CH-5 NCERT Flashcards
1
Q
What type of nucleic acid acts as the genetic material in most organisms?
A
DNA
RNA acts as genetic material in some viruses but primarily functions as a messenger.
2
Q
What are the three components of a nucleotide?
A
- Nitrogenous base
- Pentose sugar
- Phosphate group
3
Q
Name the two types of nitrogenous bases.
A
- Purines (Adenine and Guanine)
- Pyrimidines (Cytosine, Uracil, and Thymine)
4
Q
What is the role of the nitrogenous base in a nucleotide?
A
Forms nucleosides when linked to the pentose sugar.
5
Q
What type of linkage connects two nucleotides in a polynucleotide chain?
A
3’-5’ phosphodiester linkage
6
Q
Who first identified DNA as an acidic substance?
A
Friedrich Meischer in 1869
7
Q
What model did Watson and Crick propose for the structure of DNA?
A
Double Helix model
8
Q
What is Chargaff’s rule regarding base pairing in DNA?
A
The ratios between Adenine and Thymine and between Guanine and Cytosine are constant and equal one.
9
Q
What is the significance of base pairing in DNA?
A
It allows for complementary strands, enabling the prediction of one strand’s sequence from the other.
10
Q
What is the Central Dogma of molecular biology?
A
Genetic information flows from DNA to RNA to Protein.
11
Q
What is a nucleosome?
A
A structure formed by DNA wrapped around histone proteins.
12
Q
How many base pairs does a typical nucleosome contain?
A
200 base pairs
13
Q
What are the two types of chromatin based on packing density?
A
- Euchromatin (light-staining, transcriptionally active)
- Heterochromatin (dark-staining, transcriptionally inactive)
14
Q
What transformation did Frederick Griffith observe in his experiments?
A
R strain bacteria were transformed into S strain bacteria.
15
Q
What did Avery, MacLeod, and McCarty demonstrate about the transforming principle?
A
That DNA is the hereditary material.
16
Q
What experiment did Hershey and Chase conduct to prove DNA as genetic material?
A
They used radioactive labeling to track DNA and protein in bacteriophages.
17
Q
What is the difference between DNAs and DNase?
A
DNA is the genetic material, while DNase is an enzyme that digests DNA.
18
Q
Fill in the blank: DNA is a long polymer of _______.
A
deoxyribonucleotides
19
Q
What is the approximate length of DNA in a typical mammalian cell?
A
2.2 meters
20
Q
What does the term ‘nucleoid’ refer to in prokaryotes?
A
The region where DNA is organized and held with proteins.
21
Q
What is the charge of histones and why?
A
Histones are positively charged due to the abundance of lysine and arginine.
22
Q
What is the distance between two consecutive base pairs in DNA?
A
0.34 nm
23
Q
What is the pitch of the DNA double helix?
A
3.4 nm
24
Q
True or False: RNA contains uracil instead of thymine.
A
True
25
What type of radioactive material was used to grow viruses that contained radioactive DNA?
Radioactive phosphorus
## Footnote
DNA contains phosphorus, which allows for the incorporation of radioactive phosphorus.
26
What type of radioactive material was used to grow viruses that contained radioactive protein?
Radioactive sulfur
## Footnote
Protein does not contain sulfur, which is why only the protein was radioactive.
27
What indicated that DNA was the genetic material passed from virus to bacteria?
Bacteria infected with viruses that had radioactive DNA were radioactive.
## Footnote
In contrast, bacteria infected with viruses that had radioactive proteins were not radioactive.
28
What are the two main types of genetic material discussed?
DNA and RNA
## Footnote
While DNA is the predominant genetic material, some viruses use RNA.
29
List the four criteria that a molecule must fulfill to act as genetic material.
* It should be able to generate its replica (Replication).
* It should be stable chemically and structurally.
* It should provide the scope for slow changes (mutation) required for evolution.
* It should be able to express itself in the form of 'Mendelian Characters'.
