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OCR AS/A Level Biology Context > module 6.1.1:cellular control > Flashcards

module 6.1.1:cellular control Flashcards

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1
Q

what is a mutation

A

changes in the sequence of nucleotides in DNA molecules

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2
Q

when do mutation occur

A

spontaneously

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3
Q

what are mutations caused by

A

mutagenic substances

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4
Q

what are examples of physical mutagens

A

X-rays, Gamma rays, and UV light

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5
Q

what are examples of chemical mutagens

A

benzopyrene (found in tobacco smoke) mustard gas, nitrous gas, aromatic amines (found in some synthetic dyes), reactive oxygen species (free radicals), and colchicine

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6
Q

what are examples of biological mutagens

A

some viruses, transposons (remnants of viral nucleic acid that have become incorporated into our genomes), and food contaminants such as mycotoxins from fungi, and aflatoxins from contaminated nuts, charred meat, and alcohol

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7
Q

what are the different types of mutation

A

insertion
deletion
point mutation/substitution
nonsense
missense
silent

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8
Q

what is insertion mutation

A

where one or more nucleotide pairs are inserted from the sequence. this type of mutation alters the sequence of nucleotides after the insertion point known as a frameshift

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9
Q

what is deletion mutation

A

where one or more nucleotide pairs are deleted from the sequence. this type of mutation alters the sequence of nucleotides after the deletion point known as a frameshift

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10
Q

what is point mutation/substitution

A

where one base pair is replaced by another

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11
Q

what is a nonsense mutation

A

where translation is stopped early thus giving rise to a truncated polypeptide due to premature introduction of a stop codon. (i.e: Duchenne’s muscular dystrophy)

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12
Q

what is a missense mutation

A

a codon change which results in the production of a different amino acid, thus resulting in altered tertiary structure of the protein (i.e: sickle cell anaemia)

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13
Q

what is a silent mutation

A

a codon change which does not affect the amino acid sequence produced. silent mutations are possible due to the degenerate nature of the genetic code

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14
Q

what happens when expanding triple nucleotide repeats

A

when a gene contains a repeating triplet such as CAG CAG CAG. these repeats increase during meiosis from generation to generation. if the number of repeats goes over a critical number, then diseases such as Huntington’s may develop

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15
Q

what are the mutations that happen on chromosomes during meiosis

A

deletion
inversion
translocation
duplication
nondisjunction
aneuploidy
polyploidy

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16
Q

what is deletion in meiosis

A

when part of a chromosome is lost

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17
Q

what is inversion in meiosis

A

when a section of a chromosome breaks off, rotates 180 degrees, and then joins on again. Although all the genes are present, some may now be too far away from their regulatory sequences to be properly expressed

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18
Q

what is translocation in meiosis

A

when one piece of a chromosome breaks off and then becomes attached to another chromosome. this may interfere with the regulation of genes on the translocated chromosome

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19
Q

what is duplication in meoisis

A

when part of a chromosome is copied, resulting in two copies of that part. overexpression of genes can be harmful because too many of certain proteins and/or certain gene-regulating nucleic acids may disrupt metabolism

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20
Q

what is non disjunction in meiosis

A

when one pair of chromosomes or chromatids fail to separate, leaving one gamete with an extra chromosome once fertilised. Down syndrome, or trisomy 21, is caused by this

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21
Q

what is aneuploidy in meiosis

A

when the chromosome number is not an exact multiple of the haploid number of that organism
- can be caused by non disjunction

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22
Q

what is polyploidy in meiosis

A

if the chromosome number is an exact multiple of the haploid number of the organism (more than two sets of chromosomes)

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23
Q

what are the 2 instances where mutation has a neutral effect

A
  • where the mutation occurs in a non-coding region of DNA or is a silent mutation
  • when a change in tertiary structure of the protein has no effect on the organism
  • a mutation does not alter the polypeptide
  • a mutation only alters the polypeptide slightly so that its structure or function is not changed
  • a mutation alters the structure or function of the polypeptide but the resulting difference in the characteristic of the organism provides no particular advantage or disadvantage to the organism
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24
Q

what is an example for when mutations are benefical

A

humans developed trichromatic vision through a mutation

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25
Q

what will depend on whether a mutation proves to be beneficial or detrimental to an organism

