1
Q
DNA strand is read in which direction?
A
From 5’ -> 3’ end
2
Q
DNA features (4)
A
Double stranded
Sugar/phosphate backbone
Sugar backbone is 2-deoxyribose
Pairs up in an antiparallel fashion
3
Q
DNA base pairing
A
A binds with T (double hydrogen bond)
C binds with G (triple hydrogen bond)
4
Q
Which type of bonds are formed between bases in DNA?
A
Hydrogen bonds
5
Q
Mitosis
A
Production of 2 daughter cells
- identical to each other
- identical to the original parent cell
6
Q
Mitosis phases (6)
A
- S phase - duplicate genetic material
- Metaphase - chromosomes align at equator
- Anaphase - centromeres divide and chromatids move towards corresponding poles
- Telophase - nucelar envelope appears which separates duplicated material into 2 identical daughter cells
- Cytokinesis - cytoplasm divides, 2 identical daughter cells produced
- Interphase - cell rests and produces new proteins
7
Q
Meiosis
A
One diploid parent cell produces 4 haploid daughter cells
Genetic makeup is re-shuffled by crossing over
8
Q
Meiosis phases (9)
A
- Genetic material duplicated
- Prophase 1 - crossing over occurs
- Metaphase 1 - homologous chromosomes line up at equator
- Anaphase 1 - homologous pairs separate
- Telophase 1 - 2 daughter cells formed, each with only 1 chromosome
- Prophase 2 - DNA does not replicate
- Metaphase 2 - Chromosomes line up at equator
- Anaphase 2 - chromosomes separate to each pole
- Telophase 2 - cell division complete producing 4 haploid daughter cells
9
Q
Cell cycle - G1
A
Growth phase
- cells increase in size
- cells produce RNA
- protein synthesis
- checkpoint at end of G1
10
Q
Cell cycle - S phase
A
DNA replication
11
Q
Cell cycle - G2
A
Growth phase 2
- cells further increase in size
- new proteins produced
- checkpoint at end of G2
12
Q
Cell cycle - M phase
A
Mitosis occurs
13
Q
DNA replication - what is needed to initiate DNA replication?
A
RNA primer (synthesised by primase)
14
Q
DNA replication - leading strand
A
Always has a free 3’ end for next nucleotide to join
15
Q
DNA replication - lagging strand
A
Replicated in short segments (okazaki fragments)
16
Q
DNA replication - what joins the lagging strand fragments together?
A
Ligase
17
Q
DNA replication - what catalyses the reaction?
A
DNA polymerase
18
Q
RNA features (3)
A
Single stranded
Ribose backbone
Uracil is used instead of thymine
19
Q
Protein synthesis
A
DNA is transcribed to pre-mRNA
pre-mRNA is spliced to mRNA
mRNA is translated to a protein
20
Q
DNA replication - What is used to unwind the DNA double helix?
A
Helicase
21
Q
Exons
A
Coding regions
22
Q
Introns
A
Non-coding regions
23
Q
Splicing
A
Removes all introns and joins the eons together to form mRNA
24
Q
DNA replication - where does transcription occur?
A
Nucleus
25
DNA replication - where does translation occur?
