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OCR A-Level Biology > Chap 19 - Genetics of Living Systems > Flashcards

Chap 19 - Genetics of Living Systems Flashcards

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1
Q

What is a mutation? 19.1

A

a change in the sequence of bases in DNA

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2
Q

What can happen to protein synthesis if a mutation occurs within a gene? 19.1

A

it can be disrupted

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3
Q

What is the change in sequence caused by? 19.1

A

substitution, deletion or insertion of one or more nucleotides within a gene

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4
Q

What is a point mutation? 19.1

A

if only one nucleotide is affected

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5
Q

What happens when a nucleotide is substituted? 19.1

A

the codon is changed which could cause it to code for a new amino acid - the primary structure of the protein will be changed

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6
Q

What does the degenerate nature of genetic codes mean? 19.1

A

the new codon may still code for the same amino acid - no change to the protein synthesised

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7
Q

How does the position and involvement of an amino acid affect during R group interactions? 19.1

A

the position and involvement of the amino acid in R group interactions determines the impact of the new amino acid on the function of the protein

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8
Q

What is an example of how position and involvement of amino acids impacts a protein? 19.1

A

if the protein is an enzyme and the amino acid plays an important role within the active site, then the protein may no longer act as a biological catalyst

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9
Q

What happens when nucleotide is inserted or deleted? 19.1

A

it will lead to a frameshift mutation - the addition/deletion of a nucleotide shifts the reading frame of the sequence of bases (every successive codon from the point of mutation changes)

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10
Q

What is the reading frame of a sequence of bases? 19.1

A

the sequences of bases are transcribed (read) consecutively in non-overlapping groups of three

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11
Q

What is a triplet code? 19.1

A

groups of 3 nucleotides that corresponds to one amino acid

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12
Q

When will the reading frame not be changed? 19.1

A

when the number of nucleotides changed is a multiple of 3 - the final protein formed will still be affected

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13
Q

What happens if there is no effect on the phenotype of an organism? 19.1

A

normally functioning proteins are still synthesised

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14
Q

What happens if there is damaged caused to a phenotype of an organism? 19.1

A

it will be affected in a negative way - proteins are no longer synthesised/are non-functional, interfering with essential processes

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15
Q

What happens if a phenotype has a beneficial mutation? 19.1

A

it is rare for a protein to be synthesised resulting in a new/useful characteristic

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16
Q

What is an example of a beneficial mutation? 19.1

A

a mutation in the cell surface membrane of human cells means that HIV cannot bind/enter theses cells - means immunity from infection of HIV

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17
Q

What increases the rate of mutations? 19.1

A

mutagens: chemical, physical or biological agent that causes mutations

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18
Q

What is depurination and depyrimidination? 19.1

A

depurination - the loss of a purine base
depyriminidination - loss of a pyrimidine base

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19
Q

What can happen during complementary base pairing? 19.1

A

the absence of a base can lead to the insertion of an incorrect base in DNA replication

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20
Q

What are free radicals? 19.1

A

oxidising agents

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21
Q

What can free radicals affect? 19.1

A

they can affect the structures of nucleotides and base pairing in DNA replication

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22
Q

What do antioxidants do? 19.1

A

known as anticarcinogens due to their ability to negate the effects of free radicals (eg. vitamins A, C and E)

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23
Q

What is an example of a physical mutagen and what does it do? 19.1

A

ionising radiations (eg. xrays)
- break one or both DNA strands - some can be repaired but mutations can occur in the process

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24
Q

What is an example of a chemical mutagen and what does it do? 19.1

A

deaminating agents
- chemically alter bases in DNA (eg. converting cytosine to uracil in DNA, changing the base sequence)

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25
Q

What are examples of biological agents and what do they do? 19.1

A

alkylating agents - methyl/ethyl groups are attached to bases resulting in the incorrect base pairing
bae analogs - incorporated into DNA in place of the usual base during replication, changing the sequence
viruses - viral DNA may insert itself into a genome, changing the base sequence

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26
Q

What is considered a relatively new mutation? 19.1

A

the ability to digest lactose (sugar present in milk)

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27
Q

What caused lactose intolerance? 19.1

A

when majority of mammals ceased to suckle - found primarily in European populations who are more likely to farm cattle

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28
Q

What benefits does lactose tolerance have in adults? 19.1

A

prevents diseases such as osteoporosis - could have prevented individuals from starving during famines

