Genetics Flashcards
1
Q
What are nucleotides composed of?
A
a nitrogenous base, a pentose sugar and one or more phosphate groups
2
Q
What are the pentose sugars found in DNA and RNA?
A
deoxyribose
ribose
3
Q
what is the difference between deoxyribose and ribose?
A
ribose has a hydroxyl group on the second carbon
4
Q
How are carbons in pentose sugars labelled?
A
1 to 5
5
Q
What does carbon 1 (1’) bond to in the formation of nucleotide?
A
the nitrogenous base
6
Q
What is carbon 5 (5’) bonded to in the formation of a nucleotide?
A
a tail on the ring structure that is bonded to the phosphate group
7
Q
What are the two categories of nitrogenous bases?
A
purine or pyrimidines
8
Q
How many pyrimidines does DNA have?
A
2
9
Q
What are the two pyrimidine nitrogenous bases of DNA?
A
cytosine
thymine
10
Q
What are the pyrimidines found on RNA?
A
cytosine
uracil
11
Q
What are the purines present in both DNA and RNA?
A
adenine
guanine
12
Q
what is DNA a storage of?
A
genetic information
13
Q
What does RNA act as a messenger between?
A
DNA and ribosomes to make proteins
14
Q
How many strands do DNA and RNA have?
A
DNA: double strand
RNA: single strand
15
Q
What are nucleotides linked by in DNA and RNA?
A
phosphodiester bonds
16
Q
What do the phosphodiester bonds between nucleotides help to create?
A
a sugar phosphate backbone
17
Q
Is the sugar phosphate backbone hydrophilic or hydrophobic?
A
hydrophilic
18
Q
Is the sugar phosphate backbone positively or negatively charged?
A
negative
19
Q
What are the 2 free groups found on each nucleotide?
A
5’ phosphate and 3’ hydroxyl (OH) group
20
Q
In what direction is a nucleotide sequence always written?
A
5’ to 3’
21
Q
In what direction do DNA strands run?
A
in opposite directions
22
Q
What is the fact that DNA strands run in the opposite direction to each other also known as?
A
antiparallel
23
Q
Do the 2 strands of DNA have the same sequence?
A
yes, complementary strands
24
Q
What do the nitrogenous bases of the two anti-parallel strands pair together to form?
A
double stranded nucleic acids
25
What are adenine - thymine bases stabilised by?
two hydrogen bonds
26
What are guanine and cytosine bases stabilised by?
three hydrogen bonds
27
Why are the bonds between guanine and cytosine stronger than those between adenine and thymine?
because of the 3 hydrogen bonds rather than 2
28
What does the genetic code code for?
amino acids
29
How many bases code for an amino acid?
3
30
What is the name of the group of 3 bases that code for an amino acid?
codon
31
What is meant by the genetic code being degenerate?
some amino acids are coded for by more than one codon
32
What 3 bases signify the start codon (Met)?
AUG
33
What are the stop codons?
UAA, UAG, UGA
34
What do stop codons do?
direct the synthesis of the peptide to cease
35
What are genes?
sequences of DNA containing intron and exon regions
36
What do genes code for?
RNA
37
What is the DNA before the gene start site?
regulatory region
38
what is the regulatory region of DNA before the gene start site known as?
the promoter
39
What are genomes?
strands of DNA that contain genes
40
What do genomes contain as well as genes?
large amounts of non-coding DNA
41
What essential role does some of the non-coding DNA play in gene expression?
binds to transcription factors which regulate the transcription of genes
42
What is 'junk DNA'?
DNA on a genome that has no apparent function
43
How many copies of each somatic gene do individuals contain?
2
44
What are copies of genes also called?
alleles
45
How many alleles of a gene are on each chromosome?
one on each
46
What sort of DNA is always maternally inherited?
mitochondrial DNA (mtDNA)
47
What does mitochondrial DNA (mtDNA) encode for?
a small number of mitochondrial proteins
48
Why is DNA condensed into chromosomes?
DNA is much longer than the cells that contain it
49
How are nucleosomes formed?
strands of DNA wrap around histones to form nucleosomes
50
What do multiple nucleosomes together create?
chromatin
51
how does chromatin form a chromosome?
loops and condenses
52
What are homologous chromosomes?
a pair of chromosomes
53
Do chromosome numbers vary between species?
yes
54
How many homologous do humans have?
