Chapter 10Chapter 10Cell Growth & DivisionCell Growth & Division

Cell DivisionCell Division There are 2 main reasons cell divides:There are 2 main reasons cell divides:

1.1. The cell has more trouble trying to move The cell has more trouble trying to move nutrients and wastes across the cell nutrients and wastes across the cell membrane.membrane.

2.2. The larger a cell becomes, the more The larger a cell becomes, the more demands it puts on its DNA.demands it puts on its DNA.

Bottom line – cells need to be replacedBottom line – cells need to be replaced

Cell CycleCell Cycle• The sequence of The sequence of

growth and division of growth and division of a cella cell

• An average cycle may An average cycle may be 22 hoursbe 22 hours

• Two general periods:Two general periods: 1. growth phase1. growth phase 2. division phase2. division phase

Interphase (Growth phase)Interphase (Growth phase)

Most of the cell’s Most of the cell’s life is spent in life is spent in interphaseinterphase

Longest phase –Longest phase –(90% of cell’s (90% of cell’s growth)growth)

Centrioles – help to Centrioles – help to organize cell divisionorganize cell division

Chromatin – DNA bound Chromatin – DNA bound protein within the nucleusprotein within the nucleus

Interphase (Growth phase)Interphase (Growth phase)

New DNA is formed New DNA is formed during 3 phases:during 3 phases:

GG11 – 1 – 1stst period of growth period of growth 1. Increase in size.1. Increase in size.

2. Makes new proteins and 2. Makes new proteins and organelles.organelles.

SS1 1 – DNA is synthesized or – DNA is synthesized or replicated replicated

1. Chromosomes are replicated.1. Chromosomes are replicated. 2. New DNA molecules are 2. New DNA molecules are

made. made.

GG2 2 – final cell growth– final cell growth1. Shortest phase1. Shortest phase2. Prepares cell for mitosis2. Prepares cell for mitosis

Terms to knowTerms to know Chromosome – Chromosome –

contains genetic contains genetic information (DNA) information (DNA) passed from one passed from one generation to the nextgeneration to the next

Spindle – microtubule Spindle – microtubule that helps separate that helps separate chromosomeschromosomes

A – centromere: A – centromere: center of chromosomecenter of chromosome B – chromatids: two B – chromatids: two

identical “sister” parts identical “sister” parts of the chromosomeof the chromosome

Mitosis (Division phase)Mitosis (Division phase)

4 phases:4 phases:(PMAT)(PMAT)

1)1) PProphaserophase2)2) MMetaphaseetaphase3)3) AAnaphasenaphase4)4) TTelophaseelophase

MitosisMitosis

Takes place within the nucleus of the cellTakes place within the nucleus of the cell

4 phases that blend from one to another4 phases that blend from one to another

ProphaseProphase 11stst and longest phase and longest phase

of mitosisof mitosis Chromatin become Chromatin become

chromosomeschromosomes Chromatids are joined Chromatids are joined

by centromereby centromere Nucleus disappearsNucleus disappears Centrioles migrate to Centrioles migrate to

polespoles Spindles are formedSpindles are formed

MetaphaseMetaphase

22ndnd phase of mitosis phase of mitosis Chromosomes meet Chromosomes meet

in the middle of cellin the middle of cell Pulled by spindlesPulled by spindles Each chromosome is Each chromosome is

attached to top of attached to top of spindlespindle

AnaphaseAnaphase

33rdrd phase of mitosis phase of mitosis Centromeres are split Centromeres are split

apartapart Chromatids are pulled Chromatids are pulled

apart and begin to apart and begin to drift to opposite polesdrift to opposite poles

TelophaseTelophase Final phase of mitosisFinal phase of mitosis Begins when chromatids Begins when chromatids

reach polesreach poles New nucleus starts to New nucleus starts to

formform Chromosomes start to Chromosomes start to

unwindunwind Spindles disappearSpindles disappear Cytoplasm begins to Cytoplasm begins to

dividedivide

CytokinesisCytokinesis Cytoplasm Cytoplasm

pinches in pinches in halfhalf

Each daughter cell has Each daughter cell has an identical set of an identical set of chromosomeschromosomes

Plants

apical meristem

Rat – epithelial cellsRat – epithelial cells

Prophase, Metaphase, Anaphase, Prophase, Metaphase, Anaphase, or Telophase?or Telophase?