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BIOLOGY A LEVEL > CHAPTER 19 - GENETICS OF LIVING SYSTEMS > Flashcards

CHAPTER 19 - GENETICS OF LIVING SYSTEMS Flashcards

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1
Q

What is a mutation

A

A change in the sequence of bases in DNA

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2
Q

What causes a change in the DNA base sequence

A

Substitution, Deletion or insertion

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3
Q

What is a mutation called if only one nucleotide is affected

A

point mutation

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4
Q

If a base is changed, what are the outcomes

A

Either a different amino acid is synthesised - meaning a different protein or change in structure of the protein will occur

OR

degenerate code means that the change of codon still makes the same amino acid leading to no change

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5
Q

What does insertion and deletion mutations cause

A

Frameshift mutation - which will change the reading frame and change every codon from that point forward

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6
Q

What are the effects of mutations upon an organism as a whole

A

No effect - proteins are still functioning and fully synthesised

Damaging - Proteins are no longer synthesised or are non-functional, which can interfere with many essential processes

Beneficial - Can give a useful characteristic eg. mutation in human cells means that HIV cannot bind to cell surface membranes or enter the cells

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7
Q

What can increase the rate of mutations

A

Mutagens

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8
Q

What is depurination

A

Loss of a purine base

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9
Q

What is depyrimidination

A

loss of a pyrimidine base

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10
Q

Why are vitamins A, C and E known as anticarcinogens

A

Negates effects of free radicals which could cause mutations

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11
Q

What are the 3 types of mutagens

A

Physical, Chemical and Biological

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12
Q

What is an example of Physical mutagens and what do they do

A

Ionizing radiations such as X-Rays

Breaks one or both DNA strands, some breaks can be repaired but mutations occur in the process

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13
Q

What is an example of Chemical mutagens and what do they do

A

Deaminating agents

Chemically alter bases in DNA such as converting Cytosine to uracil in DNA, changing the base sequence

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14
Q

What are some examples of Biological agents and what do they do

A

Alkylating agents - Methyl or ethyl groups are attached to bases - leading to incorrect pairing during replication

Base analogs - incorporated into DNA in place of the usual base during replication

Viruses - Viral DNA may insert itself into a genome changing the base sequence

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15
Q

What is a nonsense mutation

A

A codon becoming a stop codon instead of coding for an amino acid - resulting in a shortened - normally non-functional - protein

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16
Q

What is a missense mutation

A

Incorporation of an incorrect amino acid(s) into the primary structure when the protein is synthesised, could have silent, beneficial or harmful effects

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17
Q

What is an Amorph mutation

A

Mutation that results in the loss of function of a protein

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18
Q

What is a hypomorph mutation

A

Mutation that results in a reduction of function of a protein

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19
Q

What is a hypermorph mutation

A

Mutation that results in a gain in function of a protein

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20
Q

What is sickle-cell anaemia, that type of mutation is it and why is it seen as a beneficial mutation

A

A blood disorder where erythrocytes develop abnormally

Mutation of just one base - T for A, substitution

Gives resistance to malaria

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21
Q

Evaluate the benefits of being heterozygous for sickle cell anaemia

A

Heterozygotes have one normal and one mutant allele (for haemoglobin)

normally healthy

except in low oxygen concentrations

part of malarial parasite life cycle is in red blood cells

red blood cells of heterozygotes are, sickled/destroyed, when parasites enter

infection reduced

being heterozygous is a clear advantage in an area where malaria is present and a disadvantage in an area where malaria is absent

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22
Q

Explain how the change of one amino acid in haemoglobin could reduce the oxygen-carrying ability of blood

A

Change in primary structure

change in secondary and tertiary structure

change in 3D shape

change in function

reduced oxygen carrying ability

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23
Q

How many types of chromosome mutations are there and what is involved

A

Deletion - A section of chromosome breaks off and is lost within the cell

Duplication - sections get duplicated on a chromosome

Translocation - a section of one chromosome breaks off and joins another non-homologous chromosome

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

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24
Q

The development of lactose tolerance is thought to have spread over approximately 20000 years, which in evolutionary terms is very quick

Explain why the percentage of adults with the ability to digest lactose increased at such a rate

A

Ability to digest lactose is a beneficial characteristic

drinking milk prevented starvation

reduced osteoporosis

directional selection

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25
Q

Outline why the majority of mutations do not have an influence phenotype

A

Mutation is random

majority of DNA is non-coding; mutations more likely to occur in non-coding regions

mutations in non-coding regions do not affect phenotype

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26
Q

Discuss why beneficial mutations are rare and suggest a process that beneficial mutations underpin

A

Majority of mutations are silent

Idea that random change to protein structure is more likely to reduce function

idea that beneficial mutations increase chances of survival if environment changes

surviving organisms reproduce and pass new alleles to offspring

leading to evolution

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27
Q

What are housekeeping genes?

