Transcription & Translation

Question 1

What are codons?

Answer 1

Sets of 3 bases in DNA/RNA

Question 2

How many possible codon combinations are there?

Answer 2

64

Question 3

How many stop codons are there?

Answer 3

3

Question 4

What are the stop codons?

Answer 4

TAG/UAG

TAA/UAA

TGA/UGA

Question 5

Why is the genetic code degenerate?

Answer 5

More than one codon will code for the same amino acid

Question 6

Which amino acids are coded for by only one codon?

Answer 6

Tryptophan

Methionine

Question 7

Which codon codes for methionine?

Answer 7

AUG

Question 8

What name is given to codons which code for the same amino acid?

Answer 8

Synonyms

Question 9

What is the “third base wobble”?

Answer 9

Variations in synonyms tend to occur in the third base

Question 10

Why is the genetic code universal?

Answer 10

All organisms use the same code in the formation of proteins

Question 11

What are the three major classes of RNA and how abundant are they?

Answer 11

Ribosomal RNA 71%

Messenger RNA 3%

Transfer RNA 15%

Question 12

Describe rRNA and its function.

Answer 12

Largest and most abundant type of RNA

Important structural component of ribosomes

Question 13

Describe mRNA and its function.

Answer 13

Vary considerably in length depending on the gene is was copied from

Carry genetic info from DNA to ribosome

Question 14

Describe tRNA and its function.

Answer 14

Smallest RNA (75-95 nucleotides long)

Cloverleaf structure due to internal base pairing

Transfers amino acids from cytoplasm to ribosome

Anticodon binds to mRNA codon

3’ end holds amino acid

Question 15

What end of mRNA is the polyA tail added to?

Answer 15

3’ end

Question 16

Which strand is used to create the pre-mRNA and what is the first codon?

Answer 16

Non-sense strand

TAC

Question 17

What are the stages on transcription in bacteria?

Answer 17

Initiation

Elongation

Termination

Question 18

What is polycistronic mRNA?

Answer 18

Contains information for more than 1 peptide

Question 19

When does translation occur in bacteria?

Answer 19

Straight after transcription

Question 20

What shape is RNA polymerase?

Answer 20

Claw-shaped

Question 21

How does transcription differ in bacteria and eukaryotes?

Answer 21

Bacteria = in cytosol, eukaryotes = in nucleus

Bacteria = translated as soon as mRNA is formed, eukaryotes = mRNA is processed and moves out of nucleus

Bacteria = polycistronic mRNA

Eukaryotes = requires formation of a transcription initiation complex

Question 22

What is capping?

Answer 22

7-methyl guanosine added to 5’ end of mRNA in reverse orientation by a 5’-5’ triphosphate bridge

Question 23

What are the functions of capping mRNA?

Answer 23

Protects mRNA from exonucleases (stabilisation)

Facilitates transport out of nucleus

Plays a role in attachment to 40S subunit

Question 24

What is polyadenylation?

Answer 24

Addition of a polyA tail to the 3’ end of mRNA

Carried out by proteins which bind to specific sequences in the 3’UTR

Question 25

What is the function of polyadenylation?

Answer 25

Stabilises and aids in transport

Question 26

What are always removed in splicing?

Answer 26

Introns

Question 27

What is alternative splicing?

Answer 27

Removal of all introns Removal of some exons

Question 28

How many introns and exons are there in a gene on average?

Answer 28

7. 8 introns | 8. 8 exons

Question 29

What is the function of alternative splicing?

Answer 29

Allows a single gene to code for a number of different proteins

Question 30

Where does translation occur?

Answer 30

In cytosol on ribosomes

Question 31

What are the 3 binding sites for tRNA on a ribosome?

Answer 31

A site (aminoacyl) P site (peptidyl) E site (exit)

Question 32

What is found in the A site on the ribosome?

Answer 32

Holds tRNA carrying the next AA

Question 33

What is found in the P site on the ribosome?

Answer 33

Holds tRNA carrying growing peptide

Question 34

What occurs at the E site on the ribosome?

Answer 34

Discharged tRNAs leave

Question 35

What are the two subunits of a 70S ribosome?

Answer 35

50S and 30S

Question 36

What are the two subunits of an 80S ribosome?

Answer 36

60S and 40S

Question 37

What is a Svedberg?

Answer 37

Unit of sedimentation velocity

Question 38

What is the function of aminoacyl tRNA synthetases?

Answer 38

Charge tRNA with the correct amino acid using hydrolysis of ATP

Question 39

What are the three stages of eukaryotic translation?

Answer 39

Initiation Elongation Termination

Question 40

What is the initiation stage of translation?

Answer 40

Formation of initiation complex Ribosome is bound to specific initiation site of mRNA Initiator tRNA is annealed to the initiator codon and bound to ribosome

Question 41

What is the elongation stage of translation?

Answer 41

Joining amino acids to growing polypeptide chain according to sequence specified by mRNA until termination codon is reached

Question 42

What is the termination stage of translation?

Answer 42

Termination codon gives signal for peptide to be released from ribosome Ribosomal subunits disassemble

Question 43

What is a polyribosome?

Answer 43

Several ribosomes simultaneously translating one mRNA

Question 44

What are ribosomes made up of?

Answer 44

rRNA and protein

Question 45

How does streptomycin work?

Answer 45

Binds 30S subunit to distort it and interferes with initiation of translation

Question 46

How does tetracycline work?

Answer 46

Interact with 30S to block access of aminoacyl tRNA to initiation complex of translation

Question 47

How does chloramphenicol work?

Answer 47

Inhibits prokaryotic peptidyl transferase

Question 48

How does puromycin work?

Answer 48

Similar structure to aminoacyl tRNA so becomes incorporated into polypeptide to inhibit further elongation

Question 49

How does diphtheria toxin work?

Answer 49

Inactivates eukaryotic elongation factor eEF2 to prevent translocation of tRNAs within ribosomes

Question 50

How do clindamycin and erythromycin work?

Answer 50

Bind irreversibly to 50S to inhibit translocation of tRNAs within ribosomes

Question 51

Which drug affects both eukaryotes and prokaryotes?

Answer 51

Puromycin

Question 52

Which drugs interfere with initiation of translation?

Answer 52

Streptomycin Tetracycline

Question 53

Describe prokaryotic translation.

Answer 53

1. Initiation factors help formation of 30S initiation complex with fmet 2. GTP cleaved and initiation factors released when 50S and 30S join to form 70S initiation complex 3. Elongation factors direct binding of appropriate tRNA to A site 4. Peptidyl transferase of 50S catalyses peptide bond formation 5. Ribosome moves 3 nucleotides along, 5' to 3' 6. Process repeats until termination codon is recognised by a release factor - induces peptidyl transferase to release polypeptide and complex dissociates