Molecular And Population Genetics Flashcards
1
Q
What does DNA stand for ?
A
DeoxyriboNucleic Acid
2
Q
What is the function of DNA ?
A
Stores and transmits all the cells genetic information
3
Q
What must DNA be in order to be able to replicate ?
A
-stable
-able to accurately copy itself
-able to contain coded information
4
Q
How is DNA used due to its stable condition ?
A
-can be recovered and used for genetic testing from biological samples at crime scenes
-under the right conditions fragments can survive for 50,000 to 100,000 years
5
Q
What did Miescher use in his experiment ?
A
Pus-filled bandages
6
Q
What experiment did Miescher carry out ?
A
Isolated a substance rich in phosphorus and nitrogen from the nuclei of white blood cells which he called nuclein
7
Q
What did Griffith discover ?
A
Smooth strain is virulent (causes pneumonia ) and rough strain is usually harmless
8
Q
What experiment did Griffith carry out ?
A
Injected mice with different strains.
Living S strain- killed mouse
Living R strain - Mouse healthy
Dead S strain (killed by heating)- mouse healthy
Living R strain with dead S strain - mouse dies
9
Q
What was the conclusion of Griffith’s experiment ?
A
A chemical substance from dead S strain bacteria is capable of transforming R strain bacteria making them virulent
10
Q
What did Avery, MacLeod and McCarty find ?
A
Published a key study using cell-free extracts of heat killed S strain bacteria to show that DNA is the chemical substance responsible for bacterial transformation
11
Q
What was Avery, MacLeod and McCarty’s experiment ?
A
-remove lipids and sugars from a solution of heat killed S cells. (Proteins, RNA and DNA remain)
- treat solutions with enzymes to destroy protein, RNA and DNA
- add to culture containing living R cells and observe for transformation by testing for the presence of virulent S cells
12
Q
What was the conclusion of Avery, MacLeod and McCarty’s experiment ?
A
DNA is the chemical substance from dead S strain bacteria that is capable of transforming R strain bacteria and making them virulent
13
Q
What did Franklin and Wilkins discover ?
A
Used a technique called ‘X’ray diffraction’ to obtain images of DNA
14
Q
What did Watson and Crick discover ?
A
Deduced that DNA was a double helix after seeing Franklin and Wilkins images
15
Q
What are the four bases found in DNA?
A
Adenine, Thymine, Guanine and cytosine
16
Q
What is the stucture of DNA ?
A
DNA is a double helix made up of multiple nucleotides linked together via a sugar-phosphate backbone
17
Q
How do the polynucleotide strands run ?
A
anti-parallel
18
Q
How are the polynucleotides held together ?
A
By hydrogen bonds between the bases on the different strands
19
Q
How is a nucleotide formed ?
A
-The phosphate joins to the C5 ( 5 prime) hydroxyl group of the sugar
-The nitrogen-containing base is linked to C1 of the sugar
- via a condensation reaction
20
Q
How are polynucleotides formed ?
A
-via phosphodiester bonds
-condensation reaction
21
Q
What are the complimentary base pairings ?
A
A-T
G-C
22
Q
Why do the bases always pair this way ?
A
each base pair has a similar width holding the backbone at the same distance apart along the DNA molecule
23
Q
How many hydrogen bonds between A-T
A
2
24
Q
How many hydrogen bonds between G-C
A
3
25
What holds together the antiparallel strands ?
Hydrogen bonds
26
What are minor and major grooves ?
major grooves occur where the backbones are far apart.
Minor grooves occur where they are close together
27
What type of DNA do prokaryotes have ?
Double stranded circular chromosomes
28
Diploid
Having 2 sets of chromosomes
29
How many pairs of chromosomes do humans have ?
23
30
How do chromosomes fit in the nucleotide region if they’re so long ?
-forming loops
-being ‘supercoiled’
31
What protein binds to and folds DNA into coils and loops ?
Histones
32
What is the complex between DNA and protein called ?
Chromatin
33
How do histones bind to DNA ?
histones are highly conserved basic proteins with a net +ve charge that binds the -ve charged DNA
34
What does Histones 1 do ?
Induces tighter DNA wrapping
35
How does the Histones 1 induce tighter DNA wrapping ?
Binds to both the linker DNA and the DNA wound around the Histones core pulling the chromatin together
36
What are the levels of DNA packaging ?
-short region of DNA double helix
-beads on a string forms chromatic
-packed nucleosomes
-chromosome in extended form
-condensed section of chromosome
37
What is a telomere ?
