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1
Q

What are the 4 traits of AUTOSOMAL RECESSIVE disorders?

A
  1. Usually appear equally in males & females
  2. Tend to skip generations
  3. More likely to appear among progeny of RELATED parents (inbred).
  4. Affected parents produce affected offspring.
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2
Q

Why is inbreeding not good?

A

Because it results in production of recessive autosomal traits more frequently and inbreeding depression.

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3
Q

What are the 3 traits of AUTOSOMAL DOMINANT disorders?

A
  1. Appear equally in males and females
  2. Unaffected persons DO NOT transmit the trait.
  3. Affected persons have at least one affected parent.
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4
Q

What are the 4 traits of X-LINKED RECESSIVE disorders?

A
  1. More often in males than in females
  2. NOT transmitted from Dad to sons.
  3. Affected sons usually have affected Mums.
  4. Tends to skip generations.
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5
Q

What are the 3 traits of X-LINKED DOMINANT disorders?

A
  1. Do NOT skip generations
  2. Affected males pass trait onto ALL daughters & NO sons.
  3. Affected females (if heterozygous) pass trait on to about 1/2 of their sons and 1/2 of their daughters.
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6
Q

What are the 3 traits of Y-LINKED disorders?

A
  1. ONLY appear in males
  2. ALL male offspring of an affected male are affected (because fathers give their Y chromosomes to their sons)
  3. DOES NOT skip generations.
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7
Q

What phase does DNA replication occur in?

A

S phase.

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8
Q

What happens in Prophase?

A

Chromosomes condense
Each chromosome = 2x chromatids
Mitotic spindle forms
(Prophase 1 of meiosis = homologues lay side by side, crossing over)

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9
Q

What happens in Metaphase?

A

Chromosomes line up on metaphase plate

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10
Q

What happens in Anaphase?

A

Sister chromatids separate and move toward opposite poles

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11
Q

What happens in Telophase?

A

Chromosomes arrive at spindle poles
Nuclear membrane re-forms
Chromosomes relax

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12
Q

What is the correct order of stages in the cell cycle?

A
  1. G0
  2. G1
  3. S
  4. G2
  5. Prophase
  6. Pormetaphase
  7. Metaphase
  8. Anaphase
  9. Telophase
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13
Q

What happens in Prometaphase?

A

Nuclear membrane disintegrates

Microtubules attach to chromatids

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14
Q

Which of the following events take place in Meiosis 2 but not Meiosis 1?

a) Crossing over
b) Contraction of chromosomes
c) Separation of homologous chromosomes
d) Separation of chromatids

A

d) Separation of chromatids

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15
Q

If genes A and B are linked, what is the maximum percentage of recombinant gametes that can be produced during gametogenesis?

a) 0%
b) 25%
c) 50%
d) 75%
e) 100%

A

c) 50%

Because only one chromatid is involved in crossing over which means 50% of the chromosomes will be parental

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16
Q

For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because:

a) a test cross between a homozygote and heterozygote produces 1/2 heterozygous and 1/2 homozygous progeny
b) the frequency of recombination is always 50%
c) each crossover takes place between only two of the four chromatids of a homologous pair
d) crossovers occur in about 50% of meiosis

A

c) each crossover takes place between only two of the four chromatids of a homologous pair.

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17
Q

Consider the following two-point testcross from AB/ab x ab/ab.

  • 37% dominant at both loci AB/ab
  • 37% recessive at both loci ab/ab
  • 13% dom’ at 1st & rec’ at 2nd Ab/ab
  • 13% rec’ at 1st & dom’ at 2nd aB/ab

What is the amount of map units between loci A and B (or a and b)?

A

26 map units because there is a 26% gamete recombination.

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18
Q

Aa/Bb x aa/bb produces:

  • 10 AaBb
  • 40 Aabb
  • 40 aaBb
  • 10 aabb
  1. Are the alleles in coupling or repulsion?
  2. How far apart are the linked alleles?
A
  1. Repulsion

2. 20 centimorgans (20 map units)

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19
Q

What is the difference between a genetic map and a physical map?

A

Genetic map is a map of linked genes on a chromosome which is derived from the recombination seen in crosses between those genes. The distance unit we use in genetic maps are called map units or centimorgans.
There is a rough relationship between the genetic map and physical map but its not a hard and fast one because recombination hot spots occur in chromosomes (some have more than others, sex of species can affect amount of crossovers).

