Structure of Chromosome Cell Cycle and Cell Division Class 10 ICSE Notes
ICSE Class 10 Biology Chapter 2 Structure of Chromosome Cell Cycle and Cell Division Notes, Summary, Definition, Diagram. Structure of Chromosome Cell Cycle and Cell Division Notes.
2.1 What are chromosomes?
A.) DNA serves as the genetic materialin many cells.
B.) Dna is mainly present in the nucleus arranged in structures called chromosomes
C.) Chromatin: DNA associated with proteins is called as chromatin
D.) During the process of cell division, the chromatin fibers condence. On staining these fibers, they appear darkly stained. Hencetheyget their name chromosomes which means darkly stained bodies
2.2 Discovery of chromosomes:
- WALTER FLEMMING was the 1st person to observer chromosomes in animal cells.
- He observed highly condenced chromatin fibers during cell division and called the process mitosis.
2.3 Chromatin:
- It is made up of DNA(40%) and histone protein (60%).
- Molecular structure of DNA : It is a macromolecule, composed of two strand wound round in a helix
- The strands are anti parallel.
- DNA is made of repeating units of neucleotides.
- Neucleotides = pentose sugar (ribsose) + phosphate + nitrogenous base.
- nitrogenous base = adenine, guanine, cytosine, uracil, thymine
- The nitrogenous bases are complimentry to each other, adenine pairs with thymine with 2 hydrogen bonds and guanine pairs with cytosine with 3 hydrogen bonds.
- Histones are helpful in packaging and coiling the DNA in the neucleus
- 8 Histone protein + DNA = Neucleosome
- The DNA is condencend into chromoomesso as to fit it in the nucleus
2.4 Structure of chromosomes:
- Centromere- a small area of constriction joining the two sister chromatids present along the length . it is the site of attachment for spindle fibers
- Chromatin fibers are condenced into chromosomes
2.5 What are genes?
- Genes are streches in DNA which codesfor proteins in thebody ofan organism
- These proteins have specific functons in the body.
- Genes are inherited from either of parent and are passedon to their children.
2.6 Need for new cells.
- Old cells in the body need to be replaced by new cells.
- Growth, replacement, repair and reproduction are the process in the body which require new cells
1.) For growth cells need to perform cell division, so that multiple copies of acell can be produced.
2.) If there is cell damage or death of cell these cells have to be replacedby other cells which are produced in the bone marrow.
3.) When ever there is tissue injury, it is necessary to have new cells to replace these cells with new ones.
4.) The process of reproduction also requires new cells . during meiosis which occures during reproduction the no. of chromosomes are reduced to half. On the egg and sperm fusion .
2.7 cell cycle:
1.) it is devided into two phases that is mitosis and interphase
a) Interphase: it is the phase where no division takes place.
b) The interphase has thefollowing phases: G1,S,G2, G0
c) GROWTH PHASE1 (G1) :in this phase RNAand proteins are synthesized and the cells are made ready for DNA replication. The cell may also enter a resting phase.
d) SYNTHESIS PHASE: In this dna and chromosomes are doubled.
e) GROWTH PHASE (G2) : in this shorter growth phase the RNA or protein synthesis continues
2.8 CELL DIVISION:
1.) It is the most fundamental process in growth and reproduction.
2.) Two types of division mitosis and meiosis
mitosis
3.) Mitosis produces clonesorsimilarcopies of itself . it is important process in which chromosome no is same.
4.) Karyokinesis: it is the division of nuceus in two daughter cells.
5.) The phases of mitosis are:
6.) Prophase: in this phase the chromatids start to condence. The duplication of centrioles occures in this phase. Spindle fiber start to appear in this phase and the nuclearmembranestarts to dissapers.
7.) Metaphase: the chromosomes start to arrange themselves on the plane of equator and they attach themselves to spindel fibers.
8.) Anaphae:the shortning of spindel fibers pulls the two chromosomes down towars the poles.
9.) Telophase: in this phase nuclear membrane reappears. The chromatide fibers reattain their original size.
10.) CYTOKINESIS: It is the process in which the cytoplasm is divided in the daughter cells.
11.) Mitosis helps in asexual reproduction
MEIOSIS
12.) It is reductional devision in which the no.of chromosomes is reduced to half.
13.) There is recomobination which takes place in this process.
14.) There is formation of chisama. Formed during the process of crossing over.
15.) It helps in gamate formation.
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