Pack 14 Flashcards
1
Q
Define a gene mutation
A
A change to the number or arrangement of one or more DNA bases.
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.
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.
4
Q
What can the deletion or addition of one base cause?
A
Frame shift mutation
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.
6
Q
Define ‘Duplication of bases’
A
One or more bases are repeated. May produce a frame shift.
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.
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.
9
Q
Name the 6 types of base mutation.
A
- Deletion
- Substitution
- Addition
- Duplication
- Inversion
- Translocation
10
Q
What is a spontaneous mutation?
A
A mutation that arises without outside influence during DNA replication.
11
Q
What is the basic mutation rate (mutations per 100000 genes per generation).
A
1-2
12
Q
What is a mutagenic agent?
A
An outside factor that speeds up the rate of mutation.
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)
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.
15
Q
What is cell differentiation?
A
The process by which each cell develops into a specialised structure suited to its role.
16
Q
Where are all the cells in an organism derived from?
A
The fertilised egg (zygote).
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.
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…
19
Q
What is a totipotent cell? Give an example.
A
- A cell that can mature into any body cell.
- Fertilised egg
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.
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
22
Q
What are stem cells? (4)
A
- Undifferentiated
- Dividing cells.
- Occur in adult animal tissues.
- Need to be constantly replaced.
23
Q
Is specialisation reversible in most animal cells?
A
No
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.
25
Name the 4 sources of stem cells in mammals.
- 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.
26
What are pluripotent stem cells.
Slightly more specialised than totipotent. Can differentiate into almost any type of cell.
27
Where are pluripotent stem cells found?
Found in embryos
28
Give and example of a pluripotent stem cell.
Embryonic or fetal
29
What is a multipotent stem cell.
Can differentiate into a limited number of specialised cells. Usually into a particular types e.g. any type of blood cell.
30
Where are multipotent stem cells found?
Found in adults. E.g. bone marrow
31
Give and example of a multipotent stem cell.
Adult stem cells and umbilical cord stem cells.
32
What is a unipotent stem cell.
Can only differentiate into one type of cell. Derived from multipotent.
33
Where are unipotent stem cells made?
Adult tissue
34
Give and example of a unipotent stem cell.
Cardiomyocytes
35
What are induced pluripotent stem cells (iPS Cells)?
A type of pluripotent stem cell that is produced from a unipotent stem cell.
36
How and where are iPS cells created?
- In a lab.
- From body cells
- Genes and transcriptional factors are induced.
- Turn on genes that were otherwise turned off.
37
What is the ethical benefit of iPS cells?
They could replace embryonic stem cells in research.
38
What is a useful feature of iPS cells for research?
They are capable of self-renewal.
39
What is one use of pluripotent stem cells?
To regrow tissues damaged by accident or as a result of a disease.
40
Explain how a transcriptional factor controls the expression of a gene? (4 points) (Switched on)
- 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.
41
When a gene is not expressed what has happened to the transcriptional factor? (2 points)
- The site on the transcriptional factor that binds to the DNA is not active.
- Cannot cause transcription and therefore translation.
42
What is oestrogen?
A steroid hormone.
43
Explain how oestrogen can switch on a gene and therefore start transcription.
- 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
How does oestrogen enter a cell? Why can it enter like this?
Simple diffusion across the CSM. Lipid soluble.
45
What is epigenetics?
A scientific field that provides explanations as to how environmental factors can alter the genetic inheritance of organisms offspring.
46
What is the epigenome?
The 'chemical tags' that cover the DNA and the histones it is associated with.
47
What does the epigenome determine?
The shape of the DNA-histone complex
48
What is epigenetic silencing.
When genes are kept in a tightly packed arrangement so they cannot be accessed for transcription making them inactive.
49
Why is the epigenome not fixed?
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
Where do epigenetic signals come from during early development?
The environment of the mother e.g. her diet.
| From within the foetuses cells.
51
What is the effect of a weak association between DNA and histones?
- DNA-histone complex is less condensed.
- DNA is accesible by transcription factors.
- mRNA production.
52
What is the effect of a strong association between DNA and histones?
- DNA-histone complex is more condensed.
- DNA is not accesible by transcription factors.
- No mRNA production.
53
What is acetylation?
The process by which an acetyl group is transferred to a molecule.
54
What effect does decreased acetylation have on chromatin and the expression of a gene? (5 steps)
- 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
What charge is an acetyl group?
Negative.
56
What is methylation?
Addition of a methyl group (CH₃) to a molecule.
57
Where is the methyl group added in DNA?
