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DNA Flashcards

1
Q

What is the difference between prokaryotes and eukaryotes DNA?

A

Prokaryotes - has no nuclear membrane. DNA arranged often in a single chromosome

Eukaryotes - DNA is in nucleus and bound to proteins (chromatin complex). Some DNA in mitochondria

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2
Q

Describe a chromosome

A

Each is made of two identical strands (chromatids) joined in the centre (centromere)

Each has a long arm (q) and a short arm (p) separated by the centromere

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3
Q

What nucleic acid is present in RNA but not DNA

A

Uracil

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4
Q

What nucleic acid is present in DNA but not RNA

A

Thymine

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5
Q

Name the pyrimidines
How are they different from purines?

A

Cytosine
Thymine (DNA)
Uracil (RNA)

Single ringed

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6
Q

Name the purines
How are they different from pyrimidines?

A

Girls are pure

Adenine
Guanine

Double ring

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7
Q

What is the order of DNA replication?

A
  1. DNA opens at replication fork
  2. Base sequence on each parent strand copied into a complementary daughter strand
  3. Two parental strands separate in front of the fork
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8
Q

DNA composed as a new and old strand is described as…

A

Semi-conservative

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9
Q

How fast is DNA replication?

A

700-1000bp per second
For 6 billion base pairs

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10
Q

What is the role of DNA polymerase?

A

DNA polymerase reads 3’ to 5’ prints 5’ to 3’

Substrates are deoxyribonucleotides triphosphates

Enzyme stays on the strand, at the the same time extends and proof reads

Add nucleotides to the base

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11
Q

What is the role of helicase?

A

Opens the strand

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12
Q

What are the roles of single binding proteins (SSB)?

A

Keep the strand open

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13
Q

What is the role of topoisomerase?

A

Unwinds the strand (relives supercoiling)

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14
Q

Describe mRNA

A

Printed as a long linear transcript

Genetic information is transcribed from DNA as a sequence of bases to a ribosome

It has a 5’CAP and a 3’Poly A tail

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15
Q

Describe rRNA

A

Ribosomal RNA

Combines with proteins to form 80S ribosomes

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16
Q

Describe tRNA

A

Carry amino acids to ribosomes, and check that they are incorporated in the right position

Each tRNA carries one amino acid

Very small molecules

Anticodon - triplet sequence pairs with mRNA Important for right amino acid for the right triplet

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17
Q

What are the types of variants possible in DNA?

A

Duplications of genes or part of gene

Deletions (whole gene or some exons)

Variants within the regulatory sequence

Splice site variants

Introduce premature stop codon-nonsense variant

Replace one amino acid in protein with another - mis-sense variant

Expansion of trinucleotide repeats

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18
Q

What does deletions cause?

A

Disrupts the protein

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19
Q

What does a splice-site variant cause?

A

Affects the accurate removal of an intron

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20
Q

What does a non-sense variant cause?

A

Change codon to stop

Out of frame deletion produces a stop codon either at deletion site or further along

RNA detaches from the ribosome and is eliminated

Non sense medicated decay

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21
Q

What does a mid-sense variant cause?

A

Single base substitution

Changes the type of amino acid in the protein

May or may not be pathogenic

May be a polymorphism of no functional significance

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22
Q

What expansion of a tri-nucleotide repeat causes Huntington’s

A

CAG

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23
Q

What expansion of tri-nucleotide repeat causes myotonic dystrophy

A

CTG

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24
Q

What expansion of tri-nucleotide repeat causes fragile X

A

CGG

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25
Q

Define allelic heterogeneity

A

Lots of different variants in one gene e.g. cystic fibrosis

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26
Q

Define locus heterogeneity

A

Variants in different genes give the same clinical conditions e.g. hypertrophic cardiomyopathy

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27
Q

What is loss-of-function variants

A

Only one allele functioning

Most are recessive

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28
Q

What is gain of function variants

A

Increased gene dosage

Increased protein activity

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29
Q

What is dominant negative variants

A

Protein from the variant allele interferes with the protein from the normal allele

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30
Q

What is a diagnostic test

A

Patient has signs and symptoms suggesting a particular diagnosis

Molecular genetic test will confirm diagnosis

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31
Q

What is predictive testing

A

Testing health at risk family members for a previously identified familial variant - often dominant

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32
Q

What is a pre-natal test

A

Performed in pregnancy where an increased risk of a specific condition affecting the foetus

Chorionic villous sample or amniocentesis

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33
Q

What is genetic testing

A

Testing target population not high risk families

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34
Q

How many bonds are between adenine and thymine

A

2

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35
Q

How many bonds are between guanine and cytosine

A

3

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36
Q

How many chromosomes are in the human genome

A

46 chromosomes

22 pairs and sex chromosomes XY

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37
Q

What is the long arm of a chromosome called

A

q

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38
Q

What is the short arm of a chromosome called

A

p

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39
Q

What does Giemsa staining show

A

G banding

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40
Q

What does quinacrine staining show

A

Q banding

41
Q

What is the purpose of G banding and how many bands does it give

A

Produce a visible karyotype. Chromosome abnormalities and rearrangements in genetic diseases and cancers

