IMMS > DNA > Flashcards

DNA Flashcards

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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
Define allelic heterogeneity
Lots of different variants in one gene e.g. cystic fibrosis
26
Define locus heterogeneity
Variants in different genes give the same clinical conditions e.g. hypertrophic cardiomyopathy
27
What is loss-of-function variants
Only one allele functioning Most are recessive
28
What is gain of function variants
Increased gene dosage Increased protein activity
29
What is dominant negative variants
Protein from the variant allele interferes with the protein from the normal allele
30
What is a diagnostic test
Patient has signs and symptoms suggesting a particular diagnosis Molecular genetic test will confirm diagnosis
31
What is predictive testing
Testing health at risk family members for a previously identified familial variant - often dominant
32
What is a pre-natal test
Performed in pregnancy where an increased risk of a specific condition affecting the foetus Chorionic villous sample or amniocentesis
33
What is genetic testing
Testing target population not high risk families
34
How many bonds are between adenine and thymine
2
35
How many bonds are between guanine and cytosine
3
36
How many chromosomes are in the human genome
46 chromosomes 22 pairs and sex chromosomes XY
37
What is the long arm of a chromosome called
q
38
What is the short arm of a chromosome called
p
39
What does Giemsa staining show
G banding
40
What does quinacrine staining show
Q banding
41
What is the purpose of G banding and how many bands does it give
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
How many mbp does a band have
Approx 6-8 mbp
43
Where is a telomere located
At the end of the chromosome
44
Define phenotype
The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment
45
Define genotype
The genetic constitution of an individual organism
46
Define vertical transmission
Passage of disease-causing agent (pathogen) from mother to baby during the period immediately before and after birth
47
Define recurrence risk
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
Define variable expression
Range of signs and symptoms that can occur in different people with the same genetic condition
49
Define reduced penetrance
Genetic trait is expressed in only part of the population
50
Define sex limitation
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
Define assortive mating
Tendency for people to choose mates who are similar (positive) or dissimilar (negative) to themselves in characteristics
52
Define locus heterogeneity
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
Define Down Syndrome
Trisomy 21 (extra chromosome 21) Interrupts normal course of development - causing clinical features of Down syndrome
54
Define mosaic down syndrome
Have an extra number 21 chromosome in only some of their body's cells
55
What is the downs syndrome mutation
Trisomy 21
56
What are the usual mechanisms for downs syndrome
Non-disjunction of maternal chromosomes Unbalanced chromosomal material Mosaicism
57
What is the strongest risk factor for Down's syndrome
Maternal age
58
What is the karyotype for downs syndrome
47 XX + 27
59
What are the base pairs in DNA
Adenine Thymine Guanine Cytosine
60
How many bonds does adenine and thymine have
2
61
How many bonds does cytosine and guanine have
3
62
What are the pyrimidines
Cytosine Thymine Single ring
63
What are the purines
Guanine Adenine Double ring
64
What happens in G2
Preparation for cell division
65
What happens in G1
Growth and metabolism
66
What happens in S phase
DNA replication
67
Where is G0
Beginning of G1 after mitosis
68
What direction does DNA polymerase read
3' to 5'
69
What direction does DNA polymerase print
5' to 3'
70
What direction is the top vs bottom strand of DNA
Top 5' to 3' Bottom 3' to 5'
71
What is the role of helicase
Opens the strand
72
What keeps strand open
Single stranded binding proteins (SSB)
73
What is the role of topoisomerase
Unwinds it (relieves supercoiling)
74
What enzymes joins okazaki fragments
Ligase
75
What are the structure of DNA
Phosphate (joined to by 5 or 3 carbon) Phosphodiester bond to the sugar Base pair
76
How many base pairs is one turn of DNA approx to
10
77
What is the role of p53
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
What are the base pairs of RNA
C G U A
79
What are the base pairs of DNA
C G A T
80
Where is DNA found
Nucleus Mitochondria
81
Where is RNA found
Cytoplasm
82
What is the sugar of DNA
Deoxyribose
83
What type of sugar is RNA
Ribose
84
What is the role of DNA
Long-term storage of genetic information
85
What is the role of RNA
Transfer genetic code from the nucleus to the ribosomes to make proteins
86
What comes first transcription or translation
Transcription
87
What are the stages of transcription
Initation Elongation Termination
88
Describe initation of transcription
RNA polymerase binds to promoter region on DNA (TATA BOX - TATAAA)
89
What is the promoter region on DNA
TATA box TATAAA
90
Describe elongation transcription
Non-template strand Template strand - antisense - RNA polymerase active upon
91
Describe termination transcription
5' Cap to 3' poly-A tail RNA splicing to move introns mRNA
92
What are removed to created mRNA
Introns
93
What is the role of the cap
Protect mRNA strand from being degraded by certain enzymes
94
What are stages of translation
Initation Elongation Termination
95
Describe initation of translation
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
Describe elongation of translation
2nd tRNA molecule enters A -site Continues leave via E-site
97
Describe termination of translation
Stop codon read - non-sense coding Does not code for amino acid - bind to a-site = release factor Ribosome disassembles
98
What is transcription
DNA - mRNA
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