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Year One - Principles of Disease > Genetics > Flashcards

Genetics Flashcards

1
Q

What do nucleotides consist of?

A

A sugar, a base and a phosphate group

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2
Q

Why are bases flat?

A

Allows them to be stacked up in the centre of the helix

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3
Q

What direction to DNA strands?

A

Antiparallel - one runs from 5’ to 3’ and the other runs from 3’ to 5’

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4
Q

What is the major groove in DNA?

A

Where the backbones are far apart

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5
Q

What is the minor groove in DNA?

A

Where the backbones are close together

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6
Q

What is more important, the minor or major groove in DNA? Why?

A

Major groove

Where most proteins bind

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7
Q

What does it mean when we say that DNA is right-handed?

A

If you look at DNA from the end it would spiral in a clockwise (right-handed) direction

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8
Q

How are the two DNA strands linked together?

A

Complementary base-pairing

T + A

C + G

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9
Q

What bonds exist between complementary bases?

A

Hydrogen

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10
Q

Where is DNA located within the cell?

A

Nucleus

AND

Ribosomes - contain their own DNA

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11
Q

Describe the structure of the nucleus

A

Nucleolus - middle of the nucleus

Nuclear envelope - around the nucleus, contains pores which allow the passage pf molecules into and out of the nucleus

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12
Q

What are the two sections of a chromosome?

A

P section - smaller (petite)

Q section - longer

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13
Q

What are nucleosomes?

A

DNA wrapped around histone proteins

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14
Q

What are chromatin fibres?

A

Nucleosomes folded up

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15
Q

What are chromosomes?

A

Nucleosomes wrapping around one another

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16
Q

What are the two forms of chromatin?

A

Heterochromatin - highly condensed form of chromatin, contains silenced genes

Euchromatin - extended form of chromatin, contains active genes

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17
Q

What does it mean if we say that DNA is semi-conservative?

A

Means one half of each new molecule of DNA is old and the other half is new

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18
Q

What is the role of DNA polymerase in DNA replication?

A

Joins new nucleotide molecules in the new strand of DNA.

Only adds new direction to the 3’ end of the growing stand, as DNA is replicated in the 5’ to 3’ direction.

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19
Q

What is the role of ligase in DNA replication?

A

In the lagging strand, DNA polymerase joins the nucleotides into fragments, not a whole strand

Ligase comes and joint the fragments together to form one continuous strand

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20
Q

What does it mean if we say that DNA is bi-directional?

A

Two strands of DNA run in anti-parallel directions

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21
Q

What are exons?

A

Coding regions of DNA, which exit the nucleus in the form of mRNA to be coded into proteins at the ribosome

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22
Q

What are introns?

A

Non-coding regions of DNA, stay inside the nucleus as they don’t need to be coded into proteins

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23
Q

What is a codon?

A

Three bases

Codes for one amino acid or a STOP/START instruction

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24
Q

What is degeneracy?

A

Means that the amino acids can be coded by more than one codon - with the exception of methionine and tryptophan

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25
Q

What are synonyms?

A

Codons which refer tot he same amino acid

Tend to be very similar

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26
Q

What is the advantage of degeneracy?

A

Minimises the effect of genetic mutations, as alteration to the base sequences are less likely to alter the protein being coded for

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27
Q

What amino acid codes for the START codon?

A

Methionine

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28
Q

What are the three types of RNA?

A

mRNA

tRNA

rRNA

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29
Q

What is mRNA?

A

Involved in transporting the genetic code from the nucleus to the ribosome so that proton synthesis can occur. It is transcribed from DNA

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30
Q

What is tRNA?

A

Involved in linking codons to their specific amino acid at the ribosome.

Contains anticodons which are able to pair to the codons on the mRNA chain.

When this pairing occurs, the amino acid held by the tRNA molecule is joined onto the growing chain of amino acids

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31
Q

What is rRNA?

A

Component of ribosomes and essential for them to function properly

Produced in the nucleus and transported to the cytoplasm where they combine with proteins to form a ribosome

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32
Q

What is alternative splicing?

A

A process by which different sequences of the RNA produced by transcription are treated as exons and introns.

This results in different protein isoforms results from a single gene

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33
Q

What are telomeres?

A

Caps at the end of the strands of DNA that protect our chromosomes

Repetitive sequences of DNA that code for no particular genes. They prevent important genes from being deleted during cell division and DNA replication.

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34
Q

What is the end problem of DNA replication?

A

After DNA replication, each new DNA is shorter at its 5’ end than at the parental DNA’s strands 5’ end. This produces a 3’ overhand at one end of each daughter DNA strand, as some of our DNA on the 5’ strand is not replicated

Explains why telomeres are important as they are shortened from DNA, not important genes

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35
Q

What is telomerase? What is its role?

