NIOS Class 12 Biology Chapter 23 Solution – Molecular Inheritance and Gene Expression
NIOS Class 12 Biology Solution Chapter 23 Molecular Inheritance and Gene Expression . NIOS Class 12 Biology Chapter 23 Question Answers Download PDF. NIOS Class 12 Biology Notes.
Board |
NIOS |
Class |
12th (Higher Secondary) |
Subject |
Biology |
Topic |
Question Answer, Solution, Notes |
INTEXT 23.1
1.) Expand the abbreviation DNA.
Ans: DNA is a polynucleotide, a macromolecule (macro = large) made of units called nucleotides. It stands for Deoxyribonucleic acid
2.) Name the scientists who confirmed that DNA was the genetic material in bacterial transformation. .
Ans: Avery, Mcleod and McCarty are the scientists who confirmed that DNA was the genetic material in bacterial transformation
3.) Name the sugar and the nitrogenous bases found in DNA
Ans: Deoxyribose, Adenine, Guanine, Thymine, Cytosine are the sugar and nitrogenous base found in DNA.
INTEXT 23.2
1.) In which direction does DNA polymerase proceed to catalyze DNA replication 5′ to 3′ or 3′ to 5′?
Ans: DNA polymerase proceed to catalyse DNA replicaiton in 5’-3’ direction
2.) What is a primer . a DNA molecule or an RNA molecule?
Ans: A primer is a RNA molecule
3.) Name the four enzymes needed for DNA replication.
Ans: Helicase, DNA polymerase, DNA ligase, Topoisomerase are needed for DNA replication
4.) Which enzyme joins the okazaki pieces to form a complete DNA strand?
Ans: DNA ligase is the enzyme that joins the okazaki pieces to form a complete DNA strand
INTEXT 23.3
1.) What is central dogma in molecular Biology? .
Ans: Protein synthesis takes place in the cytoplasm of the cell, while genes are found in the nucleus. The transfer of information from genes to the site of protein synthesisnconstitutes the Central Dogma.
2.) Which molecule is synthesised during transcription?
Ans: Cistronic DNA is synthesised during transcription
3.) What is a codon? What is meant by ‘code is degenerate’? .
Ans: The sequence of 3 bases called codon , it has the information of a particular amino acid.
4) Where in the cell does translation occur? .
Ans: The cell does translation in Nucleus
5) Name the three types of RNA that participate in protein synthesis.
Ans: mRNA, tRNA, hnRNA are the three types of RNA that participate in protein synthesis
INTEXT 23.4
1.) Name the components of an operon. .
Ans: Components of operon are regulator, promoter, operator and structural genes.
2.) What is mutation? When is a mutation called a transition mutation?
Ans: Mutation is the term used to describe a heritable change in the composition, organisation, and structure of the genetic material that can be transmitted to the following generation. A mutation may affect one gene and be known as a point mutation, or it may affect several genes on a portion of a chromosome and be known as a chromosomal mutation.
3) Why is “silent mutation” called so? Heredity
Ans: When the changed nucleotide does not bring about any phenotypic change because it also codes for same amino acid is called silent mutation.
4) What are mutagens?
Ans: Mutagenic substances are those that alter genetic material. Mutagens can be divided into two groups.
1.) Radiations, such as X-rays and UV rays.
2.) Chemical: Actinomycin D and mustard gas
5) Name a chemical which causes mutation in the heredity material.
Ans: Actinomycin D causes mutation in the heredity material.
TERMINAL EXERCISE
1.) How did Hershey and Chase prove that DNA is the hereditary material?
Ans: They performed a experiment using a virus which infect bacteria using They labelled the protein coat of the virus with radioactive isotope of sulphur 35S. When the virus was introduced into the bacteria, no radioactivity was found inside the bacteria. When scientists used radioactive phosphorous or 52P32 to identify viral DNA, radioactivity was discovered inside the bacteria. It became evident that viral strains in new generations were bacterial reproduction was facilitated by viral DNA
2.) Explain
(i) Transduction : Transduction is the process by which DNA is transferred from one bacterial cell to another by a virus.
(2) Lysogeny : When a virus penetrates a bacterium, the bacterial genome also divides. Thus, several virus particles can develop this is lysogeny.
3.) Describe the Watson and Crick model of DNA.
(i)The DNA molecule is a double helix made up of two DNA strands.
(ii) The two strands are arranged antiparallel, which implies that one strand’s nucleotide sequence rises in the 5′ to 3′ direction, while the other strand descends in the 3′ to 5′ direction. The carbon atom to which the phosphate group is bonded is designated as (3′ and 5′).