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20
Q

For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because:

a) A testcross between a homozygote and heterozygote produces 1/2 heterozygous and 1/2 homozygous progeny.
b) The frequency of recombination is always 50%.
c) Each crossover takes place between only two of the four chromatids of a homologous pair.
d) Crossovers take place in about 50% of meioses.

A

c) Each crossover takes place between only two of the four chromatids of a homologous pair.

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21
Q

The following testcross produces the progeny shown:

AaBb x aabb
           |
           |
- 10% AaBb
- 10% aabb
- 40% Aabb
- 40% aaBb

Were the A and B alleles in the AaBb parent in coupling or in repulsion?

A

Repulsion (Because parental alleles were in lowest percentage in progeny)

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22
Q

True or False?

The more DNA an organism has, the more complex the organism.

A

False. Some lillies have more DNA than humans.

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23
Q

What is DNA’s primary level of structure?

A

The sequence of nucleotides

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24
Q

What is DNA’s secondary level of structure?

A

The double helix

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25
Q

What is DNA’s tertiary level of structure?

A

Chromatin, DNA and proteins.

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26
Q

The antiparallel nature of DNA refers to:

a) Its charged phosphate groups.
b) The pairing of bases on one strand with bases on the other strand.
c) The formation of H bonds between bases from opposite strands.
d) The opposite direction of the two strands of nucleotides.

A

D

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27
Q

A DNA molecule 300bp long has 20 complete rotations. This DNA molecule is:

a) Positively supercoiled
b) Negatively supercoiled
c) Relaxed

A

b) Negatively supercoiled because for every rotation, there is MORE than 10 base pairs, so it is spread out more than usual.

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28
Q

Neutralizing their positive charges would have which effect on the histone proteins?

a) They would bind the DNA more tightly.
b) They would separate from the DNA.
c) They would no longer be attracted to each other.
d) They would cause supercoiling of the DNA.

A

b) because the histones are positively charged, DNA is negatively charged. If you neutralise the charge of the histone, they’d not be attracted anymore and they’d separate.

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29
Q

Describe the Griffith experiment.

A 
- 4 flasks:
1 with virulent bacteria
1 with harmless bacteria
1 with heat killed virulent bacteria
1 with heat killed virulent AND alive harmless bacteria
  • Shows that a substance in the heat killed virulent bacteria genetically transformed the originally harmless type IIR bacteria into live, virulent type IIIS bacteria.
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30
Q

Describe the Avery, MacLeod and McCarty experiment

A 
Samples of the heat killed virulent bacteria from Griffith’s experiment were treated with enzymes that destroy:
- RNA
- Proteins
- DNA
respectively.

Then these treated samples were added to samples of the harmless bacteria used in Griffith’s experiments.

Only the sample which had the DNA destroyed had UNCHANGED harmless bacteria which showed that DNA was the transforming substance in the experiment.

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31
Q

Describe the Hershy and Chase experiment

A

Demonstrated that DNA (not protein) carries genetic information in bacteriophages.
Bacteriophages were used to demonstrate that DNA is the genetic material.
Bacteriophages = A DNA molecule surrounded by a protein coat.
When bacteriophages attack bacteria, they attach to the surface and inject DNA into the bacterial cell, the protein coat remains on the outside of the cell.
FIRST EXPERIMENT
1. Phage produced in a medium containing 35S radioactively labeled amino acids. So phages had 35S labeled proteins but no label in DNA.
2. Phage attack bacteria & inject DNA but labeled coat stayed outside cell.
3. Shaking removed protein coats from cell but the shaking didn’t interfere with DNA reproduction inside cell.

SECOND EXPERIMENT
Same thing was done but with 32P labeled deoxyribonucleotides.
When the phage reproduced inside cells the labeled DNA was inside but the protein wasn’t labeled.

Second experiment showed that the DNA was the one that was transferred from the “parent” phages to create the next generation and not the protein coat.

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32
Q

Describe the Watson and Crick experiment

A

Using a technique called X-ray diffraction, in which X-rays beamed at a molecule are reflected in specific patterns that reveal aspects of the structure of the molecule, Rosalind Franklin was able to take “pictures” of the DNA structure.

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33
Q

What do single stranded binding proteins (SSBPs) do?

A

Provide stability while the helix is unwinding so entire molecule doesn’t unwind all at once.

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34
Q

What does DNA helicase do?

A

Unwids the double stranded DNA by breaking hydrogen bonds.

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35
Q

What do Initiator proteins do?

