translation

Question 1

what is tRNA?

Answer 1

transfer RNA: links information in mRNA codons w specific amino acids

Question 2

what are codons?

Answer 2

series of 3 nucleotides in mRNA that code for an amino acid. they direct the placement of specific amino acids into a protein

Question 3

what is the start codon? (name and nucleotide sequence)

Answer 3

methionine; AUG

Question 4

what are the stop codons? (nucleotide sequences)

Answer 4

UAA, UAG, UGA

Question 5

what role do ribosomes play in translation?

Answer 5

site of translation, catalyzes the formation of peptide bonds betw amino acids, so that they form a polypeptide chain

Question 6

what are the 3 stages of translation

Answer 6

initiation, elongation, termination

Question 7

what happens during initiation?

Answer 7

• small subunit of ribosome attaches to AGGAGG sequence (prokaryotes)/5’ cap (eukaryotes
• moves along mRNA until it reaches start codon AUG -> methionine tRNA UAC binds to start codon
• mRNA + ribosome small subunit + tRNA = initiation complex
• large subunit joins initiation complex, has 3 sites: A(nticodon), P(olypeptide), E(xit)

Question 8

what occurs during elongation?

Answer 8

• anticodon of an incoming tRNA binds to codon at A site of ribosome
• amino acids linked by peptidyl transferase catalysis -> bond betw amino acid and tRNA broken in P site; bond formed betw amino acid and new amino acid in A site
• free tRNA moved to E site and released as ribosome moves on to next codon
  process repeats

Question 9

what happens during termination?

Answer 9

• release factor binds to complex when a stop codon enters A site
  -> disconnects polypeptide from the tRNA in the P site
• mRNA and ribosome subunits seperate

Question 10

what are the two sets of further instructions the proteins have post translation?

Answer 10

a: stay within cell - released to an organelle or remains in cytosol
b: go to ER to finish synthesis and then transport out of cell

Question 11

what are 3 examples of post-translational modification?

Answer 11

proteolysis. glycosylation, phosphorylation

Question 12

what is proteolysis?

Answer 12

cutting the polypeptide allowing the fragments to fold into different shapes

Question 13

what is glycosylation?

Answer 13

addition of sugars to polypeptide, important for targeting and recognition, forms glycoproteins

Question 14

what is phosphorylation?

Answer 14

addition of phosphate groups, alters shape of protein

Question 15

is a new mRNA necessary every time a protein needs to be synthesized?

Answer 15

no, the same mRNA can be used to make many copies of the same protein