Teacher Notes

This PPT was revised November 19, 2008. This PPT is a companion PPT to Mitosis &

Meiosis. There is a handout for this PPT.

Reproduction &DNA Replication

How does DNA copy itself?

Why do cells divide?

to increase surface area

to repair damaged cells

to produce sex cells

to grow

Cell Reproduction

Cells reproduce either sexually or asexually.

Bacteria

Requires only one parent

Binary Fission

Budding

Vegetative Propagation

Regeneration

Asexual Reproduction

Advantages of Asexual Reproduction

offspring cells are exactly like the parent cell (clones)

Speed

Desirable Characteristics

Replacement

TRY THIS!

On your notebook paper draw a Verbal Visual table for Asexual Reproduction

Vocabulary Term

Definition

Drawing Non-Example

Sexual Reproduction

Sexual reproduction requires two parents.

Two sex cells (called gametes) must unite.

Fertilized Egg Cell

Fertilization

Fertilization is the union of egg & sperm.

New Individual

46

Mom

23

Dad

23

Advantages of Sexual Reproduction

Offspring are unlike the parent.

Sexual reproduction provides diversity in a species.

ant2 chromosomes

Chromosome Number

Every species has a specific number of chromosomes that every body cell is supposed to have.

crayfish200 chromosomes human

46 chromosomes

dog78 chromosomes

Chromosome Number

Since you inherit half of your chromosomes from each parent, you carry two complete sets of chromosomes.

mother crayfish100

chromosomes

father crayfish100

chromosomes

1 set of 1001 set of 1002 sets = 200

crayfish200 chromosomes

Homologous Chromosomes

These two complete sets of chromosomes are homologoushomologous, the chromosomes from the female parent have a corresponding chromosome from the male parent.

mother crayfish100

chromosomes

father crayfish100

chromosomes1 set of 1001 set of 1002 sets = 200

crayfish200 chromosomes

Homologous Chromosomes

Homologous chromosomes are similar in size and shape and control the same traits.fromfrom

fromfrom fromfrom

Chromosome Number

Humans inherit one set of 23 chromosomes in the egg from the mother and one set of 23 on the sperm from the father.

This gives the child 2 homologous sets of chromosomes.

46 46

23

46

23

Chromosome Number

The single set of one chromosome of each type inherited from one parent is called haploid.

Haploid:1 set of chromosomes (n)found in gametes (egg or sperm)

23 Chromosomes

Chromosome Number

A cell (such as a fertilized egg) with two sets of homologous chromosomes is called diploid.

Diploid:2 sets of chromosomes (2n)found in body cells (somatic)

46 chromosomes

Chromosome Number

Recall that every body cell in an organism must have the specific 2n chromosome number for that species.

If body cells do not have the correct 2n chromosome number, the cell will not _?_.

humans must have46 chromosomes

Why is it important for every body cell in an organism to have the specific 2n chromosome number for that species? .

How does this happen?

When we grow by our cells dividing to make two new cells, all of those new cells must have 46 chromosomes.

How do we get 92 chromosomes (46 for each new cell) from a cell with only 46 chromosomes?

46

46

46

Chromosome Number

The doubling of the chromosomes is actually DNA making an exact copy of itself. This is called DNA replication.

46

46

Then each new cell can receive the correct number of chromosomes (DNA).

46 9292

Create a Venn diagram for asexual and sexual reproduction.

TRY THIS!

A Cell’s Life Cycle

When does a cell divide?Most of a

cell’s life cycle is spent in Interphase when it performs normal life functions.

Green section

M

G1

S

G2

G1

C

A Cell’s Life Cycle

When does a cell divide?

Only a small part of the cell cycle is spent in division.

The RED section marked letter M

M

G1

S

G2

G1

C

A Cell’s Life Cycle

When does DNA replication occur?

During InterphaseInterphase, (in the S/Synthesis phase), the DNA replicates (makes a copy of itself).

M

G1

S

G2

G1

C

DNA Replication

Before a cell divides the DNA must replicate (make an exact copy of itself) so the new cells have the right 2n # of chromosomes.

DNA Replication

Each new cell must have the same chromosome number (and same DNA) as the parent cell to function properly.

DNA Replication

Replication occurs in 3 easy steps…

DNA Replication

1. DNA UnzipsAn enzyme unzips the

molecule by breaking the hydrogen bonds that hold the nitrogen bases together.

DNA Replication: 1. DNA Unzips

3’End

5’EndA

T

T

C

C

G

Left 5’ Strand of Original DNA Right 3’ Strand of Original DNA

3’End

5’End

A

T

A

G

G

C

5” End

2. Bases Pair

Complementary bases match with each base in the original DNA strand

What is the complementary base pairing rule?

A = TG C

DNA Base Pairing – Step 2

3’End

5’End

A

T

A

G

G

C

3’End

A

T

T

C

C

G

3. Two Identical DNA molecules

Two new DNA molecules each have the same DNA nitrogen base sequence.

The new DNA molecules are exactly like the original.

T

C

C

A

G

G

T

C

C

A

G

G

T

C

C

A

G

G

DNA Replication Review

Explain what is happening at each step in DNA Replication.

Step 1 Step 2 Step 3

What molecule is at I?

DNA Replication Review

What process is occurring? What is

happening at II (the arrow)?

What are the structures at III (circle)?

II

IIII

VV VVIIIIII

IVIV

What are the two molecules at V?

DNA Replication Review

What is happening at IV??

How many strands are formed?

II

IIII

VV VVIIIIII

IVIVWhat are

the new strands like compared to the original?

What are the new strands like compared to each other?

MITOSIS

Now that DNA has replicated and the cell now has two identical sets of DNA/ chromosomes

cell division (mitosis/meiosis) can begin..

46 92

T

C

C

A

G

G

T

C

C

A

G

G

MITOSIS

What is the purpose of DNA replication?

(Hint: think of the importance to the cells produced)

T

C

C

A

G

G

T

C

C

A

G

G

46

4646 9292

TRY THIS!

On your paper create a 3 Column Self-Assessment Chart for Cell Reproduction and DNA Replication

What I Know…

What I Don’t Know…

What I Wish I Knew…

Works Cited

There is a nice animation of DNA Replication at http://www.ncc.gmu.edu/dna/repanim.htm

DNA Replication diagram, artist Darryl Leja, National Human Genome Research Institute (NHGRI) http://www.genome.gov/page.cfm?pageID=10000552

Background DNA Replicaiton image, DOE Human Genome project, Department of Energy, (http://www.ornl.gov/hgmis)

DNA Replication diagram, artist Darryl Leja, National Human Genome Research Institute (NHGRI) http://www.genome.gov/page.cfm?pageID=10000552

“Fertilization - sperm fertilizing egg”, (No Date). Wikipedia.com, Retrieved June 20, 2006 from the World Wide Web: http://en.wikipedia.org/wiki/Image:Fertilisation.jpg, Website Copyright Permission: This image is copyrighted. However, the copyright holder has irrevocably released all rights to it, allowing it to be freely reproduced, distributed, transmitted, used, modified, built upon, or otherwise exploited in any way by anyone for any purpose, commercial or non-commercial, with or without attribution of the author, as if in the public domain.