MODULE 6: GENETICS, EVOLUTION AND ECOSYSTEM
6.1 Genetic and evolution
6.1.1 Cellular control
(a) types of gene - point substitution -> silent (DNA is degenerate, no effect on the primary structure)
mutations and their -> missense (a change in the base triplet sequence,
possible effects on protein change in 30)
production and function -> nonsense (alter a base triplet so it becomes a stop
codon, results
in a shortened amino acid sequence with no function)
- indel (insertion/ deletion) -> leads to a frameshift
- possible effects
-> neutral - mutation in the non-coding region
- silent mutation
- gives no particular advantage or disadvantage to the organism
-> beneficial – ability to digest lactose
-> harmful – phenylketonuria
# frameshift: every codon after mutation is affected, different sequence
Chromosomal mutation:
- Deletion: a section of chromosome breaks off and lost
- Duplication: section of chromosomes duplicated
- Translocation: section of one chromosome breaks off and joins another non
homologous chromosome
- Inversion: a section of one chromosome breaks off, reversed and back to the
chromosome
(b) The regulatory - transcription factor
mechanism that controls - proteins
, gene expressions - slide along part of a dna molecule
- involve in regulating cell cycles
- transcriptional level:
Lac operon ->
- Lactose permease -> increases the permeability of bacterial plasma membrane
to lactose
- B-galactosidase -> hydrolyses the glycosidic bond between glucose + galactose
- When lactose is present:
1. lactose binds to repressor protein + changes its shape
2. repressor protein removed from operator region
3. RNA polymerase can bind to promotor region
4. Lac Z and Lac Y genes expressed
5. B-galactosidate and lactose permease produced
- When lactose is absent: gene is transcribed and translated to
1. The lac repressor protein binds to the operator region upstream of lacZ
2. Due to the presence of the repressor protein RNA polymerase is unable to
bind to the promoter region
3. Transcription of the structural genes does not take place
4. No lactase enzyme is synthesized
Transcriptional level:
Histone modification for chromatin remodelling->
- Euchromatin:
Acetylation
decrease +ve charge on histone which reduces electrostatic attraction between -
ve DNA and +ve histones
increase gene expression
- Heterochromatin
6.1 Genetic and evolution
6.1.1 Cellular control
(a) types of gene - point substitution -> silent (DNA is degenerate, no effect on the primary structure)
mutations and their -> missense (a change in the base triplet sequence,
possible effects on protein change in 30)
production and function -> nonsense (alter a base triplet so it becomes a stop
codon, results
in a shortened amino acid sequence with no function)
- indel (insertion/ deletion) -> leads to a frameshift
- possible effects
-> neutral - mutation in the non-coding region
- silent mutation
- gives no particular advantage or disadvantage to the organism
-> beneficial – ability to digest lactose
-> harmful – phenylketonuria
# frameshift: every codon after mutation is affected, different sequence
Chromosomal mutation:
- Deletion: a section of chromosome breaks off and lost
- Duplication: section of chromosomes duplicated
- Translocation: section of one chromosome breaks off and joins another non
homologous chromosome
- Inversion: a section of one chromosome breaks off, reversed and back to the
chromosome
(b) The regulatory - transcription factor
mechanism that controls - proteins
, gene expressions - slide along part of a dna molecule
- involve in regulating cell cycles
- transcriptional level:
Lac operon ->
- Lactose permease -> increases the permeability of bacterial plasma membrane
to lactose
- B-galactosidase -> hydrolyses the glycosidic bond between glucose + galactose
- When lactose is present:
1. lactose binds to repressor protein + changes its shape
2. repressor protein removed from operator region
3. RNA polymerase can bind to promotor region
4. Lac Z and Lac Y genes expressed
5. B-galactosidate and lactose permease produced
- When lactose is absent: gene is transcribed and translated to
1. The lac repressor protein binds to the operator region upstream of lacZ
2. Due to the presence of the repressor protein RNA polymerase is unable to
bind to the promoter region
3. Transcription of the structural genes does not take place
4. No lactase enzyme is synthesized
Transcriptional level:
Histone modification for chromatin remodelling->
- Euchromatin:
Acetylation
decrease +ve charge on histone which reduces electrostatic attraction between -
ve DNA and +ve histones
increase gene expression
- Heterochromatin