30
Why is DNA considered more stable than RNA?
DNA is less reactive and has a double-stranded structure, while RNA has a 2'-OH group making it labile.
## Footnote
The presence of thymine instead of uracil also contributes to DNA's stability.
31
What is the term for the process by which DNA replicates?
Semiconservative DNA replication
## Footnote
This means each new DNA molecule contains one parental and one newly synthesized strand.
32
Who conducted the experiment that proved DNA replicates semiconservatively?
Matthew Meselson and Franklin Stahl
## Footnote
Their experiment involved growing E. coli in a medium with heavy nitrogen.
33
What is the main enzyme involved in DNA replication?
DNA-dependent DNA polymerase
## Footnote
This enzyme catalyzes the polymerization of deoxynucleotides using a DNA template.
34
What are the three regions that define a transcription unit in DNA?
* A Promoter
* A Structural gene
* A Terminator
35
What is the purpose of the promoter in a transcription unit?
It provides a binding site for RNA polymerase.
## Footnote
The promoter is located upstream of the structural gene.
36
What defines a gene in terms of DNA sequence?
A gene is defined as the functional unit of inheritance.
## Footnote
It can also refer to segments coding for tRNA or rRNA.
37
What are the three major types of RNA in bacteria?
* mRNA (messenger RNA)
* tRNA (transfer RNA)
* rRNA (ribosomal RNA)
38
During transcription, which strand of DNA serves as the template strand?
The strand with polarity 3'→5'
## Footnote
The other strand, which has the polarity 5'→3', is referred to as the coding strand.
39
What happens to RNA once RNA polymerase reaches the terminator region?
The nascent RNA is released.
## Footnote
This marks the end of the transcription process.
40
Fill in the blank: The scheme proposed by Watson and Crick for DNA replication is termed _______.
[semiconservative DNA replication]
41
What is the role of RNA polymerase in bacteria?
Catalyses transcription of all types of RNA
## Footnote
It binds to the promoter and initiates transcription, using nucleoside triphosphates as substrates.
42
What are the three main steps of transcription in bacteria?
Initiation, elongation, termination
## Footnote
RNA polymerase catalyses elongation and associates with initiation-factor (σ) and termination-factor (ρ) for initiation and termination.
43
How does transcription and translation occur in bacteria?
Transcription and translation are coupled
## Footnote
mRNA does not require processing and both processes occur in the same compartment.
44
What is the function of RNA polymerase I, II, and III in eukaryotes?
RNA polymerase I transcribes rRNAs, RNA polymerase II transcribes hnRNA, RNA polymerase III transcribes tRNA and snRNAs
## Footnote
This division of labor allows for specialized functions in gene expression.
45
What is splicing in eukaryotic transcription?
Removal of introns and joining of exons
## Footnote
This process results in the formation of functional mRNA from primary transcripts.
46
What are the additional processing steps for hnRNA?
Capping and tailing
## Footnote
Capping involves adding methyl guanosine triphosphate to the 5'-end, while tailing adds adenylate residues to the 3'-end.
47
What is the significance of introns in the genome?
They represent an ancient feature and dominance of RNA-world
## Footnote
Their presence and the process of splicing have implications for understanding genetic evolution.
48
What is the genetic code?
A set of rules that specifies the sequence of amino acids in proteins
## Footnote
It directs the synthesis of proteins based on the sequence of nucleotides.
49
What is the structure of a codon in the genetic code?
A triplet of nucleotides
## Footnote
61 codons code for amino acids, while 3 serve as stop codons.
50
What does it mean that the genetic code is degenerate?
Some amino acids are coded by more than one codon
## Footnote
This feature provides some redundancy in the genetic code.
51
What is the function of AUG in the genetic code?
Codes for Methionine and acts as the initiator codon
## Footnote
AUG signifies the start of translation.
52
What is a frameshift mutation?
Insertion or deletion of bases that alters the reading frame
## Footnote
This can lead to significant changes in the resultant polypeptide.