The protective cap at both ends of a linear chromosome
38
What is a centromere ?
Attaches the duplicated chromosomes to the mitosis spindle
39
Why must a cell copy all its genetic information before dividing ?
To ensure each new cell has a complete set of DNA
40
During which process is DNA replication needed ?
During cell division
41
What does the cell do to check for errors in duplicated chromosomes ?
The cell performs mismatch repair
42
What happens to cellular contents excluding chromosomes during G1 phase ?
They grow in preparation for DNA synthesis
43
In what states do chromosomes exist throughout the cell cycle ?
Chromosomes exist in different states
44
What are the changes in chromosome structure during mitosis ?
-chromosomes condense
-chromosome align at the metaphase plate
-sister chromatids separate
-chromosomes de-condense after mitosis
45
How does each DNA strand function during replication ?
Each strand acts as a template for the synthesis of a new strand
46
What are the three proposed models of DNA replication ?
-conservative
-semi-conservative
-dispersive
47
What did the Meselson-Stahl experiment investigate ?
DNA replication in bacteria
48
What was the first step in the Meselson-Stahl experiment ?
Bacteria was cultured in medium containing 15N
49
What happened after the bacteria was transferred to medium containing 14N ?
DNA sample centrifuged after 20 mins and contained hybrid nitrogen
50
What was the conclusion of the Meselson-Stahl experiment ?
DNA replication is semi conservative
51
What are the molecular details of DNA replication ?
-origin of replication
-parental strand
-daughter strand
-replication forks and bubbles
52
How many origins of replication do bacteria have ?
One
53
How many origins of replication do eukaryotes have ?
Many origins
54
Why do bacteria only have one origin for DNA replication while eukaryotes have many ?
Bacteria are simpler and have smaller genomes
55
How long does a full round of DNA replication take in E.coli ?
40 mins
56
How often can replication and cell division occur in E.coli ?
20 mins
57
What is the Helmstetter-Cooper model (E.Coli)?
-New DNA replication cycle can started before the first cycle finishes
-occurs in nutrient-rich conditions
58
What are the roles of DNA Polymerase III in DNA replication ?
-adds culeotides to the growing DNA strand
-proofreads for errors
Requires a 3’ end to being synthesis
59
What is the infection of toposomerase during DNA replication ?
It breaks, swivels, and rejoins the DNA ahead of the replication fork
60
What is the role of helices in DNA replication ?
It unwinds and unzips the parental DNA strands
61
What does the primate do during DNA replication ?
It synthesizes RNA primers using parental DNA as a template
62
What is the function of a single-strand binding protein during DNA replication ?
They stabilize the unwound parental strands
63
In which direction does DNA replication occur ?
IN a 5’ to 3’ direction
64
How does DNA polymerase ensure correct base pairings ?
It checks each nucleotide before adding the next one
65
How does DNA polymerase begin a new strand if it requires a base-paired 3’ end ?
Primase provides a base- paired 3’ end with an RNA strand
66
How does the leading and lagging strands differ in DNA replication ?
Leading strands: synthesized continuously towards the replication fork
Lagging strands: synthesized discontinuously away from the replication fork, forking Okazaki fragments
67
What happens during the synthesis of a leading strand ?
DNA Polymerase III moves along the template in a 3’ to 5’ direction
68
What occurs during the synthesis of the lagging strand ?
Okazaki fragments are formed and later joined together
69
What does the DNA polymerase I do during lagging strand synthesis ?
It replaces RNA primers with DNA
70
What are the steps involved in synthesizing the lagging strand ?
1. Primase syntheszes RNA primer
2. DNA polymerase III adds nucleotides to for Okazaki fragments
3. DNA polymerase I replaces RNA with DNA
4. Okazaki fragments are joined together
71
What does DNA polymerase III do during DNA replication ?
It adds DNA nucleotides to the primer, forming Okazaki fragments
72
What is the role of Primase in DNA replication ?
Primase synthesizes RNA primers needed for DNA polymerase to initiate replication
73
What are Okazaki fragments ?
Short segments of DNA synthesized on the lagging strand during replication
74
What happens after DNA polymerase III reaches the next RNA primer
DNA polymerase III detaches from the DNA strand
75
What occurs when DNA polymerase III reached fragment 1 primer ?
It detaches after adding DNA nucleotides to fragment 2
76
What is the function of DNA polymerase I ?
it replaces RNA primers with DNA nucleotides
77
How does DNA ligament contribute to DNA replication ?
DNA ligaments forms bonds between newly synthesized DNA and existing DNA fragments
78
How does DNA ligament contribute to DNA replication ?
