Genetics Flashcards
(187 cards)
0
Q
What was exhibited in the F2 generation?
A
Reappearance of the non-dominant phenotype. Ratio of Dominant : Recessive trait was 1 in 4 (or 3:1)
1
Q
What did the F1 hybrid generation exhibit?
A
One of the input phenotypes- dominant trait
2
Q
What is Mendel’s first law of segregation?
A
Law of segregation:
Gametes fuse without regard to which alleles they carry
3
Q
What are digit rid crosses?
A
When two traits are simultaneously examined
4
Q
What was Mendel’s second law?
A
Law of independent assortment: different pairs of alleles segregate independently
5
Q
What are the three principles of Charles Darwin’s mechanism for evolution?
A
- There is variation in the expression of traits in a population
- Variant forms of traits can be inherited
- Some variant traits give individuals a better chance of surviving and reproducing-thus continuous RANDOM variations, independent of environment, leads to ‘natural selection’
6
Q
What is natural selection?
A
Traits that have a greater probability of surviving to reproduce , thus leading to a population density increase in that trait.
7
Q
How can be variants occur?
A
By random mutations
8
Q
What is paleontology a study of?
A
The history and development of life on Earth
9
Q
What did fossil records show?
A
Extinctions and changes in species
10
Q
What are homologous chromosomes?
A
Chromosomes that pair up during meiosis.
Contain the same genes
One comes from each parent
11
Q
What is the karyotype of human chromosomes?
A
Visible during mitosis
Humans have 46 chromosomes
12
Q
What are autosomes?
A
The other 22 pairs of chromosomes that are homologous
13
Q
What is mitosis?
A
When eukaryotic somatic cells divide
14
Q
What is meiosis?
A
When germ cells divide. Chromosome number is halved (haploid)
15
Q
What is interphase?
A
Most of the cell cycle/longest phase, where the cell prepares for cell division (DNA replication -sister chromatids)
16
Q
What are the three stages interphase is divided into?
A
G1: growth after mitosis
S : synthesis of DNA
G2 : growth before mitosis
17
Q
What is the importance of the G1 and G2 gap phases?
A
- period of growth-size of cell and protein content increases
- Preparation for next phase- checkpoint that ensures conditions are suitable
18
Q
What is the G0 phase?
A
Contains cells that are not actively dividing
19
Q
What are the five phases of mitosis?
A
Prophase (Prometaphase) Metaphase Anaphase Telophase
20
Q
What is cytokinesis?
A
Division of the cytoplasm
21
Q
What is the difference between mitosis and meiosis?
A
Meiosis produces 4 daughter cells which are haploid. Mitosis daughter cells are diploid
22
Q
What is crossing-over?
A
When the homologous chromosomes exchange homologous parts
23
Q
Which phase does crossing over occur?
A
Prophase
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What does independent assortment result in?
Increase in genetic variation within a population
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What is linkage?
Two genes on the same chromosome:
Not independently assorted
Segregate together
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What is crossing over?
Linked genes should segregate together
| Crossing over causes them to separate
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Does crossing over reduce genetic linkage?
Yes
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What is a histones?
Protein found in chromatid
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What percentage of the human genome is genes?
1.5%
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What is the percentage genome homology between different people?
~99.9%
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What is the percentage genome homology between humans and chimpanzees?
~95%
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What does DNA act as a template for in transcription?
mRNA
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What is the difference between mRNA and DNA?
mRNA is single-stranded and contains uracil in place of thymine
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What is translation?
mRNA into proteins by ribosomes
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What does transcription make and where does it take place?
Makes RNA
| In the nucleus
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What is translation and where does it take place?
Makes proteins
| In the cytoplasm
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What is the synthesis called in which DNA is replicated?
semi-conservative replication
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What are gene promoters and what do they do?
Non-coding, non-transcribed regions
| Regulates the expression of genes
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What do spliceosomes proteins carry out?
They slice out introns
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What are the differences between DNA replication and transcription?
RNA polymerase is used
Only a small portion of DNA is copied (i.e. Genes)
Single-stranded mRNA is made
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How many amino acids does one codon make?
One
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What does ribosomes do?
Holds mRNA
| Links amino acids together
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What is the first codon that tRNA binds to?
AUG- methionine
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What are the binding sites on tRNA?
Amino acid site
| Anticodon
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How many tRNA molecules possess anticodons at one end?
