CELLULAR PROCESSES LIFE CYCLE, CELL DIVISION, DNA REPLICATION, RNA TRANSCRIPTION AND TRANSLATION

REASONS WHY CELLS DIVIDE 1.Growth 2.Replacement of Cells 3.Repair of Tissue 4.Asexual Reproduction

THE CELL LIFE CYCLE Every cell has a predetermined life span governed by its DNA. The Three main parts of the life cycle are 1. Interphase, 2. Mitosis and 3. Cytokinesis

INTERPHASE- the phase most cells are in at any given time. It is the phase at rest or the phase between divisions. The length of time spent in interphase differs widely from several weeks to months, years and sometimes decades. (Skin the shortest and Neurons the longest)

MITOSIS- Phases in which the Nuclear Material has been copied, is divided up and is separated into the two new cells. Prophase- nucleus disappears, chromosomes shorten and thicken Metaphase- Chromosomes align along the equatorial plane Anaphase- chromosomes separate and move to opposite poles of the cell Telophase- Nuclear envelopes return, chromosomes become thin.

CYTOKINESIS Final stage of cell division, the cytoplasm of the cell is evenly divided into the two new cells along with the organelles of the cell. Slight variations exist between cell types in this process such as…. In plant cells, a cell plate forms internally to divide the rigid cell In animal cells the cleavage furrow cuts into the cell until it finally divides

CLEAVAGE CELL PLATE

MEIOSIS CELL DIVISION Another form of cell division associated with Sexual Reproduction is Meiosis. It has similar physical properties to Mitosis but involves two full rounds of cell division and since DNA replication only occurs once, the number of chromosomes is reduced by ½ to produce Gametes (sex cells) The sex cells are… Sperm, Pollen, Ovum (egg) and Spores Gametes fuse during fertilization to form a Zygote which will become the embryo and fetus

MEIOSIS… There are 10 phases of Meiosis division and some significant events occur in them as stated below Interphase- DNA Replicates here Prophase I- Crossing Over may occur here Metaphase I Anaphase I Telophase I- Two Diploid cells now Interkinesis- No DNA Replication Prophase II Metaphase II Anaphase II Telophase II- Four Haploid cells now

HUMAN GAMETE PRODUCTION Sperm are formed by Spermatogenesis in the testes and Eggs are formed by Oogenesis in the Ovaries. Human body cells are Diploid with 46 chromosomes but gametes are Haploid having only 23 chromosomes. At fertilization, the Zygote now has 46 Chromosomes, 23 from the mom and 23 from the dad. Bozeman