The cytosine base.
58
In what two ways does methylation of DNA inhibit transcription?
- Preventing the binding of transcriptional factors to the DNA.
- Attracting proteins that condense the DNA-histone complex. Making the DNA inaccesible
59
What is heterochromatin and euchromatin? What causes them?
Heterochromatin - more condensed - methylation.
| Euchromatin - less condensed - acetylation.
60
What happens to the sperm and egg in terms of the epigenome? How are epigenetic tags passed on still?
Epigenetic tags are removed. Some escape this process.
61
What can the alteration of epigenetic processes cause?
Abnormal activation or silencing of genes. Can cause disease. such as cancer.
62
How can epigenetic changes increase the incidence of mutations? (3)
- 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
How could epigenetic treatments treat cancer?
- Drugs that inhibit certain enzymes involved in DNA methylation.
- Reactivates silenced genes.
- These genes could be tumour suppressor genes for example.
64
How can the translation of mRNA be inhibited without affecting transcription?
The breakdown of mRNA
65
Explain how siRNA can breakdown mRNA. (4)
- 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
What is siRNA
small interfering RNA
67
Explain how the breakdown of mRNA prevents the expression of a gene. (2)
- mRNA is cut into small sections by siRNA so is no longer able to be translated.
- The gene is not expressed.
68
What is caner?
A group of diseases caused by damage to the genes that regulate mitosis and the cell cycle. This leads to unrestrained cell division.
69
What are the two types of tumours? Which is cancerous?
Malignant - cancerous
| Benign - not cancerous
70
Which type of tumour grows more rapidly?
Malignant
71
What is the appearance of the cell nucleus of a malignant tumour?
Large and darker - abundance of DNA
72
Which tumour contains unspecialised cells?
Malignant
73
What causes cells of a benign tumour to stay together?
Adhesion molecules and a capsule
74
What is metastasis?
Tumour cells spread to other regions of the body
75
Which tumour is more life threatening?
Malignant
76
Explain how a secondary tumour forms from a primary tumour.
- 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
What is an oncogene?
A mutated proto-oncogene.
78
What does a proto-oncogene do?
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
For what two reasons can an oncogene become permanently switched on?
- 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
Are most mutations causing cancer acquired or inherited?
Most are acquired, some are inherited.
81
What are the three roles of tumour suppressor genes?
- Slow down cell division.
- Repair mistakes in DNA
- Control apoptosis (cell death)
82
What happens if a tumour suppressor gene mutates?
- Inactivated, cell division increases .
- Cells structurally and functionally different.
- Most die.
- Those that survive clone and create tumours.
83
Explain how hypermethylation of a tumour suppressor gene can lead to cancer. (4 steps)
- 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
What is hypomethylation.
- Reduced methylation
85
What effect does oestrogen have on women after the menopause?
- Increases the risk of developing breast cancer.
86
Where is more oestrogen produced after the menopause?
The fat cells of the breasts.
87
Once a breast tumour has developed what does it produce more of and what affect does this have?
- More fat cells
- More oestrogen
- Development of tumour.
88
What do white blood cells drawn to a breast tumour increase?
Oestrogen concentration.
89
How can oestrogen cause a tumour to develop? (2)
- 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
How many genes does a human have roughly?
20,000
91
What its bioinformatics?
The science of collecting and analysing complex biological data such as genetic codes. Uses algorithms.
92
Define genome
The complete set of genetic information in an organism.
93
Define proteome
All proteins produced in a given cell or organism at a given time under certain conditions.
94
Describe whole genome shotgun sequencing.
- Cut DNA into many small, easily sequenced sections.
| - Use algorithms to align overlapping segments to assemble the entire genome.
95
What are SNPs
Single nucleotide polymorphisms - single base variations in the genome associated with disease and disorders.
96
What is the advantage of whole genome sequencing?
Medical screening of individuals has led to early intervention.
97
What is the Human Microbiome Project?
Sequencing the genomes of single celled organisms.
98
What is the purpose of the Human Microbiome Project?
- 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
Why is determining the proteome of prokaryotes relatively easy? (2)
- Have just one circular loop of DNA, not associated with histones.
- There are no non-coding portions of DNA.
100
How can the sequencing of human pathogen's genomes lead to the development of vaccines?
- Identify proteins that act as antigens on the pathogen's surface.
- Antigens used in vaccines to produce memory cells.
101
Why is it difficult to identify the proteome from a complex organisms genome?
Their DNA contains many non-coding genes as well as genes that have a role in regulating other genes.
