Nucleic Acid, DNA and Replication
- Created by: farahh24
- Created on: 12-09-18 18:48
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- Nucleic Acid & DNA Replication
- Contain carbon, hydrogen, oxygen, nitrogen and phosphorous.
- Sugar
- Base
- Phosphate
- Phosphate
- Sugar
- Base
- Sugar
- Pentose mono-saccharide, either ribose or deoxyribose.
- Made up of:
- Phosphate head forming 'backbone'
- Nitrogenous base: adenine, guanine, cytosine and thymine.
- Made up of:
- Phosphate group at carbon-5 forms covalent bond with hydroxyl at carbon-3 of next nucleotide.
- Phospho-diester bonds.
- Deoxyribose has one less oxygen atom than ribose.
- Pyrimidines: single carbon ring structure. Thymine and cytosine.
- Purines: double carbon ring structure. Adanine and guanine.
- Two hydrogen bonds: Adenine and thymine.
- Three hydrogen bonds: Cytosine and guanine.
- Phosphate backbone provides rigidity and creates structure.
- Two strands of polynucleotide coiled tightly into a helix to make it more compact.
- Double Helix
- Two strands of the helix are held together by hydrogen bonds.
- Each polynucleotide strand has a phosphate group on one end (5') and a hydroxyl group on the other end (3')
- The two polynucleotide strands run anti-parallel - running in opposite directions.
- Semi-conservative replication
- One strand of DNA untwists and unzips with the help of DNA helicase.
- Free nucleotides match up with the bases, and joined up by DNA polymerase.
- Two identical molecules formed. Each has half of the original strand, and half of a new strand.
- Free nucleotides match up with the bases, and joined up by DNA polymerase.
- One strand of DNA untwists and unzips with the help of DNA helicase.
- DNA helicase 'unzips'.
- DNA polymerase 'zips up' again.
- Meselson-Stahl Experiment.
- First replication - 100% in middle
- Second replication - 50% in middle, 50% at top
- Later replication - 75% at top, 25% middle.
- Second replication - 50% in middle, 50% at top
- First replication - 100% in middle
- Continuous v. Discontinuous Replication
- DNA polymerase can only travel from 3' to 5'.
- Leading strand (3' to 5') can be replicated continuously.
- Lagging strand (5' to 3') uses discontinuous replication.
- In lagging strand, DNA polymerase must wait until a section of the strand has been zipped before working backwards.
- Forms Okasaki fragments, which then have to be joined.
- In lagging strand, DNA polymerase must wait until a section of the strand has been zipped before working backwards.
- Lagging strand (5' to 3') uses discontinuous replication.
- Leading strand (3' to 5') can be replicated continuously.
- Genetic code: series of bases coding for a sequence of amino acids.
- Start codon: ATG
- Stop codon: TAG. TGA, TAA
- Degenerate: More codons than amino acids. 20 amino acids, 64 codons. Some codons code for the same amino acid.
- Non-overlapping, universal, degenerate
- Replication errors, e.g. missing stop codon, skipping codon, can cause mutations.
- Mutations may be silent, beneficial, or harmful.
- ATP: Adenine triphosphate
- Nitrogenous base, pentose sugar, three phosphate groups
- Small amount of energy required to break bond of last phosphate.
- Releases 30.6kJ per mole.
- PROS: small enough that energy is not wasted as heat, water soluble, easily regenerated by phosphorylation.
- CONS: weak bonds = unstable. Not long-term energy store.
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