Topic 8 - Control of gene expression Flashcards
define gene mutation
a change in the sequence of bases in a DNA molecule that may result in an altered polypeptide
how can mutations occur
spontaneously and continously
when do mutations usually occur
interphase - DNA replication
why do most mutations have little or no effect
due to degeneracy of genetic code
how can mutations arise from
nucleotide changes: insertion, deletion, substitution
structural changes: inversion, duplication, translocation
give 2 examples of mutagenic agents
- high energy ionising radiation such as alpha/beta/gamma radiation
- chemicals such as NO2 from tobacco smoke
what three forms can substitution mutations take
silent, nonsense, missense
define silent mutation
no change to the amino acid sequence due to the degeneracy of the genetic code
define missense mutations
alters a single amino acid potentially affecting protein function
give an example of missense mutation
sickle cell anemia
define nonsense mutations
creates a premature stop codon, producing an incomplete non-functional protein
give an example of nonsense mutation
cystic fibrosis
when does inversion mutations usually occur
during crossing over in meiosis
what happens in inversion mutations
DNA of a single gene is cut into two places. the cut portion is inverted 180 then rejoined to the same place
results in a large section of gene is backwards and multiple amino acids are affected as they are being read incorrectly
what usually results in inversion mutations
non-functional protein, or in some cases a completely new protein
what do duplication mutations result in
a gene/section being copied on the same chromosome, original gene remains intact so mutation is not harmful
how is duplication mutation important in source of evolutionary change
the duplicate can mutate over time, developing new functions
what happens in translocation
a gene is cut into two places and the section of gene cut off attaches to a seperate gene
what is a stem cell
an undifferentiated cell of an organism that is capable of self-renewal and differentiation into specialised cells
what are the 4 types of stem cells
- totipotent
- pluripotent
- multipotent
- unipotent
what types of cells can totipotent stem cells form
all cell types including extra-embryonicc tissues
where can totipotent stem cells be found
in the zygote and the first few divisions of the early embryo
what are pluripotent stem cells
they are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra embryonic cells
what can pluripotent stem cells be used for
they can be used in treating human disorders