64
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How many of the 64 tRNA have a specific amino acid?
61
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What do the other 3 tRNA molecules have?
Termination signals which stops translation
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What is degenerate code?
Different codons specify the same amino far
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What is a point mutation?
A single base change
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What does substitution mutation result in?
Changes one amino acid
| Silent mutation
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What does a insertion or deletion result in?
```
Frameshift
Destroys proteins
Changes many amino acids
Adds a STOP codon
Changes shape of protein
```
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What causes damage to DNA?
```
Mutagens such as :
Reactive oxygen species (from metabolism)
Radiation (e.g. UV)
Environmental chemicals (e.g. Smoking)
Viruses
```
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What are the three steps of DNA repair?
1. Recognise
2. Remove
3. Replace
54
What portion of the population have cystic fibrosis and what portion are carriers?
1 in 2500 have the disease and 1 in 25 are carriers
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What type of disorder is cystic fibrosis?
A Monogenic , autosomal recessive disorder
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What chromosome is the CF gene located on?
Chromosome 7
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What is the chance of offspring being affected if there are two carriers of a autosomal recessive disease?
1/4
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What is the name of the protein the CF gene codes for?
Cystic fibrosis transmembrane conductance regulator (CFTR)
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What is the most common mutation for CF?
3 base deletion
60
What are amniocentesis used for ?
Genetic diagnosis
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What technique is used to look at specific mutations in genes?
Polymerase Chain Reaction
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What is the cause of sickle cell anaemia?
Production of Abnormal haemoglobin (HbS)
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When do HbS become sickle-shaped?
When deoxygenated through damage to the cell membrane (fragile and short lived RBCs)
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When sickle RBCs become lodged in blood vessels what does this lead to?
Poor downstream oxygen delivery
Ischemia (restricted blood supply)
Infarction (blocked artery)
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What can vessel blockage cause?
Episodes of pain
Sores/ulcers
Organ damage (e.g. Spleen , liver)
Stroke (interruption of blood supply to brain)
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What disorder is SCA?
Monogenic , autosomal recessive
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What mutation caused SCA?
Single mutation in the beta-globin in gene
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Do heterozygotes have the disorder ?
Heterozygotes have some sickle cell traits (some sickle cell) but little disease
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What is the benefits of SCA and SCT (sickle cell traits)?
Produces some resistance to malaria , as plasmodium parasite causes sickle cells to burst before they replicate
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What does the benefits of SCA result in?
High SC population in places where malaria is high
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Why can painkillers or intravenous fluid introduction be given for SCA?
To alleviate pain as sickle cells block oxygen flow to tissue/joints
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Why may a blood transfusion be give to SCA sufferers?
To increase the number of normal red blood cells in circulation
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Why might hydroxyurea an anti-cancer drug be given to SCA sufferers?
Reduces incidence of crises and acute lung syndrome (SCs blocking lung) by stimulating foetal haemoglobin production
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Why might antibiotics be given to SCA sufferers?
Sufferers are more prone to infection due to spleen damage by SCs
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Is there a cure for SCA? What are general things sufferers can do to manage the disease?
No cure.
Health maintenance- good diet, hygiene, infection monitoring.
Combined treatments lead to increase in life expectancy.
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What is huntingtons disease?
Is a neurodegenerative disease it causes jerky, involuntary movements. Eventually lead to mental deterioration and death.
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When do symptoms appear?
30-50s
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What disease is huntingtons disease?
Autosomal dominant inheritance
79
Explain the gene and repeats which cause the disease.
a CAG triplet in the HD gene Whig normally in 10-28 times, increases 36-100x in sufferers. Number of repeats increases as inherited. more repeats, earlier onset.
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What do abnormal HD proteins do?
Clumps in the brain, leading to impaired function
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Is there a cure for HD? And what is treatment for HD?
No cure. Treated with dopamine blockers and tetrabenazine to reduce abnormal behaviour and movement. Also anti-depressives.
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If one parent is affected (heterozygous) and one parent is unaffected, what % offspring(4) would be affected?
50%
83
What is haemophilia?
A group of genetic disorders where sufferers cannot control bleeding due to lack of clotting factor activity, bleeding can be external or internal , and can lead to death
84
What kind of disorder is haemophilia?
A x-linked trait predominately seen in males
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What do haemophilia sufferers lack?
