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Biology > 20. Gene Expression > Flashcards

20. Gene Expression Flashcards

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1
Q

Name all the gene mutations

A
  • Substitution
  • Deletion
  • Addition
  • Duplication
  • Inversion
  • Translocation
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2
Q

Name 3 consequences of gene substitution

A
  • One of the 3 stop codons are formed which prematurely stops the production of the polypeptide chain. This results in a significantly different protein that wouldn’t be able to function properly
  • Another codon is formed, which codes for a different amino acid. This change in the polypeptide chain may cause a change in the proteins tertiary structure meaning the protein produce will be dysfunctional.
  • The formation of different codon but codes for the same amino acid. This is because the genetic code is degenerate. It will have no effect on the overall protein shape/function
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3
Q

What is the consequence of a deletion mutation

A
  • the deletion of a base causes a frameshift for every codon downstream of the mutation
  • this alters most triplets downstream meaning the amino acids coded for are different
  • significantly altering the proteins tertiary structure and therefore its dysfunction.
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4
Q

Define substitution

A

Type of gene mutation in which a nucleotide in a section of a DNA molecule is replaced by another nucleotide.

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5
Q

Define deletion

A

The loss of a nucleotide base from a DNA molecule

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6
Q

Define addition

A

When an extra nucleotide base is inserted into the DNA molecule

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7
Q

What is the consequence of an addition mutation

A
  • the addition of a base causes a frameshift for every codon downstream of the mutation
  • this alters most triplets downstream meaning the amino acids coded for are different
  • significantly altering the proteins tertiary structure and therefore its dysfunction.
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8
Q

Why is a deletion/addition of 3 bases less detrimental to the proteins tertiary structure

A
  • there will not be a frameshift
  • the protein coded for will be slightly different
  • but not as dysfunctional as if there was a frame shift
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9
Q

Define duplication

A

When one or more nucleotide bases are repeated in a DNA molecule

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10
Q

What is the consequence of a duplication mutation

A
  • the duplication of a base causes a frameshift for every codon downstream of the mutation
  • this alters most triplets downstream meaning the amino acids coded for are different
  • significantly altering the proteins tertiary structure and therefore its dysfunction
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11
Q

Define inversion

A

When a small sequence of nucleotide bases becomes separated from the DNA molecule and rejoin at the same position but inverted.

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12
Q

What is the consequence of an inversion mutation

A
  • this portion of the base sequence codes for a completely different set of amino acids
  • can cause a dysfunctional protein
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13
Q

Define translocation

A
  • when a group of bases become separated from the DNA sequence on one chromosome
  • and become inserted into the DNA sequence of another chromosome
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14
Q

What is the consequence of translocation

A
  • often have significant effects on gene expression
  • leading to abnormal phenotype
  • can include the development of some cancers and infertility
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15
Q

What are mutagenic agents

A

Outside factors that increase mutation frequency

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16
Q

Name two mutagenic agents

A
  • high energy ionising radiation

- chemicals

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17
Q

What is cell differentiation

A

The process where cells become specialised for different functions

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18
Q

Why do all cells in the body have the potential to produce anything the body can make

A

All cells in an organism are derived by mitotic divisions of the fertilised egg (zygote) so they all contain the same genes

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19
Q

Why is it that cells contain the same genes but produce different things

A

Only certain genes are expressed at any one time

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20
Q

Give an example of gene that are permanently expressed

A

The gene that codes for the enzyme in respiration

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21
Q

Give an example of gene that are permanently not expressed

A

The gene that codes for insulin in the small intestine

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22
Q

Why do differentiated cells differ from each other visibly

A
  • each cell has different genes expressed
  • so different proteins are coded for
  • giving differences that are visible
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23
Q

Define totipotent stem cells

A
  • a cell which can mature into any body cell, e.g zygotes.

- found in early embryo

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24
Q

Name two ways in which genes are prevented from being expressed

A
  • preventing transcription and so preventing the production of mRNA
  • preventing translation
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25
Q

Why can xylem vessels and red blood vessels, specifically, not develop into other cells

A

They lose their nuclei when they mature and as the nucleus contains the genes they cannot develop into other cells

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26
Q

Define stem cells

A

Undifferentiated dividing cells that occur in embryos and in adult animal tissues .