23 (46 single chromosomes)
55
What are the sister chromatids joined at a central point by?
centromere
56
What is a kinetochore?
an associated protein that is involved in cell division
57
What are the ends of the chromosomes called?
telomeres
58
What are the telomeres?
sections of non-coding DNA that act as buffers to prevent shortening of the chromosomes during cell division
59
What can telomeres only be extended by?
telomerase
60
what is the shorter arm of the chromosome called?
the p arm
61
What is the longer arm of the chromosome called?
the q arm
62
What can be used to identify and map loci (locations) on the chromosomes?
when stained banding occurs
63
What is a chromosome karyotype?
a picture of an individuals chromosomes
64
What is a karyotype used to identify?
chromosomes, sex, characterization of cancer and any abnormalities associated with inherited defects
65
When is the DNA double helix replicated?
when the cell divides
66
Why is replication of genetic material in mitosis a semi-conservative process?
both new helixes have one parent strand of DNA in
67
What do the sequence of bases on the parent stand act as?
template for synthesis of the daughter strand
68
what are the 3 phases of genome replication?
initiation, elongation, termination
69
What happens during the initiation phase of genome replication?
Recognition of the position (s) on a DNA molecule where the replication will begin.
70
What enzyme unwinds the DNA helix?
topoisomerase
71
what enzyme unzips the double helix?
helicase
72
What is the leading strand of DNA copied by?
DNA polymerase
73
in what prime direction are bases added?
5' to 3'
74
What are Okazaki fragments?
short 5' to 3' sections of the lagging strand of DNA
75
What does DNA polymerase need in order to bind to DNA?
short RNA primers
76
What enzyme are the short RNA primers required by DNA polymerase formed by?
DNA primase
77
What enzyme joins adjacent Okazaki fragments?
DNA ligase
78
When does DNA replication end?
when the replication bubbles meet
79
What reamins on the lagging strand when DNA replication ends?
a small gap
80
Why might the extreme 3’ end of the lagging strand not be copied?
the final Okazaki fragment cannot be primed – the priming site is beyond the end of the template
81
What is removed from the very end of a DNA molecule?
a primer
82
What do the telomeres at the end of a chromosome prevent?
any genes being lost
83
What is produced from DNA in order to facilitate protein production?
RNA
84
What is the process of producing RNA from DNA known as?
transcription
85
What sequences direct the RNA polymerase to bind to DNA?
promoter
86
How many strands of DNA serve as a template for RNA synthesis?
one (the template strand)
87
What is the non-template strand of DNA called?
the coding strand
88
in what direction is RNA synthesised?
5' to 3'
89
When does RNA synthesis end?
when the termination sequence is reached
90
What happens to the resulting RNA transcript prior to translation?
modified and processes
91
What are the RNA transcripts produced from the template strand known as?
pre RNA
92
Why are RNA transcripts known as pre RNA?
they still have non coding introns in them
93
What is added to protect the RNA from degradation by nucleases and aid binding to the ribosome?
a modified guanosine 5' cap
94
What is added at the 3' end of the pre RNA to protect from degradation?
a poly A tail
95
What happens during splicing of pre RNA?
introns are removed and exons joined together before RNA is exported to the cytoplasm
96
What are the 3 main classes of RNA involved in protein production?
mRNA: messenger RNA
tRNA: transfer RNA
rRNA: ribosomal RNA
97
What does mRNA do?
encodes the amino acid sequences of proteins
98
What does tRNA do?
reads the information encoded on mRNA and transfers the appropriate amino acid to the polypeptide chain during protein synthesis
99
What does rRNA do?
is a constituent of ribosomes
100
Where does translation occur?
in the ribosomes in the cytoplasm/on the endoplasmic reticulum.
101
what do ribosomes catalyse?
the joining of amino acid monomers
102
What is the joining of amino acid monomers directed by?
mRNA sequence
103
in what prime direction do ribosomes read the mRNA?
5' to 3'
104
In what segments is the mRNA read by ribosomes?
