Cell Growth and Division

Growth vs. Division When an animal or plant grows, what happens to its cells? Does an animal get larger because each cell increases in size (grows) or because it produces more of them?

Why can’t cells grow forever? REASON 1: Not enough DNA!...as the cell increases in size, it keeps the same amount of DNA. Eventually the cell will grow too much for the DNA to control all its activities Memory Trick: Think of DNA like a library of books. If a town (cell) is too big, people may have to wait for books!

Why Can’t Cells Grow Forever? REASON #2: Surface area of membrane doesn’t increase as quickly as cell volume Too little membrane  not enough exchange of materials in and out of the cell

The Solution? Before a cell becomes too large, it divides to form 2 “daughter cells”. This process is called cell division Cell division can only happen once a cell has made a copy of its DNA so that each daughter cell can have a full genetic library

Cell Division in Prokaryotes DNA is copied and divided into two cells Creates two identical daughter cells Process is called Binary Fission

Cell Division in Eukaryotes DNA is found in the nucleus Chromatin is DNA & protein threads that coil into chromosomes during cell division.

Structure of Chromosomes Coiled threads of DNA and proteins. Contains genes (hereditary information) Must successfully divide for new cells to be made

Structure of Chromosome Chromatids: 2 identical copies Of DNA that are connected to Form a chromosome Centromere: the area where chromatids are attached (usually at the middle of the chromatids)

Chromosome #’s The cells of every organism have a specific number of chromosomes Cell Type# of Chromosomes Fruit Flies8 Carrots18 Human46

Diploid vs. Haploid Cells Diploid Cells (2n) = 2 sets of chromosomes…one from each parent (Example: human body cell) Haploid Cells (n)= only have 1 set of chromosomes (Example: Sperm or Egg Cell)

Types of Chromosomes Sex chromosomes = determine the sex of an organism; either X or Y Autosomes = all the other chromosomes in an organism

Cell Cycle The series of events that cells go through as the grow and divide During the cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each of which then begins the cycle again 2 Main Parts 1) Interphase 2) Cell Division

Interphase Time between divisions where cell grows and replicates DNA 3 Parts 1) G1 = cell grows and matures 2) S = DNA is copied 3) G2 = cell prepares for division

Mitosis This involves division of the nucleus 4 Phases 1) Prophase 2) Metaphase 3) Anaphase 4) Telophase

Part 1: Prophase Coiling of DNA into chromosomes Nuclear membrane breaks down Mitotic Spindle forms

What is the mitotic spindle? 2 Structures located in the cytoplasm called centrioles move towards opposite sides of the nucleus Microtubules (protein tubes) called spindle fibers grow from the centrioles Spindle fibers attach to chromosomes at the centromere and help pull chromatids apart

NERD

Part 2: Metaphase Spindle fibers move chromosomes to the center of the dividing cell

Part 3: Anaphase Chromatids of each chromosome separate at the centromere and move toward opposite poles of the dividing cell

Part 4: Telophase Chromosomes reach poles of cell Spindle breaks down Chromosomes uncoil into chromatin Nuclear envelopes and 2 nucleoli form

Cytokinesis Division of the cytoplasm Animal Cell: Cleavage Furrow (cell membrane pinches in ) Plant Cell: Cell Plate (cell wall grows between daughter cells)

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