53
What is tRNA and its role in translation?
An adapter molecule that reads the genetic code and binds to specific amino acids
## Footnote
tRNA has an anticodon that pairs with the mRNA codon.
54
What is the role of the ribosome in translation?
Synthesizes proteins by polymerizing amino acids into polypeptides
## Footnote
It consists of structural RNAs and proteins and has two subunits.
55
What is the significance of untranslated regions (UTRs) in mRNA?
They are required for efficient translation
## Footnote
UTRs are present at both the 5'-end and 3'-end of the mRNA.
56
How is gene expression regulated in prokaryotes?
Primarily at the transcriptional initiation level
## Footnote
Regulatory proteins interact with RNA polymerase and promoter regions.
57
What is the lac operon?
A transcriptionally regulated system in E. coli for lactose metabolism
## Footnote
It consists of a regulatory gene and structural genes that code for enzymes involved in lactose hydrolysis.
58
What genes are involved in the lac operon and their functions?
* i gene - codes for repressor
* z gene - codes for beta-galactosidase
* y gene - codes for permease
* a gene - encodes transacetylase
## Footnote
These genes work together to metabolize lactose.
59
What does the i gene code for in the lac operon?
The repressor of the lac operon
## Footnote
The repressor prevents RNA polymerase from transcribing the operon.
60
What is the role of the z gene in the lac operon?
Codes for beta-galactosidase (β-gal)
## Footnote
β-gal is responsible for hydrolyzing lactose into galactose and glucose.
61
What does the y gene code for in the lac operon?
Permease
## Footnote
Permease increases the permeability of the cell to β-galactosides.
62
What is the function of the a gene in the lac operon?
Encodes a transacetylase
## Footnote
All gene products in the lac operon are required for lactose metabolism.
63
What is lactose classified as in the context of the lac operon?
Inducer
## Footnote
Lactose regulates the switching on and off of the operon.
64
True or False: Glucose can act as an inducer for the lac operon.
False
## Footnote
Only lactose or allolactose can act as inducers.
65
What type of regulation is the lac operon under due to the repressor?
Negative regulation
## Footnote
The lac operon is also under positive regulation, which is not discussed here.
66
When was the Human Genome Project (HGP) launched?
In the year 1990
## Footnote
HGP aimed to sequence the entire human genome.
67
What is the estimated total number of genes in human DNA?
Approximately 20,000-25,000 genes
## Footnote
This number is lower than previous estimates of 80,000 to 140,000 genes.
68
What percentage of the human genome codes for proteins?
Less than 2 percent
## Footnote
The majority of the genome consists of non-coding sequences.
69
What is the total number of base pairs in the human genome?
Approximately 3 x 10^9 bp
## Footnote
This vast amount of data required advanced computational resources for analysis.
70
What are Expressed Sequence Tags (ESTs) used for in the HGP?
Identifying all the genes that are expressed as RNA
## Footnote
ESTs help in understanding gene expression.
71
What is the purpose of Sequence Annotation in genome sequencing?
Assigning different regions in the sequence with functions
## Footnote
This helps in understanding the roles of various DNA segments.
72
What is the largest known human gene?
Dystrophin
## Footnote
Dystrophin is 2.4 million bases long.
73
What are single nucleotide polymorphisms (SNPs)?
Locations where single-base DNA differences occur
## Footnote
SNPs are important for understanding genetic variation and disease associations.
74
What is DNA fingerprinting?
A technique to identify differences in specific regions of DNA sequence
## Footnote
It is particularly useful for forensic applications.
75
What kind of DNA is used as a probe in DNA fingerprinting?
Variable Number of Tandem Repeats (VNTR)
## Footnote
VNTRs show high degrees of polymorphism.
76
What does the technique of DNA fingerprinting involve?
Isolation of DNA, digestion, separation by electrophoresis, and hybridization
## Footnote
It requires multiple steps to compare DNA samples.
77
What is the significance of polymorphism in DNA?