A

Bind to origin of replication and wunwinds a short stretch of DNA allowing helicase and SSBPs to bind.

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36
Q

What does DNA gyrase do?

A

Relieves strain/torsion ahead of the replication fork that results from unwinding.

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37
Q

How many RNA polymerases do eukaryotes have?

A

5

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38
Q

How many RNA polymerases do prokaryotes have?

A

1

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39
Q

What does Topoisomerase do?

A

Its an enzyme that adds or removes rotations in a DNA helix by temporarily breaking nucleotide strands; controls the degree of DNA supercoiling.

40
Q

What do single strand binding proteins (SSBPs) do?

A

After helicase has unwound DNA, SSBPs attach tightly to exposed single strand of DNA. They protect nucleotide chains and prevent hairpins from forming that interfere with replication.

41
Q

What does DNA Ligase do?

A

Catalyzes the formation of phosphodiester bonds after primers have been removed & seals breaks in sugar-phosphate backbone of Okazaki fragments.

42
Q

What is licensing of DNA replication?

A

Eukaryotic cells have thousands of “origin sites” so that their genome can be replicated quickly. So eukaryotic cells have replication licensing factors to ensure the precise replication of DNA and that it’s not replicated multiple times.

43
Q

What is the “One gene, one enzyme” hypothesis?

A

The idea that genes that function by encoding enzymes & each gene encodes a separate enzyme.

Many genes encode proteins that AREN’T enzymes, so more generally their idea was that each gene encodes a protein.

When research showed that some proteins = >1 polypeptide chain and different polypeptide chains are encoded by separate genes, the model was modified to “One gene, one polypeptide” hypothesis.

44
Q

What are the 4 stages of protein synthesis?

A

1) tRNA charging
2) Initiation
3) Elongation
4) Termination

45
Q

Elongation requires…

A

1) 70S complex
2) tRNAs charged with their amino acids
3) Several elongation factors
4) GTP

46
Q

What are Chargaff’s Rules?

A

Within each species, there is some regularity in the ratios of the bases:

  • The amount of adenine is always equal to the amount of Thymine ( A=T)
  • The amount of Guanine is always equal to the amount of Cytosine (G=C)
47
Q

Approximately how many base pairs of DNA are wound around a single histone?

A

About 200bp

48
Q

What is the start codon and what amino acid does it code for?

A

AUG

Methionine

49
Q

What are the 3 stop codons?

A

UAA
UGA
UAG

50
Q

Describe the Beadle and Tatum experiment?

A

Neurospora is a fungi which can create its own amino acids (all 20).

  • These guys created mutant neurospora where the genes for encoding amino acids were damaged by puttin g neurospora into medium and xraying to mutate.
  • Many spore samples were grown in minimal medium. The fungi with autotrophic mutations would not grow in minimal medium (because it would need the amino acid its missing to flourish).
  • The spores from this mutant fungi were then grown in 20 different test tubes, each with a different amino acid in it.
  • The test tube where the mutant fungi grows tells you the amino acid gene which is defective because it is only able to grow when that amino acid is present (It can make all of the other amino acids)
51
Q

Describe the Srb and Horowitz experiment

A

Arginine pathway:
Precursor compound –> Enzyme A (Gene A) –> Ornithine –> Enzyme B (Gene B) –> Citrulline –> Enyzyme C (Gene C) –> Arginine.

They extended the Beadle and Tatum study to look for the biochemical pathway of the synthesis of arginine and other amino acids using neurospora as well.

  • They took spores of different mutant neurospora who’s growth required arginine and put them in minimal medium and minimal medium with a supplement.
  • 3 groups:
    1. Supplemented with ornithine, citrulline AND arginine. Group 1 mutants grew so the mutation blocks a step PRIOR to the synthesis of ornithine, citruline and arginine. So they lack enzyme A.
    2. Supplemented with citrulline and arginine, NO ornithine. Group 2 mutants grew only from Citrulline on so they lack enzyme B.
    3. Supplemented with arginine only. Group 3 mutants only grew on arginine supplemented medium which means they lack enzyme C.
52
Q

What is a base substitution mutation?

A

The simplest type.
Alteration of a single nucleotide in the DNA.
Two types:
1. Transition (Purine replaced by different purine/pyrimidine replaced by different pyrimidine)
2. Transversion (Purine replaced by pyrimidine or vice versa)

53
Q

What are the two purines?

A

Adenine and Guanine

Two cyclic structures

54
Q

What are the two pyrimidines?

