MGD * Flashcards
0
Q
Briefly describe 2D-PAGE.
A
2D-PAGE is a variant of protein electrophoresis that combines SDS-PAGE and isoelectric focusing to separate complex mixtures of proteins according to their size and charge. This can be used to diagnose disease states.
1
Q
Are cancer-causing alleles normally dominant or recessive?
A
Recessive
2
Q
Briefly describe isoelectric focussing.
A
Isoelectric focusing is a variant of protein electrophoresis. The gel contains a pH gradient, so the proteins will move either up or down the gel depending on their charge, until they reach their isoelectric point at which point they will have no charge and will stop moving. Isoelectric focusing separates proteins based on their charge alone.
3
Q
Briefly describe native gel electrophoresis.
A
Separates proteins on the basis of their size, shape and charge.
4
Q
Briefly describe SDS-PAGE
A
Involves the action if a detergent (SDS) and reducing agents to denature the protein same, so the proteins are separated only on the basis of their size.
5
Q
Briefly describe Southern blotting.
A
A technique used to transfer DNA fragments to a more permanent membrane after electrophoresis. A nitrocellulose sheet is placed on the gel and covered with paper towels. This is left for a period of time, after which the fragments have transferred to the nitrocellulose sheet.
6
Q
Briefly describe Southern hybridisation.
A
Southern hybridisation combines DNA hybridisation with Southern blotting. The DNA fragments are separated by electrophoresis and then Southern blotting is carried out. The hybridisation is carried out on the nitrocellulose paper, and the positions of the specific DNA sequences can be visualised on exposure to photosensitive film/UV light.
7
Q
Briefly describe Western blotting.
A
A technique used to transfer proteins from gel after protein electrophoresis to a more permanent membrane. A nitrocellulose sheet, which has antibodies on it’s surface specific to particular protein(s), is laid on top of the gel and covered in paper towels. The protein(s) bind to the antibodies.
8
Q
Briefly outline the mechanism for targeting proteins destined for lysosomes.
A
A mannose-6-phosphate signal is added in the Golgi body which causes the protein to be transported to a lysosome.
9
Q
Briefly describe the mechanism for targeting proteins destined for retention in the ER.
A
The proteins have a KDEL sequence which is recognised at the Golgi body and causes the protein to be transported back to the ER.
10
Q
Briefly outline the mechanism for targeting proteins destined for the mitochondria.
A
The protein contains an amphipatic N-terminal sequence which is recognised by TOM proteins (transporter outer membrane) to cross the outer membrane and TIM proteins (transporter inner membrane) to cross the inner membrane. The proteins are not folded until they reach the inside of the mitochondrion.
11
Q
Briefly outline the mechanism for targeting proteins destined for the nucleus.
A
The proteins contain a Nuclear Localisation Sequence (NLS). Proteins called importins bind to the NLS and the complex travels through a nuclear pore.
12
Q
Define ‘recombination’
A
Where the crossing over between the loci of 2 linked alleles causes them to be separated from each other.
13
Q
Define ‘activity’
A
A measurement of the amount of an enzyme, equal to the moles of substrate converted per unit time.
14
Q
Define ‘allele’
A
A variant of a particular gene
15
Q
What is aneuploidy?
A
Numerical chromosome abnormality in which the chromosome number is not a multiple of the haploid number. This can be monosomy or trisomy.
16
Q
Define ‘complementation’ with regard to genetics.
A
Complementation occurs when expression of an allele at one gene locus is affected by an allele at another locus.
17
Q
Define ‘dominant allele’
A
The allele in a heterozygote which determines the phenotype
18
Q
Define gene
A
A length of DNA that codes for a protein
19
Q
Define ‘isoelectric point’
A
The pH at which the protein has no nett charge.
20
Q
Define ‘Km’
A
The concentration of substrate required to give a rate of reaction equal to 1/2 of Vmax
21
Q
Define ‘linkage’
A
When the loci for two genes are on the same chromosome, those genes are said to be linked. How close the loci are on the chromosome determines how tightly linked they are - the closer the loci, the tighter the linkage.
22
Q
Define ‘monosomy’
A
A type of aneuploidy in which an individual has lost one copy of a certain chromosome.
23
Q
Define ‘oncogene’
A
A gene that can transform a cell into a cancerous phenotype.
24
How do you calculate pH?
pH = -log[H+]
25
Define 'point mutation'
Change of one nitrogenous base for another
26
Define 'polyploidy'
Numerical chromosome abnormality in which the chromosome number is a multiple of the haploid number greater than the diploid number, eg. triploidy and tetraploidy.
27
Define 'proto-oncogene'
A gene that is very similar in sequence to an oncogene and can become an oncogene by mutation
28
Define 'recessive allele'
The non-dominant allele in a heterozygote
29
Define 'trisomy'
A type of aneuploidy in which an individual has gained one copy of a particular chromosome.
30
Define 'Vmax'
The maximum rate of reaction that occurs when all sites are saturated with substrate.
31
Define 'zymogen' and give two examples.
An inactive precursor of an enzyme, which is activated by proteolytic cleavage. Examples include trypsinogen (converted to trypsin) and pepsinogen (pepsin)
32
Define co-dominance and five and example.
A co-dominant characteristic is one where both alleles contribute to the phenotype eg. blood group
33
What is the formula for the concentration of H+ ions
[H+] = 10^(-pH)
34
Define the 'international unit of enzyme activity'
The amount of enzyme that catalyses the conversion of 1 micromoleof substrate to product per minute
35
Describe and explain the oxygen binding pattern for Hb
The oxygen dissociation curve for Hb shows a sigmoidal relationship between % saturation and partial pressure of oxygen. The Hb is in it's T state, with a low affinity for oxygen, when it's deoxygenated, but when the first molecule of oxygen binds it changes to it's R state which has an increased affinity for oxygen, so subsequent oxygen molecules bind more easily. This cooperative binding gives rise to the sigmoidal oxygen dissociation curve.
36
Describe and explain the oxygen binding pattern for myoglobin.
The oxygen dissociation curve for myoglobin shows a hyperbolic relationship between % saturation and partial pressure of oxygen. This is because myoglobin only has one subunit so it doesn't exhibit cooperative binding to oxygen.
37
Describe DNA hybridisation
DNA hybridisation involved adding DNA probes which have been fluorescently marked to a sample of DNA which has been denatured. The sample is then renatured and the probes anneal to complementary DNA sequences, allowing specific sequences to be detected.
38
Describe gene cloning
To carry out gene cloning you must first identify and isolate the desired gene using a restriction enzyme. You then get a sample of bacterial plasmids and add the same restriction enzyme to this sample. The desired gene is added to the plasmids and DNA lipase is added to make the plasmids take up the gene. The recombinant plasmids are then mixed with bacteria and a technique such as heat shock is used to make the bacteria take up the plasmids. The cells which have taken up recombinant plasmids are selected for by using antibiotics. These cells are then cultures so that the gene is cloned when they replicate.
