The Cell Cycle & Mitosis Let’s Watch!

Learning goals We are learning the components of the cell cycle. We are learning the process of mitosis.

Layers of skin lose 30000-40000 skin cells every minute why doesn’t our skin simply wear away? Layers of skin

Cell cycle repeating cycle of events in the life of a cell main goal is cell division, but most time spent preparing for cell division four phases: first growth phase (G1) synthesis phase (S) second growth phase (G2) mitosis (M)

chromosomes every cell contains chromosomes each chromosome is a long piece of coiled DNA and proteins number of chromosomes in each cell differs between organisms typical human cell has 46 chromosomes – 23 matching pairs of chromosomes

chromosomes visible only when the cell is dividing when cell not dividing, DNA and proteins that make up chromosomes are spread throughout cell in form of chromatin at beginning of cell division, chromosomes condense into visible structures before cell division, each chromosome is copied the chromosome consists of two identical copies, called sister chromatids when the cell divides, one chromatid goes to each of the new cells

interphase often called resting phase 90 percent of cell cycle cell takes in nutrients, grows, copies DNA and conducts other normal cell functions

Chromatin Centrioles: “Barrel” shaped organelles used in division.

interphase First Growth Phase (G1) a period of growth for the cell new organelles produced if healthy and conditions are favourable, cell moves to next phase. Synthesis Phase (S) cell makes an entire copy of its DNA Second Growth Phase (G2) cell produces the organelles and structures needed for cell division shortest phase

Mitosis (M) all cell’s energy devoted to division creates two identical cells 4 phases: prophase, metaphase, anaphase, telophase (PMAT)

prophase the chromatin, which consists of the cell’s DNA and proteins, condenses at this point, there are two copies of each chromosome (sister chromatids), held together at the centromere chromosomes become connected to the mitotic spindle fibres at the centromere nuclear membrane dissolves

Nuclear Membrane Centromere Spindle Fibres Sister Chromatids

metaphase Chromosome pairs line up in middle of cell spindle fibres from centriole attach to centromeres of each chromosome all must be in line for mitosis to continue

Attached spindle fibres Sister chromatids lined up

anaphase sister chromatids separate at the centromere each chromatid is now a complete chromosome separated chromosomes are pulled to opposite ends of the cell

Daughter chromosomes

telophase final stage of mitosis daughter chromosomes stretch out, become thinner, and are no longer visible turn back into chromatin new nuclear membrane forms around each area of chromatin cell appears to have two nuclei

Daughter chromosomes stretching out

cytokinesis final stage of cell division cytoplasm divides producing two genetically identical daughter cells different for each type of cell: Animal cell: Cytoplasm pinches in half. Plant cell: Plate between two cells turn into a cell wall. each new cell enters G1 phase and cell cycle is repeated

Chromatin Two daughter cells

Learning goals We are learning the components of the cell cycle. We are learning the process of mitosis.

Group questions 1. What is the purpose of the cell cycle? 2. Define the term “interphase” and describe its purpose. 3. (a) What is mitosis? (b) Why is mitosis important to the cell? 4. Define and distinguish between the following terms: chromosome, centromere, and sister chromatids. 5. Explain the meaning and importance of the term “cytokinesis.”

Homework P.44 #1-7