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biology > Genetics Of Living Systems > Flashcards

Genetics Of Living Systems Flashcards

1
Q

what are mutations

A

a random error in DNA nucleotide - an alteration in the nucleotide sequence of a cell in a living organism

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2
Q

what is the most common mutation

A

loss of purine or pyrimidine base

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3
Q

what are the effects of mutations
beneficial, neutral and harmful

A

beneficial: mutations offer a selective advantage to an individual and is the driving force behind natural selection

neutral: has no effect so the mutation occurs in the non coding part of DNA or is silent

harmful: thalassemia, sickle cell, cystic fibrosis (deletion), Huntington disease. Huntington is an expanding triple nucleotide repeat (CAG-CAG-CAG-CAG)

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4
Q

what are point mutations

A

changes in an individual gene due to miscopying of one of more nucleotides
occurs at a single point in the nucleotide sequence
there can be more than one point mutation in a sequence

examples:
- substitution mutations
- insertion mutations
- deletion mutations

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5
Q

what are substitution mutations

A

result in a change of one base
results in one triplet code being changed

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6
Q

what are insertion mutations

A

when a new base is inserted into DNA base sequence
this changes the triplet code at the point of mutation, but can have a FRAMESHIFT EFFECT on bases further down the sequence

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7
Q

what are deletion mutations

A

when a random base is DELETED from the nucleotide base sequence
like insertions they change the triplet code at the point of mutation but also have a frameshift effect

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8
Q

what can substitution mutations be further categorised into

A

silent mutations
nonsense mutations
missense mutations

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9
Q

what are silent mutations

A

a silent mutation occurs when substitution of a base still codes for the same amino acid as the original base

possible due to the DEGENERATE nature of genetic code

mutation has no effect on the final polypeptide

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10
Q

what are nonsense mutations

A

occurs when a substitution results in a premature ‘stop codon’ being coded for

leading to premature end to synthesis of polypeptide

very unlikely that final protein would function normally

stop codons are - UAA, UAG and UGA

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11
Q

what is thalassemia

A

autosomal recessive blood disease caused by nonsense mutation

sufferers have reduced rate or no synthesis of one of the beta globin chains that make up haemoglobin = anaemia

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12
Q

what are missense mutations

A

occur when a change in base leads to a different amino acid being coded for
polypeptide will have a single amino acid that is different

the effect of mutation is determined by the role of the amino acid in the final polypeptide

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13
Q

what is sickle cell disease

A

caused by missense mutation in the haemoglobin gene

the hydrophilic amino acid GLUTAMIC ACID is replaced by the hydrophobic amino acid valine

valines form bonds with themselves that stick haemoglobin molecules together, producing long chains of stuck-together haemoglobin molecules

this distorts the shape of the red blood cell and decreases its elasticity

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14
Q

when is vitamin D synthesised

A

when skin is exposed to sunlight and through diet

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15
Q

what is melanin and what does it do

A

a skin pigment that protects cells from harmful effects of UV and reduces vitamin D production

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16
Q

what is the cradle of mankind in Ethiopia

A

early humans that had dark skin

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17
Q

what is the result of genetic mutations in skin

A

lighter skin
less melanin
light skin does not shield against harmful UV - causes skin cancer
however, vitamin D can be synthesised with less sunlight
therefore suited migration to more temperature climes as increased melanin not needed to protect against sun
skin can synthesise enough vitamin D from low UV levels

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18
Q

when is high melanin and low melanin advantageous

A

high melanin in hotter climates
low melanin in colder climates

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19
Q

Who discovered that some genes are only turned on when conditions require the proteins they code for

What did they use this information for

A

Jacob and Monod

Used it to suggest that the control of enzyme levels in all cells occurs through regulation of transcription

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20
Q

What is e.coli capable of synthesising

A

A variety of different enzymes depending on their environment

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21
Q

What does lactose permease do

A

Transports lactose into the cell

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22
Q

What does Beta-galactosidase do

A

Catalyses hydrolysis of lactose into glucose and galactose

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23
Q

Why do E.coli only produce enzymes needed to metabolise lactose when lactose is present in substrate

A

Because it would be a waste to produce

Therefore expression of these proteins is induced by the presence of lactose

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24
Q

Describe the regulation of the lac operon

A

Structural genes encode proteins involved in the uptake and utilisation of lactose

Regulatory gene encodes a protein which controls when the structural gene is expressed (on/off switch)

RNA polymerase binds to the promoter region to initiate transcription of gene

MRNA is translated by ribosomes to produce a repressor protein

The repressor protein has two binding sites
- one site binds to lactose
The other site binds to LacO (operator region)

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25
Q

What does LacI encode for

A

A repressor protein

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26
Q

What does LacO do

A

The operator region of DNA

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27
Q

What does LacZ encode for

A

Beta-galactosidase

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28
Q

What does LacY code for

A

Permease proteins

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29
Q

When does the Lac operon switch off

A

When lactose is ABSENT the repressor protein binds to LacO

This blocks the promotor region (LacP) so that RNA cannot bind to it and the structural genes cannot be transcribed

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30
Q

When does the lac operon switch on

A

When lactose is PRESENT it binds to the lactose-binding site on repressor protein

This changes the shape of the DNA binding site so that it cannot bind to LacO

This allows RNA polymerase to bind to lacP so that the structural genes can be transcribed

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31
Q

What is an inducible operon

A

Lactose induces transcription of the enzyme that break it down

It is called the inducer

32
Q

A mutation that renders the regulatory gene of a repressible operon non-functional would result in…?

