Biology AS AQA Unit 2 DNA and Meiosis

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 12:44
Preview of Biology AS AQA Unit 2 DNA and Meiosis

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DNA and Meiosis
It is an information carrying molecule.
DNA strand is a polymer of nucleotides.
A DNA molecule is made from two strands.
The strands run antiparralel with each other.
It has hydrogen bonds.
Has a deoxyribose phosphate backbone to protect the
bases and make the molecule more compact.
There are 10 base pairs per turn of the helix.
PURINES are Adenine and Guanine
PYRIMIDINES are Thymine and Cytosine
Alan Titchmarsh George Clooney
Only 20 amino acids regularly occur in proteins.
Each amino acid must have its own code of bases on the
Only 4 bases in DNA, if paired only 16 (42) codes which is too small. If 3 bases produce 64
codes, then that is too big. Hence different sequences code for the same amino acid-
degenerate code.
Codon- A group of 3 bases that code for 1 amino acid.
Degenerate- several codons may code for the same amino acid.
Gene- A sequence of DNA bases that determine a polypeptide.
Polypeptide- Sequence of amino acids.
The start code for an amino acid methionine. If it is not needed in the polypeptide then it is later
The stop coded is a section which doesn't code for any amino acid.
For growth and repair.
Needs many copies of all 4 nucleotides (free nucleotides)
DNA POLYMERASE joins nucleotides together.
DNA HELICASE breaks hydrogen bonds between base pairs.
Once strands break apart, they act as templates. ATP then acts as energy to activate new
nucleotides. Complementary DNA nucleotides are then attracted to exposed bases. They
are then joined together.
46 chromosomes.
Parent and daughter DNA.

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Copy of exact DNA.
Daughter DNA built from new molecules of deoxyribose, phosphate and organic bases.
Could lead to mistakes which would lead to mutation of proteins.
Both strands of DNA molecule act as template for attachment of nucleotides.
Enzyme DNA polymerase catalyses the reaction (ATP needed)
Enzyme DNA helicase breaks the hydrogen bonds.
Each exposed polynucleotide strand acts as a template.
Each new DNA molecule contains one original DNA strand.
Test...…read more

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DNA doubles.
Organelles replicate.
Protein synthesis occurs.
Chromosomes become visible.
Chromosomes attach to spindle at
the centromere.
Chromosomes lining up on the
Chromosomes migrate to
opposite poles.
Chromosomes disintegrate.
Daughter nuclei form at poles,
Spindles disintegrate and cells
about to divide.
Cell splits.
G protein growth
G synthesis (DNA replicating)
S growth of organelles
80% of time in interphase.…read more

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Uncontrolled cell division
A single cell loses its mitosis control mechanisms due to mutation in ONCOGENES and divides without
Normal cells stay in G stage until given a specific signal to enter s phase.
Cancer phases has S phase without a signal.
Normal cells are mortal and divide about 50 X and die
Cancer cells are immortal.…read more

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1. Homologous chromosomes (one maternal, one paternal) pair up and their chromatids wrap
round each other. Crossing over of the chromatids may occur. One chromosome from each
pair goes into one of the 2 daughter cells.
2. The chromatids move apart. Four cells have been formed (humans have 23)
During meiosis, each chromosome lines up alongside its homologous partner randomly.
One chromosome of each pair will pass to each daughter cell.…read more


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