Factor VIII
86
What is Factor VII?
Liver-derived glycoprotein forming part of the coagulation cascade leading to fibrinogen - fibrin-blood clotting
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Where can factor VIII be taken from for haemophilia sufferers? What's could be the problem with this? How can this problem be solved?
Factor VIII is isolated and concentrated from donated blood.
Problem of HIV, hepatitis infections
Heat-treated to kill
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What treatments can be given to haemophilia sufferers?
Genetic engineering had enabled the production of recombinant factor VIII
Desmopressin is a hormone that releases stored factor VIII in cases of mild haemophilia
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Whereis factor VII gene located and what trait?
X-chromosome and defect is a recessive trait
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What causes rare causes of female haemophilia?
Lyonisation- where one X is mostly inactive so the defective gene in the active chromosome define the trait
91
What is x-linked inheritance?, who pass on the disorder? , which gender most likely to get disorder?
Genes on X chromosome
50% of males are affected
Mothers who are carriers pass this on
Females rarely get these diseases
92
What is Down syndrome characterised by?
Learning disabilities
Impaired physical growth
Distinct facial features
93
What causes Down syndrome?
In 95% cases occurs when one the gametes (usually the egg) contain two chromosome no. 21s, due to chromosome partition mistake cell division -meiotic nondisjunction.
During fertilisation another is gained dorm another parent. The zygote and offspring have 3 no. 21 chromosomes (trisomy 21)
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What happens in some cases to the 21 chromosome in Down syndrome?
Duplicate dot translocation to another chromosome
95
What is cancer?
A genetic disorder which can be caused by mutations in DNA , including genes
96
What is the muti-hit hypothesis of cancer?
The hypothesis that cancer is the result of accumulations of mutations acquired during life time in a cells DNA
97
How do cells usually respond to DNA damage?
Pausing cell cycling
| Transcribing cell growth control/repair genes or even initiating programmed cell death or apoptosis
98
What can mutations to genes encoding for proteins involved in DNA repair,cell cycle,cell differentiation , apoptosis and cell-cell contact result in?
Deregulated cell growth which can lead to neoplastic (cancer) phenotype and malignant tumours
99
What can exposure to high levels of UV radiation for long periods result in?
Extensive DNA damage
Apoptosis (cell death)
If apoptosis fails cells may become cancerous
100
What is Xeroderma pigmentosum?
Recessive disorder in which alleles produce nonfunctional repair protein so cannot repair simple DNA damage from UV exposure
101
What are the problems with Xeroderma pigmentosum?
Brief exposure to sunlight causes blistering
| Highly susceptible to skin cancer
102
What cells do gene mutations occur in?
Somatic cells so can't be inherited
103
What causes genetic predisposition of cancer?
If gametes are affected by mutations a trait is inherited
104
What % of cancer cases are inherited?
1-2%
105
What are the four ways that chromosome structure can change?
Deletion
Inversion
Translocation
Duplication
106
What is a proto-oncogene?
A positive growth regulator - promote controlled cell division and proliferation
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What are oncogenes?
Cancer causing gene (hyperactive proto-oncogene)
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What is a tumour suppressor gene?
A negative growth regulators- inhibit cell numbers in the body and inhibit tumour formation
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Name some genes in a person with a predisposition that drives cell towards the neoplastic phenotype.
p53, ras, retinoblastoma, BRCA1 (breast and ovarian cancer)
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What do tumour suppressor genes do?
Stop cell division
Negative growth regulators
Oppose the action of positive growth regulators
Block signal cascades
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What is p53 gene?
A vital tumour suppressor that stops cells with damage DNA from dividing. Allows DNA repair ( activated DNA repair enzymes) or causes cell death(apoptosis)
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What percentage of tumours have a mutation in the p53 gene?
~50%
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How can mutations in p53 occur?
Environmental mutagens making cell more prone to carcinogenesis.
Inherited- individuals with only one functional allele have reduced tumour suppression/more cancer prone
114
What is Li-Fraumenti syndrome? And if inherited what percentage of is spring would have the disorder?
A predisposition inherited autosomal dominant cancer disorder which is caused by mutant p53 gene.
50%
115
What is the dominant negative effect of the Li-Fraumeni syndrome?
