Wednesday 11/4/15

Learning Goal: Identify the events take place during the three stages of the cell cycle.

Warm-up:When an organism grows, what is happening to their cells?

Homework: Finish pages 28-30 if you didn’t finish in class

CHAPTER 3 SECTION 5

Cell Division

Cell Cycle

The regular sequence of growth and division that cells undergo Cell grows Prepares for division Divides into two new cells, “daughter cells”

Three main stages: Interphase Mitosis cytokinesis

Stage 1: Interphase

Period before cell division The cell grows to full size Replicates

Makes an EXACT copy of its DNA in its nucleus Each daughter cell must have a complete set of DNA to

survive End of replication, cell contains two identical sets of DNA

Prepares to divide

Stage 2: Mitosis

Mitosis The second stage of the cell cycle Cell’s nucleus divides into two new nuclei One copy of the DNA is distributed into each of the

two daughter cells4 Parts of Mitosis

Prophase Metaphase Anaphase Telophase

4 Parts of Mitosis

Prophase Threadlike chromatin in the nucleus condenses to

form double-rod structure called chromosomes Each chromosome has two rods, due to replication Each identical rod in a chromosome is called a

chromatid Two chromatids are held together by a centromere

4 Parts of Mitosis

Metaphase The chromosomes line up at the center of the cell Each chromosome attaches to a spindle fiber at its

centromere

4 Parts of Mitosis

Anaphase The centromeres split The chromatids separate by spindle fibers (go to

opposite ends of the cell)

4 Parts of Mitosis

Telophase Chromosomes begin to stretch out, lose rodlike

appearance Nuclear envelope forms around each region of

chromosomes

Stage 3: Cytokinesis

Cytokinesis Final stage of the cell cycle The cytoplasm divides Organelles are distributed into each of the two new cells

The cell will then enter interphase… and the cycle begins again.

Cytokinesis in Animal Cells: cell membrane squeezes together

Cytokinesis in Plant Cells: cell wall cannot squeeze together, a cell plate forms that gradually will develop into the cell membrane

The Structure of DNA

Looks like a twisted ladder, or spiral staircase

The sides of the ladder are made up of Deoxyribose (sugar) Phosphate

Each rung of the ladder is made up of a pair of molecules called nitrogen bases Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

The Replication Process

The two sides of the DNA molecule unzip and separate

Nitrogen bases floating in nucleus pair up with the bases on each half of the DNA molecule

New bases attach, two new DNA molecules form