Transcription And Translation

Question 1

What is the difference between the expression of genes in chromatin?

Answer 1

• EUCHROMATIN genes are expressed

- HETEROCHROMATIN genes are not expressed

Question 2

What are the 3 stages of both transcription and translation?

Answer 2

• INITIATION
• ELONGATION
• TERMINATION

Question 3

What is the promotor sequence commonly found in eukaryotes?

Answer 3

• TATA box

TATAAAA
ATATTTT

Question 4

What is the role of the promotor region?

Answer 4

Signals where transcription factor binds, therefore the initiation of transcription

Question 5

What is the role of transcription factors?

Answer 5

• Binding of transcription factor determines DIRECTION of transcription of gene (5’ to 3’)
• Determines where RNA polymerase will bind

Question 6

What is the difference between upstream and downstream?

Answer 6

• UPSTREAM is in the 3’ to 5’ direction (right to left)

- DOWNSTREAM is in the 5’ to 3’ direction (left to right)

Question 7

What does a mutation at -10 indicate?

Answer 7

Mutation is 10 bases upstream of the transcription initiation site

Question 8

Where is the promotor sequence (TATA) located?

Answer 8

-30 upstream of the transcription initiation site

Question 9

In which direction is mRNA synthesised?

Answer 9

5’ to 3’

Question 10

Which strand is used as the template strand for mRNA?

Answer 10

3’ to 5’ bottom strand, so mRNA synthesised is a copy of the 5’ to 3’ coding strand

Question 11

What is the enzyme responsible for the synthesis of mRNA?

Answer 11

RNA polymerase

Question 12

What is the ORF?

Answer 12

Open reading frame of mRNA

Question 13

What processing is required to transform pre mRNA to mature mRNA?

Answer 13

• 5’ Capping
• 3’ Polyadenylation
• Splicing of introns

Question 14

Describe the process of 5’ capping

Answer 14

Addition of a methylated guanine to the 5’ end of the mRNA forming a 5’-5’ link

Question 15

What is the role of 5’ capping?

Answer 15

• PROTECTS mRNA FROM DEGRADATION

- Recognised by translation initiation factors which allows subsequent binding of the 40s subunit to the mRNA strand

Question 16

How is transcription terminated?

Answer 16

Transcription termination site sequence is recognised by SPECIFIC ENDONUCLEASE which cuts the chain a few bases downstream

Question 17

What enzyme is used for the addition of a 3’ polyA tail?

Answer 17

PolyA polymerase

Question 18

Describe how splicing occurs

Answer 18

• Removal of introns from pre mRNA using a SPLICOSOME
• HIGHLY SEQUENCE DEPENDANT
• Remaining exons are joined together using a ligase enzyme

Question 19

What are the consequences of a mutation in an intron splice site?

Answer 19

• Results in the skipping and removal of the adjacent exon
• Shorter mRNA chain formed
• Shorter protein formed

Question 20

What is UTR?

Answer 20

Untranslated regions of mRNA e,g, the 5’ cap and the 3’ polyA tail

Question 21

What are the three types of RNA?

Answer 21

• rRNA (ribosomal)
• mRNA (messenger)
• tRNA (transfer)

Question 22

How can 100000+ mRNA strands be synthesised from 25000 genes?

Answer 22

• SPLICING in eukaryotes can result in introns being left in (variable, sequence dependant)
• Transcription initiation can happen at different regions on the promotor

Question 23

How many RNA polymerase molecules are present in eukaryotes?

Answer 23

• e
• RNA polymerase I (rRNA)
• RNA polymerase II (mRNA)
• RNA polymerase III (tRNA)

Question 24

How is translation catalysed?

Answer 24

By RIBOSOMES

Question 25

How do the structure of ribosomes differ in prokaryotes and eukaryotes?

Answer 25

- Prokaryotes have 70s ribosomes (30s+50s) | - Eukaryotes have 80s ribosomes (60s+40s)

Question 26

What are ribosomes comprised of?

Answer 26

Many strands of rRNA and proteins

Question 27

What is the role of translation?

Answer 27

Change the laughter of the mRNA code of nucleotides into polypeptide code of amino acids

Question 28

What is a codon?

Answer 28

Triplet of bases that codes for one amino acid

Question 29

Why is the genetic code described as ambiguous and degenerate?

Answer 29

- AMBIGUOUS as each codon only codes for one amino acid | - DEGENERATE as one amino acid Dan be coded for by multiple codons

Question 30

What is the initiation codon that begins translation?

Answer 30

AUG which codes for methionine

Question 31

What are the 3 termination (STOP) codons?

Answer 31

- UGA - UAG - UAA

Question 32

Describe the structure of tRNA

Answer 32

- RNA stem loop that forms a clover model | - Contains an anticodon that is specific to a codon on mRNA that codes for an amino acid

Question 33

Where does the amino acid bind on tRNA?

Answer 33

3' end forming AMINO-ACYL tRNA

Question 34

What is the significance of the wobble position?

Answer 34

- 5' base of anticodon is IONISINE which can form a loose bond with the 3' base of the codon, hence a wobble position as the tRNA is not tightly bound - This allows the tRNA molecule to recognise more than one codon

Question 35

What processes during translation require energy?

Answer 35

- MULTIPLE PROCESSES REQUIRE ENERGY IN THE FORM OF GTP - Binding of 5' cap binding initiation factors on 40s subunit - Binding of tRNA to 60s subunit - TRANSLOCATION of tRNA molecules from the P site to the A site

Question 36

What is the role of peptidyl transferase?

Answer 36

- Catalyses the formation of a peptide bond between adjacent amino acids on the 3' ends of tRNA molecules - TRANSFER OF THE AMINO ACID FROM THE P SITE TO THE A SITE

Question 37

What is a polysome?

Answer 37

- mRNA chain with multiple ribosomes attachted which are translating simultaneously - Ribosomes attach at the 5' and and fall off the 3' end

Question 38

How does bacterial transcription and translation differ from humans?

Answer 38

- Simple promotor region (Prinbow -10) - Different transcription factors - Single RNA polymerase - NO POST TRANSCRIPTIONAL PROCESSING - Smaller ribosomes (70s) - Coupled transcription-translation (no nucleus)

Question 39

What is a gene?

Answer 39

Section of DNA that codes for a polypeptide