cell division slides set

INTRODUCTION

• mitosis - somatic cells - repair, growth, asexual reproduction
• meiosis - germ cells - reproduction
• Hertwig proposed Kernplasm theory - repair and maintenance. According to this theory, the mitosis occurs due to the disturbance in the karyoplasm index of the cell. Kayoplasmic index. As the number of cells increases, it is essential to maintain the surface area : volume ratio
• phase 1 - reduction division - splitting of a cell into 2 with each half having half the number of chromosomes
• phase 2 - equational division - 2 cells give rise to 4 cells with the same number of chromosomes
• cell division occurs - to maintain the cell surface area and volume
• phase 1 - interphase (23 hours)
• phase 2 - mitosis (1 hour)
• cell cycle - interphase and m-phase (mitotic phase)
• interphase - also called resting phase - it is the preparatory phase - has G1 (growth 1) , G2 (growth 2) , S (synthetic) phase
• m-phase - actual division phase - has 2 phases - karyokinesis and cytokinesis
• karyokinesis - prophase, metaphase, anaphase, telophase
• cytokinesis - division of cytoplasm

INTERPHASE

• G1 phase or Gap 1 - metabolic activity increases and growth takes place
• protein synthesis takes place
• enzymes required for duplication of DNA
• duplication of cell organelle
• RNA synthesis takes place (since it's required for protein synthesis)
• ATP synthesis takes place (since for all of these, energy is required)
• therefore, cell size increases, surface area and volume get affected thus there is a requirement for division

S-PHASE (SYNTHETIC PHASE)

• very important
• DNA replication (DNA copying is the basis of reproduction because it's the blueprint for life)
• centriole divides (when they divide, they get aligned at right angles and that is called diplosomes)
• G not phase - differentiation into specific cells and perform specific function (quiscent or inactive phase) - some cells would not divide further after G1 or during G1 and they get specialized and perform particular functions
• differentiation - getting morphological change in the cell to perform specific role to play (meristems - divide rapidly - permanent tissue)
• de-differentiation - permanent tissue - divide rapidly - morphological changes to become meristematic tissue
• re-differentiated
• DNA replication - chromosome number increases, number of chromosomes stays the same
• content value is given by picogram

TYPES OF CELL DIVISION

• mitosis
• meiosis
• amitosis - prokaryotes - absence of mitosis - division without spindle formation since no nucleus
• Arresting mitosis - delaying the pace by releasing colchicine which belongs to Lilliaecea. It is used to stop cytokinesis and for research work while studying
• colchicine - helps in bringing about polyploidy
• mustard gas - arrest cytokinesis

MEIOSIS