CELL CYCLE

INTERPHASE

G1 - Cells undergo majority of growth

S - Each chromosome replicates (Synthesizes) to produce sister chromatids

G2 - Chromosomes condense - Assemble machinery for division such as centrioles

G2 OF INTERPHASECentrosomes(with centriole pairs) Chromatin

(duplicated)

Nucleolus Nuclearenvelope

Plasmamembrane

MITOSIS

 is the process of forming (generally) identical daughter cells by replicating and dividing the original chromosomes, in effect making a cellular xerox. Commonly the two processes of cell division are confused. Mitosis deals only with the segregation of the chromosomes.

FUNCTIONS OF CELL DIVISION

20 µm100 µm 200 µm

(a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).

B. Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming

C. C. Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM two cells (LM).

PROPHASE

•The chromosomes condense and become visible•The centrioles form and move toward opposite ends of the cell ("the poles")•The nuclear membrane dissolves•The mitotic spindle forms (from the centrioles in animal cells)•Spindle fibers from each centriole attach to each sister chromatid at the kinetochore.

PROPHASE

Early mitoticspindle

Aster

Centromere

Chromosome, consistingof two sister chromatids

METAPHASE

The Centrioles complete their migration to the poles

The chromosomes line up in the middle of the cell ("the equator")

METAPHASE

Spindle

Metaphaseplate

Centrosome at one spindle pole

ANAPHASE

Spindles attached to kinetochores begin to shorten.

This exerts a force on the sister chromatids that pulls them apart.

Spindle fibers continue to shorten, pulling chromatids to opposite poles.

This ensures that each daughter cell gets identical sets of chromosomes

ANAPHASE

Daughter chromosomes

TELOPHASE AND CYTOKINESIS

• Two daughter nuclei begin to form in the cell.

• Nuclear envelopes forms.

• The chromosomes become less condensed.

• Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.

CYTOKINESIS

 the process of splitting the daughter cells apart. Whereas mitosis is the division of the nucleus, cytokinesis is the splitting of the cytoplasm and allocation of the golgi, plastids and cytoplasm into each new cell.

TELOPHASE AND CYTOKINESIS

Nucleolusforming

Cleavagefurrow

Nuclear envelopeforming

MITOSIS IN A PLANT CELL

1 Prophase. The chromatinis condensing. The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is staring to from.

Prometaphase.We now see discretechromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelop will fragment.

Metaphase. The spindle is complete,and the chromosomes,attached to microtubulesat their kinetochores, are all at the metaphase plate.

Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomesare moving to the ends of cell as their kinetochoremicrotubles shorten.

Telophase. Daughternuclei are forming. Meanwhile, cytokinesishas started: The cellplate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell.

2 3 4 5

NucleusNucleolus

ChromosomeChromatinecondensing

CYTOKINESIS IN ANIMAL AND PLANT CELLS

Daughter cells

Cleavage furrow

Contractile ring of microfilaments

Daughter cells

100 µm1 µmVesicles

forming cell plate

Wall of patent cell Cell plate

New cell wall

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

PROKARYOTIC CELL DIVISION

MEMBRANE STRUCTURE AND FUNCTION

TRANSPORT MECHANISMS

The movement of materialsacross membranes takesmany routes but the mechanism’s are categorized as either passive or active transport mechanisms

PASSIVE TRANSPORT

moves molecules along a concentration gradient

no cellular energy required

Concentration Gradient: When a solute in a cell is in high concentration on one side of a membrane compared to the other.

PASSIVE TRANSPORT MECHANISM

Outside of cell

Inside of cell (cytoplasm)

Lipid Bilayer

Proteins

Transport Protein Phospholipids

Carbohydratechains

Structure of the Cell Membrane

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Animations of

membrane structure

SIMPLE DIFFUSION

• the movement of a substance from higher concentration to lesser concentration

• occurs across the lipid bilayer

OSMOSIS

the diffusion of water (solvent) across a membraneinfluenced by total solute concentration Water always moves toward the side with a greater

concentration of solute

Tonicity: the ability of a solution to move water Hypertonic: Greater ability to move H2O; gains water

Hypotonic: Lesser ability to move H2O; loses water

Isotonic: equal ability to move H2O; no net water movement

ACTIVE TRANSPORT

moves molecules against a concentration gradient

requires cellular energy