All About Cell All About Cell DivisionDivision

• Mitosis Presentation• Observe Onion

Mitosis• Mitosis Paper Plate

Activity

MitosisMitosis

• Cells are constantly being replaced or making new cells

• Why do cell divide instead of just continuing to grow larger?

Cell Growth??Cell Growth??

• There are two main reasons why cells divide instead of growing larger.1. The larger a cell becomes, the more demands

the cell places on its DNA.

Cell Growth??Cell Growth??

2. The cell has more trouble moving enough nutrients and waste across the membrane

– The rate at which food, oxygen and water enter a cell through its cell membrane. Waste products leave in the same way. The rate of which this exchange takes place depends on the surface area of the cell.

– The rate at which food, oxygen and water are consumed and waste products are produced depends on the cell’s volume.

Ratio of Surface Area to VolumeRatio of Surface Area to Volume

• Ratio of surface area to volume = SA/V• Surface Area= 1cm x 1cm x 6= 6cm2

• Volume= 1cm x 1cm x 1cm = 1 cm3

• The Ratio of surface area to volume is this example would be 6:1

Ratio of Surface Area to VolumeRatio of Surface Area to Volume

• Look at chart on pg 243• Notice…the large the cell… (surface area and

volume)…• Note that the volume increases much more rapidly

than the surface area, causing the ratio of surface area to volume to decrease.

• This decrease creates serious problems for the cell • So in order to avoid this…the cell will divide!

MitosisMitosis

• As microscopes evolved, this enabled scientists to study the stages of reproduction of a cells’ life

Chromosomes:Chromosomes:• Carry genetic material

which is copied and passed from generation to generation

• Always present in cells but are usually too small to see with a microscope

• Reside within a well-defined nucleus

Chromosomes:Chromosomes:

• Chromosomes carry DNA.

• Most all chromosomes cannot be seen in the cell EXCEPT prior to division and throughout.

CHROMOSMESCHROMOSMES

• Chromosomes will appear as Chromatin most of a cells life.

• Long strands of protein and DNA.

The Cell Cycle:The Cell Cycle:

• Is the sequence of growth and division of a cell

• A cell goes through 3 stages/periods

• 1. Interphase: Growth period. (G1, S, and G2)

• 2. Mitosis: Division period

• 3. Cytokinesis- the actual dividing of the membrane.

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Interphase:Interphase:

• Most of a cell’s life is spent in Interphase• Here a cell grows and carries on daily activities• Divided into 3 phases• 1) G1 • 2) S• 3) G2

G1 Phase of Interphase:G1 Phase of Interphase:

• G1 phase: G stands for growth.

• The period prior to the replication of DNA.

• In this phase, the cell begins its preparation for division.

• The number of organelles and cytoplasm will increase.

S Phase of S Phase of InterphaseInterphase::• S phase: The period

during which DNA is replicated (or copied).

• In most cells, this is a narrow window of time. Note the S represents synthesis.

• Cell copies its chromosomes and DNA is doubled.

Replication:

•Remember if the Chromosomes are duplicated it is safe to say that the DNA is also replicated!!

•You have two identical copies of your Chromosomes/DNA inside your cell at this point.

•We will talk in more detail about DNA replication in the Ch 11

You don’t have to copy anything here…similar to your notes!

G2 Phase of Interphase:G2 Phase of Interphase:• G2 phase: • The period after DNA

replication has occurred but prior to the start of prophase.

• The cell synthesizes proteins and continues to increase in size.

• The cell is making any substance and organelles need for division.

Mitosis:Mitosis:

• Mitosis is the process by which a cell ensures each daughter cell will have a complete set of chromosomes.

• There are four key stages of mitosis: (PMAT)• Prophase, Metaphase, Anaphase, and Telophase

Prophase:Prophase:• DNA condenses into movable packages called chromosomes.

They become thicker and more visible.

• Remember…..Sister chromatins and the DNA they contain are exact copies of each other.

