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A Level Biology OCR > 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

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51
Q

What 2 things do control elements contain?

A
  1. Promoter 2. Operator
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52
Q

What is a promoter?

A

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

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53
Q

What is an operator?

A

A DNA sequence which transcription factors bind to

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54
Q

What 2 things can regulatory genes code for?

A

Activators or repressor

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55
Q

What allows bacteria to respond to environmental changes?

A

Gene regulation

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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
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57
Q

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

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

How can genes be regulated at a transcriptional level?

A

Genes can be turned on or off

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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

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60
Q

How can genes be regulated at a translational level?

A

Can stop or start translation

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61
Q

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

A

Proteins can be regulated after translation, which changes their function

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62
Q

What are 4 methods of transcriptional gene regulation?

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

What is a chromatin?

A

DNA molecules that are tightly coiled around proteins call histones.

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64
Q

What is heterochromatin?

A

Tightly packed chromatin

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65
Q

When does heterochromatin allow chromosomes to be seen?

A

During cell division

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66
Q

When does euchromatin allow chromosomes to be seen?

A

During interphase

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67
Q

What is euchromatin?

A

Loosely packed chromatin

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68
Q

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

A

Euchromatin, as heterochromatin is too tightly packed

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69
Q

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

A

No as you can’t transcribe genes from heterochromatin

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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

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71
Q

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

A

Transcriptional

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72
Q

Why does DNA condense around histones?

A

Because they are positively charged and DNA is negatively charged

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73
Q

What are 2 methods of making histone groups less positive?

A

Acetylation and phosphorylation

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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

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75
Q

How does methylation of histones affect them?

A

Makes them more hydrophobic

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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

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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

125
Q

what are the different types of chromosome mutations?

A

deletion
inversion
translocation
duplication

126
Q

what is a chromosome mutation?

A

where large sections of the chromosome are altered rather than just a single base

127
Q

what is a nonsense mutation?

A

where there is a mutation that changes the codon into a stop codon so cuts the sequence short

128
Q

what is a missense mutation?

A

where the codon is changed completely so it codes for a different amino acid

129
Q

what are the three effects of a mutation?

A

1) silent
2) beneficial
3) damaging

130
Q

what causes a silent mutation?

A

when there is a change in the base sequence but because the genetic code is degenerate, this means that even after a mutation it could still code for the same amino acid.

131
Q

what increases the chance of a mutation occuring?

A

mutagen/mutagenic agent

132
Q

what does a deletion/insertion mutation lead to?

A

frameshift mutation which changes all subsequent codons

133
Q

what are the three levels of controlling gene expression?

A

1) transcriptional
2) post transcriptional
3) translational
4) post translational

134
Q

what controls whether transcription can occur or not?

A

transcription factors

135
Q

what are transcription factors?

A

molecules that bind to DNA and can either inhibit or allow transcription to occur

136
Q

if there is no transcription factor bound to the DNA, what is the state of the gene?

A

the gene is inactive so therefore transcription will not occur and the protein will not be made

137
Q

what happens when the transcription factor is bound?

A

once the transcription factor binds to DNA, transcription can begin and mRNA can be made and will undergo translation to create the protein

138
Q

what type of molecule is a transcription factor?

A

protein

139
Q

how do transcription factors prevent transcription?

A

they bind to the DNA which prevents RNA polymerase from binding

140
Q

describe the control of transcription in eukaryotes?

A
  • transcription factors move from the cytoplasm to the nucleus and attach to DNA
  • they either initiate or inhibit transcription by turning genes on/off
  • therefore either allow/prevent certain proteins from being made
141
Q

DNA is wrapped around proteins called…

A

histones

142
Q

what is chromatin?

A

the tightly bound DNA wrapped around histones

143
Q

what is heterochromatin and when is it present?

A

the tightly wound DNA in cell division (tightly wound to prevent damage)

144
Q

how does the shape of heterochromatin affect RNA polymerase?

A

because the heterochromatin is so tightly bound this means the gene is compact inside so does not allow RNA polymerase to bind

145
Q

what is euchromatin and when is it present?

A

the loosely wound DNA in interphase (to allow transcription to occur)

146
Q

how does the shape of euchromatin affect RNA polymerase?

A

because it is loosely bound this means the gene is exposed so that allows the RNA polymerase to bind to the gene therefore allowing transcription to occur

147
Q

how do you convert heterochromatin to euchromatin?

A

add an acetyl or phosphate group - which increases the negative charge so causes DNA to less tightly wind around the histones

148
Q

what is the charge of histones?

A

positive

149
Q

what is the charge of DNA?

A

negative

150
Q

how do you convert euchromatin to heterochromatin?

A

add a methyl group to euchromatin and this increases the hydrophobic nature of the histones so makes DNA tightly wind around again

151
Q

what is the example of gene expression in prokaryotes?

A

lac operon (lactose breakdown)

152
Q

what is an operon?

A

a group of genes controlled by the same regulatory mechanism and are all expressed at the same time

153
Q

what are structural genes?

A

codes for proteins that are not involved in DNA regulation

154
Q

what are the three structural genes in lac operon and what enzymes do they produce?

A

lac Z: B-galactosidase
lac Y: lactose permease
lac A: lactose transacetylase

^all these enzymes metabolise lactose

155
Q

the structural genes in lac operon produce enzymes that do what?

A

metabolise lactose

156
Q

what are regulatory genes?

