12th Class Biology Chapter 6 Chromosomes and DNA Short Questions Answer
1.Who first observed the chromosomes?
The German embryologist Walther Fleming first observed them in 1882.When he was examining the rapidly dividing cells of salamander larvae.
2.What is euchromatin?
The protion of the chromosome except heterochromatin is called euchromatin.It is condensed only during cell division.when compact packaging facilitates the movement of the chromosome.At all other time euchromatin is present in an open configuration and its genes can be expressed.
3.What is transformation?
Transformation is the transfer of genetic material from one cell to another and can alter the gentic make up of the recipient cell.Recipient cell will express some the characteristics of the donar cell.
4.What is nuclein?
Miescher extracted a white substance from the nuclei of human cells and fish sperm.He called substance Nuclein because it seemed to be specifically associated with the nucleus.
5.What is semi-conservative replication?
In this form of DNA replication the daughter DNAs have one of the original strands and the other strand is newly synthesized from complementary nucleotides.
6.How DNA polymerase III can initiate synthesis of DNA?
DNA polymerase can initiate synthesis of DNA only if another enzyme primase constructs an RNA primer.DNA polymerase III recognizes the primer and adds DNA nucleotides to it to construct the DNA strands.The RNA nucleotides in the primers are then replaced by DNA nucleotides.
7.What are Okazaki fragments?
The lagging strand which elongates away from the replication fork is synthesized discontinuously as a series of short segments that are later connected.These segments are called Okazaki fragments.
8.What is the length of Okazaki fragments?
They are about 100-200 nucleotide3s long in eukaryotes and 1000-2000 nucleotides long in prokaryotes.
9.What is one gene/ one polypeptide?
Many enzymes contain multiple protein or polypeptide subunits,each encoded by a separate gene this relationship is referred to as one gene/one polypeptide.
10.What is transcription?
The first step of central dogma is the transfer of information from DNA to RNA, which occurs when an mRNA copy of gene is produced.The process is called transcription.
11.Which codons are called stop codons and consense codon and why?OR what are non-sense codons?Quote examples?
Out of 64 codons UAA,UAG and UAG do not code for any amino acid and hence are known as nonsense codon.These codons are usually present at the end of the gene and hence are also called stop codons.
12.What is initiation codon?
Every gene starts with initiation codon AUG which encodes the amino acid methionine.
13.How long DNA would stretch if the DNA in all of the cells of an adult human were lined up end to end?
If the DNA in all of the cells of an adult human were lined up end to end it would stretch nearly 100 billion kilometer-60 times the distance from Earth to Jupiter.
14.What is primer?
The primer is a sequence of about 10 RNA nucleotides complementary to the parent DNA template.It is synthesized by enzyme primase.
15.What are the three major classes of RNA?
mRNA,tRNA and rRNA.
16.What is the function RNA Polymerase in transcription?
Transcription is initiated when the enzyme RNA polymerase binds to a particular binding site called a promoter located at the beginning of the gene.
17.What is triplet code?
The genetic code for specifying amino acids does consist of 3-bases.This is called the triplet code.
18.What is anticodon?
A sequence of three nucleotides in tRNA that is complementary to mRNA is called anticodon.
19.What are chromosomes?
Chromosomes are thread like structures that appear inside the nucleus at the time of cell division.They were first observed by Walther Fleming in 1882, when he was examining the repidly dividing cells of salamander larvae.
20.What is the number of chromosomes in Penicillin and ferns?
Penicillin a fungus has only one pair of chromosomes while some ferns have more than 500 pairs.
21.What a typical chromosome is made up of ?
Typically a chromosome is made of chromatids centromere and secondary constriction.
22.What is Karyotype?
The particular array of chromosomes that an individual possesses is called its Karyotype.They vary in size staining properties the location of centromere the relative length of the two arms neither side of centromere and the position of constricted regions along the arms.
23.What are different types of chromosomes depending upon location of centromere?
The Chromosomes are called.Telocentric acrocentric sub metacentric and metacentric depending upon the location of centromere between the middle and tip of the chromosomes.
24.What are different shapes of chromosomes?
The usual shapes of chromosomes are i,j and v.
25.What is the composition of chromosomes?
Chromosomes are comosomes of DNA and protein.Most are about 40% DNA and 60% protein.
