Friday, October 28,2011

Brainteaser

You enter a dark room. You have only one match. There is an oil lamp, a furnace, and a stove in the room. Which would you light first?

Cell Growth and Reproduction

MitosisNuclear Division

Mitosis produces identical offspring (2N---2N)

Cell Growth and Reproduction

• So how does cell division take place?

• Scientists recognized that just before cell division, stringy structures appeared in nucleus.– These structures are

duplicated strands of chromatin that have been coiled into chromosomes.

Cell cycle = Growth & Reproduction

• Before cell division, the DAN is in its stringy active CHROMATIN state.

As cell division begins, chromatins condense

into a tightly packed DUPLICATED CHROMOSOME .• Genes are found on chromosomes Genes are made of segments of DNA DNA is made up of nucleotides of

Deoxyribose sugars, a phosphates and specific N-base pairs. A - T G - C

The Cell Cycle -the cell’s life cycle- I - M – CInterphaseMitosisCytokinesis

Cell Cycle - Interphase• INTERPHASE:• DNA has replicated (s-phase), but

has not formed the condensed structure of chromosome. They remain as loosely coiled chromatin.

• The nuclear membrane is still intact to protect the DNA molecules from undergoing mutation.

Cell Cycle and Mitosis

• MITOSIS:– As cell gets to the maximum size, it

begins to undergo MITOSIS (cell division)

– FOUR PHASES:• Prophase• Metaphase• Anaphase• Telophase

Cell Cycle and Mitosis - Prophase

• PROPHASE – 1st Stage of Mitosis• Long stringy chromatin coils up

into visible chromosomes

Spindle fibers

Disappearing nuclear envelope

Doubled Chromosome

Cell Cycle & Mitosis - Prophase

• PROPHASE – 1st stage of Mitosis– Towards end of Prophase, nucleus

begins to disappear as nuclear envelope and nucleolus disintegrate.

– The nuclear membrane and nucleolus are no longer visible.

– Centrioles begin to migrate to opposite ends of cells.

Cell Cycle & Mitosis - Prophase• PROPHASE: Let’s break it down

– Chromosomes coil up.– Sister Chromatids form.– Nucleolus and Nuclear Envelope

disintegrates.– Centrioles migrate to opposite ends.– Spindles form between Centrioles.

Cell Cycle & Mitosis - Metaphase

• METAPHASE – Line Up!

• The spindle fibers attach themselves to the centromeres of the chromosomes. One spindle extends to one pole while another spindle extends to the opposite pole.

• The chromosomes align at the equator or middle.

Cell Cycle & Mitosis - Metaphase

• METAPHASE– What is the importance?

• This arrangement of the chromatids ensures that each new cell receives identical and complete set of chromosomes (DNA).

Cell Cycle & Mitosis - Anaphase

• ANAPHASE – Go to your room!– Centromeres split and sister chromatids

separate.– Spindle fibers contract and pull the

chromatids to opposite poles.

Cell Cycle & Mitosis - Telophase

• TELOPHASE – “Call me girl”– Chromatids reach opposite poles.– Nucleolus and nuclear envelope reappears

around new set of chromosomes.– Spindle fibers breaks down.– Chromosomesbegin to unwind and return toChromatin(active DNA).

Cell Cycle & Mitosis - Telophase

• TELOPHASE = Reverse Prophase– Nuclear membrane & nucleolus reappear.– Chromosomes unwind back into Chromatids.– Spindle fibers disintegrate and disappear.

Cell Cycle and Cytokinesis• Cytokinesis: Division of the cytoplasm.

– Some time during Telophase, cell’s cytoplasm begins to divide.

– Animal Cells: During Telophase,the plasma membrane pinchestogether/off to form two separate cells.

Plant Cells: A cell Plate is laid across cell’s equator—thereis no pinching off. Cell membrane forms around each cell and new cell walls form on each side of cell plate.

Cell Cycle and Cytokinesis

• Cytokinesis:

Mitosis• What are the results of Mitosis?

– 2 genetically identical daughter cells with the complete number of chromosomes (2n).

– Unicellular organism remains a single cell but has replicated itself.

– Multicellular organisms have grown or created another cell that will work together as a tissue to perform a certain function.

Cell Cycle and Mitosis• Recall BIOLOGICAL ORGANIZATION:

ChemicalsOrganelles

CellsTissuesOrgans

Organ SystemOrganism

Cell Cycle and Mitosis

• Section Quiz:1. The stringy structures in the cell nucleus

that contain DNA are __________.

a. Centromeresb. Chromatinc. Genesd. Chlorophylls