DNA

Question 1

what is the function of mRNA? (ITS)

Answer 1

1. (eukaryote) takes the information out of the nucleus via the nuclear pore to the cytoplasm for translation
2. acts a template for translation
3. as each codon within coding region of mRNA represents an aa in a polypeptide, sequence of codons will determine polypeptide sequence

Question 2

what is the function of tRNA? (AT)

Answer 2

1. bring in specific aa in a sequence corresponding to sequence of codon in mRNA to growing polypeptide
2. facilitate translation due to its dual specificity
   - ability to bind to a specific single aa
   - ability of anticodon to base pair with mRNA codon

Question 3

what is the function of rRNA? (RICE)

Answer 3

1. forms ribosomes by associating with a set of proteins
2. main constituent of interface between large & small ribosomal subunit -> small ribosomal subunit can bind to mRNA as CBP occurs between rRNA in mRNA binding site of small ribosomal subunit and mrna
3. main constituent of P site (peptidyl-tRNA binding site) & A site (amino-acyl tRNA binding site) on large ribosomal subunit -> enables binding of aminoacyl-tRNA to P and A site
4. rRNA enzyme (peptide transferase) on large ribosomal subunit catalyse formation of peptide bond btw amino group of new aa in A site & carboxyl end of growing polypeptide in p site

Question 4

where does DNA replication occur?

Answer 4

S phase of interphase

Question 5

what is the process of DNA replication? (5272)

Answer 5

1. begins at ORI
2. HELICASE & other proteins recog. & bind to ORI -> break H bonds btw complementary base pairs to unzip DNA DOUBLE HELIX using ATP
3. replication fork forms & spread in both directions -> creating REP. BUBBLE
4. SSBP bind to each separated DNA strand -> prevent reannealing
5. topoisomerase relieve overwinding stress by swiveling, breaking & rejoining DNA strand
6. primase add RNA primer to BOTH strand
7. provide 3’OH end -> DNA POL synthesize complementary DNA strand in 5’ to 3’ direction by adding deoxyribonucleotide to existing 3’OH end
8. DNA POL use parental DNA strand as template to synthesise complementary strand -> add dNTPs in seq. complementary to parental strand
9. adenine base pair w/ thymine, C > G
10. DNA pol catalyse formation of phosphodiester bonds btw adjacent nucleotides on new strand
11. DNA pol proofread previous synthesized seq -> remove & replace incorrect nucleotide to ensure correct BP
12. leading strand synthesized continuously (5’ to 3’) // lagging strand synthesized discontinuously (3’ to 5’) in okazaki fragments
13. another DNA pol excise RNA primer -> replace with dN
14. DNA ligase seal nicks -> catalyse (same as DNA POL)
15. parent DNA strand & newly synthesized complementary strand rewind -> double helix
16. resultant helix: 1 parental + 1 daughter -> SCR

Question 6

explain why DNA is known as ANTIPARALLEL double helix (

Answer 6

1. 1 strand runs in 5’ to 3’ other 3’ to 5’
   2 (if DNA pol shown) DNA POL can only work in 5’ to 3’ -> extend new strand in opp. direction wrt rep. fork
2. 2 sugar phosphate backbone aligned // to e/o but pointing in opp. directions

Question 7

where does transcription take place at?

Answer 7

nucleus
*synthesise mRNA (coding strand) from DNA using non-coding strand as template

Question 8

what is the process of transcription? (IET: 371)

Answer 8

1. (EU) GTF assemble at promoter (PRO) RNA POL bind to promoter w/ aid of protein factors
2. recruit RNA POL & position correctly at promoter -> form TIC
3. RNA POL unzip DNA double helix by…
4. only non-coding strand: used as template to synthesis complementary mRNA
5. RNA POL adds free ribonucleotides -> CBP w/ dN on template strand
6. A-T: 2H bonds // C-G: 3
7. T replaced by U in mRNA
8. RNA POL catalyse formation of PB btw adj. free ribonucleotides -> form sugar phosphate backbone
9. mRNA synthesized 5’ to 3’ while template opp -> ribonucleotides added to 3’OH end of growing mRNA strand
10. TIC moves down double helix -> previous transcribed region REANNEALS
11. RNA POL transcribes through termination sequence-> pre-mRNA released

Question 9

what is the process of post-transcriptional modification?

Answer 9

1. addition of 7-methylguanosine cap to 5’ end of premRNA -> prevent degradation by ribonuclease + facilitate export of mature mRNA + help cell recog mRNA
2. RNA splicing by spliceosome
3. synthesis of poly-A-tail: cleave pre-mRNA by endonuclease + add A nucleotide by enzyme poly A pol downstream of polyadenylation signal (AAUAAA) -> (1)(2) + interacts with/ initiation factors to form TIC (translation)

Question 10

where does translation takes place at?

Answer 10

cytosol

Question 11

what is the process of activation of aa?

Answer 11

1. each SPECIFIC aa is covalently bonded to 3’ CCA stem of SPECIFIC tRNA w/ SPECIFIC anticodon -> catalyzed by specific aminoacyl-tRNA synthetase
2. 20 aa -> 20 synthetase
3. synthetase has SPECIFIC A.S that are complementary C&C to SPECIFIC aa & SPECIFIC tRNA w/ SPECIFIC anticodon -> demonstrate dual specificity -> ensure correct aa & tRNA joined to form correct aminoacyl-tRNA**

Question 12

what is the process of translation? (IET: 534)

Answer 12

1. EIF & initiator tRNA carrying methionine bind to small ribosomal subunit -> recognise & bind to 5’ 7-methylguanosine cap of mRNA & move 5’ to 3’ to find start codon (AUG)
2. anticodon (UAC) of initiator tRNA CBP w/ AUG of mRNA
3. large ribosomal subunit bind to complete ribosome -> form TIC
4. initiator aminoacyl-tRNA position at P site -> leave A site vacant for addition of next aminoacyl-tRNA
5. GTP req
6. incoming aminoacyl-tRNA bind to A site by CBP -> H bonds btw anticodon & mRNA (QUOTE)
7. peptide bond formed btw methionine & incoming aa in A site catalyzed by peptidyl transferase in large ribosomal subunit + methionine dissociate from initiator tRNA it was bounded to & remain bounded to 2nd aa at A site
8. ribosome translocate by shifting 1 codon down mRNA in 5’ to 3’ (