XII Chap 6 Molecular Inheritance Flashcards
1
Q
Adenine pairs with?
A
Thymine
2
Q
Guanine pairs with?
A
Cytosine
3
Q
DNA is a long polymer of _______________
A
deoxyribonucleotides
4
Q
Length of DNA is defined as:
A
number of base pairs (pairs of nucleotides)
5
Q
What are the 3 components of nucleotides?
A
- Nitrogenous base
- Pentose (5-carbon) sugar
- Phosphate group
6
Q
Two types of nitrogenous bases?
A
Purines (Adenine and Guanine) - 2 rings
Pyrimidines (Cytosine, Thymine and Uracil) - 1 ring
7
Q
How long is the haploid content of human DNA?
A
3.3 x 10^9
8
Q
______ (nitrogenous base) is only present in DNA and ______ only in RNA
A
Thymine in DNA
Uracil in RNA
9
Q
DNA was first identified by ?
A
Friedrich Meischer in 1869 - “acidic substance in nucleus”
Named it Nuclein
10
Q
What is a nucleoside?
A
Sugar attached to nitrogenous base;
nitrogenous base is linked to OH of 1’ C pentose sugar through an N-glycosidic linkage
11
Q
Examples of nucleosides
A
Adenosine or deoxyadenosine Guanosine or deoxyguanosine Cytidine or deoxycytidine Uridine or Deoxythymidine
12
Q
How is nucleotide formed from nucleoside?
A
Phosphate group is linked to OH of 5’ C of a nucleoside through phosphoester linkage
13
Q
What is a dinucleotide?
A
Two nucleotides linked through 3’ - 5’ C phosphodiester linkage to form a dinucleotide
14
Q
What are at the 2 ends of a polymer?
A
One end a free phosphate moeity at 5’ end of sugar
One end a free OH of 3’ C group
15
Q
Backbone of polynucleotide chain is formed due to _____ and ______
A
sugar and phosphates
16
Q
The _________ linked to sugar moiety project from the backbone
A
nitrogenous bases
17
Q
In RNA, every nucleotide residue has an additional ________ present at the ______ position in the ribose
A
-OH group;
2’-position
18
Q
__________ is another chemical name for thymine
A
5-methyl uracil
19
Q
In ________ Watson and Crick suggested the _________ model based on the X-ray diffraction data produced by __________
A
1953;
Double Helix;
Rosalind Franklin + Maurice Wilkins
20
Q
___________ observed that for a double stranded DNA the ratios of Adenine:Thymine:Guanine:Cytosine are constant and equals one
A
Erwin Chargaff
21
Q
What are the 5 salient features of the Double-helix structure of DNA?
A
- Made of 2 polynucleotide chains, sugar-phosphate backbone and bases project inside
- Two chains have anti-parallel polarity
- Bases in 2 strands are paired through hydrogen bonds forming base pairs; purine always opposite to a pyrimidine => uniform distance between the 2 strands of helix
- Two chains are coiled in right-handed fashion; helix pitch is 3.4 nm; 10 bp in each turn; distance between bps is 0.34 nm
- Stacking of bp planes and H-bonds => stable helix structure
22
Q
1 Nanometer = ____ meters
A
1 billionth => 1 / 10^9
23
Q
What is anti-parallel polarity?
A
One chain has polarity 5’ -> 3’ then the other has 3’ -> 5’
24
Q
Adenine and Thymine form how many hydrogen bonds? Same Q for Cytosine and Guanine?
A
AT - 2 bonds
CG - 3 bonds
25
What is the Central Dogma? Who proposed it?
Francis Crick;
| genetic information flows from DNA to RNA (transcription) to Protein (translation)
26
In some viruses, flow of information is reversed from RNA to DNA. This is called?
Reverse transcription
27
What is the distance between 2 consecutive base pairs?
0.34 nm
28
If length of human DNA is calculated it comes out to be ____ metres
2.2
29
How is DNA arranged in prokaryotes?
No nucleus
Large loops of DNA (negatively charged) - proteins (positively charged) - 'nucleoid' region
30
How is DNA arranged in eukaryotes?