Ribosome
26
Polymorphism
Any variation in the human genome that does NOT cause disease in it's own right
27
Mutation
A genetic variation that can cause:
- a genetic disorder (disease)
- any change in the genome
28
Balanced chromosomal rearrangement
All chromosomal material is present
| Chromosomal material is just switched around and not in the same order
29
Unbalanced chromosomal rearrangement
Extra/missing chromosomal material
| eg: miscarriage, trisomy 14
30
Aneuploidy
A whole extra or missing chromosome
| X chromosome aneuploidy is better tolerated (due to X-inactivation)
31
FISH
Fluorescently tagged copy of a specific genetic sequence
| Useful to identify where a particular gene falls within an individuals chromosomes
32
Microarray CGH
Detects missing or duplicated pieces of chromosomes
33
Array CGH
Searches the whole of the genome
Can find polymorphisms
For deletions/duplications of DNA
Patient DNA is dyed red
Control DNA (perfect DNA) is dyed green
Place these both in wells and there should be an equal amount of red and green
34
Mosaicism
Different cells have different genetic constritution
35
Result of changes of chromosomes
Activate an oncogene
| Delete a tumour supressor gene
36
Translocation
Section of one chromosome is attached to another chromosome
37
How to search for deletions of chromosomes
| + e.g. of disease
FISH
| di George syndrome
38
Trisomy 21
Downs syndrome
39
PCR
Select one small section of the human genome and amplify it
Focussed test
Detect pathogenic material
72*c - select target DNA
100*c - denature DNA causes strands to separate
50*c - primers anneal (starting point)
72*c - optimum temp for taq polymerase to copy DNA
40
Next Generation Sequencing
Sequence entire genome of a person
41
Point mutation
Single base change
| Not every base change causes a change in amino acid
42
Penetrance
Likelihood of having the disease if you have the mutation
43
Monozygotic twins
Share all genes
| Predispose to disease
44
Dizygotic twins
Share 50% of genes
45
High penetrance disease e.g.
| Low penetrance disease e.g.
High - Mendelian disorders (eg achondroplasia)
| Low - multifactorial disease
46
Autosomal dominant
Only need 1 faulty copy of the gene to cause disease
Affects males and females equally
Disease is seen in every generation
If parent is affected, 50% risk that child will be affected
47
Autosomal recessive
Need 2 faulty copies of the gene to cause disease
Affects men and women equally
Disease is usually one seen in 1 generation
1 in 4 risk of child being affected if parents are carriers
Occurs if related family members (e.g. cousins) have kids
48
X-linked recessive
Gene fault on the X chromosome
Males (XY) will be affected
Females (XX) will be carriers
No male-male transmission
If a male is affected:
- all daughters will be carriers
- no sons will be affected
If a female is a carrier:
- 50% of sons will be affected
- 50% of daughters will be carriers
49
X inactivation
In females only 1 X chromosome is active
| Methylation is one mechanism of X inactivation
50
SNP
Alterations in DNA sequence every 100-300 base pairs
| Most have no effects
51
Copy number variation (CNV)
Extra/missing stretches of DNA
| Deletions/duplications
52
Methylation
Occurs on C bases just before G bases
No transcription occurs
Makes the mutation "C" to "T" more likely
53
Imprinting
Differences in gene expression depends on whether a gene was maternally or paternally inherited
54
Mitochondrial DNA
Inherited maternally
| Affects sons and daughters equally
55
How a cell becomes cancerous
Mutation makes happy cells -> unhappy cells
Body kills off unhappy cells (apoptosis)
- if body doesn't kill off unhappy cells then the cells become even more unhappy and starts to proliferate, invade and metastasise
56
2 hit hypothesis
If you inherit a mutation (e.g. from a relative) then you only need 1 more mutation to cause cancer
If you don't inherit a mutation then you need to inherit 2 mutations before it causes cancer
57
Breast cancer and ovarian cancer mutations
BRCA 1 and BRCA 2
58
Testing for mutations
Test an affected (symptomatic) individual first and if there is a mutation then test other family members (pre-symptomatic)
59
High medium or low risk?
| Mother with cancer at 70
Low
60
High medium or low risk?
| People with some FHx: (mother and sister with cancer at 45)
Medium
61
High medium or low risk?
| Lots of FHx, known BRCA 1 mutation
High
62
Symptomatic testing
Find the cause of the disease in a person with a disease
- finding a mutation: confirms diagnosis and allows testing of family members
- not finding a mutation: treatment based on clinical parameters
63
Pre-symptomatic testing
Patient has a relative with a KNOWN mutation and wants to find out if they have it
64
Turner's syndrome
Only occurs in females
| Individual with normal number of autosomes but only one X chromosome
65
Inheritance pattern for CF
Autosomal recessive
Principles SOH
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