DNA ligaments forms bonds between newly synthesized DNA and existing DNA fragments
79
What is the replisome ?
It;s the complex of all components involved in DNA replication
80
How does DNA polymerase ensure accuracy during replication ?
It proofreads base pairings before adding the next nucleotide
81
What is the frequency if mistakes made by DNA polymerase during replication ?
1 mistake per 10 million nucleotides
82
What is the mismatch repair ?
Mismatch repair corrects error in DNA replication by removing and resynthesizing mismatched nucleotides
83
What happens to telomeres during cell division ?
Telomeres shorten by approximately 100 base pairs with each division
84
What are common sources of DNA damage ?
Chemicals, radioactivity, X-rays, UV light, cellular metabolism and replication errors
85
What is the function of nucleotide excision repair ?
NER removes damaged nucleotides and replaces them with correct ones
86
How does Xeroderma pigmentosum relate to DNA repair mechanisms ?
caused by mutations in genes involved in nucleotide excision repair
87
What are the key points of DNA replication ?
• DNA is copied during the S phase of the cell cycle.
• A DNA strand acts as a template for a new strand.
• DNA replication is semi-conservative.
• Replication starts at a replication origin.
• Replication proceeds in a 5' to 3' direction.
• An RNA primer is required to start replication.
• The leading strand is synthesized continuously.
• The lagging strand is synthesized in Okazaki fragments.
• DNA damage can be repaired using various mechanisms.
88
What is the process called when a gene is copied from DNA into RNA ?
Transcription
89
What is gene expression ?
Process by which genetic information is used to make a gene product
90
What is the role of mRNA in gene expression ?
It’s translated into proteins
91
What are the copies of genes made during transcription ?
mRNA
92
How do cells with identical DNA produce different proteins ?
Depends on life-stage, tissue and disease state
93
What is the central Dogma of molecular biology ?
Genetic information flows from DNA to RNA and from RNA to protein
94
Who first stated the Central Dogma of molecular biology ?
Francis Crick
95
What are the steps of transcription ?
1. Initiation
2. elongation
3. Termination
96
What is the structure of RNA ?
RNA is a single-stranded polymer of four different nucleotide subunits
97
What are the four nucleotide subunits of RNA
A, G, C and U
98
how does transcription produce RNA ?
-Opening and unwinding of DNA double helix
-One strand of DNA serves as template for the synthesis of RNA
-ribonucloetides are added by complementary base pairings with the DNA template and being covalently joined together
-RNA transcript is single stranded and complementary to the template strand
99
In which direction are ribonucleotides added during transcription ?
5’ to 3’ direction
100
What enzyme is responsible for transcribing DNA to RNA ?
RNA polymerase
101
What are the three types of RNA polymerases in eukaryotes ?
RNA polymerase I, II and III
102
How is DNA transcribed into RNA ?
-RNA polymerase prises the DNA strands apart
-hooks the RNA nucleotides to the bases along the exposed template by base complementation
-adds nucleotides only to 3’ end, via phosphodiester bonds to make RNA
-no primer is required
103
What is the difference is bases between DNA and mRNA ?
mRNA doesn’t have thymine so A binds with U and T binds with U
104
How does transcription occur in bacteria ?
- RNA polymerase latches tightly onto DNA when it encounters a promoter, recognized by its subunit
-RNA polymerase can then open up the double helix that is ahead of it
-one of the exposed strands acts as a template for complimentary base pairs with incoming ribonucleoside triphosphates and sigma factor is released
-RNA chain elongation continues until RNA polymerase encounters the termination site within the gene, after transcribing this the template is released
105
What is the difference in transcription between prokaryotes and eukaryotes ?
-prokaryotes only have one type of RNA polymerase
-eukaryotic RNA polymerases need other proteins called transcription factors which must assemble at the promoter
106
What does the processing of mRNA involve in eukaryotes ?
Capping, polyadenylation and splicing
107
What is capping ?
A guanine with a methyl group caps the 5’ end of eukaryotic mRNAs
108
What is polyadenylation ?
The 3’ end of the full length mRNA is trimmed and 150-200 adenines is added
109
What is splicing ?
Introns (non-coding) are removed from the mRNA and exons are joined
110
What is the significance of the SMN gene in humans ?
A mutation in the SMN1 gene leads to spinal muscular atrophy
111
how do some gene therapies work in relation to the SMN gene ?
They alter splicing on the SMN2 gene to produce functional protein
112
What does capping and polyadenylation do to mRNA ?