• Nucleolus and nuclear envelope disappear.

• Spindle fibers and centrioles begin to assemble.

Metaphase:Metaphase:

• Chromosomes will begin to aligning at the cell’s equator.

• The chromosomes are moved to the center of the cell by the spindle fibers attached to the centromeres.

• The spindle is highly visible.

Anaphase:Anaphase:

• The centromeres of each chromosome are pulled by the spindle fibers toward the ends of the cell

• The sister chromatids are thus separated from each other

• They are now in their most tightly condensed form

Telophase:Telophase:

• Final stage of Mitosis• New nuclear envelope

and nucleolus begin to appear

• Two complete sets of chromosomes

• The chromosomes begin to uncoil and become invisible

Review of Mitosis:Review of Mitosis:

Cytokinesis:Cytokinesis:

• The cytoplasma of the cell divides into 2 new cells called daughter cells

• Exact copies of each other

• Daughter cell nuclei are identical to the parent in every way

• All of your cells come from ONE fertilized egg

• Now there are two separate nuclei, but they are in the same cell. The cell needs to be split in half.

Cytokinesis Differences:Cytokinesis Differences:

• Plant Cell• Cell plate will begin

to form separating the 2 cells.

• Animal Cell• The cytoplasma will

pinch into 2 separate cells.

• A cleavage furrow begins to form.

Onion Root MitosisOnion Root Mitosis

• Interphase, Prophase, Metaphase, Anaphase, and Telophase

Regulating the Cell CycleRegulating the Cell Cycle

• It’s very amazing how our human body works. Not all cells in the body move through the cell cycle at the same time or speed.

• For example human muscle cells and nerve cell rarely divide at all once they have developed…this is in great contrast with skin, digestive tract, bone marrow cell which are continuously grow and divide throughout their life.

Regulating the Cell CycleRegulating the Cell Cycle

• Scientist have been studying and observing cell behavior for years.

• They soon discovered a family of closely related proteins that regulate the timing of the cell cycle in eukaryotic cells.

• They called these proteins cyclin.

• They have been divided into two types of regulatory proteins: those that occur inside the cell (Internal Regulators) and those that occur outside the cell. (External Regulators)

What if?What if?

• What if the cyclin or the regulators are not working properly?

• Uncontrolled cell growth?

• What is this called?

CANCERCANCER

•Cancer is abnormal cell growth. Called tumors. Usually uncontrollable

•Benign- Non-spreading

•Malignant- Spreading

ASEXUAL REPRODUCTIONASEXUAL REPRODUCTION

• This is reproduction in which one parent produces offspring by cell division.

• This is common in plants though their leaves, buds, steams or flowers

• Seen less common in animals.

BUDDINGBUDDING

• Seen in Animals• A new organism

will grow from a piece of another.

• Ex: jellyfish, corals and in some parasitic animals (tapeworms)

FRAGMENTATIONFRAGMENTATION

• As certain tiny worms grow to full size, they spontaneously break up into 8 or 9 pieces. Each of these fragments develops into a mature worm, and the process is repeated.

• Also seen in Animals

• Separated pieces of the parent organism develop into a new organism.

                                                 

     

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ParthenogenesisParthenogenesis

• Parthenogenesis• In parthenogenesis

("virgin birth"), the females produce eggs, but these develop into young without ever being fertilized.

• Parthenogenesis occurs in some fish, several kinds of insects, and a few species of frogs and lizards.

RegenerationRegeneration

•The growing back of a lost body part through mitosis.

COLORING ASSIGNMENTCOLORING ASSIGNMENT

• Draw, color, and label the following….Get 2 sheets of plain white/yellow paper

• First side of first sheet, pg 245….Pie Chart!! 2nd side of first sheet….Pg 244 Chromosome…draw and label the animated version. This needs to be large and take up most of the side of paper.

• 2nd piece of paper draw the animated version of Interphase-Cytokinesis. (I-PMAT-C) It must be in the correct order!!!! Page 246-247..