Nucleosomes (negatively charged DNA wrapped around 8 molecules of positively charged protein => histone octamer) in chromatin (repeating structure) like 'beads-on-string' structure
31
What is a histone?
Set of positively charged basic proteins;
rich in basic amino acid residues lysine and arginine;
amino acid residues carry positive charges
32
What is a histone octamer?
8 units of histomes (o.e. positively charged proteins)
33
Typical nucleosome contains _______ base pairs of DNA
200
34
How are chromosomes formed in eukaryotes?
Beads-on-string structure in chromatin is packaged to form chromatin fibers, coiled and condensed at metaphase stage of cell division to form chromosomes
35
What are NHC proteins?
Additional set of proteins to pack chromatin at higher level - Non-histone Chromosomal protein
36
What is euchromatin?
Region of chromatin that is loosely packed, stains light and transcriptionally active
37
What is heterochromatin?
Region of chromatin that is tightly packed, stains dark and transcriptionally inactive
38
Explain Griffith's Transforming Principle
Some genetic material was transferred from heat-killed S strain bacteria to R bacteria that allowed R bacteria (previously benign) to develop a smooth polysaccharide coat and kill the mice
39
When did Griffith conduct his experiments to yield the transforming principle? What was his experiment
1928,
Mice were infected with 2 different strains of bacteria Streptococcus pneumoniae (pneumococcus). One killed mice (S strain) and the other (R strain) was benign. A mixture of heat-killed S strain and benign R strain showed some kind of 'transformation' because R strain was now able to kill the mice.
40
What contribution did Avery, MacLeod and McCarty make to the study of DNA?
They determined the biochemical nature of Griffith's transforming principle
Previously genetic material was though to be a protein. They purified proteins, RNA, DNA, etc. and discovered that DNA alone transformed R bacteria.
41
In Avery, MacLeod and McCarty's experiment, digestion with ____ and _____ did not inhibit transformation but digestion with _______ did.
Protease or RNase did not inhibit;
| DNase did => DNA caused the transformation
42
What are protein-digesting enzymes called?
Proteases
43
What are RNA-digesting enzymes called?
RNase
44
________ experiment proved unequivocally that DNA was the genetic material
Hershey-Chase experiment involving viruses (bacteriophages) and E. coli bacteria
45
Describe the Hershey-Chase experiment
bacteriophages - DNA made radioactive with phosphorus - protein made radioactive with sulfur - infection => blending to separate viral coat => centrifugation to separate virus from bacteria
bacteria with radioactive DNA => radioactive;
bacteria with radioactive protein => not radioactive
Therefore, DNA is the genetic material passed from virus to bacteria
46
When does RNA act as genetic material?
In some viruses e.g. Tobacco Mosaic, QB bacteriophage
47
Criteria of a molecule that can act as genetic material?
1. Replication
2. Stability (chemical and structural)
3. Scope for Mutation
4. Express itself in 'Mendelian Characters'
48
______ molecules fail to fulfill the first criteria (replication) itself
Protein
49
_____ present at every nucleotide in RNA make it ______ and _______
2'-OH group;
| labile/unstable and easily degradable
50
RNA is known to be ______ and hence reactive
catalytic
51
Both RNA and DNA are able to mutate. T or F?
True
52
_________ can directly for the synthesis of proteins. RNA or DNA?
RNA
53
_______ is better for storage of genetic material whereas _________ is better for transmission of genetic material
DNA - storage
| RNA - transmission
54
Compare the characteristics of RNA and DNA as genetic material
DNA - more stable, less reactive, better for storage
RNA - mutates and evolves faster, can directly code for protein synthesis, better for transmission
55
______ was the first genetic material
RNA
56
Some important biochemical reactions in living systems are catalyzed by ________ instead of protein enzymes.
RNA catalysts
57
DNA has evolved a process of _________
repair
58
What is the semiconservative DNA replication model? Who is credited with it?
Credit - Watson and Crick
Two strands of DNA separate, act as template for new complementary strands;
after replication each DNA molecule will have one parental strand and one newly synthesized strand
59
Who & which experiment proved that DNA replicates semiconservatively?
