CHAPTER 12

The Cell Cycle

The Key Roles of Cell Division

cell division = reproduction of cellsAll cells come from pre-exisiting cells

Omnis cellula e cellula

Unicellular organisms division of 1 cell reproduces organism

Binary fission

Why cells reproduce Development/Growth Replacement Repair

Multicellular organisms

100 µm 200 µm 20 µm

(a) Reproduction (b) Growth and development

(c) Tissue renewal

Cellular Organization of Genetic Material

chromosome = strand of DNA 2 sets of 23 chromosomes in humans = 46

genome = All DNA in a cell

20 µm

chromatin complex of DNA and protein

Somatic cells= body cells (2 trillion in adult) two sets of chromosomes (pairs= diploid) Produced by mitosis - 1 diploid cell 2 identical

diploid cells

Gametes sperm and eggs have 1 set = haploid Produced by meiosis– 1 diploid cell 4 unique cells Occurs only in ?

Identical cells Unique cellsDiploid Haploid

Concept check

1. start with a fertilized egg 5 cell divisions produce how an embryo of ______ cells

2. a chicken has 78 chromosomes in a somatic cell. How many chromosomes in a chicken sperm?

Human Arabidposis

The cell cycle = time from new cell to when it divides

Interphase – 90% of time

Mitosis 4o min

S(DNA synthesis)

MITOTIC(M) PHASE

G1

G2

Cell Division

Mitosis = division of the nucleusCytokinesis = division of cytoplasm

INTERPHASEG1 phase – cell grows, gets readyS phase – DNA replicatesG2 phase – cell grows, gets ready

S(DNA synthesis)

MITOTIC(M) PHASE

G1

G2

If cycle is 24 hrs, how longeach phase?

Signs of interphase?

S phase of Interphase

Chromosomes (DNA) replicate

Sister chromatids = 2

Centromere = constricted region

0.5 µm Chromosomes

Chromosomeduplication(including DNAsynthesis)

Chromosome arm

Centromere

Sisterchromatids

DNA molecules

Separation ofsister chromatids

Centromere

Sister chromatids

Prophase Prometaphase Metaphase Anaphase Telophase

Cytokinesis by late telophase

MITOSIS video

Chromosomes condense Mitotic spindle forms from centrioles Nuclear membrane breaks apart

I. Prophase

The mitotic spindle (formation begins in prophase)

Prophase G2 of Interphase

AsterCentrosomes

Aster = radial array of microtubules

Prophase

II. Prometaphase

Spindle microtubules attach to kinetochores of chromosomes Chromosomes pulled towards center of cell

III. Metaphase

chromosomes (sister chromatids) line up at the metaphase plate

midway between spindle’s two poles

MicrotubulesChromosomes

Sisterchromatids

Aster

Metaphaseplate

Centrosome

Kineto-chores

Kinetochoremicrotubules

Overlappingnonkinetochoremicrotubules

Centrosome1 µm

0.5 µm

Prophase PrometaphaseG2 of Interphase

PrometaphaseProphaseG2 of Interphase

Nonkinetochoremicrotubules

Fragmentsof nuclearenvelope

Aster CentromereEarly mitoticspindle

Chromatin(duplicated)

Centrosomes(with centriolepairs)

Nucleolus Nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Kinetochore Kinetochoremicrotubule

Metaphase Anaphase Telophase and Cytokinesis

Metaphase Anaphase Telophase and Cytokinesis

Cleavagefurrow

Nucleolusforming

Metaphaseplate

Centrosome atone spindle pole

SpindleDaughterchromosomes

Nuclearenvelopeforming

IV. Anaphase

sister chromatids separate

microtubules shorten – depolymerize to move chromosomes toward opposite ends of cell

V. Telophase

Identical nuclei form at opposite ends of cellChromosomes less condensed

Cytokinesis

Division of cytoplasmanimal cells

cleavage furrow

plant cells cell plate

Cleavage furrow100 µm

Daughter cells

(a) Cleavage of an animal cell (SEM)

Contractile ring ofmicrofilaments

Daughter cells

(b) Cell plate formation in a plant cell (TEM)

Vesiclesformingcell plate

Wall ofparent cell

New cell wallCell plate

1 µm

Nucleus

Prophase1

NucleolusChromatincondensing

Prometaphase2

Chromosomes

Metaphase3

Anaphase4

Telophase5

Cell plate10 µm

Evolution of Mitosis

mitosis is thought to have evolved from binary fission

Some protists exhibit cell division intermediate between binary fission and mitosis

The cell cycle is regulated by a molecular controls

Short length – ex. skin cell Longer length – ex. Neurons

Specific signal molecules in cytoplasm

SG1

M checkpoint

G2M

Controlsystem

G1 checkpoint

G2 checkpoint

Application: Cancer

Mutation in cell cycle genes

Breast cancer cells dividing