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Biology > Pack 14 > Flashcards

Pack 14 Flashcards

1
Q

Define a gene mutation

A

A change to the number or arrangement of one or more DNA bases.

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2
Q

What is substitution of bases?

A

A nucleotide in a section of a DNA molecule is replaced by another nucleotide with a different base.

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3
Q

What are the three possible changes to the genetic code due to a base substitution and what are the effect of each one?

A
  • Formation of a STOP CODON - production of polypeptide stopped prematurely - non functional.
  • Formation of a CODON for a DIFFERENT AMINO ACID - one amino acid will vary in the structure of the polypeptide - may differ in shape therefore not function.
  • Formation of DIFFERENT codon that codes for the SAME amino acid (Degenerate code). No effect on polypeptide.
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4
Q

What can the deletion or addition of one base cause?

A

Frame shift mutation

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5
Q

When will there not be a frame shift mutation after the deletion or addition of bases?

A
  • When a multiple of three bases is added or removed.

- When it occurs in the final codon of a gene.

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6
Q

Define ‘Duplication of bases’

A

One or more bases are repeated. May produce a frame shift.

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7
Q

What is the inversion of bases?

A

A group of bases becomes separated from the DNA sequence and rejoins at the same position but in the reverse order.

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8
Q

What is the translocation of bases?

A

A group of bases becomes separated from the DNA sequence and is inserted into the DNA sequence of another chromosome. Significant effects.

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9
Q

Name the 6 types of base mutation.

A
  • Deletion
  • Substitution
  • Addition
  • Duplication
  • Inversion
  • Translocation
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10
Q

What is a spontaneous mutation?

A

A mutation that arises without outside influence during DNA replication.

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11
Q

What is the basic mutation rate (mutations per 100000 genes per generation).

A

1-2

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12
Q

What is a mutagenic agent?

A

An outside factor that speeds up the rate of mutation.

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13
Q

Give 4 specific mutagenic agents.

A

Ionising radiation:

  • ⍺ and β particles
  • short wavelength radiation - X-rays, UV

Chemicals:

  • Nitrogen dioxide
  • Benzopyrene (tobacco smoke)
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14
Q

What is one advantage and one disadvantage of mutations on an organism?

A
  • Produce genetic diversity necessary for natural selection and speciation.
  • Almost away harmful - lead to cancer.
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15
Q

What is cell differentiation?

A

The process by which each cell develops into a specialised structure suited to its role.

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16
Q

Where are all the cells in an organism derived from?

A

The fertilised egg (zygote).

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17
Q

Why do some cells produce different proteins?

A

Although all cells contain the same genes, only certain genes are expressed in any one cell at any time.

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18
Q

Give an example of a gene that is permanently switched on in all cells?

A
  • Enzymes involved in respiration

- Enzymes and other proteins involved in transcription, translation…

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19
Q

What is a totipotent cell? Give an example.

A
  • A cell that can mature into any body cell.

- Fertilised egg

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20
Q

How do cells become specialised? (3)

A

Only certain genes necessary for their functions are expressed. Others are not expressed. (Switched off). Only certain proteins are produced via translation.

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21
Q

In what two ways are genes that are not needed for a specialised cell prevented from being expressed?

A
  • Preventing transcription - production of mRNA

- Reventing translation

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22
Q

What are stem cells? (4)

A
  • Undifferentiated
  • Dividing cells.
  • Occur in adult animal tissues.
  • Need to be constantly replaced.
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23
Q

Is specialisation reversible in most animal cells?

A

No

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24
Q

What is self-renewal in stem cells? Why is this important?

A
  • The ability to divide and produce an identical copy of themselves.
  • Stem cells need to be constantly replaced.
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25
Q

Name the 4 sources of stem cells in mammals.

A
  • Embryonic Stem Cells - Early embryo
  • Umbilical cord blood stem cells (similar to adult)
  • Placental stem cells (develop into specific types)
  • Adult stem cells - foetus though to adult - specific to a type of tissue or organ.
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26
Q

What are pluripotent stem cells.

A

Slightly more specialised than totipotent. Can differentiate into almost any type of cell.

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27
Q

Where are pluripotent stem cells found?

A

Found in embryos

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28
Q

Give and example of a pluripotent stem cell.

A

Embryonic or fetal

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29
Q

What is a multipotent stem cell.

A

Can differentiate into a limited number of specialised cells. Usually into a particular types e.g. any type of blood cell.

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30
Q

Where are multipotent stem cells found?

A

Found in adults. E.g. bone marrow

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31
Q

Give and example of a multipotent stem cell.

A

Adult stem cells and umbilical cord stem cells.

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32
Q

What is a unipotent stem cell.

A

Can only differentiate into one type of cell. Derived from multipotent.

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33
Q

Where are unipotent stem cells made?

A

Adult tissue

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34
Q

Give and example of a unipotent stem cell.

A

Cardiomyocytes

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35
Q

What are induced pluripotent stem cells (iPS Cells)?

A

A type of pluripotent stem cell that is produced from a unipotent stem cell.

