Chapter 2: Structure of Chromosomes and Cell Division

What is a chromosome?

Coiled and condensed chromatin fibre which is only seen during cell division.

Who studied the chromosome first?

Walther Flemming on larvae of salamander.

Function of centromere

It is a point of contact of the two sister chromatids.

What is a chromosome made up of?

40% DNA and 60% Histone

What is DNA?

It is a macromolecule which is made up of repeating units called nucleotides ( polynucleotide chain ).

What is a DNA consist of?

It is double-stranded, where the complementary strands are wound around each other to form a double helix.

Nucleotide Composition

Phosphate, pentose (sugar), and nitrogenous bases.

Name the nitrogenous bases

Adenine, Thymine, Cytosine, Guenine

Which bases combine together?

Adenine and thymine with 2 H₂ bonds, and Cytosine and Guenine with 3 bonds.

Why are there only hydrogen bonds?

Bcz they are easier to break at room temp

What are histones?

Proteins which help in coiling and packing DNA into structural units called nucleosomes.

Nucleosome

A complex that is formed by a DNA strand wound around a core of eight histones (histone octamere).

Genes

Specific sequences of nucleotides on a chromosome that encode a particular protein which appears in the form of some particular feature of the body.

Cell Cycle

A series of events that are predictable and organized taking place in a cell to gove rise to a new cell.

The two steps of Cell Cycle

Interphase and M-phase

Phases in Interphase

First Growth phase, Synthesis Phase, and Second groeth phase

What happens in the First Growth phase?

RNA and proteins get synthesised

What happens in the Synthesis phase?

Replication of DNA and duplicates chromatin fibres

What happens in Second Growth Phase?

More of RNA and protein is synthesised.

Parts of Cell Division

Mitosis and Meiosis

Parts in Mitosis

Karyokinesis and Cytokinesis

What is Karyokinesis

Division of the Nucleus

Cytokinesis

Division of Cytoplasm

Phases of Karyokinesis

Prophase, Metaphase, Anaphase and Telophase.

Need for Cell Division

Repair, growth, and reproduction of cells.

What happens during prophase?

Centrosomes split into centrioles, which start moving to the poles, the nuclear membrane and nucleolus disappear, and the formation of spindle fibres and asters occurs.

What happens during metaphase?

Chromosomes line up at the equator of the cell, the centromere is attached to the spindle fibres.

What happens during Anaphase?

The chromosomes split, and the two sister chromatids move to the opposite poles due to the shortening of spindle fibres. A furrow is formed in the animal cell.

What happens during Telophase

Daughter chromosomes thin into fires, Spindle fires and asters dissappear, Nuclear membrane and nucleolus reappear

How does Cytokinesis occur in plant cells?

Cell plate formation

How does Cytokinesis occur in animal cell

Furrow formation

Haploid

Half set of chromosomes are passed