A

An enzyme that attaches to the end of a chromosome and contains a catalytic part and a built-in RNA template.

It helps add complementary RNA bases to the 3’ end of the DNA strand to elongate it and prevent an overhang. DNA polmerase then connects these RNA bases together to form a continuous strand

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36
Q

What are centromeres?

A

Join sister chromatids together to form a chromosome

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37
Q

What are kinetochores?

A

Contained within the centromere

Protein complex that binds to microtubules

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38
Q

What interaction is present between DNA and histones?

A

Ionic

DNA - negatively charged backbone

Histones - positively charged

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39
Q

Why do we package DNA into chromosomes?

A

Neutralises negative charge

DNA takes up less pace

Inactive DNA folded into inaccessible locations

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40
Q

What two techniques do we use to analyse chromosomes?

A

Karyotype

FISH

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41
Q

What is a karyotype?

A

An image of individual chromosomes

The chromosomes are ordered in size and grouped into pairs

We visualise both autosomal and sexual chromosomes

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42
Q

What are metacentric chromosomes?

A

Those which have a the centromere in the centre so that both sections are equal in length

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43
Q

What are submetacentric chromosomes?

A

Those which have the centromere slightly offset from the centre leading to a slight asymmetry in the length of the two sections

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44
Q

What are acrocentric chromosomes?

A

Those which have a centromere severely offset from the centre leading to a very long and very short section

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45
Q

What is fluorescent in situ hybridisation (FISH)?

A

Identifies where a particular gene falls within an individual’s chromosomes

We use fluorescent probes that are complementary to the geese we are tying to locate within the chromosomes

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46
Q

What are the four types of probes used in FISH?

A

Unique sequence probes

Centromeric probes

Telomeric probes

Whole chromosome probes

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47
Q

What are unique sequence probes?

A

Binds to specific small segments of certain chromosomes

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48
Q

What are centromeric probes?

A

Target the centromeric region of the particular chromosome

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49
Q

What are telomeric probes?

A

Bind to telomeres

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50
Q

What are whole chromosome probes?

A

Bind to a different sequence along the length of a given chromosome

We use multiple probes labelled with a mixture of different fluorescent dyes, able to label each chromosome its own unique colour

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51
Q

What mutations do unique sequence probes detect?

A

Deletion

Insertion

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52
Q

What mutations do whole chromosome probes detect?

A

Translocations

Rearrangements

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53
Q

What is the role of cell division?

A

Allows organisms to grow and develop

Replace dead cells

Repair tissue

54
Q

What are the three stages of cell cycle?

A

Interphase

Mitosis

Cytokinesis

55
Q

What phases are involved in interphase?

A

G1

S

G2

56
Q

What occurs during G1?

A

The cell synthesis new proteins and organelles

57
Q

What occurs during S?

A

DNA replication

58
Q

What occurs during G2?

A

The cell synthesis more proteins and organelles

Checks for any errors that occurred during the S phase

59
Q

What are the stages of mitosis?

A

Prophase - chromosomes condense, nuclear membrane disappears, the cell’s microtubules start to disassemble and assemble the spindle fibres

Metaphase - chromosomes line up along the metaphysic plate, due to the assembly and disassembly of the microtubules to form spindle fibres

Anaphase - spindle fibres attached to the kinetochores of the chromosome start to disassemble, pulling the sister chromatids apart to the opposite sides of the cell

Telophase - cell forms two daughter nuclei as the chromosomes are fully separated to opposite poles of the cell. The nuclear membrane is reformed around the two nuclei

60
Q

What occurs during cytokinesis?

A

Cytoplasm splits and we form two new daughter cells

61
Q

What is meiosis?

A

Cell division of gametes in the reproductive organs

Diploid cells in the ovaries and testes divide to form haploid egg and sperm cells

62
Q

What is the product of meiosis?

A

Four haploid cells

63
Q

What occurs during meiosis one?

A

Homologous chromosomes are separated

64
Q

What occurs during meiosis two?

A

Chromosomes are separated into chromatids

65
Q

What occurs during prophase I?

A

Chromosomes condense, then pair with their homologous chromosome to form a tetrad/

66
Q

What is crossing over?

A

Process that occurs during prophase I in meiosis.

When the homologous chromosomes pair, the inner non-sister chromatids touch each other at points called chiasmata. Chiasmata allow crossing over of genetic information between the chromosomes. This leads to the formation of recombinant chromosomes and increases variation in gametes

67
Q

What occurs during metaphase I?

