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AS and A level > Biology A2 Chapter 20 - Gene Expression > Flashcards

Biology A2 Chapter 20 - Gene Expression Flashcards

1
Q

What is a substitution mutation?

A

A gene mutation in which a nucleotide in a section of a DNA molecule is replaced by another nucleotide which has a different base

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2
Q

What are the three possible consequences of a substitution mutation?

A
  1. Formation of a stop codon which would stop the production of the polypeptide
  2. Formation of a codon for a different amino acid, so the structure of the protein produced would be different
  3. Formation of a different codon but it codes for the same amino acid and so there is no effect on the protein produced
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3
Q

What is a deletion mutation?

A

The loss of a nucleotide base from a DNA sequence

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4
Q

What is the consequence of a deletion at the start/middle of the chain?

A

It creates a frame shift because the reading frame which contains each three letters of the code has been shifted one to the left. The codons are now read differently and most triplets will now code for different amino acids, and hence the polypeptide will differ meaning a non-functional protein is produced

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5
Q

What is an addition mutation?

A

When an extra base becomes inserted into the sequence

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6
Q

What is the consequence of an addition mutation?

A

A frame shift to the right resulting in a different polypeptide produced and hence a potentially non-functional protein

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7
Q

What is a duplication of bases and the consequence?

A

One or more bases are repeated, thereby causing a frame shift

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8
Q

What is an inversion of bases and the consequence?

A

When a group of bases become separated from the DNA base sequence and rejoin at the same position but in the inverse order. This affects the amino acid added to the polypeptide chain

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9
Q

What is a translocation of bases and the consequences?

A

When a group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome. These often lead to an abnormal phenotype and include the development of specific cancers and reduced fertility

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10
Q

What is a mutagenic agent?

A

A factor that increases the basic mutation rate/the probability of a mutation occurring

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11
Q

What are some examples of mutagenic agents?

A
  • High energy ionising radiation
  • Exposure to chemicals
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12
Q

What is cell differentiation?

A

The process by which each cell develops into a specialised structure suited to the role it will carry out

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13
Q

What is a totipotent cell and an example?

A

A cell which can mature into any body cell, such as a fertilised egg

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14
Q

How are cells specialised?

A

During cell specialisation, only some of the genes are expressed. This means only part of the DNA is translated into proteins, so the cell only produces the specific proteins related to its function

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15
Q

How are genes prevented from expressing themselves?

A
  • Preventing transcription and so preventing mRNA production
  • Preventing translation
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16
Q

What are stem cells?

A

Cells in mature mammals which still retain the ability to differentiate into other cells

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17
Q

Where do stem cells originate from in mammals?

A
  • Embryonic stem cells
  • Umbilical chord blood stem cells
  • Placental stem cells
  • Adult stem cells
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18
Q

What are the four different types, not examples, of stem cells and their definitions?

A
  • Totipotent stem cells: can differentiate into any type of cell (embryonic)
  • Pluripotent stem cells: can differentiate into almost any type of cell (foetal stem cells)
  • Multipotent stem cells: can differentiate into a limited number of specialised cells (stem cells in the bone marrow)
  • Unipotent stem cells: only differentiate into a single type of cell (made in adult tissue)
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19
Q

What are induced pluripotent stem cells (iPS cells) and what are they used for?

A

A type of pluripotent cell that is produced from unipotent stem cells. They are genetically altered in labs to make them acquire the characteristics of embryonic stem cells by inducing genes an transcription factors to turn on genes that were off. They are capable of self renewal so can provide a limitless supply

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20
Q

What is a transcriptional factor?

A

A molecule which switches genes on and they move from the cytoplasm to the nucleus

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21
Q

How do transcriptional factors work?

A
  • Each one has a site that binds to a specific base sequence of the DNA in the nucleus
  • When it binds, it causes the region of DNA to begin the process of transcription
  • mRNA is produced and the information it carries is translated into a polypeptide
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22
Q

What happens to a gene when it is not being expressed?

A

The site on the transcriptional factor that binds to DNA is not active

23
Q

How does oestrogen switch on a gene and start transcription?

A

1) Oestrogen is lipid soluble and so diffuses through the phospholipid portion of cell surface membranes
2) Once inside the cytoplasm, it binds with a site on a receptor molecule of the transcriptional factor as they are complementary
3) By binding with the site, the oestrogen changes the shape of the DNA binding site on the transcriptional factor which is now activated and can bind to DNA
4) The transcriptional factor can now enter the nucleus through a nuclear pore and bind to specific sequences on DNA
5) The combination of DNA with the transcriptional factor stimulates transcription of the gene that makes up that portion of DNA

24
Q

What is epigenetics?

A

The belief that environmental factors can cause heritable changes in gene function without changing the base sequence of DNA

25
Q

What are some examples of environmental factors?

A

Diet, stress, alcohol, drugs, chemical exposure

26
Q

What is the epigenome?

A

The second layer of chemical tags which covers the DNA and histones

27
Q

Why is the epigenome flexible?

