DNA - Chapter 8 AQA AS Biology
- Created by: H.N
- Created on: 09-11-12 19:38
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- DNA
- structure
- Phosphate - deoxyribose sugar- base
- Single ring bases: C (cytosine) and T (thymine)
- Double ring bases: A (adenine) and G (guanine)
- A + T = 2 H bonds
- G+ C = 3 H bonds
- long and coiled - lot of info in small space in cell nucleus
- contains genes - sections of DNA on chromosomes
- Functions
- stable -pass down generations
- H bonds allows it to separate during DNA replication and protein synthesis
- large molecule - lots of info
- base pairs in helical cylinder - protected from outside
- paired structure - easier to copy itself (self-replication)
- The triplet code
- 3 bases code for each amino acid (a.a)
- 1 sequence can code for many different a.a
- to find the minimum no. of bases needed to code for a molecule that is 127 a.a long = 127 x 3
- to find out how many a.a 33 base pairs code for = 33 / 3
- Chromosomes
- eukaryotic cells - large DNA molecules, linear, chromosomes
- structure
- 2 threads = chromatids, single point = centomere
- visible when cell dividing
- DNA-protein complex, coiled + looped, packed inside
- contains a single molecule of DNA
- homologous pair - 2 sets of chromosomes, total no. = diploid no.
- genes exist in different forms = allele
- different base sequence of allele = difference a.a sequence = production of different protein
- enzyme-substrate complex no longer formed
- meiosis
- 4 daughter cells, half no. of chromosomes as parent cell
- 1 chromosome from each pair enters each gamete
- 2 nuclear divisions
- 1) homologous chromosomes pair up and chromatids wrap around each other
- 2) equivalent portions exchanged by crossing over
- 3) homologous pair separated, 1 chromosome from each pair into 1 of the 2 daughter cells
- 2) equivalent portions exchanged by crossing over
- 2) chromatids move apart - 4 cells formed
- 1) homologous chromosomes pair up and chromatids wrap around each other
- genetic variation
- independent segregation of homologous chromosomes
- chromosomes randomly line up, so combination of chromosomes going into daughter cells is random
- new genetic combinations
- alleles may differ - random distribution
- crossing over
- recombination - produces 4 different cells, not just 2
- independent segregation of homologous chromosomes
- structure
- polynucleotide
- structure
- Phosphate - deoxyribose sugar- base
- Single ring bases: C (cytosine) and T (thymine)
- Double ring bases: A (adenine) and G (guanine)
- A + T = 2 H bonds
- G+ C = 3 H bonds
- long and coiled - lot of info in small space in cell nucleus
- contains genes - sections of DNA on chromosomes
- structure
- join to form sugar-phosphate backbone
- polynucleotide
- condensation reaction
- Double helix
- polynucleotide
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