A

The nuclear membrane breaks down, chromosome pairs line up along the metaphasic plate

The centrioles also start to create microtubules which extend and attach to the chromatids

68
Q

What is independent assortment?

A

Process that occurs during metaphase I in meiosis

When the chromosomes line up along the metaphasic plate, they are positioned randomly, irrespective of their parental origin. This results in new combinations of alleles and increases variation

69
Q

What occurs during anaphase I?

A

The microtubules shorten and pull on the chromosomes so that they are pulled to opposite sides of the cell

70
Q

What occurs during telophase I?

A

As the chromosomes approach opposite ends of the cell, the cell begins to divide

71
Q

What occurs during cytokinesis I?

A

The gamete mother cell fully separates into two daughter cells. Each cell has 23 chromosomes, 46 chromatids. This means that they are haploid cells.

72
Q

What occurs during prophase II?

A

Chromosomes condense

No crossing over occurs

73
Q

What occurs during metaphase II?

A

The nuclear membrane breaks down, chromosome pairs line up along the metaphasic plate

74
Q

What occurs during anaphase II?

A

The microtubules shorten and pull on the chromosomes so that the chromatids are pulled to opposite sides of the cell

75
Q

What occurs during telophase II?

A

As the chromatids approach opposite ends of the cell, the cell begins to divide

76
Q

What occurs during cytokinesis II?

A

Each cell divides into, forming four haploid cells, which have 23 chromosomes and 23 chromatids each.

77
Q

What is oogenesis?

A

Process of egg formation

78
Q

What is spermatogenesis?

A

Process of sperm formation

79
Q

Hoe does gamete formation occur in males?

A

Meiosis one occurs at puberty and all four haploid cells develop into sperm cells

80
Q

Hoe does gamete formation occur in females?

A

Meiosis one occurs in the last three months before birth but doesn’t complete

Fully completes during each menstrual stage, though only one will reach the metaphase II stage before stopping again.

After an egg is released from the ovary, it will not complete meiosis II until a sperm nucleus has entered it

81
Q

What is X-inactivation? Why does it occur

A

During embryonic development in females, one X chromosome in each cell is inactivated so the cells have a single working copy of the X chromosome genes.

Dosage compensation, ensuring that the females have ht same level of gene products as a male

Prevents harmful mutation in female cells

82
Q

What are the three types of chromosomal abnormalities?

A

Numerical

Structural

Mutational

83
Q

What are numerical chromosome abnormalities?

A

Result from whole chromosomes missing from or extra to the normal pair

84
Q

What are structural chromosome abnormalities?

A

Result from a part of an individual chromosome being missing, added or switched to another chromosome

85
Q

What are the two types of translocations?

A

Reciprocal

Robertsonian

86
Q

What are reciprocal translocations?

A

Involves breaks in two chromosomes with the formation of two new derivative chromosomes

87
Q

What are Robersonian translocations?

A

Involve the fusion of two acrocentric chromosomes

Result in no genetic material being lost

88
Q

What two arrangements do reciprocal arrangements result in?

A

Balanced

Unbalanced

89
Q

What are balanced translocations?

A

When the exchange of genetic material between the two chromosomes is equal, with no genetic information extra or missing

This means that they are fully functional and the individual is a carrier.

90
Q

What are unbalanced translocations?

A

When the exchange of genetic material between the two chromosomes is uneven, with extra or missing genes resulting.

This means that one chromosome will have partial trisomy (extra) and another will have partial monosomy (missing)

91
Q

What are deletions?

A

Deletion of one or more bases in a DNA sequence

92
Q

What are the two types of deletions?

A

Terminal

Interstitial

93
Q

What are terminal deletions?

A

The loss of the end of a chromosome

94
Q

What are interstitial deletions?

A

Results after two breaks are induced

95
Q

What are insertions?

A

When one or more bases is added into a nucleotide sequence

96
Q

What are inversions?

A

When a segment of a chromosome is reversed end to end. This occurs when a single chromosome undergoes breakage and rearrangement within itself.

Leads to balanced rearrangements as no genetic material is added or lost

97
Q

What are the two types of inversions?

A

Paracentric

Pericentric

98
Q

What are paracecntric inversions?

A

Do not include the centromere and both breaks occur in one arm of the chromosome

99
Q

What are pericentric inversions?

A

Include the centromere and there is a break point in each arm.

100
Q

What do chromosome abnormalities result from? What is this?

A

Non-disjunction

Failure of the homologous chromosomes or sister chromatids to separate properly during cell division.

101
Q

What happens if non-disjunction occurs during anaphase I?

A

At least one pair of the homologous chromosomes did not separate.

This means that two cells will have an extra copy of one chromosome and two cell will have a missing copy/

102
Q

What happens if non-disjunction occurs during anaphase II?