3 nucleotide segements/codons
105
What do tRNA molecules match to codons on the mRNA?
amino acids
106
What does de novo synthesis of nucleotides begin with?
their metabolic precursors
107
What are the metabolic precursors of nucleotides?
amino acids, ribose 5-phosphate, CO2 and NH3
108
adenosine triphosphate (ATP) is the nucleotide that contains ___?
adenine
109
guanosine triphosphate is the nucleotide that contains ___?
guanine
110
Cytidine triphosphate (CTP) is the nucleotide that contains ____?
cytosine
111
Uridine triphosphate (UTP) is the nucleotide that contains ___?
uracil
112
Deoxythymidine triphosphate (dTTP) is the nucleotide that contains ____?
thymine
113
What is the precursor for purines?
inosinate (IMP)
114
How is adenylate (AMP) created?
Aspartate is added to inosinate (IMP) to form adenylosuccinate by adenylosuccinate synthetase, using GTP for energy. Adenylosuccinate is converted to adenylate/adenosine monophosphate (AMP)
115
How is guanylate created?
IMP is converted to xanthylate (XMP). An amine group from glutamine is added to xanthylate to form Guanylate/guanosine monophosphate (GMP) using ATP for energy.
116
What are pyrimidines synthesised from?
carbamoyl phosphate and aspartate
117
What is added to carbamoyl phosphate and aspartate to create pyrimidine ribonucleotides?
ribose
118
What inhibits the creation of
carbamoyl aspartate.
119
What molecule does the production of dTMP start with?
cytidine diphosphate (CDP) or uridine diphosphate (UDP)
120
Once dTMP is formed what is it converted from and to?
monophosphate to triphosphate in the same way as the other nucleotides
121
What are nucleoside monophosphates converted to?
nucleoside triphosphates
122
what enzyme is phosphorylation of AMP to ADP promoted by?
adenylate kinase
123
How are other nucleoside diphosphates formed?
by the action of nucleoside monophosphate kinases
124
Nucleoside diphosphates (NDPs) are converted to triphosphates (NTPs) by the action of which molecule?
nucleoside diphosphate kinase
125
What do salvage pathways recycle?
the free bases and nucleosides released from nucleic acid breakdown
126
how does the salvage pathway of purines work?
The enzyme adenosine phosphoribosyltransferase catalyses the formation of AMP from free adenine and 5-phosphoribosyl-1-pyrophosphate (PRPP). The enzyme hypoxanthine-guanine phosphoribosyltransferase catalyses the same reaction with guanine instead of adenine
127
how does the salvage pathway of pyrimidines work?
Pyrimidines are recycled by a similar pathway as purines
128
Give 5 examples of drugs that affect the way nucleotides are biosynthesised
Azaserine and acivicin – glutamine analogues which inhibit glutamine amidotranferases
Fluorouracil – converted to FdUMP via salvage pathways and binds to and inactivates thymidylate synthase Methotrexate – folate analogue which inhibits dihydrofolate reductase
Trimethoprim – antibiotic which binds to bacterial dihydrofolate reductase nearly 100,000 times better than to the mammalian enzyme
129
What are drugs that affect the way nucleotides are biosynthesised often used for?
to target cancer cells which have greater requirements for nucleotides due to their excessive growth, and are therefore more susceptible to nucleotide synthesis inhibition
130
What does cytogenetics do?
Cytogenetics uses an individual’s karyotype to determine its sex
131
What does polymerase chain reaction allow?
PCR allows detection of DNA with a very high sensitivity
132
What is meant by high sensitivity in PCR?
it can detect a very small amount of the DNA
133
How does PCR work?
having primers that bind to specific fragments of DNA, and then using DNA polymerase to repeatedly copy that DNA fragment.
134
how does the number of DNA copies change through each cycle of PCR?
doubles with each cycle
135
What does PCR exponentially ampilfy and for what reason?
the DNA target region so that the product can be visualised
136
How is DNA seperated by size in PCR?
by agarose gel electrophoresis
137
What dye is DNA stained with during PCR?
commonly ethidium bromide
138
What are used as markers in PCR?
Ladders (sequences of DNA with known sizes)
139
What can be done with DNA amplified by PCR?
sequenced in order to identify genetic mutations
140
What is RT-PCR or RT-qPCR?
