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Phase 1 > IMMS 1: Genetics > Flashcards

IMMS 1: Genetics Flashcards

DNA; Autosomal inheritance; X-linked inheritance; Multifactorial & non-Mendelian inheritance; DNA mutations; Genetic testing & society

1
Q

What is a macromolecule?

A

A large complex molecule, often polymers of smaller molecules (monomers). Examples of macromolecules include DNA, proteins, carbohydrates, and lipids.

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2
Q

What is a heterogenous structure?

A

Made up of different types of elements e.g. DNA, haemoglobin.

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3
Q

Why is water polar but uncharged?

A

Water molecules are polar because they have an uneven distribution of charge: oxygen end = negative, hydrogen end = positive. Overall they have no net charge.

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4
Q

What is the chemical structure of a carbohydrate?

A

Chain of carbon with attached water molecule.
Cn(H2O)n

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5
Q

What is a disaccharide?

A

Two monosaccharides (carbohydrates) linked together.

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6
Q

What is the difference between an oligosaccharide and a polysaccharide?

A

Oligosaccharide = 3-10 monosaccharides.
Polysaccharide = more than 10 monosaccharides.

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7
Q

What is an isomer?

A

Molecules made up of the same atoms but have a different structure.

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8
Q

What is a hexose?

A

A monosaccharide with 6 carbon atoms. E.g. Glucose.

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9
Q

What is a tetrose?

A

A monosaccharide with 4 carbon atoms.

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10
Q

Name two ways to classify a monosaccharide.

A
  1. Number of carbon atoms. E.g. Triose = 3 carbon atoms.
  2. Type of carbonyl group (if carbonyl group is a ketone, monosaccharide is a ketose, if an aldehyde, it’s an aldose).
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11
Q

What is a carbonyl group?

A

A carbon atom double bonded to an oxygen atom.

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12
Q

What is the difference between a ketone and an aldehyde?

A

An aldehyde is a carbonyl group at the end of the carbon backbone chain. A ketone is a carbonyl group somewhere in the middle of the carbon backbone chain.

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13
Q

What is a glycoside?

A

A carbohydrate bound to another functional group with a glycosidic bond.

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14
Q

What sort of bond joins monosaccharides to make di/oligo/polysaccharides?

A

O-gylcosidic bond (bond via oxygen atom)

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15
Q

What bond joins the nitrogenous base and pentose sugar in nucleotides?

A

N-glycosidic bond (bond via nitrogen atom)

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16
Q

What are the three components of a nucleotide?

A

Nitrogenous base (e.g. adenine), pentose sugar (deoxyribose in DNA, ribose in RNA), phosphate group.

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17
Q

Name the purines.

A

Adenine and guanine.

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18
Q

Name the pyrimidines.

A

Cytosine and thymine (uracil in RNA).

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19
Q

Which nitrogenous bases are joined by 2 hydrogen bonds?

A

Adenine and thymine (uracil in RNA).

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20
Q

Which nitrogenous bases are joined by 3 hydrogen bonds?

A

Cytosine and guanine.

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21
Q

How are nucleotides joined together to form DNA?

A

Polymerised by covalent bonds into long chains.

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22
Q

What does antiparallel mean in relation to DNA?

A

DNA alpha helix is made up of two antiparallel strands. One running 5’ to 3’ and the other in the opposite direction 3’ to 5’ (which way up the pentose sugar is) this causes the twisting of the two strands.

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23
Q

How is DNA supercoiled to fit into the nucleus?

A

Antiparallel double helix wrapped around histone proteins to form a nucleosome. Nucleosomes fold together to make a chromatin fibre. Chromatin is tightly coiled together to form a chromosome.

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24
Q

How long does DNA replication take?

A

8-12 hours.

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25
Q

What enzyme unwinds the double helix in DNA replication?

A

Topoisomerase

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26
Q

What is the function of DNA helicase?

A

Enzyme which separates double-stranded nucleic acids into single strands in DNA replication, repair, and transcription.

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27
Q

Which enzyme reads the DNA strand for replication and what are its other functions?

A

DNA polymerase alpha. Reads 3’ to 5’, prints 5’ to 3’. Proof-reads and edits - repeats replication if wrong.

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28
Q

What are Okazaki fragments?

A

The sections of the lagging DNA strand which has to be replicated in these Okazaki fragment sections, because DNA polymerase alpha only reads in one direction and DNA is antiparallel.

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29
Q

What is the main function of primase?

A

Synthesises short RNA sequences called RNA primers. These primers act as starting point for the synthesis of Okazaki fragments. DNA polymerase later removes them and fills in the gaps with DNA.