A

the environment of organism

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26
Q

what is an example of neutral mutation

A

the ability to taste a bitter-tasting chemical that is found in Brussel sprouts
- caused by a mutated allele of the TAS2R38 gene
- the mutated allele of this gene causes an increased perception of bitterness, meaning that people with this mutation can taste the bitter-tasting chemical in Brussel sprouts

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27
Q

what is an example of cystic fibrosis and explain

A
  • in around 70% of cystic fibrosis sufferers, the mutation that causes this disease is a deletion mutation of three nucleotides in the gene coding for the protein CFTR
  • the loss of function of the CFTR protein caused by this deletion mutation results in a number of symptoms, including lung and pancreatic problems as a result of extremely thickened mucus
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28
Q

what is an example of beneficial mutation

A
  • early humans living in Africa had dark skin as they produced high conc of the pigment melanin
  • this provided protection from harmful UV radiation from the Sun, whilst still allowing vitamin D to be synthesised (due to the high sunlight intensity)
  • however, at lower sunlight intensities, pale skin synthesises vitamin D more easily than dark skin
  • as humans moved into cooler temperate climates, certain mutations occurred that led to a decrease in the production of melanin
  • these paler-skinned individuals would have had a selective advantage, as they could synthesis more vitamin D
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29
Q

what is the mechanism called where correct genes are expressed in the correct cell

A

regulatory mechanism

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30
Q

what are the 3 main types of regulatory mechanisms

A
  • transcriptional level
  • post transcriptional level
  • post translational level
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31
Q

what are regulatory mechanisms controlled by

A

different regulatory genes

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32
Q

what is a structural gene

A

codes for a protein that has a function within a cell

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33
Q

what is a regulatory gene

A

code for proteins (or various forms of RNA) that control the expression of structural genes

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34
Q

what is lac operon an example of

A

regulatory mechanism at the transcriptional level

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35
Q

how do you know if the gene control is occuring at the transcriptional level

A

If the structural genes being controlled are in any way involved in the process of transcription

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36
Q

what is an operon

A

a cluster of genes under the control of a promoter

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37
Q

structural genes in prokaryotes can form a(n) ……..

A

operon

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38
Q

where is lac operon found

A

in some bacteria

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39
Q

what does lac operon control

A

the production of the enzyme lactase (also called β-galactosidase) and two other structural proteins
- lactase breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell
- known as an inducible enzyme (this means it is only synthesized when lactose is present)
- helps prevent the bacteria from wasting energy and materials

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40
Q

what are the components of the lac operon

A
  • promoter for structural genes
    • perator
    • structural gene lacZ that codes for lactase
    • structural gene lacY that codes for permease (allows lactose into the cell)
    • structural gene lacA that codes for transacetylase
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41
Q

what is located on the left of the lac operon on the bacterium’s DNA

A
  • promoter for regulatory gene
  • regulatory gene lacI that codes for the lac repressor protein
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42
Q

how many binding sites does the lac repressor protein have

A

2

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43
Q

what binds to the lac repressor protein

A

the operator and lactose(effector molecule)

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44
Q

what happens when lac repressor binds to the operator

A

it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter

45
Q

what happens when lac repressor binds to lactose

A

the shape of the repressor protein distorts and it can no longer bind to the operator

46
Q

what happens when lactose is absent

A
  • the regulatory gene is transcribed and translated to produce lac repressor protein
  • the lac repressor protein binds to the operator region upstream of lacZ
  • due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region
  • transcription of the structural genes does not take place
  • no lactase enzyme is synthesized
47
Q

what happens when lactose is present

A
  • there is an uptake of lactose by the bacterium
  • the lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site
  • RNA polymerase is then able to bind to the promoter region and transcription takes place
  • the mRNA from all three structural genes is translated
  • enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium
48
Q

what do eukaryotes use to control gene expression

A

transcription factors

49
Q

what are transcription factors

A

proteins that bind to specific regions of DNA to control the transcription of genes

50
Q

it is estimated that what percentage of human gene code for transcription factors

A

approximately 10%

51
Q

what do transcription factors allow

A

organisms to respond to their environment

52
Q

some hormones achieve their effect…….

A

via transcription factors

53
Q

where do some of the transcription factors bind to

A

the promoter region

54
Q

what does the binding of the transcription factors affect

A

allow or prevent the transcription of the gene from taking place

55
Q

the presence of a transcription factor will …….