G banding gives approx. 400-500 bands per haploid chromosome set

42
Q

How many mbp does a band have

A

Approx 6-8 mbp

43
Q

Where is a telomere located

A

At the end of the chromosome

44
Q

Define phenotype

A

The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

45
Q

Define genotype

A

The genetic constitution of an individual organism

46
Q

Define vertical transmission

A

Passage of disease-causing agent (pathogen) from mother to baby during the period immediately before and after birth

47
Q

Define recurrence risk

A

Statistic that estimates the probability that a condition present in one or more family members will recur in another relative in the same or future generations

48
Q

Define variable expression

A

Range of signs and symptoms that can occur in different people with the same genetic condition

49
Q

Define reduced penetrance

A

Genetic trait is expressed in only part of the population

50
Q

Define sex limitation

A

Some traits are only in individuals of one sex e.g. where the gene affects an organ only possessed by one of both sexes

51
Q

Define assortive mating

A

Tendency for people to choose mates who are similar (positive) or dissimilar (negative) to themselves in characteristics

52
Q

Define locus heterogeneity

A

When mutations at multiple genomic loci are capable of producing the same phenotype (e.g. single trait, patterns of traits or disorder), and each individual mutation is sufficient to cause the specific phenotype independently

53
Q

Define Down Syndrome

A

Trisomy 21

(extra chromosome 21)

Interrupts normal course of development - causing clinical features of Down syndrome

54
Q

Define mosaic down syndrome

A

Have an extra number 21 chromosome in only some of their body’s cells

55
Q

What is the downs syndrome mutation

A

Trisomy 21

56
Q

What are the usual mechanisms for downs syndrome

A

Non-disjunction of maternal chromosomes

Unbalanced chromosomal material

Mosaicism

57
Q

What is the strongest risk factor for Down’s syndrome

A

Maternal age

58
Q

What is the karyotype for downs syndrome

A

47 XX + 27

59
Q

What are the base pairs in DNA

A

Adenine

Thymine

Guanine

Cytosine

60
Q

How many bonds does adenine and thymine have

A

2

61
Q

How many bonds does cytosine and guanine have

A

3

62
Q

What are the pyrimidines

A

Cytosine

Thymine

Single ring

63
Q

What are the purines

A

Guanine

Adenine

Double ring

64
Q

What happens in G2

A

Preparation for cell division

65
Q

What happens in G1

A

Growth and metabolism

66
Q

What happens in S phase

A

DNA replication

67
Q

Where is G0

A

Beginning of G1 after mitosis

68
Q

What direction does DNA polymerase read

A

3’ to 5’

69
Q

What direction does DNA polymerase print

A

5’ to 3’

70
Q

What direction is the top vs bottom strand of DNA

A

Top 5’ to 3’

Bottom 3’ to 5’

71
Q

What is the role of helicase

A

Opens the strand

72
Q

What keeps strand open

A

Single stranded binding proteins (SSB)

73
Q

What is the role of topoisomerase

A

Unwinds it (relieves supercoiling)

74
Q

What enzymes joins okazaki fragments

A

Ligase

75
Q

What are the structure of DNA

A

Phosphate (joined to by 5 or 3 carbon)

Phosphodiester bond to the sugar

Base pair

76
Q

How many base pairs is one turn of DNA approx to

A

10

77
Q

What is the role of p53

A

DNA damage detected - initiate repair mechanism

Pause cell cycle until repair is carried out - halt cell cycle if DNA not repaired

Apoptosis - command cell to commit suicide if DNA damage not repaired

78
Q

What are the base pairs of RNA

A

C
G
U
A

79
Q

What are the base pairs of DNA

A

C
G
A
T

80
Q

Where is DNA found

A

Nucleus

Mitochondria

81
Q

Where is RNA found

A

Cytoplasm

82
Q

What is the sugar of DNA

A

Deoxyribose

83
Q

What type of sugar is RNA

A

Ribose

84
Q

What is the role of DNA

A

Long-term storage of genetic information

85
Q

What is the role of RNA

A

Transfer genetic code from the nucleus to the ribosomes to make proteins

86
Q

What comes first transcription or translation

A

Transcription

87
Q

What are the stages of transcription

A

Initation

Elongation

Termination

88
Q

Describe initation of transcription

A

RNA polymerase binds to promoter region on DNA (TATA BOX - TATAAA)

89
Q

What is the promoter region on DNA

A

TATA box

TATAAA

90
Q

Describe elongation transcription

A

Non-template strand

Template strand - antisense - RNA polymerase active upon

91
Q

Describe termination transcription

A

5’ Cap to 3’ poly-A tail

RNA splicing to move introns

mRNA

92
Q

What are removed to created mRNA

A

Introns

93
Q

What is the role of the cap

A

Protect mRNA strand from being degraded by certain enzymes

94
Q

What are stages of translation

A

Initation

Elongation

Termination

95
Q

Describe initation of translation

A

Ribosome has small and large subunit

Has 3 active sites E P A

Step 1 - start condon AUG enters p-site where peptide bonds are formed

96
Q

Describe elongation of translation

A

2nd tRNA molecule enters A -site

Continues leave via E-site

97
Q

Describe termination of translation

A

Stop codon read - non-sense coding

Does not code for amino acid - bind to a-site = release factor

Ribosome disassembles

98
Q

What is transcription

A

DNA - mRNA

IMMS (16 decks)

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