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A Level Biology OCR A > 19 - Genetics of living systems > Flashcards

19 - Genetics of living systems Flashcards

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1
Q

What is a mutation?

A

Change in the base sequence of DNA

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2
Q

What are the 3 types of mutation?

A
  1. Substitution 2. Deletion 3. Insertion
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3
Q

What is a substitution mutation?

A

Replacement of one or more DNA bases with others

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4
Q

What is a deletion mutation?

A

When one or more nucleotides are removed (i.e., deleted) from the DNA sequence

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5
Q

What is an insertion mutation?

A

Where one or more bases are added to the DNA sequence

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6
Q

What is it called when a mutation only affects one nucleotide?

A

Point mutation

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7
Q

When might a mutation affect a protein’s primary structure?

A

When it creates a new codon which codes for a different amino acid

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8
Q

What are the 3 different types of mutation effects?

A
  1. No effect 2. Damaging 3. Beneficial
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9
Q

When would a frameshift mutation occur?

A

When a deletion or addition mutation occurred in a number of bases that is not a multiple of 3

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10
Q

What would a frameshift mutation cause?

A

Every successive codon from the point of the mutation onwards would be different, so the protein produced would be completely different

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11
Q

Would a protein still be affected by a deletion or insertion mutation which wasn’t a frameshift mutation?

A

Yes, as there would still be a new amino acid added, but the effects would likely be less

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12
Q

What are 3 possible reasons why a mutation may have a neutral effect on a protein’s structure?

A
  1. Mutation changes a base, but the amino acid which the triplet codes for is the same 2. Mutation causes a different amino acid to be produced which is chemically similar to the original 3. The triplet affected may code for an amino acid which isn’t essential to the protein’s function, such as one located away from the active site
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13
Q

Would a mutation with a neutral effect affect the whole organism?

A

No it wouldn’t affect the whole organism

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14
Q

How can a mutation make a protein more or less active?

A

By changing the shape of its active site

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15
Q

Does a mutation which changes a protein’s active site mean the organism is less likely to survive?

A

Not necessarily- the mutation may even be beneficial

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16
Q

Give an example of a mutation with a beneficial effect for an organism?

A

A mutation which enabled a bacterial enzyme to break down an antibiotic more effectively

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17
Q

Give an example of a mutation with a negative effect for an organism?

A

Deletion mutation causing changes in the CFTR protein which lead to cystic fibrosis

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18
Q

How can a mutation prevent a protein from being produced?

A

If the mutation is at the start of the gene and RNA Polymerase can’t bind to it, so the protein won’t be produced

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19
Q

What are 2 reasons a mutation may be harmful to an organism?

A
  1. Protein may not be produced at all 2. Protein may be produced, but in a non-functional form
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20
Q

What increases the rate of mutation?

A

Mutagens

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21
Q

What is a mutagen?

A

A chemical, biological or physical agent which causes mutations

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22
Q

What is depurination?

A

The loss of a purine base from DNA

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23
Q

What is depyrimidination?

A

Loss of a pyrimidine base from DNA

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24
Q

How does depurination or depyrimidination usually happen?

A

Spontaneously

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25
Q

What type of mutation could depurination or depyrimidination lead to?

A

Insertion if a new base filled the gap left

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26
Q

What are 2 chemical mutagens?

A
  1. Free radicals 2. Deaminating agents
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27
Q

What could a deaminating agent do to cytosine?

A

Change it to uracil

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28
Q

Why are antioxidants also known as carcinogens?

A

Due to their ability to negate the effects of mutagenic free radicals

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29
Q

What is an example of a physical mutagen?

A

Ionising radiation such as x-rays

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30
Q

How would x-rays act mutagenically?

A

Break one or both DNA strands, with the repair of the strand often causing mutations

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31
Q

What are 3 examples of biological mutagens?

A
  1. Alkylating agents 2. Base analogues 3. Viruses
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32
Q

How does a virus act as a mutagen?

A

By inserting viral DNA into the genome

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33
Q

How do alkylating agents act as mutagens?

A

Attach methyl or ethyl groups to bases, causing incorrect pairing during replication

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34
Q

How do base analogues act as mutagens?

A

They are incorporated into DNA in lieu of a normal base

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35
Q

What is a chromosome mutation?

A

One which affects the whole chromosome or a number of chromosomes within the cell

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36
Q

When do most chromosome mutations occur?

A

During meiosis

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37
Q

What is a deletion chromosome mutation?

A

A section of a chromosome breaks off and is lost within a cell

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38
Q

What is a duplication chromosome mutation?

A

Sections of a chromosome duplicated

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39
Q

What is a translocation chromosome mutation?

A

A section of one chromosome breaks off and attaches to a non-homologous chromosome

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40
Q

What is an inversion chromosome mutation?