A

either increase or decrease the rate of transcription of a gene

56
Q

what is PIF

A

a transcription factor found in plants that activates the transcription of the amylase gene

57
Q

in mammals, what does the hormone oestrogen involved in controlling

A

the oestrus cycle and also in sperm production

58
Q

is oestrogen lipid soluble or insoluble and explain what it means

A

oestrogen is a lipid-soluble molecule and can therefore diffuse through the plasma membrane of cells

59
Q

what are the stages of oestrogen can stimulate the transcription of a gene

A
  1. oestrogen diffuses through the plasma membrane
  2. it then moves to the nucleus and binds to an oestrogen receptor
  3. these receptors are actually transcription factors that are able to initiate transcription for many different genes by binding to their promoter regions
  4. once bound, oestrogen causes a change in the shape of the receptor
  5. as a result, the receptor moves away from the protein complex it is normally attached to and binds to the promoter region of one of its target genes
  6. this allows RNA polymerase to bind and to begin transcribing that gene
60
Q

where is gibberellins found

A

in plants

61
Q

what are gibberellin

A

a hormone that controls seed germination by stimulating the synthesis of the enzyme amylase

62
Q

what happens when gibberellin is applied to a germinating seed

A

there is an increased amount of the mRNA for amylase present

63
Q

why does the breakdown of DELLA happen

A

because it has to be broken down by gibberellin for the synthesis amylase

64
Q

what are the components involved in the breakdown of DELLA

A
  • repressor protein DELLA
  • transcription factor PIF
  • promoter of amylase gene
  • amylase gene
  • gibberellin
  • gibberellin receptor and enzyme
65
Q

what are the stage of the breakdown of DELLA

A
  1. DELLA protein is bound to PIF, preventing it from binding to the promoter of the amylase gene so no transcription can occur
  2. gibberellin binds to a gibberellin receptor and enzyme which starts the breakdown of DELLA
  3. PIF is no longer bound to DELLA protein and so it binds to the promoter of the amylase gene
  4. transcription of amylase gene begins
  5. amylase is produced
66
Q

what are the 2 types of DNA within eukaryotic genes

A

coding and non-coding

67
Q

what are the coding sequences called and what do they do

A

called exons
- these are the sequences that will eventually be translated into the amino acids that will form the final polypeptide

68
Q

what are the non coding sequences called and what does it do

A

called introns
- are not translated (they do not code for any amino acids)

69
Q

what is transcribes when transcription of a gene occur

A

the exons and introns

70
Q

when the transcribed gene has both introns and extrons, what is it called

A

pre- mRNA

71
Q

what is splicing

A

the modification of the RNA molecule after transcription but before translation occurs

72
Q

what does splicing ensure

A

ensures that only the coding sections of mRNA are used to form proteins by translation

73
Q

as introns are not translated, what happens to them

A

they are removed from the pre-mRNA

74
Q

after the introns are removed what happens to the extrons

A

the exons are then all fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated

75
Q

what do some polypeptides need for activation

A

cyclic AMP - cAMP

76
Q

what is cAMP derived from

A

ATP and is formed by the action of the enzyme adenyl cyclase

77
Q

in eukaryotic cells, what does cAMP activate

A

protein kinase A (PKA)

78
Q

what is protein kinase A

A

an inactive precursor enzyme

79
Q

what can happen once PKA is activated

A

it can activate other proteins

80
Q

explain an example where cAMP is used to activate a process

A

when muscle cells require energy, an enzyme called glycogen phosphorylase releases glucose from glycogen
- this enzyme is activated by cAMP, which changes the shape of the enzyme to expose its active site

81
Q

how would cells be able to differentiate and specialise for different roles

A

they must be able to control which genes are functioning at a particular time
- this is achieved by ‘switching on’ and ‘switching off’ genes. this must occur in a specific, tightly controlled sequence

82
Q

what is a homebox

A

a DNA sequence that codes for a protein transcription factor
- the transcription factors (that homeobox sequences code for) attach to DNA at specific locations and regulate the transcription of genes (e.g. genes that control the early development of eukaryotic organisms) by turning various different genes on and off in the correct order

