Cell Growth and Division

Purpose of the cell cycle which includes the mitosis:

-To produce new and identical body cells with identical copies of DNA.

-Example: 1 skin cell will divide into 2 new and identical skin cells

-All human body cells contain :46 chromosomes or pieces of DNA

-23 from your mom-23 from your dad

Mitosis produces body cells known as 2N or diploid cells.

Known as 2N or diploid because they contain 2 of every chromosome in each cell.

-one of each from your mother

-one of each from your dad

When a sperm with 23 chromosomes (1N)fertilizes an egg with 23 chromosomes (1N) it produces the first body cell, called the 2N zygotewhich has a total of 46 chromosomes.

Fertilization: 1N sperm unites with 1N egg creating a 2N zygote.

11 N egg is fertilized by a 1N sperm creating a 2N zygote or body cell.

Twin Formation

Identical twins: -1 sperm and 1 egg unit forming one zygote. -Zygote goes through mitosis creating two identical cells. -The two identical cells split apart and both form into a fetus/baby. -Babies must be of the same sex.

Fraternal twins: -2 separate sperm fertilize 2 separate eggs forming two separate zygotes. -Each zygote goes through mitosis creating 2 separate babies. -The two babies may be the same sex or of opposite sex.

DNA-DNA is our

genetic code-we inherit our DNA from

our parents

-DNA has the code for making all of our proteins which determine our traits.

Examples of human traits

1. DNA is located in the nucleus of every cell in a relaxed, uncondensed form known as chromatin.

2. DNA supercoils into chromatids the loops of tightly coiled DNA of a chromosome.

Chromosome: -1 piece of DNA

Gene: -1 segment of DNA on a chromosome that codes for a protein.

Allele: -a specific form of a gene

Allele:A specific form of a geneEach trait has 2 possible forms

Dominant form or allele:The overpowering form of a geneRepresented by a capital letter

Recessive form or allele:The weaker form of a geneRepresented by a lower case letter

2 alleles combine to determine a trait.

1 allele/gene from the sperm

1 allele/gene from the sperm

Phenotype:A physical trait that you can see

Examples: Red hair, blue eyes, etc…

Genotype:The genetic make up /gene or allele combination

Three types of genotypes:BB…..

Homozygous dominantBb……

Heterozygousbb…….

Homozygous recessive

Law of Dominance

Anytime a dominant allele is present the dominant trait will be seen, it overpowers the recessive allele.

Example:

Black fur is dominant ………… BWhite fur is recessive………… b

B B

B

B

b

bb

b

b

b

BB

Bb

Purpose of the cell cycle which includes the mitosis:

Let us review:

To produce new and identical body cells with identical copies of DNA.

-Example: 1 skin cell will divide into 2 new and identical skin cells

One cell cycle is made up of:1. Interphase

Gap 1Synthesis phaseGap 2

2. Mitosis

ProphaseMetaphaseAnaphaseTelophase

3. Cytokinesis

DNA Replicates

Cell divides in half

Interphase• A. Occurs in three sub phases:

– Gap 1: Cell grows and matures from a daughter cell into a parent cell.

– S phase: DNA is replicates– Gap 2: New and needed organelles are formed

• B. DNA is in a loosely coiled, uncondensed from of chromatin.

• C. Two pairs of centrioles are present outside the nucleus.

Gap 0

Non dividing cells like nerve, brain and heart cells do not go through cell division.

Therefore, they remain in Interphase for their entire existence. This is referred to as Gap 0.

Interphase

Prophase• A. First phase of

mitosis.• B. Longest phase of

mitosis.• C. Sets the stage for

the rest of cell division.

Early prophase

• 1. Nucleus and nucleolus breakdown into their components of proteins, lipids and carbs.

• 2. Chromatin supercoils into chromatids.• 3. Centrioles pairs split apart and move to

opposite sides of the cell/the poles.• 4. Centrioles stretch spindle

fibers/microtubules across the cell.

Late prophase

Metaphase• A. Second phase of mitosis• B. Shortest phase of mitosis.

– 1. Replicated chromosomes move to the middle/equator of the cell.

- 2. Each chromosome attaches to its own spindle fiber using the centromere.

Metaphase

Anaphase• A. Third phase of mitosis• B. Replicated chromosomes split apart and

move away to opposite poles.

1.Sister chromatids split apart from each other.

2.One single, unreplicated copy of the chromosome is at each pole.

3.Spindle fibers break down.

ASTERS

Asters• End of spindle fibers at the pole• Push against cell membrane causing the cell to

elongate or get wider.

Anaphase

Telophase

• A. Final phase of mitosis• B. Exact opposite of prophase.

– 1. A nucleus reappears around each set of chromosomes at the poles

- 2. A nucleolus reappears in each nucleus.

- 3. Chromatid uncoils into chromatin.

Telophase

Cytokinesis

• A. One cell divides into two new identical daughter cells.

– Animal cells:• Cell membrane pinches together forming a cleavage

furrow.• Two ends eventually join separating the one cell into

two cells.

Plant cells: - The formation of a cell plate occurs. - The cell plate is a collection of sacks of cellulose that collect in the center of the cell. -The cell plate eventually matures into a cell wall.

Cytokinesis

End Result:One mature parent cell divides into two new and

genetically identical daughter cells.

Cell starts over…………………………hence the cell cycle.

MITOSIS

Cell division video