Notes covering chapters 20-21 (Module 8) of AQA A Level Biology Textbook
Written by A* Student.
Includes glossary and extra info for 25 mark synoptic essays.
Gene expression 3
Gene Mutations
Stem cells and totipotency 4
In vitro culture of embryonic stem cells
Stem cell treatments
Totipotency in plants
Regulation of transcription and translation
Regulating transcription
Regulating translation
Epigenetic control of gene expression
Gene expression and Cancer
Proto-Oncogenes and Oncogenes
Tumour-suppressor genes
Effect of Oestrogen on breast cancer
Genome projects 11
Recombinant DNA technology 12
Producing DNA fragments 12
In vivo gene cloning 13
In vitro gene cloning 15
Genetic fingerprinting 16
Gel electrophoresis
Genetic screening
, Glossary:
Mutation A change in the DNA sequence, leading to a different sequence of amino acids being
made and thus a different proton being assembled
Deletion The loss of a nucleotide base from a DNA sequence
Insertion When one or more bases are repeated
Substitution When an extra base becomes inserted in the sequence
Inversion When a group of bases become separated from the DNA sequence and rejoin at the
same position but in the reverse order
Translocation a group of bases become separate from the DNA sequence on one chromosome and
become inserted into the DNA sequence on a different chromosome. Similar to
crossing over during meiosis
Totipotent Stem cells found in the early embryo and can differentiate into any cell
Pluripotent Stem cells found in the later embryo and can differentiate into almost any cell
Multipotent found in adults and can differentiate into several cells of the same type; eg stem cells
in bone marrow can differentiate into any type of blood cell
Unipotent Can only differentiate into a single type of cell - derived from multipotent cells but
made in adult tissue
Induced pluripotent stem Pluripotent stem cells produced from unipotent cells that can be genetically altered by
cell (iPS) using transcription factors to express genes that were otherwise turned off
Transcription factor Proteins that regulate transcription
Oestrogen The hormone that binds to and activates transcription factors
siRNA Double-stranded RNA that interferes with RNA, meaning it cannot be translated
Epigenetics The study of changes in organisms caused by the modification of gene expression as
opposed to alterations to the genetic code itself
Epigenome The accumulation of chemical compounds that determine the shape of the
DNA-histone complex.
Methylation The addition of a -CH3 group to cytosine bases in DNA, resulting in chromatin
tightening and the gene being switched off
Acetylation The addition of a -CH3CO group to a histone, resulting in chromatin loosening and a
gene being switched on
Chromatin A DNA-histone complex
, Gene expression
Gene Mutations
A change in the DNA sequence, leading to a different sequence of amino acids being made and
thus a different proton being assembled
Types of mutation:
- Deletion - The loss of a nucleotide base from a DNA sequence
- Substitution- When an extra base becomes inserted in the sequence
- Insertion - When one or more bases are repeated
- Inversion - When a group of bases become separated from the DNA sequence and rejoin at
the same position but in the reverse order
- Translocation - a group of bases become separate from the DNA sequence on one
chromosome and become inserted into the DNA sequence on a different chromosome. Similar
to crossing over during meiosis
Not all mutations lead to change:
- Change occurs to stop codon / intron
- DNA is degenerate - each amino acid is coded for by several triplets of DNA
Rate of mutation is increased by
- Radiation, eg UV or X-Ray
- Chemicals, eg cigarette smoke/benzoyl peroxide
- Pathogens, eg H pylori/HPV
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