Cell Cycles

Biology: Chapter 11 & 12(Pictures from: taggart.glg.msu.edu/bs110/meiosis.htm)

Cell Cycle

A cell cycle is the sequence of a cell’s growth

and division.

There are two periods in the cell cycle of your

somatic cells (body cells): Period of Growth is called Interphase.

Cell grows in size

Before division, DNA duplicates

Period of Division is called Mitosis.

Nucleus and cytoplasm divide into two daughter cells.

What do cells do?

Most of the time, a cell is in Interphase.

Interphase A cell in interphase:

Produces proteins

Functions normally

Grows

Interphase is the longest

phase of the cell cycle.

At the end of interphase,

the cell prepares for

division by:

Copying DNA and

organelles

How does DNA replicate (copy)?

At the end of INTERPHASE, a cell prepares for division. During this phase the DNA is uncoiled and spread out in the nucleus. To prepare for cell division, or MITOSIS, the DNA makes a copy of itself.

The DNA molecule “unzips”. An enzyme breaks the hydrogen bonds between the

nitrogen base pairs.

Free DNA nucleotides, that are in the nucleus, pair up with the nitrogen base it is attracted to. Another enzyme bonds the new nucleotides into a

chain.

DNA Replication Animations http://www.lewport.wnyric.org/jwanamaker/animation

s/DNA%20Replication%20-%20long%20.html

http://www.johnkyrk.com/DNAreplication.html

http://www.ncc.gmu.edu/dna/repanim.htm

http://biotech-adventure.okstate.edu/low/basics/dna_replication/replication4/animation/

http://www.bioteach.ubc.ca/TeachingResources/MolecularBiology/DNAReplication.swf

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

Fill in the nitrogen bases.

REPLICATION continues until the entire DNA

molecule is copied.

What do you notice about the new strands of DNA?

The two new strands are INDENTICAL to the

original DNA molecule!

After DNA has replicated, the cell is ready to divide.

When Do Cells Divide?

Cells divide for reproduction, growth and repair.

Cell division occurs when tissues are damaged, cells

die, or when change or growth is occurring.

Mitosis

The process of cell division.

The steps of Mitosis:

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

The Results of Mitosis

Two IDENTICAL daughter cells with:

identical chromosome sets as the parent cell.

the same functions as the parent cell.

The daughter cells will grow and function

normally in INTERPHASE until they get large

enough to divide again.

Prophase

Cell prepares the nucleus for division:

DNA (or chromatin) coils into chromosomes Because the DNA has replicated,

the genetic information is doubled.

A chromosome is 2 sister chromatids.

Nuclear membrane disappears

Centrioles migrate to opposite ends of cell. (animal cells only)

Spindle fibers form between centrioles.

Metaphase

Cell prepares for

division of the

chromosomes:

Chromosomes line up in

the middle of the cell.

Spindle fibers attach to the

centromere of each

chromosome.

Anaphase

Sister chromatids

separate:

Spindle fibers pull sister

chromatids apart at the

centromere.

Sister chromatids move to

opposite ends of the cell.

Telophase Cytoplasm divides

(cytokinesis):

Each pole has identical

genetic information.

Chromatids begin to unwind

and spindle fibers break

down.

Nucleolus reappears.

Nuclear membrane reforms

around DNA (chromatin).

Two daughter cells begin to

separate.

Telophase cont.

In Animal Cells Plasma membrane pinches in the

middle to separate the cells.

In Plant Cells A cell plate forms across the middle of

the two cells.

This dividing is called cytokinesis.

Mitosis is a continual process.

How fast do cells divide?

The rate of cell division depends on

the type of cell.

Nerve cells do not divide at all once they

mature.

Cells that line the intestine will complete a cell

cycle in 24 to 48 hours.

What if cells get out of control?

A mistake in 1 or more

genes can disrupt the

production of enzymes

(proteins) that regulate cell

reproduction.

Cells that reproduce too

much create masses of

tissue, or tumors, which

could result in cancer.

Remember, mitosis is only a small part of

the cell cycle. Try to identify each of the phases of the cell cycle in

these animations: http://www.cellsalive.com/mitosis.htm

http://www.lewport.wnyric.org/jwanamaker/animations/mitosis.html

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/mitosis_movie.html

http://www.johnkyrk.com/mitosis.html

http://www.csuchico.edu/~jbell/Biol207/animations/mitosis.html

http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf

Mitosis Review Movie

http://highered.mcgraw-

hill.com/sites/0073031216/student_view0/exe

rcise13/mitosis_movie.html

Gamete Cell Cycle

How is the cell cycle different for

GAMETES?

Gametes are sex cells Male- sperm

Female- egg

Gametes are produced for sexual reproduction

Gametes are haploidhalf the number of chromosomes as found in body cells (somatic cells)

Fertilization: When two haploid cells combine, a diploid zygote is

formed.

The zygote gets half of its chromosomes from each of the parents.

Interphase

Gametes in interphase

are the same as body

cells in interphase:

Cell grows

Cell functions normally

When the cell is large

enough to divide:

DNA is copied.

Genetic material still

appears as chromatin.

What is meiosis?

Division part of the gamete cell cycle

Produces haploid cells

(contain half the number of normal chromosomes)

Cells go through phases similar to mitosis

Prophase I Nuclear membrane

disappears.

Centrioles move to opposite

sides of cell.

Spindle fibers form.

Homologous pairs of sister

chromatids join to create a

tetrad.

homologous: pairs of sister

chromatids containing

information for the same traits

Crossing over can occur.

Tetrad of

chromosome #1

#2

Metaphase I

Tetrads line up in the

middle of the cell.Spindle fibers

Tetrads

Anaphase I

Also called disjunction.

Homologous pairs of sister

chromatids are pulled apart

(tetrads separate) as spindle

fibers are pulled back.

Centromeres do not tear

apart, so sister chromosomes

stay attached.

Non-disjunction can occur.

Telophase I

Cell splits in two (cytokinesis)

Each cell contains pairs of

sister chromatids.

Cell

pinches

Prophase II

Centrioles split, move

to opposite sides of the

cell; form spindle fibers.

Sister chromatids

attach to spindle fibers.

Metaphase II

Sister chromatids line

up in the middle of the

cell.

Anaphase II

Spindle fibers tear the

centromere.

Sister chromatids are

pulled apart to opposite

sides of the cell.

Telophase II

Cytokinesis occurs.

Nuclear membrane reforms.

A total of four haploid gametes cells are produced. Haploid = Half of the

chromosomes as the parent.

Males: 4 sperm

Females: 1 egg

3 polar bodies

http://www.sumanasinc.com/webcontent/anis

amples/majorsbiology/meiosis.html

http://www.lewport.wnyric.org/jwanamaker/an

imations/meiosis.html

http://www.johnkyrk.com/meiosis.html

What are differences between mitosis and

meiosis?

Mitosis

One cellular division

2 cells produced

diploid cells produced

Contains the same

number of chromosomes

as the parent.

somatic cells (body

cells) produced

Meiosis

Two cellular divisions

4 cells produced

haploid cells produced

Contains half the number

of chromosomes as the

parent.

gametes (sex cells)

produced

Mitosis Vs. Meiosis

http://www.pbs.org/wgbh/nova/baby/divi_flas

h.html

http://biology.clc.uc.edu/courses/bio104/meio

mito.htm

http://www.pbs.org/wgbh/nova/miracle/divide.

html#

Meiosis Movie

http://highered.mcgraw-

hill.com/sites/0073031216/student_view0/exe

rcise14/meiosis_movie.html