Chapter 5 Section 3Chapter 5 Section 3

Cell DivisionCell Division

““The Cell Cycle”The Cell Cycle”

The cell cycle is the regular sequence of The cell cycle is the regular sequence of growth and division that cells undergogrowth and division that cells undergo

One “parent” cell divides into two identical One “parent” cell divides into two identical “daughter” cells“daughter” cells

The length of the cell cycle depends on the The length of the cell cycle depends on the type of cell. Some cells such as the human type of cell. Some cells such as the human brain cells, never divide.brain cells, never divide.

The Cell Cycle-Stage 1: InterphaseThe Cell Cycle-Stage 1: Interphase

Interphase is the period before cell division Interphase is the period before cell division occursoccursThe cell grows to its mature size, makes a The cell grows to its mature size, makes a copy of its DNA, and prepares to divide copy of its DNA, and prepares to divide into two cells.into two cells.GrowthGrowth

*during the 1*during the 1stst part of interphase, the cell part of interphase, the cell doubles in size and produces all the doubles in size and produces all the structures needed to carry out its functionstructures needed to carry out its function

Stage 1: InterphaseStage 1: Interphase

Growth Growth

*the cell enlarges its endoplasmic *the cell enlarges its endoplasmic reticulum, makes new ribosomes, and reticulum, makes new ribosomes, and produces enzymes. Both mitochondria produces enzymes. Both mitochondria and chloroplasts make copies of and chloroplasts make copies of themselves. The cell matures and grows themselves. The cell matures and grows to its full size.to its full size.

Stage 1: InterphaseStage 1: InterphaseDNA Replication-The next part of interphaseDNA Replication-The next part of interphase

**replicationreplication-the cell makes a copy of its nucleus in -the cell makes a copy of its nucleus in this processthis process

* DNA is a nucleic acid found in the chromatin in a * DNA is a nucleic acid found in the chromatin in a cell’s nucleuscell’s nucleus

* DNA is the genetic material that holds all the * DNA is the genetic material that holds all the information that a cell needs to carry out its information that a cell needs to carry out its functionsfunctions

*Each daughter cell must have a complete set of *Each daughter cell must have a complete set of DNA to surviveDNA to survive

*At the end of DNA replication, the cell contains two *At the end of DNA replication, the cell contains two identical sets of DNA-one for each daughter cellidentical sets of DNA-one for each daughter cell

InterphaseInterphase

Stage 2: MitosisStage 2: Mitosis

Mitosis-the stage in which the cell’s Mitosis-the stage in which the cell’s nucleus divides into two new nuclei.nucleus divides into two new nuclei.

During mitosis, one copy of DNA is During mitosis, one copy of DNA is distributed into each of the two daughter distributed into each of the two daughter cells.cells.

Mitosis is divided into 4 parts or phases:Mitosis is divided into 4 parts or phases:

Prophase, Metaphase, Anaphase, and Prophase, Metaphase, Anaphase, and TelophaseTelophase

ProphaseProphaseDuring this stage the chromatin in During this stage the chromatin in the cell’s nucleus begins to the cell’s nucleus begins to condense and coil, like fishing line condense and coil, like fishing line wrapping around a ball.wrapping around a ball.

The condensed chromatin looks like The condensed chromatin looks like tiny rods which doubled during DNA tiny rods which doubled during DNA replicationreplication

Each double rod of condensed Each double rod of condensed chromatin is called a chromosome chromatin is called a chromosome

Each rod/strand of the chromosome Each rod/strand of the chromosome is called a chromatid.is called a chromatid.

The two strands are held together by The two strands are held together by a structure called a centromerea structure called a centromere

ProphaseProphase

MetaphaseMetaphase

Metaphase-the Metaphase-the chromosomes line up chromosomes line up across the center of across the center of the cell. Each the cell. Each chromosome attaches chromosome attaches to a spindle fiber at its to a spindle fiber at its centromere, which centromere, which still holds the still holds the chromatids together.chromatids together.

MetaphaseMetaphase

AnaphaseAnaphase

The centromere split The centromere split and the two and the two chromatids separate.chromatids separate.The chromatids move The chromatids move along the spindle fiber along the spindle fiber to opposite ends of to opposite ends of the cellthe cellThe cell becomes The cell becomes stretched out as the stretched out as the opposite ends pull opposite ends pull apart.apart.

AnaphaseAnaphase

TelophaseTelophase

The chromosomes The chromosomes begin to stretch out begin to stretch out and lose their rod-like and lose their rod-like appearance .appearance .Occurs at the two Occurs at the two regions at the ends of regions at the ends of the cell.the cell.A new nuclear A new nuclear membrane forms membrane forms around each region of around each region of chromosomeschromosomes

TelophaseTelophase

Stage 3: CytokinesisStage 3: CytokinesisDuring cytokinesis, the During cytokinesis, the cytoplasm divides, cytoplasm divides, distributing the distributing the organelles into each of organelles into each of the two new cells.the two new cells.

Cytokinesis usually Cytokinesis usually starts about the same starts about the same time as telophase.time as telophase.

CytokinesisCytokinesis

**Animal CellsAnimal Cells -the cell membrane squeezes -the cell membrane squeezes together around the middle of the cell. The together around the middle of the cell. The cytoplasm pinches into two cells with about half cytoplasm pinches into two cells with about half of the organelles in each daughter cell.of the organelles in each daughter cell.

**Plant Cells – Plant Cells – a plant cell’s rigid cell wall can’t a plant cell’s rigid cell wall can’t squeeze together, instead a structure called a squeeze together, instead a structure called a cell plate forms across the middle of the cell. cell plate forms across the middle of the cell. The cell plate gradually develops into new cell The cell plate gradually develops into new cell membranes between the 2 daughter cells, then membranes between the 2 daughter cells, then new cell walls then form around the cell new cell walls then form around the cell membranes.membranes.

CytokinesisCytokinesis

The Entire Cell CycleThe Entire Cell Cycle

DNA ReplicationDNA Replication

Ensures that each daughter cell will have Ensures that each daughter cell will have all of the genetic information it needs to all of the genetic information it needs to carry out its activities.carry out its activities.

James Watson and Francis Crick, figured James Watson and Francis Crick, figured out the structure of DNA. out the structure of DNA.

The Structure of DNAThe Structure of DNADNA molecules look like a twisted ladder, DNA molecules look like a twisted ladder, or spiral staircase. or spiral staircase.

Often called a “double helix”Often called a “double helix”

The two sides of the DNA ladder are made The two sides of the DNA ladder are made up of molecules of a sugar called up of molecules of a sugar called deoxyribose, alternating with molecules deoxyribose, alternating with molecules known as phosphates. known as phosphates.

The Structure of DNAThe Structure of DNAEach rung of the DNA ladder is made up of a Each rung of the DNA ladder is made up of a pair of molecules called nitrogen bases. pair of molecules called nitrogen bases.

Four kinds of nitrogen bases: Adenine (A), Four kinds of nitrogen bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C)Thymine (T), Guanine (G) and Cytosine (C)

Adenine Adenine onlyonly pairs with Thymine pairs with Thymine

Guanine Guanine onlyonly pairs with Cytosine pairs with Cytosine

The Structure of DNAThe Structure of DNA

The Replication ProcessThe Replication ProcessDNA replication begins DNA replication begins when the two sides of a when the two sides of a DNA molecule unwind DNA molecule unwind and separates or “unzips” and separates or “unzips” between the paired between the paired nitrogen bases on each nitrogen bases on each rung. New bases pair rung. New bases pair with the base on each with the base on each strand. As a result, two strand. As a result, two identical DNA molecules identical DNA molecules form.form.