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27
Q

Name 4 sources of stem cells in mammals and how they are different

A
  • embryonic stem cells. From embryos in the early stages of development. Can differentiated into any type of cell.
  • umbilical cord blood stem cells. From umbilical cord. Specific to a particular tissue or organ within which they produce the cells to maintain and repair tissues
  • placental stem cells. From placenta. Develop into specific types of cells
  • adult stem cells. Found in the body of fetus to adult. Specific to a particular tissue or organ within which they produce the cells to maintain and repair tissues
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28
Q

Name 4 types of stem cells

A
  • totipotent stem cells
  • pluripotent stem cells
  • multipotent stem cells
  • unipotent stem cells
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29
Q

Define pluripotent stem cells

A
  • can differentiate into almost any type of cell.
  • found in embryos.
  • eg. embryonic stem cells and fetal stem cells
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30
Q

Define multipotent stem cells

A
  • can differentiate into a limited number of specialised cells.
  • usually develop into cells of a particular type (eg. stem cells in the bone marrow can produce any type of blood cell
  • e.g adult stem cells and umbilical cord blood stem cells
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31
Q

Define unipotent stem cells

A
  • can only differentiate into a single type of cell
  • derived from multipotent stem cells
  • made in adult tissue
  • e.g cardiomyocytes
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32
Q

What are cardiomyocytes

A
  • a type of unipotent stem cell

- a heart muscle cell that can divide to produce new heart tissue and so repair damage to heart muscle

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33
Q

What does iPS cells stand for

A

Induced pluripotent stem cells

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34
Q

What are iPS cells

A

A type of pluripotent that is produced from unipotent stem cells

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35
Q

How are iPS cells produced

A
  • body cells are genetically altered in a lab to make them require the characteristics of embryonic stem cells (a type of pluripotent cell)
  • acquiring these these characteristics changes involves inducing genes and transcriptional factors (switching on genes)
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36
Q

What does the fact genes in iPS cells were able to be reactivated show

A

Adult stem cells retain the same genetic information that was present in the embryo

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37
Q

How are iPS cells different to embryonic stem cells

A

iPS cells are capable of self renewal. This means they can provide a limitless supply. Could replace embryonic stem cells in medical research which would overcome ethical issues

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38
Q

How may iPS be able to treat human disorders

A
  • cells can be used to regrow tissues that have been damaged

- e.g heart muscle cells (damaged from heart attack), skin grafts, and B cells of the pancreas (Type 1 diabetes).

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39
Q

Before transcription can begin what must first happen

A

The gene must first be switched on by transcriptional factors

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40
Q

What is are transcriptional factors

A

Specific molecules that move from the cytoplasm into the nucleus that switch on genes for transcription

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41
Q

How do transcriptional factors switch on genes for transcription

A
  • transcriptional factors have a site that binds to a specific base sequence of DNA in the nucleus
  • when it binds it causes the region of DNA to begin the process of transcription
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42
Q

What is happening when a gene is not being expressed (i.e why)

A

The site on the transcriptional factor that binds to the DNA is not active. This means it cannot bind and cause transcription

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43
Q

Describe briefly how hormones such as oestrogen can switch on a gene

A
  • the hormone combines with the receptor site on the transcriptional factor
  • this activates the DNA binding site causing it to change shape
  • allowing it to bind to the DNA and begin transcription
44
Q

Describe in detail the effect of oestrogen on gene transcription

A
  • oestrogen is lipid soluble so diffuse through the phospholipid bilayer of the cell-surface membrane
  • oestrogen then binds with a site on a receptor of the transcriptional factor, the site and the shape of the oestrogen molecule are complementary
  • binding causes the shape of the DNA binding site on the transcriptional factor to change (it has been activated)
  • the transcriptional factor can then enter the nucleus through a nuclear pore and bind to a specific base sequence on DNA
  • this stimulates transcription of the gene
45
Q

Why can oestrogen easily diffuse through the phospholipid bilayer of the cell-surface membrane

A

Oestrogen is a lipid-soluble molecule

46
Q

What does oestrogen bind to

A

A complementary receptor site on the transcriptional factor

47
Q

What does the binding of oestrogen on the transcriptional factor cause

A
  • causes it to be activated
  • the DNA binding site on the transcriptional factor changes shape
  • so it is able to bind with DNA
48
Q

How does the transcriptional factor enter the nucleus

A

Through a nuclear pore

49
Q

What is epigenetics

A

A scientific field studying how environmental influences can alter the genetic inheritance of an organisms offspring

