Cell Cycle Cells are the basic unit of

Cell Cycle

Cells are the basic unit of life. Just like you and me, as they get older they grow bigger. This triggers the cell to divide. First, let’s talk about the stages of the cell cycle…

G 1 Phase Or the Growth 1 Phase is the first event in the life cycle of a cell.

G 1 Phase During this phase: • the cell is metabolically active with chemical reactions mostly in the cytoplasm • Cellular respiration (makes ATP) • Produces protein • At the end organelles are duplicated

S Phase Or the Synthesis phase. Synthesis=to put parts together to equal a whole. During this phase: • DNA is replicated in the nucleus

G 2 Phase Or Growth 2 Phase is a second period of growth after the DNA has been replicated. (SO the cell has TWICE the amount of genetic material it needs) During this phase: • Cell resumes making proteins and other molecules

Interphase =G 1, S, G 2 Cells spend most of their life in interphase During Interphase: • The cell appears normal • Nucleus is visible • DNA is loosely organized (bowl of spaghetti) – This is called Chromatin

M phase Or Mitosis Phase During Mitosis: • The nucleus divides in a series of steps to form two nuclei • The nuclei, duplicated organelles and cytoplasm are separated in cytokinesis.

Stages of Mitosis 1. 2. 3. 4. Prophase Metaphase Anaphase Telophase

Prophase The FIRST step in Mitosis. During Prophase: • DNA condenses to form chromosomes – To make a chromosome the DNA is wrapped around proteins called histones • Chromosome looks like a X

Prophase Chromosomes: • Each half of the “X” is called a chromatid. • These chromatids are held together in the center of the “X” in a region called the centromere.

Prophase • Microfiliments in the cytoskeleton begin to break down • In animals, Centrioles move to the opposite sides of the cell and form spindle fibers toward the center of the cell • In plants, spindle fibers form at the opposite ends of the cell in regions called asters

Prophase By the end of prophase, the nuclear membrane has been broken down and the nucleolus disappears. This is the longest phase of Mitosis

Metaphase The second phase of mitosis During Metaphase: • Spindle fibers attach to the centromeres on each chromosome • Chromosomes are lined up down the middle of cell.

Anaphase The third phase of mitosis During Anaphase: • The chromatids are pulled apart at the centromere by spindle fibers • Spindle fibers pull the chromatids to opposite sides of the cell

Telophase The last phase in mitosis During Telophase: • Chromatids arrive at the opposite poles of the cell • The nuclear membrane forms around each new set of chromosomes • DNA uncoils and the nucleoli reappear

Telophase • Once the nuclear membrane completely forms, the new nuclei appear • Each nuclei contains a complete set of chromosomes identical to the parent cell • Microfiliments reform the cytoskelton and move the duplicated organelles to opposite sides

Just Remember… Prophase. Metaphase. Anaphase. Telophase

Cytokinesis The division of the cytoplasm • In animals, the cytoplasm pinches in from the top form the cleavage furrow • The cleavage furrow continues to constrict towards the center until pinching off the two cells.

Cytokinesis • In plants, a cell plate forms in the middle of the cell which turns into the new cell wall.

Controlled Cell Growth • Cell growth and division is controlled by internal and external factors • These can tell a cell to divide or to continue to grow • Example: Human growth hormone which tells bone cells to grow and divide

Uncontrolled Cell Growth • If uncontrolled by internal or external factors cells will divide continuously. • Example: Cancer – Causes cells to form masses called tumors – Malignancy is when a cancer cell breaks away and forms a new mass

Uncontrolled Cell Growth • Cancer cells use up nutrients and oxygen and do not provide any function for the organism • The tumor can add stress to surrounding cells

Causes of Cancer • A carcinogen is something that causes cancer. – Causes a mutation in the genetic material (DNA) which can prevent the cell from responding to external and internal signals. • Examples: smoking, exposure to excessive radiation from the Sun, pollution, and some viruses.