26.How many nucleotides are contained in a typical human chromosome?
A typical human chromosomes contains about 140 million nucleotides in its DNA.
27.How much information is contained in one chromosomes?
The amount of information one chromosome contains would fill about 280 printed books of 1000 pages each if each nucleotide corresponds to a word and each page had about 500 words on it.
28.What is the length of a strand of DNA from a single chromosome?
If the strand of DNA from a single chromosome were laid out in a straight line it would be about 5 centimetre long.
29.What is nucleosomes?
Every 200 nucleotides the DNA duplex is coiled around a core of eight histone proteins forming a complex known as a nucleosomes.
30.Why histones are positively charged?
Histones are positively charged due to an abundance of the basic aminon acids arginine and lysine.They are thus strongly attracted to the negatively charged phosphate groups of the DNA.
31.What are supercoils of DNA?
The histone cores act as magnetic forms that promote and guide the coiling of the DNA.Further coiling occurs when the string of nucleosomes wraps up into higher order coils called supercoils.
32.What are heteromatin?
Highly condensed portions of the chromatin are called heterochromatin.Their DNA is never expressed.
33.Define the chromosome theory of ingeritance?
According to this theory the genes are physical units located on the chromosomes.It means that one member of gene pair is located on one homologous chromosome and the other member of a gene pair is located on the other homologous chromosome.
34.What is a sex linked trait?
A trait determined by a gene on the X chromosome is said to be sex linken.
35.Who repeated the experiments of Griffith?
In 1944 in a classic series of experiments Oswald Avery along with colin Macleod and Maclyn McCarty repeated Griffith’s experiments and characterized what they referred to as the Transforming principle.
36.Why hershey and chase are famous for?
In 1952 by Alfred Hershey and Martha Chase experimented with bectriophages T2 and provided additional evidence supporting Avery’s conclusion.
37.What are the main components of DNA?
1) Phosphate (PO4) groups.
2) Five carbon sugars and
3) Nitrogen containing bases called purines and pyrimidines.
2) Five carbon sugars and
3) Nitrogen containing bases called purines and pyrimidines.
38.What is the structure of a typical nucleotide?
In a typical nucleotide nitrogen base is attached to carbon number 1 of a pentose suger and phosphate group is attached to carbon number 5 of the suger.In addition a free hydroxyl (-OH) group is attached to the 3 carbon atom.
39.What is phosphodiester bond or linkage?
In a polynucleotide chain the linkage between two groups is called a phosphodiester bond because the phosphate group is now linked to the two sugars by means of a pair of ester bonds.
40.What is the work of Chargaff?
Erwin Chargaff showed that the amount of adenine in DNA always equals the amount of thymine and the amount of guanine always equals the amount of cytosine.
41.What is X-ray diffraction?
In this analysis a molecule is bombardede with a beam of X-rays.When individual rays encounter atoms their path is bent or diffracted and the diffraction pattern is recorded on the photographic film.When carefully analyzed this pattern gives three dimensional structure of a molecule.
42.Who prepared the X-ray diffraction of DNA?
Rosalind Franklin prepared this X-ray diffraction pattern fo DNA in the laboratory of Birtish Biochemiest Maurice Wilkins who propared DNA fibres.
43.What does X-Ray diffraction of DNA suggest?
The diffraction pattern prepared suggested that the DNA molecule had a shape of a helix with a diameter of 2 nm and a complete helical turn every 3.4 nm.
44.Who proposed the double helical structure of DNA?
In 1953 james Watson and Francis Crick proposed structure of the DNA molecule.
45.Define replication or what is replication?
The process by which DNA of a living organism gives rise to a copy of itself is called DNA replication.
46.What is Semi-conservative replication of DNA?
In semi conservative replication the two strands of the duplex separate out each acting as a model or mold along which new nucleotides are arranged thus giving rise to two new duplexes.
47.Define Conservative Replication of DNA?
The conservative model stated that the parental double helix would remain intact and henerate DNA copies consisting of entirely new molecules.
48.What is Dispersive Replication of DNA?
The dispersive model predicted that parental DNA would become dispersed throughout the new copy so that each strand of all the daughter molecules would be amixture of old and new DNA.
49.What was work of Meselson-Stahl?
The three hypothesis of DNA replication were evaluated by Mathew Meselson and Franklin Stahl of the California Institute of Technology in 1958.
