With your partner, discuss the following questions:

1. Are you taller? Did your hair grow? Did you clip your toenails?

2. Have you broken a bone?3. How does your body repair itself?4. How does a human being grow from

a single fertilized cell into an individual containing billions of cells?

5. Do all the cells of the body look the same? Do they all perform the same function?

6. Do all the cells of the body contain the same genetic information?

Mitosis Videos:

The Mini Mitosis Tutorial BrainPOP Mitosis Video

Cell Cycle

How do baby elephants

grow up to be big

elephants?

Why do

organisms

need

more

cells?

Why do organisms need new cells?

• When you are growing!

• When you need to replace damaged cells!

How do cells make new cells?

smaller

nutrients grow

• All cells are created from other cells. The only way to get more cells is for cells to divide.

• Cell division is the process by which a parent cell divides into two or more daughter cells (IDENTICAL CELLS!).

• The parent cell provides the genetic code to each daughter cell.

Identical Daughter Cells

Parent Cell

Two identical daughter

cells

interphase

Cell Cycle

• In order for new somatic (body) cells to be made, they must go through the cell cycle:• Interphase • Mitosis

interphase

Interphase• Before dividing, cells

spend most of their time finding nutrients and growing.

• This phase is called interphase.

• During interphase, there are two growth phases. These are known as G1 and G2.

DNA replication occurs during the

synthesis (S) phase of

interphase.

Interphase - DNA Replication

Why Replicate?

Remember: ALL cells need genetic material….DNA!

So….before a cell can divide, the DNA must be replicated (copied).

If a cell doesn’t get a copy of DNA, it is USELESS and essentially DEAD!

DNA Replication

DNA → DNA (copy)

DNA is a HUGE molecule, in fact it

is so HUGE it cannot exit the nucleus EVER!

Sooo… DNA Replication occurs in the NUCLEUS!

3 EASY STEPSSTEP 1:

◦DNA Unzips

◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

5’

5’3’

3’

STEP 1: ◦DNA Unzips

◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

3 EASY STEPS

STEP 1: ◦DNA Unzips

◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

3 EASY STEPS

STEP 1: ◦DNA Unzips

◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

3 EASY STEPS

STEP 1: ◦DNA Unzips

◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds

3 EASY STEPS

Replication ForkThe areas where the

double helix separates are called replication forks because of their Y shape. Once the 2 strands are separated, additional proteins attach to each strand, holding them apart.

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STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

3 EASY STEPS

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

5’

5’

3’

3’ 5’

3’ 5’

3’

3 EASY STEPS

STEP 2: ◦Complimentary Base Pairing

◦DNA Polymerase adds matching

nucleotides

STEP 3: ◦DNA Ligase Rezips DNA

5’

5’

3’

3’ 5’

3’ 5’

3’

3 EASY STEPS

DNA REPLICATED!Two IDENTICAL copies of

DNA; one copy goes into each new cell

Blue – Original DNA

Green – New DNA

DNA replication is a semi-conservative process; there is not 1 new set and 1 old set. Each set of DNA contains 1 old strand and 1 new strand.

5’

5’

3’

3’ 5’

3’ 5’

3’

Checking for Errors Errors sometimes occur and the

wrong nucleotide is added to the new strand.

An important feature of DNA replication is that DNA polymerases have a “proofreading” role.

It can backtrack to remove the incorrect nucleotide.

Reduces errors in DNA replication to about one error per 1 billion nucleotides.

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G1: The cell grows – makes more cytoplasm & organelles; cell carries on normal metabolic activity (respiration, cell transport, etc).

S: DNA is replicated.

G2: The cell continues to grow, preparing for mitosis.

Let’s recap Interphase…

Mitosis• Once the cell is ready to begin dividing, it

enters MITOSIS. The purpose of mitosis is to separate the two sets of DNA into TWO DIFFERENT NUCLEI – each having it’s own complete set of chromosomes.

• Cells are diploid (2n)

If the parent cell has 46 chromosomes before mitosis, how many chromosomes will be in each genetically identical daughter cell

after mitosis?

Each daughter cell would be identical and have 46 chromosomes.

MitosisMitosis has four phases:

• Prophase• Metaphase• Anaphase• Telophase

Prophase: The DNA coils to form chromosomes, the chromosomes condense and become visible. The nuclear membrane dissolves.

Metaphase: Special proteins called spindle fibers line the chromosomes up in a straight. line.

Anaphase: The chromosomes (which are doubled due to replication) divide in half so that each complete and identical set of chromosomes move to opposite sides of the cell.

Telophase: A nucleus reforms around each set of chromosomes.

CytokinesisOnce two nuclei have been formed, the cell can divide its cytoplasm, which includes all its organelles, into two new daughter cells. This process is known as cytokinesis.

• Mitosis occurs in Eukaryotes.

• Why?• Because they have a

nucleus!

• Binary Fission occurs in Prokaryotes.• Asexual reproduction

Cellular Division in Prokaryotes Fission

Throughout the cell cycle, there are several checkpoints. These are the

points where the cell checks to make sure no mistakes have been made.

CheckpointsFissin

Certain mutations can cause cells to ignore these checkpoints. Cells can begin to divide very rapidly, and they do not stop dividing.

Ignoring Checkpointsn

When someone’s cells begin uncontrollably

dividing, they develop a tumor. Cancer is a form

of uncontrolled cell division, the cancer cells continuously

repeat the cell cycle.

Cancer