Khulna University

1. By- Md. Alamgir Sarder
Student ID-MS 172010

2. Outline
• History of Chromosome
• Structure and organization

3. History of Chromosome
• The word chromosome comes from the Greek χρῶμα (chroma,
"colour") and σῶμα (soma, "body"), describing their strong staining
by particular dyes.
• The German scientists Schleiden, Virchow and Bütschli were among
the first scientists who recognized the structures now familiar as
chromosomes.

4. What is Chromosome?
• DNA molecule with part or all of the genetic material (genome) of an organism.
• During cell division, the nucleus of cells in the nucleioplasmae have a kind of yarn type. These formative
organisms in the nucleus are called chromosomes.
• thread-like molecules that carry hereditary information for everything from height to eye color.
• They are made of protein and one molecule of deoxyribonucleic acid (DNA)
• Visible under a light microscope only when the cell is undergoing the metaphase of cell division.
• They are made of protein and one molecule of DNA, which contains an organism's genetic instructions,
passed down from parents.
• In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell.
Humans have 22 of these chromosome pairs, called autosomes.

5. Structure and organization

6. Structure and organization

7. Parts of Chromosome
Different Physical Parts of Chromosome:
1. Chromonemata
2. Centromere/primary constrictions
3. Chromomeres
4. Pellicle
5. Matrix
6. Secondary constrictions
7. Satellite bodies

8. Parts of Chromosome (Cont.)
• Chromonemata:
 Embedded in the matrix of each chromosome are two identical, spirally coiled threads, the
chromonemata.
 At metaphase each chromosome consists of two symmetrical structures, the chromatids, each of
which contains a single DNA molecule. The chromatids are attached to each other only by the
centromere and become separated at the start of anaphase, when sister chromatids migrate to
opposite poles.

9. Parts of Chromosome (Cont.)
• Centromere
 A lighter staining region appears as a constriction or thinner segment of the chromosome and is usually called
centromere or primary constriction or kinetochore.
• Depending upon position of centromere and comparative length of two arms of the chromosome, chromosomes may
be of following types:
Acrocentric:
• I-shaped, rod like chromosomes having one arm of very small size. Thus, arms are unequal. Position of centromere is sub-
terminal.
 Sub-metacentric
• ‘L’ or J-shaped. Centromere is not present in the centre of the chromosome. Arms are unequal.
 Metacentric
• V shaped. Centromere is present in the centre of chromosome. Arms are equal in length.
 Telocentric
• Darlington (1939) defined telocentric chromosome as chromosome having a terminal centromere. I-shaped,
single armed.

10. Parts of Chromosome (Cont.)

11. Parts of Chromosome (Cont.)
• Chromomeres
It was demonstrated that the chromosomes particularly in early meiotic prophase, were
differentiated into morphologically distinct regions which were constant in size and
position. These regions called chromomeres.

12. Parts of Chromosome (Cont.)
• Pellicle
 Each chromosome is bounded by a membrane called pellicle. It is very thin and is formed of achromatic
substance. This membrane encloses a jelly-like substance which is usually called matrix. In the matrix is
present the chromonemata. The matrix is also formed of achromatic or nongenic material.
• Matrix
The function and structure of the matrix is not known. Presumably it aids in keeping the
chromonemata with in bounds so that the manoeuvres of the chromosome during cell
division can take place unhindered. It may also serve as an insulating sheath for the genes
during cell division.

13. Parts of Chromosome (Cont.)
• Secondary constrictions
 Secondary constrictions mark the locations at
which the nucleoli are assembled. The
chromosomes in addition to primary
constriction (centromere), possess secondary
constriction at any point of the chromosome.
It is often associated with the nucleolus during
interphase and may take part in the
reorganization of the nucleolus at the end of
cell division.

14. Parts of Chromosome (Cont.)
• Satellite bodies:
The part of the chromosome which is present
beyond the secondary constriction is called
satellite body or trabant. It varies in size
according to the position of the secondary
constriction. If secondary constriction is very
close to an end of the chromosome, the satellite
may be a baiely perceptible dot.