When the mutant p53 bind to the wild-type p53 making the complex nonfunctional
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What happens when to p53 when DNA is damaged by chemicals or radiation?
p53 becomes phosphorylated, accumulates and initiates transcription of >50 genes
Mutant p53 is often unable to bind DNA (gene promoters) and so can't initiate gene transcription.
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What are the main three functions of p53 in response to DNA damage?
Cell cycle arrest
DNA repair
Apoptosis
118
What is retinoblastoma?
Eye cancer and is a sporadic or hereditary condition
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What causes retinoblastoma?
Mutations in the retinoblastoma(Rb) tumour suppressor gene
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What causes the inherited disease (49% cases) of retinoblastoma?
Mutation in one allele of Rb gene. Retinal cell gains another mutation in the wild type allele no more Rb protein is produced and tumour develops. Tumour is bilateral (both eyes)
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What causes the sporadic disease (60% cases , usually unilateral tumours) of retinoblastoma?
Both alleles acquire mutations before tumours form
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What can be used to treat retinoblastoma?
Radiotherapy if tumour treated in early stages
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What is the retinoblastoma (Rb) involved in regulating?
Checkpoint between G1 and S phases
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What causes Rb gene to become phosphorylated?
Specific growth factors
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What does phosphorylated Rb cause?
Rb to become dissociated form cell cycle regulatory protein called E2F, which the permits transcription of genes required for DNA synthesis S phase
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What does mutated Rb cause?
Unstable binding to transcription genes, leading to uncontrolled cell growth which can causes Point-mutations and deletions
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What are BRCA1 and BRAC2 tumour suppressor genes involved in?
Cell cycle and DNA repair
128
What lead to the discovery of Src gene which is s protein kinase gene?
Tumours caused by Rous Sarcoma virus
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What are Ras genes code for?
Membrane-associated signal transduction proteins - regulate cell growth and division
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What causes Ras to become activated?
External growth factors bind to corresponding receptors in membrane, causing autophosphorylation of cytoplasmic portion and recruitment of nucleotide exchange factors that cause Ras to release GDP and bind GTP becoming activated.
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What does Ras initiate?
A cascade of protein phosphorylations (by kinases) leading to activation of cell cycle genes. Once Ras has passed on the signal it hydrolyses GTP to GDP
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What does mutated Ras gene prevent?
GTP hydrolysing and so leaves Ras permanently activated- oncogene
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predominance of single nucleotide substitution produce single amino acid changes at what positions in K- ras, H-ras and N-ras oncogenes?
K-ras and H-ras: Position 12 glycine to another amino acid
| N-ras: position 61glutamins to another amino acid
134
What do osteoclasts cells do?
Remove old portion of bone
135
What do acinar cell do?
Secretes digestive enzymes in pancreas
136
What could variations in gene expression be a result of?
Different cell types
Stage in organisms development
Phase of cell cycle
Response to internal and external (i.e. Environmental) factors
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What two essential elements are needed for gene expression?
Regulatory DNA: switches gene on/off
| Regulatory protein: binds to regulatory DNA
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What is transcriptional control of gene expression governed by?
Gene promoters (sections of DNA usually upstream of coding region)
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What is gene promoters the recognition site for?
RNA polymerase and transcription factors
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What is the core promoter necessary for initiating?
Transcription at basal (baseline) level
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What do essential/basal transcription factors allow?
RNA polymerase to bind to promoter region
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What do enhancer sequence do?
Bind transcription factors which change rate and timing of transcription and so gene expression
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What are activators?
Transcription factors that increase transcription
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What are repressors?
Decrease transcription
145
What can activators and repressors alter the rate up to?
100-fold
146
Why do DNA loops form?
DNA loops directed by protein allow distant regulatory sequences to be brought together
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What do TFs activators and repressors bind to?
DNA sequences called enhancers/silencers respectively
148
What are co activators?
Adapter molecules that integrate signals from activators and perhaps repressors
149
What is a basal transcription factors?
TFs that respond to injunctions form activators, these factors position RNA polymerase at the start
150
What are some examples of steroid hormones which regulate transcription?
Steroid hormones (either endogenous or delivered as a drug: estradiol, testosterone;corticosterone)
151
Steroid hormones bind to specific receptor proteins. How many many domains do theses proteins have and what are they?
3 domains.
Unique N-terminus
Central DNA-binding section
Hormone-binding C-terminus
152
Where are the hormone-receptor complex translocation to? And what does in bind to in there? What does this lead to?