Meselson & Stahl (1958);
Grew E. coli in medium containing 15N (heavy nitrogen) for several generations => 15N was incorporated into DNA
Then placed E. Coli with heavy DNA in a medium with normal 14N.
20 minutes => 100% hybrid / intermediate density
40 minutes => 50% hybrid and 50% 'light' DNA
60
Who & which experiment proved that DNA in chromosomes replicate semi-conservatiely?
Taylor et al, 1958
radioactive thymidine, Vicia faba (faba beans)
61
The main enzyme in DNA replication is _________
DNA-dependent DNA polymerase
62
In living cells, the process of replication requires a set of _________
catalysts / enzymes
63
What is DNA polymerase?
Enzyme that uses DNA template to catalyze the polymerisation of deoxyribonucleotides; highly efficient; high degree of accuracy
64
Any mistake during replication would result in _________
mutations
65
What are deoxyribonucleoside triphosphates
Act as substrates during replication;
| Provide energy for polymerisation reaction
66
The two terminal phosphates in a deoxynucleoside triphosphates are _____________
high-energy phosphates
67
What is a replication fork?
Small opening of the DNA helix where replication occurs (because DNA cannot be separated in its entire length - too much energy required)
68
DNA polymerases catalyse polymerisation only in one direction: _________
5' -> 3'
69
On ________ strand the replication is continuous;
| on _____ strand discontinuous
3' -> 5' - continuous
| 5' -> 3' - discontinuous
70
Discontinuously synthesized fragments in DNA replication are later joined by __________
DNA ligase
71
DNA polymerase can initiate the process of replication on their own. T or F?
False
72
Where does replication begin in DNA?
Origin of replication
73
Why are vectors required in recombinant DNA procedure?
Because they provide the origin of replication
74
In eukaryotes the replication of DNA takes place at ______ phase of cell-cyle
S-phase
75
A failure in cell division after DNA replication can lead to __________
polyploidy or chromosomal anomaly
76
What is transcription?
The process of copying genetic information from ONE strand of DNA into RNA
77
In transcription adenosine forms base pair with _______ instead of _______
uracil instead of thymine
78
Difference between replication and transcription
Replication: entire DNA gets copied
Transcription: only one of strands and only ONE segment is copied
79
Why are both strands of DNA not copied during transcription?
1. IDK
| 2. Two RNA molecules would be complimentary and would form double-stranded RNA => cannot be translated into protein
80
What are the 3 regions in a transcription unit?
1. Promoter - regulatory sequence where RNA polymerase attaches
2. Structural gene - set of genes that control one characteristic or function
3. Terminator - defines end of transcription
81
Template vs coding strand?
Template strand - polarity 3' -> 5', acts as a template
Coding strand - 5' -> 3', does not code for anything, reference point when defining transcription unit, same sequence as RNA (except U in place of T)
82
_______ and _______ flank the structural gene in a transcription unit
Promotor and Terminator
83
Where are promoter and terminator located?
Promoter - 5'-end, upstream
| Terminator - 3'-end, downstream, end of process of transcription
84
_________ is the functional unit of inheritance
Gene
85
The DNA sequence coding for tRNA and rRNA also define a gene. T or F?
True
86
What is a cistron?
segment of DNA coding for a polypeptide/protein
87
Monocistronic vs polycistronic
Monocistronic - eukaryotes
| Polycistronic - bacteria / prokaryotes
88
What are exons and introns?
Exons - coding segments, expressed sequences
| Introns - non-coding segments, interruptions / intervening sequences.
89
__________ appear in mature / processed RNA, ______ do not.
Exons - appear
| Introns - don't appear
90
Eurokaryotes have ____ genes
Split
91
Regulatory sequences are also called regulatory genes even though they do not code for any RNA or protein. Why?
Because regulatory sequences (and promoters) also affect inheritance of a character
92
What are the 3 major types of RNAs?
mRNA - messenger - provides template / info to make protein
tRNA - transfer - brings aminoacids and reads the genetic code (adaptor)
rRNA - ribosomal - structural and catalytic role in translation
93
Which RNAs are needed to synthesise a protein in a cell?
All three
94
How many DNA dependent RNA polymerases are needed to catalyse transcriptions of the different types of RNA in bacteria?
