The Cell Cycle Mitosis and Interphase

Cells Make Cells…..Why? Grow Grow Repair Repair Regenerate or Replace Regenerate or Replace So wouldn’t it be easier to just be ONE cell?

Hhmm…let’s check out the surface area to volume ratio…. As the cell increases in size, could it move substances in and out of the cell fast enough? As the cell increases in size, could it move substances in and out of the cell fast enough?

Therefore, cells are… SMALL!! SMALL!! SMALL!! HAVE UNIQUE SHAPES TO INCREASE SURFACE AREA HAVE UNIQUE SHAPES TO INCREASE SURFACE AREA

Prokaryotic Cell Division Bacterial cells reproduce by Binary Fission Bacterial cells reproduce by Binary Fission Much simpler process than in eukaryotic organisms (why?) Much simpler process than in eukaryotic organisms (why?)

Begins with DNA replication (why?); each copy moves to opposite sides of cell Begins with DNA replication (why?); each copy moves to opposite sides of cell Followed by elongation of cell, and formation of a septum (separation) between the two halves, forming two new cells Followed by elongation of cell, and formation of a septum (separation) between the two halves, forming two new cells Prokaryotic Cell Division

Results in two cells that are identical (clones) of original cells Results in two cells that are identical (clones) of original cells

Eukaryotic Cell Division Two forms Mitosis Mitosis grow, replace dead or worn out cells, or to repair wounds grow, replace dead or worn out cells, or to repair wounds Asexual reproduction in fungi, protists, some plants/animals Asexual reproduction in fungi, protists, some plants/animals Meiosis Meiosis Sexual reproduction Sexual reproduction

DNA and Cell Division During cell division, the genetic material DNA, needs to be copied and divided between the two new cells During cell division, the genetic material DNA, needs to be copied and divided between the two new cells DNA in cells is divided into long chains called chromosomes DNA in cells is divided into long chains called chromosomes

All living things.... begin life as a single fertilized cell. Humans begin as a fertilized OVUM or human egg cell.

The egg cell … ….then begins to divide into exact duplicate “stem cells”. ….then begins to divide into exact duplicate “stem cells”. these first cells will be the basis for all future cells in the human body. these first cells will be the basis for all future cells in the human body. ---->note the ovum has divided into 8 stem cells ---->note the ovum has divided into 8 stem cells

How does this work? Let’s go back to the little batch of 8… Let’s go back to the little batch of 8… We will now look at cells when they are dividing…and when they aren’t! We will now look at cells when they are dividing…and when they aren’t!

This little batch of cells… …will not stay the same. Cells specialize and take on different jobs. …will not stay the same. Cells specialize and take on different jobs.

Interphase The time between cell division The time between cell division Cell is doing its job Cell is doing its job DNA duplicates- chromosomes make exact copies of themselves DNA duplicates- chromosomes make exact copies of themselves Genetic material is all strung out as chromatin Nuclear membrane clearly in place

G0 The Cell Cycle

The Cell Cycle: Interphase When a cell is not dividing it is said to be in Interphase: G1: Gap, cells are recovering from an earlier cell division G1: Gap, cells are recovering from an earlier cell division S: Synthesis, DNA replication occurs S: Synthesis, DNA replication occurs

The Cell Cycle: Interphase G2 Gap, cells are making sure all the DNA was replicated correctly; a little more growth; the chromosomes start to become tightly coiled; Centrioles replicate and one centriole moves to each pole. *Animal Cells* Gap, cells are making sure all the DNA was replicated correctly; a little more growth; the chromosomes start to become tightly coiled; Centrioles replicate and one centriole moves to each pole. *Animal Cells*

REVIEW: In a non-dividing cell, the DNA is called CHROMATIN. In a non-dividing cell, the DNA is called CHROMATIN. During the S phase of the cell cycle, the DNA replicates to form sister CHROMATIDS. During the S phase of the cell cycle, the DNA replicates to form sister CHROMATIDS. In a dividing cell, the DNA is called CHROMOSOMES. In a dividing cell, the DNA is called CHROMOSOMES.

Cell cycle Two main parts: Two main parts:  Interphase  Cell division

Eukaryotic Chromosome Structure Normally, chromosomes are spread out in a form called chromatin Normally, chromosomes are spread out in a form called chromatin During mitosis, chromosomes fold up and condense During mitosis, chromosomes fold up and condense

Chromosome structure The replicated chromosomes stay together and are called sister chromatids The replicated chromosomes stay together and are called sister chromatids Sister chromatids are attached at the centromere Sister chromatids are attached at the centromere

The Cell Cycle: Cell Division Mitosis (M Phase) Mitosis (M Phase) Nuclear Division Nuclear Division Cytokinesis (C phase) Cytokinesis (C phase) Cytoplasmic Division Cytoplasmic Division

The Cell Cycle The length of time the cell cycle takes depends on the type of cell. Usually the more specialized the cell the less likely it is to divide. The length of time the cell cycle takes depends on the type of cell. Usually the more specialized the cell the less likely it is to divide. Red blood cells are replaced at a rate of 2-3 million/sec Red blood cells are replaced at a rate of 2-3 million/sec Nerve cells usually never divide, they enter G0 Nerve cells usually never divide, they enter G0

Mitosis Cell divides to form two new cells Cell divides to form two new cells Can look at four different stages Can look at four different stages Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase

Prophase DNA condenses to form distinct chromosomes DNA condenses to form distinct chromosomes Nuclear membrane disappears Nuclear membrane disappears

Metaphase Chromosomes line up in the middle (equator) of the cell Chromosomes line up in the middle (equator) of the cell Spindle fibers attach Spindle fibers attach

Anaphase Chromosomes separate and move toward the opposite ends of the cell (poles) Chromosomes separate and move toward the opposite ends of the cell (poles)

Telophase Chromosomes reach the poles Chromosomes reach the poles New nuclear membrane forms New nuclear membrane forms Chromosomes unwind to become thread-like chromatin again Chromosomes unwind to become thread-like chromatin again

Cytokinesis (End of Telophase) The cytoplasm is evenly divided The cytoplasm is evenly divided New cell membrane forms in animal cells New cell membrane forms in animal cells New cell wall is built across for plant cells New cell wall is built across for plant cells

OK, fine…but who really cares about MITOSIS and dividing cells???

Nerve cells… … remain in INTERPHASE for long periods of time. … remain in INTERPHASE for long periods of time. They go through mitosis about once every 75 years. They go through mitosis about once every 75 years. So?… So?…

Damage to these cells… …is often very serious. …is often very serious.

Some damage is not permanent Gloria Estefan was involved in a tragic tour bus accident. Gloria Estefan was involved in a tragic tour bus accident. Surgeons were able to repair her nearly severed spinal chord. Surgeons were able to repair her nearly severed spinal chord. She recently donated $1,000,000 for spinal cord injury research---> She recently donated $1,000,000 for spinal cord injury research--->

Cancer cells… … behave much differently than nerve cells. … behave much differently than nerve cells. …spend very little time in interphase and go through mitosis uncontrollably. …spend very little time in interphase and go through mitosis uncontrollably. Approx. 1/10,000 of your cells are cancerous-the good news-your defense cells usually kill them fast. Approx. 1/10,000 of your cells are cancerous-the good news-your defense cells usually kill them fast.