2.7 Flashcards
Helicase
Breaks hydrogen bonds between complimentary bases
Starts at origin
Single stranded binding proteins
Attaches to ‘unzippes’ DNA bases where hydrogen bonds were broken by helicase.
Prevents two strands re attaching
DNA Gyrase
Prevents DNA from re-winding and supercoiling back into a helix
DNA Primase
Lays down a primer/ RNA that acts as a foundation for the new DNA strand
Adenine - Uracil (NOT Thymine)
Cytocine - Guarine
DNA Polymerase 1
Builds and adds nucleotides to split DNA and remove the primer
Adds new strand to old one from 5’ to 3’
DNA Polymerase 3
Works in okozake fragments
Synthesis of the leading & lagging strand 5’ to 3’
Ligase
Glues the nucleotides together by building covalent bonds between the P, Sugar and Base
Introns
Stay inside nucleous & are recycled into nucleotides
Telomeres
Protect DNA by inhibiting DNA replication to the end of the chromosome
Sanger Sequencing
uses chain-terminating dideoxynucleotides
1. Gel electrophoresis seperate base fragments
2. Smaller molecule travel further on the gel
E.g. If a ddGTP terminates the sequence on the 8th nucleotide, then the 8th nucleotide in the sequence must be Cytocine. (G-C)
DNA Replication (8 Mark)
Is semiconservative.
- Helicase seperates and breaks hydrogen bonds of the complementary base pairs from origin
- SSBP attach to the DNA and make sure the bases don’t reform hydrogen bonds
- DNA Gyrase prevents DNA from supercoiling again & releases tension
- DNA primase adds a primer in short double strand region on the Primary Strand of RNA
- DNA Polymerase 3 binds to the primer creating sections starting at the origins. Works from 5’ to 3’
- Lagging strand has multiple origins due to having to work backwards in okozake fragments from 5’ to 3’. Leading strand has 1 origin.
- DNA Polymerase 1 removes each RNA primer & replaces with DNA Nucleotides to build the DNA strands.
- Free DNA nucleotidesbind to expose nucleotide strands by base pairing
- DNA Ligase is an enzyme that then glues & builds covalent bonds between the P, sugars and bases.
Transcription
- occurs in a 5’ to 3’ direction
- DNA allows the mRNA to code for different Amino acids in your body with the help of ribosomes.
- RNA polymerase binds to the promotor region of the DNA strand
- RNA polymerase separates the DNA strands and synthesises a complementary RNA copy from one of the DNA strands
- When the DNA strands are separated, ribonucleoside triphosphates align opposite their exposed complementary base partner
- RNA polymerase removes the additional phosphate groups and uses the energy from this cleavage to covalently join the nucleotide to the growing sequence
- Once the RNA sequence has been synthesised, RNA polymerase detaches from the DNA molecule and the double helix reforms
Genetic code & Codons
Codons:
- The base sequence of an mRNA molecule encodes the production of a polypeptide
- eg. AUG (found at the beginning of every mRNA)
Genetic code:
- The genetic code identifies the corresponding amino acid for each codon combination
- The coding region of an mRNA sequence always begins with a START codon (AUG) and terminates with a STOP codon
translation
https://ib.bioninja.com.au/_Media/translation.mp4
EPA
Initiation
1. assembly of the mRNA, tRNA, ribosome
2. The small ribosomal subunit binds to the start codon (AUG)
3. tRNA molecule bind to the codon via its anticodon (UAC)
4. the large ribosomal subunit binds to the P site and forms a complex with the small subunit
- Elongation
- A second tRNA molecule pairs at the A site with anticodon
- amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site
- The tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site carries the peptide chain
- Translocation
- The ribosome moves along the mRNA strand by one codon position (in a 5’ → 3’ direction)
- The P-site tRNA moves into the E site and is released, while the E-site tRNA moves to the P site.
- Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated
- Termination
- Stop codon found
- recruit a release factor that signals for translation to stop
- The polypeptide is released and the ribosome disassembles back into its two independent subunits