39
Describe how nucleotides are bonded together in a nucleic acid.
Nucleotides are bonded by phosphodiester bonds. The phosphate group bonds to the -OH group on carbon-3
40
Describe in detail the features of a B-sheet
A B-sheet forms from fully extended strands of amino acids. The distance between each amino acid is 0.35nm. The R groups alternate on each side of the strand. The strands lie side to side and H bonds form between them, forming sheets. The sheet may be parallel if the strands all run in the same direction or antiparallel if they run in opposite directions.
41
Describe in detail the structure of an alpha helix
It's a right-handed helix with a pitch of 0.54nm. There are 3.6 amino acid residues per turn of the helix. The R groups all face toward the outside of the helix, and the carboxyl and amine groups of each residue face in opposite directions. The helix is stabilised by H bonds between carboxyl and amine groups which are 4 amino acids away from each other.
42
Describe in detail the structure of tropocollagen
Tropocollagen is a right-handed triple helix consisting of 3 left-handed alpha chains twisted around each other. Every third amino acid in the chain is glycine with many other amino acids being proline, hydroxyproline or lysine. Tropocollagen is 300nm in length.
43
Describe phosphorylation and de-phosphorylation of an enzyme
Phosphorylation is carried out by kinase enzymes. A phosphate group is added to an amino acid with an -OH group. Phosphate groups have large negative charges and can form H bonds so they affect protein structure. De-phosphorylation is the removal of a phosphate group, carried out by phosphatase enzymes. Phosphorylation and de-phosphorylation may both either activate or inhibit an enzyme.
44
Describe restriction analysis
Restriction analysis involves the use of restriction enzymes. These are endonucleases that cut polynucleotides at particular base sequences called restriction sites. Restriction analysis involves mixing a particular restriction enzyme with a DNA sample and analysing the resultant fragments by electrophoresis. The fragments of different DNA samples can be compared to investigate if there has been a mutation that has added or removed a restriction site, for example.
45
Describe the action of a reversible competitive inhibitor
A reversible competitive inhibitor binds non-covalently to the active site of an enzyme and blocks it temporarily so that no substrate can bind to it. This decreases turnover rate and lowers Km, but Vmax is unaffected. The effect of competitive inhibitors can be overcome by increasing the substrate concentration.
46
Describe the actin of reversible non-competitive enzyme inhibitor.
A reversible non-competitive inhibitor binds non-covalently to a site on the enzyme which is not the active site and decreases the turnover rate. The effect of non-competitive inhibitors can't be overcome by increasing substrate concentration. They affect Vmax but no Km.
47
Describe the action of an irreversible enzyme inhibitor
Irreversible inhibitors bind irreversibly to the enzyme and destroy it's function.
48
Describe the activity of X chromosomes in a cell.
Only one X chromosome is ever active in a cell, any others form structures called Barr bodies at the periphery of the nucleus.
49
Describe the allosteric regulation of phosphofructokinase
PFK catalyses step 3 of glycolysis. This step is irreversible and is therefore a controlling step. PFK is allosterically activated by AMP and fructose-2,6-bisphosphate, it is allosterically inhibited by ATP, citrate and H+
50
Describe the binding of 2,3-bisphosphoglycerate to Hb
One molecule of 2,3-BPG binds to each Hb molecule. 2,3-BPG binds in the centre of the tetramer to positively charged residues.
51
Describe the bonds responsible for secondary structure of proteins.
The secondary structure is entirely determined by H bonds between the H of the NH part of a peptide bond and the O of the C=O part of a peptide bond)
52
Describe the cause of thalassaemia
Caused by an imbalance in the number of alpha and beta subunits of Hb. This can be alpha thalassaemia, where not enough alpha subunits are produced, or beta thalassaemia, where not enough beta subunits are produced.
53
Describe the cell cycle
Starting at the beginning of interphase. G1 is the first phase of interphase. During G1 the components of the cell duplicate. After G1 there is a cell cycle checkpoints during which it's checked that G1 has been successfully completed. Then there is S phase in which DNA replicates, followed by G2 in which the DNA replication is checked for errors and any errors are repaired. After G2 there is a second cell cycle checkpoint in which the cell can decide whether to replicate or not. If the cell is going to replicate, G2 is followed by mitosis and then cytokinesis. The 2 daughter cells begin at G1.
54
Describe the concept of enzyme cascades.
Enzyme cascades involve one enzyme which activates another enzyme, which activates another enzyme and so on. Each enzyme can activate multiple other enzymes. This means the number of affected molecules can increase by orders of magnitude. Usually the enzymes catalyses phosphorylation/dephosphorylation of the next enzyme.
55
Describe the difference between the constitutive and regulated secretory pathways.
In the constitutive secretory pathway the protein is continually being synthesised, packaged into vesicles and released by exocytosis. In the regulated secretory pathway the protein is packaged into vesicles but the vesicles aren't released until a stimulus is received.
56
Describe the differences in structure between Hb and myoglobin
Hb consists of 4 polypeptide subunits, normally 2 alpha and 2 beta subunits, with a haem group bound to each subunit. Myoglobin consists of a single subunit with a haem group attached.
57
Describe the different physiological roles of Hb and myoglobin
Hb is present in erythrocytes. It's role is to pick up oxygen at the lungs and transport it to the tissues where it's needed for aerobic respiration. Myoglobin is present in muscles. It's role is to store oxygen for when oxygen is scarce in the muscle so that aerobic respiration can continue to occur.
58
Describe the effect of 2,3-BPG on the binding of oxygen by Hb and the physiological significance of this effect.
2,3-BPG decreases the affinity of Hb for oxygen. This is significant because it makes oxygen transport more efficient as it increases the amount of oxygen deposited at the tissues. The amount of oxygen picked up at the lungs is relatively unaffected as the lungs have such a high partial pressure of oxygen.
59
Describe the effect of CO on the binding of oxygen by Hb and the physiological significance of this effect
CO affects oxygen transport by Hb in two ways; by binding irreversibly to haem groups and in binding, increasing the affinity of Hb for oxygen. This means oxygen is prevented from binding to Hb and also less oxygen is released at tissues. CO poisoning can be lethal.
60
Describe the effect of CO2 on the binding of oxygen by Hb and the physiological significance of this effect
High concentration of CO2 decrease the affinity of Hb for oxygen as the CO2 molecules bind to the Hb molecules. This is called the Bohr effect. It ensures that oxygen is released at metabolically active tissues, which release a lot of CO2.
