Download App

Molecular basis of Inheritance — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular basis of Inheritance4 Marks
Question
How are DNA molecule replicate? Describe it.###Describe the process of DNA replication.
✓

Answer

DNA Replication : DNA is the only molecule on earth which is capable of self-replication. It occurs during S-phase of the cell cycle when chromatin remain in extended form. During replication, the weak hydrogen bonds between complementary nitrogenous bases break thus separate and uncoil two polynucleotide strands of DNA molecule. Each strand act as a template for synthesis of new complementary strands. After the completion of replication, each daughter DNA molecule has one parental and one newly synthesized strand thus restoring 50% characteristics of parent DNA. This scheme of replication of DNA is known as 'Semi-conservative DNA replication'.
Image
The Mechanism of DNA Replication : DNA replication is a complex process involving many enzymes. The first step is unwinding of DNA molecule at a specific point called initiation point. The enzyme topoisomerase helps in making a nick in the DNA molecule. The two strands of DNA start separating by breaking of hydrogen bonds between complementary nitrogenous bases. Each strand serve as a template for synthesis of new strand. The point of origin is marked as replication fork as it resamble a fork on either side of point of replication specific initiator proteins recognise point of initiation on DNA. RNA polymerase initiates synthesis of RNA primer on DNA template.
With the help of enzyme DNA polymerase a new DNA strand is synthesized in 5'-3' direction on 3'-5' template DNA. This is called leading strand and it is synthesized as one piece. On the other parent 5'-3' strand short DNA segments are formed in 5'-3' direction starting from RNA primer. These DNA segments are called Okazaki fragments and have 1000-2000 nucleotides. These fragments are later joined together forming a continuous lagging strand. The enzyme DNA ligase help in joining the fragments. (fig.)
Image

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "4 Marks Questions" from Molecular basis of Inheritance→Molecular basis of Inheritance — all question types→BIOLOGY STD 12 Science question papers→Rajasthan Board STD 12 Science question papers→Rajasthan Board question paper generator→

Similar questions

Taking a small pond as an example of an ecosystem, list the four components of this ecosystem. How do these components function as a unit in a small pond?
→
Polymerase chain reaction (PCR) is a laboratory technique used to amplify DNA sequences. The method involves using short DNA sequences called primers to select the portion of the genome to be amplified. The temperature of the sample is repeatedly raised and lowered to help a DNA replication enzyme copy the target DNA sequence. The technique can produce a billion copies of the target sequence in just a few hours.
Image
i. List the three steps involved in Polymerase Chain Reaction (PCR).
ii. Name the source organism of Taq polymerase.
iii. Explain the specific role of this enzyme in PCR.
→
Answer the following questions:
Explain the role of ovarian hormones in inducing changes in the uterus during menstrual cycle.
→
Explain why a recessive allele is unable to express itself in a heterozygous state.
→
What does the lac operon consist of? How is the operator switch on and off in the expression of gene in this operon? Explain.
→
Describe the functions of the following:
Vagina.
→
From which plant is cocoa alkaloid or cocaine obtained? What are its effect on the human body? Write the chemical structure of morphine.
→
  1. How is mature insulin different from proinsulin secreted by pancreas in humans?
  2. Explain how was human functional insulin produced using rDNA technology.
  3. Why is the functional insulin thus produced considered better than the ones used earlier by diabetic patients?
→
  1. Represent diagrammatically three kinds of age-pyramids for human populations.
  2. How does an age pyramid for human population at given point of time helps the policymakers in planning for future?
→
What do you mean by biofertilizer? How do biofertilizers increase soil fertility?
→