15. Parts of Chromosome(Cont.)
• Different Chemical Parts of Chromosome:
1. Nucleic Acid(DNA, RNA).
2. Protein
3. Others

16. Nucleic Acid
• Nucleic acids (DNA or RNA) are polymers of nucleotides – each nucleotide consists of a pentose
sugar, a phosphate group and one of the nitrogenous bases (purines and pyrimidines). Nucleic
acids function in encoding, transmitting and expressing genetic information in either the double-
stranded form (mostly for DNA) or in single-stranded form (mostly for RNA).
Nucleic Acid
DNA
(Deoxyribonucleic Acid)
RNA
(Ribonucleic Acid)

17. Deoxyribonucleic Acid
Definition:
• Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the
development and function of living things.
• All known cellular life and some viruses contain DNA.
• The main role of DNA in the cell is the long-term storage of information.
Characteristic:
• DNA is made up of molecules called nucleotides.
• Each nucleotide contains a phosphate group, a sugar group (five carbon) and a nitrogen base.
• Structure of two strands, intertwining around an axis like a twisted ladder.
• The four types of nitrogen bases are (i) Adenine (ii), thymine (iii), guanine (iv) and cytosine.
• Adenine and Thymine pair (A-T),Cytosine and Guanine pair (C-G) .
• Principle in which the nitrogenous bases of the DNA molecules bond with one another
• The order of these bases is what determines DNA's instructions, or genetic code. Human DNA has around 3 billion
bases, and more than 99 percent of those bases are the same in all people, according to the U.S. National Library of
Medicine (NLM).

18. Deoxyribonucleic Acid

19. Deoxyribonucleic Acid

20. RNA (Ribonucleic Acid)
Defination:
Like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a
single-strand folded onto itself, rather than a paired double-strand.
• The complementary base to adenine in DNA is thymine, whereas in RNA, it is uracil, which is
an unmethylated form of thymine.
• RNA can form into double-stranded structures, such as during translation, when mRNA and tRNA
molecules pair.
• It is an important molecule with long chains of nucleotides.
Characteristic:
• A nucleotide contains a nitrogenous base, a ribose sugar, and a phosphate.
• RNA uses the sugar ribose instead of deoxyribose.
• RNA is generally single-stranded instead of double-stranded.
• RNA contains uracil in place of thymine.
• Adenine and Uracil pair (A-U),Cytosine and Guanine pair (C-G) .

21. RNA (Ribonucleic Acid)

22. DNA vs RNA
Comparison DNA RNA
Full Name Deoxyribonucleic Acid Ribonucleic Acid
Function DNA replicates and stores
genetic information. It is a
blueprint for all genetic
information contained within an
organism
RNA converts the genetic
information contained within
DNA to a format used to build
proteins, and then moves it to
ribosomal protein factories.
Structure DNA consists of two strands,
arranged in a double helix.
These strands are made up of
subunits called nucleotides.
Each nucleotide contains a
phosphate, a 5-carbon sugar
molecule and a nitrogenous
base.
RNA only has one strand, but
like DNA, is made up of
nucleotides. RNA strands are
shorter than DNA strands. RNA
sometimes forms a secondary
double helix structure, but only
intermittently.
Length DNA is a much longer polymer RNA molecules are variable in

23. Comparison DNA RNA
Sugar The sugar in DNA is
deoxyribose, which contains one
less hydroxyl group than RNA’s
ribose.
RNA contains ribose sugar
molecules, without the hydroxyl
modifications of deoxyribose.
Bases The bases in DNA are Adenine
(‘A’), Thymine (‘T’), Guanine (‘G’)
and Cytosine (‘C’).
RNA shares Adenine (‘A’),
Guanine (‘G’) and Cytosine (‘C’)
with DNA, but contains Uracil
(‘U’) rather than Thymine.
Base Pairs Adenine and Thymine pair (A-T)
Cytosine and Guanine pair (C-
G)
Adenine and Uracil pair (A-U)
Cytosine and Guanine pair (C-
G)
Location DNA is found in the nucleus, with
a small amount of DNA also
RNA forms in the nucleolus, and
then moves to specialised

24. Comparison DNA RNA
Reactivity Due to its deoxyribose sugar, which
contains one less oxygen-containing
hydroxyl group, DNA is a more
stable molecule than RNA, which is
useful for a molecule which has the
task of keeping genetic information
safe.
RNA, containing a ribose sugar, is
more reactive than DNA and is not
stable in alkaline conditions. RNA’s
larger helical grooves mean it is
more easily subject to attack by
enzymes.
Ultraviolet (UV) Sensitivity DNA is vulnerable to damage by
ultraviolet light.
RNA is more resistant to damage
from UV light than DNA.