61
Describe the effect of H+ on the binding of oxygen by Hb and the physiological significance of this effect
High concentrations of H+ decrease the affinity of Hb for oxygen as the H+ molecules bind to the Hb molecules. This is called the Bohr effect. It ensures that oxygen is released at metabolically active tissues, which release H+
62
Describe the elongation stage of transcription
RNA polymerase travels along the DNA template strand in the 5' to 3' direction, adding complementary RNA nucleotides. A nearly identical copy of the coding strand is produced.
63
Describe the elongation stage of translation
Elongation begins with Met-tRNA in the P site of the ribosome. The ribosome has two sites where tRNA can bind, the P site and the A site. An aminoacyl-tRNA molecule, with a complementary anticodon to the next codon in the sequence, binds to the A site. The amino acid from the aminoacyl-tRNA binds to the methionine on the Met-tRNA molecule, catalysed by peptidyl-transferase, and the methionine moves over to the amino acid attached to the A site. The tRNA molecule at the P site is now empty and it leaves the ribosome. The tRNA in the A site, with it's attached polypeptide, moves over to the P site. Another aminoacyl-tRNA moves into the A site and the process repeats to elongate the polypeptide chain.
64
Describe the formation of the mature insulin molecule
Insulin is initially synthesised as pre-proinsulin in the ER lumen. This consists of the signal peptide and peptides A, B and C. The signal sequence is removed by signal peptidase in the ER lumen, and 3 disulphide bonds form with 2 between peptides A and B. This gives proinsulin. Proinsulin undergoes further proteolytic processing in the Golgi body and the C peptide is cleaved, leaving the A and B peptides joined by disulphide bonds. This is mature insulin.
65
Describe the general concept of enzyme assays
Enzyme assays measure the activity of an enzyme in a sample. To carry out an enzyme assay you add saturating amounts of substrate under optimum conditions and measure the disappearance of substrate or the appearance of product.
66
Describe the initiation stage of transcription.
A 'TATA box' sequence upstream of the gene is recognised and bound to by transcription factors. RNA polymerase then binds to the site and separates the DNA strands.
67
Describe the initiation stage of translation
The 5' cap on the mRNA molecule is recognised and bound to by cap binding proteins, initiation factors and the small 40s ribosomal subunit. The 40s subunit has Met-tRNA bound to it. The 49s subunit then moves down the mRNA molecule until it reaches a start codon (AUG, which codes for methionine). The 60s ribosome subunit then binds, forming a functional ribosome which can carry out the elongation stage.
68
Describe the key features of the DNA double helix
The strands in the double helix run antiparallel to each other and are bonded to each other by H bonds between complementary base-pairs. The pitch of the helix is 3.4nm. The helix has a major groove and a minor groove, with the major groove being longer in height and shallower than the minor groove.
69
Describe the mechanism of allosteric regulation
Allosteric enzymes have multiple subunits and exist in two states, the T state (has a low affinity for the substrate), and the R state (has a high affinity for the substrate). A graph of rate of reaction/substrate concentration for an allosteric enzyme shows a sigmoid relationship. Allosteric activators bind to the R state and stabilises it, so the enzyme has a high affinity for the substrate. Allosteric inhibitors bind to the T state and stabilise it, so the enzyme has a low affinity for the substrate.
70
Describe the middle stage of DNA replication. What is this stage called?
The DNA double helix unzips, catalysed by helicase, as the replication fork moves along. One strand of DNA is being replicated in the same direction as the movement of the replication fork. This is the leading strand and is replicated continuously. The other strand of DNA is being replicated in the opposite direction to the movement of the replication fork and thus must be replicated discontinuously. This is the lagging strand. The fragments of newly replicated DNA are joined together by DNA ligase. The formation of the new DNA strands is catalysed by DNA polymerase. This stage is called elongation.
71
Describe the process of 3' tailing/polyadenylation of pre-mRNA and it's purpose
A specific endonuclease cuts the mRNA strand as it's being transcribed and many RNA nucleotides with A as the nitrogenous base are added. These nucleotides protect against degradation.
72
Describe the process of 5' capping and it's purpose
A nucleotide 'cap' is added at the 5' end of the pre-mRNA molecule by a 5'-5' linkage. This helps to protect against degradation of the mRNA molecule.
73
Describe the process of an ELISA. What type of assay is this?
An ELISA is used to determine the concentration of a protein in a sample. The protein (or an antibody specific to the protein) is immobilised on the sides of a well and the antibody (or protein) is added to the well. A second antibody which binds to the protein-antibody complex is then added. This antibody has an enzyme attached. The well is then washed out to remove any unbound antibodies. The substrate for the enzyme on the second antibody is then added and the reaction produces a coloured product. The rate of formation of product, which is proportional to the amount of protein initially present, is measured by a colorimeter. An ELISA is an immunoassay.
74
Describe the process of carrying out a microarray
Microarrays analyse the expression of thousands of genes simultaneously. They can be used to compare the expression of mRNA from 2 different sources e.g. tumour cell and healthy cell. The 2 DNA samples are each labelled with a different colour eg. red and green. Each dot on the microarray represents a gene, and the proportion of each colour in the dot (which will be some mixture of the two colours) represents the relative expression of that gene by each source.
75
Describe the process of gel electrophoresis
A technique used to separate DNA fragments on the basis of their size. The apparatus consists of an agarose gel, with wells at one end in which the DNA samples are placed, an anode and cathode at either end of the gel to generate a potential difference (cathode at the end nearest the wells) and a buffer solution on the gel. The DNA fragments are placed in the wells and a potential difference is applied across the gel for a fixed amount of time. The fragments will move towards the anode at the other end of the gel because they are negatively charged due to their phosphate groups. Similar fragments can move through the gel more easily and thus move quicker and further through the gel in the fixed amount of time. At the end of the electrophoresis a stain is added or some form of detection is used so the positions of the fragments can be detected.
76
Describe the process of PCR
Used to amplify a sample of DNA. The process consists of a 3 stage cycle which is repeated over and over to exponentially increase the amount of sample DNA. You start with a mixture of sample DNA, specific DNA primers, the enzyme Taq polymerase, and free DNA nucleotides. First, the sample is heated to 95C to separate the strands of DNA into single strands. Secondly, the sample is cooled to 55C and the DNA primers bind to their complementary sequences in the sample DNA. Thirdly, the heat is increased to 72C and Taq polymerase catalyses replication of the stretch of DNA between the primers. The amount of the desired stretch of DNA has now doubled, and will double for every repeat of the cycle.
77
Describe the process of splicing and it's purpose
Splicing involves the removal of introns, non-coding regions, from the pre-mRNA molecule by endonucleases. Only exons remain, giving an open reading frame to be translated. Introns are not intended to be translated so splicing is necessary to give the correct protein sequence.