A

Genes that code for enzymes necessary for metabolic reaction pathways eg. respiration

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28
Q

When are protein-based hormones only required for?

A

Needed by Certain cells at certain times to carry out short lived responses

Coded for by tissue-specific genes

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29
Q

What is morphogenesis

A

The regulation of the pattern of anatomical development

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30
Q

What is the usual choice in species for genetic studies and why

A

Fruit Flies

Small, easy to keep and have a short life cycle

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31
Q

What are homeobox genes

A

Group of genes which all contain a homeobox

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32
Q

What is a homeobox

A

A section of DNA 180 base pairs long coding for a part of the protein 60 amino acids long that is highly conserved (very similar) in plants, animals and fungi

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33
Q

What is a homeodomain?

A

Part of the protein that binds to DNA and switches other genes on or off

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34
Q

What are homeobox genes an example of

A

Regulatory genes

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35
Q

What happens when the Pax6 gene (a homeobox gene) mutates

A

Causes a form of blindness due to an underdevelopment of the retina in humans, causes blindness in mice and fruit flies who also have the gene

Pax6 involved in development of eyes in all 3 species - highly conserved

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36
Q

What are hox genes?

A

A group of Homeobox genes that are only present in animals

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37
Q

What are hox genes responsible for

A

Correct positioning of body parts

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38
Q

How are hox genes found?

A

Gene clusters

eg. mammals have 4 clusters on different chromosomes

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39
Q

How many hox genes do humans have and how has it arisen?

A

39, believed to have arisen from one ancient homeobox gene by duplication and accumulated mutations over time

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40
Q

How is the order in which genes along the chromosome are organised

A

In order in which their effects are expressed in the organism

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41
Q

How are body plans usually represented

A

As cross-sections through the organism showing fundamental arrangement of tissue layers

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42
Q

What are Diploblastic animals

A

Animals which have 2 primary tissue layers

43
Q

What are Tripoblastic animals

A

Animals which have 3 primary tissue layers

44
Q

What is a common feature of animals

A

Segmentation

eg. Head, thorax, abdomen of an insect
Backbone of vertebrates
Rings of a worm

45
Q

What do segments in an organism do

A

Segments have multiplied over time and specialised to form different functions

46
Q

What do hox genes in the head control

A

Development of mouthparts

47
Q

What do hox genes in the thorax control

A

Development of wings, limbs or ribs

48
Q

What are Somites and what have developed from them

A

Somites are segments in the embryo

From which individual vertebrae and associated structures have all developed

49
Q

What are somites directed by

A

Hox genes to develop in a particular way depending on their position in the sequence

50
Q

What is radial symmetry

A

Seen in diploblastic animals like jelly fish

No Left or right sides, only top and bottom

51
Q

What is bilateral symmetry

A

Seen in Most mammals

The organisms have both left and right sides and a head and tail rather than just a top and bottom

52
Q

What is Asymmetry

A

Seen in Sponges

No lines of symmetry

53
Q

What is the role of mitosis

A

Increase the number of cells leading to growth (growth and repair)

54
Q

What is apoptosis

A

Controlled cell death

(pg 516)

55
Q

What are both mitosis and apoptosis controlled by

A

Hox genes

56
Q

What is the role of apoptosis

A

Shaping different body parts by removing unwanted cells and tissue

57
Q

What is cell proliferation

A

Rapid increase in the number of cells

58
Q

What factors can affect the expression of regulatory genes

A

External - Change in temperature or intensity of light

Internal - Psychological stress or hormone release, Drugs (eg. thalidomide)

59
Q

What affect did thalidomide have and how is it being used now?