A

Its chemical tags respond to environmental changes such as diet and stress. This means the chemical tags adjust the wrapping and unwrapping of the DNA and so switches genes on and off

28
Q

What is the epigenome of a cell?

A

The accumulation of the signals it has received throughout its lifetime

29
Q

What is the difference between the association of histones with DNA being weak and strong?

A

Weak - the DNA histone complex is less condensed and so the DNA is accessible to transcriptional factors and switch the gene on
Strong - the DNA histone complex is more condensed so the DNA is not accessible by transcriptional factors and so the gene is switched off

30
Q

What is acetylation?

A

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

31
Q

How does acetylation work?

A

Acetylcoenzyme A donates the acetyl group

32
Q

What is the effect of decreased acetylation?

A

It increases the positive charges on histones and therefore increases their attraction to the phosphate groups on DNA. The association between DNA and histones is stronger and the DNA is not accessible to transcriptional factors and so the gene is switched off

33
Q

What is methylation?

A

The addition of a methyl group to a molecule

34
Q

What base is methyl added to?

A

Cytosine

35
Q

What are the two ways in which methylation inhibits the transcription of genes?

A
  • Prevents the binding of transcriptional factors to DNA
  • Attracts proteins which condense the DNA histone complex making the DNA inaccessible to transcriptional factors
36
Q

Describe the process whereby translation is inhibited by breaking down mRNA before it is translated to a polypeptide

A

1) An enzyme cuts large double stranded molecules of RNA into smaller sections called small interfering RNA (siRNA)
2) One of the two siRNA strands combines with an enzyme
3) The siRNA molecule guides the enzyme to a mRNA molecule by paring up its bases with the complementary ones on the section of the mRNA molecule
4) Once in position, the enzyme cuts the mRNA into smaller sections
5) The mRNA is no longer capable of being translated into a polypeptide, and so the gene is not expressed

37
Q

What are three differences between a malignant and benign tumour?

A
  • Malignant are cancerous, benign are not
  • Malignant grow rapidly, benign grow slowly
  • Malignant have whole body effects, benign are localised
  • Malignant needs chemotherapy, benign needs surgery to remove
  • Malignant often reoccur after treatment, benign do not
38
Q

What do photo-oncogenes do?

A

Stimulate a cell to divide when growth factors attach to a protein receptor on its cell surface membrane. This then activates genes that cause DNA to replicate and the cell to divide

39
Q

If a photo-oncogene mutates into an oncogene it can become permanently activate for two reasons. What are these?

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 which is then produced in excessive amounts, thereby stimulating cell division
40
Q

What is the purpose of tumour suppressor genes?

A

They slow down cell division, repair mistakes in DNA, and stimulate apoptosis

41
Q

What happens if a tumour suppressor gene mutates?

A

It is inactivated and so stops inhibiting cell division and cells can grow out of control. While most die, those that survive can make clones of themselves and form tumours

42
Q

What protein does the TP53 gene code for?

A

p53 protein

43
Q

What does the p53 protein do?

A

It is activated when a cell is unable to repair DNA and so is involved in the process of apoptosis (programmed cell death)

44
Q

What happens if the p53 gene is not functioning correctly?

A

Cells with damaged DNA continue to divide, leading to cancer

45
Q

What is hypermethylation?

A

An increased rate of methylation

46
Q

What is the process by which hypermethylation leads to cancer?

A
  • Hypermethylation occurs in a specific region (promoter region) of tumour suppressor genes
  • This leads to the tumour suppressor gene being inactivated
  • As a result, transcription of the promoter regions of tumour suppressor genes is inhibited
  • The tumour suppressor gene is switched off
  • As the tumour suppressor gene slows the rate of cell division, its inactivation leads to increased cell division and hence the formation of a tumour
47
Q

Why are women going through the menopause more likely to develop breast cancer?

A

The breasts tend to produce more oestrogen after the menopause. This local production triggers the development of a tumour and once it has grown and developed, it further increases oestrogen concentration, leading to a larger tumour. White blood cells are then drawn to the tumour and these increase oestrogen production, leading to greater development of the tumour

48
Q

What are some lifestyle factors which may contribute to the likelihood of developing cancer?

A

Smoking, diet, obesity, physical activity, sunlight

49
Q

Define the term genome

A

A complete map of all the genetic material in an organism

50
Q

What is whole genome shotgun (WGS) sequencing?

A

It involves researchers cutting DNA into small, easily sequenced sections and then using computer algorithms to align overlapping sections to assemble the entire genome

51
Q

What are SNPs (single nucleotide polymorphisms)?

A

Single base variations in the genome that are associated with disease and other disorders

52
Q

Define the term proteome

A

All the proteins produced in a given type of cell or organism at a given time under specified conditions

53
Q

Why is determining the proteome of prokaryotic organisms relatively easy?

A
  • The vase majority of prokaryotes have one circular piece of DNA which is not associated with any histones
  • There are none of the non-coding portions of DNA which are typical of eukaryotic cells

AS and A level (30 decks)

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