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Biology A2 > Genetics > Flashcards

Genetics Flashcards

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1
Q

Gene Mutation

A

change to order or number of nucleotides in a base sequence of a gene

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2
Q

Causes of genetic mutations

A
  • spontaneously during DNA replication
  • high energy ionising radiation
  • carcinogenic chemicals
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3
Q

Suggest types of substitution genetic mutations and explain what is meant by each

A

nonsense - codes for stop codon preventing production of polypeptide
mis-sense - codes for different amino acid = non functional protein
silent - codes for same amino acid since genetic code is degenerate

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4
Q

Describe impact of insertion or deletion mutations

A
  • frame shift
  • change nature of all base triplets downstream of mutation
  • different sequence of amino acids coded for
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5
Q

Suggest ways in which the body responded to mutated cells

A
  • apoptosis

- attacked by immune response of white blood cells

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6
Q

Chromosome Mutation

A

change to number or structure of chromosomes

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7
Q

Suggest types of chromosomal mutations

A

duplication - extra copies
deletion - whole sections lost
inversion - sequence breaks off and rejoins in reverse order
translocation - fragments break and join onto another chromosome

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8
Q

Explain in detail how a genetic mutation can lead to a non functional protein

A
  • base sequence of DNA changes
  • different codon in mRNA
  • different anticodon so different tRNA attaches to ribosome
  • different primary structure
  • changes in bonding / tertiary structure
  • shape of polypeptide affects function
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9
Q

Germline Mutation

A

mutations in cells that give rise to gametes so mutation is passed onto offspring

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10
Q

Cell Specialisation

A

cell only translates part of its DNA to develop structures specific to its role

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11
Q

Totipotency

A

ability of cells to differentiate into any type of body cell

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12
Q

Sources of stem cells

A
  • embryo
  • umbilical cord/placenta
  • adult stem cell tissue
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13
Q

Totipotent

A

cells that can differentiate into any cell type (embryonic stem cells)

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14
Q

Pluripotent

A

cells that can differentiate into several cell types (embryonic cells in inner mass of blastocyst)

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15
Q

Multipotent

A

cells that can differentiate into a limited number of specialised cells (bone marrow cells)

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16
Q

Unipotent

A

cells that can only differentiate into a single type of cell (cardiomyocytes)

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17
Q

Induced Pluripotent Stem Cells (iPS)

A

made from adult somatic cells genetically reprogrammed to turn on genes that would be otherwise switched off using protein transcription factors

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18
Q

Advantages of induced pluripotent stem cells

A
  • capable of self renewal so there is an endless supply

- alternative embryonic stem cells have ethical considerations

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19
Q

Arguments FOR embryonic stem cell research

A
  • provide cures for people with debilitating diseases

- embryos left over from IVF are often discarded

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20
Q

Arguments AGAINST embryonic stem cell research

A
  • destroying a potential life / unethical to produce blastocyst for research
  • alternatives exist such as adult and induced pluripotent stem cells
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21
Q

Cancer

A

when cells from tumour have spread to other parts of boy/ metastasis occurred

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22
Q

Tumour

A

mass of abnormal cell growth

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23
Q

Benign tumour

A
  • surrounded by a capsule and held together by adhesion molecules
  • lacks the ability to invade neighbouring tissue or metastasize so localised effects
  • slow growth
  • removed with surgery/rarely reoccurs
24
Q

Malignant tumour

A
  • tumour that invades surrounding tissues in finger-like projections
  • metastasises
  • rapid uncontrolled growth
25
Q

Compare benign and malignant tumours

A
  • normal vs larger/darker nucleus
  • specialised vs unspecialised cells
  • form adhesion molecules so remain within tissue they arise vs spread via metastasis forming secondary tumours
  • surrounded by capsule so localised effects vs grow in finger-like projections into surrounding tissue
  • slow vs rapid growth
  • remove via surgery + rarely reoccur vs radio/chemotherapy + reoccurring
26
Q

Suggest how a tumour metastases

A
  • angiogenesis occurs where tumour develops blood and lymphatic vessels
  • tumour cells squeeze into vessels
  • spread via blood and lymph
27
Q

Proto-oncogenes

A

genes whose products accelerate MITOSIS when activated by growth factors

28
Q

Oncogenes

A
  • mutated proto-oncogenes
  • permanently switched on resulting in uncontrolled cell division
  • cause cancer growth
29
Q

Tumour suppressor genes

A

genes whose products slow down MITOSIS by repairing DNA or causing apoptosis

30
Q

Suggest how oncogenes cause uncontrolled cell division

A
  • products stimulate cell division even in absence of growth factors
  • code for excessive amounts of growth factors
31
Q

