3.8 control of gene expression

Question 1

what is a gene mutation

Answer 1

change in the base sequence of DNA which arises spontaneously during DNA replication during interphase of the cell cycle

Question 2

what is a mutagenic agent

Answer 2

a substance that increases the rate of gene mutation e.g. UV light, X-rays or carcinogens

Question 3

6 types of gene mutation

Answer 3

deletion
substituion
addition
inversion
duplication
translocation of genes

Question 4

what is a deletion mutation

Answer 4

a nucleotide is deleted from the sequence

Question 5

what is the substitution mutation

Answer 5

a nucleotide is swapped with another

Question 6

what is the addition mutation

Answer 6

a nucleotide is added to the sequence

Question 7

what is the inversion mutation

Answer 7

a segment of DNA detaches and then reattaches in the opposite direction

Question 8

what is the duplication mutation

Answer 8

when one or more DNA bases are repeated causing a frame shift

Question 9

what is the translocation of gene mutation

Answer 9

a segment of DNA is moved from one chromosome to another which interferes with gene expressions

Question 10

which mutations have an affect on the polypeptide sequence and how

Answer 10

deletion, addition, duplication and translocation of gene.
all result in a frame shift therefore different amino acids are coded for.

Question 11

how may mutations code for shorter polypeptides

Answer 11

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

Question 12

what can unspecialised cells do

Answer 12

divide to replicate themselves and differentiation

Question 13

how do stem cells become specialised

Answer 13

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

Question 14

what are totipotent cells

Answer 14

cells which can differentiate into any cell and extra embryonic cells

Question 15

what are pluripotent cells

Answer 15

cells which can differentiate into any cell but not extra embryonic cells

Question 16

what are multipotent cells

Answer 16

cells which can differentiate into most cells

Question 17

what are unipotent cells

Answer 17

cells which can only differentiate into one type of cell

Question 18

what are the 3 different types of stem cells

Answer 18

embryonic, adult and plant stem cells

Question 19

where are embryoinc stem cells found

Answer 19

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

Question 20

where are adult stem cells found

Answer 20

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

Question 21

where are plant stem cells found

Answer 21

found int the meristemic tissue or the meristems at the tips of shoots and roots. cells are pluripotent

Question 22

how are induced pluripotent stem cells porduced

Answer 22

produced from adult somatic cells that are genetically altered to have the characteristic of embryonic stem cells

Question 23

what are the advantages of IPS cells

Answer 23

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

Question 24

what are transcription factors

Answer 24

proteins which regulate transcription of specific target genes by binding to promoter regions on specific parts of DNA

Question 25

how is transcription regulated by transcription factors

Answer 25

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.

Question 26

explain how oestrogen affects transcription

Answer 26

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.

Question 27

what is epigenetics

Answer 27

heritable changes in gene function without changes to the DNA sequence caused by changes in the environment

Question 28

epigenetic control of inhibiting transcription

Answer 28

increased methylation of DNA and decreased acetylation of histones

Question 29

how does methylation affect transcription

Answer 29

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

Question 30

how does acetylation affect transcription

Answer 30

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

Question 31

explain the relevance of epigenetics on disease development and treatment

Answer 31

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

Question 32

what is RNA interferance

Answer 32

inhibition of translation of MRNA produced from target genes, by RNA molecules, which inhibits expression of a target gene

Question 33

describe the regulation of transcription by RNA interferance

Answer 33

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.