It provides genetic variation within a population
## Footnote
Polymorphisms arise due to mutations and can be inherited.
78
True or False: DNA fingerprinting can be performed using DNA from a single cell.
True
## Footnote
PCR has increased the sensitivity of DNA fingerprinting techniques.
79
What are the complementary base pairs in DNA?
Adenine with Thymine and Guanine with Cytosine through three H-bonds.
80
What term refers to a segment of DNA that codes for RNA?
Gene
81
What is the process by which DNA replicates?
Semiconservative replication
82
In transcription, which strand of DNA serves as a template?
One of the strands of DNA
83
What happens to the transcribed mRNA in bacteria?
It is functional and can be directly translated.
84
What are the coding sequences in a gene called?
Exons
85
What are the non-coding sequences in a gene called?
Introns
86
What is the process by which introns are removed and exons are joined?
Splicing
87
How is the genetic code read?
In combinations of three (triplet genetic code) to code for an amino acid.
88
What role does tRNA play in protein synthesis?
Acts as an adapter molecule that binds to specific amino acids and pairs with mRNA.
89
Where does translation (protein synthesis) occur?
Ribosomes
90
What acts as a catalyst for peptide bond formation during translation?
One of the rRNA
91
Why are transcription and translation tightly regulated?
They are energetically very expensive processes.
92
What is the primary step for regulation of gene expression?
Regulation of transcription
93
What is an operon?
A unit of genes arranged together and regulated in bacteria.
94
What is the prototype operon in bacteria that codes for genes responsible for lactose metabolism?
Lac operon
95
How is the lac operon regulated?
By the amount of lactose in the medium.
96
What was the aim of the Human Genome Project?
To sequence every base in the human genome.
97
What technique is used to find variations in individuals at the DNA level?
DNA Fingerprinting
98
What principle does DNA fingerprinting work on?
Polymorphism in DNA sequences.
99
List two applications of DNA fingerprinting.
* Forensic science
* Genetic biodiversity
* Evolutionary biology
100
What is the sequence of the complementary strand for 5'-ATGCATGCATGCATGCATGCATGCATGC-3'?
5'-GCATGCATGCATGCATGCATGCATGC-3'
101
What is the sequence of mRNA if the coding strand is 5'-ATGCATGCATGCATGCATGCATGCATGC-3'?
5'-AUGCAUGCAUGCAUGCAUGCAUGCAUGC-3'
102
Fill in the blank: The function of a _______ is to initiate transcription.
Promoter
103
Fill in the blank: The _______ is responsible for bringing amino acids to the ribosome.
tRNA
104
Fill in the blank: The coding sequences that are part of the final RNA product are called _______.
Exons
105
What is the significance of the Human Genome Project being called a mega project?
It aimed to sequence every base in the human genome and opened new areas of research.
106
Briefly describe transcription.
The process of synthesizing RNA from a DNA template.
107
Briefly describe translation.
The process of synthesizing proteins from mRNA.
108
What is bioinformatics?
The application of computer technology to manage biological information.
109
Differentiate between repetitive DNA and satellite DNA.
Repetitive DNA consists of sequences that are repeated, while satellite DNA consists of longer repeats found in certain regions.
110
Differentiate between mRNA and tRNA.
mRNA carries the genetic code from DNA to ribosomes, while tRNA brings amino acids to ribosomes.
111
Differentiate between template strand and coding strand.
Template strand is used for RNA synthesis, while coding strand has the same sequence as mRNA (except for T/U).
112
List two essential roles of ribosome during translation.
* Provide a platform for joining amino acids
* Catalyze peptide bond formation
113
Why does the lac operon shut down some time after the addition of lactose?
The levels of lactose decline or the enzymes are no longer needed.
114
How did Hershey and Chase differentiate between DNA and protein?
By using radioactive isotopes to label DNA and protein and observing which entered bacterial cells.
115
What types of nucleic acid polymerases exist?
* DNA polymerases
* RNA polymerases
