gene expression Topic 20 Flashcards
what is a gene mutation
a change to the structure of the DNA nucleotide base sequence of an organism (most likely during DNA replication)
when do chromosome mutations occur
in meiosis
non-disjunction - chromatids are pulled apart
what are the causes of gene mutations
gen mutations occur spontaneously - may arise during DNA replication
mutation may be increased by env factors (MUTAGENIC AGENTS);
- chemicals (bromine compounds)
- ionising radiation (x-rays)
- high energy radiation (UV light)
what is deletion and its effects on the encoded polypeptide
loss of a nucleotide base from a DNA sequence
- impact on phenotype might be enormous because:
- creates frame shift (reading frame that contains each 3 letters of the code has been shifted to the left by 1)
- gene is now read in the wrong 3 base groups
- coding information altered
- most triplets + amino acids they code for will be different
- diff polypeptides = non- functional protein which could alter the phenotype
deletion at the start could alter every triplet but deletion at the end is likely to have a smaller impact
what is the duplication of bases as a mutation
one or more bases are repeated
producing a frame shift to the right
what is the inversion of bases as a mutation
group of bases become separated from DNA sequence
re-join at the same position but in INVERSE order (back to front)
base sequence of this portion is reversed and effects the amino acid sequence
what is the translocation of bases as a mutation
group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a diff chromosome
translocations have sig effects on gene expression , leading to abnormal phenotype
what does development involve in the growth and development of stem cells
arranging specialised cells into tissues which are arranged into organs
cells become specialised via cellular differentiation
a zygote is the precursor for all cells in the body (divides by mitosis) and contains all genetic info required to produce all cell types
what are totipotent stem cells
can differentiate into any type of specialised body cell
undifferentiatedwh
what are pluripotent stem cells
produce any body cell but can’t become whole organism
how do cells lose their totipotency and become specialised
during development, totipotent cells translate only part of their DNA
= cell specialisation
some genes are expressed in all cells - suggest which genes are expressed in all cell types
mitochondrial
name two encoded proteins whose genes are not expressed ina small intestine epithelial cell
collagen
salivary amylase
actin + myosin
what are multipotent stem cells
can divide to form a limited number of different cell types (cells in the bone marrow produce differentiated types of blood cells)
what are unipotent stem cells
can divide to form only a single cell type (phagocyte)