Two-Hit Hypothesis

A
  • cancer results from accumulated mutations

- mutations in both alleles to inactivate tumour suppressor genes

32
Q

Suggest why individuals who inherit a mutated tumour suppressor gene are more likely to develop cancer

A
  • mutated tumour suppressor genes are recessive in nature so both must be mutated
  • most people will develop at least one mutation in their lifetime
  • individuals who inherit mutated tumour suppressor genes are more likely to have both copies mutated
33
Q

Suggest why risk of developing cancer increases with age

A
  • mutations are slow

- more likely to acquire mutations over time

34
Q

Describe how radiotherapy works

A

targets high energy radiation at cancer cells creating mutations in DNA until cell is no longer viable

35
Q

Describe how chemotherapy works

A

damages DNA of cells as they divide so cells dividing quickly are more sensitive

36
Q

Transcription Factors

A
  • proteins that bind to DNA
  • regulate gene expression
  • by promoting or suppressing transcription of gene
37
Q

Operon

A

group of closely linked genes that produce a single mRNA in transcription (consisting of both regulatory and functional DNA)

38
Q

Regulatory Sequence

A

sequence of bases capable of increasing or decreasing the expression of specific genes

39
Q

Describe how transcription factors activate gene expression

A
  • TF activated and move into nucleus via nuclear pores
  • bind to regulatory regions on DNA called promoters by complementarity of shape
  • RNA polymerase stimulated to bind to promoter region and begin transcription
40
Q

Describe how elevated oestrogen levels promotes progression of some breast cancers

A
  • (steroid hormone) lipid soluble so diffuses through plasma membrane
  • binds to ER-α receptor in inhibitor-transcription complex
  • induces change in shape which activates TF to enter nucleus from cytoplasm
  • TF stimulate transcription of oncogenes
41
Q

Suggest what is meant by RNAi

A
  • RNA inference
  • inhibits translation of target genes
  • by destroying mRNA before it can be translated into a polypeptide
42
Q

Describe how RNAi inhibits gene expression and suggest reasons gene might still be expressed

A
  • RISC activated by unwinding siRNA complex and single strand of siRNA remains attached
  • single stranded siRNA is complementary to gene
  • siRNA binds to mRNA
  • mRNA cut using enzymes found in RISC
  • mRNA destroyed so cannot be translated
  • more mRNA than siRNA
  • not all mRNA destroyed
43
Q

Suggest how siRNA can act as oncogene/tumour suppressor gene

A
  • oncogene by preventing translation of tumour suppressor gene
  • tumour suppressor gene by preventing translation of oncogene
44
Q

Epigenetics

A
  • heritable changes to gene function
  • without changing base sequence of DNA (genotype)
  • caused by changes in environment
45
Q

Epigenome

A

all epigenetic tags added to genome which regulate gene expression

46
Q

Describe how the epigenome regulates gene expression

A
  • epigenetic tags determine the shape of DNA-histone complex
  • by methylation and acetylation
  • determine whether transcription factors can bind to DNA base sequence
47
Q

Suggest how the epigenome is flexible what factors affect it

A

epigenetic tags respond to environmental changes

  • diet
  • stress
  • physical activity
  • exposure to toxins
48
Q

Heterochromatin

A
  • DNA-histone complex condensed
  • no access by transcription factors
  • decreased acetylation
  • increased methylation
49
Q

Euchromatin

A
  • DNA-histone complex less condensed
  • access by transcription factors
  • increased acetylation
  • decreased methylation
50
Q

Imprinted Genes

A

genes whose expression is determined by heritable epigenetic tags from the parent that contributed them

51
Q

Describe how increased methylation of DNA inhibits transcription

A
  • addition of methyl group to cytosine base on DNA
  • prevents binding of TFs hence RNA polymerase
  • attracts proteins which induce de-acetylation of histone so inaccessible to TFs
52
Q

Describe how increased histone acetylation of DNA promotes transcription

A
  • addition of acetyl group to lysine (amino acid) found at the end of DNA-histone complex
  • histone more negatively charged
  • repels phosphate groups on DNA
  • less affinity/loose bonds so accessible to TFs
53
Q

Suggest characteristic features of stem cells

A
  • undifferentiated

- replace themselves continually

54
Q

Suggest why cancer is more likely to be treated successfully if diagnosed early

A
  • smaller tumours/ fewer cancer cells

- tumour has not metastasised

55
Q

Suggest why organisms regulate gene expression

A
  • not all cells require all genes

- more efficient and less wasteful to only synthesise substances cell requires

56
Q

Explain why cells in our body have different functions but all contain the same genes

A
  • not all genes expressed

- some genes are methylated to prevent transcription of them

57
Q

Suggest why inactivation of tumour suppressor genes results in cancer

A

no control over mitosis

Biology A2 (15 decks)

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