MP Board Class 12th Biology Solutions Chapter 6 Molecular Basis of Inheritance
Molecular Basis of Inheritance NCERT Textbook Questions and answers
Question 1.
Group the following as nitrogenous bases and nucleosides:
Adenine, Cytidine, Thymine, Guanosine, Uracil, and Cytosine.
Answer:
Nitrogenous bases Adenine, Thymine, Uracil, Cytosine. NucleosidesCytidine, Guanosine.
Question 2.
If a double-stranded DN A has 20 % of cytosine, calculate the percent of adenine in the DNA.
Answer:
According to Chargaff’s rule, the DNA molecule should have an equal ratio
Cytosine = 20% therefore, Guanine = 20%
A+T = 100 – (G + C)
A + T = 100 – 40 since, both Adenine and Thymine are in equal amounts.
Thymine = Adenine = \(\frac { 60 }{ 2 }\) = 30%
So, the quantity of Adenine is 30% in the DNA helix.
Question 3.
If the sequence of one strand of DNA is written as follows:
5′ -ATG CATGCA TGC ATG CAT GCA TGCATGC – 3′
Write down the sequence of the complementary strands in 5′-3’direction.
Answer:
5′ – ATGCATGC ATGC ATGC ATGC ATGC ATGC – 3′ (In question)
complement 3′ – TACG TACG TACG TACG TACG TACG – 5′
complement in 5′ – 3′ direction 5′ – GCAT GCAT GCAT GCAT GCAT GCAT GC AT – 3′.
Question 4.
If the sequence of the coding strand in a transcription unit is written as follows:
5’ – ATG CAT GCA TGC ATG CAT GCA TGC ATGC – 3’
Write down the sequence of mRNA.
Answer:
5’ – AUGCAUGCAUGC AUGCAUGCAUGCAUG-3’
Question 5.
Which property of DNA double helix led Watson and Crick to hypothesis semiconservative mode of DNA replication? Explain.
Answer:
2 strands of DNA have complementary base pairs which run in the opposite direction. The property was that during DNA replication one strand was conserved while the complementary is formed new.
Question 6.
Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acid synthesized from it (DNA or RNA) list the types of nucleic acid polymerases.
Answer:
These are two different types of nucleic acid polymerases :
- DNA – dependent DNA polymerases
- DNA – dependent RNA polymerases
The DNA-dependent DNA polymerases use a DNA template for synthesizing a new strand of DNA, whereas DNA-dependent RNA polymerases use a DNA template strand for synthesizing RNA.
Question 7.
How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?
Answer:
Hershey and Chase experiment:
- They grew some bacteriophages on a medium that contained radioactive phosphorus and some in another medium that contained radioactive sulphur.
- Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein as phosphorus is present only in DNA.
- Viruses grown on radioactive sulphur contained radioactive protein but not radioactive DNA because DNA does not contain sulphur.
- It was found that bacteria which were infected with bacteriophages that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria.
- Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicated that proteins did not enter the bacteria from the viruses.
- This was clear-cut proof that DNA is the dead genetic material that is passed from virus to bacteria.
Question 8.
Differentiate between the followings:
(a) Repetitive DNA and Satellite DNA
(b) mRNA and tRNA
(c) Template strand and Coding strand.
Answer:
(a) Differentiate between Repetitive DNA and Satellite DNA:
(b) Differentiate between mRNA and fRNA:
(c) Differentiate between Template strand and Coding strand:
Question 9.
List two essential roles of ribosomes during translation.
Answer:
- Provides sites for attachment of m-RNA and charged t – RNA for polypeptide synthesis.
- One of its r – RNA functions as peptidyl transferase for peptide bond formation.
Question 10.
In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down sometime after the addition of lactose in the medium?
Answer:
Lactose regulates switching on and off of the lac operon. If lactose is provided in the growth medium of the bacteria, it is transported into the cells through the action of permease.
The lactose then induces the operon in the following manner:
- The repressor of the operon is synthesized all the time from the is a gene.
- It binds the repressor protein which binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon.
- In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer.
- This allows RNA polymerase access to the promoter and transcription proceeds.
Question 11.
Explain (in one or two lines) the function of the followings:
(a) Promoter
(b) tRNA
(c) Exons.
Answer:
(a) Promoter is an essential component of the transcription unit. It is located at the beginning of 5′ -end.
It provides a site for the attachment of transcription factors and RNA polymerase.
