- attaches to specific A.A. at 3' end - brings A.A. to ribosome via its anticodon

translation Flashcards by Nayla Blaine

what is the start codon. what A.A. does it code for

AUG= Met

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broadly, what does translation do (2)

synthesis of polypeptide directed by mRNA

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1 codon= how many nucleotides = how many A.A.

3 nucleotides =1 A.A.

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each codon specifies what

an A.A.

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What is redundancy in translation

most amino acids are specified by more than one mRNA codon

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What is no ambiguity in translation

each codon specifies one A.A.

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in ribosome, what does P site do

tRNA holding growing PP bound here

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in ribosome, what does A site do

tRNA holding next A.A.

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in ribosome, what does E site do

empty tRNA goes there

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what is in the large subunit of ribosome

P site
A site
E site

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what is in the small subunit of ribosome

mRNA binding site

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wobble theory

when tRNA goes to bind to codon, only 1st 2 need to match. If 3rd doesn’t, will wobble

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what does rRNA do

associates w protein to form ribosome

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what does mRNA do (3)

generated from DNA
serves as template for prot. synthesis
contains info in form of codons

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what does tRNA do ?

attaches to specific A.A. at 3’ end
brings A.A. to ribosome via its anticodon

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what is an anticodon

sequence of 3 bases that are complimentary to the bases on mRNA

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of tRNA identical

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what enzyme catalyzes attachment of A.A. to tRNA

aminoacyl-tRNA synthetase (each A.A. has specific one)

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is the catalysis of attachment of A.A. to tRNA endo or exo

endergonic

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how does aminoacyl-tRNA synthetase get its energy

AMP from ATP

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what are the 3 steps of translation

initiation, elongation, termination

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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

1. free (cytosolic proteins) 2. 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)

1. all prt synthesis starts on free rib 2. srp recognizes signal peptide, protein synthesis pauses 3. srp binds to srp receptor, bringing growing PP to ER 4. srp detaches and port synthesis continues 5. 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

1. E 2. P 3. E 4. P 5. E 6. 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

1. base pair substitution (replace one nucleotide with another) 2. base pair insertion or deletion (addition/ loss of nucleotides)

what are the 4 types of base pair substitutions

1. silent mutation (no change in AA sequence) 2. missense (AA changes, new AA different properties) 3. neutral (AA changes, similar proprties) 4. 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

1. spontaneous mutations: errors occur during DNA replication, repair, recombination 2. mutagens: physics/chem agents interacting w dna