A

Continuous transcription of the structural genes encode proteins

33
Q

Describe gene expression in eukaryote

A

Eukaryotes are multicellular
So instead of having sections of DNA that are switched on and off, they have cells that have different sections of the DNA switched on off or

Cell differentiation

34
Q

What are transcription factors

A

Proteins or non-coding pieces of RNA that work within the nucleus to control the expression of genes

35
Q

How do transcription factors work in eukaryotes

A

Factors bind to their specific promotor region and either activate or repress RNA polymerase from binding to the DNA

36
Q

What is post-transcriptional gene regulation

A

Splicing

  • not all DNA codes for protein, some is essentially ‘junk’ DNA
  • coding DNA = Exons
  • non-coding DNA = introns

Non-coding is removed from the strand before translation occurs - splicing

37
Q

Define monogenic inheritance
Give an example

A

The inheritance of characteristic controlled by a single gene
E.g. wing length in fruit flies

38
Q

Who was Gregor Mendel?
What did he discover?
and why was his work important

A

An Austrian monk
In his garden he noticed how characteristics in plants were passed from one generation to the next
His research, published in 866 became the foundation of modern genetics

39
Q

What did Mendel do a lot of experiments with and what was the conclusion of his results

A

Pea plants

Crossed a homozygous tall pea plant with a homozygous dwarf pea plant,
Continuously bred them and because dwarf offspring was passed from the original dwarf it only showed sometimes

This shows that genes are passed to offspring but some are dominant over others.

40
Q

What are the three biological agents

A

Alkylating agents - methyl or ethyl groups are attached to bases resulting in incorrect base paring

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

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

41
Q

Different mutations have a range of effects on the protein synthesised. What are these categorised as?

A

Amorph - mutation that results in the loss of function of a protein

Hypomorph - mutation that results in a reduction of function of a protein

Hypermorph - mutation that results in a gain in function of a protein

42
Q

What are the four changes in chromosome structure?

A

Deletion - section breaks off and is lost within the cell

Duplication - sections get duplicated

Translocation - 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

43
Q

What are the different ways (4) genes are regulated

A

Transcriptional - genes can be turned on or off

Post-transcriptional - mRNA can be modified which regulates translational and the types of proteins produced

Translational - translations can be stopped or started

Post-translational - proteins can be modified after synthesis which changes their functions

44
Q

What are the ways in which transcription is controlled

A

Chromatin remodelling
Histone modification

45
Q

Describe acetylation and phosphorylation in histone modification

A

Addition of acetyl or phosphate groups

Reduces the positive charge on the histones
Causes DNA to coil less tightly, allowing certain genes to be transcribed

46
Q

Why does DNA coil around histones

A

Because histones are positively charged and DNA is negatively charged

47
Q

Describe methylation in histone modification

A

Addition of methyl groups make histones more hydrophobic so they bind more tightly to each other

Causes DNA to coil more tightly and preventing transcription of genes

48
Q

What are homeobox genes

A

A group of genes which all contain 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

Homeobox genes are regulatory genes

49
Q

Why are homeobox genes regulatory genes

A

Because a part of the protein (homeodomain) binds to DNA and switches other genes on or off. Therefore, homeobox genes are regulatory genes

50
Q

Why are homeobox genes regulatory genes

A

Because a part of the protein (homeodomain) binds to DNA and switches other genes on or off. Therefore, homeobox genes are regulatory genes

51
Q

What are HOX genes

A

HOX genes are one group of homeobox genes that are only present in animals,
- responsible for the correct positioning of body parts

  • found in gene clusters
  • mammals have four clusters on different chromosomes
52
Q

How are body plans usually represented

A

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

53
Q

What do HOX genes in the head and thorax control

A

Head - development of mouthparts
Thorax - development of wings, limbs or ribs

54
Q

What are the three types of symmetry shown in body shapes

A

Radial symmetry - have no left or right sides, only top and bottom

Bilateral symmetry - organisms have both left and right sides and head and tail

Asymmetry is seen in sponges which have no lines of symmetry

55
Q

Define diploblastic and triploblastic organisms

A

Diploblastic = two primary tissue layers

Triploblastic = three primary tissue layers

56
Q

What are somites and what have the developed into

A

Somites are segments in the embryo that are directed by HOX genes to develop in a particular way depending on their position in the sequence.

