Cell Growth and Division Todays Objectives LO 4

Cell Growth and Division

Today’s Objectives LO 4. a. i- Describe the purpose of mitosis LO 4. a. ii- Describe the steps of mitosis

Activating Questions! Imagine you are a newly formed fetus in your mom’s belly: What would happen if your cells were not able to grow and divide? Imagine you fall down outside and scrape your knee What would happen if your cells were not able to grow and divide?

The Cell Cycle

Purpose of the Cell Cycle Many unicellular organisms reproduce this way (asexual reproduction) Multicellular organisms use mitotic cell division for numerous reasons Growth Development Repair **NOT FOR SEXUAL REPRODUCTION (that is meiosis)

The Cell Cycle: An overview Before divide: It a cell can must copy DNA and grow in size (Interphase) The nucleus must divide (Mitosis) The cytoplasm must divide and form two separate cells (Cytokinesis)

How does the DNA copy itself DNA replication DNA strands condense into chromosomes Chromosomes copied (duplicated) Sister chromatids remain connected by a centromere Eventually, they will be separated into the two daughter cells

Interphase First and longest stage of the cell cycle How much of the cell cycle is in interphase?

Interphase centriole Three steps: G 1: The cell grows. S: The cell replicates DNA. G 2: The cell continues to grow and replicates centrioles. DNA (chromatin) nuclear envelope nucleus

Mitosis During Mitosis, the nucleus will be divided into two through 4 phases: Prophase Metaphase Anaphase Telophase

Prophase (Preparation) 1) The DNA (chromatin) condenses into chromosomes. spindle 2) The centrioles separate, and a spindle begins to form. 3) The nuclear envelope breaks down. DNA (chromosomes)

Metaphase (Middle) 1) The chromosomes line up across the center of the cell. 2) Each chromosome is connected to a spindle fiber at its centromere. Spindle

Anaphase (Apart) 1) The sister chromatids separate into individual chromosomes and are moved apart.

Telophase (Two) 1) Chromosomes uncoil. 2) Two new nuclear envelopes form.

Telophase (Two) 1) Chromosomes uncoil. 2) Two new nuclear envelopes form. Mitosis is complete! What else needs to happen?

Cytokinesis (Cytoplasm) 1) The cytoplasm pinches in half. 2) Each daughter cell has an identical set of chromosomes.

Cytokinesis Cleavage furrow in animal cells Cell plate in plant cells

Cell Cycle in Action! See a Newt lung cell divide: http: //video. google. com/videoplay? docid=- 990474875075679903

Let’s Practice! A. You will be shown images of cells in various stages of the cell cycle. Identify each stage. You may discuss with a partner B. We will go over the answers.