Chapter 10 Cell Growth & Division

CELL GROWTH, DIVISION & REPRODUCTION

Why does a cell divide? If the cell is too large…  its DNA cannot meet all of the cell’s needs  Ex: library for a growing town  nutrients and wastes cannot be moved across the cell membrane well  surface area : volume ratio

Surface area : Volume  rate of exchange over the cell membrane depends on its’ surface area  rate at which food and oxygen are used and waste is produces depends on its’ volume  as a cell grows larger, its’ surface area : volume ratio gets SMALLER  waste will be produced faster (bigger volume), but it can’t be removed as quickly (smaller surface area)  Sooo… The cell must divide!

Cell division  process by which a cell divides, forming two daughter cells  before dividing, each cell duplicates its DNA so that each daughter cell gets one copy

THE PROCESS OF CELL DIVISION

Chromosomes  Made of DNA & proteins.  Carry the cells genetic info.  Every organism has a specific number of chromosomes  Bacteria = 1 circular chromosome in the cytoplasm  Humans = 46 chromosomes

Chromosomes (continued)  In eukaryotes, they are normally spread throughout the nucleus & aren’t visible (called chromatin).  Before cell division, each chromosome is replicated, forming 2 chromatids, attached by a centromere. attached by a centromere.

The Prokaryotic Cell Cycle = Binary Fission

The Eukaryotic Cell Cycle  During the cell cycle, the cell grows, prepares for division, and divides into 2 daughter cells, each of which begins the cycle again.  Phases:  G1: cell growth  S: DNA replicationInterphase  G2: preparation for mitosis  M: mitosis (division of the cell nucleus) & cytokinesis

Mitosis  Interphase  Prophase  Metaphase  Anaphase  Telophase/Cytokinesis

Interphase  Chromosomes are copied.  Chromosomes and copies appear as chromatin.

Prophase  Chromosomes become visible.  Centrioles appear and move to opposite ends of cell.  Spindle fibers form.  Nuclear membrane disappears.

Metaphase  Chromosomes line up across center of cell.  Spindle fibers attach to centromeres.

Anaphase  Sister chromatids are pulled apart.

Telophase/Cytokinesis  Chromosomes lose shape, appearing as chromatin.  Nuclear membranes reform.  Cytoplasm pinches in half (cytokinesis).  Clip1 Clip1  Clip2 Clip2

REGULATING THE CELL CYCLE

How long does cell division take?  Some cells (ex: muscle & nerve cells) do not divide at all once developed, while others (ex: skin & digestive tract cells) divide every few hours.

How is the cell cycle regulated?  Regulatory Proteins regulate the timing of the cell cycle  Both internal & external to the cell.  Most cells will stop growing when they come in contact with other cells.

Apoptosis  programmed cell death  Cells chromatin shrinks, its cell membrane breaks apart & neighboring cells clean up the remains.  AIDs & Parkinson’s disease can result when apoptosis doesn’t occur as it should.

Cancer  uncontrolled cell growth  Tumor: mass of cells formed from cancer  May be benign (nonspreading) or malignant (spreads to other tissue).  Lecture 1: min Lecture 1: min Lecture 1: min

Stem Cells  Cells that have not differentiated yet.  Can sometimes be manipulated and become different cells.  Differentiation: the process where cells become specialized