structure and functions of genetical materials

1. Biology for faculty of science (pre-medical)
Section-4 Continuity of life
Chapter 23 Chromosomes and DNA
Mr. Rahmat Ullah Albotanist
Master of Philosophy in Botany
Faculty of chemical and life sciences
(Abdul Wali Khan University Mardan Pakistan)

2. Eukaryotic cell chromosome

3. Purine is an aromatic heterocyclic organic
compound.

4. Pyrimidine is a heterocyclic aromatic organic
compound.

6. Diagram of a replicated and condensed metaphase eukaryotic
chromosome. (1) Chromatid – one of the two identical parts of the chromosome after S
phase. (2) Centromere – the point where the two chromatids touch. (3) Short strand. (4) Long strand.

7. 23.1 CHROMOSOMES
• In the nucleus of each cell, the DNA molecule is packaged into
thread-like structures called chromosomes. Each chromosome
is made up of DNA tightly coiled many times around proteins
called histones that support its structure.
• Observed by German embryologist Walther Fleming in 1882.
• Term Proposed by Waldeyer.

8. 23.1.1 Number of chromosome
• Varies from species to species
• A fungus, Penicillium has one pair of chromosomes
• Ferns have more than 500 pairs
• Diploid, two sets of chromosomes in their somatic cells, with one
member of each chromosome pair derived from the ovum and one
from the spermatozoon
• Haploid, number of chromosome exactly half than the somatic
number of chromosome e.g. gametes and spores cells

9. Diploid & Haploid number of chromosome

10. 23.1.2 Structure of chromosome

11. 23.1.3 Composition & organization of
chromosome
• Generally 40% DNA & 60% protein (histone)
• Human chromosome approximately 5 cm long DNA and about 140
million nucleotides
• DNA is a negatively charged molecule because of phosphate group
• Histone proteins have positively charged molecule due to the
abundance of some basic amino acid i.e. arginine and lysine
• 5 types of histone protein
• H1, H2A, H2B, H3 & H4

12. Nucleotides & Phosphate group

14. 23.2 CONCEPT OF GENE
• Wilhem Johansson term as gene in 1909
• Father of genetics Gregor Mendel “ each trait in the pea plant is
controlled by the discrete units “. Elementen or factors
• “ A gene is composed of nucleotide sequence of a short segment of
DNA which encodes the sequence of amino acid of a particular
polypeptide “
• Genes are found in the chromosome
• Position on a chromosome where a gene is located locus
• Alternative version or form of genes alleles
• Gene ABO blood group i.e. “I” exist in three alleles ( IA, IB, i )

16. Gene and alleles
• An allele is one of the possible forms of a gene. Most genes have
two alleles
• A dominant allele and a recessive allele.
• If an organism is heterozygous for that trait, or possesses one of
each allele, then the dominant trait is expressed
• A gene is a particular region of a DNA that controls a specific trait

18. Structure of gene
• A gene usually has regulatory regions and a structural region
• Regulatory region located to the 5’ end of coding strand of the gene is
called promoter that controls the binding RNA polymerase during
transcription
• Regulatory region located to the 3’ end of coding strand of the gene is
called terminator that stop the binding RNA polymerase during
transcription
• The region between promoter & terminator is structural region
• Non functional sequences of structural region is intron
• Functional sequences of structural region is exon
• In prokaryotes regulatory region regulated by same promoter and
terminator regions is operon

20. 23.3 Chromosomes theory of inheritance
• Behavior of chromosomes: Diploid cells have two copies of each
chromosome while gametes (after meiosis) have only one copy of
chromosome e.g. in pea plant diploid cells have 7 pairs of
homologous chromosomes while gametes have single 7
chromosomes
• Behavior of genes: According to the Mendel, diploid cells have two
copies of gene (pair of alleles) while gametes have only one e.g. in
pea plant, diploid cells have a pairs of alleles for each gene like Rr, Yy,
and Tt while gametes have single R or r, Y or y, T or t.
• During meiosis e.g. Genes like Yy and Rr segregate into Y or y & R or r

22. 23.4 DNA as heredity material Griffith’s experiment

23. Avery experiment… Hershey & chase experiment

24. 23.5 DNA replication

25. Process of DNA replication
• Continuous process….
• 1. Initiation phase. 2. Extension/Polymerization phase. 3.
Termination phase
• Several enzymes work such that
• DNA gyrase (topoisomerase), DNA helicase, Single stranded binding
proteins, DNA polymerase I, II & III, primase and exonuclease.

29. DNA Polymerase
DNA Polymerase I
Termination of replication
DNA Polymerase II
Repairing process of DNA
damage
DNA Polymerase III
Synthesizes daughter
strand

32. 23.6 Gene expression
• DNA into mRNA by transcription and convert into protein by
translation.
• Transcription: 3 Phases i.e. initiation, elongation & termination