A

code for proteins that are involved in DNA regulation

157
Q

what is the regulatory gene in lac operon and what does it code for?

A

lac I: repressor protein

158
Q

what does the repressor protein do?

A

it inhibits the processes of the structural genes so it does not produce the enzymes that will metabolise lactose

159
Q

what is the operator region?

A

(DNA sequence) where the repressor protein binds

160
Q

what is the promoter region?

A

(DNA sequence) where the RNA polymerase binds

161
Q

what is the order of components in the lac operon?

A

LacI
operator
promoter
LacZ
LacY
LacA

162
Q

describe how to lac operon works when glucose is present?

A
  • when glucose is present the prokaryotes wants to use this for respiration
  • the LacI gene produces the repressor protein
  • which binds to the operator region
  • due to the shape of the repressor protein, it blocks the promoter region, SO the RNA polymerase cannot bind
  • this means the transcription of the structural genes cannot occur
163
Q

describe how the lac operon works when glucose is no longer present but lactose is?

A
  • when glucose is no longer present that means lactose needs to be metabolised
  • the lactose binds to the repressor protein which causes it to change shape
  • so the repressor protein can no longer bind to the operator
  • this leaves the promoter region exposed allowing the RNA polymerase to now bind to the promoter
  • allows transcription of the structural genes
  • therefore lactose can be metabolised
164
Q

in the lac operon with lactose how can transcription be made more efficient (what molecule)?

A

CRP can bind to cAMP and this forms a complex (CRP-cAMP) which then binds to the RNA polymerase speeding up the transcription of the structural genes

then it can move along the structural genes and produce the proteins/enzymes which can then be used to metabolise lactose for respiration and energy

165
Q

when the lac operon is working in the presence of lactose, what happens when glucose once again becomes available?

A

the lactose unbinds from the repressor protein which allows it to bind again to the operator , and once again blocks to promoter region

166
Q

in the lac operon, what is the relationship between glucose and cAMP?

A

glucose leads to a decreases in cAMP conc. and therefore the cAMP unbinds to the CRP so transcription becomes less efficient.

167
Q

CRP only works is ? is bound to it.

A

cAMP

168
Q

in control of gene expression, what is made in the transcriptional level?

A

mRNA

169
Q

in control of gene expression, what needs to be done in the post-transcriptional level?

A

the mRNA needs to be modified

170
Q

what is an intron?

A

sections of DNA that do not code for proteins

171
Q

what is an extron?

A

sections of DNA that do code for proteins

172
Q

the mRNA strand produced in translation contains a mix of ? and ?

A

introns and extrons

173
Q

why does the mRNA produced in transcription need to be modified?

A

the mRNA contains a mix of introns and extrons sop before it is taken to the ribosomes for translation, it needs to be modified

this strand is called pre-mRNA

174
Q

what is pre-mRNA?

A

the mRNA strand that contains a mix of introns and extrons that needs to be spliced and modified before it can move to translation.

175
Q

what are the three stages of converting pre-mRNA into mRNA that can be taken to the ribosomes (aka mature mRNA)?

A

1) RNA splicing where the introns are removed
2) add a cap (modified nucleotide)
3) add a tail of adenine (stabilises mRNA)

steps 2+3 are to protect the mRNA strand from damage and degradation when travelling to the ribosomes

176
Q

how can the mature mRNA strand be edited further?

A

can be edited to get different versions of the mRNA that code for different proteins

177
Q

in the translational level of gene expression, how can the translation be decreased? (2)

A

1) degrade the mRNA so the protein cannot be produced
2) use inhibitory proteins that bind to the mRNA - stops it from being able to bind to ribosomes

178
Q

in the translational level of gene expression, how can the translation be increased?

A

1) activate initiation factors
^ these allow the mRNA to bind to the ribosomes
^ occurs by phosphorylation and protein kinases catalyse the addition of phosphate groups to the protein

179
Q

in the translational level of gene expression, to increase the translation, what helps activate protein kinases?

A

cAMP (secondary messenger)

179
Q

what is the post translational level of gene expression?

A

this is when the polypeptide chains made can be further modified for specific functions

180
Q

explain the 4 ways that a polypeptide chain is modified in the post translational level of gene expression?

A
  • adding a non protein group like a lipid, carbohydrate or phosphate group
  • amino acids can be modified to form different bonds like disulphide bridges
  • folding or shortening of proteins
  • modification by cAMP
181
Q

what are homeobox genes?

A

sequences of genes that code for proteins and are important in the early stages of development of the body

182
Q

homeobox gene sequences are very similar in __, __ and __

A

animals, plants and fungi

183
Q

what are hox genes?

A

a type of homeobox gene found in animals

184
Q

what are hox genes responsible for?

A

correct body development and positioning of body parts

the order of the genes in the DNA is the order in which they are expressed in the organism

185
Q

what does mitosis do?

A

increases the number of cells which leads to growth

186
Q

what does apoptosis do?

A

removed unwanted cells through programmed cell death

187
Q

what is the cell cycle controlled by and why?

A

controlled by genes to ensure that new cells being produced are actually needed for growth and prevents tumour formation

188
Q

mitosis and apoptosis are regulated by what genes?

A

hox genes

189
Q

what factors affect the expression of regulatory genes?

A
  • drugs
  • internal stimuli: psychological stress, hormones
  • external stimuli: temp, intensity of light

A Level Biology OCR (23 decks)

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