-define RNA as mRNA
-mark the mRNA as complete
-increase the stability
-allow its export from the nucleus to the cytoplasm
113
What does mRNA have to be before it can leave the nucleus ?
Bound by a specialized set of proteins
-Cap-binding complex
-Ply-A binding proteins
-exon junction complex
114
Where does translation occur
Cytoplasm
115
How Mandy amino acids are there ?
20
116
How many nucleotides are there in a codon ?
3
117
What is the role of tRNA ?
Matches amino acids to codons
118
What is the start codon ?
AUG
119
What is the role of an adaptor molecule ?
Recognize and bind to a codon at one site, corresponding amino acids at another (tRNA)
120
What subunits is a ribosome made from ?
Proteins and ribsosomal RNA
121
What enzyme catalyses the formation of peptide bonds that covalently link the amino acids together
Peptidyl transferase
122
How does the initiation of translation occur ?
The small ribosomal subunit loaded with the initiator tRNA binds to the 5’ end of mRNA marked by 5’ cap and moved along the mRNA searching for the first AUG.
123
What happens when the first AUG codon is found during translation ?
Several initiation factors dissociate from the small ribosomal subunit to make way for the large ribosomal subunit to bind
124
What do bacteria have instead of 5’ caps to tell them where to begin ?
Ribosome- binding sites
125
What is the stop signal for translation ?
UAA, UAG/UGA
126
What happens when a stop signal is reached ?
- signals for the ribosome to STOP translation
-release factor bind to any stop codon that reaches the A site
-alters activity of peptidyl transferase so adds water instead of an amino acid
-this frees the carboxyl end of the polypeptide, releasing the polypeptide
127
What is genetic variation ?
Causes differences between individuals of the same species
128
What does genetic variation cause differences in ?
-appearance
-personality
-longevity
-risk of disease
129
What is a phenotype ?
An observable characteristic of an individual
130
What are examples of phenotypes ?
-hair color
-eye color
-blood group
-height
131
What is genetic variation caused by ?
Changes in the DNA sequence
132
What are changes in the DNA sequence called ?
-mutation or variant
133
What is the DNA sequence that controls a trait called ?
Gene or locus
134
What is an allele ?
A variant form of a gene
135
What is genetic inheritance ?
how traits are passed down from one generation to the next
136
When are genes inherited ?
Meiosis
137
What is meiosis
Cell division that generates gametes
138
What does diploid mean ?
An organism with two copies of each type of chromosome
139
Are humans haploid or diploid ?
Diploid
140
How many alleles do somatic cells have ?
2 allies at each genetic locus
-one from biological female parent
-one is from the male biological parent
141
What is a genotype ?
There are several different combinations of alleles and individual could have
142
How does genotype determine phenotype ?
The combination of the alleles from both chromosomes determines the trait
143
What does homozygous mean ?
Same allele
144
What does heterozygous mean ?
Different alleles
145
What is a dominant allele
Shows in the trait if an individual has at least one dominant allele
146
What is a recessive allele ?
Will only show in the trait if an individual has both recessive alleles
147
how are human diploid cells formed ?
-human gametes are haploid
-one haploid gamete from each parent combine to create a new diploid individual
148
What other factors can influence genetic variation ?
Environmental factors
149
Who discovered that alleles can be dominant or recessive ?
Gregor Mendel
150
What was Mendel’s experimental technique ?
-used ‘true-breeding’ strains of garden pea to study inheritance
-strains varied in appearance but each strain always produced the same type of pea
151
What is the F1 generation
All F1 offspring resemble only one of the parents
152
How do you get the F2 generation
Self-crossing F1 generation
153
What occurs in the F2 generation ?
The trait that disappeared in the F1 generation reappears
154
What is the ratio of an F2 generation
3:1
155
What is Mendel’s law
The principle of segregation
156
What does the principle of segregation say ?
two members of a gene pair segregate from each other in the formation of gametes: half the gametes carry one allele and the other half carry the other allele
157
What does polygenic mean ?
Human traits are influences by allelic variants at multiple genes
158
how are Mendel’s laws relevant to human traits ?
Most common disorder with an inherited component are also polygenic (type 2 diabetes )
159
What is pedigree analysis ?
-study an existing population
-use multiple generations
-predict inheritance of disease
160
What is dominant pedigree ?
-affected individuals have at least one affected parent
-the trait appears every generation
-two unaffected parents only have unaffected offspring
161
What is recessive pedigree ?
-unaffected parents can have affected offspring
-‘carriers’ of the mutation are heterozygous