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29
Q

What differences are there between gene mutations and chromosome mutations? 19.1

A
  • chromosome mutations affect the whole chromosome or a number chromosomes within a cell
  • gene mutations occur in single genes or sections of DNA
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30
Q

Describe deletion as a change in chromosome structure 19.1

A

section of chromosome breaks off and is lost within the cell

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31
Q

Describe duplication as a change in chromosome structure 19.1

A

sections get duplicated on a chromosome

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32
Q

Describe translocation as a change in chromosome structure 19.1

A

a section of one chromosome breaks off, is reversed and then joins back onto the chromosome

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33
Q

Describe inversion as a change in chromosome structure 19.1

A

a section of chromosome breaks off, is reversed, then joins back onto the chromosome

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34
Q

What is a silent mutation? 19.1

A

they do not change any proteins or the activity of proteins synthesised - no effect on phenotype of an organism - may result in change to primary structure but do not change overall structure

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35
Q

Where do silent mutations occur? 19.1

A

in non-coding regions of DNA (introns) or code for the same amino acid due to degenerate code

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36
Q

What is a nonsense mutation? 19.1

A

result in codon becoming a stop codon

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37
Q

What is the result of a nonsense mutation? 19.1

A

result is shortened protein being synthesised which is normally non-functionally - normally have negative/harmful effects on phenotypes

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38
Q

What is a missense mutation? 19.1

A

result in the incorportation of an incorrect amino acid into primary structure when protein is synthesised

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39
Q

What do missense mutations depend on? 19.1

A

the role the amino acid plays in the structure and function of protein synthesised - could be silent, beneficial or harmful

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40
Q

When do conservative mutations occur? 19.1

A

when the amino acid change leads to an amino acid being coded for which has similar properties to the original - the effects of mutation are less severe

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41
Q

When do non-conservative mutations occur? 19.1

A

when the new amino acid has different properties to the original - more likely to have an effect on protein structure (may cause disease)

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42
Q

What are housekeeping genes? 19.2

A

the genes that code for enzymes necessary for reactions present in metabolic pathways (eg. respiration)

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43
Q

What are protein-based hormones required for? 19.2

A

growth and development of an organism or enzyme - only required by certain cells at certain times to carry out a short-lived response - coded for by tissue-specific genes

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44
Q

Where are entire genomes present? 19.2

A

in every prokaryotic cell or eukaryotic cell containing a nucleus - includes genes not required by that cell so the expression of genes and the rate of synthesis of protein products

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45
Q

What can genes do as demand changes? 19.2

A

turn off - or the rate of product synthesis can increase/decrease

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46
Q

Why are bacteria able to respond to changes in environment? 19.2

A

due to gene regulation - genes expressed only when products are needed prevents vital resources being wasted

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47
Q

Why is gene regulation different in eukaryotes? 19.2

A

the stimuli that cause changes in gene expression and the responses produced is more complex - multicellular organisms have to respond to change in external environment but also internal environment

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48
Q

Why is gene regulation required? 19.2

A

for cells to specialise and work in a coordinated way

49
Q

What 4 ways can genes be regulated? 19.2

A
  • transcriptional: genes can be turned on/off
  • post-transcriptional: mRNA can be modified which regulations translation and types of proteins produced
  • translational: translation can be stopped/started
  • post-translational: proteins can be modified after synthesis which changes their functions
50
Q

What happens to DNA in orderfor it to pack into the nucleus? 19.2

A

as DNA is very long, it has to be wound around proteins (histones) - resulting complex is chromatin

51
Q

What is heterochromatin? 19.2

A

tightly wound DNA causing chromosomes to be visible during cell division

52
Q

What is eurchromatin? 19.2

A

loosely wound DNA present during interphase

53
Q

When is transcription of genes not possible? 19.2

A

when DNA is tightly wound - RNA polymerase cannot access the genes

54
Q

Why does protein synthesis happen during interphase? 19.2

A

ensures proteins necessary for cell division are synthesised in time + prevents complex, energy-consuming process of protein synthesis from occuring when cells are actually dividing

55
Q

Why does DNA coil around histones? 19.2

A

they are positively charged (DNA is negatively charged) - histones can be modified to increase/decrease degree of packing (or condensation)

56
Q

What causes DNA to coil less tightly and allow certain genes to be transcribed? 19.1

