Strand 1 - genes Flashcards
(109 cards)
1
Q
Which nitrogenous bases are purine and pyrimidine?
A
Adenine and guanine are purine
Thymine and cytosine are pyrimidine
2
Q
Which pair of nitrogenous bases bind via 2 hydrogen bonds and which via 3?
A
Adenine and thymine bond with 2 hydrogen bonds
Cytosine and guanine bond with 3 hydrogen bonds
3
Q
What charge are DNA and histones?
A
DNA is negatively charged and histones are positively charged
4
Q
What is DNA wrapped round a histone called?
A
Nucleosome
5
Q
What do nucleosomes form when coiled?
A
Chromatin fibres
6
Q
What do chromatin fibres form?
A
Arranged on a protein scaffolding to form a chromosome
7
Q
Name 7 examples for non coding DNA
A
Introns
Viral DNA
pseudogenes
Genes for RNA
Tandem repeats
Telomeres
Promotor regions
8
Q
Why do tandem repeats occur?
A
DNA polymerase III slips during DNA replication
9
Q
What are telomeres?
A
Caps at the end of each chromosome for protection which get worn down over time
10
Q
What are Pseudogenes?
A
They are mutated genes which have evolved to become inactive
11
Q
Give 2 examples of coding RNA
A
MRNA
Viral genomes
12
Q
Give two examples of structural RNA
A
RRNA
TRNA
13
Q
Give two examples of regulatory RNA
A
MicroRNA
Xist
14
Q
What is xist
A
Xist switches off one copy of X chromosome
15
Q
What is another name for the template strand?
A
The antisense strand
16
Q
What do single stranded DNA binding proteins do?
A
Keep strands unzipped
17
Q
What does topoisomerase do?
A
Stops the strands from over coiling
18
Q
What direction does DNA polymerase III add the bases?
A
5’-3’
19
Q
How does DNA polymerase III remove incorrect bases?
A
Using 3’-5’ exonuclease activity
20
Q
How is DNA replicated on the lagging strand?
A
Primer binds close to helicase forming Okazaki fragments which are joined by DNA ligase
21
Q
What ingredients do you add to the test tube for PCR
A
DNA sample
Primers
DNA taq polymerase
Nucleotides
Buffer
22
Q
What are the steps to carrying out PCR?
A
Denaturing (94-95)
Annealing (50-56)
Extension (72)
Repeat approx 30 times
23
Q
What is a gene mutation?
A
An alteration in the nucleic acid sequence of the genome of an organism
24
Q
How do mutations arise?
A
Errors during replication (point mutations/replication slippage)
Mutagens (radiation/chemicals)
25
What is the difference between purine and pyrimidine
Purine has two rings, pyramidine has one
26
What are the three types of RNA function?
Coding structural regulatory
27
What are three ways to prevent mutations?
Melanin (to protect DNA in the skin)
Peroxisomes (organelle that makes antioxidant enzymes)
Making good life choices
28
How do we repair mutations due to nicks (breaks of phosphodiester bonds)?
DNA ligase
29
How do we repair mutations due to single stranded damage to bases?
Base excision repair for small damage
Nucleotide excision for larger damage
30
How do we repair damage due to double stranded DNA breaks?
Non-homologous end joining
31
What does DNA polymerase III do to fix mutations in DNA replication?
Proofreading activity
32
For the mutations which DNA polymerase III can’t repair what happens?
Mismatch repair (4 proteins detect lack of H bonds between mismatched base pairs)
33
If there are too many mutations for the cell to repair what happens?
Apoptosis is initiated
34
What is a frame shift mutation?
Shifts the reading frame. Caused by deletions that are not in multiples of 3
35
What are the 4 types of mutation?
Frame shift
Silence
Missence
Nonsense
36
What happens with a silence mutation?
A base is substituted but it still codes for the same amino acid so no effect
37
What happens with a missense mutation?