(b) tRNA is a small-sized RNA molecule that takes part in transcription. It physically picks up activated amino acids from the cytoplasm and carries (transfers) them to ribosomes, where they join together through peptide bonds and leave the tRNA to fetch more amino acids.
(c) Exons are the coding sequences of DNA that are transcribed and translated.
Question 12.
Why is the human genome project called a megaproject?
Answer:
The human genome project is called a megaproject because:
- Its aim was to determine the nucleotide sequence of the complete human genome which was a task of enormous magnitude.
- A total of 3 x 109 base pairs were to be sequenced and the cost was about 9 billion US dollars.
- It required bioinformatics database techniques and other contemporary devices for the analysis, storage, and retrieval of information.
- May countries worked jointly to complete this timed project.
Question 13.
What is DNA Fingerprinting? Mention its application.
Answer:
DNA fingerprinting is a technique of determining the similarity and dissimilarity of VNTR’s between 2 samples of DNA so as to bring out a relationship if any VNTR’s are specific for each individual. They are derived from parents in 50: 50 ratio.
Applications
- Identification – of criminals
- Paternity and Maternity disputes.
- Migrations
- Human Lineage.
DNA fingerprinting involves the following steps:
The DNA of the organism to be tested is isolated, it is called host DNA.
Host DNA is cleaved with the help of specific restriction enzymes into several fragments.
Double-stranded DNA fragments are denatured to produce single-stranded DNA by alkali treatment.
DNA segments are separated by electrophoresis.
Question 14.
Briefly describe the following:
(a) Transcription
(b) Polymorphism
(c) Translation
(d) Bioinformatics.
Answer:
(a) Transcription: It is the formation of RNA over the template of DNA. It forms single-stranded RNA which has coded information similar to the sense or coding strand of DNA with the exception that thymine is replaced by uracil. One strand of DNA is used as a template strand for the synthesis of a complementary strand of RNA called tRNA.
(b) Polymorphism: Genetic polymorphism means the occurrence of genetic material in more than one form. It is of three major types, i. e„ allelic, SNP and RFLP.
Allelic polymorphism: Allelic polymorphism occurs due to multiple alleles of a gene. Allele possesses different mutations which alter the structure and function of a protein formed by them as a result, change in phenotype may occur.
SNP or single nucleotide polymorphism: Over 1-4 million single-base DNA differences have been observed in human beings. According to SNP, every human being is unique. SNP is very useful for locating alleles, identifying disease-associated sequences, and tracing human history.
(c) Translation: It is the process during which the genetic information which is stored in the sequence of nucleotides in an mRNA molecule is converted, following dictations of the genetic code, into the sequence of amino acids in the polypeptide. It takes place in the cytoplasm in both eukaryotes and prokaryotes.
(d) Bioinformatics: The science which deals with handling storing of huge information of genomics as databases, analyzing, modeling, and providing various aspects of biological information, especially the molecules connected with genomics and proteomics is called bioinformatics.
Molecular Basis of Inheritance Other Important Questions
Molecular Basis of Inheritance Objective Type Questions
1. Choose the Correct Answer:
Question 1.
Which component they have free amino acid and carboxylic group:
(a) Glucose
(b) Nucleotide
(c) Amino acid
(d) None of these.
Answer:
(c) Amino acid
Question 2.
Nucleotide which is participating in energy transfer:
(a) NAD
(b) FAD
(c) FMN
(d) ATP.
Answer:
(d) ATP.
Question 3.
What is the unit of protein:
(a) Fatty acid
(b) Monosaccharides
(c) Amino acid
(d) Glycerol.
Answer:
(c) Amino acid
Question 4.
Nucleic acids are polymers of:
(a) Amino acid
(b) Nucleoside
(c) Nucleotide
(d) Globulin.
Answer:
(c) Nucleotide
Question 5.
Peptide bonds are found in:
(a) Protein
(b) Fat
(c) Nucleic acid
(d) Carbohydrate.
Answer:
(a) Protein
Question 6.
Glycosidic bonds are found in:
(a) Nucleic acid
(b) Protein
(c) Polysaccharides
(c) Monosaccharides.
Answer:
(c) Monosaccharides.
Question 7.
By which the control and coordinate of heredity:
(a) By DNA
(b) By RNA
(c) Mostly DNA but some organisms by RNA
(d) None of these.
Answer:
(c) Mostly DNA but some organisms by RNA
Question 8.
It is not a protein:
(a) Myosin
(b)Actin
(c) Haematind
(d) Albumin.
Answer:
(c) Haematind
Question 9.