A

the addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces positive charge on the histones (making them more negative)

57
Q

What causes DNA to coil more tightly and prevent transcription of genes? 19.2

A

the addition of methyl groups (methylation) makes histones more hydrophobic - they bind more tightly to each other

58
Q

Define epigenetics? 19.2

A

describe the control of gene expression by modification of DNA - sometimes used to include all all the different ways in which gene expression is regulated

59
Q

What is an operon? 19.2

A

a group of genes that are under the controll of the same regulatory mechanism and are expressed at the same time

60
Q

Why are prokaryotic genome structures smaller and simpler? 19.2

A

operons are more common in prokaryotes

61
Q

Why are operons an efficient way to save resources? 19.2

A

if certain gene products aren’t needed, all genes involved in their production can be switched off

62
Q

What happens if glucose is in short supply? 19.2

A

lactose can be used as a respiatory substrate

63
Q

Why is glucose the preferred substrate of Escherichia coli (and other bacteria)? 19.2

A

it is easier to metabolise

64
Q

What is a lac operon? 19.2

A

a group of 3 genes, lacZ, lacY and lacA involved in metabolism of lactose - structural genes (code for three enzymes and are transcribed onto a single long molecule of mRNA

65
Q

What 3 enzymes are coded for by lac operons? 19.2

A

beta-galactosidase, lactose permease and transacetylase

66
Q

Describe the role of the regulatory gene, lacI 19.2

A

it is located near the operon - codes for repressor proteins that prevents transcription of structural genes in the absense of lactose

67
Q

Where does the repressor protein bind to? 19.2

A

an area called the operator - close to structural genes

68
Q

What does the binding of the repressor protein prevent? 19.2

A

prevents RNA polymerase binding to DNA and beginning transcription - known as down regulation

69
Q

What is the promoter? 19.2

A

the section of DNA that is the binding site for RNA polymerase

70
Q

How are enzymes synthesised when lactose is present? 19.2

A

lactose binds to repression protein causing it to change shape so it can’t bind to operator - RNA polymerase can bind to the promoter, the three structural genes are transcribed and enzymes are synthesised

71
Q

How is the required quantity of enzymes produced to efficiently metabolise lactose? 19.2

A

binding of RNA polymerase results in relatively slow rate of transcription that can be increased/up-regulated

72
Q

How is this achieved? 19.2

A

the binding of cAMp reception protein (CRP) - only possible when CRP is bound to cAMP (a secondary messenger)

73
Q

What happens as glucose is transported into an E. coli cell? 19.2

A

cAMP levels decrease, reducing transcription of genes responsible for metabolism of lactose

74
Q

What happens if both lactose and glucose are present? 19.2

A

the preferred respiratory substrate, glucose, is metabolised

75
Q

What is pre-mRNA? 19.2

A

the precursor molecule produced in transcription

76
Q

What happens to pre-mRNA? 19.2

A

it is modified to mature mRNA before binding to ribosome to code for synthesis of required protein

77
Q

What are caps and tails, what do they do? 19.2

A

caps are added to 5’ end (modified nucleotide), tails are added to 3’ end (long chain of adenine)
- help stabilise mRNA and delay degradation in cytoplasm
- caps also add binding of mRNA to ribosomes

78
Q

What is splicing? 19.2

A

where RNA is cut at specific points - introns (non-coding DNA) are removed and exons (coding DNA) are joined together

79
Q

What happens in RNA editing? 19.2

A

nucleotide sequence of mRNA molecules can be changed by addition, deletion or substitution - similar effect to point mutations and result in synthesis of different proteins (may have different functions)

80
Q

What is the result of RNA editing? 19.2

A

the range of proteins produced from a single mRNA molecule or gene increases

81
Q

Describe how degradation of mRNA regulates the process of protein synthesis 19.2

A

the more resistant the molecule, the longer it will last in the cytoplasm - a greater quantity of protein synthesised

82
Q

Describe how the binding of inhibitory proteins regulates protein synthesis 19.2

A

binding of inhibitory proteins to mRNA prevents it binding to ribosomes and synthesis of proteins

83
Q

Describe how activation of initiation factors regulate protein synthesis 19.2

A

aids the binding of mRNA to ribosomes - eggs of many organisms produce large quantities of mRNA which is not required until after fertilisation when initiation factors activate

