M6 CH19: genetics Flashcards
distinguish euchromatin and heterochromatin
chromatin, DNA wrapped around histones
euchromatin: loosely wound DNA, can be transcribed
heterochromatin: tightly wound DNA, can’t be transcribed
state the 3 types of transcriptional control
operon: lac operon
chromatin remodelling
transcription factors: cAMP
state the 2 types of post transcriptional control
splicing
RNA editing
state the 3 types of translational control
binding of inhibitory proteins to mRNA
initiation factors
mRNA degradation
state the 3 types of post-translational control
- modification of cAMP
- addition of non protein groups
- modification of primary proteins
explain how the lac operon takes place when lactose is present
- lactose binds to repressor protein
explain what the difference is between a structural and regulatory gene.
structural gene: codes for a protein
regulatory gene: controls whether the structural gene is expressed or not
outline the two types of gene mutations
point mutation:
- the substitution/deletion or insertion of one base into a nucleotide
- only affects one nucleotide
frameshift mutation:
- insertion/deletion of a nucleotide shifts the reading frame of bases, which changes the triplet codes of all the following base orders.
state the 3 possible different effects of mutations
no effect
damage
beneficial
explain how mutations can have a negative effect on the overall production of proteins
(3)
- some needed proteins may not be synthesised due to frameshift mutation (or point mutation)
- or some non-functional proteins may be synthesised
- these factors may interfere with essential body processes
give an example of a mutation that has been proven to be beneficial in humans (2)
- mutation in the cell surface membrane of human cells
- results in HIV not being able to bind and enter the cells
outline the 3 umbrella terms for the causes of mutations
physical mutagens
chemical mutagens
biological agents
explain what physical mutagens are, give an example and explain how they can cause mutations
cause mutations
e.g. ionizing radiations such as x ray break DNA strands and mutations can occur in the process
explain what chemical mutagens are, give an example and explain how they cause mutations
cause mutations
deaminating agents
- chemically altered bases in DNA
- e.g. C converted to U which changes the base sequence, causing different amino acids to be coded for, :. different protein synthesised
explain what biological mutagens are, give 3 examples and explain how they cause mutations.
cause mutations
1. alkylating agents
methyl or ethyl groups are attached to bases, resulting in incorrect base pairings
2. base analogs
incorporated into DNA in place of usual base during replication, changing the base sequence
3. viruses
viral DNA may insert itself into a genome, changing the base sequence
outline the 4 ways chromosome mutations can take place
- deletion: section of chromosome breaks off and is lost in cell
- duplication: sections of chromosome are duplicated
- translocation: section of chromosome breaks off and joins another homologous chromosome.
- inversion: section of chromosome breaks off, is reversed and then reattached to chromosome
outline why the majority of mutations do not have an influence on an individuals phenotype.
majority of DNA is non coding, mutations are random and so more likely to occur in non coding regions of DNA. mutations in non coding DNA will not impact phenotype
- also, majority of mutations are silent; they do not change any proteins or the activity of proteins so don’t affect phenotype
explain how mutations may be beneficial in a changing environment
mutations result in extreme characteristics (v rare)
due to environment changes these extremes prove to be more beneficial than the normal characteristics
directional selection takes place: rare characteristics from mutations are selected for, causing them to increase in frequency as a consequence of natural selection
state the name of the enzyme that catalyses the hydrolysis of lactose
b galactosidase (lactase)
hydrolyses lactose into glucose and galactose
what are homeobox genes?
- a group of regulatory genes containing a homeobox
- code for transcription factors; T.F and homeodomain bind to DNA and switch genes on/off
- appear in clusters
what are hox genes?
- a group of homeobox genes found only in animals
- responsible for the development of body plans; correct body part positioning
describe an example of a homeobox gene
pax 6
- when mutated it causes a form of blindness
- found in mice and fruit flies
