3.8 control of gene expression Flashcards
what is a gene mutation
change in the base sequence of DNA which arises spontaneously during DNA replication during interphase of the cell cycle
what is a mutagenic agent
a substance that increases the rate of gene mutation e.g. UV light, X-rays or carcinogens
6 types of gene mutation
deletion
substituion
addition
inversion
duplication
translocation of genes
what is a deletion mutation
a nucleotide is deleted from the sequence
what is the substitution mutation
a nucleotide is swapped with another
what is the addition mutation
a nucleotide is added to the sequence
what is the inversion mutation
a segment of DNA detaches and then reattaches in the opposite direction
what is the duplication mutation
when one or more DNA bases are repeated causing a frame shift
what is the translocation of gene mutation
a segment of DNA is moved from one chromosome to another which interferes with gene expressions
which mutations have an affect on the polypeptide sequence and how
deletion, addition, duplication and translocation of gene.
all result in a frame shift therefore different amino acids are coded for.
how may mutations code for shorter polypeptides
a change in the amino acid coded for, may result in a stop codon which do not code for amino acids but result in the termination of translation
what can unspecialised cells do
divide to replicate themselves and differentiation
how do stem cells become specialised
a stimulus will cause selective activation of genes
activation of genes occurs when transcription factors bind to specific DNA sequences.
some genes are inactivated so the transcription factors dont bind to the DNA.
mRNA is only transcribed from the activated genes, and the proteins produced modify the cells to determine cell structure and function
what are totipotent cells
cells which can differentiate into any cell and extra embryonic cells
what are pluripotent cells
cells which can differentiate into any cell but not extra embryonic cells
what are multipotent cells
cells which can differentiate into most cells
what are unipotent cells
cells which can only differentiate into one type of cell
what are the 3 different types of stem cells
embryonic, adult and plant stem cells
where are embryoinc stem cells found
found in the early stage of embryo where they can differentiate into cells to form a foetus.
after 7 days of development cells become pluripotent
where are adult stem cells found
found in the adult tissue to replace faulty cells. can be either multipotent or unipotent. cells in the bone marrow replace red or white blood cells
where are plant stem cells found
found int the meristemic tissue or the meristems at the tips of shoots and roots. cells are pluripotent
how are induced pluripotent stem cells porduced
produced from adult somatic cells that are genetically altered to have the characteristic of embryonic stem cells
what are the advantages of IPS cells
avoid immune rejection as the patients own cells are used ti produce the IPS cells, this method also overcomes issues with using embryonic stem cells
what are transcription factors
proteins which regulate transcription of specific target genes by binding to promoter regions on specific parts of DNA
how is transcription regulated by transcription factors
transcription factors move from the cytoplasm to the nucleus.
the protein bind to DNA on a promoter region upstream of the target gene.
this stimulates or inhibits transcription of target genes by helping/preventing RNA polymerase from binding.
explain how oestrogen affects transcription
oestrogen is a steroid hormone, therefore lipid soluble.
oestrogen diffuses through the phospholipid bilayer into cells.
oestrogen binds to oestrogen receptors (an inactive transcription factor)
this changes the shape of the inactive transcription factor, causing the inhibitor to be released, the transcription factor becomes activated.
which then diffuses into the nucleus and binds to a specific DNA sequence on the promoter region.
this stimulates RNA polymerase to bind.
what is epigenetics
heritable changes in gene function without changes to the DNA sequence caused by changes in the environment
epigenetic control of inhibiting transcription
increased methylation of DNA and decreased acetylation of histones
how does methylation affect transcription
methyl groups are added to cytosine bases of DNA which prevent RNA polymerase from binding to the promoter by causing the nucleosome to pack and coil more tightly
how does acetylation affect transcription
acetyl groups are added to histones which makes the chromatin less condensed as the histone becomes less positive and the DNA is negative, so they bind less tightly allowing transcription factors and RNA polymerase to bind to the promoter region
explain the relevance of epigenetics on disease development and treatment
environmental factors can lead to epigenetic changes which can stimulate or inhibit expression of certain genes that lead to development of diseases.
diagnostic tests can be run to detect the epigenetic changes before symptoms present.
drugs can be developed to reverse these epigenetic changes
what is RNA interferance
inhibition of translation of MRNA produced from target genes, by RNA molecules, which inhibits expression of a target gene
describe the regulation of transcription by RNA interferance
siRNA - small interfering RNA - or miRNA -micro RNA- binds to a protein as double stranded molecules, forming an RNA induced silencing complex.
single stranded siRNA/miRNA is binds to target mRNA strand due to complementary base sequence.
the protein associated with siRNA/miRNA cuts up the mRNA strand into fragments - the hydrolysis causes the molecule to be degraded and silencing the gene.
