DNA Revision

Everything you need to know for a good grade on DNA. Made for the old sylabus but still contains lots of useful information which is still relevant. Includes transcription, translation, mitosis, chromosome structure and number... etc.

Hope you find this useful!


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  • Created by: Hope
  • Created on: 19-11-08 14:52
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Nucleic Acids
DNA (deoxyribose nucleic acid) and RNA (ribose nucleic acid) are
nucleic acids.
Nucleic acids made up of nucleotides.
Nucleotides made up of 3 parts
Phosphate or phosphoric acid
5carbon pentose sugar
Organic base (nitrogenous)

Formation of nucleotides-
Nucleotides are formed by two condensation reactions.
These happen between…

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Formation of DNA

Polynucleotides join together by condensation reactions to form a
polynucleotide chain.
Phosphodiester bonds form between the phosphate of one nucleotide
and the 4carbon of another. This is a covalent bond.
In DNA two polynucleotide chains twist around each other to form a
double helix.
The phosphate and…

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Amount of RNA varies from cell to Amount constant for all cells of a
cell and within cell due to metabolic species (except gametes + spores)
Chemically less stable Very stable
Maybe tempory existing for short Permanent
periods only
3 basic forms messenger, transfer Only one basic form but…

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Only 20 different amino acids in the body
Different enzymes are made by different arrangements of amino acids.
1 amino acid is coded for by 3 DNA bases
for example ­ GGA codes for Glycine

Why 3 bases?

3 bases codes for all the different amino acids found in the…

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Protein synthesis uses 3 types of RNA

Messenger RNA _ mRNA

Single polynucleotide chain
Formed from DNA, uses DNA as template
Uracil not Thymine
Formed in nucleus during transcription.
Carries instructions from DNA to ribosomes.

Transfer RNA tRNA

Single polynucleotide chain folded into a clover shape
Has a binding site…

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The polyA tail acts as a signal for the mRNA to leave the nucleus. It provides
some protection from the enzyme action.


Translation is the process in which the information carried on the mRNA is
used in the synthesis of polypeptide chain. The base sequence of the mRNA

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Notes Peptide bonds between the amino acids forms a polypeptide chain
The polypeptide chain doesn't become and enzyme or a protein until it
is folded.

Chromosome Number
And Structure

Chromosones occur in pairs, this is that there are two identical sets of
chromosomes in each cell.
Diploid (2n) 46 chromosones…

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The Cell Cycle

Cell cycle is the events from when a cell is formed to when it divides. It
contains three stages

1. Interphase
2. Mitosis
3. Cytokinesis


Interphase is the longest stage in the cell cycle (more than ¾)

Split into three parts
G1 ­ growth phase ­…

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Four stages
Prophase (DNA present as mass of threads)


DNA present as chromatin
Threads of chromatin thicken and shorten due to spiralisation.
Now two chromatids held together by centromere, this is a
Centrioles move to opposite ends of the cell.
Microtubules form the spindle

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Use 5mm of root tip.
Cover with 9 drops of aceitic orcein and 1 drop of hydrochloric acid.
The hydrochloric acid breaks it up.
Heat gently.
Cut away 1mm of root tip.
Add acetic acid to stain the cells.
Use a cover slip and gently squash the root tip.


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