OCR Biology Cellular control 6.1.1 Revision Summary - By A* Student
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Course
Cellular control 6.1.1 (H420)
Institution
OCR
A revision summary of OCR A level Biology Cellular Control 6.1.1
Made by a student who achieved A* in A level Biology.
Covers all the points within the OCR Biology Specification.
Condenses 3 OCR specification books and class notes.
Gene mutation – random change in genetic material (DNA) Homeobox genes – Determine body plan by identifying each body section. In
of an organism animals, plants, fungi.
- Occur spontaneously during replication before cell Contain Homeobox sequence of 180 base pairs (excluding introns).
division - Highly conserved & within every organism
- Source of variation within species o A section of the gene e.g. togeTHEr, boTHEr, gaTHEring.
- Mutagenic agents – x rays, UV, tobacco increase risk Hox genes – subset of homeobox genes only in animals. Responsible for
Mitosis mutation (somatic) – not passed on & correct positioning of each body part.
contributes to ageing/cancer - Conservation implies their activity is fundamental to development of
Meiosis mutation – inherited so scan be passed to animals
offspring. - Homeosis – mutation of hox gene causes transformation of one area of the
Substitution mutations – one base substitute another. body into another area.
Affects only the gene. - Arranged in clusters – order along chromosome = order along body
1. Silent mutation - change in base triplet but triplet still - Colinearity – the pattern between thee order of hox genes & expression
codes for same aa (degenerate code), chemically similar - Encode for homeodomain proteins – binds to DNA & acts as a transcription
aa, an intron. Primary structure of protein does not factor to activate/ repress transcription of developmental gene. This alters the
change. production of proteins involved in development of the body plan.
2. Missense mutation – change in base triplet changes aa
sequence. Alters primary & overall structure of protein.
3. Nonsense mutations – change in base triplet codes for
stop codon. A truncated protein will not function.
Frameshift mutation – 1+ nucleotide pairs inserted/
deleted from length of DNA resulting in entirely different
sequence. Affects whole chromosome.
- (Code is non-overlapping & read in triplets) Apoptosis – programmed cell death (triggered by internal/ external stimulus)
- adding/ removing single base alters translation of all 1. Enzymes break down cell cytoskeleton
other triplets. (Base pairs are not read in correct triplets) 2. Cytoplasm becomes dense with tightly packed organelles
- Primary & subsequent structure of protein is altered. 3. CSM changes & blebs form
Protein cannot function. 4. Chromatins condense, nuclear envelope breaks.
- Expanding triple nucleotide repeats (Huntingdon 5. Cell breaks into vesicles ingested by phagocytic cells.
disease) – a repeating triplet increases at meiosis with - Cells in apoptosis can release chemicals to stimulate mitosis & cell
each generation. proliferation leading to remodelling of tissues.
Beneficial Neutral Harmful Development - Apoptosis causes limbs/digits to separate
Ability to Mutation could Missense - Proto-oncogenes – stimulate cell division (mitosis)
digest produce base triplet mutation - sickle - Tumour suppressor genes – reduce cell division & stimulate apoptosis.
lactose that still codes for: cell anaemia - Not enough apoptosis = tumour formation or syndactyly
prevents - same aa changes aa Valine - To much apoptosis = cell loss & degeneration (Parkinson’s)
osteoporosi - chemically similar (non-polar) to - Rate of cells dying = rate of cells produced.
s. aa so it functions Glutamine (polar) Stress – when homeostatic conditions within organism is unbalanced
like original & haemoglobin Internal factors to apoptosis External factors to apoptosis
- an aa not involved crystalises with Irreparable genetic damage (found by Cytokines, Hormones, UV light
in protein function RBC. cyclins in cell cycle) Nitric oxide – makes inner
RNA decay mitochondrial membrane more
Internal biochem changes (oxidation) permeable to H+ ions so proton
gradient is lost.
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