Chapter 20 - Gene expression

Question 1

state the 3 possible outcomes of a base substitution

Answer 1

• formation of a stop codon which prematurely ends the addition of amino acids
• formation of a codon which codes for a different amino acid
• codon for the same amino acid known as a silent mutation

Question 2

what is caused by the deletion of bases

Answer 2

frame shift

Question 3

why might a deletion at the end of the sequence have less of an impact on the final polypeptide sequence than a deletion at the start?

Answer 3

deletion at the beginning will change all subsequent codons

Question 4

how is addition of bases similar to deletion of bases?

Answer 4

can also cause a frame shift but to the right

Question 5

what is duplication of bases

Answer 5

when one or more bases are repeated, causing a frame shift to the right

Question 6

what is inversion of bases?

Answer 6

when a group of bases become separated form the DNA strand and rejoin in inverse order, only effects the amino acids of this portion

Question 7

what is translocation of bases?

Answer 7

when a group of bases become detached from the sequence at one chromosome and become inserted into a different chromosome, often has severe effects on phenotype

Question 8

what are the two main causes of gene mutations?

Answer 8

• high ionising radiation such as alpha and beta particles or x-rays
• chemicals such as nitrogen dioxide can directly interfere with transcription and the structure of DNA

Question 9

what are the causes of mutations known as?

Answer 9

mutagenic agents

Question 10

why must cells become specialised or differentiated in multicellular organisms

Answer 10

no single cell structure could carry out all functions required for survival

Question 11

how are cells able to become specialised in multicellular organisms if they all contain the same genes?

Answer 11

only certain genes are expressed in each cell or ‘switched on’

Question 12

what is totipotency

Answer 12

any cell, such as a fertilised egg, which can mature into any body cell

Question 13

how are genes prevented from expressing themselves (2)

Answer 13

• preventing transcription and therefore preventing the production of mRNA
• preventing translation

Question 14

what are stem cells

Answer 14

undifferentiated dividing cells which occur in adult animal

Question 15

what are embryonic stem cells?

Answer 15

come from embryos in the early stages of developement that can differentiate into any type of cell

Question 16

what are umbilical cord blood stem cells

Answer 16

cells derived from umbilical cord blood, similar to adult stem cells

Question 17

what are placental stem cells?

Answer 17

cells found in the placenta which develop into specific types of cells

Question 18

what are adult stem cells

Answer 18

found in the body cells of a fetus through to the adult, specific to a particular tissue or organ

Question 19

what are totipotent stem cells

Answer 19

found in an early embryo and can differentiate into any type of cell, zygotes are totipotent

Question 20

pluripotent stem cells

Answer 20

found in embryos and can differentiate into almost any type of cell

Question 21

multipotent stem cells

Answer 21

found in adults and can differentiate to a limited number of specialised cells

Question 22

unipotent stem cells

Answer 22

can only differentiate into a single type of cell, derived from multipotent stem cells and are found in adult tissue

Question 23

what are induced pluripotent stem cells

Answer 23

unipotent stem cells whcih have been genetically altered in a lab to create pluripotent stem cells, similar to embryonic stem cells in function, also able to possibly divide infinately

Question 24

how might iPS cells be used to treat humans?

Answer 24

e.g. skin grafts

Question 25

outline the process by which transcriptional factors control transcription (3)

Answer 25

- each transcriptional factor has a specific site that binds to a specific base sequence on the DNA - when it binds it causes the region of DNA to begin transcription - when a gene is not being expressed, the the site on the transcriptional factor is not active

Question 26

outline the process by which oestrogen can activate transcriptional factors (4)

Answer 26

- lipid soluble so diffuses across phospholipid bilayer - oestrogen then binds to a receptor on the transcriptional factor - this causes the transcriptional factor to change in shape and therefore be able to bind to the DNA - begins process of transcription

Question 27

what are epigenetics

Answer 27

explanations of how environmental influences can alter the genetic inheritance of an organisms offspring

Question 28

what is the epigenome

Answer 28

the accumulation of the chemical tags, or signals, over a lifetime. the chemical tags form a layer surrounding the DNA-histone complex which determine the shape of the DNA-histone complex and, thus, transcription

Question 29

what is the effect on transcription of decreased acetylation?

Answer 29

- deacetylation increases the positive charges on histones therefore increasing there attraction to the phosphate groups of DNA - this causes the association between the DNA and histones to become stronger and the DNA less accessible to transcription - therefore the gene becomes switched off

Question 30

what is the effect of increased methylation?

Answer 30

- methyl group added to cytosine - attracts proteins that condense the DNA-histone complex and thus prevent transcription - preventing the binding of transcriptional factors

Question 31

what is epigenetic therapy

Answer 31

use drugs to inhibit or counteract changes to histone acetylation or DNA methylation

Question 32

outline the process by which siRNA interferes with gene expression

Answer 32

- enzyme cuts double stranded RNA into smaller sections (siRNA) - one of the two strands of siRNA combines with an enzyme - siRNA guides enzyme to mRNA - enzyme cuts mRNA into smaller sections - mRNA no longer able to carry out translation

Question 33

state 5 main features of a malignant tumour

Answer 33

- grows to large size - grow rapidly - large and dark nucleus (much DNA) - cells become de-differentiated (unspecialised) - cells do not produce adhesion molecules - tumours not surrounded by capsule so grow finger-like projections - often have systemic effects - more likely to be life threatening - removal usually involves radiotherapy and or chemotherapy aswell as surgery - more frequently reoccur after treatment

Question 34

what are oncogenes

Answer 34

mutations of proto-oncogenes that are permanently active (cells divide constantly)

Question 35

what are tumour suppressor genes?

Answer 35

slow down cell division, repair mistakes in DNA and 'tell' cells when to die

Question 36

what is the process by which hypermethylation can lead to cancer? (3)

Answer 36

- hypermethylation occurs in specific region of tumour suppressor genes which leads to the tumour suppressor genes being inactivated - transcription of promoter regions of tumour suppressor genes is inhibited meaning it is silenced - its inactivation leads to increased cell division and the formation of a tumour

Question 37

what is the effect of oestrogen concentrations on breast cancer?

Answer 37

after menopause,oestrogen production in breast tissues is increased. once a tumour develops, oestrogen concentrations increase further and white blood cells which are attracted further increase oestrogen concentration, leading to further development of the tumour

Question 38

what is WGS sequencing

Answer 38

whole genome shotgun sequencing, when the DNA is cut into many small pieces for easy sequencing then using computer algorithms to assemble it

Question 39

what are SNP's

Answer 39

single nucleotide polymorphisms, single base variations which cause disease and stuff

Question 40

what is the proteome

Answer 40

all the proteins produced by a genome

Question 41

why is determining the proteome of prokaryotes relatively easy?

Answer 41

- most have only 1 circular piece of DNA wich is not associated with histones - no non-coding portions of DNA

Question 42

how much of human DNA is thought to be coding?

Answer 42

around 1.5%