Genetics Flashcards
1
Q
What do nucleotides consist of?
A
A sugar, a base and a phosphate group
2
Q
Why are bases flat?
A
Allows them to be stacked up in the centre of the helix
3
Q
What direction to DNA strands?
A
Antiparallel - one runs from 5’ to 3’ and the other runs from 3’ to 5’
4
Q
What is the major groove in DNA?
A
Where the backbones are far apart
5
Q
What is the minor groove in DNA?
A
Where the backbones are close together
6
Q
What is more important, the minor or major groove in DNA? Why?
A
Major groove
Where most proteins bind
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
8
Q
How are the two DNA strands linked together?
A
Complementary base-pairing
T + A
C + G
9
Q
What bonds exist between complementary bases?
A
Hydrogen
10
Q
Where is DNA located within the cell?
A
Nucleus
AND
Ribosomes - contain their own DNA
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
12
Q
What are the two sections of a chromosome?
A
P section - smaller (petite)
Q section - longer
13
Q
What are nucleosomes?
A
DNA wrapped around histone proteins
14
Q
What are chromatin fibres?
A
Nucleosomes folded up
15
Q
What are chromosomes?
A
Nucleosomes wrapping around one another
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
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
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.
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
20
Q
What does it mean if we say that DNA is bi-directional?
A
Two strands of DNA run in anti-parallel directions
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
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
23
Q
What is a codon?
A
Three bases
Codes for one amino acid or a STOP/START instruction
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
25
What are synonyms?
Codons which refer tot he same amino acid
Tend to be very similar
26
What is the advantage of degeneracy?
Minimises the effect of genetic mutations, as alteration to the base sequences are less likely to alter the protein being coded for
27
What amino acid codes for the START codon?
Methionine
28
What are the three types of RNA?
mRNA
tRNA
rRNA
29
What is mRNA?
Involved in transporting the genetic code from the nucleus to the ribosome so that proton synthesis can occur. It is transcribed from DNA
30
What is tRNA?
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
31
What is rRNA?
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
32
What is alternative splicing?
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
33
What are telomeres?
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.
34
What is the end problem of DNA replication?
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
35
What is telomerase? What is its role?
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
36
What are centromeres?
Join sister chromatids together to form a chromosome
37
What are kinetochores?
Contained within the centromere
Protein complex that binds to microtubules
38
What interaction is present between DNA and histones?
Ionic
DNA - negatively charged backbone
Histones - positively charged
39
Why do we package DNA into chromosomes?
Neutralises negative charge
DNA takes up less pace
Inactive DNA folded into inaccessible locations
40
What two techniques do we use to analyse chromosomes?
Karyotype
FISH
41
What is a karyotype?
An image of individual chromosomes
The chromosomes are ordered in size and grouped into pairs
We visualise both autosomal and sexual chromosomes
42
What are metacentric chromosomes?
Those which have a the centromere in the centre so that both sections are equal in length
43
What are submetacentric chromosomes?
Those which have the centromere slightly offset from the centre leading to a slight asymmetry in the length of the two sections
44
What are acrocentric chromosomes?
Those which have a centromere severely offset from the centre leading to a very long and very short section
45
What is fluorescent in situ hybridisation (FISH)?
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
46
What are the four types of probes used in FISH?
Unique sequence probes
Centromeric probes
Telomeric probes
Whole chromosome probes
47
What are unique sequence probes?
Binds to specific small segments of certain chromosomes
48
What are centromeric probes?
Target the centromeric region of the particular chromosome
49
What are telomeric probes?
Bind to telomeres
50
What are whole chromosome probes?
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
51
What mutations do unique sequence probes detect?
Deletion
Insertion
52
What mutations do whole chromosome probes detect?
Translocations
Rearrangements
53
What is the role of cell division?
Allows organisms to grow and develop
Replace dead cells
Repair tissue
54
What are the three stages of cell cycle?
Interphase
Mitosis
Cytokinesis
55
What phases are involved in interphase?
G1
S
G2
56
What occurs during G1?
The cell synthesis new proteins and organelles
57
What occurs during S?
DNA replication
58
What occurs during G2?
The cell synthesis more proteins and organelles
Checks for any errors that occurred during the S phase
59
What are the stages of mitosis?
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
What occurs during cytokinesis?
Cytoplasm splits and we form two new daughter cells
61
What is meiosis?
Cell division of gametes in the reproductive organs
Diploid cells in the ovaries and testes divide to form haploid egg and sperm cells
62
What is the product of meiosis?
Four haploid cells
63
What occurs during meiosis one?
Homologous chromosomes are separated
64
What occurs during meiosis two?
Chromosomes are separated into chromatids
65
What occurs during prophase I?
Chromosomes condense, then pair with their homologous chromosome to form a tetrad/
66
What is crossing over?
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
What occurs during metaphase I?
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
What is independent assortment?
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
What occurs during anaphase I?
The microtubules shorten and pull on the chromosomes so that they are pulled to opposite sides of the cell
70
What occurs during telophase I?