Codes for a different amino acid. Only effects one so usually has small effect especially if similar shape/charge
38
What happens with a nonsense mutation?
Changes to a stop codon. Has big effect if at start of protein
39
What type of inheritance does cystic fibrosis follow?
Autosomal recessive
40
Why does cystic fibrosis occur and what does the mutation do?
Caused by mutation in gene encoding the CFTR protein. The CFTR protein is a membrane protein that transports chloride ions
41
How does the mutation in the gene encoding for the CFTR protein cause thick mucus?
Cl ions can’t exit the cells. Sodium then follows the Cl and exits the mucus into the the cell so there is less water in the mucus making it thick
42
What effects does having thick mucus cause?
In the lungs there are recurrent infections
In the pancreatic ducts there is malabsorption
43
What kind of condition is neurofibromatosis?
Autosomal dominant
(Half of the cases aren’t from parents and just occur due to mutation)
44
What are the two types of neurofibromatosis and what protein is damaged?
NF1 - Neurofibrin
NF2 - Merlin
Both proteins are normally tumour suppressor genes
45
What tumours are most common in NF1and NF2?
NF1 - neurofibromas
NF2 - schwannomas
46
What kind of condition is phenylketonuria?
Autosomal recessive
47
What protein is affected by phenylketonuria?
Phenylalanine hydroxylase
48
What does phenylalanine hydroxylase do?
Metabolises the amino acid phenylalanine
49
What kind of diet do you need to follow if you have phenylketonuria?
A strict phenylalanine free diet
50
What happens if phenylketonuria patients don’t follow a phenylalanine free diet?
Phenylalanine builds up in the body and damages the brain
Effects such as microcephaly (small head), intellectual disability, seizures
51
What type of condition is Huntington’s disease?
Autosomal dominant
52
What causes Huntington’s disease?
Caused by CAG repeats in the gene that codes for the huntingtin protein
53
What affects the severity of your symptoms in Huntington’s?
The amount of repeats on the gene that codes for the huntingtin protein
Gets progressively worse through generations as slipping of polymerase increases
54
What is genetic anticipation?
When a disease gets progressively worse through generations
55
Describe the anatomy of a normal metaphase chromosome
P arm = short arm
Q arm = long arm
Centromere in middle
Telomeres on the ends
56
Why is the photo of all the chromosomes lined up in order called
Karyotype
57
How do scientists identify chromosomes?
Size
Banding pattern
Centromere position
58
Which chromosomes are acrocentric?
13, 14, 15, 21, 22, Y
59
What abnormalities can be picked up on a karyotype?
Number of chromosomes
Material location
Amount of material
60
What is the word for having an abnormal number of copies of an individual chromosome?
Aneuploidy
61
What are the two types of aneuploidy called?
Monosomy - missing one
Trisomy - one extra
62
What is the word for having an abnormal number of sets of chromosomes?
Polyploidy (e.g monopolid, diploid, triploid)
63
What is the difference in chromosomes for people with Down syndrome?
They have trisomy 21
64
What are the clinical features of Down’s syndrome?
Characteristic facial features
Mild-moderate intellectual disability
Short stature
Congenital heart disease
Endocrine problems
Increased risk of leukaemia and Alzheimer’s
65
What change in the chromosomes causes Edward’s syndrome?
Trisomy 18
66
What are the clinical features of Edward’s syndrome?
Intra-uterine growth restriction
Most die during pregnancy
Overlapping fingers
Rocker-bottom feet
Congenital heart/kidney disease
Microcephaly (small head)
67
What change in chromosomes causes patau syndrome?
Trisomy 13
68
What are the clinical features of patau syndrome?
Intra uterine growth restriction
Most die during pregnancy
Cleft lip/palate
Extra fingers/toes
Brain abnormalities
Congenital heart disease
69
What syndromes does the 12 week pregnancy screening look for?
Edward’s, Down’s, Patau’s
70
What changes in chromosomes causes Klinefelter syndrome?
47 XXY
71
What are the clinical features of klinefelters syndrome?
