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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  • Created by: Laurie
  • Created on: 26-05-13 13:44
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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
polypeptides.
Genes code for polypeptides which have
structural and metabolic roles e.g. keratin,
collagen, channel proteins, etc.…read more

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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
protein.
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 amino acid, so, 43 = 64 different
triplet codes.…read more

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Transcription
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 coding strand.
mRNA is released from DNA & passes
out the nucleus via nuclear pore to a
ribosome.…read more

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Transcription…read more

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Translation
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 two
amino acids, catalysed by an enzyme.
Ribosome moves along mRNA to the next
codon. 3rd tRNA brings the next amino
acid, which forms a peptide bond to the
adjacent amino acid.…read more

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Translation
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
complete.…read more

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DNA Mutations
Are random changes in the genetic
material.
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 are inserted or deleted
from a length of DNA.…read more

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Chromosome
Mutations
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.…read more

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Effects of
Mutations
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 in
countries such as Africa, dark skin was an
advantage due to the protection against
UV rays as dark skin contains lots of
melanin. As humans migrated north, dark
skin was a disadvantage.…read more

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