A

Used to treat morning sickness in pregnant women

Prevented normal expression of particular hox gene

Resulted in the birth of babies with shortened or no limbs

Now being used as a treatment for cancer, to stop its growth

60
Q

What is the theory of recapitulation

A

As organisms develop from a fertilised egg to embryo, they repeat the evolutionary process they have been through

61
Q

How can the theory of recapitulation be summarised

A

Ontology (development of an organism) mimics phylogeny (evolutionary history of an organism)

62
Q

Explain with reference to the body shape, while human beings are referred to as bilaterally, symmetrical, but jellyfish are radially symmetrical

A

Bilateral symmetry is along (single plane through) central axis
e.g., two arms, two legs

radial symmetry is along a plane at any angle through central axis
e.g., tentacles around central axis

63
Q

The hox gene Pax6 is necessary for the normal development of the retina in humans. Mutation in this gene can lead to blindness. Pax6 mutations can also cause blindness in mice and fruit flies. Describe how scientist could have tested the idea that Pax6 plays a role in our development in all three species.

A

Isolate (Pax6) gene from one species

detail e.g., PCR, restriction enzymes

test in different, tissue/species

example of positive result e.g., eyes develop on legs

switch gene off early in development and eyes will not develop

DNA sequencing and compare genes from different species

64
Q

Consider the statement:

“All hox genes are homeobox genes but not all homeobox genes are hox genes”

Discuss the validity of this statement

A

Statement is valid

Hox genes are one form of homeobox gene

present in vertebrates

in Hox clusters

other forms of homeobox gene present in other clusters

65
Q

Where is the entire genome of an organism present

A

in every prokaryotic cell or eukaryotic cell that contains a nucleus

66
Q

How do bacteria respond to changes in the environment

A

Gene regulation

Expressing genes only when the products are needed also prevents vital resources being wasted

67
Q

How are genes regulated and categorised (by the level at which they operate)

A

Transcriptional - genes can be turned on or off

Post-transcriptional - mRNA can be modified which regulates translation and they types of proteins produced

Translational - Translation can be stopped or started

Post-translational - Proteins can be modified after synthesis which changes their function

68
Q

What type of gene regulation is chromatin remodelling

A

Transcriptional control

69
Q

What is chromatin

A

DNA/Protein complex when DNA is wound around histones in order to be packed into the nucleus

70
Q

What is Heterochromatin

A

Tightly wound DNA causing chromosomes to be visible during cell division

71
Q

What is Euchromatin

A

Loosely wound DNA present during interphase

72
Q

Why is transcription of genes not possible when DNA is tightly wound (heterochromatin)

A

RNA polymerase cannot access the genes

73
Q

Why is transcription of genes possible when DNA is loosely wound (Euchromatin)

A

RNA polymerase can access the gene

74
Q

Why doesnt protein synthesis occur during cell divisions but does during interphase

A

Simple form of regulation, Ensures proteins are synthesised in time,

Prevents the complex and energy-consuming process of protein synthesis occuring when cells are actually dividing

75
Q

What is chromatin remodelling (brief summary)

A

Tightness at which DNA binds to histones

76
Q

What is Histone modification (brief summary)

A

Adding of groups to either increase or decrease packing and coil tightness of DNA/histone complex

77
Q

What charge is on DNA coils

A

Negative

78
Q

What charge is on histones

A

Positive

79
Q

What is condensation of DNA

A

Increasing the degree of packing - tightness of DNA/histone complex

80
Q

What is Acetylation and phosphorylation upon DNA packing and Chromatin complex (DNA/Histone)

A

Reduces positive charge on histones (makes them more negative)

Repels DNA more/ Makes bonds weaker/ less EFOA so they coil less tightly

So genes can be translated

81
Q

What affect does methylation have upon DNA/Histone complex

A

Makes histones more hydrohpobic

Binds tighter to DNA, preventing transcription of genes

82
Q

What are epigenetics

A

The control of gene expression by the modification of DNA, or all the different ways in which gene expression is regulated

83
Q

What is an operon

A

A group of genes that are under the control of the same regulatory mechanism and are expressed at the same time`

84
Q

Why are operons efficient at saving resources

A

If a certain gene product arent needed, then all of the genes involved in their production can be switched off

85
Q

What are the 3 genes in the lac operon

A

LacZ, LacY, LacA

86
Q

What are the 3 enzymes the Lac Operon

A

Beta-galactosidase, Lactose permease and transacetylase

87
Q

Describe the events in the Lac Operon activation

A

Repressor protein binds and blocks to the promotor and operator, preventing RNA polymerase from copying the necessary DNA