Quantitative Reverse Transcriptase Polymerase Chain Reaction
141
what is qPCR or qRT-PCR?
Quantitative Real Time Polymerase Chain Reaction
142
What is Quantitative Reverse Transcriptase PCR (RT-PCR or RT-qPCR) used for?
to determine the levels of mRNA in a sample by using reverse transcriptase (RT), an enzyme from retroviruses (e.g. FIV and HIV) that converts RNA to DNA
143
what can the resulting DNA from Quantitative Reverse Transcriptase PCR (RT-PCR or RT-qPCR) be amplified by?
PCR
144
What sort of organisms often only have RNA and protein?
viruses (including coronavirus)
145
What is quantitative real time PCR (qPCR or qRT-PCR) use to quantify DNA (or mRNA) concentration?
a florescent readout
146
What dye does the simplest method of quantitative real time PCR (qPCR or qRT-PCR) use?
SYBR green which fluoresces when it binds to double-stranded DNA
147
What can be useful in multiplex PCRs using quantitative real time PCR (qPCR or qRT-PCR)?
Specific probes can also be used which will only label specific DNA strands
148
What is the level of florescence of SYBR green related to in quantitative real time PCR (qPCR or qRT-PCR)?
the quantity of DNA, useful for comparing different samples
149
What are quantitive PCR results often quoted as?
Cycle Threshold (CT) values
150
With every quantitative real time PCR (qPCR or qRT-PCR) cycle what is measured in real time?
the fluorescence, related to the DNA quantity
151
When do samples with a lower (CT) value reach target florescence value?
after fewer cycles, meaning they had higher initial DNA concentrations.
152
What are the advantages of testing for DNA?
identify mutations in patient genes or detect pathogen DNA or RNA
Quantitative or qualitative
very high sensitivity (few false negatives)
153
what are the disadvantages of testing for DNA?
Currently require samples to be sent to a lab –less convenient but better quality control
Poorer sample stability, DNA more stable than RNA (heat, pH, nuclease enzymes degrade both)
Lower specificity (some false positives)
Typically more expensive than routine protein tests
154
What does gene therapy aim to do?
replace a defective gene with a functional copy
155
What 2 ways can functional copies of genes be delivered to the defective genes?
via vectors such as modified viruses that are able to directly enter the target cells in the individual
via cells from the individual that have had the genes grown in them in a lab
156
How does direct delivery gene therapy via vectors work?
therapeutic transgene is packaged into a delivery vehicle such as a virus and injected into the patient
157
How does cell based delivary gene therapy via an individuals cells work?
therapeutic transgene is packaged into a delivery vehicle such as a virus, the therapeutic transgene is then introduced into a delivery cell, such as a stem cell, that is usually derived from the patient. The genetically modified cells (e.g. stem cells) are multiplied in the laboratory and re-administered to the patient
158
What are GMOs?
organisms that have modified genomes that are able to be transmitted to subsequent generations
159
What are examples of GM bacteria?
Genetically modified bacteria that produce insulin Genetically modified plaque bacteria which reduce tooth decay
160
What are examples of GM mice?
Models of human and animal disease
| “Knockout” mice to study gene function
161
What are examples of GM pigs?
Engineered so that their organs can be transplanted into humans
162
what are examples of GM foods?
Genetically modified to be resistant to diseases or pests Engineered to have a higher nutritional value
163
What is a clone?
a genetically identical copy of an animal
164
What are the 2 donors involved in cloning?
mammary cell donor and egg cell donor
165
What happens to the mammary and egg cells once they are removed from their donors?
mammary cells are cultured
| egg cell from ovary has nucleus removed
166
What happens once the cultured mammary cells and egg cell without it's nucleus are fused?
they are grown in a culture until an early embryo forms. they are then implanted into the uterus of a third sheep who beocomes the surrogate mother.
167
Who will the offspring produced by cloning be genetically identical to?
the mammary cell donor
168
what is the difference between de novo synthesis and salvage pathways?
de nonvo synthesis is the main pathway for synthesis of brand new nucleotides.In salvage pathways used nucleotides are recycled.
