F215 Cellular Control Revision Notes

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Overview of cellular control topic on the F215 OCR Biology syllabus.

Includes; DNA, transcription, translation, mutations, the lac operon, homeobox/hox genes & apoptosis.

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OCR F215 Biology

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What is a Gene?

A gene is a unit of heredity
A gene is a sequence of nucleotide bases
found in DNA that codes for one or more
Genes code for polypeptides which have
structural and metabolic roles e.g. keratin,
collagen, channel proteins, etc.

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The Genetic Code

The sequence of nucleotides on a gene
(length of DNA) provides a code with
instructions for making a polypeptide or
There are 4 different types of nucleotide
bases found in DNA: A,C,T,G. The genetic
code is a triplet code which means 3 bases
code for 1…

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Gene unwinds & unzips. H-bonds break
between complimentary bases.
Activated RNA nucleotides bind to
exposed bases. U-A, G-C, A-T on template
strand. Catalysed by RNA polymerase.
The 2 extra phosphates are released-
energy released ­ adjacent bonding
between nucleotides.
mRNA is complementary to template
strand is a copy of…

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mRNA binds to a ribosome ­ first codon is
always AUG
tRNA with the complementary anticodon
forms H bonds with codon using ATP &
an enzyme.
A second tRNA with a different amino
acid binds to the next codon with its
complementary codon.
A peptide bond forms between the…

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The 1st tRNA leaves and picks up another
of its amino acids.
The polypeptide chain grows until a stop
codon is reached & the chain is now

cAMP (cyclic AMP) is a nucleotide
derivative which activates proteins by
changing their 3D shape so they are a
better fit…

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DNA Mutations

Are random changes in the genetic
Substitution mutations ­ one base pair
replaces another is likely to change 1
amino acid. Changes to 2nd or 3rd base
pairs are less likely to cause a change in
amino acid production.
Insertion/Deletion mutations ­ one or
more base pairs…

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Chromosome mutations are random
changes in the structure of a chromosome
such as translocations, deletions or
inversions of large sections.
May occur during DNA replication, or
may be caused by mutagens e.g. UV light,
x-rays & tar.

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Effects of

Neutral effects ­ some mutations change
the base sequence, but if the mutation is in
the `jumk' DNA, it is a `silent mutation.'
This is also the case if a change in bases
has no advantage/disadvantage.
Harmful/beneficial effects ­ e.g. skin
colour; when the first humans lived…


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