83
Q

what is a homebox gene

A

any gene that contains a homeobox sequence

84
Q

homebox gene sequence in what 3 kingdoms are similar

A

animal plant and fungi

85
Q

what are other properties of homebox genes

A

highly conserved
- they have been maintained by natural selection

86
Q

what does mutation of these homeobox sequences lead to

A

lead to organisms that are not viable (not properly developed) so they are not favoured by natural selection
- this strong negative selection pressure explains why the sequences are highly conserved

87
Q

what are homeobox genes responsible

A

the genetic control of the development of body plans in different organisms
- this means they help to form the basic pattern of the body
they also control the segmentation of organisms such as insects and mammals into distinct body parts and they control the development of body parts such as wings and limbs, as well as what organs are present in each section of the body

88
Q

what are hox genes

A

a very important subset of homeobox genes
organised into groups known as Hox clusters

89
Q

how many hox clusters does vertebrates

A

4 - which are found on different chromosomes

90
Q

what do hox genes determine

A

the identity of embryonic body regions along the anterior-posterior axis (i.e. the head-tail axis)

91
Q

what is the order of Hox genes in each Hox cluster

A

linear

92
Q

what is apoptosis

A

programmed cell death

93
Q

what happens during apoptosis

A

old cells that have already undergone a large number of mitotic cell divisions (approximately 50 divisions, although this depends on the cell type) are systematically taken through various processes leading to cell death

94
Q

what are the process involved in apoptosis

A
  • the DNA of the cell becoming denser and more tightly packed
  • the nuclear envelope of the cell’s nucleus breaking down and chromatin condensing
  • vesicles forming that contain hydrolytic enzymes
  • phagocytes engulfing and digesting the cell via phagocytosis
95
Q

what are the importances of mitosis and apoptosis in controlling body plan development

A

by constantly replacing and destroying cells throughout the early development of an organism, mitosis and apoptosis are both key mechanisms controlling the development of body form
in apoptosis, some cells that are produced (by mitosis) earlier on in development may no longer be needed. these cells are destroyed (by apoptosis) as part of the development of the organism
- structures like fingers and toes first develop as a single combined unit and are then separated later via apoptosis of the cells in between the digits

96
Q

what are the 2 groups of the genes that control mitosis

A

proto-oncogenes
tumour suppressor genes

97
Q

what are proto-oncogenes

A

genes that stimulate cell division

98
Q

what are tumour-suppressor genes

A

genes that reduce cell division

99
Q

what can tumour suppressor genes stimulate

A

stimulate apoptosis in cells with damaged DNA that cannot be repaired
- this protects the body as it ensures that any cells that are genetically damaged (and that could, therefore, lead to cancer) are destroyed

100
Q

what are the 2 groups of proteins that these controls are regulated by, that ensure the cell is prepared for the mitosis phase of its cell cycle and that any DNA damage is repaired

A

cyclins and cyclin-dependent kinases (CDKs)

101
Q

what do cyclins act as

A

regulators

102
Q

what do CDK stand for

A

cyclic-dependent kinases

103
Q

what do CDKs act as

A

catalysts (once activated by cyclins)
- CDKs that have been activated by cyclins will catalyse the phosphorylation of particular target proteins, which can either activate or inactivate them

104
Q

different cyclins are produced ……..

A

at different stages of the cell cycle in response to internal molecular signals

105
Q

what are some examples of internal cell stimuli factors

A
  • irreparable genetic damage
  • RNA decay
  • internal biochemical changes that lead to cell changes or cellular injury (e.g. oxidative reactions)
  • production of cyclin D
106
Q

what do the internal cell stimuli factors intiate

A

initiate apoptosis in cells that are undergoing cell stress

107
Q

what are examples of external cell stimuli factors

A
  • the presence of cell signalling molecules such as cytokines from the immune system, hormones and growth factors
  • viruses and bacteria, harmful pollutants or ultraviolet light can affect the delicate balance of mitosis and apoptosis by damaging or destroying cells faster than they can be repaired or replaced
108
Q

how do cells often respond to stressful stimuli

A

by activating pathways to increase their chance of survival, or by initiating apoptosis
- eg. a cell will often begin by defending itself and trying to recover from the stressful stimulus by counteracting any damage caused to it
if the stressful stimuli remain, cell death pathways are activated
- eg. apoptosis is initiated

OCR AS/A Level Biology Context (24 decks)

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