As the chromosomes approach opposite ends of the cell, the cell begins to divide
71
What occurs during cytokinesis I?
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
What occurs during prophase II?
Chromosomes condense
No crossing over occurs
73
What occurs during metaphase II?
The nuclear membrane breaks down, chromosome pairs line up along the metaphasic plate
74
What occurs during anaphase II?
The microtubules shorten and pull on the chromosomes so that the chromatids are pulled to opposite sides of the cell
75
What occurs during telophase II?
As the chromatids approach opposite ends of the cell, the cell begins to divide
76
What occurs during cytokinesis II?
Each cell divides into, forming four haploid cells, which have 23 chromosomes and 23 chromatids each.
77
What is oogenesis?
Process of egg formation
78
What is spermatogenesis?
Process of sperm formation
79
Hoe does gamete formation occur in males?
Meiosis one occurs at puberty and all four haploid cells develop into sperm cells
80
Hoe does gamete formation occur in females?
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
What is X-inactivation? Why does it occur
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
What are the three types of chromosomal abnormalities?
Numerical
Structural
Mutational
83
What are numerical chromosome abnormalities?
Result from whole chromosomes missing from or extra to the normal pair
84
What are structural chromosome abnormalities?
Result from a part of an individual chromosome being missing, added or switched to another chromosome
85
What are the two types of translocations?
Reciprocal
Robertsonian
86
What are reciprocal translocations?
Involves breaks in two chromosomes with the formation of two new derivative chromosomes
87
What are Robersonian translocations?
Involve the fusion of two acrocentric chromosomes
Result in no genetic material being lost
88
What two arrangements do reciprocal arrangements result in?
Balanced
Unbalanced
89
What are balanced translocations?
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
What are unbalanced translocations?
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
What are deletions?
Deletion of one or more bases in a DNA sequence
92
What are the two types of deletions?
Terminal
Interstitial
93
What are terminal deletions?
The loss of the end of a chromosome
94
What are interstitial deletions?
Results after two breaks are induced
95
What are insertions?
When one or more bases is added into a nucleotide sequence
96
What are inversions?
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
What are the two types of inversions?
Paracentric
Pericentric
98
What are paracecntric inversions?
Do not include the centromere and both breaks occur in one arm of the chromosome
99
What are pericentric inversions?
Include the centromere and there is a break point in each arm.
100
What do chromosome abnormalities result from? What is this?
Non-disjunction
Failure of the homologous chromosomes or sister chromatids to separate properly during cell division.
101
What happens if non-disjunction occurs during anaphase I?
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
What happens if non-disjunction occurs during anaphase II?
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
What are autosomal aneuploid syndromes?
Abnormalities that do not involve the sex chromosomes
104
What is trisomy 21?
Downs syndrome
Extra 21 chromosome from mother
105
What is trisomy 13?
Patu syndrome
Extra 13 chromosome from mother
106
What is trisomy 18?
Edwards syndrome
Extra 18 chromosome from mother
107
What are sex chromosomes aneuploid syndromes?
Abnormalities that involve the sex chromosomes
108
What is 45, X?
Turner syndrome
Female partly missing or completely missing X chromosome
109
What is 47, XXY?
Klinefelter syndrome
Males inheriting an additional Y chromosome.
110
What are germline mutations?
A mutation with germ cells
Can be passed on to offspring
111
What are somatic mutations?
A mutation with somatic cells
Cannot be passed on to offspring
112
What are non-coding sequence mutations?
Mutations that arise in non-coding sequences of DNA, which are sequences that do not encode for proteins
113
What are coding sequence mutations?
Mutations that arise in coding sequences of DNA, which are sequences that do code for proteins
114
What are the four types of coding sequence mutations?
Silent
Missense
Nonsense
Frameshift
115
What are silent mutations?
Mutations in DNA that do not have an observable effect on the organisms phenotype
116
What are missense mutations?
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
What are nonsense mutations?
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
What are frameshift mutations?
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
What is mutation nomenclature?
Terminology used to describe mutations
120
What are the techniques used to detect mutations?
PCR
Gel electrophoresis
RFLP analysis
ARMS
DNA sequencing
121
Describe PCR
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
What are the advantages of PCR?
Doesn't take long
Easy
Robust
123
What is gel electrophoresis?
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
What is RFLP analysis?
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
What are restriction endonucleases?
Enzymes from bacterial cells which are able to recognise specific DNA sequences and always cut DNA at the same site.
126
What are the advantages of RFLP analysis?
Simple
Cheap
127
What are the disadvantages of RFLP analysis?
Not always feasible.
128
What is DNA sequencing?
Determines the nucleic acid sequence in DNA.
Usually uses dideoxynucleotides
129
What are the disadvantages of DNA sequencing?
Expensive equipment
Poor-quality
130
What is ARMS?
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
What are the advantages of ARMS?
Cheap
132
What are the disadvantages of ARMS?
Require sequence information
Limited amplification size
