Chapter 10 Cell Growth Division CELL GROWTH DIVISION

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: § § G 1: cell growth S: DNA replication G 2: preparation for mitosis M: mitosis (division of the cell nucleus) & cytokinesis Interphase

Mitosis § § § Interphase Prophase Metaphase Anaphase Telophase/Cytokinesis

Interphase § Chromosomes are copied. § Chromosomes and copies appear as chromatin. § Nucleolus and nuclear envelope are visible. (Nucleolus makes ribosomes. )

Prophase § Chromosomes become visible. § Centrioles appear and move to opposite ends of cell. § Spindle fibers form. § Nuclear envelope 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). § Clip 1 § Clip 2

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