3.5 - Translation & Genetic Code

Question 1

Translation

Answer 1

• Protein synthesis using RNA as template

- occurs outside of nucleus (unlike DNA replication and transcription)

Question 2

RNA classes involved in translation

Answer 2

mRNA - encodes protein
rRNA - comprises machinery
tRNA - decoding adaptor

Question 3

Prokaryotic ribosome components

Answer 3

Large ribosomal subunit: 23S rRNA + 5S + 31 proteins

Small ribosomal subunit:
16S rRNA + 21 proteins

Question 4

Functional sites on the ribosome

Answer 4

• Acyl site
• Peptidyl site
• Exit site
• mRNA binding site (below P and A sites)
• peptidyltransferase site

Question 5

Transfer RNA

Answer 5

• transport amino acids from the cytoplasm of a cell to a ribosome
• at least 20 different tRNAs, one for each amino acid

Question 6

Anticodon loop

Answer 6

-basepairs with codon on mRNA

Question 7

Acceptor stem

Answer 7

-amino acid attachment site

Question 8

Translation: Initiation

Answer 8

• binds to Shine-Dalgarno sequence just before the start codon
• Results in fully assembled ribosome w/ bound mRNA start codon under P and fmet-tRNA in the P site
• includes: initiation factors (IF1, IF2, IF3), small & large ribosomal subunit, fmet-tRNA, mRNA (including Shine-Dalgarno sequence)

Question 9

Translation: Elongation (of the polypeptide chain)

Answer 9

• Amino acids are brought to the ribosome by tRNAs and linked together to form a chain
• Acyl-tRNA binds to A site (amino acid attached), peptide bond forms between amino acids, translocation via GTP, new acyl-tRNA binds to A site, tRNA in E site leaves, new protein synthesized
• includes: elongation factors (EF-Tu, EF-G, EF-Ts), acyl-tRNAs, ribosome, mRNA

Question 10

Translation: Termination

Answer 10

• Release factors required to cleave polypeptide from final tRNA
• Dissociation of all components including completed polypeptide occurs
• include: release factors (RF1, RF2, RF3)

Question 11

Codons

Answer 11

• 3 nucleotide long code words on mRNA that translate to amino acids by way of the tRNAs
• AUG is start (met)

Question 12

Redundancy of the genetic code

Answer 12

-More than one codon for a given amino acid (wobble)

Question 13

Point mutations

Answer 13

-single base changes

Question 14

Base substitutions: Synonymous

Answer 14

• same amino acid

- no effect on function

Question 15

Base substitutions: Missense conservative

Answer 15

• similar amino acid

- may not effect function

Question 16

Base substitutions: Missense nonconservative

Answer 16

• dissimilar amino acid

- may alter function

Question 17

Base substitutions: Nonsense

Answer 17

• stop codon

- destroys function

Question 18

Indels: frameshift

Answer 18

• addition of nt
• new polypeptide
• alters function