A

One of the sister chromatids did not separate

End result is that two cells have the normal haploid number of chromosomes but one cell will have an extra chromosome and one will be missing a chromosome

103
Q

What are autosomal aneuploid syndromes?

A

Abnormalities that do not involve the sex chromosomes

104
Q

What is trisomy 21?

A

Downs syndrome

Extra 21 chromosome from mother

105
Q

What is trisomy 13?

A

Patu syndrome

Extra 13 chromosome from mother

106
Q

What is trisomy 18?

A

Edwards syndrome

Extra 18 chromosome from mother

107
Q

What are sex chromosomes aneuploid syndromes?

A

Abnormalities that involve the sex chromosomes

108
Q

What is 45, X?

A

Turner syndrome

Female partly missing or completely missing X chromosome

109
Q

What is 47, XXY?

A

Klinefelter syndrome

Males inheriting an additional Y chromosome.

110
Q

What are germline mutations?

A

A mutation with germ cells

Can be passed on to offspring

111
Q

What are somatic mutations?

A

A mutation with somatic cells

Cannot be passed on to offspring

112
Q

What are non-coding sequence mutations?

A

Mutations that arise in non-coding sequences of DNA, which are sequences that do not encode for proteins

113
Q

What are coding sequence mutations?

A

Mutations that arise in coding sequences of DNA, which are sequences that do code for proteins

114
Q

What are the four types of coding sequence mutations?

A

Silent

Missense

Nonsense

Frameshift

115
Q

What are silent mutations?

A

Mutations in DNA that do not have an observable effect on the organisms phenotype

116
Q

What are missense mutations?

A

Mutation when there is a change in a single nucleotide base causes the substitution of a different amino acid in the resulting protein

May have no effect, cause the protein to have a different function or not function at all

117
Q

What are nonsense mutations?

A

Mutation when there is a change in a single nucleotide base causes the substitution of a different amino acid that leads to the appearance of a STOP codon where there was a codon that codon for an amino acid

Results in the production a shortened, likely non-functional protein

118
Q

What are frameshift mutations?

A

Mutation caused by insertions or deletions of a number of bases in a DNA sequence. These insertion and deletions will affect the whole DNA sequence after the mutation

119
Q

What is mutation nomenclature?

A

Terminology used to describe mutations

120
Q

What are the techniques used to detect mutations?

A

PCR

Gel electrophoresis

RFLP analysis

ARMS

DNA sequencing

121
Q

Describe PCR

A
  1. Denaturation - denature DNA with heat, separates double-stranded DNA as this breaks the hydrogen bonds between the complementary bases.
    Temperature - 93-95 degrees
  2. Annealing - involves the primer binding to the target DNA sequences on the two DNA strands
    Temperature - 50-70 degrees
  3. Extension - new strands of DNA are made using the original strands as templates. A DNA polymerase enzyme joins free DNA nucleotides together. Results in two DNA molecules.
    Temperature - 70-75 degrees
122
Q

What are the advantages of PCR?

A

Doesn’t take long

Easy

Robust

123
Q

What is gel electrophoresis?

A

Used to separate DNA, RNA fragments or proteins based on their size and charge.

Run a current through an agarose gel containing the molecules of interest

Travel at different speed and direction depending on htheir size and charge - allowing separation

124
Q

What is RFLP analysis?

A

Exploits variation in homologous DNA sequences, known as polymorphisms.

It involves fragmenting a sample of DNA with the application of enzymes, known as restriction endonucleases.

These enzymes can selectively cleave a DNA molecule wherever a short, specific sequences is recognised.
A restriction fragment length polymorphism is said to occur when the length of a detected fragment varies between individuals, indicating non-identical sequence homologies

125
Q

What are restriction endonucleases?

A

Enzymes from bacterial cells which are able to recognise specific DNA sequences and always cut DNA at the same site.

126
Q

What are the advantages of RFLP analysis?

A

Simple

Cheap

127
Q

What are the disadvantages of RFLP analysis?

A

Not always feasible.

128
Q

What is DNA sequencing?

A

Determines the nucleic acid sequence in DNA.

Usually uses dideoxynucleotides

129
Q

What are the disadvantages of DNA sequencing?

A

Expensive equipment

Poor-quality

130
Q

What is ARMS?

A

Used to detect any mutation involving single base changes or small deletions

Uses specific PCR primers that allow amplification of DNA, only when the target allele contained within the sample.

131
Q

What are the advantages of ARMS?

A

Cheap

132
Q

What are the disadvantages of ARMS?

A

Require sequence information

Limited amplification size

Year One - Principles of Disease (15 decks)

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