Tall stature
Normal intellect,
Infertile
Little facial/ body hair
72
What changes in chromosomes causes turner syndrome?
Monosomy X
73
What are the clinicial features of turner syndrome?
Infertility
Short stature
Lymphoedema (puffy hands and feet)
Webbed neck
Endocrine abnormalities
Congenital heart disease
Normal intellect
74
What is a deletion in genetics?
Loss of a segment of genetic material from a chromosome
75
What is duplication in genetics?
Gain of a segment of genetic material from a chromosome
76
What genetic change causes di George syndrome?
22q11.2 microdeletion
77
What are the clinical features of di george syndrome?
Congenital heart and kidney disease
Nasal speech
Characteristic facial features
Hypocalcaemia
Intellectual disability
Increased risk of psychiatric disorders
78
What genetic change causes Prader Willi syndrome?
15q11 -q13 deletion
79
What are the clinical features of Prader willi syndrome?
Low tone at birth
Short stature
Characteristic facial features
Challenging behaviours and hyperphagia (excessive eating)
Intellectual disability
Incomplete pubertal development
80
What is translocation?
The relocation of chromosome material to the wrong place
81
What are the two types of translocation?
Reciprocal
Robertsonian
82
What is reciprocal translocation?
When 2 different chromosomes have exchanged segments with each other
83
What is robertsonian translocation?
An entire acrocentric chromosome attaches at another centromere
84
What pregnancy complications are associated with balanced reciprocal translocations?
Recurrent miscarriage
Multiple congenital abnormalities
85
What condition is reciprocal translocation the leading cause for?
Chronic myeloid leukaemia
86
What is the chromosomal abnormality that is the leading cause of chronic myeloid leukaemia?
Reciprocal translocation between chromosomes 9 and 22
87
Define locus?
Specific location on a chromosome
88
Define allele
Alternate forms of as gene at the same locus
89
Define homozygous
Both alleles at a gene locus are the same
90
Define homozygous
Both alleles at a gene locus are the same
91
Define heterozygous
The two alleles at a gene locus are different from one another
92
Define genotype
A persons DNA sequence at a particular locus
93
Define genotype
A persons DNA sequence at a particular locus
94
Define phenotype
A persons clinical features
95
Define phenotype
A persons clinical features
96
Define syndrome
A group of traits or conditions that tend to occur together and characterise a recognisable disease
97
Name 5 common autosomal dominant conditions
Huntingtons
BRCA 1 and 2
Neurofibromatosis
Autosomal dominant polycystic kidney disease
Marfan syndrome
98
What does it mean if a condition arises de novo?
Occurs for the first time in an affected individual without a family history
99
Name 4 common autosomal recessive conditions
Cystic fibrosis
Sickle cell anaemia
Spinal muscular atrophy
Phenylketonuria
100
Name 3 common x linked conditions
Duchenne muscular dystrophy
Fragile X syndrome
Haemophilia A
101
Name 2 common X linked dominant conditions
Rett syndrome
Craniofrontonasal syndrome
102
Describe the mitochondrial genome
Circular chromosome containing 37 genes
103
Why is there increased risk of aneuploidy with advanced maternal age?
Increase in nondisjunction and aneuploidy is often incompatible with life
104
What are some examples of conditions that become more likely with increased paternal age?
Achondroplasia
Noonan syndrome
Thanatophoric dysplasia
Osteogenesis imperfecta
Apert syndrome
105
Define penetrance
The likelihood that a clinical condition will occur when a particular genotype is present
E.g Huntingtons is penetrant
106
What is variable expressivity?
The range in signs and symptoms that can occur in different people with the same genetic condition
107
What is allelic heterogeneity?
Different pathogenic variants in a single gene associated with multiple different phenotypes
108
What is locus heterogeneity?
When one phenotype can be caused by pathogenic variants in multiple different genes
109
What is mosaicism?
When only some of an individuals cells have a specific variant
