12/9/14

Objective: What is the structure of a chromosome and what is its role in the cell cycle?

Do Now: How many cells does mitosis produce?

Cell Division: 1 cell divides into 2 identical DAUGHTER cells

Getting from there to here…

• For reproduction – asexual reproduction

• one-celled organisms

• For growth– from fertilized egg to

multi-celled organism

• For repair & renewal– replace cells that die

from normal wear & tear or from injury

Why do cells divide?

amoeba

Nucleus Cell

Chromosomes

Chromosomes are made of DNA!!

• Thread-like structures found in the nucleus of cells that contain DNA

• A combination of DNA and protein that make up a chromosome

The Cell Cycle

Interphase

• 90% of cell cycle• cell doing its “everyday job”• makes proteins, etc Prepares for duplication if triggered

• Interphase can be divided into subphases– G1 phase

– S phase

– G2 phase

Interphase• Divided into 3 phases:

– G1 = (Growth)• cell grows

– S = DNA Synthesis• copies chromosomes

– G2 = (Growth)• prepares for division • cell grows (more)

G0

signal to

divide

double-strandedmitotic humanchromosomes

Mitotic PhaseMitotic Phase

- Stage where the cell is actually dividing

• Before you can share your notes,

You have to

make

a copy

- Chromatin condenses- Can see sister chromatids - Nuclear membrane breaks down- Spindle fibers form

Prophase

Prophase

• Protein fibers cross cell to form mitotic spindle– coordinates movement of

chromosomes

Microtubules: protein fibers that make up the spindle

- Sister Chromatids: two identical joined chromosomes

- Centromere: the region where the 2 chromatids are joined together

Metaphase • Chromosomes align along

middle of cell– metaphase plate

• meta = middle plane

– spindle fibers coordinate movement

Anaphase • Sister chromatids separate

– move to opposite poles

– pulled at centromeres

Telophase• Chromosomes arrive at

opposite poles– Nuclear membrane

reforms– Chromosomes disperse

• no longer visible under light microscope

• Spindle fibers disperse

Cytokinesis• Animals

• Splitting of cytoplasm• cleavage furrow forms

(shallow groove near old metaphase plate)

• splits cell in two

Cytokinesis in Animals

Mitosis in whitefish blastula

Cytokinesis in Plants• Plants

– cell plate forms new cell wall

The Cell Cycle Control System• The sequential events of the cell cycle

– Are directed by a distinct cell cycle control system, which is similar to a clock

Control system

G2 checkpoint

M checkpoint

G1 checkpoint

G1

S

G2M

• The clock has specific checkpoints– Where the cell cycle stops until a go-ahead signal is

received

G1 checkpoint

G1G1

G0

(a) If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues      on in the cell cycle.

(b) If a cell does not receive a go-ahead signal at the G1checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.

G0 phase: a non-dividing state

Fig. 12-15

G1

G0

G1 checkpoint

(a) Cell receives a go-ahead signal

G1

(b) Cell does not receive a go-ahead signal

Cancer

• A disease caused by the disruption of the mechanism that normally controls the cell cycle

• Leads to uncontrolled cell divison

Tumor

• A mass produced by out-of-control cell reproduction

Types of Tumors

Benign tumor: An abnormal mass of normal cells that can usually be removed by surgery

Malignant tumor: masses of cells from the reproduction of cancer cells (can spread if not removed or killed)

Metastasis

The spread of cancer beyond their original site

Prevention/Early Detection/Treatment

Getting Started

Interphase

Prophase

Metaphase

Drawing Metaphase

Anaphase

Telophase

Cytokinesis