(iii) The helix’s support structure is composed of phosphate and sugar. Bases containing nitrogen are connected to the sugar.
(iv) Hydrogen bonds bind the bases of the two strands.
(v) According to Chargaff’s rule, base pairing is quite particular. Thymine, a pyrimidine base, is always paired with the purine base adenine. Guanine, a purine base, interacts with Cytosine, a pyrimidine. Complementary bases are the name given to these base pairs.
4.) Explain how replication takes place.
Ans: )1. DNA double helix unwinding
The enzyme Helicase separates the two strands of the replicating DNA molecule. The enzyme topoisomerase maintains it open.
2.) Primer synthesis
Primer is a small, 5–10 base RNA molecule. It is created when the enzyme primase is present. The new DNA strand can be attached to the primer using its 3′-OH group.
3.) Synthesis of a new DNA strand
The template is made up of the opened DNA strands. Synthesis occurs of new, complementary strands to the template. In the presence of the enzyme DNA polymerase, a new DNA strand starts to be synthesised at the replication fork and attaches to the primer. From its 5′ end, it starts to synthesise a DNA strand that is complementary to one of the parental DNA strands that haven’t been wound. The leading strand of DNA is the one that continues to be created without interruption.
5.) Write a note on Central Dogma
Ans: The cytoplasm of the cell is where proteins are made, while the nucleus of the cell contains the genes.The Central Dogma is that information travels from genes to the location of protein production.
6.) State the properties of the genetic code.
Ans: 1. The triplet code that makes up DNA. This indicates that a codon, which is a sequence of three nucleotides, has information about a specific amino acid. The order of the amino acids in a protein is determined by the sequence of codons.
2.) The genetic code is unambiguous, meaning that a given codon can only represent one amino acid.
3.) There are no duplicates or overlaps in the genetic code. This indicates that it is read constantly from start to finish.
7.) Explain transcription in Eukaryotes and processing of hnRNA.
Ans: Through RNA, information is transferred from DNA (a specific gene) to the specific protein. The information encoded in DNA is copied as a complementary messenger RNA molecule before being used to create proteins. This is what is meant by transcription.
Eukaryotic genes have coding sequences called exons and non-coding sequences called introns (I) in between exons, Exons (E) and introns (I) are both transcribed in mRNA. Introns are removed during mRNA processing, whereas exons combine to create mRNA. At the 5′ end of mRNA, a nucleoside known as methyl guanosine enters and binds. This is referred to as capping. At the 3′ end, a brief segment of RNA that consists solely of nucleotides with the base Adenine is joined. The poly A tail is what signifies by this. The nuclear membrane’s pores allow the m RNA with cap and tail to exit.
RNA processing is the process of converting hnRNA into functional mRNA.
8.) What do you mean by regulation of genes?
Ans: Regulation of a gene means production of proper protein which have many functions to perform.
9). Explain how the lac operon gets switched on in the presence of lactose in E.coli.
Ans: The Lac-operon is a prime example of how prokaryotes (bacteria) regulate the expression of genes. It is an inducible mechanism that activates when the substrate lactose is present. The genes that code for the lactose-metabolizing enzymes galactosidase, permease, and transacetylase are activated.
10.) Name three levels at which regulation takes place in a eukaryotic cell.
Ans (i) Transcription
(ii) Translocation
(iii) Post translocation
11.) Write notes on :
i) Types of mutations :
Transition: When one pyrimidine base is swapped out for another pyrimidine base, or vice versa, ATGCATGC ⎯⎯→ AGGC AGGC
Transversion: When a pyrimidine base is switched out for a purine base,
and vice versa. ATGC ATGC ATGT ATGC
(c)Frameshift : The reading frame of the genetic coding for a complete protein can occasionally alter as a result of a loss or gain of one nucleotide.
(d) Missense: A mutation in the genetic code caused by the substitution of a nucleotide (base) might result in the emergence of a new protein, such as sickle cell haemoglobin.
(e) Nonsence : If a stop codon appears in the middle of a genetic code, no protein is produced.
(f) Silent: When the altered nucleotide still codes for the same amino acid, there is no phenotypic change.
(ii) Okazaki fragments : DNA is always synthesised in a 5′ to 3′ orientation. The other new DNA strand is created in the opposite direction from the leading strand. Small portions of this new strand, known as Lagging strand, accumulate.
The lagging strand’s production is thus interrupted. The new DNA strands are known as Okazaki fragments. The fragments of the Okazaki structure are linked to form a DNA strand in the presence of the enzyme ligase and the energy source ATP.
(iii) Chain termination during translation: The polypeptide is created when the mRNA stop codon is reached. It departs off the ribosome, which then splits into its two components.