The Cell Cycle

Biology

Standards you are responsible

for mastering. • SB1a: Explain the role of cell organelles

for both prokaryotic and eukaryotic cells,

including the cell membrane, in

maintaining homeostasis and cell

reproduction.

• SB2b: Explain the role of DNA in storing

and transmitting cellular information.

The next two slides aren’t for

the notes…just pay attention.

• A Question for you…

– Cells need to be small.

• That’s a fact.

• But, WHY do they need to be small?

• Why is it better to have many small cells

than just a couple of big cells?

Ok, good.

• So, how do organisms get more cells and

prevent cells from getting too large??

• Cell Division.

Two main reasons why cells divide:

• 1.) To prevent DNA overload if the cell

grows too big, there will be an information

crisis.

• 2.) Bigger is not better if the cell grows

too large, it would take too long for

nutrients and wastes to travel through the

cell.

Cell Division

• A.) the cell divides forming 2 daughter

cells before growing too big.

B.) solves the problems of:

1.) Information crisis

2.) Increasing size

Cell Division

• A.) Chromosomes:

1.) pass on genetic information

2.) made of DNA and proteins

3.) every organism has a specific number of

chromosomes. (Humans = 46)

4.) are only visible during cell division

5.) are replicated BEFORE cell division

a.) chromatids 2 identical “sister”

parts of a duplicated chromosome.

1.) are attached at the centromere

Chromosome

Chromosome

The Cell Cycle

• 1.) The cell cycle is a series of events that

the cell goes through as it grows and

divides.

2.) During the cell cycle, the cell grows,

prepares for division, and divides to

form two daughter cells.

The 2 phases of the cell cycle

• A.) Interphase

• B.) Cell Division Mitosis & cytokinesis

Interphase -NOT A PART OF MITOSIS; NOT CELL DIVISION!

• 1.) contains the G-1, S, and G-2 phases.

• 2.) G-1 phase the cells grow in size and make new molecules and organelles.

• 3.) S phase chromosomes are replicated

• 4.) G-2 phase shortest phase, molecules & organelles needed for cell division are made.

Cell Cycle

Interphase

Interphase

Mitosis

• 1.) part of the cell cycle when the chromosomes separate from each other and the cell splits in half.

• 2.) This is how somatic cells reproduce.• Somatic cells are normal body cells (i.e., not sperm and egg)

• 3.) Mitosis has 4 phases:• Prophase - Nucleus breaks down, chromosomes become thick

(visible) and pair up.

• Metaphase - Chromosomes line up in the middle of the cell

• Anaphase - Chromosomes move to the opposite ends of the cell

• Telophase - Chromosomes unwind (become invisible) and nucleus reforms.

Prophase – more info…

• 1.) The chromatin condenses to form

chromosomes (DNA is visible)

• 2.) Centrioles separate and the spindle

fiber forms.• A.) spindle fiber helps to separate the

chromosomes.

• 3.) The nuclear envelope breaks down

Prophase

Prophase

Prophase

Prophase –

Draw This in the Box…

Nuclear Membrane

Spindle Fibers

Centriole

Cell Membrane

Metaphase …more info

• 1.) Chromosomes line up at the equator of

the cell.

• 2.) Each chromosome is connected to a

spindle fiber at its centromere.

Metaphase

Metaphase

Metaphase

Metaphase –

Draw this in the box

Anaphase …more info

• 1.) The sister chromatids separate into

individual chromosomes and are moved to

the opposite ends of the cell.

Anaphase

Anaphase

Anaphase

Anaphase –

Draw this in the box…

Telophase…more info

• 1.) Chromosomes gather at opposite ends

of the cell.

• 2.) chromosomes lose their shape

• 3.) Two new nuclear envelopes form.

Telophase

Telophase

Telophase

Telophase –

Draw this in the box…

Cytokinesis

- Starts during Telophase• 1.) Cytoplasm divides separating the two

identical nuclei.

• 2.) in animals the cell membrane is

pulled inward until the cytoplasm is

pinched into 2 almost equal parts.

• 3.) in plants a cell plate forms half way

between the two new nuclei.

Animal Cell Cytokinesis

Cleavage furrow

Contractile ring of

microfilamentsDaughter cells

100 µm

(a) Cleavage of an animal cell (SEM)Figure 12.9 A

Plant cell cytokinesis

Daughter cells

1 µmVesicles

forming

cell plate

Wall of

patent cell Cell plateNew cell wall

(b) Cell plate formation in a plant cell (SEM)Figure 12.9 B

End result of Mitosis

• 2 genetically identical daughter cells.

Review Questions

Review 1

• During which part of interphase is the DNA

copied?

• A.) G1

• B.) S

• C.) G2

• D.) Mitosis

Review 2

• Which stage in a cell’s life cycle is the

longest?

• A.) mitosis

• B.) metaphase

• C.) interphase

• D.) cytokinesis

3

• Which of the following is the correct name

of DNA when it is uncoiled (not in a

chromosome form)?

• A.) Chromatid

• B.) Chromatin

• C.) Chromosome

• D.) Spindle Fiber

4

• If a cell has 32 chromosomes in G1 of

interphase, how many chromosomes will

each daughter cell have after mitosis &

cytokinesis?

• A.) 16

• B.) 32

• C.) 64

• D.) 128

5

• During which stage of mitosis do the

chromosomes line up at the equator of the

cell?

• A.) prophase

• B.) metaphase

• C.) anaphase

• D.) telophase

6

• Each side of a copied chromosome is

called:

• A.) a chromosome

• B.) a sister chromatid

• C.) chromatin

• D.) centromere

7

• The part of a copied chromosome where

the two sides are linked together is called

the:

• A.) centriole

• B.) centromere

• C.) chromatid

• D.) spindle fiber

8

• During which stage of mitosis do the sister

chromatids separate?

• A.) prophase

• B.) metaphase

• C.) anaphase

• D.) telophase

9

• Division of the nucleus is called:

• A.) interphase

• B.) cell cycle

• C.) mitosis

• D.) cytokinesis

10

• Division of the cytoplasm is called:

• A.) interphase

• B.) cell cycle

• C.) mitosis

• D.) cytokinesis

11

• What organelle has the job of pulling on

the spindle fibers to separate the

chromatids?

• A.) DNA

• B.) ribosome

• C.) centromere

• D.) centriole