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30
Q

What enzyme joins the Okazaki fragments?

A

Ligase

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31
Q

What is the difference between mitosis and meiosis?

A

In mitosis the cell divides to produce 2 genetically identical daughter cells each containing 46 chromosomes. Mitosis occurs for growth in tissues and to replace dead cells.

Meiosis only occurs in gametes. Cell divides twice and produces 4 genetically diverse haploid daughter cells, each only contain 23 chromosomes. Meiosis is NOT a cycle.

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32
Q

What does mitotically active mean?

A

Tissue where there is high cell turnover e.g. in bone marrow, epithelial lining of gut, skin.

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33
Q

What is the difference between labile cells, stable cells, and permanent cells?

A

Labile cells = constantly in the cell cycle, repeatedly undergo mitosis throughout their life e.g. epidermis.

Stable cells = spend most of their existence outside the cell cycle in G0 but can be induced to enter the cell cycle and undergo mitosis. E.g. hepatocytes.

Permanent cells = unable to replicate in postnatal life. Do not undergo mitosis and remain in G0. E.g. neurons, erythrocytes.

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34
Q

Is interphase part of mitosis?

A

No, it is part of the cell cycle which occurs before mitosis. The majority of the cell cycle is interphase.

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35
Q

What are the stages of interphase?

A

G1 = cell growth.
S = DNA synthesis.
G2 = further cell growth.

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36
Q

What is DNA synthesis?

A

The step of DNA replication where DNA polymerase adds complementary nucleotides to duplicate DNA into 2 chromatids joined at centromere. The centrosome is also replicated in DNA synthesis.

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37
Q

Name the stages of mitosis in order.

A
  1. PROPHASE
  2. PRO-METAPHASE
  3. METAPHASE
  4. ANAPHASE
  5. TELOPHASE
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38
Q

What happens in prophase?

A

Chromatin condenses into chromosomes. Centrosomes move to opposite sides of the cell. Microtubules assemble between them - this is the mitotic spindle forming.

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39
Q

What happens in pro-metaphase?

A

Nuclear membrane breaks down. Microtubules of mitotic spindle invade nuclear space. Chromatids attach to microtubules at centromeres.

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40
Q

What happens in anaphase?

A

Sister chromatids separate and are pulled to opposite poles of the cell as microtubules depolymerise and shorten.

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41
Q

In which phase of mitosis do the chromatids line up on equatorial plane?

A

Metaphase.

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42
Q

In which phase of mitosis do the nuclear membranes reform, and what else happens in this phase?

A

Telophase.
In telophase the nuclear membranes reform and chromosomes unfold into chromatin.

43
Q

What is cytokinesis?

A

Cytokinesis is the process where the cell membrane develops a cleavage furrow, which increases to the point at which the cell and cytoplasm is divided into two. Cytokinesis might start to occur in anaphase or telophase and completes shortly after telophase.

44
Q

What is the relationship between chromatin, chromosomes, and chromatids?

A

Chromatin condenses to form chromosomes which split into two identical strands called chromatids

45
Q

What is a karyotype?

A

The number, size and shape of the chromosomes of an individual. The term also describes a photomicrograph of an individual’s chromosomes, arranged in descending order of size (but strictly, this is a karyogram).

46
Q

Taxol is a drug which stops the mitotic spindle from developing. Why would this be helpful in treating cancer?

A

If the mitotic spindle doesn’t develop then mitosis won’t be completed, the cell can’t divide, so the cancer cannot continue growing.

47
Q

In what phase of meiosis does crossover occur and how does it happen?

A

Prophase 1, when homologous pairs form. Non-sister chromatids of homologous pairs break and reconnect to each other, causing exchange of genetic material.

48
Q

What are primordial germ cells?

A

Embryonic stem cells which differentiate into spermatogonia or oogonia.

49
Q

How many sperm cells are in one ejaculate?

A

100-200 million cells!

50
Q

How many days does spermatogenesis take and what does it involve?

A

60-65 days, spermatogonia undergo meiosis to become spermatozoa. Process starts in puberty and millions of sperm cells are continuously produced.

51
Q

What is the difference between spermatogenesis and oogenesis?

A

Spermatogenesis begins at puberty and the cytoplasm divides equally to create 4 haploid daughter cells.
Oogenesis begins in the foetus, and the cytoplasm divides unequally to create 1 haploid daughter cell and 2 polar bodies which undergo apoptosis.

52
Q

When does oogenesis complete meiosis-II?

A

At fertilisation.

