DNA Flashcards
1
Q
what is the function of mRNA? (ITS)
A
- (eukaryote) takes the information out of the nucleus via the nuclear pore to the cytoplasm for translation
- acts a template for translation
- as each codon within coding region of mRNA represents an aa in a polypeptide, sequence of codons will determine polypeptide sequence
2
Q
what is the function of tRNA? (AT)
A
- bring in specific aa in a sequence corresponding to sequence of codon in mRNA to growing polypeptide
- facilitate translation due to its dual specificity
- ability to bind to a specific single aa
- ability of anticodon to base pair with mRNA codon
3
Q
what is the function of rRNA? (RICE)
A
- forms ribosomes by associating with a set of proteins
- 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
- 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
- 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
4
Q
where does DNA replication occur?
A
S phase of interphase
5
Q
what is the process of DNA replication? (5272)
A
- begins at ORI
- HELICASE & other proteins recog. & bind to ORI -> break H bonds btw complementary base pairs to unzip DNA DOUBLE HELIX using ATP
- replication fork forms & spread in both directions -> creating REP. BUBBLE
- SSBP bind to each separated DNA strand -> prevent reannealing
- topoisomerase relieve overwinding stress by swiveling, breaking & rejoining DNA strand
- primase add RNA primer to BOTH strand
- provide 3’OH end -> DNA POL synthesize complementary DNA strand in 5’ to 3’ direction by adding deoxyribonucleotide to existing 3’OH end
- DNA POL use parental DNA strand as template to synthesise complementary strand -> add dNTPs in seq. complementary to parental strand
- adenine base pair w/ thymine, C > G
- DNA pol catalyse formation of phosphodiester bonds btw adjacent nucleotides on new strand
- DNA pol proofread previous synthesized seq -> remove & replace incorrect nucleotide to ensure correct BP
- leading strand synthesized continuously (5’ to 3’) // lagging strand synthesized discontinuously (3’ to 5’) in okazaki fragments
- another DNA pol excise RNA primer -> replace with dN
- DNA ligase seal nicks -> catalyse (same as DNA POL)
- parent DNA strand & newly synthesized complementary strand rewind -> double helix
- resultant helix: 1 parental + 1 daughter -> SCR
6
Q
explain why DNA is known as ANTIPARALLEL double helix (
A
- 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 sugar phosphate backbone aligned // to e/o but pointing in opp. directions
7
Q
where does transcription take place at?
A
nucleus
*synthesise mRNA (coding strand) from DNA using non-coding strand as template
8
Q
what is the process of transcription? (IET: 371)
A
- (EU) GTF assemble at promoter (PRO) RNA POL bind to promoter w/ aid of protein factors
- recruit RNA POL & position correctly at promoter -> form TIC
- RNA POL unzip DNA double helix by…
- only non-coding strand: used as template to synthesis complementary mRNA
- RNA POL adds free ribonucleotides -> CBP w/ dN on template strand
- A-T: 2H bonds // C-G: 3
- T replaced by U in mRNA
- RNA POL catalyse formation of PB btw adj. free ribonucleotides -> form sugar phosphate backbone
- mRNA synthesized 5’ to 3’ while template opp -> ribonucleotides added to 3’OH end of growing mRNA strand
- TIC moves down double helix -> previous transcribed region REANNEALS
- RNA POL transcribes through termination sequence-> pre-mRNA released
9
Q
what is the process of post-transcriptional modification?
A
- addition of 7-methylguanosine cap to 5’ end of premRNA -> prevent degradation by ribonuclease + facilitate export of mature mRNA + help cell recog mRNA
- RNA splicing by spliceosome
- 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)
10
Q
where does translation takes place at?
A
cytosol
11
Q
what is the process of activation of aa?
A
- each SPECIFIC aa is covalently bonded to 3’ CCA stem of SPECIFIC tRNA w/ SPECIFIC anticodon -> catalyzed by specific aminoacyl-tRNA synthetase
- 20 aa -> 20 synthetase
- 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**
12
Q
what is the process of translation? (IET: 534)
A
- 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)
- anticodon (UAC) of initiator tRNA CBP w/ AUG of mRNA
- large ribosomal subunit bind to complete ribosome -> form TIC
- initiator aminoacyl-tRNA position at P site -> leave A site vacant for addition of next aminoacyl-tRNA
- GTP req
- incoming aminoacyl-tRNA bind to A site by CBP -> H bonds btw anticodon & mRNA (QUOTE)
- 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
- ribosome translocate by shifting 1 codon down mRNA in 5’ to 3’ (