50
Q

What are DNA wrapped around

A

Proteins called histones

51
Q

What are the DNA and histones covered in

A

Chemical tags

52
Q

What is the epigenome

A

The second layer formed from the chemical tags

53
Q

What does the epigenome determine

A

The shape of the DNA histone complex and therefore which genes can be expressed

54
Q

How does the epigenome control the expression of genes

A
  • epigenome determines the shape of the DNA histone complex
  • genes that aren’t expressed are inactive in a tightly packed arrangement ensuring they cannot be read
  • keeping them switched off which is known as epigenetic silencing
  • genes that are active are unwrapped and the DNA is exposed so it can be transcribed
55
Q

What is epigenetic silencing

A

When genes aren’t expressed due to the shape of the DNA histone complex due to the epigenome

56
Q

Name 2 ways transcription can be inhibited by the epigenome caused by environmental factors

A
  • decreased acetylation of histones

- increased methylation of DNA

57
Q

When association of histones with DNA is weak…

A

the DNA histone complex is less condensed. DNA is therefore easily accessible to transcription factors

58
Q

Condensation of the DNA histone complex does what to transcription

A

Inhibits

59
Q

What is acetylation

A

The process whereby an acetyl group is transferred to a molecule.

60
Q

In the case of acetylation of histones what is donating the acetyl group

A

acetyl coenzyme A

61
Q

What does decreased acetylation do to the histone

A
  • increase the positive charges
  • therefore increase the attraction to the phosphate groups of DNA
  • association between DNA and histones is stronger
  • DNA less accessible to transcription factors
  • so decreased acetylation means gene is switched off
62
Q

What is methylation

A

The addition of a methyl group to a molecule

63
Q

In the case of methylation of DNA what is the methyl added to

A

The cytosine bases of DNA

64
Q

How does methylation inhibit the transcription of genes

A
  • preventing the binding of transcriptional factors to the DNA
  • attracting proteins that condense the DNA-histone complex (by inducing deacetylation of the histones) making the DNA inaccessible to transcription factors
65
Q

How is epigenetics related to disease

A
  • activation or silencing of genes can rise to disease

- e.g cancer

66
Q

How can diseases be treated with epigenetic therapy

A
  • drugs can be used to inhibit certain enzymes involved in either histone acetylation or DNA methylation
  • this can be used to reverse activated or silenced genes causing diseases
67
Q

Why must epigenetic therapy specifically targeted on diseased cells (e.g cancer cells)

A

If drugs were to affect normal cells they could activate gene transcription and make them cancerous

68
Q

Name another use of epigenetics in disease treatment

A
  • can be used in early diagnostic tests that can help detect the early stages of disease
  • detecting level of DNA methylation or histone acetylation
  • allowing those with these diseases to receive early treatment
69
Q

Name another way, apart from the prevention of translation, that genes can be not expressed

A

mRNA from transcription can be broken down before it can be translated into a polypeptide by siRNA

70
Q

What does siRNA stand for

A

Small interfering RNA

71
Q

Briefly how does siRNA work

A

It pairs with an enzyme and binds to a complementary section of mRNA and cuts it into smaller sections so it cannot be translated

72
Q

Describe in detail the mechanism of blocking a gene involving siRNA

A
  • an enzyme cuts large double stranded molecules of RNA into smaller sections called siRNA
  • one of the two siRNA strands combines with an enzyme
  • the siRNA molecule guides the enzyme to a messenger RNA molecule by pairing up its bases with the complementary ones on a section of the mRNA molecule
  • the enzyme then cuts the mRNA into smaller sections
  • the mRNA is no longer capable of being translated into a polypeptide
  • this means the gene has not been expressed (blocked)
73
Q

How is siRNA made from RNA

A

An enzyme cuts large double stranded molecule of RNA into smaller sections called siRNA

74
Q

What is a malignant tumour

A

A cancerous tumour

75
Q

What is a benign tumour

A

A non-cancerous tumour

76
Q

Name some characteristics of benign tumours

A
  • can grow to large size
  • grow slowly
  • must less likely to be life threatening but can disrupt organ function
  • have localised effect on the body
  • cells are often well differentiated
77
Q

Name some characteristics of malignant tumours

A
  • can grow to large size
  • grow rapidly
  • more likely to be life threatening as abnormal tissue replaces normal
  • have a systemic (whole body) effect such as weight loss and fatigue
  • cells become de-differentiated
78
Q

What happens during the development of cancer

A
  • cancer cells are derived from a single mutant cell
  • the initial mutation causes uncontrolled mitosis
  • later a further mutation in one of the descendant cells leads to other changes that cause subsequent cells to be different from normal in growth and appearance
79
Q