A source which gives immediate energy:
(a) Glucose
(b) NADH
(c) AIP
(d) Pyruvic acid.
Answer:
(c) AIP
Question 10.
Who discovered ATP:
(a) Karl Lohmann
(b)Lipman
(c) Bowman
(d) Blackman.
Answer:
(a) Karl Lohmann
Question 11.
Which nitrogenous base is found in the only RNA:
(a) Cytosine
(b) Adenine
(c) Uracil
(d) Guanine.
Answer:
(c) Uracil
Question 12.
A molecule which shows very different from other molecules in the cell:
(a) Mineral salt
(b) Lipids
(c) Proteins
(d) Carbohydrate.
Answer:
(c) Proteins
Question 13.
Who prescribes the double helix structure of DNA:
(a) Nirenberg
(b) Komberg
(c) Holley and Nirenberg
(d) Watson and Crick.
Answer:
(d) Watson and Crick.
Question 14.
Which is non-essential for the plants:
(a) Ca
(b) Zn
(c) Cu
(b) Na.
Answer:
(b) Na.
Question 15.
A number of nucleotides are found in one whorl of DNA:
(a) 9
(b) 10
(c) 11
(d) 12.
Answer:
(b) 10
Question 16.
Which are microelements:
(a) Ca
(b) N
(c) Mg
(d) Mn.
Answer:
(d) Mn.
Question 17.
Which similarities are found in DNA and RNA:
(a) the Same type of pyrimidine is found in both
(b) Thymine is present in both
(c) Some sugar is found in both
(d) Both are polymers of nucleotide.
Answer:
(d) Both are polymers of nucleotide.
Question 18.
Cholesterol is a:
(a) Simple lipids
(b) Complex lipids
(c) Derivatives lipids
(d) Protein.
Answer:
(c) Derivatives lipids
2. Fill in the Blanks:
- Cut up and join of polynucleotide chain is called …………………….
- Changes ……………………. done by genetic engineering.
- UAA, UAG, and UGA are …………………….codon.
- …………………….code is universal and non-ambiguous.
- Transcription of DNA information is the form of …………………….
- ……………………. enzyme is involved in transcription.
Answer:
- Genetic engineering
- Characters of organisms
- Termination
- Codon
- mRNA
- RNA Polymerase.
3. Match the Following:
I.
Answer:
- (c)
- (e)
- (b)
- (a)
- (d)
- (f)
II.
Answer:
- (c)
- (d)
- (a)
- (b).
III.
Answer:
- (c)
- (a)
- (b)
- (e)
- (d).
4. Answer in One Word/Sentence:
- Who discovered nucleic acid for the first time?
- Name the Indian-American scientist who is well known for the chemical synthesis of genes.
- Name the small-RNA which is synthesized before DNA replication.
- Which codon is known as the starting codon?
- Name the RNA which function as an enzyme.
- Who proposed the operon model of gene regulation?
- What chemical is produced by the regulator gene of Lac-operon?
- What term is used for those genes which are active in all the cells and tissues of an individual?
- Name the operon which regulates the metabolism of lactose in E. coli.
- Name the organism which contains single-stranded DNA.
Answer:
- Friedrich Miescher
- H.G. Khorana
- RNA-primer
- AUG or GUG
- Ribozyme
- Jacob and Monod
- Repressor
- Housekeeping genes
- Lac-operon
- Φ × 174phage.
Molecular Basis of Inheritance Very Short Answer Type Questions
Question 1.
Expand the term DNA, RNA, and tRNA.
Answer:
DNA – Deoxy ribonucleic acid RNA – Ribo nucleic acid tRNA – transfer – RNA
Question 2.
What are the animals that have a foreign gene deliberately inserted into their genome?
Answer:
Transgenic animals.
Question 3.
What are Okazaki fragments?
Answer:
The small stretches of DNA formed due to the opposite running of the DNA template at the time of replication is called Okazaki fragments.
Question 4.
By which the instructions of our DNA are converted into a functional product?
Answer:
Gene expression.
Question 5.
Write the name of sugar found in RNA.
Answer:
Ribose sugar.
Question 6.
Which codon is AUG?
Answer:
Anticodon.
Question 7.
Define Transcription?
Answer:
It is the process of the formation of m-RNA on a DNA template.
Question 8.
Who tell that DNA is a heredity material?
Answer:
Alfred Hershey and Martha Chase. ,
Question 9.
What is the genetic material of the tobacco mosaic virus (TMV)
Answer:
RNA.
Question 10.
