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.

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 replication Interphase 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).

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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: 9.20- 22 min

Stem Cells

Cells that have not differentiated yet. Can sometimes be manipulated and become

different cells.

Differentiation: the process where cells become specialized