A

A section of chromosome breaks off, is reversed, and then rejoins onto the chromosome

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41
Q

What is a housekeeping gene?

A

One which codes for enzymes necessary for metabolic processes such as respiration

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42
Q

What are tissue-specific genes?

A

Ones which code for protein-specific hormones

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43
Q

What is a transcription factor?

A

Proteins which bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription

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44
Q

What are the two types of transcription factor?

A
  1. Activators 2. Repressors
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45
Q

What do activators do?

A

Factors which increase the rate of transcription

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46
Q

What do repressors do?

A

Factors which decrease the rate of transcription

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47
Q

How do transcription factors work?

A

Bind to specific DNA sites near the start of their target genes (in eukaryotes) and promote/repress the action of RNA Polymerase

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48
Q

What do transcription factors bind to in prokaryotes?

A

Operons

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49
Q

What 3 things can be contained in an operon?

A
  1. Clusters of structural genes 2. Control elements 3. A regulatory gene (sometimes)
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50
Q

What do structural genes do?

A

Code for useful proteins i.e. enzymes

51
Q

What 2 things do control elements contain?

A
  1. Promoter 2. Operator
52
Q

What is a promoter?

A

DNA located before the structural genes, which RNA polymerase binds to

53
Q

What is an operator?

A

A DNA sequence which transcription factors bind to

54
Q

What 2 things can regulatory genes code for?

A

Activators or repressor

55
Q

What allows bacteria to respond to environmental changes?

A

Gene regulation

56
Q

What 4 things is gene regulation necessary for in eukaryotes?

A
  1. Responding to changes in external environment 2. Responding to changes in internal environment 3. Cell specialisation 4. Cell coordination
57
Q

What are the 4 stages at which genes can be regulated?

A
  1. Transcriptional 2. Post-transcriptional 3. Translational 4. Post-translational
58
Q

How can genes be regulated at a transcriptional level?

A

Genes can be turned on or off

59
Q

How can genes be regulated at a post-transcriptional level?

A

mRNA can be modified, which regulates translation and the types of proteins produced

60
Q

How can genes be regulated at a translational level?

A

Can stop or start translation

61
Q

How can genes be regulated at a post-translational level?

A

Proteins can be regulated after translation, which changes their function

62
Q

What are 4 methods of transcriptional gene regulation?

A
  1. Cyclic AMP 2. Histone modification 3. Chromatin remodelling 4. Lac operon
63
Q

What is a chromatin?

A

DNA molecules that are tightly coiled around proteins call histones.

64
Q

What is heterochromatin?

A

Tightly packed chromatin

65
Q

When does heterochromatin allow chromosomes to be seen?

A

During cell division

66
Q

When does euchromatin allow chromosomes to be seen?

A

During interphase

67
Q

What is euchromatin?

A

Loosely packed chromatin

68
Q

In which of heterochromatin and euchromatin can genes be transcribed and why?

A

Euchromatin, as heterochromatin is too tightly packed

69
Q

Does protein synthesis occur during cell division, and why/why not?

A

No as you can’t transcribe genes from heterochromatin

70
Q

Why is it important that genes cannot be transcribed from heterochromatin?

A

Prevents complex and energy-consuming process of protein synthesis occurring when cells are dividing

71
Q

What type of gene regulation is the fact that genes can’t be transcribed from heterochromatin?

A

Transcriptional

72
Q

Why does DNA condense around histones?

A

Because they are positively charged and DNA is negatively charged

73
Q

What are 2 methods of making histone groups less positive?

A

Acetylation and phosphorylation

74
Q

How is the acetylation or phosphorylation of a histone an example of transcriptional gene regulation?

A

Makes DNA bind to histones more loosely, allowing certain genes to be transcribed

75
Q

How does methylation of histones affect them?

A

Makes them more hydrophobic

76
Q

How is methylation of histones an example of transcriptional gene regulation?

A

Because it makes them more hydrophobic they bind together more tightly, so the DNA coils around them more tightly and less gene transcription can take place

77
Q

What is epigenetics?

A

The control of gene expression by the modification of DNA

78
Q

What is an operon?

A

A unit made up of linked genes that is thought to regulate other genes responsible for protein synthesis. Its genes are expressed at the same time

79
Q

Are operons present in eukaryotes?

A

Yes

80
Q

Why are operons more common in prokaryotes?

A

Prokaryotic genomes are smaller and simpler

81
Q

What is an advantage of using operons?

A

They are a very efficient way of saving resources as if certain gene products aren’t needed you can switch off all the genes involved in their production

82
Q

What 3 genes make up the lac operon?

A

lacZ, lacY, lacA

83
Q

What is the lac operon involved in?

