This document provides information on the structure of chromosomes. It begins by defining a chromosome as a threadlike structure found in the nucleus of cells that carries genetic information in the form of genes. Chromosomes are made up of 50% protein and 50% DNA, and contain many genes. The document then discusses the specific structures of chromosomes, including chromatids, centromeres, and chromosome arms. It also describes the chemical composition of chromosomes, noting they are made up of DNA, histone proteins, and other non-histone proteins involved in DNA replication and expression. The document concludes by discussing how DNA is packaged into nucleosomes and higher order structures to achieve its packing ratio within the chromosome.

2. MOLECULAR BIOLOGY 
TOPIC OF PRESENTATION:
STRUCTURE OF CHROMOSOMES

3. GROUP MEMBERS:
RABAB MAQSOOD
RABIA IQBAL
AYESHA KABEER
SHADAB ARIF
RUKHMA JAVEED
SHAFAQ QAISER
RIMSHA
STRUCTURE OF
CHROMOSOMES

4. STRUCTURE OF CHROMOSOMES
 DEFINITION:
 A threadlike structure of nucleic acids and protein
found in the nucleus of most living cells, carrying genetic information
in the form of genes.
 Chromosomes are made of 50% proteins and 50% DNA.
 Chromosomes are made of many chromatin threads, each containing
DNA and proteins.
 Each chromosome contains many GENES that act as a blueprint or set
of instructions for the cell.

5. STRUCTURE OF CHROMOSOMES
 The duplicated condensed chromosomes are known as
dyads.
 The duplicated chromosomes are held together at the
region of centromeres.
 Typically a chromosome is made of two chromatids, a
centromere and a secondary constriction.
 Sister chromatids are two identical copies of the
chromosome connected by a centromere.
 The two chromatids of one homologous chromosome with
respect to those of the other homologue are called Non-
sister chromatids.
 The shorter arm of the two arms of the chromosome
extending from the centromere is called the p arm and the
longer arm is known the q arm.

6. CHEMICAL COMPOSITION OF CHROMOSOMES
 The packing of DNA is due to Histone protein.
 Composed of thin chromatin threads called Chromatin Fibers.
 Interphase chromatin consists of about 30 - 40% DNA, 50 -
65% protein and 1-10% RNA.
 Metaphase chromosomes contain 15 - 20% DNA, 10 - 15%
RNA and 65 - 75 % protein.
 DNA consists of nucleotides while the primary protein
component is histones.
 Histones strongly attracted to the negatively charged
phosphate groups of the DNA.
 There are 5 major types of Histones.
 Thousand of other types of proteins involved in DNA
replication and gene expression.
 The degree to which DNA is condensed is expressed as its
packing ratio.

7. PACKING RATIO:
 The length of DNA divided by the length into which it is packaged.
 To achieve the overall packing ratio, DNA is not packaged directly into
final structure of chromatin.
 Chromatin is composed of repeating 200 base pair unit, which were
called nucleosome.
 Nucleosome was described by Roger Kornberg in 1974.
 146 base pairs of DNA wrapped 1.75 times around a histone core.
 One molecule H1 is bound to the DNA as it enters and exits each
nucleosome core particle.
 This forms a chromatin subunit known as Chromatosome; consist of 166
base pairs of DNA.
 The histones cores act as magnetic forms for the coiling of DNA.
 Nucleosomes wraps up into higher order coils called super coils.

8. THANK YOU 