Chapter 2:- structure of chromosomes

What contains most of the cells DNA

Nucleus

DNA is organised into discrete structures called

Chromosomes

Complex of DNA and protein is called

Chromatin

Chromosomes are highly coiled and condensed of

Chromatin fibres

Chromatin is composed of

DNA and histone

Full form of DNA

Deoxyribonucleic acid

Histone

A particular type of protein

A single DNA molecule is very large and hence it it described as

Macromolecule

DNA is composed of two complentary strands wound around each other in

Double helix

8 single DNA strand is composed of repeating nucleotides which are made of three components

Phosphate
Sugar (pentose)
Nitrogenous base

A is for

Adenine

G is for

Guanine

C is for

Cytosine

T is for

Thymine

C and G have a

Triple bond

A and T have a

Double bond

4 types kf nitrogenous base found in the DNA

Adenine
Guanine
Thymine
Cytosine

Nitrogenous base are joined with eachother with

Hydrogen bond

What does histone help in

Coiling and packaging of NDA into structural units called nucleosomes

The Dna strand winds around the core of

8 histone proteins

8 histone proteins are called

Octamer

Each octamer complex is called

Nucleosome

How much of DNA does each human cell contains

2 metres of stretched end to end

DNA needs to be ____________ in order to fit inside the nucleus

Condensed

Chromatin fibre eventually form

Chromosomes

In a chromosome the part where the sister chromatids are joined are called

Centromere

As a spindle fibre contracts the sister chromatid are

Separated at the centromere

Genes

The biochemical units of heredity that makes up the chromosome

Why do we need new cells

Growth
Repair
Reproduce

Cell cycle

Series of events that sells go through as a grow and divide this synthesize materials like proteins, RNA etc

Two phases of the cell cycle

Interphase (non dividing)
Mitosis (dividing)

Is interphase dividing?

No

Is mitosis dividing

Yes

Three phases of interphase

G2 phase
S phase
G2 phase

G1 phase of interphase

RNA and proteins are synthesized and the vol of cytoplasm increases

S phase of interphase

More DNA is synthesized
Chromosomes are duplicated

G2 phase of interphase

Short growth phase
RNA n proteins never for cell division continue to be synthesized

Duplication of DNA

S phase of interphase

How are DNA duplicated?

DNA double helix opens at 1 end making the two strands free to which news strands begin to form

2 types of cell division

Mitosis and meosis

Mitosis

Mitosis is the cell division in which one parent cell divides into 2 identical daughter cells

The most imp aspect of mitosis

Same normal chromosome number is maintained at each cell division

2 phases of mitosis

Karyokinesis
Cytokinesis

4 phases of Karyokinesis

Prophase
Metaphase
Anaphase
Telophase

Karyokinesis is the division of

Nucleus

Cytokinesis is the division of

Cytoplasm

Are asters formed during mitosis in animals

Yes

Where does mitosis occur in animals

Most tissues
Thruout the body

Are asters formed during mitosis in plants

No

Where does mitosis occur in plants

growing tips and sides

Significance of mitosis

Asexual reproduction
Growth
Tissue repair

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms

Significant aspect of meiosis

Number of chromosomes in the sex cells is halved

Significance of meiosis

Maternal and paternal chromosomes get mixed up during the first division as they separate from the homologous pairs

Where does mitosis occur

Somatic cells

Why does mitosis occurs

To provide growth and replacement

When does mitosis occur

Thruout lyf

No. Of daughter cells produced in mitosis

2

Number of chromosomes passed on to each daughter cell in mitosis

Full set

Number of nuclear divisions in mitosis

Single nuclear division after chromosome duplication

Identify of chromosomes and genes and daughter cell in mitosis

Identical

Where does meiosis occur

Reproductive cells

Why does meiosis occur

Gamate formation

When does meiosis occur

Reproductively active age

No. Of daughter cells passed on to each daughter cell

Half

Number of nuclear divisions in meiosis

2 after chromosome duplication

Identity of chromosomes and genes in daughter cell in meosis

Randomly assorted between the gamates produced

Haploid

23

Diploid

46