Chapter 7 AQA Syllabus Notes

  • Created by: naomi
  • Created on: 29-05-13 19:29

Chapter 7


DNA = deoxyribose nucleic acid.

DNA holds genetic information.

DNA has a double helix structure.

DNA is made of double polynucleotide chains.

DNA is a polymer made out of nucleotides.

DNA is a long molecule.

A nucleotide:

A nucleotide = a phosphate + a base + a deoxyribose sugar.

A deoxyribose sugar = 5 carbon sugars in DNA.

Sugar phosphate back bone is made up of phosphates and deoxyribose.

Base Pairs fit by complimentary base pairing.

Adenine + Thymine    Guanine + Cytosine

Base pairs are linked with hydrogen bonds.

The sugar phosphate backbone makes the molecule stable.

The molecule coils up to become compact. 

The sequence of bases codes for making proteins.

Complimentary base pairing allows for DNA to replicate accurately.

3 bases code of 1 amino acid.

Amino acids form a protein.


A gene is a length of DNA that codes for a particular protein.


 A small organelle which synthesises proteins in a cell.


 A variation of a gene coding for individual characteristics.


            A characteristic of an organism resulting of its alleles.


            Tightly coiled DNA of a thread like structure found in the nucleus of a cell.

Each body cell contains 23 pairs of chromosomes, therefore each body cell contains 46 single chromosomes.

Homologous pairs of chromosomes: a pair of chromosomes that have the same genes but different alleles.

Chromosomes are made up of long threads of DNA wounds around protein molecules called histones.


Enzymes are proteins whose synthesis is controlled by DNA. They control metabolic pathways and therefore influence the phenotype of an organism


            RNA = ribonucleic acid.

A ribose sugar = 5 carbon sugars in DNA.

A nucleotide = a phosphate + a base + a ribose sugar.

Adenine + Uracil        Guanine + Cytosine

RNA is a single polynucleotide strand.

RNA is quiet short.

RNA is used to transfer copies of small segments of DNA to the ribosomes.

RNA brings amino acids to the ribosome and joins them in the correct order.

Semi conservative replication

In this method of replication one strand of the old molecule is kept in tact and the other strand is newly made.

1.      In the first step the DNA coil unravels and the hydrogen bonds between the bases break.

2.      Free nucleotides are attracted to their complimentary bases.

3.      The nucleotides are joined by the enzyme DNA polymerase and the strands coil up.

DNA replication occurs during interphase before the cell divides by mitosis.

Mitosis and cell division

            Mitosis is the process by which cells divide to give exact copies of      


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