84
Q

What are protein kinases? 19.2

A

enzymes that catalyse the addition of phosphate groups to proteins

85
Q

What does the addition of a phosphate group do? 19.2

A

changes the tertiary structure and therefore function of the protein

86
Q

What are protein kinases important regulators of cell activity? 19.2

A

many enzymes are activated by phosphorylation

87
Q

What are protein kinases activated by? 19.2

A

by the secondary messenger cAMP

88
Q

What does post-translational control involve? 19.2

A

modifications to proteins that have been synthesised

89
Q

What controls the growth & development of most life forms? 19.3

A

the same small group of genes

90
Q

What is morphogenisis? 19.3

A

the regulation of the pattern of anatomical development

91
Q

How were the genes discovered? 19.3

A

scientists investigated strange mutations in fruit flies - legs on head, extra wings

92
Q

Why are fruit flies (Drosophola) a popular choice for genetic studies? 19.3

A

small, easy to keep and short life cycle

93
Q

What are homeobox genes? 19.3

A

group of genes that contain a homeobox

94
Q

What is a homeobox? 19.3

A

sectin of DNA 180 base pairs long coding for a part of the protein 60 amino acids long that is similar in plants, animals and fungi

each amino acid contains 3 bases (60x3=180)

95
Q

What is a homeodomain? 19.3

A

the part of the protein that binds to DNA and switches other genes on/off

96
Q

Why do homeobox genes in mice and humans have identical nucleotide sequences? 19.3

A

accumulated mutations and evolution from a common ancestor (approx. 60 million years ago)

97
Q

What is Pax6? 19.3

A

a homeobox gene

98
Q

What happens when Pax6 is mutated? 19.3

A

causes a form of blindness (due to underdevelopment of retina) in humans, mice and fruit flies

99
Q

What has been found about the Pax6 gene? 19.3

A

it is a gene involved in development of eyes in humans mice and fruit flies

100
Q

What are the 3 types of body symmetry in animals? 19.3

A
  • radial: seen in diploblastic animals (eg. jellyfish) - no left or right, just top and bottom
  • bilateral: both left and right sides, head and tail
  • asymmetry: seen in sponges - no lines of symmetry
101
Q

What is the role of apoptosis in genetics? 19.3

A
  • shapes different body parts - removing unwanted cells and tissues
  • release chemical signals to stimulate mitosis and proliferation - leads to remodelling of tissues

(compared to a sculptor shaping a block of wood/stone)

102
Q

What is the role of mitosis in genetics? 19.3

A

increase number of cells leading to growth

103
Q

What regulates mitosis and apoptosis? 19.3

A

hox genes

104
Q

What are hox genes? 19.3

A

one group of homeobox genes only present in animals

term is often interchanged with homeobox genes

105
Q

What are hox genes responsible for? 19.3

A

correct positioning of body parts

106
Q

How are hox genes found in animals? 19.3

A

in gene clusters - mammals have 4 clusters on different chromosomes

107
Q

The order in which genes appear along the chromosome is..? 19.3

A

the order in which their effects are expressed in the organism

108
Q

How many hox genes do humans have? 19.3

A

39 - believed to have arisen from one ancient homeobox gene by duplication and accumulated mutations

109
Q

How are body plans represented? 19.3

A

as cross-sections through the organism - showing funamental arrangement of tissue layers

110
Q

How many tissue layers do diploblastic and triploblastic animals have? 19.3

A

diploblastic: 2
triploblastic: 3

111
Q

What is a common feature of animals? 19.3

A

segmentation - eg. rings of a worm, back bone vertebrates

112
Q

What do different hox genes control? 19.3

A
  • hox genes in head: development of mouthparts
  • hox genes in thorax: development of wings, limbs, ribs
113
Q

How are vertebrae and associated structures developed? 19.3

A

from segments in the embryo - somites

114
Q

How are hox genes involved with somites? 19.3

A

somites are directed by hox genes to develop in a particular way depending on position in sequence

115
Q

What can expression of regulatory genes be influenced by? 19.3

A

internal + external environment

116
Q

What is stress in genetics? 19.3

A

condition produced when homeostatic balance within an organism is upset - due to change in temp/light intensity

117
Q

What causes internal changes in genetics? 19.3

A

release of hormones/psychological stress

118
Q
A

OCR A-Level Biology (16 decks)

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