53
Q

What is a homologous pair of chromosomes?

A

A set of one maternal and one paternal chromosome which pair up with each other during meiosis-I.

54
Q

What is the function of tRNA?

A

tRNA has an amino acid at 3’ end, and an anticodon which corresponds to the codon on mRNA for the specific amino acid it caries.

55
Q

What is a polypeptide?

A

Chain of amino acids joined by peptide bonds (type of covalent bond) between carboxyl group and amino group. Primary structure of a protein.

56
Q

What is splicing?

A

Removal of introns (non-coding sections) from mRNA so only exons (coding sections) remain. Occurs inside the nucleus.

57
Q

What is the codon for methionine and why is it important?

A

Adenine, Uracil, Guanine (AUG). The START codon for all proteins.

58
Q

Why is the genetic code redundant and non-ambiguous?

A

There are multiple codons for the same amino acid. Each codon only codes for one amino acid.

59
Q

How many amino acids are in a protein?

A

Can be anywhere between 10 and 1000s!

60
Q

Why is the 3D shape of a protein important?

A

The shape/structure affects the protein’s function.

61
Q

What bonds form the secondary structure of a protein?

A

Hydrogen bonds.

62
Q

Name the two types of secondary protein structure.

A

Alpha helix spiral, where side chains face outwards. Beta sheet, can be folded or straight.

63
Q

What bonds can be involved in the tertiary structure of a protein?

A

Electrostatic, hydrophobic, hydrogen, covalent (disulphide bonds between cysteine side chains). All can be involved to create the 3D structure of a protein.

64
Q

What are Van der Waals forces?

A

Weak electrostatic forces which attract neutral molecules to one another.

65
Q

Do all proteins have a quaternary structure?

A

No, only proteins made up of multiple subunits have a quaternary structure.

66
Q

What does it mean if a fatty acid is unsaturated?

A

There’s at least one double bond between carbon atoms.

67
Q

In which phase does ring mitosis occur?

A

Anaphase, when chromosomes are being pulled to opposite sides of the cell. Visible on light microscopy.

67
Q

What is the relationship between melting point and degrees of unsaturation in a fatty acid?

A

The melting point decreases with increasing degrees of unsaturation. For example, at room temperature butter is solid, oil is liquid.

68
Q

What is the 3’ tail on mRNA made of?

A

Adenine, repeating 50-250 times. Added during splicing.

69
Q

What is allelic heterogeneity?

A

Different mutations at the same genetic locus result in the same or very similar phenotypes. E.g. a range of different mutations in the same gene can cause Duchenne muscular dystrophy.

70
Q

Huntington’s disease exhibits anticipation. What does this mean?

A

Signs/symptoms of the genetic condition become more severe and appear at an earlier age in successive generations. In Huntington’s is caused by trinucleotide repeat expansion. The number of repeats can increase with each generation, and the severity of the disorder worsens.

71
Q

What is “regression towards the mean” in genetics?

A

Statistical phenomenon where offspring tend to be close to the average population than their parents. E.g. two parents with high IQ are more likely to have a child of average IQ.

72
Q

What affects a person’s phenotype?

A

A combination of their genotype and environmental factors.

73
Q

Which are the Robertsonian (acrocentric) chromosomes and what do they have in common?

A

13,14,15,21,22. All have very short p arm with similar repetitive DNA sequences that predispose to their fusion e.g. in Robertsonian translocation the whole of one acrocentric chromosome is joined end-to-end with another.

74
Q

Which chromosome abnormality is more likely to cause disease, deletion or duplication?

A

Deletion.

75
Q

Why might chromosomal abnormalities cause disease?

A

Many genes are “dosage sensitive” - they need 100% of the signal (made by proteins) to be healthy. Deletion/duplication means the cell produces a different amount of that protein, so can affect development/gene function.

76
Q

Why does unbalanced translocation cause disease?

A

There is loss/gain of genetic material.

77
Q

How many genomes does the human body have and what are they?

A
  1. Germline (sperm/eggs, heritable).
  2. Somatic (in every other tissue, not heritable).
  3. Mitochondrial (heritable).
78
Q

What is mutagenesis ?

A

Alteration to genomic code by exposure to a mutagen, either pre or postnatally. e.g. smoking -> damage DNA in lining of lungs -> lung cancer. Mutagens can cause damage to DNA and then act in a teratogenic manner.

79
Q

What is teratogenesis?

A

Damaging effect on embryonic/foetal development by exposure to teratogen. Not necessarily causing damage to DNA. Teratogen can also be a mutagen e.g. ionising radiation might cause developmental issues in foetus but also cause damage to DNA in mother causing mutations -> cancer.

