genetics + body plans Flashcards
1
Q
what is a mutation
A
- changes in sequence of bases in DNA
2
Q
describe substitution
A
- mutation
- one or more bases are swapped for another
- E.g ATGCCT becomes ATTCCT
- changes the codon
- new codon could code for a different amino acid
- this changes the primary structure of the protein
3
Q
describe deletion + insertion
A
- one or more bases are removed/added
- E.g ATGCCT becomes ATCT/ATGCCT becomes ATGACCT
- leads to a frameshift mutation
- shifts the reading frame of the sequences (added/removed)
- so changes every consecutive codon from the point of mutation
4
Q
effects of different mutations
A
- no effect :
- on phenotype because normal proteins are still synthesised.
- Damaging :
- phenotype is affected in a negative way - proteins aren’t being synthesised/synthesised in a non-functioning way.
- interferes with essential processes.
Beneficial :
- new and useful characteristic in the phenotype
- due to synthesis of protein
5
Q
what increases rate of mutation
A
- mutagens
- chemical, physical or biological agent which causes mutations
- radiation (break strands of DNA)
- viruses (inserts into a genome changes base sequence)
6
Q
describe how chromosome mutations occur
A
- affect the whole chromosome / no. of chromosomes
- caused by mutagens
- during meiosis
7
Q
how can chromosome mutations affect its structure
A
- deletion : section of the chromosomes breaks of and is lost
- translocation : part of one chromosome break off and joins another non-homologous chromosome
- inversion : section of C breaks off, is reversed and then joins back onto C
8
Q
what are housekeeping genes
A
- these are always expressed
- the products (e.g enzymes) of these genes are always required to allow the cell to grow
9
Q
what ways can genes be regulated
A
- transcriptional : genes turned on/off
- post-transcriptional : mRNA is modified and regulates translation and the proteins produce
- translational : translation can be stopped/started
- post translational : modifying proteins after synthesis, changing their function
10
Q
describe chromatin remodelling
A
- transcriptional control
- transcription isn’t possible when DNA is tightly wound
- RNAP cant access the genes
- heterochromatin is tightly wound DNA
- euchromatin is loosely wound DNA
- genes in euchromatin transcribed during interphase between cell divisions
- ensure necessary proteins are synthesised
11
Q
describe histone modification
A
- negative DNA coils around positive histones
- histones can be modified to increase/decrease degree of packing
- acetylation/phosphorylation causes histone to become more negatively charged so DNA coils less tightly
- allows transcription of certain genes
- methylation causes histones to be more
positive so DNA coils more tightly and prevents transcription - Epigenetics = term used to describe this control of gene expression
12
Q
describe lac operon
A
- if glucose is in short supply, lactose can be used as a respiratory substrate
- regulatory gene lacI codes for a repressor gene
- prevents transcription of structural genes in absence of lactose (down regulation)
- binds to operator
- prevents RNA polymerase binding to promoter region
When lactose present:
- binds to repressor protein
- changes shape
- repressor proteins can’t bind to operator
- RNA polymerase can bind to promoter
- three structural genes transcribed
- enzymes are synthesised
13
Q
why is glucose preferred over lactose
A
- easier to metabolise
14
Q
what is an operon + lac operon
A
- group of genes that are under the control of same regulatory mechanism + expressed at the same time
- LO is a group of 3 structural genes (lacY, lacZ, lacA) - code for enzymes
- lacI is a regulatory gene located near the operon.
15
Q
what increases rate of trancription
A
- up regulated
- cAMP receptor proteins (CRP)
- only possible when CRP binds to cAMP
- transport of glucose into E.coli decreases levels of cAMP
- ## decreases rate of transcription for metabolism of lactose
