Cell Growth and Reproduction

Cell Growth  All cells come in different sizes and shapes.  Diffusion in fast and effective over short distances.  It become slow and inefficient over long distances.  If a cell and a mitochondria 20cm in diameter – it would take months before it would receive molecules that entered the cell membrane.

Cell Growth  Surface area-to-volume ratio  Area: the surface included in a set of lines.  Volume: space occupied as measured in cubic inches.  Ratio: the relationship in quantity, amount, or size between two or more things.

Cell Growth  Due to the surface area-to-volume ratio cells divide before they become to large.  DNA is what directs the cell when it is becoming to large.

Cell Reproduction  Cell division in necessary to form multi-cellular organisms.  Asexual Reproduction:  Production of offspring from one parent cell.  Sexual Reproduction:  Formation of offspring from the union of two gamete cells.

Asexual Reproduction  Steps:  Chromosomes duplicate (called replication)  Both attach to a site located in the cell  They are forced apart.  Cell membrane constricts them till they separate.

Asexual Reproduction  Some examples include:  Strawberry Runners  Potatoes  Star Fish

Sexual Reproduction  Results from the joining of two highly specialized cells.  Sperm Cells  Ovum Cells or Egg Cell  Fertilization:  Sperm cell and ovum combine to form a Zygote.

Chromosomes  Chromatids:  Long strands of DNA.  Chromosomes:  Made of two sister chromatids.  Held together by a centromere

Diploid (2n) Cells  A cell with two of each kind of chromosomes are called Diploid Cells.

Haploid (n) Cells  A cell with one kind of each chromosome is called a Haploid cell.

Mitosis  Cells undergo mitosis as they reach their maximum cell size.  There are four steps in mitosis:  Prophase  Metaphase  Anaphase  Telophase Turn and talk

Mitosis:   Stage 1 - Prophase   Chromatids coil up into visible chromosomes.   Nucleus Disappears   Centrioles migrate to the polar ends of the cell   Spindle Fibers begin to form.

Mitosis:  Stage 2 – Metaphase   Chromosomes become attached to the spindle fibers by their centromeres.   They are lined up across the center of the cell.

Mitosis:  Stage 3 – Anaphase   Sister chromatids begin to separate   Chromatids are pulled apart, and separate from each other.

Mitosis:  Stage 4 – Telophase   New cells prepare for their new existence.   Chromosomes uncoil and direct metabolic activity   Spindle Fibers break down   Nucleolus reappears   Double membrane forms between them

Mitosis  Animal Cytokinesis: Plasma Membrane pinches in along the equator of the cell. Plant Cytokinesis: Plants - Cell Plate is laid across the equator. Cell walls form around the plate

Results of Mitosis  As a result,  Each daughter cell receives and exact copy of the chromosomes present in the parent cell.  They copy their chromosomes during Interphase.  They become a diploid cell 2n  The process can then start over.

Results of Mitosis  Process that guarantees that genetic continuity.  The two new cells formed will carry out the same functions of the parent cell.  They will grow and divide just like the parent cells.

Results of Mitosis  As a result of cell division we have groups of cells working together, until they create and organism, i.e.  Cells  Tissues  Organs  Organs Systems  Organisms

The Cell Cycle  Cell Cycle:  The sequence of growth and division in the cell.  A cell goes though two periods:  A period of growth  A period of division

The Cell Cycle Mitosis 1 hour Rapid Growth and Metabolic Activity 9 hours DNA Synthesis and Replication 10 Hours INTERPHASE Prepare for cell division 2 hours

Interphase  The busiest part of the cell cycle  Part I: Cell grows and protein production is high.  Part II: Cell copies its chromosomes  Part III: Parts manufactured for cell division.

The Cell Cycle  The cell cycle is controlled by;  Proteins  Enzymes  Area – to – Volume Ratio  Occasionally, cells lose control.  Cancer, malignant growth resulting from uncontrolled cell division.

Cancer – A mistake in the cell cycle!  Tumors  Masses of tissue that deprive normal cells of nutrients.  Cancer is the second leading cause of death in the United States, exceeded only by heart disease.

Meiosis  Meiosis forms haploid daughter cells from diploid parent cells.  Meiosis is divided into two parts;  Meiosis I  Meiosis II

Meiosis I  Synapsis  Homologous Chromosomes line up next to each other.  Forming a structure called a tetrad.

Meiosis I Turn and Talk

Meiosis I  Prophase I  Homologous Chromosomes are formed  Spindle fibers form  Tetrads are visible and have lined up along the equator.

Meiosis I  Metaphase I  Each tetrad becomes attached to the spindle fibers

Meiosis I  Anaphase I  Homologous chromosomes are pulled apart.  One pair goes to the on polar end while the other goes to the other end.

Meiosis I  Telophase I  Cytokinesis takes place.  The cell divides.

Meiosis I  At the end of Meiosis I;  One chromosome from each parent cell is present in the daughter cell.  Meiosis I is a reductive division;  Reduce the chromosomes from diploid (2n) to a haploid (n).

Meiosis II  Each daughter cell produced in Meiosis I undergoes another division.  Meiosis II is very similar to Mitosis except, it is not proceeded by a replication of the chromosomes.

Meiosis II Turn and talk

Meiosis II  There are four stages;  Prophase II  Metaphase II  Anaphase II  Telophase II

Meiosis II  Resulting in;  Four daughter cells  Each daughter cell produced is haploid.  Each cell has four chromosomes.  One from each of the homologous pairs of parent cells.

Meiosis II  Prophase II  New spindle fibers formaround the chromosomes.

Meiosis II  Metaphase II  Chromosomes line up along the equator.  Attach the centromere to the spindle fibers

Meiosis II  Anaphase II  The centromere divides and the chromatids separate.  Each chromatids becomes it on chromosomes with their own centromere.

Meiosis II  Telophase II  The nuclear envelope forms around each set of chromosomes.  Cell undergoes Cytokinesis.

Meiosis – Why?  The result;  Cells used for reproduction  Sperm Cells  Ovum Cells