78
Describe ether secondary structure of RNA molecules
RNA strands can form stem-loops, in which complementary base-pairs form between nucleotides, running antiparallel, in the same strand.
79
Describe the structure of a chromosome (unreplicated)
Each chromosome consists of one DNA molecule complexed with proteins. Histone proteins form octamers and the DNA molecule loops twice around each octamer, forming a structure called a nucleosomes. This 'beads on a string' arrangement, with the DNA as the string and the nucleosomes as beads, is then organised into hanging loops attached to a protein scaffold.
80
Describe the structure of a eukaryotic ribosome. Where in the cell are ribosomes assembled?
A eukaryotic chromosome consists of a 60s subunit and a 40s subunit, making an 80s subunit overall. Ribosomes are made of rRNA and proteins. They are assembled in the nucleus.
81
Describe the structure of a nucleotide
A nucleotide consists of a pentose sugar (ribose in RNA, deoxyribose in DNA) with a phosphate group attached at carbon-5 and a nitrogenous base at carbon-3. The nitrogenous base may be C, G, A, T or U
82
Describe the structure of chromatin
In chromatin each DNA molecule is associated with octamers of histones proteins. Each molecule loops around a histone molecule twice forming structures called nucleosomes. This gives rise to a 'beads on a string' arrangement with nucleosomes as beads and DNA as the string. In euchromatin, the DNA and nucleosomes remain in the beads on a string arrangement. In heterochromatin the DNA and nucleosomes are further condensed into a solenoid arrangement which is much denser than euchromatin and is not transcribed.
83
Describe the termination stage of transcription
Transcription stops when a specific DNA sequence is recognised. The product of transcription is pre-mRNA, which must be converted to mature mRNA after transcription.
84
Describe the termination stage of translation
Translation stops when a stop codon is reached. There is no complementary tRNA molecule for a stop codon, instead a release factor binds and the finished polypeptide and tRNA molecules are released.
85
Do silent mutations cause disease?
Most don't, but some can by disrupting splicing.
86
Explain why the genetic code is degenerate and the significance of this
Some amino acids are coded for by more than one codon. This means a mutation may not necessarily cause a change in amino acid sequence.
87
Explain why the genetic code is a triplet code.
The genetic code is a triplet code because each amino acid is coded for by a specific set or sets of three bases
88
Give 2 ethical conundrums of genetic testing
If a patient tests positive for a dominant genetic disease you know that one of their parents must have it - should you then tell them?
If you start genotyping individuals the information could be used by many different people; government, police, insurance companies - is this fair?
89
Give 2 ethical conundrums of karyotyping an unborn child
Obtaining foetal DNA samples is invasive and can cause miscarriage. Diagnosis of genetic disease in an unborn child could cause the parents to decide to terminate the pregnancy.
90
Give 2 examples of proteins secreted by each of the secretory pathways
Constitutive: albumin, collagen.
Regulated: insulin, neurotransmitter
91
Give 3 mechanisms involved in clot breakdown
Removal of activated factors, proteolytic digestion of fibrin and inhibitor molecules for the enzymes involved.
92
Give 5 ways in which the blood clotting process is regulated.
1) Most factors are present in inactive zymogen form and in very low concentration so that clotting is not triggered by accident.
2) The cascade mechanism amplifies the original signal
3) Clotting factors are localised at the site of damage because carboxyglutamate binds to damaged tissue
4) Thrombin feeds back and activates factors in the intrinsic pathway
5) Multiple processes terminate clotting including the removal of activated proteins, proteolytic digestion and binding of inhibitors
93
Give 6 ways in which bacterial protein synthesis is different to protein synthesis in humans
- Simpler ribosomes with smaller subunits
- Only one type of RNA polymerase
- Different transcription/translation factors
- Transcription and translation are coupled (in bacteria)
- Short-lived mRNA with no post-transcriptional processing
- Distinct translation initiation mechanism
94
Give an example of a disease which results from misfolding of proteins, with brief detail about the misfolding
Alzheimer's disease. Misfolded proteins arise from beta-sheets in different proteins interacting with each other, giving rise to amyloid plaques. Misfolded proteins stimulate other proteins to misfold.
95
Give an example of an enzyme regulated by phosphorylation
Insulin or glucagon
96
Give an example of an enzyme regulated by proteolytic cleavage
Trypsin (from trypsinogen) or pepsin (from pepsinogen)
97
Give an example of an enzyme that is regulated by allosteric regulation
Phosphofructokinase, activated by AMP and fructose-2,6-bisphosphate, inhibited by ATP, citrate and H+
98
Give an overview of the secretory pathway
A free ribosome in the cytoplasm begins translating the mRNA molecule for a protein. During translations, a signal sequence is produced (hydrophobic aa sequence). An SRP molecule (signal recognition peptide) recognises the signal sequence and binds to it which halts translation. SRP, bound to GTP, then directs the ribosome to a SRP receptor on the ER membrane. SRP dissociates when the ribosome reaches the SRP receptor, and protein synthesis resumes. The polypeptide is fed into the ER lumen as it is synthesised, through a peptide translocation complex. Once the entire protein has been formed the signal sequence is cleaved by the enzyme signal peptidase. The ribosome dissociates and is recycled.
99
Give names and descriptions of 3 different structural abnormalities involving interaction between chromosomes
1) Translocation: a part of one chromosome is transferred to another non-homologous chromosome, with no loss of genetic material overall.
2) Reciprocal translocation: two non-homologous chromosomes swap sections of genetic material with no loss of genetic material overall.
3) Robertsonian translocation: the P arms of two acrocentric chromosomes join together to form one super-chromosome
100
Give names and descriptions of 5 different structural abnormalities within one chromosome
Deletion - loss of genetic information from the chromosome
Duplication - doubling of genetic information in the chromosome
Inversion - genetic information is rearranged within the chromosome with no loss
Ring chromosome - the ends of both arms of the chromosome are lost and it forms a ring structure
Isochromosome - two structures form from one chromosome, one made from the p arms and one made from the q arms
101
Give the cause, in words and in a karyotype report, of Down's syndrome
Trisomy 21: 47, XY, +21
102
Give the cause, in words and in a karyotype report, of Edward's syndrome
Trisomy 18: 47, XY, +18
103
Give the cause, in words and in a karyotype report, of Klinefelter syndrome
3 sex chromosomes (two X and one Y): 47, XXY
104
Give the cause, in words and in a karyotype report, of Patau syndrome
Trisomy 13: 47, XY, +13
105
Give the cause, in words and in a karyotype report, of triple X syndrome
Three X chromosomes: 47, XXX
106
Give the cause, in words and in a karyotype report, of Turner syndrome
Only having one sex chromosome (X): 45, X
107
Give the cause, in words and in a karyotype report, of XXY syndrome
Three sex chromosomes (1 X and 2 Y): 47, XYY
108
Give the karyotype report for a normal human male and a normal human female.
