Summary
Summary 20 Gene expression
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- AQA
Concise gene expression summary notes for the new linear A-level biology 7401/7402
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Gene expressionGene mutations
1. Substitution:
Nonsense mutation
Base changes, resulting in a stop codon in the middle of the sequence
Mis-sense mutation
Base changes, resulting in a different amino acid
Silent mutation
Base changes, resulting in the same amino acid
2. Deletion:
When a nucleotide is deleted a frame shift occurs, changing the whole polypeptide
3. Insertion:
Extra nucleotide is added
4. Duplication:
Bases repeated, frame shift to right
5. Inversion:
Bases separated from DNA, reinserts the wrong way round
6. Translocation:
Bases separated from DNA, reinserted in a different gene
Causes of mutations:
Ø Mutagens – e.g. Alcohol, X-rays, radiation
Ø Spontaneous errors in DNA replication
Totipotent cells
Cells which have the ability to differentiate into any body cell
Found in the embryo, sometimes called embryonic stem cells
Specialisation:
® Small part of DNA molecule codes for protein needed to carry out function of body cell
® Part of DNA that is required is transcribed
® The rest is not, these genes are prevented from being expressed by:
Ø Preventing transcription & production of mRNA
Ø Preventing translation
Cell differentiation – process by which cells become specialised
Types of stem cells
Found in embryos:
Ø Totipotent – can form any body cell, including extra-embryonic cells
Ø Pluripotent – can form almost any body cell, not including extra-embryonic cells
Found in adults:
Ø Multipotent – can form a limited number of specialised cells, e.g. bone marrow
Ø Unipotent – can only form single type of cell
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