A

Thymine and Cytosine (Uracil instead of Thymine for RNA)

One cyclic structure

55
Q

What are indel mutations?

A

Insertions or deletions in which either the addition or removal of one or more nucleotide pairs occurs. It CAN lead to frameshift mutations but not always.

56
Q

What are expanding nucleotide repeat mutations?

A

Mutations in which the number of copies of a set of nucleotides increases.
The number of copies of the nucleotide repeat often correlates with the severity or age of onset of the disease.

57
Q

Name the 7 types of base substitution mutations.

A
  1. Missense
  2. Nonsense
  3. Silent mutations
  4. Neutral mutations
  5. Loss of function
  6. Gain of function
  7. Conditional mutation
58
Q

What is the difference between a reverse mutation and a suppressor mutation?

A

A reverse mutation means the mutated site changes back into the original wild type sequence.
A suppressor mutation occurs at a completely different site and suppresses the effect of the other mutation… so the individual is a double mutant.

59
Q

What is mismatch repair?

A

Enzymes cut out a section of newly synthesised strand and fill in the gap using the original DNA strand as a template.

60
Q

How do mismatch repair enzymes know which strand is old and which is new?

A

The old strand has methyl groups and the enzymes recognise this.

61
Q

What is direct repair?

A

Doesn’t replace altered nucleotides, but instead, changes them back to original (correct) structures. (Removal of methyl group).

62
Q

What is base-excision repair?

A

Modified base is first excised, then entire nucleotide is replaced.

63
Q

What is nucleotide-excision repair?

A

Removes bulky DNA lesions (such as pyrimidine dimers) that distort the double helix.

64
Q

What do endonuclease enzymes do?

A

They cut DNA at specific palindromic sequences.

65
Q

A contig is________?

a) A set of molecular markers used in genetic mapping
b) A set of overlapping fragments that form a continuous stretch of DNA
c) A set of fragments generated by a restriction enzyme
d) A small DNA fragment used in sequencing

A

b)

66
Q

How does methylation suppress gene expression?

A

The methyl group of 5-methylcytosine sits within the major groove of the DNA which is recognised by binding proteins. The presence of them in major grooves stop transcription factors from binding.

67
Q

Ras proteins are activated when they:

a) bind GTP
b) release GTP
c) bind GDP
d) undergo acetylation

A

a)

68
Q

What would be the most likely effect of a mutation that caused cyclin B to be unable to bind to CDK?

a) Cells pass through the G2/M checkpoint and enter mitosis even when DNA has not been replicated.
b) Cells never pass through the G1/S checkpoint.
c) Cells pass through mitosis more quickly than unmutated cells do.
d) Cells fail to pass through the G2/M checkpoint and do not enter mitosis.

A

d)

69
Q

What are cyclin-dependent kinases and what do they do?

A

They are enzymes that add phosphate groups to other proteins and control key events of the cell cycle.
Sometimes this phsophorylation ACTIVATES the other protein and sometimes they INACTIVATE.
CDKs are only functional when they associate with another protein called Cyclin.

70
Q

During transcription, the RNA polymerase read the template DNA strand in the ___(a)___ direction, but the mRNA is formed in the ___(b)___ direction.

A

a) 3’→5’

b) 5’→3’

71
Q

The ribosome reads the mRNA in the ______ direction.

A

5’→3’

72
Q

What is the order of steps in translation?

A

Initiation
Elongation
Termination

73
Q

What are the necessary components of translation initiation?

A
  • mRNA
  • Ribosomal subunits
  • Initiation factors (Eg. IF-3)
  • Initiator tRNA (fMet-tRNA)
  • GTP (energy source)
74
Q

What are the necessary components of translation elongation?

A
  • A site ]
  • P site ] – on ribosome
  • E site ]
  • 70S complex
  • Elongation factor (EF-Tu)
  • GTP (energy source)
  • tRNA charged with AA.
75
Q

What are the necessary components of translation termination?

A
  • Release factors (RF1, RF2)

- GTP (energy source)

76
Q

What happens if no 5’ cap is formed on pre-mRNA?

A
  • It will affect the removal of introns
  • It will be less stable & will quickly degrade.
  • If it travels to cytoplasm, ribosome won’t recognise mRNA without 5’ cap, THEN it will degrade.
77
Q

What happens if introns are not removed from pre-mRNA

A

mRNA won’t be able to move out of nucleus & it will be degraded.

78
Q

What happens if no 3’ end is added on pre-mRNA?