ONE
95
What is initiation?
RNA polymerase binds to promoter, initiates transcription by associating transiently with initiation factor (σ sigma)
96
RNA polymerase catalyzes all 3 steps: initiation, elongation and termination while also facilitating the opening of the helix. T or F?
True
97
What is the termination factor?
ρ (rho)
98
In bacteria, transcription and translation are decoupled. T or F?
False, they are coupled and take place in same compartment (no separation of cytosol and nucleus)
99
In bacteria, many times translation can begin much before mRNA is fully transcribed. How?
since mRNA does not require any processing to become active
100
What are the additional complexities of transcription in eukaryotes compared to bacteria?
1. Three different polymerases required to catalyze process
| 2. Splicing required to remove introns and join exons in defined order (and hnRNA has to be processed into mRNA)
101
What is the division of labor among RNA polymerases in eukaryotes?
RNA polymerase I - rRNAs (28S, 18S, 5.8S)
RNA polymerase II - hnRNA
RNA polymerase III - tRNA, 5srRNA, snRNAs
102
What is capping?
Met GTP (methyl guanosine triphosphate, which is a nucleotide) added to the 5'-end of hnRNA
103
What is tailing?
Adenylate residues (200-300 of them) added at 3'-end in a template independent manner
104
Fully processed hnRNA is called ______ and transported out of the ______ for translation
mRNA;
| nucleus
105
The presence of _______ is reminiscent of antiquity
introns / split-gene arrangements
106
The process of _____ represents the dominance of RNA-world
splicing
107
What is translation?
transfer of genetic information
from polymer of nucleotides
to synthesize
a polymer of amino acids
OR
polymerisation of amino acids to form a polypeptide
108
________ argued that there would be 64 codons in genetic code
George Gamow, physicist
109
Marshall Nirenberg's ____________ finally helped genetic code be deciphered
cell-free system for protein synthesis
110
What was Har Gobind Khorana's contribution to genetic code?
chemical method to synthesize RNA molecules with defined combinations of bases (homopolymers and copolymers)
111
______________ was helpful in polymerising RNA with defined sequences in enzymatic synthesis of RNA (a template independent manner)
Severo Ochoa enzyme
112
What are the features of the genetic code?
1. triplet, 61 codons for amino acids, 3 stop codons
2. Degenerate (some amino acids are coded by more than one codon) & unambiguous (one codon can only code for one amino acid)
3. no punctuations "comma-free", codons read in mRNA in contiguous fashion
4. (nearly) universal (except some mitochondria and protozoans)
5. AUG has dual function - codes for Methionine and is initiator codon
6. UAG, UGA, UAA are stop terminator codons
113
Relationships between genes and DNA are best understood by ________ studies
mutation
114
What is point mutation vs. frameshift mutation?
Point mutation - change of single base pair (nucleotide) in the gene
Frameshift - insertion or deletion of bp that changes reading frame
115
What is tRNA?
transfer RNA is an adapter molecule;
an anticodon loop that has bases complementary to code on mRNA;
amino acid acceptor end which binds to amino acids;
clover shape & an inverted L-shape
116
tRNA was called _______ before the genetic code was postulated
soluble RNA (sRNA)
117
tRNAs are universal for amino acids. T or F?
False, they are specific for each amino acid
118
tRNA has no specific initiator or stop versions. T or F?
False;
| no tRNA for stop codon BUT there is initiator tRNA
119
Amino acids are joined by a __________ bond
Peptide
120
Formation of peptide bond requires energy. T or F?
True
121
What is charging of tRNA? What's another name for it?
Amino acids are activated
in the presence of ATP
linked to their cognate tRNA
another name - aminoacylation of tRNA
122
If two charged tRNAs are brought close enough what happens?
Formation of peptide bond, since it is favored energetically
123
What is a ribosome?
Cellular factory responsible for protein synthesis;
consists of structural RNAs and 80 different proteins;
large and small subunit
124
How does protein synthesis occur in ribosome?