Male: 46, XY
Female: 46, XX
109
Give the name of a chemotherapy drug that targets mammalian cell growth and describe it's action
Methotrexate - an antifolate, it inhibits DHFR, an enzyme which synthesises tetrahydrofolate (needed for DNA synthesis), so methotrexate inhibits cell growth
110
Give a name of an antibiotic that targets bacterial cell wall synthesis and describe it's action
Amoxicillin (or penicillin). Amoxicillin inhibits transpeptidase (enzymes which form cross-links in the peptidoglycan cell walls of bacteria). This causes the cell wall to break down and thus the bacteria lyse due to osmotic pressure
111
Give the name of an antibiotic that targets bacterial transcription and describe it's action
Rifampicin - binds to and inhibits RNA polymerase
112
Give the name of an antibiotic that targets bacterial translation and describe it's action
Chloramphenicol - binds to the 50s subunit of the ribosome and inhibits the peptidyl transferase enzyme
113
Give the names (abbreviated) of the deoxyribonucleotides
dGMP, dCMP, dAMP, dTMP
114
Give the names (abbreviated) of the ribonucleotides
GMP, CMP, AMP, UMP
115
Give two examples of diseases caused by mutations in globin genes
Sickle cell disease and thalassaemia
116
How are Hb molecules in the T state different from those in the R state?
In the T state, the molecule is stabilised by ionic interactions between histidine and positively charged residues. These interactions are not present in the R state.
117
How are induced mutations caused?
Induced mutations are caused by exposure to mutagenic chemicals or to ionising radiation. Mutagens including alkylating agents, which remove bases, and acridine agents, which add or remove bases. Ionising radiation includes UV radiation, which causes adjacent thymin bases to form dimers, and X-rays, which can break down chromosomes or delete nucleotides.
118
How are mutations classified according to their cause?
Spontaneous or induced mutations.
| Spontaneous are caused by error of DNA replication, induced are caused by mutagens or ionising radiation.
119
How are spontaneous mutations caused?
Spontaneous mutations are caused by errors of DNA replication. This could be due to rare tautomeric forms of bases, or it could be due to slippage during replication, where one of the DNA strands loops out.
120
How are the chromosomes numbered?
In order of decreasing size, except for 21 and 22 which are the wrong way round
121
How can amino acid charge affect the isoelectric point of a protein?
If a protein contains a high proportion of negatively charged amino acids it will have a low isoelectric point. If a protein contains a high proportion of positively charged amino acids it will have a high isoelectric point. The isoelectric point is the average of the pKa values of the constituent amino acids of a protein
122
How do acidic and basic proteins differ by their isoelectric points?
An acidic protein has an isoelectric point lower than 7. A basic protein has an isoelectric point greater than 7.
123
How do enzymes increase the rates of reactions?
They catalyse the reactions by stabilising the high energy transition state, which decreases the activation energy
124
How do the number of types and number of copies of each type of RNA compare?
rRNA = few types, many copies, mRNA = 100,000s of types, few copies, tRNA = around 100 types, very many copies
125
How does 2,3-BPG concentration in the blood change with altitude and why?
2,3-BPG concentration increases as altitude increases because there is less oxygen available at high altitudes, so more oxygen must be released from Hb at the tissues
126
How does DNA replication finish? What is this stage called?
(In circular DNA) The end of a lagging strand meets the beginning of a leading strand and the end of a leading strand meets the beginning of a lagging strand and DNA ligase seals the strands together. This stage is called termination.
127
How does extreme pH cause denaturation?
pH can change the charge of amino acids within the protein and disrupt ionic interactions, disrupting the structure of the protein.
128
How does heat cause denaturation?
Increased heat causes increased vibration of atoms which breaks bonds that are responsible for secondary and tertiary structure
129
How does Km indicate the affinity of an enzyme for it's substrate?
A high Km indicates a low affinity and vice versa
130
How does the amino acid change in sickle cell disease affect the behaviour of the Hb molecule?
The change of glutamate (negatively charged) to valine (non-polar) creates a hydrophobic region on the molecule. The hydrophobic regions on different Hb molecules stick together, forming aggregates called Heinz bodies. This alters the shape of the RBC, making it sickle shaped.
131
How does the cell deal with premature termination codons?
mRNA transcripts which contain premature termination codons are degraded by a process called nonsense mediated decay. This is a protective mechanism that causes little or no protein to be produced.
132
How does the tightness of linkage affect recombination frequency?
The tighter the linkage, the lower the recombination frequency
133
How far apart are residues which H bond to each other in an alpha helix?
4 amino acids
134
How is procollagen different to tropocollagen?
Procollagen has N- and C-terminal peptides which are cleaved to form tropocollagen
135
How is the charge on an amino acid affected by pH?
At pH values higher than the pKa of a particular amino acid, the amino acid will be negatively charged. If the pH value is lower than the pKa value of the amino acid, it will be positively charged. If the pH is the same as the pKa, the amino acid will exist as a zwitterion and have no nett charge.
136
How is vitamin K involved in the clotting cascade?
Vitamin K is required to create carboxyglutamate, which is needed for clotting factors to bind to damaged endothelium.
137
How many alleles does an individual have for any one gene?
Two
138
How many amino acids are there per turn of an alpha helix?
3.6
139
How many base pairs are contained within the human genome?
3.2 billion
140
How many chromosomes does each daughter cell have after mitosis?
46
141
How many coding genes are there in the human genome and what promotion of the genome is this?
22,000 genes, 1-2%
142
How many DNA molecules are present in each chromosome before and after DNA replication
1 before and 2 after
143
How might aneuploidy be caused?
Either by non-disjunction at meiosis or anaphase lag at mitosis or meiosis. Non-disjunction is where the chromosomes fail to separate at meiosis 1 or meiosis 2. Anaphase lag is where a chromosome is left behind in mitosis or meiosis because of a defect in spindle function or attachment to chromosomes.
144
How often does DNA polymerase make a mistake in DNA replication?
About 1 in 100,000 nucleotides are incorrect.
145
How would you signify the miss of part of the p arm on chromosome 5 in a karyotype report?
46, XY, 5p-
146
In what conformation are all peptide bonds found in the body?
Trans
147
In which direction does DNA replication proceed?
5' to 3'
148
In which direction is a DNA sequence written?
5' to 3'
149
Is an alpha helix left or right handed?
Right handed
150
Is the tropocollagen triple helix left or right handed?