To nucleus.
Binds to steroid hormone response elements in promoters of genes that can be activated by the specific hormone.
Leads to alteration in gene transcription and so altered production of steroid-induced proteins
153
What do gene promoters contain?
Specific sequences of DNA that bind transcription factors(proteins) that effect gene expression
154
What are restriction enzymes?
Enzymes that cleave DNA at specific DNA sequences producing restriction fragments
155
Where do restriction enzymes cut?
At the phosphate backbone of the double helix, without damaging the bases
156
What does DNA ligase do?
Connects DNA fragments by sealing gaps between the two strands by forming convent phosphodiester bonds
157
What does DNA polymerase do?
Makes copies DNA using a template
158
What cut do restriction enzymes produce?
Sticky ends with either 5' or 3' overhangs.
Or
Blunt ends
159
Why do blunt ends join less easily then sticky ends?
Lack of initial hydrogen bonding
160
How does molecular cloning occur?
Recombinant DNA is introduced into a cell (usually a microbe)
On a suitable carrier or vectors , this is then replicated along with the host DNA, at the cell divides clones are produced
161
What was the 1st recombinant drug?
Humulin which was extracted human insulin cloned in bacteria, used for the treatment of diabetes
162
What was used before human insulin drug was produced for diabetics?
Animal insulin (from pigs or cows) . Human insulin has a better efficacy.
163
What is gel electrophoresis?
Separates DNA according to size for analyse of patterns of DNA fragments. Short DNA fragments move further.
164
Where does DNA migrate to in gel electrophoresis? And why?
DNA migrates away from the anode terminal and towards the cathode terminal because DNA is negatively charged
165
What does gel electrophoresis involve?
Loading DNA into wells in an agarose gels submerged in electrolyte buffer and applying a electric current. Distance moved related to length of fragment.
166
What does genetic cloning refer to?
Refers to clinal expansion of a single cell into a population (without the introduction of foreign DNA)
167
Why is reproductive cloning not molecular cloning?
No recombinant DNA is involved
168
Issued by the recombinant DNA laws which cell can only be modified?
Somatic cells ( not germ cells -gametes)
169
What is a vector?
A carrier that allows the transport of an entity from one host to another
170
What were the first cloned vectors?
Plasmid DNAs naturally found in bacteria
171
What is the origin or replication (ori)?
A specific region of DNA that the cell DNA polymerases bind to, then synthesise new copies of the plasmid DNA. The ori also determines how many plasmids are maintained in each cell (10s-100s)
172
What are the essential features that most vectors have?
Origin of replication
Marker gene
Multiple cloning site or Polylinker
173
What is the marker gene?
These usually confer resistance to specific antibiotics to enable selection of cells that have picked up the vector
174
What is the multiple cloning site or Polylinker?
Synthetic DNA that has been added to the vector. It contains recognition sites for restriction enzymes. The MCS is where foreign DNA (e.g. Genes) is inserted into the vector during cloning.
175
Give an example of a reporter gene.
lacZ
176
What colour does lacZ confer in bacterial cells containing the vector?
Blue
177
What causes the cell with the lacZ to turn white?
When foreign DNA is inserted in the MCS within the lacZ gene it is disrupted and this prevents lacZ protein production so the cells are not blue but are white
178
What is transformation?
When plasmids are introduced into recipient cells by pre-treating the cell with chemicals to enable the uptake of DNA and with aid of heat shock.
179
What is done to see which cells are transformed?
Cells are spread on to nutrient agar plate containing the correct antibiotic. Only cells combating the vector survive to produce a colony.
180
What is Taq polymerase?
Enzyme isolated from thermophilic bacteria from hot springs and hydrothermal vents
181
What does PCR do?
Amplifies DNA
182
What is a possible problem with the large amplification from PCR?
If sample is cross-contaminated then a large amount is copied
183
What is PCR used for?
Forensics and paternity
184
Give examples of some infections PCR is used to diagnose?
Viruses: HIV, HPV
Bacteria: Chlamydia trachmatis , Mycobacterium tuberculosis, Neisseria Gonorrhoeae
185
What cancers can PCR be used to diagnose?
Cancers involved in chromosome translocation events: leukaemia, lymphoma
186
What are primers?
Small single-stranded DNAs