Name the segment in which any nucleotide sequence within a gene is removed by RNA splicing during maturation of the final RNA products.
Answer:
Intron.
Question 11.
Who gave the Operon model?
Answer:
Jacob and Monod.
Question 12.
What do you mean by commaless due to genetic code ?
Answer:
Between two codon has no internal punctuation.
Question 13.
If the base sequence of one strand of DNA is CAT TAG TAC GAC, what will be the base sequence
(a) Of complementary DNA strand, and
(b) Of its complementary RNA strand? (CBSE 1991)
Answer:
(a) GTA ATC ATG CTG
(b) GUA AUCAUGCUG.
Molecular Basis of Inheritance Short Answer Type Questions
Question 1.
What are the 5′ end, 3′ end of a polynucleotide chain?
Answer:
- The polynucleotide chain has at one end a free phosphate at the 5′ end of the pentose sugar. Which is referred to as 5′ end.
- The other end of the polynucleotide chain has a free. 3′ – OH group at the 3rd end of the pentose sugar which is referred to as 3′ end of a polynucleotide chain.
Question 2.
What are oncogenes?
Answer:
Genes which are responsible for the production of cancer in the host by uncontrolled mitotic cell division are called oncogenes.
Question 3.
What are Okazaki fragments and leadings strands?
Answer:
Okazaki fragments: On the second parental DNA template new complementary DNA strands are formed in smaller fragments starting from an RNA primer. These short fragments are called Okazaki fragments.
Leading strands: Second strand is formed on 5’→ 3’ strand of parental DNA in a continuous stretch in reverse direction 3’→ 5’ and is called a leading strand.
Question 4.
DNA nucleotide is formed which molecule?
Answer:
Components are DNA Nucleotides:
Question 5.
Explain the Watson and Crick model of DNA.
Answer:
The structure of DNA was proposed by Watson and Crick. It is a twisted ladder-like structure. It has got two coiled polynucleotides which are joined together by nitrogen bases with hydrogen bond in the centre. The longitudinal strands of DNA are made of sugars and phosphates of nucleotides. The horizontally placed nitrogen bases are of two types, purine, and pyrimidine. Purines are adenine and guanine whereas pyrimidines are cytosine and thymine.
Question 6.
What is RNA primer ? Why it is necessary from DNA synthesis ?
Answer:
A primer is a short strand of RNA or DNA. RNA primer serves as a starting point for DNA polymerase, which builds complementary DNA. It is reqiured for DNA replication because the enzymes that catalyze this process. DNA polymerase can only add new nucleotide to an existing strand of DNA.
Question 7.
What is a peptide bond?
Answer:
The bond formed between the carboxylic group (- COOH) of one amino acid and the amino group (- NH2) of another amino acid is called a peptide bond. A molecule of water is released during the formation of the peptide bond.
Question 8.
Define Codon and Anticodon.
Answer:
Codon: A specific sequence of three consecutive nucleotides that is a part of the genetic code and that specifies a particular amino acid in a protein or starts or stops protein synthesis e.g., AUG codon which is situated on-die mRNA, code methionine amino acid.
Anticodon: A sequence of three adjacent nucleotides located on one end of transfer RNA. It bounds to the complementary coding triplet of nucleotides in mRNA during the translation phase of protein synthesis.
For example, the anticodon for Glycine is ccc that binds to the codon (which is GGE) of mRNA.
Molecular Basis of Inheritance Long Answer Type Questions
Question 1.
Explain DNA duplication in short
Answer:
Watson and Crick after giving the double-helix model of DNA also postulated the mechanism of DNA duplication, also known as replication. According to them, during duplication, the weak hydrogen bonds between the nitrogenous base of the nucleotides get separated, so that two polynucleotide chains of DNA also separate and uncoil. The chains thus, separated are complementary to one another. These strands act as templates and because of the specificity of base pairing each nucleotide of the separated chain attracts its complementary nucleotide from the cell cytoplasm. Once the nucleotides are attached by their hydrogen bonds their sugar radicals write through their Fig. DNA duplication, phosphate components completing the formation of a new polynucleotide chain. This results in the formation of two double helixes of DNA wherein each molecule has one old strand contributed by parent DNA and one synthesized new. This method of DNA duplication is known as the semi-conservative method.
Question 2.
Describe the functions of nucleic acids.
Or
Explain the utility of nucleic acids.
Answer:
Utility of Nucleic acids:
- Nucleic acids are the hereditary materials of organisms which involve in the transfer of hereditary characters
- from one generation to the next.