50.What is the role of DNA polymerase I?
DNA polymerase I is a relatively small enzyme that plays a supporting role in DNA replication.
When and where were the chromosomes first seen by whom?
The chromosomes were first seen by Walther Flemming in 1882 in the dividing cells of salamander larvae.
What is the normal number of chromosomes in mosquito, honeybee, corn, frog, mouse and man?
The number of chromosomes in 6, 32, 20, 26, 40 and 46, respectively.
What is a chromosome typically made of?
A chromosome is typically made of chromatids, centromere and a secondary constriction.
How do the chromosomes differ from one another?
The chromosomes differ in size staining properties, the location of centromere; the relative length of the two arms and the position of the constricted regions along the arms.
What is telocentric chromosome?
A chromosome having the centromere located at its one end is called telocentric chromosome.
What is the difference between the acrocentric and sub metacentric chromosomes?
The centromere of the acrocentric chromosome lies very near to one end with the result that one arm of the chromosome is very small or even imperceptible. In sub-metacentric chromosome the centromere lies at some distance from one end so that the two arms of the chromosome are unequal.
How would you identify a metacentric chromosome?
In metacentric chromosome the centromere lies at or near the center and both the arms of the chromosome are equal or almost equal.
The total chromosome complement of a cell is called karyotype.
Name the basic proteins in the chemical composition of chromosomes?
These are the histones.
What are the chromosomes chemically composed of and in what percentage?
The chromosomes are chemically composed of 40% DNA and 60% protein.
What is the number of nucleotides in the DNA of a typical human chromosome?
It is about 140 million.
After every 200 nucleotides, the DNA duplex (double strand) is coiled around a core of eight histone proteins forming a complex known as a nucleosome.
Why histones are positively charged as against most of the proteins which are negatively?
It is so because histones have an abundance of the basic amino acids arginine and lysine.
Differentiate between heterochromatin and euchromatin?
The portions of the chromatin which are highly condensed are called heterochromatin while the rest of the chromatin which is condensed only during cell division is called euchromatin.
What is Karl Correns famous for?
Karl Correns, a German geneticist first suggested central role of chromosomes in heredity in 1900.
Who and when proposed the chromosomal theory of inheritance?
Walter Suttan proposed the chromosomal theory of inheritance in 1902.
What is the normal and the mutant eye colour of Drosophila?
The normal eye colour of Drosophila is red while the mutant one is white.
How do X and Y chromosomes of Drosophila differ with respect to eye colour gene?
The gene for eye colour in Drosophila is located only on the X-chromosome and not on the Y-chromosome.
What is meant by sex-linked trait?
A trait, the gene for which is situated on the sex chromosome (X- chromosome in Drosophila) is called, a sex-linked trait.
Who provided first evidence that ‘DNA’ is the hereditary material?
The first evidence that DNA is the hereditary material was provided by a British microbiologist, Frederick Griffith.
Which type of streptococcus pneumonia bacteria are virulent, those with polysaccharide coat or without it?
The bacteria with polysaccharide coat are virulent which are commonly referred to as the s-type (smooth type).
What does transformation mean in the life cycle of pneumonia bacteria?
Transformation is the transfer of genetic material from one bacterium to another which can alter the genetic makeup of the recipient bacterium.
What is Friedrick Miescher famous for?
Friedrick Miescher, a biochemist isolated a material in 1869 from the nuclei of human cells and fish sperms that he called nuclei which was later named as nucleic acid.
Name the kinds of nucleic acids?
These are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
What are the units of the DNA molecule known as?
These units are known as the nucleotides.
Name the nitrogenous bases of the nucleotides of DNA?
The nitrogenous bases of the nucleotides of DNA are the adenine, guanine, thymine and cytosine.
What are the components of a nucleotide of DNA according to P.A. Levene?
The components of a nucleotide of DNA are the deoxyribose sugar, a phosphate group and a nitrogenous base, according to P.A. Levene.
Who presented the model of the structure of DNA and when?
James Watson and Francis Crick presented the model of the structure of DNA in 1953.
What is anticodon?
An anticodon is a group of three nucleotides (nucleotide triplet) on transfer RNA which is complimentary to the codon of messenger RNA.
What is the genetic code?
It is the sequence of bases along the DNA molecule that serves as code for the amino acid.
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