A
  • No poly-A tail will be created

- Splicing will still occur but will be degraded quickly by cellular enzymes.

79
Q

What are the functions of a 5’ cap?

A
  • Added rapidly after the initiation of transcription.
  • Cap binding proteins recognise & attach to it
  • It is the attachment site for the ribosome
  • Increases stability of mRNA
  • Influences removal of introns.
80
Q

What are the functions of a poly-A tail?

A
  • Added AFTER transcription
  • Increases stability
  • Gives mRNA more time to be translated before its degraded.
  • Facilitates the attachment of the ribosome to the mRNA (flicks around and helps attach)
  • Helps export mRNA out of nucleus, into cytoplasm
81
Q

What are the three stop codons?

A

UAA
UAG
UGA

82
Q

What are the 4 stages of protein synthesis?

A
  1. tRNA charging - tRNAs bind to AAs
  2. Initiation - Components necessary for translation are assembled at the ribosome
  3. Elongation - AAs are joined, one at a time to the growing polypeptide chain.
  4. Protein synthesis halts @termination codon & translation components are released from ribosome.
83
Q

What part of AA binds to acceptor of tRNA?

A

The COO- group on AA binds to the adenine nucleotide of the CCA at the 3’ end of tRNA.

84
Q

What are the components necessary for protein synthesis?

A
  • mRNA
  • Sml & Lge sub units of ribosome
  • Set of 3 proteins called “initiation factors”
  • Initiator tRNA with N-formylmethionine attached (fMet-tRNA)
  • Guanosine triphosphate (GTP)
85
Q

30S initiation complex contains….?

A
  • Sml subunit of ribosome
  • mRNA
  • Initiator tRNA with AA (fMet-tRNA)
  • 1 molecule of GTP
  • Several initiation factors.
86
Q

What is 70S initiation complex?

A

When large subunit of ribosome joins the 30S initiation complex it is called the 70S initiation complex

87
Q

What does the A in A site stand for?

A

Aminoacyl

88
Q

What does the P in P site stand for?

A

Peptidyl

89
Q

What does the E in E site stand for?

A

Exit

90
Q

What are the 3 steps of elongation?

A
  1. Charged tRNA binds to A site
  2. Formation of peptide bond between AAs that are attached to the tRNAs in P & A sites.
  3. Translocation - the movement of the ribosome down the mRNA in 5’-3’ directions. (This step positions ribosome over the next codon)
91
Q

Name 3 molecular processes known to lead to epigenetic changes.

A 
1. DNA methylation
 Eg. Methyl group added to cytosine
2. Alterations in chromatin structure
 Eg. Histone protein modification
3. RNAs (like lncRNA)
 Eg. X inactivation
92
Q

Oncogenes

A

Mutated proto-oncogenes
Stimulatory
“Accelerators” in cell division
Dominant

93
Q

Tumour Suppressor Genes

A

Inhibitory
“Brakes” in cell division
Recessive but also stimulatory
Normally produce cell-division inhibiting factors

94
Q

How does the multistep model of cancer explain the observation that sporadic cases of retinoblastoma usually appear in only one eye, whereas inherited forms of the cancer appear in both eyes?

A

Retinoblastoma results from at least two separate genetic defects, both of which are necessary for cancer to develop. In sporadic cases, two successive mutations must occur in a single cell, which is unlikely and therefore typically affects only one eye. In people who have inherited one of the two required mutations, every cell contains this mutation and so a single additional mutation is all that is required for cancer to develop. Given the millions of cells in each eye, there is a high probability that the 2nd mutation will occur in at least one cell of each eye, producing tumours in both eyes and the inheritance of this type of retinoblastoma.

95
Q

How can chromosome deletions cause cancer?

A

Deletions can cause the loss of one or more tumour-suppressor genes. Tumour suppressor genes suppress the cell cycle so if one of these genes is lost, cell proliferation increases.

96
Q

How can chromosome inversions & translocations cause cancer?

A

They can inactivate tumour-suppressor genes if the chromosomal break points are within the TSG

Translocation can also place a proto-oncogene in a new location where it is activated by different regulatory sequences.

97
Q

How do viruses cause cancer?

A
  • They have strong promoters and inject their own DNA into host cells. If a virus injects its DNA and promoter near a proto-oncogene, the virus promoter can drive overexpression of a proto-oncogene.
    The integration of a virus can also inactivate TSGs.
    A few viruses can carry altered versions of host proto-oncogenes.

Human Molecular Genetics (3 decks)

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