🌸 Chapter 5
Molecular Basis Of Inheritance
( 2 Marks)
1. What are nucleotides?
Answer:
Nucleotides are the basic structural units of nucleic acids (DNA and RNA). Each
nucleotide consists of a nitrogenous base, a pentose sugar (deoxyribose or
ribose), and a phosphate group.
2. Differentiate between purines and
pyrimidines.
Answer:
- Purines: Adenine (A) and Guanine (G);
have double-ring structures.
- Pyrimidines: Cytosine (C), Thymine (T), and
Uracil (U); have single-ring structures.
3. What is the length of human DNA
if stretched out end to end?
Answer:
The total length of DNA in a diploid human cell is about 2.2 meters.
4. Name the scientists who proposed
the double-helix model of DNA.
Answer:
James Watson and Francis Crick (1953) proposed the double-helix model
of DNA structure.
5. State Chargaff’s rule.
Answer:
Chargaff’s rule states that in any double-stranded DNA, the amount of adenine
equals thymine (A = T) and the amount of guanine equals cytosine (G = C).
6. Why is DNA more stable than RNA?
Answer:
Because DNA lacks the 2’-OH group on the sugar and has thymine instead of
uracil, making it less reactive and more stable.
7. What is the chemical difference
between DNA and RNA?
Answer:
- DNA contains deoxyribose
sugar and thymine.
- RNA contains ribose sugar
and uracil instead of thymine.
8. What are histone proteins?
Answer:
Histones are positively charged proteins around which negatively charged DNA is
wrapped to form nucleosomes in eukaryotic chromosomes.
9. What is a nucleosome?
Answer:
A nucleosome is the structural unit of chromatin, consisting of DNA wrapped
around an octamer of histone proteins (H2A, H2B, H3, and H4 — two of each).
10. Name the bond that links
nucleotides in a DNA strand.
Answer:
Phosphodiester bonds link adjacent nucleotides in a DNA strand.
11. What is meant by antiparallel
strands of DNA?
Answer:
The two strands of DNA run in opposite directions: one in the 5′→3′ direction
and the other in the 3′→5′ direction.
12. What is the pitch and base pair
per turn in B-DNA?
Answer:
Pitch = 3.4 nm;
Base pairs per turn = 10 base pairs.
13. Name the scientist who
discovered transforming principle.
Answer:
Frederick Griffith (1928) discovered the transforming principle
during his experiment with Streptococcus pneumoniae.
14. What did Avery, MacLeod, and
McCarty conclude from Griffith’s experiment?
Answer:
They concluded that DNA is the transforming principle or genetic
material.
15. What was proved by Hershey and
Chase experiment?
Answer:
They proved that DNA is the genetic material, not protein, in
bacteriophages.
16. Why is replication called semiconservative?
Answer:
Because each daughter DNA molecule has one parental (old) strand and one newly
synthesized strand.
17. Name the enzyme that unwinds the
DNA helix during replication.
Answer:
Helicase enzyme unwinds the DNA strands during replication.
18. What is the function of DNA
polymerase?
Answer:
DNA polymerase synthesizes new DNA strands complementary to the template strand
in the 5′→3′ direction.
19. What are Okazaki fragments?
Answer:
Short DNA fragments synthesized on the lagging strand during replication
are called Okazaki fragments.
20. What is a primer?
Answer:
A short RNA sequence that provides a free 3′-OH group for DNA polymerase
to initiate DNA synthesis.
21. Define transcription.
Answer:
The process of copying genetic information from a DNA template to form an RNA
molecule is called transcription.
22. What is the main enzyme involved
in transcription?
Answer:
RNA polymerase catalyzes the synthesis of RNA from the DNA template.
23. Name the three types of RNA
polymerases in eukaryotes and their functions.
Answer:
- RNA Pol I: Synthesizes rRNA.
- RNA Pol II: Synthesizes mRNA.
- RNA Pol III: Synthesizes tRNA and snRNA.
24. What is a promoter?
Answer:
A DNA sequence that signals the binding site for RNA polymerase to
initiate transcription.
25. What is the function of a
terminator sequence?
Answer:
It signals the end of transcription and releases the RNA transcript.
26. What are exons and introns?
Answer:
Exons: Coding sequences of a gene.
Introns: Non-coding sequences removed during RNA splicing.
27. What is meant by splicing?
Answer:
The process of removing introns and joining exons in pre-mRNA to form mature
mRNA.
28. What is a genetic code?
Answer:
A set of rules by which the sequence of nucleotides in mRNA determines the
sequence of amino acids in a protein.
29. Name the start and stop codons.
Answer:
Start codon: AUG
Stop codons: UAA, UAG, UGA
30. What is meant by degeneracy of
genetic code?
Answer:
It means that multiple codons can code for the same amino acid.
31. Why is genetic code called
universal?
Answer:
Because the same codon specifies the same amino acid in almost all organisms.
32. What is translation?
Answer:
The process by which the sequence of codons in mRNA is decoded to synthesize a
polypeptide chain (protein).
33. What are the main components
required for translation?
Answer:
mRNA, ribosomes, tRNA, amino acids, and enzymes.
34. What is the function of tRNA?
Answer:
tRNA carries specific amino acids to the ribosome and pairs its anticodon with
the codon on mRNA during translation.
35. What is a ribozyme?
Answer:
An RNA molecule that acts as a catalyst in biochemical reactions (e.g., rRNA in
ribosomes).
36. Define the term operon.
Answer:
A group of genes under the control of a single promoter and operator,
functioning together in regulation of gene expression.
37. Name the components of the lac
operon.
Answer:
Structural genes (Z, Y, A), promoter, operator, and regulator gene (i).
38. What is an inducer in the lac
operon?
Answer:
Lactose acts as an inducer by inactivating the repressor, allowing
transcription of structural genes.
39. What is a genome?
Answer:
The total genetic material contained in a cell or organism.
40. What was the main goal of the
Human Genome Project (HGP)?
Answer:
To determine the complete nucleotide sequence of the human genome and identify
all human genes.
41. What percentage of human DNA
actually codes for proteins?
Answer:
Less than 2% of the human genome codes for proteins.
42. Define DNA fingerprinting.
Answer:
A technique used to identify individuals based on unique patterns in their DNA
sequences (VNTRs).
43. Who developed the technique of
DNA fingerprinting?
Answer:
Alec Jeffreys (1985) developed the technique.
44. What are VNTRs?
Answer:
Variable Number Tandem Repeats — short sequences of DNA that are
repeated in varying numbers among individuals; basis of DNA fingerprinting.
45. What is a codon?
Answer:
A sequence of three nucleotides on mRNA that codes for a specific amino
acid.
46. What is meant by central dogma?
Answer:
It describes the flow of genetic information: DNA → RNA → Protein.
47. What is a replication fork?
Answer:
A Y-shaped region where the DNA strands separate during replication.
48. What is the role of DNA ligase?
Answer:
DNA ligase joins Okazaki fragments on the lagging strand during replication.
49. Why is RNA considered the first
genetic material?
Answer:
Because RNA can both store genetic information and catalyze
biochemical reactions (as ribozymes).
50. What is the difference between
leading and lagging strands in DNA replication?
Answer:
- Leading strand: Synthesized continuously in
the 5′→3′ direction.
- Lagging strand: Synthesized discontinuously as
Okazaki fragments.