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36
Q

How and where are iPS cells created?

A
  • In a lab.
  • From body cells
  • Genes and transcriptional factors are induced.
  • Turn on genes that were otherwise turned off.
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37
Q

What is the ethical benefit of iPS cells?

A

They could replace embryonic stem cells in research.

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38
Q

What is a useful feature of iPS cells for research?

A

They are capable of self-renewal.

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39
Q

What is one use of pluripotent stem cells?

A

To regrow tissues damaged by accident or as a result of a disease.

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40
Q

Explain how a transcriptional factor controls the expression of a gene? (4 points) (Switched on)

A
  • Transcriptional factor moves from cytoplasm to the nucleus.
  • Each transcriptional factor has a site that binds to a specific DNA base sequence.
  • When it binds, it causes transcription of this region of DNA to begin.
  • mRNA is produced -> translation.
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41
Q

When a gene is not expressed what has happened to the transcriptional factor? (2 points)

A
  • The site on the transcriptional factor that binds to the DNA is not active.
  • Cannot cause transcription and therefore translation.
42
Q

What is oestrogen?

A

A steroid hormone.

43
Q

Explain how oestrogen can switch on a gene and therefore start transcription.

A
  • Oestrogen diffuses into the cell and binds with a site on a receptor of the transcriptional factor. (Complementary shape)
  • This binding causes the DNA binding site of the transcriptional factor to change shape. It can now bind to DNA.
  • Transcriptional factor enters nucleus through nuclear pore. and binds to a specific base sequence.
  • Stimulates transcription of the gene.
44
Q

How does oestrogen enter a cell? Why can it enter like this?

A

Simple diffusion across the CSM. Lipid soluble.

45
Q

What is epigenetics?

A

A scientific field that provides explanations as to how environmental factors can alter the genetic inheritance of organisms offspring.

46
Q

What is the epigenome?

A

The ‘chemical tags’ that cover the DNA and the histones it is associated with.

47
Q

What does the epigenome determine?

A

The shape of the DNA-histone complex

48
Q

What is epigenetic silencing.

A

When genes are kept in a tightly packed arrangement so they cannot be accessed for transcription making them inactive.

49
Q

Why is the epigenome not fixed?

A

It responds to environmental factors. Diet and stress for example can cause the chemical tags to adjust the structure of the DNA-histone complex.

50
Q

Where do epigenetic signals come from during early development?

A

The environment of the mother e.g. her diet.

From within the foetuses cells.

51
Q

What is the effect of a weak association between DNA and histones?

A
  • DNA-histone complex is less condensed.
  • DNA is accesible by transcription factors.
  • mRNA production.
52
Q

What is the effect of a strong association between DNA and histones?

A
  • DNA-histone complex is more condensed.
  • DNA is not accesible by transcription factors.
  • No mRNA production.
53
Q

What is acetylation?

A

The process by which an acetyl group is transferred to a molecule.

54
Q

What effect does decreased acetylation have on chromatin and the expression of a gene? (5 steps)

A
  • Increases the positive charge on histones.
  • Increases their attraction to DNA
  • Stronger DNA and histone association.
  • DNA not accessible.
  • Transcriptional factors cannot bind and initiate mRNA production.
55
Q

What charge is an acetyl group?

A

Negative.

56
Q

What is methylation?

A

Addition of a methyl group (CH₃) to a molecule.

57
Q

Where is the methyl group added in DNA?

A

The cytosine base.

58
Q

In what two ways does methylation of DNA inhibit transcription?

A
  • Preventing the binding of transcriptional factors to the DNA.
  • Attracting proteins that condense the DNA-histone complex. Making the DNA inaccesible
59
Q

What is heterochromatin and euchromatin? What causes them?

A

Heterochromatin - more condensed - methylation.

Euchromatin - less condensed - acetylation.

60
Q

What happens to the sperm and egg in terms of the epigenome? How are epigenetic tags passed on still?

A

Epigenetic tags are removed. Some escape this process.

61
Q

What can the alteration of epigenetic processes cause?

A

Abnormal activation or silencing of genes. Can cause disease. such as cancer.

62
Q

How can epigenetic changes increase the incidence of mutations? (3)

A
  • Some active genes normally help repair DNA and so prevent cancers.
  • Increased methylation has led to these protective genes being switched off.
  • Therefore damaged base sequences in DNA are not repaired and so can lead to cancer.
63
Q

How could epigenetic treatments treat cancer?

A
  • Drugs that inhibit certain enzymes involved in DNA methylation.
  • Reactivates silenced genes.
  • These genes could be tumour suppressor genes for example.
64
Q

How can the translation of mRNA be inhibited without affecting transcription?

A

The breakdown of mRNA

65
Q

Explain how siRNA can breakdown mRNA. (4)

A
  • An enzyme cuts large sections of double stranded RNA into siRNA
  • One of the two siRNA strands combines with an enzyme.
  • The siRNA’s bases pair with the complementary bases of mRNA, bringing the enzyme with it.
  • Once in position. the enzyme cuts the mRNA into smaller sections.
66
Q

What is siRNA

A

small interfering RNA

67
Q

Explain how the breakdown of mRNA prevents the expression of a gene. (2)

A
  • mRNA is cut into small sections by siRNA so is no longer able to be translated.
  • The gene is not expressed.
68
Q

What is caner?

