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Biology A level AQA > Chapter 20 - Gene expression > Flashcards

Chapter 20 - Gene expression Flashcards

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1
Q

state the 3 possible outcomes of a base substitution

A
  • 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
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2
Q

what is caused by the deletion of bases

A

frame shift

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3
Q

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?

A

deletion at the beginning will change all subsequent codons

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4
Q

how is addition of bases similar to deletion of bases?

A

can also cause a frame shift but to the right

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5
Q

what is duplication of bases

A

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

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6
Q

what is inversion of bases?

A

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

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7
Q

what is translocation of bases?

A

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

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8
Q

what are the two main causes of gene mutations?

A
  • 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
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9
Q

what are the causes of mutations known as?

A

mutagenic agents

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10
Q

why must cells become specialised or differentiated in multicellular organisms

A

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

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11
Q

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

A

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

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12
Q

what is totipotency

A

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

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13
Q

how are genes prevented from expressing themselves (2)

A
  • preventing transcription and therefore preventing the production of mRNA
  • preventing translation
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14
Q

what are stem cells

A

undifferentiated dividing cells which occur in adult animal

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15
Q

what are embryonic stem cells?

A

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

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16
Q

what are umbilical cord blood stem cells

A

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

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17
Q

what are placental stem cells?

A

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

18
Q

what are adult stem cells

A

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

19
Q

what are totipotent stem cells

A

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

20
Q

pluripotent stem cells

A

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

21
Q

multipotent stem cells

A

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

22
Q

unipotent stem cells

A

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

23
Q

what are induced pluripotent stem cells

A

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

24
Q

how might iPS cells be used to treat humans?

A

e.g. skin grafts

25
Q

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

A
  • 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
26
Q

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

A
  • 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
27
Q

what are epigenetics

A

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

28
Q

what is the epigenome

A

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

29
Q

what is the effect on transcription of decreased acetylation?

A
  • 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
30
Q

what is the effect of increased methylation?

A
  • methyl group added to cytosine
  • attracts proteins that condense the DNA-histone complex and thus prevent transcription
  • preventing the binding of transcriptional factors
31
Q

what is epigenetic therapy

A

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

32
Q

outline the process by which siRNA interferes with gene expression

A
  • 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
33
Q

state 5 main features of a malignant tumour

A
  • 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
34
Q

what are oncogenes

A

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

35
Q

what are tumour suppressor genes?

A

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

36
Q

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

A
  • 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
37
Q

what is the effect of oestrogen concentrations on breast cancer?

A

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

38
Q

what is WGS sequencing

A

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

39
Q

what are SNP’s

A

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

40
Q

what is the proteome

A

all the proteins produced by a genome

41
Q

why is determining the proteome of prokaryotes relatively easy?

A
  • most have only 1 circular piece of DNA wich is not associated with histones
  • no non-coding portions of DNA
42
Q

how much of human DNA is thought to be coding?

A

around 1.5%

Biology A level AQA (19 decks)

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