Somites developed into individual vertebrae and associated structures

57
Q

What animals have radial symmetry

A

Diploblastic animals like jellyfish

58
Q

What is the role of mitosis and apoptosis in body plan development

A

Mitosis - increase the number of cells leading to growth

Apoptosis - removes unwanted cells and tissues

  • cells undergoing apoptosis can also release chemical signals to stimulate mitosis and cell proliferation - remodelling tisssues
59
Q

How are mitosis and apoptosis regulated

A

By HOX genes

60
Q

What factors affect the expression of regulatory genes

A

Environment - internal and external
Stress - homeostatic balance within an organism is upset
External - change in light intensity or temperature
Internal - release of hormones or psychological stress
Drugs - e.g. thalidomide

61
Q

Explain how thalidomide affected the activity of regulatory genes

A
  • given to pregnant women to treat morning sickness
  • prevented expression of HOX gene related to limb length
  • thalidomide prevents the formation of networks of capillaries which are necessary for some tumours to grow and develop
62
Q

how is gene expression regulated at the transcription level?

A

transcription factors
- proteins that can either initiate or inhibit the transcription of genes so that only certain parts of DNA are expressed

63
Q

describe the function of the lac operon in LOW lactose concentrations

A

E.coli can use lactose as a respiratory substrate via use of an enzyme

when lactose conc is low, lac operon binds to the gene that makes the enzyme and inhibits its expression

64
Q

describe the function of the lac operon in high lactose concentrations

A

lactose binds to operon, causing it to change shape and unattach from the gene.
allows RNA polymerase to bind and the gene to be expressed

65
Q

how is development controlled by homeobox genes

A

code for transcription factors that activate genes when they’re needed during development of a zygote

66
Q

what best describes an operon

A

a cluster of genes under control of a promotor

67
Q

what feature of a pathogen could be altered by a mutation making a vaccine ineffective

A

shape of proteins/ antigens on plasma membrane

68
Q

What type of adaptation is represented by tigers stripes

A

Anatomical

69
Q

Describe and explain how a tiger with striped fur may have evolved from a non-striped ancestor
(Discuss the different types of genes that might be involved)

A
  • Mutations (e.g. of pigment gene and of regulatory genes)
  • selection pressure of prey availability
  • adaptation helped tigers to hide from prey/ camouflage
  • striped tigers had greater survival probability - more likely to reproduce
  • beneficial alleles passed onto next generation
  • allele frequency of relevant genes would have increased with each generation
  • after many generations, all tigers of that population were striped

Roles of regulatory genes:

  • regulatory genes control the pattern/ where pigments produced/ expression of other genes
  • genes switched on or off during development
70
Q

Outline how a dominant allele codes for the production of an enzyme and explain why the recessive allele codes for an enzyme with a different primary structure

A

Genetic code:
- DNA base sequence codes for amino acid sequence
- ref to mRNA base sequence
- triplet code/ 3 bases = 1amino acid
- degenerate code
- substitution could result in same amino acid

Transcription C:
- transcription then translation
- complementary base pairing
- synthesis of mRNA strand
- role of RNA polymerase

Translation L:
- mRNA binds to ribosome
- tRNA binds to mRNA
- tRNA brings specific amino acid
- mRNA translated into polypeptide

Effect of y allele
- substitution/ frameshift
- different base sequence of DNA
- different mRNA codon
- different tRNA anticodon
- tRNA brings different amino acids
- different sequence of amino acids
- amino acid sequence is primary structure

71
Q

Describe how gene expression can be regulated after transcription

A

Primary mRNA is modified
Removal of introns to produce mature mRNA
Alternative splicing can produce different versions of mRNA
Protein must be activated by cAMP/ phosphorylation
Binding of cAMP alters shape of protein

72
Q

Suggest and explain why lactose is unable to cross membranes

A
  • too big
  • unable to pass between phospholipids

Or

  • no/small concentration gradient
  • needs carrier protein/ pump
73
Q

Define epistasis

A

Interaction between genes that influences a phenotype

74
Q

Suggest how an allele may inhibit the expression of another allele (both dominant)

A

Allele 1 produces/ codes for repressor protein/ transcription factor
Product of allele 1 binds to promotor of allele 2/ mRNA/ ribosome
Product of allele 1 stops transcription/ translation of allele 2
Product of allele 1 inhibits the enzyme encoded by allele 2

75
Q

Fill in the blanks:

Development of eukaryotic body plan is controlled by _____ genes
These genes code for proteins that are able to bind to ______and turn specific genes on and off and are known as ______factors. These proteins contain a sequence of base pairs that varies little between species within the animal, _______ or fungus______

A

Homeobox
DNA
Transcription
Plant
Kingdoms

biology (24 decks)

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