A

A group of diseases caused by damage to the genes that regulate mitosis and the cell cycle. This leads to unrestrained cell division.

69
Q

What are the two types of tumours? Which is cancerous?

A

Malignant - cancerous

Benign - not cancerous

70
Q

Which type of tumour grows more rapidly?

A

Malignant

71
Q

What is the appearance of the cell nucleus of a malignant tumour?

A

Large and darker - abundance of DNA

72
Q

Which tumour contains unspecialised cells?

A

Malignant

73
Q

What causes cells of a benign tumour to stay together?

A

Adhesion molecules and a capsule

74
Q

What is metastasis?

A

Tumour cells spread to other regions of the body

75
Q

Which tumour is more life threatening?

A

Malignant

76
Q

Explain how a secondary tumour forms from a primary tumour.

A
  • Tumour develops lymph ducts and blood vessels.
  • Tumour cells squeeze into these vessels.
  • Tumour cells adhere to blood vessel walls and squeeze through to form distant metastases.
77
Q

What is an oncogene?

A

A mutated proto-oncogene.

78
Q

What does a proto-oncogene do?

A

Stimulates a cell to divide when growth factors attach to a protein receptor on its CSM. This activates genes that cause DNA to replicate and the cell to divide.

79
Q

For what two reasons can an oncogene become permanently switched on?

A
  • The receptor protein on the CSM can be permanently activated. Cell division is permanently switched on even in the absence of growth factors.
  • The oncogene may code for a growth factor which is produced in excessive amounts therefore stimulating cell division.
80
Q

Are most mutations causing cancer acquired or inherited?

A

Most are acquired, some are inherited.

81
Q

What are the three roles of tumour suppressor genes?

A
  • Slow down cell division.
  • Repair mistakes in DNA
  • Control apoptosis (cell death)
82
Q

What happens if a tumour suppressor gene mutates?

A
  • Inactivated, cell division increases .
  • Cells structurally and functionally different.
  • Most die.
  • Those that survive clone and create tumours.
83
Q

Explain how hypermethylation of a tumour suppressor gene can lead to cancer. (4 steps)

A
  • Occurs in promotor region leading to inactivation of tumour suppressor gene.
  • Transcription is inhibited.
  • Tumour suppressor gene is silenced.
  • Increased cell division and formation of a tumour.
84
Q

What is hypomethylation.

A
  • Reduced methylation
85
Q

What effect does oestrogen have on women after the menopause?

A
  • Increases the risk of developing breast cancer.
86
Q

Where is more oestrogen produced after the menopause?

A

The fat cells of the breasts.

87
Q

Once a breast tumour has developed what does it produce more of and what affect does this have?

A
  • More fat cells
  • More oestrogen
  • Development of tumour.
88
Q

What do white blood cells drawn to a breast tumour increase?

A

Oestrogen concentration.

89
Q

How can oestrogen cause a tumour to develop? (2)

A
  • Oestrogen can activate a gene by binding to a receptor that promotes transcription.
  • If the gene controls cell division and growth then it will be activated and could produce a tumour.
90
Q

How many genes does a human have roughly?

A

20,000

91
Q

What its bioinformatics?

A

The science of collecting and analysing complex biological data such as genetic codes. Uses algorithms.

92
Q

Define genome

A

The complete set of genetic information in an organism.

93
Q

Define proteome

A

All proteins produced in a given cell or organism at a given time under certain conditions.

94
Q

Describe whole genome shotgun sequencing.

A
  • Cut DNA into many small, easily sequenced sections.

- Use algorithms to align overlapping segments to assemble the entire genome.

95
Q

What are SNPs

A

Single nucleotide polymorphisms - single base variations in the genome associated with disease and disorders.

96
Q

What is the advantage of whole genome sequencing?

A

Medical screening of individuals has led to early intervention.

97
Q

What is the Human Microbiome Project?

A

Sequencing the genomes of single celled organisms.

98
Q

What is the purpose of the Human Microbiome Project?

A
  • Help cure disease
  • Provide knowledge of genes that can be usefully exploited. e.g. ones from organisms that can withstand extreme conditions could have uses in cleaning up pollutants or manufacturing biofuels.
99
Q

Why is determining the proteome of prokaryotes relatively easy? (2)

A
  • Have just one circular loop of DNA, not associated with histones.
  • There are no non-coding portions of DNA.
100
Q

How can the sequencing of human pathogen’s genomes lead to the development of vaccines?

A
  • Identify proteins that act as antigens on the pathogen’s surface.
  • Antigens used in vaccines to produce memory cells.
101
Q

Why is it difficult to identify the proteome from a complex organisms genome?

A

Their DNA contains many non-coding genes as well as genes that have a role in regulating other genes.

Biology (18 decks)

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