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

CHAPTER 19 - GENETICS OF LIVING SYSTEMS Flashcards

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
Outline why the majority of mutations do not have an influence phenotype
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
26
Discuss why beneficial mutations are rare and suggest a process that beneficial mutations underpin
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
27
What are housekeeping genes?
Genes that code for enzymes necessary for metabolic reaction pathways eg. respiration
28
When are protein-based hormones only required for?
Needed by Certain cells at certain times to carry out short lived responses Coded for by tissue-specific genes
29
What is morphogenesis
The regulation of the pattern of anatomical development
30
What is the usual choice in species for genetic studies and why
Fruit Flies Small, easy to keep and have a short life cycle
31
What are homeobox genes
Group of genes which all contain a homeobox
32
What is a homeobox
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
33
What is a homeodomain?
Part of the protein that binds to DNA and switches other genes on or off
34
What are homeobox genes an example of
Regulatory genes
35
What happens when the Pax6 gene (a homeobox gene) mutates
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
36
What are hox genes?
A group of Homeobox genes that are only present in animals
37
What are hox genes responsible for
Correct positioning of body parts
38
How are hox genes found?
Gene clusters eg. mammals have 4 clusters on different chromosomes
39
How many hox genes do humans have and how has it arisen?
39, believed to have arisen from one ancient homeobox gene by duplication and accumulated mutations over time
40
How is the order in which genes along the chromosome are organised
In order in which their effects are expressed in the organism
41
How are body plans usually represented
As cross-sections through the organism showing fundamental arrangement of tissue layers
42
What are Diploblastic animals
Animals which have 2 primary tissue layers
43
What are Tripoblastic animals
Animals which have 3 primary tissue layers
44
What is a common feature of animals
Segmentation eg. Head, thorax, abdomen of an insect Backbone of vertebrates Rings of a worm
45
What do segments in an organism do
Segments have multiplied over time and specialised to form different functions
46
What do hox genes in the head control
Development of mouthparts
47
What do hox genes in the thorax control
Development of wings, limbs or ribs
48
What are Somites and what have developed from them
Somites are segments in the embryo From which individual vertebrae and associated structures have all developed
49
What are somites directed by
Hox genes to develop in a particular way depending on their position in the sequence
50
What is radial symmetry
Seen in diploblastic animals like jelly fish No Left or right sides, only top and bottom
51
What is bilateral symmetry
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
What is Asymmetry
Seen in Sponges No lines of symmetry
53
What is the role of mitosis
Increase the number of cells leading to growth (growth and repair)
54
What is apoptosis
Controlled cell death (pg 516)
55
What are both mitosis and apoptosis controlled by
Hox genes
56
What is the role of apoptosis
Shaping different body parts by removing unwanted cells and tissue
57
What is cell proliferation
Rapid increase in the number of cells
58
What factors can affect the expression of regulatory genes
External - Change in temperature or intensity of light Internal - Psychological stress or hormone release, Drugs (eg. thalidomide)
59
What affect did thalidomide have and how is it being used now?
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
What is the theory of recapitulation
As organisms develop from a fertilised egg to embryo, they repeat the evolutionary process they have been through
61
How can the theory of recapitulation be summarised
Ontology (development of an organism) mimics phylogeny (evolutionary history of an organism)
62
Explain with reference to the body shape, while human beings are referred to as bilaterally, symmetrical, but jellyfish are radially symmetrical
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
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.
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
Consider the statement: "All hox genes are homeobox genes but not all homeobox genes are hox genes" Discuss the validity of this statement
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
Where is the entire genome of an organism present
in every prokaryotic cell or eukaryotic cell that contains a nucleus
66
How do bacteria respond to changes in the environment
Gene regulation Expressing genes only when the products are needed also prevents vital resources being wasted
67
How are genes regulated and categorised (by the level at which they operate)
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
What type of gene regulation is chromatin remodelling
Transcriptional control
69
What is chromatin
DNA/Protein complex when DNA is wound around histones in order to be packed into the nucleus
70
What is Heterochromatin
Tightly wound DNA causing chromosomes to be visible during cell division
71
What is Euchromatin
Loosely wound DNA present during interphase
72
Why is transcription of genes not possible when DNA is tightly wound (heterochromatin)
RNA polymerase cannot access the genes
73
Why is transcription of genes possible when DNA is loosely wound (Euchromatin)
RNA polymerase can access the gene
74
Why doesnt protein synthesis occur during cell divisions but does during interphase
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
What is chromatin remodelling (brief summary)
Tightness at which DNA binds to histones
76
What is Histone modification (brief summary)
Adding of groups to either increase or decrease packing and coil tightness of DNA/histone complex
77
What charge is on DNA coils
Negative
78
What charge is on histones
Positive
79
What is condensation of DNA
Increasing the degree of packing - tightness of DNA/histone complex
80
What is Acetylation and phosphorylation upon DNA packing and Chromatin complex (DNA/Histone)
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
What affect does methylation have upon DNA/Histone complex
Makes histones more hydrohpobic Binds tighter to DNA, preventing transcription of genes
82
What are epigenetics
The control of gene expression by the modification of DNA, or all the different ways in which gene expression is regulated
83
What is an operon
A group of genes that are under the control of the same regulatory mechanism and are expressed at the same time`
84
Why are operons efficient at saving resources
If a certain gene product arent needed, then all of the genes involved in their production can be switched off
85
What are the 3 genes in the lac operon
LacZ, LacY, LacA
86
What are the 3 enzymes the Lac Operon
Beta-galactosidase, Lactose permease and transacetylase
87
Describe the events in the Lac Operon activation
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
What are the three components of the lac operon
Regulatory gene, promotor, operator
89
What is the role of cAMP
cAMP acts as a secondary messenger, binds to CRP (cAMP receptor protein) Increases or up-regulates production of enzyme to metabolise lactose
90
What are RNA processing and RNA editing an example of
Post-transcriptional/pre-translational control
91
Describe the events in RNA processing
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
What is a cap in RNA processing
A modified nucleotide that is added to the 5' end
93
What is a tail in RNA processing
A long chain of adenine nucleotides added to the 3' end
94
What is splicing in RNA
Introns are removed and exons are joined together in the nucleus
95
What are introns
non-coding regions of DNA
96
What are exons
coding regions of DNA
97
What is RNA editing
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
What are some examples of translational control
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
What do protein kinases do
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
What are some examples of post-translational control
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
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
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
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
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
Using your knowledge of enzymes, explain how enzyme cofactors could play a role in gene regulation
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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