Translation

Question 1

stop codons

Answer 1

3 (UAA, UAG, UGA)
signal to terminate transcription
do not code for amino acids

Question 2

start codon

Answer 2

only one in eukaryotes
signal to start translation
codes for methionine (AUG)

Question 3

large subunit of ribosome

Answer 3

contains tRNAs
made up on RNA and protein

Question 4

small subunit of ribosome

Answer 4

binds to mRNA
made of protein and RNA

Question 5

what synthesises rRNA

Answer 5

RNA polymerase 1

Question 6

rRNA main concepts

Answer 6

not synthesised into protein
processed by cleavage and chemical modifications into its final form
packaged with proteins of the small and large subunits in the nucleolus then transported into the cytoplasm

Question 7

what is a ribozyme

Answer 7

ribonucleic acid + enzyme
complex secondary structure

Question 8

rRNA maturation in nucleolus

Answer 8

Precursor rRNA cleaved into 4
smaller products and processed

Question 9

snoRNA

Answer 9

processes rRNA by guiding chemical modifications
non-protein coding
comes from introns

Question 10

assembly of ribosome

Answer 10

in cytoplasm in presence of mRNA

Question 11

what transcribes tRNA

Answer 11

RNA polymerase III

Question 12

how does a specific amino acid link to the tRNA

Answer 12

covalent linkage

Question 13

how is tRNA aminoacylated

Answer 13

aminoacyl-tRNA synthetase is an enzyme complex with binding sites for a specific amino acid, a specific tRNA and a molecule of ATP. pyrophopshate expelled from atp, amino acid covalently linked to 3’ of tRNA

Question 14

translation pre initiation complex

Answer 14

small ribosomal subunit and tRNA with methionine

Question 15

formation of pre initiation complex

Answer 15

cytoplasm: Met-tRNA binds small ribosomal
subunit then comes together with eIF2 and GTP
forms 40S complex

Question 16

sedimentation coefficient

Answer 16

large number=travelled further=larger complex

Question 17

mRNA binding to 40S complex

Answer 17

eIF4 proteins bind 5’ cap and more eIF proteins to form large complex. mRNA folded on itself through interaction between polyA tail binding
protein and eIF4 complex. eIF4 complex binds to eIF2 in the 40S subunit complex. 43S complex formed.

Question 18

scanning for start site

Answer 18

mRNA unfolds once 43S complex formed. 40S complex moves along mRNA until it hits the first AUG codon (start site)
Met-tRNA anticodon binds AUG
ATP hydrolysis used

Question 19

recruitment of large ribosomal subunit

Answer 19

GTP hydrolysis leads to release of eIF proteins and binding of Met-tRNA to large subunit

Question 20

structure of large ribosomal subunit (binding sites)

Answer 20

3 binding sites: A site (aminoacyl-tRNA), P site (peptidyl-tRNA), E site (empty)
MET-tRNA in middle pocket

Question 21

aminoacyl-tRNA binding

Answer 21

next aa-tRNA binds codon to A site
aa-tRNA is bound to EF1a + GTP
GTP hydrolysis

Question 22

EF1 alpha

Answer 22

protein that helps bring charged tRNA into contact with assembled ribosome

Question 23

result of GTP hydrolysis

Answer 23

conformational change in ribosome causing tRNA in A site to move, bringing the amino acid closer to tRNA in P site

Question 24

transpeptidation

Answer 24

ribozyme catalyses the formation of peptide bond
Peptidyl transferase transfers the peptide onto the growing chain
Amino acid dissociates from tRNA
in the P site
tRNA now uncharged so can dissociate
tRNA in A position slides to P position

Question 25

translocation

Answer 25

tRNA with polypeptide chain
(peptidyl-tRNA) moves into
the P site. ‘Empty’ tRNA moves to the E
site and is released. Powered by GTP hydrolysis

Question 26

termination

Answer 26

Release factor protein complex binds a STOP codon
(eRF1 subunit)
No more peptide bonds can be formed as complex in A site
GTP hydrolysis (eRF3 subunit) à complex falls apart, releasing the new polypeptide

Question 27

polyribosome

Answer 27

cluster of ribosomes translating the same mRNA molecule simultaneously so that multiple copies of protein are produced

Question 28

free polyribosomes in cytosol

Answer 28

translate mRNA into proteins that function within the cytosol, cytoskeleton, mitochondria, peroxisomes, and the nucleus.

Question 29

ER-bound poly ribosomes

Answer 29

translate mRNA into proteins that are processed in the ER and Golgi apparatus, and then directed to secretory vesicles, lysosomes, the cell membrane, or for secretion out of the cell.

Question 30

which position in a codon has most variability

Answer 30

third

Question 31

wobble base pairing

Answer 31

Base pairing is loose in the third position of tRNA-mRNA interaction]
Accounts for redundancy in last letter of codons in genetic code

Question 32

Correlation between amino acid structure and 2nd position

Answer 32

Neutral or silent mutation – does not affect protein sequence- occurs in 2nd or 3rd positions
changes in this position often result in amino acids with similar properties

Question 33

Ribonucleoprotein

Answer 33

RNA + protein complexes
eg ribosomes, eIF

Question 34

RNA world hypothesis

Answer 34

RNA World: Early life forms relied solely on RNA for both genetic information and enzymatic functions.

RNA-Protein World: RNA molecules started interacting with proteins, with ribozymes (RNA-based enzymes) evolving into RNA-protein complexes.

Modern Molecular Biology: Today’s biology features distinct roles for DNA (genetic storage), RNA (intermediary and catalytic roles), and proteins (structural and functional).
dT is synthesised from dU
(suggests that U came first