Monday, March 19, 2012If you were absent on Friday, you need to makeup the checkup… in tutorial TODAY.

Homework:

None

Make an entry-

Entry 23: Mitosis- 3/19/12

Answer the following questions:

1.Why would a cell need to copy its DNA?

2.DNA is in the nucleus and doesn’t leave it. If both new cells need DNA how could this problem be solved?

3.Once DNA is copied, how could you make sure that exactly half goes in one cell and exactly half in the other cell?

4.If a cell divides into two cells, why don’t cells get smaller and smaller with each division?

5.How could two new cells be made from one original cell?

Regents Biology 2006-2007

Biology is the only subject in which multiplication is the same thing as division…

Regents Biology

Making New CellsMaking New DNA

Regents Biology

Where it all began…

You started as a cell smaller than a period at the end of a sentence…

Regents Biology

And now look at you…

How did you get from there to here?

Regents Biology

Going from egg to baby…. the original fertilized egg has to divide…

and divide…and divide…

and divide…

Getting from there to here…

Regents Biology

Why do cells divide… For growth & development

from fertilized egg to multi-celled

organism

For repair replace cells that die from

normal wear & tear or from injury

for reproduction Transmit genetic information to later

generations (meiosis) We will study this later.

amoeba

Regents Biology

Dividing cells… What has to be copied

DNA organelles cell membrane lots of other

molecules enzymes

animal cellplant cell

nucleus

chromosome

In the cell, DNA forms structures called chromosomes

• A eukaryotic chromosome is typically a very long, single chain of DNA

Chromosomes of Human Female

46 chromosomes23 pairs

Chromosomes of Human Male

46 chromosomes23 pairs

chromosome

• A gene is a region of the chromosome which contains information for making a protein

gene

• A chromosome has thousands of genes

Mitosis• Produces two identical daughter cells• Each daughter cell has the same kind and

number of chromosomes as the original parent cell

• Mitosis takes place after DNA replication.

Regents Biology

DNA must be duplicated…

nucleus

cell

DNA in chromosomes

nucleus

cell

duplicated chromosomes

chromosomes in cell

4 single-stranded chromosomes

duplicatedchromosomes

4 double-stranded chromosomes

Regents Biology

Mitosis: Dividing DNA & cells Stage 1: cell copies DNA

nucleus

cell

DNA Copy DNA!

(interphase)

Regents Biology

Mitosis: Dividing DNA & cells Stage 2: DNA winds into chromosomes

DNA is wound up into chromosomes to keep it organized

nucleus

cell

duplicated chromosomes Wind up!

(prophase)

Regents Biology

double-strandedhuman chromosomesready for mitosis

Regents Biology

Mitosis: Dividing DNA & cells Stage 3: Chromosomes line up

chromosomes line up in middle attached to protein “cables” that will

help them move

duplicated chromosomeslined up in middle of cell

Line up!

(metaphase)

Regents Biology

Mitosis: Dividing DNA & cells Stage 4: Chromosomes separate

chromosomes split, separating pairs start moving to opposite ends

chromosomes split & move to opposite ends

Separate!

(anaphase)

Regents Biology

Mitosis: Dividing DNA & cells Stage 5: Cell starts to divide

cells start to divide nucleus forms again

Divide!

(telophase)

Regents Biology

Mitosis: Dividing DNA & cells Stage 6: DNA unwinds again

cells separate now they can do their every day jobs

(cytokinesis)

Regents Biology

New “daughter” cells Get 2 exact copies of original cells

same DNA “clones”

Regents Biology

Cell division in Animals

Regents Biology

Mitosis in whitefish embryo

Regents Biology

Mitosis in plant cell

Regents Biology

onion root tip

Regents Biology

Overview of mitosis

Copy DNA Wind Up

Line Up Separate Divide

Regents Biology 2006-2007

Any Questions??

Any Questions??

Can you identify the different stages of mitosis from the diagram below?

metaphase

anaphase

prophase

interphase

telophase

ABNORMAL CELL DIVISION• Sometimes cells cannot stop

dividing and they go through uncontrolled cell division becoming cancerous cells or tumors.

• Uncontrolled cell division in white blood cells causes leukemia.

Skin cancer

DNA checkups returned

11/15 or less to raise to 12/15