- DNA controls the synthesis of enzymes which control the various activities of the body.
- Nucleic acids also control protein synthesis.
- Nucleic acids form maximum portion of chromatin network.
- It causes mutation in living beings.
- They form enzymes.
Question 3.
Explain the structure of RNA.
Answer:
RNA molecules are single stranded nucleic acids composed of nucleotides. Four types of bases are present in RNA. These nitrogenous bases joint in different manner and form the ribonucleoside. Ribonucleoside joins together and make a polyribonucleotide chain.
AH four types of nucleoside and nucleotide are as follows :
Question 4.
Elaborate the term RNA. Also describe the types and functions of RNA.
Or
Write location and kinds of RNA in the cell.
Answer:
RNA(Ribonucleic acid): RNA located in the nucleus, cytoplasm, ribosomes, and in some other cell organelles.
Types of RNA and their functions: RNA is of three types:
1. Messenger RNA (mRNA): It makes a small fraction of 5-10%. This RNAdirects the sequence of amino acids in protein synthesis after joining with ribosomes. It carries the genetic information contained in DNA. It is short-lived and has rapid turnover. It is formed of 700-1500 nucleotides and has a molecular weight from 5,00,000 to 20,00,000. The sequence of three nitrogenous bases of mRNA forms a codon which is responsible for coding one amino acid.
2. Ribosomal RNA (rRNA): It makes 80% of total cell RNA. It is the most stable type of RNA and is associated with ribosomes.
3. Transfer RNA (tRNA): It makes a small fraction (10-15%) of RNA. These are the smallest molecules formed of 73-93 nucleotides with a molecular weight ranging between 25,000 to 30,000. rRNA works as adaptor molecules for carrying amino acids to the mRNA template during protein synthesis.
Question 5.
Describe the structure of nucleotides.
Answer:
Structure of Nucleotides: Nucleotides are the basic unit of nucleic acids and, they are also involved in the energy transfer reactions of the body. A nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group. A nucleotide possessing two groups of nitrogenous bases :
- Purines and
- Pyrimidines.
Purines are double-ringed nitrogenous bases, e.g., Adenine and Guanine. Pyrimidines are single-ring nitrogenous bases like cytosine, thymine, and uracil.
The pentose sugar of nucleotides is also of two types:
- Ribose sugar [CH2OH(CHOH)2.CHOH.CHO].
- Deoxyribose sugar [CH2OH(CHOH2.CH2CHO].
A nucleotide may have one, two, or three phosphates to form a nucleotide. A combination of a base and sugar is called nucleoside and a combination of a base, a sugar, and phosphate group is known as a nucleotide. As there are five bases so, five different kinds of nucleosides and nucleotides are known. These are listed in the table given below:
Question 6.
Give the functions of nucleotides.
Answer:
Functions of Nucleotides:
- It works as an activated precursor of DNA and RNA.
- They perform the storage and conduction of energy to the form of ATP.
- It required for the activation of intermediates in many biosynthetic pathways.
- It works as a Carrier of the methyl group in the form of SAM.
- Its Components of co-enzyme: NAD, FAD, and Co A.
- Some functions are as a vitamin. ,
- They are controlled and coordinates different activities in our bodies.
Question 7.
Write four features of genetic code.
Answer:
According to Nirenberg, Khorana, and Holley, a genetic code is a sequence of nitrogenous bases of DNA in which genetic information for the synthesis of protein is coded.
Characteristic features of genetic code:
- The code is a triplet: The codon is a specific sequence of three nitrogenous bases of mRNA.
- The code is commaless: The sequence of bases read in blocks of three at a time from a particular position. There is no gap between the two subsequent codons.
- Code is degenerating: The presence of more than one codon for one amino acid is called as degeneracy of codons, e.g., Serine having three codons UCU, UCA, AGU.
- Codes are universal: Codons are similar in all organisms, e.g., serine is coded by UCU codon in all the living beings.
- Codes are non-ambiguous: The position of genetic code in the cellular medium is nonambiguous because a codon always codes only one amino acid. Sometimes a codon codes more than one amino acid, e.g., in E. coli. UUV codon generally codes phenylalanine, after treatment of their ribosome with streptomycin. It can also code isoleucine, leucine and serine.
- Initiation and termination codon: Codons responsible for the initiation of the polypeptide chain are called initiation codons, e.g., AUG. Likewise, codons responsible for the termination of the polypeptide chain are called chain termination codon, e.g., UAA, UAG, UGA.
