Transcription and translation

Question 1

In the area of molecular biology, what is meant by the term transcription?

Answer 1

Transcribing DNA into RNA

Question 2

List three types of RNA found in a cell and briefly explain their function.

Answer 2

• mRNA: messenger RNA encodes for a protein
• rRNA: ribosomal RNA read AA order and link them tog.
• tRNA: transfer RNA carries specific AA & has anticodon that should match codon of mRNA
• snRNA: small nuclear RNa

Question 3

For transcription in prokaryotic cells, explain what is meant by the term Holoenzyme.

Answer 3

Core enzyme (big unit) + Sigma factor (sml) = holoenzyme

Question 4

Provide two examples each of DNA sequences upstream of a gene transcription initiation site in prokaryotic cells and eukaryotic cells and where is it located

Answer 4

• Pro: -10 Pribnow box (TATAAT); -35 TTGACA

- Euk: -35 TATA box; -80 CAAT box

Question 5

Are there any types of RNA molecules that are found only in eukaryotic cells? If so name one

Answer 5

Pre-mRNA which contain introns that must be cut out before translation

Question 6

T or F: DNA Polymerase and RNA Polymerase are similar in that their newly synthesized nucleotide sequence is produced in a 5’ to 3’ direction?

Answer 6

True

Question 7

T or F: DNA Polymerase and RNA Polymerase are different in that one requires a primer and one does not?

Answer 7

True: DNA pol. require primer, RNA pol. start @ promoter region on DNA

Question 8

What are the two types of transcription termination known of in bacterial cells?

Answer 8

Rho dependent: require a protein to roll up RNA to break strong H bond b/w DNA & RNA
Rho independent: Complementary bases on mRNA quickly attract to form a hairpinloop (2º structure) forcing the RNA to break from weak H bond w/ DNA

Question 9

List three main modifications required to convert pre-mRNA molecule to mature mRNA molecule in eukaryotes.

Answer 9

1. 5’ cap
2. Intron splicing
3. Poly (A) tail

Question 10

What’s an intron and exon?

Answer 10

Intron: non-coding section
Exon: codes for a protein

Question 11

Define translation in molecular biology

Answer 11

Translating the sequence of codes in mRNA into a sequence of AA

Question 12

explain what is meant by “coupled” and “uncoupled”. When transcript+slate in prok. are coupled while euk. is uncoupled

Answer 12

Prok. = coupled: these 2 steps are done together at the same time
Euk. = Uncoupled: the steps are completed seperately

Question 13

What is a ribosome and what is it composed of?

Answer 13

ribosome is a protein that translates mRNA into AA (protein). It is composed of rRNA attached to proteins forming a large sub unit and a small sub unit

Question 14

Describe the order in which the ribosome sub units and any other relevant molecules assemble on the mRNA during Initiation of Translation

Answer 14

1. Sml subunit aligns onto Shine-dalgarno sequence
2. anticodon of tRNA links on codon of mRNA
3. Lrg sub unit assemble over it

Question 15

Name the enzyme that attaches AA onto tRNA (charges tRNA)

Answer 15

aminoacyl tRNA synthase

Question 16

What’s a codon and where is it found

Answer 16

3 base sequences on the mRNA

Question 17

What’s an anti-codon and where is it found

Answer 17

3 base sequence on the tRNA

Question 18

What is the “start codon” for most translated genes?

Answer 18

AUG (Met)

Question 19

What’s the significance of the Shine-Dalgarno sequence in translation initiation in prokaryotes?

Answer 19

Where ribosome attaches onto for translation initiation & upstream from start codon

Question 20

Explain the A-site (aminoacyl site), the P-site (peptidyl site) and the E site (exit
site) found in a ribosome during translation elongation.
And what happens when a stop codon is reached

Answer 20

• A-site: where anticodon on new tRNA binds onto codon of mRNA
• P-site: where a peptide bond forms w/ a AA in A-site with another on P-site
• E-site: when ribosome shuffle down (5’ to 3’) the tRNA moves to E-site where it exits ribosome
• tRNA for stop codon release factors => cleavage of polypeptide on tRNA in P site

Question 21

Explain the “wobble hypothesis”.

Answer 21

3rd base of codon and 1st base of anticodon (run antiparallel) doesn’t have to match = non-standard base pairing

Question 22

What is an operon? Are operons found in Prokaryotic cells, Eukaryotic cells, both cell types, or neither?

Answer 22

• Multiple genes on a segment of DNA. So when transcribed the mRNA has 1x promoter & terminator and multiple genes = multiple protein (translated indiv.)
• prokaryotic cells

Question 23

Give an example of an eukaryotic Core Promoter and an example of an eukaryotic Regulatory sequence

Answer 23

Core promoter: RNA Pol II

Reg. sequence: CAAT box

Question 24

What is the Golberg-Hogness box (TATA box)?

Answer 24

-35 (35th nucleotide upstream). One of the sequences that help to recognise/enhance the start gene to start transcription

Question 25

What’s the diff. b/w ribose & deoxyribose?

Answer 25

ribose: has -OH on C 2
deoxyribose: has H on C 2

Question 26

Describe the 3 steps in transcription/translation (not the same process)

Answer 26

1. Initiation
2. Elongation
3. Termination

Question 27

What’s the sense & antisense strand?

Answer 27

sense: non-template (/coding : same sequence as mRNA but T replaced w/ U)
anti: template (/non-coding)

Question 28

What are the 3 types of transcription termination in eukaryotic cells?

Answer 28

• RNA pol. I: similar to Rho dependent
• RNA pol. III: stop transcribing after string of U produced
• RNA pol. II: doesn’t stop @ terminator

Question 29

What’s the 5’ cap & what does it do?

Answer 29

G nucleotide reverses structure = stabilise mRNA = correct initiation of translation

Question 30

Describe translation initiation in eukaryotes

Answer 30

1. Risobome attach onto 5’ cap & slide to start codon

2. Kozak consensus seq. (AUG) helps identify start codon