Why do cells divide?

Growth Repair Replace dead cells

What cells divide often?

Skin Stomach lining Red Blood cells Embryo Plant roots Hair Nails

What cells rarely/never divide?

Nervous System Liver

Why do we age?

Eventually cells stop being replaced

“Apoptosis” Cell death

“We die because out cells die.” William R. Clark

“C” Terms Chromosomes

Long threads of genetic material

Found in nucleus

Chromatid One side of a

duplicated chromosome

“C” Terms

Centromere Structures that

hold sister chromatids together

NOTE 2 sister chromatids

= 1 duplicated chromosome

“C” Terms

Chromatin DNA tnagled around a histone (a

protein) Condensed chromatin = chromosome

Huh?

B. ChromatinA. DNA histone

C. Duplicated chromosome

“C” Terms

Centrioles Small protein bodies In cytoplasm Animal cells only

Cell Division in a Nutshell Before:

Chromosome duplicates = 2 sister chromatids

During: Sister chromatids separate

After: 2 “daughter” cells Genetically identical

Cell Cycle

Mitotic phase 10%

Interphase 90%

Interphase

Made up of three phases: G1, S, G2

What happens? Things necessary to

divide

Interphase

G1 Phase Cell Growth

8-10 hours S Phase

DNA replication Chromosome replication

6-8 hours G2 Phase

More Cell Growth Centriole replication

4-6 hours

Mitotic Phase

Mitosis Division of nucleus (chromosomes) Occurs after interphase

Cytokinesis Division of cytoplasm

Creates 2 daughter cells Occurs at the end of mitosis

Mitosis Phases

Interphase Prophase Prometaphase Metaphase Anaphase Telophase

Task

Draw a diagram of mitosis Label 6 phases & give each a short

description

Interphase

“Resting Phase” Cell NOT dividing

Precedes mitosis Prepares cell for division

How?

Early Prophase

Centrioles: Make spindle fibres Move towards

opposite plates Chromosomes now

visible

Late Prophase

Centrioles reach poles Nuclear membrane

(envelope) & nucleolus start to disappear

Metaphase

Spindle fibres attach to centromeres

Duplicate chromosomes line up at equator Guided by spindle

fibers

Anaphase

Spindle fibers retract

Pull sister chromatids apart Towards opposite polls

Telophase

Chromatin reappears Nuclear membrane &

nucleolus reappear Cytokinesis occurs

Result Two daughter cells

What phases do you see?A

D

B

C

Cytokinesis

Why would it occur differently in animal and plant cells?

Plant cells have a rigid cell wall!

Cytokinesis

Animal Cells

Plant Cells

Cell membrane pinches inward

Creates cleavagefurrow

Think: Pull a string around a

balloon

Cell Plate forms between two new nuclei

Becomes cell wall

Cytokinesis

Cytokinesis

Plant vs. Animal – Another Difference? Centrioles not present in

plant cells

What makes spindle fibers in plant cells? Form from cytoskeleton

Concept Map