Cell Division We reviewed DNA Structure – Nucleotides & base pairing – Chromosomes, chromatin, and genes Time to move on to: Cell Cycle – Interphase- main part of cell cycle. – Mitosis- division of the DNA – Cytokinesis- division of the cytoplasm Overview

The Cell Cycle Page 7 on the notes packet.

Cell life, including division, occurs in a cyclic manner. The Cell Cycle What happens? The cell grows The cell has divided into two cells p.6

Why do cells in an organism divide? Growth

Why do cells in an organism divide? Development : Embryogenesis

Why do cells in an organism divide? Development : Embryogenesis

Why do cells in an organism divide? Tissue Repair : Wound healing

Why do cells in an organism divide? Reproduction (in unicellular organisms), divide via FISSION Bacillus (Bacteria) Amoeba (Protista)

So, why do cells in an organism divide? Multicellular: to grow; to develop; to repair tissues. Unicellular: to reproduce.

Why is the cell cycle important for growth? A Every time a cell goes through the cell cycle, the cells get larger and larger. B Each new cell must have chromosomes identical to the parent cell in order to do its job. C Each cycle, the parent cells must have three times the number of organelles for the daughter cells. D Cells must cycle several times to have enough cytoplasm to divide. Mastery Check 5

The Cell Cycle The cell cycle is divided into three distinct phases: Interphase (I) Mitosis (M) Cytokinesis (C) In which phase does the cell spend most of its life? Interphase p.8

Cell Cycle: Interphase It’s the major part of a cell’s life cycle. What happens: the cell grows, develops, and does what a cell does (metabolism, homeostasis, etc.) preparation of DNA for cell division (DNA replication)

Why is it important to prepare the DNA? Let’s see what would happen if it didn’t. A human cell contains 46 chromosomes (23 pairs). 1.If a human skin cell divides into two “daughter” cells, how many total chromosomes does each daughter cell have? 2.Now, imagine that each of those daughter cells divides again. How many total chromosomes would each new daughter cell contain? 3.What is happening to the number of chromosomes in each new daughter cell? 46/2 =  It’s decreasing

Why is it important to prepare the DNA? A human cell contains 46 chromosomes (23 pairs). 4.How many total times could this cell division cycle be repeated before the cells could no longer split the number of chromosomes? 5.Why do you think that real cells are able to divide over countless cell cycles without running out of DNA to pass on to the next generation? (what happens during interphase?) About 6 times 46  23  12 (+11)  6  3  2 (+1) * They must replicate their DNA before splitting. Is this what really happens? NO!

What is the role of DNA replication in the process of cellular reproduction? A DNA replication must occur so that each daughter cell has an exact copy of the DNA. B DNA replication must occur so that more cytoplasm can be made before the cell divides. C DNA replication must occur so that DNA can be hydrolyzed. D DNA replication must occur so that each resulting cell can have different combinations of genes. Mastery Check 6 video

DNA Replication p.9

Which of the following describes the process of replication? A The bonds between the nitrogen bases of DNA break apart and new nucleotides pair with each nucleotide of the original strands of DNA. B The bonds between the deoxyribose sugars of RNA break apart and new nucleotides pair with each nucleotide of the original strands of DNA. C The bonds between the phosphate groups of DNA break apart and new nucleotides pair with each nucleotide of the original strands of DNA. D The bonds between the ribose sugars break apart and new nucleotides pair with each nucleotide of the original strands of DNA. Mastery Check 7

DNA Replication OLD NEW 1. What is the product? How much of it is made? 2. What reactants are used (building blocks and template) ? 3. What is the name of the enzyme unzipping the double helix and assembling the product? 2 new DNA strands (each double strand is half-new, half-old) Nucleotides and original DNA double strand Helicase & DNA polymerase

A G G T A A C T T G C G 1.If the strand of nitrogen bases above were to undergo replication, what would be the nitrogen bases that match? T C C A T T G A A C G C Mastery Check 8