When lactose is present, it binds and changes the shape of the repressor protein, meaning it is no longer fits the binding region

RNA polymerase can now code for the new proteins to code for necessary enzymes

(pg 511)

88
Q

What are the three components of the lac operon

A

Regulatory gene, promotor, operator

89
Q

What is the role of cAMP

A

cAMP acts as a secondary messenger, binds to CRP (cAMP receptor protein)

Increases or up-regulates production of enzyme to metabolise lactose

90
Q

What are RNA processing and RNA editing an example of

A

Post-transcriptional/pre-translational control

91
Q

Describe the events in RNA processing

A

pre-mRNA is the product of transcription

Modified forming mature mRNA before it can bind to a ribosome and code for the synthesis of required protein

A cap (modified nucleotide) is added to 5’ end and a tail (long chain of Adenine nucleotides) is added to the 3’ end

Both help stabilise mRNA and delay degradation in the cytoplasm

cap aids binding of mRNA to ribosomes. Splicing also occurs where the RNA is cut at specific points introns (non-coding DNA) are removed and the exons (coding DNA) are joined together

Process occurs within the nucleus

92
Q

What is a cap in RNA processing

A

A modified nucleotide that is added to the 5’ end

93
Q

What is a tail in RNA processing

A

A long chain of adenine nucleotides added to the 3’ end

94
Q

What is splicing in RNA

A

Introns are removed and exons are joined together in the nucleus

95
Q

What are introns

A

non-coding regions of DNA

96
Q

What are exons

A

coding regions of DNA

97
Q

What is RNA editing

A

Changing of some mRNA molecules through base addition, deletion or substitution.

Same affect as point mutations and result in the synthesis of different proteins which may have different functions

Increases the range of proteins that can be produced from a single mRNA molecule or gene

98
Q

What are some examples of translational control

A

Degradation of mRNA - the more resistant the molecule, the longer it will last in the molecule, so more of the protein is synthesised

Binding of inhibitory proteins - to mRNA prevents it binding to ribosomes and the synthesis of proteins

Activation of initiation factors which aid the binding of mRNA to ribosomes - the eggs of many organisms produce large quantities of mRNA which isn’t required until after fertilisation

99
Q

What do protein kinases do

A

Enzymes that catalyse the addition of phosphate groups to proteins.

Phosphate groups changes the tertiary structure and so the function of a protein

Many enzymes are activated by phosphorylation, so protein kinases are important regulators of cell activity, and activated sometimes by cAMP

100
Q

What are some examples of post-translational control

A

Addition of non-protein groups eg. Carbohydrate chains, lipids or phosphates

Modifying amino acids and the formation of bonds such as disulfide bridges

Folding or shortening of proteins

Modification by cAMP - eg. Lac Operon cAMP binds to CRP increasing rate of transcription

101
Q

The lac operon is often referred to as being ‘leaky’ meaning that it is still transcribed to a limited extent even if even in the absence of lactose.

1) Using your knowledge of how the lac operon works, explain why this is necessary

2) Suggest the functions of beta-galactosidase and lactose permease synthesised by the lac operon

A

1) enzyme coded for by lac operon enables lactose to enter bacteria

lactose binds to repressor
protein; (repressor) protein changes shape

transcription no longer blocked
enzymes needed
to metabolise lactose are synthesised

2) β-galactosidase catalyses the hydrolysis of lactose

to galactose and lactose

lactose
permease enables the entry of lactose into cells

102
Q

Another example of gene regulation in prokaryotes in the trp operon. This operon codes for the production of tryptophan, an essential amino acid for the bacterium E.coli. When tryptophan is available in the environment the structural genes in the trp operon are not expressed.

Suggest a mechanism for the genetic regulation of this operon

A

Tryptophan binds to repressor protein

shape of repressor protein changes

repressor protein
binds to promoter

blocks RNA polymerase from binding

transcription prevented

of genes
coding for enzymes responsible for tryptophan synthesis

103
Q

Using your knowledge of enzymes, explain how enzyme cofactors could play a role in gene regulation

A

Cofactors bind to proteins that regulate transcription

changes binding of proteins to control
elements

rate of transcription changed

RNA polymerase activated

BIOLOGY A LEVEL (24 decks)

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