20 gene expression

Question 1

what is a mutation?

Answer 1

any change to quantity or structure of DNA in an organism

Question 2

what is a gene mutation?

Answer 2

change to nucleotide bases or rearrangement of the bases

Question 3

what are the three possible consequences of a substitution mutation?

Answer 3

nonsense: formation of stop codon so production of polypeptide coded for by that section of DNA would stop, different, non-functioning protein
missense: formation of codon for different amino acid, structure of polypeptide differ in single amino acid, not function properly
silent: formation of different codon but codes for same amino acid, no effect

Question 4

consequence of deletion mutation

Answer 4

frame shift, so gene read in wrong groups so triplets will be different and code for different amino acids

Question 5

other types of gene mutation

Answer 5

addition of bases: frame shift to the right, no frame shift if three bases added

duplication of bases: produces frame shift to right

inversion of bases: base sequence of portion is reversed

translocation of bases: abnormal phenotype, development of cancer and reduced fertility

Question 6

what are causes of mutations?

Answer 6

mutation rate can be increased by mutagenic agents

high energy ionising radiation: disrupt structure of DNA (x-rays and UV light)

chemicals: benzopyrene of tobacco smoke, alter structure of DNA or interfere with transcription

Question 7

what are totipotent cells?

Answer 7

cells such as fertilised eggs that can mature into any body cell

Question 8

how are genes prevented from expressing themselves?

Answer 8

preventing transcription (production of mRNA)
preventing translation

Question 9

why can’t specialised cells develop into any other cell?

Answer 9

once matured they lose their nuclei which contains genes so can’t develop into other cells

Question 10

what are stem cells?

Answer 10

the few cells in mature mammals with the ability to differentiate into other cells

Question 11

what are sources for stem cells in mammals

Answer 11

embryonic stem cells

umbilical cord blood stem cells

placental stem cells

adult stem cells

Question 12

different types of stem cells

Answer 12

totipotent: early embryo, differentiate into any type of cell
pluripotent: found in more developed embryos, differentiate into almost any type of cell (embryonic and fetal stem cells)
multipotent: adults, differentiate into limited number of cells, e.g. stem cells in bone marro can produce any type of blood cell (adult and umbilical cord blood)
unipotent: differentiate into single type of cell, made in adult tissue

Question 13

what are induced pluripotent stem cells?

Answer 13

type of pluripotent cells produced from unipotent cells, body cells genetically altered in lab so acquire characteristics of embryonic stem cells

uses genes and transcriptional factors within cell to express themselves, shows adult cells contain same genetic information in embryos

self-renewal: can divide indefinitely to provide limitless supply, overcome ethical issues surround use of embryonic cells

Question 14

controlling transcription normally

Answer 14

for transcription to begin, gene switched on by transcriptional factors which have a site that binds to specific base sequence of DNA in nucleus

when binded, causes region of DNA to begin process of transcription, mRNA produced which is translated to polypeptide

when gene not expressed, the site on transcriptional factor that binds to DNA not active

Question 15

how do hormones like oestrogen control transcription

Answer 15

oestrogen lipid soluble so diffused through phospholipid bilayer

binds with complementary site on receptor of transcriptional factor

causes oestrogen to change shape of DNA binding site on transcriptional factor which can now bind to specific base sequence on DNA (activated)

Question 16

what is epigenetics?

Answer 16

environmental factors that cause heritable changes in gene function without changing base sequence of DNA

Question 17

what is the epigenome?

Answer 17

chemical tags that form second layer that covers DNA and histones

Question 18

what is the function of the epigenome?

Answer 18

determines shape of DNA-histone complex, tightly packed or unwrapped

flexible because chemical tags respond to environmental changes, stress and diet can cause chemical tags to adjust

Question 19

structure of DNA-histone complex (chromatin)

Answer 19

when association of histones with DNA is weak, complex is less condensed so accessible by transcription factors

when association is stronger, complex is more condensed so not accessible by transcription factors

condensation inhibits transcription

Question 20

decreased acetylation

Answer 20

increases positive charge on histones so increases attraction to phosphate groups of DNA

association between histones and DNA is stronger so DNA not accessible to transcription factors

Question 21

increased methylation

Answer 21

methyl group added to cytosine base of DNA, inhibits transcription:

preventing binding of transcriptional factors to DNA

attracting proteins that condense DNA-histone complex so inaccessible to transcription factors

Question 22

increased methylation

Answer 22

methyl group added to cytosine base of DNA, inhibits transcription:

preventing binding of transcriptional factors to DNA

attracting proteins that condense DNA-histone complex so inaccessible to transcription factors

Question 23

how can epigenetic therapy be used to treat diseases?

Answer 23

drugs used to inhibit enzymes involved in either histone acetylation or DNA methylation

must be specifically targeted to cancer cells

Question 24

RNA interference

Answer 24

translation can be inhibited by breaking down mRNA

enzyme cuts RNA into smaller sections called small interfering RNA

one of two siRNA strands combines with enzyme, siRNA guides enzyme to an mRNA molecule by pairing up complementary bases

enzyme cuts mRNA into smaller sections so can’t be translated

Question 25

comparison of benign and malignant tumours

Answer 25

both can grow to large size

benign grow slowly, malignant grow rapidly

benign cells well specialised, malignant cells unspecialised

benign produce adhesion molecules so stick together so remain within tissue from which they arise, malignant don’t so spread to other regions (metastasis, forming secondary tumours)

benign removed by surgery malignant involves radio/chemotherapy

Question 26

what are main types of genes that play role in cancer?

Answer 26

oncogenes

tumour suppressor genes

Question 27

oncogenes

Answer 27

protons-oncogenes stimulate cell to divide when growth factors attach to receptor on cell-surface membrane, if mutates into oncogene it can be permanently activated because:

receptor protein on cell-surface membrane permanently activated so cell division switched on even in absence of growth factors

oncogene code for growth factor that is produced in excessive amounts, stimulating excessive cell division

Question 28

tumour suppressor genes

Answer 28

slow down cell division, repair mistakes in DNA. and apoptosis

maintains normal rates of cell division preventing formation of tumours, if mutated and inactivated cells grow out of control forming tumours

Question 29

how does hypermethylation lead to cancer?

Answer 29

occurs in promoter region of tumour suppressor genes so they are inactivated

transcription of promoter regions of tumour suppressor cells inhibited so silenced

leading to increased cell division and formation of tumour

Question 30

what is a genome?

Answer 30

all genetic material in an organism

Question 31

what is bioinformatics?

Answer 31

science of collecting and analysing complex and biological data such as genetic codes

Question 32

what is whole-genome shotgun?

Answer 32

researchers cut DNA into many small, easily sequenced sections and uses computer algorithms to align overlapping segments to assemble entire genome

Question 33

advantages of medical screening

Answer 33

allowed quick identification of potential medical problems and early intervention to treat them

Question 34

what is proteome?

Answer 34

all proteins in an organism

Question 34

what is proteome?

Answer 34

all proteins produced by the genome

or

all proteins produced by given type of cell or organism at given time, under specified conditions

Question 35

why is determining proteome of prokaryotic organism easy?

Answer 35

most have one, circular piece of DNA not associated with histones

there are none of non-coding portions of DNA which are in eukaryotic cells

Question 36

advantages of proteome of organisms like bacteria

Answer 36

identification of proteins that act as antigens on surfaces of human pathogens

can be used in vaccines against diseases cause by these pathogens

Question 37

how many gene in human genome?

Answer 37

20,000

Question 38

why is determining proteome of complex organisms difficult?

Answer 38

genome of complex organisms contains many non-coding genes

1.5% of genes in humans code for proteins