Right handed
151
List all of the different types of non-covalent bond found between molecules
Van der Waals, ionic interactions, hydrogen bond, hydrophobic interactions
152
List the key features of a peptide bond
Rigid, planar, carbonyl oxygen and amide hydrogen are in trans orientation
153
List the major mechanisms of regulating enzyme activity
Change in substrate/product concentration, allosteric regulation, covalent modification (eg. phosphorylation), proteolytic cleavage, change in rate of enzyme synthesis, change in rate of enzyme degradation.
154
List the types of covalent bond that may exist between amino acids
Peptide bonds, disulphide bonds
155
Name the three types of enzyme inhibitor
Irreversible, reversible non-competitive and reversible competitive
156
Name 2 forms of ionising radiation and their effect on DNA
UV radiation causes adjacent thymine bases to form dimers. X-rays can break chromosomes or delete nucleotides.
157
Name 2 mutagens and give their effects
Alkylating agents remove bases. Acridine agents add or remove bases.
158
Name 4 variants of protein electrophoresis
SDS-PAGE, isoelectric focussing, 2D-PAGE, native gel electrophoresis
159
Name 5 inheritance patterns
Autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked
160
Name and describe the first method of DNA sequencing
DNA sequencing is the process of determining the order of individual nucleotides in a DNA molecule. The first method of DNA sequencing was Sanger chain termination. This involves mixing the sample DNA, DNA polymerase, free dNTPs and free ddNTPs which have been fluorescently labelled (specific coloured label for each particular base). The DNA polymerase catalyses DNA replication, adding dNTPs to the growing chain until a ddNTP is added. When a ddNTP is added no further nucleotides may be added, so replication stops. The DNA strands are then analysed by gel electrophoresis. The strands will line up in size order, with a fluorescent label indicating the base at that position in the DNA strand. By looking at the colour of each label in order you can determine the sequence of bases in the original DNA sample.
161
Name and describe the first process by which the errors of DNA replication are repaired
Proof-reading - carried out by polymerase enzyme itself. It detects wrongly paired bases and replaces them with the correct base for 99% of the errors.
162
Name and describe the process by which damaged nitrogenous bases in DNA are repaired.
Excision repair. The are 2 types of excision repair:
1) Base excision repair - repairs non-helix-distorting damage
2) Nucleotide excision repair - repairs helix-distorting damage eg. UV light damage.
Overall, excision repair repairs the damage caused by mutagens and ionising radiation
163
Name and describe the second process by which incorrectly matched bases are rectified.
Mismatch repair. After replication (and after proof-reading), enzymes detect incorrect base pairing and replace a patch of DNA on the newly synthesised DNA strand.
164
Name the negatively charged amino acids
Aspartate and glutamate
165
Name the phases of mitosis
Prophase, prometaphase, metaphase, anaphase and telophase
166
Name the positively charged amino acid
Lysine, histidine, argentine
167
Name the processes that consist of a initiation, elongation, and termination stage sequence.
Transcription, translation and DNA repair
168
Name the purines
G and A
169
Name the pyrimidines
C, T and U
170
Outline the basis of DNA fingerprinting
Every individual has certain DNA sequences called short tandem repeats at certain gene loci. The number of repeats at these loci varies between individuals and is inherited from their mother and father. Analysing the number of repeats for each short tandem repeat allows paternity and maternity testing and forensic DNA testing.
171
Outline the clotting cascade
There are two initial pathways in the clotting cascade, the intrinsic pathway and the extrinsic pathway. Both of these pathways begin with very small amounts of a certain factor being released. Both pathways culminate in the activation of factor X. Activated factor X then activates thrombin (from prothrombin) and thrombin activates fibrin by proteolytic cleavage of fibrinogen. The fibrin molecules bind together to form a clot. Thrombin also feeds back and activates factors before it in the intrinsic pathway, so clotting is a self-sustaining process
172
Outline the synthesis of collagen
CHADPOGRA
Cleavage of signal peptide (by signal peptidase)
Hydroxylation of selected lysine and proline residues
Addition of N-linked oligosaccharides and galactose to selected residues
Disulphide bond formation between alpha chains
Procollagen is formed as the alpha chains twist around each other
O-linked glycosylation
Golgi body to exocytosis, by vesicle
Removal of N- and C-terminal peptides to form tropocollagen
Aggregation of fibrils
173
State the characteristics of protein molecules that the 4 variants of protein electrophoresis separates on the basis of
SDS-PAGE = size only
Isoelectric focussing = charge only
2D-PAGE = size and charge
Native gel electrophoresis = size, shape and charge
174
State the contents of a normal human karyotype
46 chromosomes, consisting of 22 pairs of autosomes and 2 sex chromosomes
175
State the secondary structure of DNA
Double helix
176
What 2 processes rectify wrongly paired bases?
Proof-reading and mismatch repair
177
What 6 capabilities must a cell acquire in order to become cancerous?
It must be able to:
- divide without the need for external growth signals
- ignore growth inhibiting signals
- avoid apoptosis
- divide indefinitely without senescence
- stimulate angiogenesis (formation of new blood vessels)
- invade other tissues to establish a secondary tumour
178
What are DNA and RNA?
Nucleic acids, linear polymers of nucleotides
179
What are epitopes, monoclonal antibodies and polyclonal antibodies?
An epitope is the specific amino acid sequence on an antigen recognised and bound to by an antibody. Monoclonal antibodies are identical antibodies which recognise one epitope and one antigen. Polyclonal antibodies are multiple different antibodies which are specific to one antigen but recognise many epitopes
180
What are Southern, Northern and Western blotting used for?
```
Southern = DNA
Northern = RNA
Western = proteins
```
181
What are the two different types of point mutation and what do these involve?
Transition and transversion.
Transition is a change of pyrimidine to pyrimidine or purine to purine
Transversion is a change of pyrimidine to purine, or vice versa
182
What are the 2 enzymes that convert glucose to glucose-6-phosphate and where are they found?
Hexokinase - in all cells that carry out glycolysis
| Glucokinase - in hepatocytes
183
What are the two types of numerical chromosome abnormality?
Polyploidy and aneuploidy
184
What are the 3 antibodies and 1 antifolate you need to know about?
Amoxicillin, rifampicin, chloramphenicol and methotrexate
185
What are the 3 stages of DNA replication?
Initiation, elongation, termination
186
What are the 3 stages of transcription?
Initiation, elongation, termination
187
What are the 3 stages of translation?
Initiation, elongation, termination
188
What are the three types of shape of chromosome? Describe each
Metacentric - centromere is in the centre
Sub-metacentric - centromere is above the centre
Acrocentric - centromere is above the centre and have satellites on the p arms
189
What are the abbreviations for deletion, duplication and inversion on a karyotype report?
