14. Translation - the process

Question 1

what do ribosomes do in translation?

Answer 1

act as a platform or scaffolding to hold aminoacyl tRNAs and mRNA codons

catalytic machinery to join the alligned amino acids together to form a polypeptide

Question 2

what are the three stages of translation and what do they require? (4 points)

Answer 2

initiation, elongation and termination. require aditional protein factors as well as mRNA, tRNA and ribosomes

Question 3

what is the start codon, what does it do and what cell is it in?

Answer 3

the start codon is the first codon of a mRNA transcript translated by a ribosome. it begins translation. the codon is AUG and this is only in eukaryotes

Question 4

how does translation occur in prokaryotes?

Answer 4

ribosomes bind before AUG - it must have AGGAGG before AUG

Question 5

what is the starting codon, what amino acid is it and what does it do

Answer 5

the start codon is AUG and they are the leader sequence that allow mRNA to interact stably with a ribosome before translation begins. they code for methionine

Question 6

what is the shine dalgarno sequence?

Answer 6

its in prokaryotic cells found in the initiator region - about 10 nucleotides upstream from the start codon AUG. influences where the translation process starts in prokaryotes

Question 7

how and what is the energy provided for translation

Answer 7

hydrolysis of guanosine triphosphate (GTP)

LOOK AT IMAGE

Question 8

what is the protein ‘inititation factor’

Answer 8

bringing all the components required for translation together - mRNA, inititator tRNA and a small ribosomal subunit

Question 9

what are the three tRNA binding sites?

Answer 9

protein (P) amino acid (A) exit (E)

Question 10

what is elongation? what are the three steps called?

Answer 10

amino acids are added one by one to the previous amino acid of the growing chain. three steps are

codon recognition

peptide bond formation

translocation

Question 11

what is codon recognition in elongation?

Answer 11

a charge tRNA is delivered to the A site of the ribsome and base pairs with its codon. energy from GTP is necessary for accuracy and protein factors

Question 12

what is peptide bond formation in elongation?

Answer 12

a covalent bond is formed between the two amino acids attached to the tRNAs and the A and P sites. its to keep the amino acids bonded after elongation

Question 13

what is translocation?

Answer 13

the ribosome translocates the tRNA in the A site to the P site, at the same time the tRNA in the P site is moved to the E (exit) site where its released and the polypeptide chain continues to grow

Question 14

what is termination? what are the three codons?

Answer 14

the stopping of elongation. it will stop when a ‘stop’ codon in the mRNA reaches the A site in the ribosome. the three codons are UAG, UAA and UGA

Question 15

what are the components necessary in inititaion? (2)

Answer 15

GTP, start codon

Question 16

what is a polyribosome?

Answer 16

when multiple ribosomes translate a mRNA molecule at the same time. makes one copy of the same polypeptide

Question 17

where does transcription and translation occur in eukaryotes and prokaryotes?

Answer 17

eukaryotes: transcription in the nucleus, translation in cytoplasm - spatially seperated

prokaryotes: transcription and translation occur in the same celluar compartment as there is no nucleous

Question 18

what is coupling of transcription and translation? what cell is it in?

Answer 18

there is no sepereation spatially OR temporally of transcription and translation in prokaryotes. translation begins while the mRNA is still being synthesied.

Question 19

what is the defintion of a gene?

Answer 19

a gene is a region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule

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