A.A.s
what is the signal recognition particle (SRP) (3)
composed of protein and rna
recognizes signal peptide
brings ribosome (w/ polypeptide) to a receptor on ER
what is the SRP receptor (2)
- protein complex
- built into mb of ER
how do signal peptides target protein to ER (5 steps)
- all prt synthesis starts on free rib
- srp recognizes signal peptide, protein synthesis pauses
- srp binds to srp receptor, bringing growing PP to ER
- srp detaches and port synthesis continues
- signal peptide is cleaved off by an enzyme
what happens after proteins brought to ER (3)
- secreted proteins remain in ER lumen
- membrane proteins embedded in ER membrane
- ribosomes without signal peptide stay free in cytosol.
say if these characteristics are for eukaryotic or prokaryotic protein synthesis
1. have nucleus
2. lack nucleus
3. transcription and translation are seperated
4. transcription and translation are coupled
5. mRNA processing occurs
6. RNA polymerase requires transcription factors
- E
- P
- E
- P
- E
- E
what is a mutation
any change in genetic material of cell (at DNA level not at polypeptide sequence level)
what is a point mutation
changes in one base pair in a single gene
what are the 2 types of point mutations
- base pair substitution (replace one nucleotide with another)
- base pair insertion or deletion (addition/ loss of nucleotides)
what are the 4 types of base pair substitutions
- silent mutation (no change in AA sequence)
- missense (AA changes, new AA different properties)
- neutral (AA changes, similar proprties)
- nonsense (new codon codes for stop codon, translation prematurely terminated, truncated prot)
what is the type of base pair insertion or deletion
frame shift mutation: alter reading frame of mRNA, insertion/deletion is not a multiple of 3, all nucleotides downstream mutation are not properly grouped
what are the two causes of mutations
- spontaneous mutations: errors occur during DNA replication, repair, recombination
- mutagens: physics/chem agents interacting w dna