Del, dup, inv
190
What are the fragments of the lagging strand in DNA replication called?
Okazaki fragments
191
What are the indications for karyotyping of a child?
Birth defects, impaired mental, physical or sexual development
192
What are the indications for karyotyping an unborn foetus?
Maternal age > 35, family history of chromosomal abnormalities, abnormal ultrasound scan, recurrent loss of previous foetuses
193
What are the names for the short and long arms or replication chromosomes? Where are these arms located in drawings of the chromosome?
Short = p arm (petit)
Long = q arm
The p arm is located at the top of the chromosome and the q ar. Is located at the bottom
194
What are the phases of meiosis?
Prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II
195
What are the phases of the cell cycle, beginning at the start of interphase?
G1, S, G2, mitosis, cytokinesis
196
What are the possible uses of gene cloning?
Making useful proteins (eg. insulin), finding out what a certain gene does, carrying out genetic testing, and in the future possibly useful for gene therapy
197
What are the signs and symptoms of Down's syndrome?
Intellectual disability, congenital heart disease, eye and hearing disorders
198
What are the signs and symptoms of Edwards syndrome?
Normally death between 5 and 15 days, 8% of babies survive beyond a year
199
What are the signs and symptoms of Klinfelter syndrome? What is the gender of affected individuals?
Male. Appears at onset of puberty, gynaecomastia ("man boobs"), reduced testosterone production, reading and language impairment
200
What are the signs and symptoms of Patau syndrome?
Most affected children die within a year of birth and there are multiple congenital abnormalities.
201
What are the signs and symptoms of Triple X syndrome? What is the gender of affected individuals?
Female. Tall stature, small head, impaired development of motor skills and speech, scoliosis. Mostly undiagnosed.
202
What are the signs and symptoms of Turner syndrome? What is the gender of affected individuals?
Short stature, webbed neck, cardiovascular and renal problems, infertility (normal intelligence)
203
What are the signs and symptoms of XYY syndrome? What is the gender of affected individuals?
Male. Phenotype essentially normal apart from tall stature and slightly lower IQ than normal
204
What are the symbols for affected and unaffected in a pedigree?
Gender symbol coloured in white (affected) or black (unaffected)
205
What are the temperatures of each stage in PCR?
95C, 55C, 72C
206
What are the two types of beta-sheet, how are they different structurally, and which is the stronger type?
Parallel and antiparallel. Parallel sheets have strands which all run in the same direction. Antiparallel sheets have strands which run in opposite directions. Parallel sheets have the stronger arrangement.
207
What bonds stabilise DNA and RNA secondary structure?
Hydrogen bonds between complementary nitrogenous bases on polynucleotide strands run antiparallel to each other
208
What determines the solubility of any given substance?
Whether it can form H bonds with water molecules.
209
What determines whether a mutation is inherited or not?
What type of cell it occurs in. Mutations in somatic cells are not inherited, mutations in germline cells are inherited.
210
What feature do DNA fragments cut by restriction enzymes have? How would these fragments be joined to other fragments?
A restriction enzyme gives a staggered cuz of the double stranded DNA (sticky ends). These can anneal to the sticky ends of other DNA fragments cut by the same restriction enzyme. To join the sugar-phosphate backbone of these fragments you need to add DNA ligase.
211
What happens in anaphase I of meiosis?
The homologous pairs of chromosomes are pulled apart and one chromosome from each pair is pulled to each pole by spindle fibres
212
What happens in anaphase II of meiosis?
The chromosomes are pulled apart and one chromatid from each chromosome goes to each pole
213
What happens in anaphase of mitosis?
The chromosomes are pulled to the poles by spindle fibres
214
What happens in metaphase I of meiosis?
The chromosomes line up at the metaphase plate in homologous pairs. Crossing over occurs, in which chiasmata form between homologous chromosomes and genetic material is swapped between non-sister chromatids.
215
What happens in metaphase II of meiosis?
The chromosomes line up at the metaphase plate, randomly assorted
216
What happens in metaphase of mitosis?
The chromosomes line up at the centre of the cell (at the metaphase plate)
217
What happens in prometaphase of mitosis?
The spindle fibres attach to centromeres and the chromosomes are positioned within the cell
218
What happens in prophase I of meiosis?
The chromosomes condense and the nuclear envelope disappears
219
What happens in prophase II of meiosis?
The nuclear envelopes break down
220
What happens in prophase of mitosis?
The chromosomes condense and the nuclear envelope disappears
221
What happens in telophase I of meiosis?
The nuclear envelope reforms around each pole and the cell membrane undergoes cleavage
222
What happens during telophase II of meiosis?
The nuclear envelopes reform. 4 haploid daughter cells have been formed
223
What happens during telophase of mitosis?
A nuclear envelope reforms around each pole and the cell begins to divide
224
What information does gel electrophoresis give about a sample of DNA fragments?
The size of the fragments
225
What is a nucleoside?
A pentose sugar attached to a nitrogenous base (no phosphate group)
226
What is a zwitterion?
A form of an amino acid that exists when the pKa of the amino acids equals the pH of solution. It has no net charge.
227
What is FISH and how is it carried out?
FISH (fluorescence in situ hybridisation) is a method which allows you to locate specific sequences of DNA on chromosomes within a cell. Fluorescent probes are added to the cell which bind to specific DNA sequences that can then be visualised. FISH can investigate chromosome structure, number and/or behaviour
228
What is karyotyping and how is it carried out?
Karyotyping is imaging the full set of chromosomes present in a cell at metaphase. The chromosomes are stained so they can be visualised. The karyotype (image) can be manipulated to rearrange the chromosomes or give them false colour. Large abnormalities in chromosomes structure, deletions of chromosomes and duplications of chromosomes can be seen in a karyotype.
229
What is meant by amphipathic?
An amphipathic molecule has both a polar (hydrophilic) region, and a non-polar (hydrophobic) region
230
What is meant be the primary structure of a protein?
The sequence of amino acids in the polypeptide chain
231
What is meant by the quaternary structure of a protein?
The entire 3D arrangement of the protein subunits which may include several different polypeptides and/or prosthetic groups
232
What is meant by the secondary structure of a protein?
The local arrangement of the polypeptide backbone. This only involves hydrogen bonds, and interactions between R groups are not involved.
233
What is meant by the tertiary structure of a protein?
The overall 3D structure of atoms within the polypeptide (including R groups)
234
What is meant by the wild-type phenotype and mutant phenotype?
The wild-type phenotype is the phenotype most common in the population. A mutant phenotype is one that is not the most common in the population and is caused by a mutation.
235
What is meant by a frameshift mutation?