Name the two main types of genes that play a role in cancer

A
  • tumour suppressor genes

- oncogenes

80
Q

What are proto-oncogenes

A
  • genes that stimulate a cell to divide
  • when growth factors attach to a complementary protein receptor on its cell surface membrane
  • this activates the genes causing DNA to replicate and the cell to divide
81
Q

How do proto-oncogenes cause the cell to divide

A
  • when growth factors attach to a complementary protein receptor on its cell surface membrane
  • it activates the genes causing DNA to replicate and the cell to divide
82
Q

What happens when a proto-oncogene mutates into an oncogene

A

It becomes permanently switched on

83
Q

Why does a proto-oncogene become permanently switched on

A
  • the receptor protein on the cell-surface membrane can be permanently activated so that cell division is switched on even in the absence of growth factors
  • the oncogene may code for a growth factor that is then produced in excessive amounts again, stimulating excessive cell division
84
Q

Name two ways cancer can occur

A
  • mutation of proto-oncogenes

- mutation of tumour suppressor genes

85
Q

What do tumour suppressor genes do

A
  • slow down cell division
  • repair mistakes in DNA
  • and ‘tell’ cells when to die (undergo apoptosis)
86
Q

What is apoptosis

A

Cell programmed death

87
Q

How do tumour suppressor genes prevent the formation of tumours

A

They maintain normal rates of cell division

88
Q

How can the mutation of tumour suppressor genes cause cancer

A
  • mutation of tumour suppressor gene causes it to become inactive
  • as a result it stops inhibiting cell division
  • cells growth becomes out of control
  • therefore cancer
89
Q

How does the hypermethylation of tumour suppressor genes cause the formation of a tumour

A
  • hypermethylation in a specific region of tumour suppressor genes (promotor region)
  • this leads to inactivation of the gene
  • transcription of the promotor regions of the tumour suppressor genes is inhibited
  • inactivation means cell growth rate cannot be controlled
  • leading to the formation of the tumour
90
Q

What is hypermethylation

A

Increased methylation

91
Q

Why does the hypermethylation of the on the tumour suppressor cause it to be inactivated

A
  • preventing the binding of transcriptional factors to the gene
  • attracting proteins that condense the DNA-histone complex (by inducing deacetylation of the histones) making the DNA inaccessible to transcription factors
92
Q

What other type of abnormal methylation can occur that leads to tumours

A
  • hypomethylation of oncogenes
  • therefore activating these oncogenes
  • therefore causing the formation of tumours
93
Q

What happens during menopause

A

Increased production of oestrogen in fat cells of breasts

94
Q

How does oestrogen cause a tumour to develop

A
  • oestrogen activates a gene by binding to a transcription factor which stimulates transcription of a gene
  • if oestrogen acts on a gene that controls cell division and growth it will be activated
  • can produce a tumour
95
Q

What can oestrogen cause

A

Breast cancer

96
Q

Define genome

A

The complete set of genes in a cell including those in mitochondria and or chloroplasts

97
Q

What does WGS sequencing stand for

A

Whole genome shotgun sequencing

98
Q

What is WGS sequencing

A

Researches cut the DNA into many small pieces, easily sequenced sections and then using computer algorithms to align overlapping segments to assemble the entire genome

99
Q

What is WGS sequencing used for

A

Determining the complete DNA base sequence of an organism (its genome)

100
Q

Give an example of medical advancements that have been made as a result of the human genome project

A

Over 1 million SNP’s have been found in the human genome which has advanced our understanding of diseases and disorders

101
Q

What is an SNP

A
  • single nucleotide polymorphism

- single base variations associated with disease and disorders

102
Q

What is a proteome

A

All the proteins that can be coded for by the genome

103
Q

What uses could the information gained from the human microbe project have

A

Provide knowledge if genes that can be exploited for example from organisms that can withstand extreme or toxic environments

104
Q

Why is determining the proteome of prokaryotic organisms like bacteria relatively easy

A
  • most prokaryotes have just one circular piece of DNA which is not associated with histones
  • there are no introns (non coding parts of DNA0
105
Q

What application does knowledge of the proteome project have

A
  • identification of the proteins that act as antigens on the surface of human pathogens
  • which can then be used in the production of vaccines
106
Q

Why is determining the proteome of complex organisms difficult

A
  • the genome contains many non-coding parts
  • genome cannot directly be translated into proteome
  • also everyone has different base sequences in their DNA, making it far more difficult

Biology (23 decks)

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