When small sub-unit encounters mRNA => binds to the start codon (AUG) recognized by the initiator tRNA => translation begins
=> elongation phase => complexes of amino aid linked to tRNA bind to codon in RNA in large subunit,
ribosome moves from codon to codon along mRNA, peptide bonds formed,
at the end, release factor binds to stop codon => terminating translation and releasing polypeptide from ribosome
125
Apart from being a cellular factory, ribosome acts as a _______ in the formation of peptide bond
catalyst
126
_________ in bacteria is the enzyme ribozyme
23S rRNA
127
What are UTRs?
Untranslated regions - sequences in mRNA that are not translated; required for efficient translation process;
present before start codon (5' end) and after stop codon (3' end)
128
What is a "translational unit" in mRNA?
sequence of RNA that codes for polypeptide,
| flanked by start codon (AUG) and the stop codon
129
In eukaryotes, regulation can be exerted at which 4 levels?
1. Transcription level (DNA to hnRNA)
2. Processing level (splicing, hnRNA to mRNA)
3. Transport of mRNA from nucleus to cytoplasm
4. Translational level
130
__________ conditions regulate the expression of genes
Metabolic, physiological or environmental conditions
131
In prokaryotes, regulation of gene expression occurs at which level?
rate of transcriptional initiation
132
Activity of RNA polymerase at a promoter in prokaryotes is regulated by ________
accessory/regulatory proteins - could act positively (activators) or negatively (repressors)
133
What are operators?
region adjacent to the promoter; regulates the access to promoter by binding to a repressor
134
Each operon has its specific operator and repressor. T or F?
True
135
What is an operon? Examples?
Polycistronic structural gene regulated by a common promoter + regulatory genes (operators)
e.g. lac, trp, ara, his, val
136
Lac operon consists of:
One regulatory gene (i gene) - operator
| Three structural genes (z, y, a)
137
What do the genes in the lac operon code for?
i - repressor
z - beta-galactosidase (β-gal) which is responsible for hydrolysis of disaccharide lactose into monomeric units - galactose + glucose
y - permease, which increases permeability of cell to β-galactosides
a - transacetylase
138
Not all three structural genes in lac operon are required for metabolism of lactose. T or F?
False, all are required
139
________ is the substrate for the enzyme beta-galactosidase
Lactose
140
What is an inducer?
Regulates switching on and off of the operon by its presence or absence
141
What happens if lactose is provided in growth medium of bacteria in absence of glucose?
lactose is transported into cell through action of permease
=> then lactose induces operon
=> repressor is inactivated
=> RNA polymerase has access to the promoter
=> transcription proceeds
142
Very low level of expression of lac operon is required at all times in the cell. Why?
Else lactose cannot enter cell. Inducing lac operon & y-gene only **increases** permeability, doesn't stop/start it entirely.
143
________ is the inducer for the lac operon
Lactose or allalactose
144
What does the repressor protein in the lac operon do?
Prevent RNA polymerase from transcribing the operon
145
Regulation of lac operon can be visualized as regulation of _______
enzyme synthesis by its substrate
146
Regulation of lac operon by repressor is referred to positive regulation. T or F?
False, negative regulation
147
When was HGP launched and completed?
| Who was involved?
1990, 2003 (13-year project)
US Dept of Energy, National Institute of Health, Wellcome Trust (UK), Japan, France, Germany, China
148
HGP was closely associated with development of new area in biology called ____________
bioinformatics
149
What were the goals of HGP?
1. identify all 20-25k genes in human DNA
2. determine sequences of 3 billion chemical bps
3. store info in databases
4. improve tools for analysis
5. transfer related tech to other sectors e.g. industry
6. address ELSI (ethical, legal, social issues)
150
What non-human organisms have also had their DNA sequenced as part of HGP?
```
bacteria
yeast
Caenorhabditis elegans (free living, non-pathogenic nematode)
Drosophila (fruit fly)
plants like rice and Arabidopsis
```
151
What were 2 methodologies used in HGP?
1. Expressed Sequence Tags (EST) - Identifying all genes expressed as RNA
2. Blind approach - sequencing the whole set of genome and later assigning different regions with functions (Sequence Annotation)
152
Commonly used hosts in HGP
BAC and YAC
| bacterial/yeast artificial chromosomes
153
Fragments of DNA in HGP were sequenced using ________ in a principle / method developed by _______
automated DNA sequencers (computer programs);
| Frederick Sanger
154
What is Sanger credited with developing?