An insertion or deletion mutation which causes the reading frame of the mRNA to change. This occurs when there is an insertion or deletion of a number of base pairs not in a multiple of three (or a mutation in a splice site)
236
What is meant by insertion mutation and deletion mutation?
An insertion mutation is Where one or more base pairs are inserted into the DNA sequence. A deletion mutation is where one or more base pairs are removed from the DNA sequence.
237
What is meant by missense mutation?
A point mutation which causes an amino acid codon to change into a codon for another amino acid
238
What is meant by a nonsense mutation?
A nonsense mutation is a point mutation that causes an amino acid to change into a stop codon (premature termination codon)
239
What is meant by a silent mutation?
A point mutation that doesn't change the amino acid sequence of the protein the gene codes for. This is possible because the genetic code is degenerate - more than one codon codes for some amino acids
240
What is meant by the wobble position?
Some tRNA molecules have an inosine base at the third position in the anticodon which can bind to any base in a codon. This creates a wobble position at the third position so the anticodon can bind to 4 possible codons. This reduces the number of tRNA molecules required for translation as some amino acids are coded form by the first 2 positions in the codon only and the third position doesn't matter
241
What is proteolytic processing?
The removal of parts of the protein molecules by endonucleases and exoproteases
242
What is RT-PCR? Describe the process of carrying out RT-PCR
Reverse transcriptase PCR. It's similar to PCR but uses mature mRNA as the template instead of DNA. The primers used bind to the 3' tail of mature mRNA molecules and elongate from there, creating a cDNA molecule. This is then amplified by PCR.
243
What is the amino acid change in sickle cell Hb?
Glutamate to valine
244
What is the difference between a balanced structural chromosome abnormality and an unbalanced structural chromosome abnormality?
A balanced abnormality is one in which there is no extra or missing genetic information overall. An unbalanced abnormality is one in which there is missing or extra genetic information.
245
What is the difference between endonucleases and exonucleases?
Endonucleases cut bonds within polynucleotide strands, exonucleases cut bonds at the ends of polynucleotide strands
246
What is the difference between the action of glucokinase and of hexokinase?
Hexokinase has a higher affinity for glucose (lower Km) than glucokinase, but hexokinase is subject to product inhibition by glucose-6-phosphate whereas glucokinase is not. This means that if a person is active then most glucose will be used by hexokinase in the tissues for glycolysis and little will be used for glucokinase in the liver. If a person is sedentary, glucose-6-phosphate will build up in the tissues and inhibit hexokinase, so glucokinase will convert the glucose to glucose-6-phosphate for glycogen synthesis.
247
What is the difference in the gels used for DNA and protein electrophoresis?
DNA electrophoresis uses agarose gel, protein electrophoresis uses acrylamide gel
248
What is the difference between each amino acid in a beta-sheet?
0.35nm
249
What is the general structure of an amino acid?
A central carbon atom covalently bonded to a carboxyl group, an amino group, a hydrogen atom and an R group
250
What is the part of the protein removed in the ER and what is the part removed in the Golgi body?
The pre- segment (or signal peptide) and the pro- segment
251
What is the pitch of an alpha helix?
0.54nm
252
What is the pitch of the DNA double helix?
3.4nm
253
What is the role of vitamin C in collagen synthesis? How is this related to scurvy?
Vitamin C is a cofactor for the enzyme which catalyses hydroxylation of proline and lysine. Scurvy is caused by a lack of vitamin C in the diet, so collagen can't be synthesised properly, causing the observed signs and symptoms.
254
What is the start codon and what does it code for?
AUG, methionine
255
What is the stripy pattern seen on chromosomes called?
Geimsa banding pattern
256
What is the symbol for carrier in a pedigree?
The normal gender symbol either half-shaded or with a dot in the centre
257
What is the symbol for deceased in a pedigree?
Normal symbol with a diagonal line through it (bottom left to top right)
258
What is the symbol for unknown gender in a phenotype diagram?
Diamond
259
What normally happens to a gene that has a frameshift mutation?
Normally the gene is not expressed because the frameshift causes the insertion of a premature termination codon and the mRNA transcripts are degraded by nonsense mediated decay.
260
What part of an amino acid determines it's classification?
The R group
261
What process does DNA polymerase catalyse?
DNA replication
262
What process does RNA polymerase II catalyse?
Transcription
263
What process must hydrolytic enzymes undergo before section and why?
Proteolytic cleavage, because they must be synthesised in an inactive for so they don't digest contents of the cell
264
What process rectifies damaged bases?
Excision repair
265
What proportion of the total RNA in the cell is each type of RNA?
```
rRNA = over 80%
mRNA = 2%
tRNA = 15%
```
266
What residues are involved in disulphide bonds?
Cysteine
267
What sort of protein does a proto-oncogene code for?
Proto-oncogenes code for proteins important for control of the cell cycle
268
What two molecular analysis techniques use antibodies?
Immunoassays and Western blotting
269
What type of inheritance does inheritance of cancer show and why?
Dominant inheritance, because despite cancer-causing alleles being recessive, it only takes one mutation of the wild-type alert to occur in one cell of the body for cancer to develop. As this will happen eventually all individuals with the allele will at some point develop cancer, thus the dominant inheritance pattern.
270
What type of molecule is used in an immunoassay?
Antibody
271
What type of mutation must a cell have in order to become cancerous?
A mutation which raises the chance of future mutations occurring, i.e. a mutation that affects one of the DNA repair mechanisms
272
What type of protein structure is the amino acid sequence of a protein responsible for?
It determines all of them
273
What types of post-transitional modification occur in the ER?
N-linked glycosylation, cleavage of signal peptide (signal peptidase), disulphide bond formation (protein disulphide isomerise)
274
What types of post-transitional protein modifications take place in the Golgi body?
O-linked glycosylation, modification of N-linked oligosaccharides (which were added in the ER), further proteolytic processing
275
When are the cell cycle checkpoints in the cell cycle?
After G1 and after G2
276
When in the cell cycle does DNA replication occur?
The S phase of interphase
277
Where and how does DNA replication begin? What is this stage called?
DNA replication begins at points on the DNA strand called origins of replication. The enzyme primase kick-starts the process, the double helix unzips and DNA polymerase attaches. This is called initiation.
278
Where do the 2 types of glycosylation occur in the cell?
N-linked glycosylation occurs in the ER
| O-linked glycosylation occurs in the Golgi
279
Where would you find telomeres?
At the end of each arm of a chromosome
280
Which enzyme catalyses the formation of polypeptide bonds in ribosomes?
Peptidyl transferase
281
Which enzymes are markers for liver damage when present in the blood?
ALT and AST
282
Which enzymes are the 3 types of RNA synthesised by?
```
rRNA = RNA polymerase I
mRNA = RNA polymerase II
tRNA = RNA polymerase III
```
