DNA structure, bases, chromosomes & sex chromosome

1. By :shubham kumar
vishwakarma
B. Pharm

2. DNA stands for deoxyribose nucleic acid
This chemical substance is present in the nucleus
of all cells in all living organisms
DNA controls all the chemical changes which
take place in cells
The kind of cell which is formed, (muscle, blood,
nerve etc) is controlled by DNA
Genes are composed of very long strands of DNA the
total length of DNA in each cell is about meter.
DNA 2

3. DNA Structure
 DNA consists of two molecules that are arranged into a
ladder-like structure called a Double Helix.
 A molecule of DNA is made up of millions of tiny
subunits called Nucleotides.
 Each nucleotide consists of:
1. Phosphate group
2. Pentose sugar
3. Nitrogenous base

4. Nucleotides
Phosphate
Pentose
Sugar
Nitrogenous
Base

5. Nucleotides
 The phosphate and sugar form the backbone of the
DNA molecule.
 There are four types of nitrogenous bases.

6. Nucleotides
A
Adenine
T
Thymine
G
Guanine
C
Cytosine

7. Nucleotides
 Each base will only bond with one other specific base.
 Adenine (A)
 Thymine (T)
 Cytosine (C)
 Guanine (G)
Form a base pair.
Form a base pair.

8. G
G
A
T
T
A
A
C
T
G
C
A
T
C

9. DNA Structure
 The function of DNA is carrying huge amount of
information that determine all biological of organism
and which is transmitted from one generation to next
generation .
 The bases are arranged in triplets called codons.
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C

10. DNA Structure
 A gene is a section of DNA that codes for a protein.
 Each unique gene has a unique sequence of bases.
 This unique sequence of bases will code for the
production of a unique protein.
 It is these proteins and combination of proteins that
give us a unique phenotype.

11. sugar-phosphate
chain
bases
THE DOUBLE HELIX

12. The Shape of the Molecule
DNA is a very long
polymer.
The basic shape is like a
twisted ladder or zipper.
This is called a double
helix.
12

13. Two Kinds of Bases in DNA
Pyrimidines are
single ring bases.
Purines are double
ring bases.
13
C
C
C
C
N
N
O
N
C
C
C
C
N
N
N
N
N
C

14. Thymine and Cytosine are
pyrimidines
 Thymine and cytosine each have one ring of
carbon and nitrogen atoms.
14
C
C
C
C
N
N
O
N
cytosine
C
C
C
C
N
N
O
O
thymine
C

15. Adenine and Guanine are purines
 Adenine and guanine each have two rings of
carbon and nitrogen atoms.
15
C
C
C
C
N
N
N
Adenine
N
N
C
C
C
C
C
N
N
O
N
Guanine
N
N
C

18. Parts of a
Chromosome

19. DNA
 Chromatin- DNA histone material is chromatin. The
chromatin is supercoilled and packaged into the
chromosomes.
 Histone- the double helix itself twisted wrapped in a
highly organized way around structural protein called
histone.
 Centromere-is a region of DNA i.e. is responsible for
the movement of the replicated chromosome into the
two daughter cell during mitosis & meiosis.
 Telomere- to protect end of chromosome.

20. Chromosome
StructureSupercoils within chromosome
Histones- Protein that DNA wraps
around
DNA - Stores genetic
information

23. Close up of
the histones
that make the
nucleosome

24.  Diploid cells contain both
parental chromosomes. (Ex.
every cell other than sex cells in
the body)
•Haploid cells contain half of
the parents chromosomes. (Ex.
sperm and egg cells are
considered haploid)

25. What is a Homologous Chromosome?
 Homologous chromosomes are the same size and
shape carrying the same genes for the same traits. One
comes from the father one from the mother.

26. Can you find the homologous
chromosomes?

27. Homologous
chromosomes
(pairs)

28. What is a Karyotype?
 A Karyotype is a picture of chromosomes arranged in
homologous pairs from largest to smallest.

29. Pairs of Chromosomes from largest to smallest

30.  Autosomes – are chromosomes that do
not determine sex
 Sex Chromosomes- are chromosomes
that determine the sex
of the organism.
 Female = XX and Male =XY

31. Sex Chromosomes
Autosomes