80
Q

What is the difference between a malformation and a deformation?

A

A malformation is an intrinsic issue with the development of organ/tissue, commonly genetic. Minor malformations are common, but if have multiple minor malformations (e.g. skin change) or a major malformation (e.g. cleft palate) then could indicate an underlying genetic condition.

A deformation is where extrinsic factors impinge upon development of organ, less commonly genetic e.g. not enough amniotic fluid, causes compression, affects development.

81
Q

How might you identify an autosomal dominant disorder from a pedigree?

A

Males & females are affected equally.
Multiple generations are affected.
Affected males can have affected sons.
50% recurrent risk.

82
Q

What is the term for when the same gene variant has a wide range of symptoms or physical features?

A

Variable expressivity. Only occurs in autosomal dominant conditions.

83
Q

Why might someone with an autosomal dominant disorder variant not develop the disease?

A

The variant might have incomplete penetrance, or could be sex-limiting. For example, a variant causing ovarian cancer would still be present in a male but the variant would not be expressed.

84
Q

Why are sperm cells more likely to be the cause of de novo mutations?

A

Sperm cells are being made continuously. DNA is copied less accurately as males age, which increases the likelihood of a sperm cell having a de novo mutation.

85
Q

How might you identify an autosomal recessive disorder from a pedigree?

A

Males & females are affected equally.
Often only see disease in single generation.
Affected males can have affected sons.
25% recurrent risk.
Increased risk in consanguineous mating.

86
Q

What is the carrier frequency of cystic fibrosis in Northern European population?

A

1 in 25.

87
Q

Why is somatic mosaicism not detected in normal genetic testing?

A

Because, by definition of mosaicism, not all cells have the variant. The variant is only present in the particular tissue e.g. cancer.

88
Q

What is heteroplasmy?

A

Some mitochondria in a cell have a mutation. Other mitochondria might compensate to prevent disease.

89
Q

Why can a non-synonymous change cause disease?

A

A missense (code is for wrong amino acid), can cause loss of function by changing protein structure. Change from amino acid to a premature STOP -> nonsense mediated decay, mRNA is destroyed.

90
Q

What is the difference between in-frame and out-of-frame insertion/deletion?

A

In-frame insertion/deletion will always be a multiple of 3 nucleotides, lose/gain single amino acid.
Out-of-frame insertion/deletion will not be divisible by 3 and leads to frameshift mutation. This is more likely to cause disease. Can lead to a premature STOP codon -> nonsense mediated decay.

91
Q

What is a splice site mutation?

A

Splice sites are mutated, intron gets retained, faulty protein is formed.

92
Q

What are copy number variants?

A

Phenomenon where sections of the genome are repeated and the number of repeats in the genome varies between individuals. Duplication/deletion affecting large number of base pairs.

93
Q

How might you identify an x-linked disorder on a pedigree?

A

Females are less affected.
Affected males cannot have affected sons with an unaffected female in x-linked dominant.
Unaffected males cannot have affected daughters in x-linked recessive.

94
Q

What is lyonisation?

A

Random x-inactivation where female cells randomly inactivate one of their X-chromosomes. Normally 50-50 which x-chromosome is inactivated.

95
Q

What is the difference between locus heterogeneity and allelic heterogeneity?

A

Locus heterogeneity is where variants in different genes cause the same disease.
Allelic heterogeneity is where multiple variants in the same gene can cause the same disease.

96
Q

Proteins can form a variety of different structures. Alpha helixes and beta sheets are examples of which type of protein structure?

A

Secondary structure

97
Q

DNA replication involves several stages. Which enzyme causes the double helix to unzip?

A

Helicase

98
Q

What is the basic structure of a ribosome?

A

One large and one small subunit.

99
Q

Where are ribosomes assembled?

A

In the nucleolus, inside the nucleus.

100
Q

DNA replication is dependent on the action of various enzymes. Which enzyme unwinds supercoiled DNA?

A

Topoisomerase

101
Q

How does deoxygenated sickle cell haemoglobin cause sickling of RBCs?

A

Deoxygenated HbS polymerises and binds to the cell cytoskeleton which distorts the normal biconcave disc shape into a sickle shape.

102
Q

Sickle cell disease can be treated with hydroxyurea. Describe the action of hydroxyurea.

A

Increases the synthesis of HbF (foetal Hb)

103
Q

mRNA plays a key role in protein formation. Which process describes how mRNA specifies the amino acids required for protein formation?

A

Translation

Phase 1 (16 decks)

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