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OCR Biology A level 6.1.1 Cellular control summary notes
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Summary notes for topic 6.1.1 Cellular control of OCR Biology A level Module 6. Detailed electronic notes with diagrams.
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6.1.1 Cellular ControlGenes code for polypeptides, including enzymes;
Gene:
A length of DNA (sequence of nucleotide bases) that codes for one or more polypeptides
Each gene occupies a specific locus on the chromosome
o Each chromosome consists of one molecule of DNA
o Each gene is just one part of a DNA molecule
Codes for (e.g):
Enzymes
Structural proteins - collagen/keratin
Haemoglobin
Immunoglobulins (antibodies)
The genetic code;
TRIPLET CODE:
- Sequence of three nucleotides codes for an amino acid
DEGENERATE CODE:
- All amino acids (except methionine) have more than one code
Some codes don't correspond to an amino acid but indicate "STOP" - end of a polypeptide chain
Widespread but NOT universal
- Some base sequences code for the same amino acids in all organisms but it is not always the same
(they may code for different things/more than one thing)
Mutations cause changes to the sequence of nucleotides in DNA molecules (unpredictable)
Explain how mutations can have beneficial, neutral or harmful effects on the way a protein functions;
Occur:
During DNA replication Can be SILENT MUTATION:
Meiosis Triplet still codes for same amino acid
No effect on polypeptide produced
Can be NEUTRAL MUTATION:
Substitution (point mutation): Resultant differentiation gives organism no
One base pair replaces another advantage/disadvantage
o Mutation causes change to structure of protein
o Another version of same gene - different ALLELE
o Different characteristic
OR mutation in non-coding region of DNA
OR silent mutation
Harmful = e.g pale skin in hot weather
Beneficial = e.g pale skin - absorb more vitamin D
Insertion: Causes a FRAME SHIFT:
Nucleotide base inserted into genetic code Inserted/deleted base pair changes entire coding of
DNA molecule
Deletion: Triplet codons change
One base removed from genetic code Alters all amino acids after mutation
State that cyclic AMP activates proteins by altering their three-dimensional structure;
Cyclic AMP is a nucleotide derivative
Activates proteins by changing their 3D shape
Shape is a better fit to their complementary shape
Explain genetic control of protein production in a prokaryote using the lac operon;
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