A

The metabolism of lactose

84
Q

What types of genes are lacA, lacY and lacZ and why?

A

Structural genes as they code for enzymes and are transcribed onto one long piece of mRNA

85
Q

What is the preferred respiratory substrate of E.coli?

A

Glucose

86
Q

When would E.Coli use lactose as a respiratory substrate?

A

When glucose is in short supply

87
Q

What is located near the lac operon and what does it code for?

A

The regulatory gene lac L, which codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose

88
Q

What is down regulation?

A

Binding of repressor protein to an operator, whcih prevents binding of RNA polymerase

89
Q

What happens to the lac operon when lactose is present?

A

Lactose binds to the repressor protein and causes it to change shape so that it can no longer bind to the operator, so gene transcription can occur

90
Q

When is CRP binding possible?

A

When CRP is bound to cyclic AMP

91
Q

How can the rate of transcription of RNA polymerase be increased?

A

By binding CRP

92
Q

How does glucose regulate the lac operon?

A
  1. When glucose levels are high, cAMP levels are low. 2. cAMP receptor protein (CRP), aka CAP, binds cAMP 3. cAMP-CRP acts as an activator of the operon
93
Q

What is a cap?

A

Modified nucleotide

94
Q

What is a tail?

A

Long chain of adenine nucleotides

95
Q

Which ends do the cap and tail bind to?

A

Cap to 5’ end, tail to 3’ end

96
Q

What 2 things do the cap and tail both do?

A
  1. Stabilise mRNA 2. Delay degradation in the cytoplasm
97
Q

What does the cap do which the tail doesn’t?

A

Aids binding of mRNA to ribosomes

98
Q

Where does splicing and the addition of cap and tail occur?

A

In the nucleus

99
Q

Why would point mutations be done deliberately by the cell?

A

So that a greater range of proteins can be produced from the same mRNA molecule or gene

100
Q

What are 2 methods of post-transcriptional gene regulation?

A
  1. RNA processing 2. RNA editing
101
Q

What are 4 methods of translational gene regulation?

A
  1. Degradation of mRNA, with quicker degradation in cytoplasm meaning less protein synthesis 2. Protein kinases 3. Activation of initiation factors which aid binding of mRNA to ribosomes 4. Binding of inhibitory proteins to mRNA which prevent it from binding to ribosomes
102
Q

What are protein kinases?

A

Enzymes that activate or inactivate other proteins by phosphorylating them

103
Q

What often activates protein kinases?

A

cAMP

104
Q

How does phosphorylating a protein activate it?

A

Changes its tertiary structure

105
Q

What are 5 methods of post-translational gene regulation?

A
  1. Addition of non-protein groups 2. Modifying amino acids 3. Formation of bonds such as disulfide bridges 4. Folding and shortening of proteins 5. Modification by cAMP
106
Q

What is morphogenesis?

A

The regulation of the pattern of anatomical development

107
Q

What is a body plan?

A

The general structure of an organism

108
Q

What are body plans controlled by?

A

Proteins produced by Hox genes

109
Q

What are homeobox genes?

A

Sequences of genes that control the development of specific structures

110
Q

What is a homeobox?

A

A 180-nucleotide sequence within homeotic genes and some other developmental genes that is widely conserved in animals, plants and fungi

111
Q

What does the homeodomain do?

A

Binds to DNA and switches other genes on or off

112
Q

What do homeobox sequences code for?

A

Part of a protein called the homeodomain

113
Q

What 2 processes are involved in the development of body plans?

A

Mitosis and apoptosis

114
Q

What are Hox genes found in in animals?

A

Clusters

115
Q

What are Hox genes?

A

A group of homeobox genes only present in animals

116
Q

What does the order in which Hox genes appear along the chromosome determine?

A

The order in which their effects are expressed in the organism

117
Q

What is the difference between diploblastic and triploblastic animals?

A

Diploblastic have 2 primary tissue layers, triploblastic have 3

118
Q

What is a common feature of animals?

A

They are segmented

119
Q

What are somites?

A

Segmented blocks of tissue in the embryo that later differentiate into vertebrae, ribs, and skeletal muscles due to the effects of Hox genes

120
Q

What 2 types of symmetry are found in the body shape of animals?

A
  1. Radial 2. Bilateral
121
Q

Do all types of animal show symmetry?

A

No, for example sponges show asymmetry. But most do.

122
Q

What are 2 ways apoptosis can regulate the development of the body?

A
  1. Remove unwanted cells and tissues 2. Release chemical signals which stimulate mitosis and cell proliferation
123
Q

What can influence the expression of regulatory genes?

A

The internal and external environmental

124
Q

What is an example of a drug which interferes with Hox genes?

A

Thalidomide

A Level Biology OCR A (23 decks)

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