1. principle used in HGP to sequence fragments
| 2. method for determination of amino acid sequences in proteins
155
Sequence of Chromosome 1 was the last to be completed in ________ as part of HGP
May 2006
156
How many chromosomes were sequenced in HGP?
24 (22 autosomes + X + Y)
157
Human genome contains ________ bp
3164.7 million
158
The total number of genes discovered in HGP were ________
30,000
159
Average gene has ______ bases
3000
160
Largest known human gene?
Dystrophin at 2.4 million bases
161
What percent of genome codes for protein?
<2%
162
________ nucleotide bases are exactly the same in all humans
99.9%
163
We know the functions of what percent of discovered genes?
50%
164
Repeated sequences that have no direct coding functions make up very large portion of human genome. T or F?
True
165
Repetitive sequences don't code directly for functions but they can shed light on ________
chromosome structure, dynamics & evolution
166
Which chromosome has the most genes? Least?
Chromosome 1 - 2968
| Chromosome Y - 231
167
Scientists have identified _______ locations where single-base DNA differences occur. These are called?
1.4 million locations;
| "snips" - Single Nucleotide Polymorphism (SNP)
168
What is DNA fingerprinting?
quick way to compare the DNA sequences of 2 individuals; identifying differences in repetitive DNA
169
Repetitive vs satellite DNA?
Repetitive DNA - small stretch of DNA repeated many times
| Satellite DNA - small peaks which different from bulk genomic DNA (consists of repetitive DNA)
170
What is polymorphism?
variation at genetic level that arises due to mutations;
| inheritable mutation that exists in 1% or more of the population (high frequency)
171
New mutations may arise in ____ or ____ cells
somatic or germ
172
Who developed DNA fingerprinting?
Alec Jeffreys
173
What is VNTR
Variable Number of Tandem Repeats is a satellite DNA that shows a high degree of polymorphism. Used as a probe in DNA Fingerprinting
174
What are the steps in DNA Fingerprinting?
1. Isolation of DNA
2. Digestion of DNA by restriction endonucleases
3. separation of DNA fragments by gel electrophoresis
4. transferring/Southern blotting of separated DNA fragments to synthetic membranes
5. hybridisation using radiolabelled VNTR probe
6. detection of hybridised DNA fragments by autoradiography
175
VNTR belongs to which class of satellite DNA?
mini-satellite
176
_________ varies from chromosome to chromosome in an individual
Copy number
177
The size of VNTR varies in size from _____ to ______
0.1 to 20 kb
178
The numbers of repeat show very low degree of polymorphism in the DNA sequence used in fingerprinting. T or F?
False, HIGH degree of polymorphism
179
Sensitivity of DNA fingerprinting has been increased by use of _________
PCR - polymerase chain reaction
180
DNA from a single cell is enough to perform fingerprint analysis. T or F?
True
181
Applications of DNA fingerprinting?
1. forensic science
| 2. population and genetic diversities
182
Paternal and maternal alleles of chromosome contain same or different copy numbers of VNTR?
Different
183
Nucleic acids are ________ of nucleotides
long polymers
184
Hallmark of double-stranded helix structure is ______ between the bases from opposite strands
Hydrogen bonding
185
A segment of DNA that codes for RNA can be referred to simplistically as _______
a gene
186
tRNA binds to specific amino acid at one end and pairs through ____-bonding with codes on mRNA through anticodons
H-bonding
187
Translation can also be known as _________
protein synthesis
188
_______ acts as a catalyst for peptide bond formation
One of the rRNA
189
__________ are energetically expensive processes
Transcription and translation
190
Why do transcription and translation have to be regulated?
Since they are very expensive energetically
191
Very low level of expression of lac operon is required at all times in the cell. Why?
Else lactose cannot enter cell. Inducing lac operon & y-gene only **increases** permeability, doesn't stop/start it entirely.
192
The repressors of the lac operon is synthesized all the time from the i gene. What's another word for "all the time"?
Constitutively