Question 8.
Write five characters of the gene hypothesis.
Answer:
Sutton, Bridges, Muller and Morgan suggest this theory. The character’s of the gene of this theory are as follows:
- Genes are situated on the chromosome.
- They make the physiological character of organisms.
- These are called a functional unit of specific characters.
- Genes have the capacity of self-transcription.
- They perform mutation.
- Characters are goes to one generation to other by parents.
Question 9.
Write the functions of DNA polymerase.
Answer:
- DNA polymerase catalyses the polymerisation of nucleotides into a polynucleotide strand of DNA.
- It carries out proof reacting in prokaryotes; it moves back and removes any wrong bases added before polymerisation continues.
Question 10.
What is proofreading and repair of DNA?
Answer:
A variety of environmental factors such as radiation, chemicals, etc. may cause damage to the DNA of a cell. The bacterial DNA polymerase III can do proofreading, in the sense that it can go back and remove the wrong base before it proceeds to add new bases in the 5′ → 3′ direction. It is called proofreading. Obviously, the survival of the cell depends on its availability of damages:
(i) Monoadduct: Which involves alterations in a single nitrogenous base.
(ii) Diadducts: They are the alterations involving more than one nitrogenous base. Number of nucleases have been found to be involved in repair replication such as Exonucleases (defined as phosphodiesterases which require a terminus for hydrolysis and cut off terminal nucleotides), Endonucleases (which are also phosphodiesterases which do not require a terminus for hydrolysis and break internal bonds). The endonucleases which act on the damaged DNA and cause repair or correction of this molecule are referred to as correctional nucleases. The following steps are said to be involved in the repair replication i.e., Incision, Excision, Reinsertion, and joining of newly formed strands.
Question 11.
Write any four differences between DNA and RNA.
Answer:
Differences between DNA and RNA:
Question 12.
Write the names of enzymes used in DNA replication.
Ans.
The names of enzymes used in DNA replication are as follows :
- DNA helicase: For unwinding of two strands.
- DNA gyrase: For relieving tension.
- Primase: For formation of primer.
- DNA polymerase: For DNA synthesis.
- RNA primer: For initiation of the synthesis of DNA segments.
- DNA ligase: For joining of DNA Okazaki segments.
Question 13.
Why is it essential that RNA binds to both an amino acid and an mRNA codon, during protein synthesis?
Answer:
(a) By binding an amino acid at its 3′ end the tRNA transports the amino acid to the site of protein synthesis.
(b) It binds to the codon on mRNA through hydrogen bonds with its anticodon as it is recognized by the codon of the amino acid it carries, it is to release the amino acid at the correct site for polypeptide elongation.
Question 14.
What is translation? Explain it
Answer:
Translation: The translation step of protein synthesis involves the translation of the language of nucleic acids (available in the form of mRNA) into language of protein. The sequence of bases in mRNA, decides the sequence of amino acids in proteins. Each amino acid is programmed by a triplet code. It consists of a sequence of three bases in the DNA and the complementary bases in mRNA. The synthesis of protein occurs in three steps, initiation, elongation and termination. After the final step i.e., termination, the proteins are transported out of the cell or translocated within the cell. Thus, the transformation of the nucleotides chain of RNA into a polypeptide chain of protein is called as translation.
It is completed in the following steps:
- Activation of amino acids.
- Binding of activated amino acids with rRNA.
- Binding of mRNA with smaller unit of ribosome.
- Initiation of polypeptide chain.
- Elongation of polypeptide chain.
- Termination of polypeptide chain.
Question 15.
Describe the evidence given by Griffith in support of DNA as genetic material. Explain it along with a suitable diagram.
Answer:
Griffith had done transformation experiments in mice to prove that DNA is the genetic material. He took the virulent strain of Diplococcus pneumonae (S-III) which causes pneumonia in mice and injected it into mice which resulted in the production of pneumonia in mice. He also injected a non-virulent strain of that bacteria in the body of mice and found that all the mice were unaffected.
In third experiment he injected heat-killed (S-III) strain and non-virulent strain R-II strain together in the body of mice and found that all the mice suffered from pneumonia and became dead. After analysis it was found that these mice contained both the strains of Diplococcus pneumonae. Thus, this experiment proved that any substance of S-III strain is transferred into R-II strain due to which R-II strain become virulent. Later, McLeod, Avery and McCarty observed that DNA molecules are transferred from S-III to R-II strain and make virulent. Thus, it is proved that DNA is the genetic material.