Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
22 Cards in this Set
- Front
- Back
|
DNA replication requires DNA Polymerase |
DNA Polymerase - catalysed step by step addition of deoxyribonucleotide units to DNA - New DNA assembled on template DNA - Requires primmer (with free 3’-OH) to begin synthesis - New DNA grows at 3’ (synthesis is 5’ to 3’)
|
|
|
DNA Replication |
DNA template Primase RNA primer DNA Polymerase Newly synthesised DNA |
|
|
Strands in DNA replication |
Second (anti parallel) strand of DNA is synthesised in fragments called OKAZAKI FRAGMENTS in a 5’ to 3’ direction. Fragments are joined together by ligase |
|
|
Types of RNA and RNA Polymerases |
mRNA Template for protein synthesis RNA polymerase 2 [Pol 2] ATP dependent tRNA Carries activated amino acids to ribosomes RNA polymerase 3 [Pol 3] rRNA Major component of Ribosomes RNA polymerase 1 [Pol 1]
All require template DNA, ribonucleotides and a divalent metal ion (Mg+) |
|
|
RNA Synthesis Steps |
Initiation RNA polymerase 2 and transcription factors assemble at promoter; RNA synthesis begins Elongation RNA polymerase 2 moves alone template strand as a RNA molecule grows in a 5’ to 3’ direction Termination RNA molecule completed and stabilised by modifications |
|
|
Initiation step |
Pol 2 bunds to a specific region of DNA - the PROMOTER TATA box [-25] CAAT box [-75] GC box |
|
|
Other RNA Pols and their Specific Promoters |
Pol 1 : UPE (upstream Promoter Element) and rInr Pol 3 : type 1 5sRNA type 2 tRNA |
|
|
How does RNA Polymerase read DNA |
RNA Polymerase must unwind the DNA to allow the template strand to be read [unwound DNA usually 17bp open] |
|
|
What is Required for Initation? |
Transcription Factors are also required, assembled in a complex with “mediator” Phosphorylation of Pol 2 allows it to move along the template |
|
|
Elongation Step |
RNA molecule grows 5’ to 3’ (new nucleotides added to 3’) |
|
|
Termination and Modification Step |
Modifications provide stability to RNA molecule Requires 5’ cap and a Poly A Tail |
|
|
Translation Requirements [Synthesis of Protein] |
mRNA - template with code of protein to be synthesised tRNA - adapters that make the link between nucleus acid and protein Amino Acids - in the form of aminoacyl tRNA requires aminoacyl tRNA Synthase Ribosomes
|
|
|
The Genetic Code |
STOP CODONS : UAA, UAG START CODON : Met AUG
|
|
|
Aminoacyl Transfer RNA Synthase |
Links a specific amino acid with a specific tRNA (defined by its anticodon) 3 Steps: 1) Amino Acid Activation step 2) Transfer of aminoacyl-AMP to specific tRNA 3) Driven by hydrolysis of pyrophosphate (PPi) using ATP (as reaction is energetically unfavourable) Amino Acid + 2ATP + tRNA + H2O = Aminoacyl tRNA + AMP + 2Pi |
|
|
Qualities of Aminoacyl tRNA Synthases |
Highly Discriminating One for each TYPE of amino acid Attachment of amino acid to tRNA occurs at activation site Have proof reading ability An editing site which can reject incorrect amino acids (recognised by incorrect sizing) Recognise tRNA on the basis of size, shape and/or by anticodon |
|
|
Ribosomes |
Has E, P and A sites |
|
|
Translation initiation in Eukaryotesi |
Requires initiation factors, GTP, Met-tRNAi and 40S ribosomal subunit Contains 4 stages |
|
|
STAGE 1 of Translation |
Assembly of complex on 5’cap Includes 40S Ribosomal Subunit and Met-tRNAi Met-tRNAi is a special initiation tRNA bearing methionine |
|
|
STAGE 2 of Translation |
ATP Hydrolysis to allow 40S to scan the mRNA for the start codon AUG (encoding Methionine) |
|
|
STAGE 3 of Translation |
Pairing of anticodon of Met-tRNAi with AUG codon if mRNA |
|
|
STAGE 4 of Translation |
Recruitment of 60S Ribosomal subunit (and removal of initiation factors) to form 80S initiation complex |
|
|
Elongation of Protein |
1). Aminoacyl-tRNA binds to A site 2). Peptide bond formed between growing polypeptide chain and new amino acid 3). Elongation factor hydrolysis GYP, driving mRNA through ribosome. Vacant tRNA moves to P site 4). Vacant tRNA dissociates 5). Repeated until STOP CODON release factor at the A site stimulates release of newly synthesised protein. Growing Protein exits via Tunnel |
