DO NOW

1. Objective: 1) Explain the problems that growth cells causes for cells. 2)Describe how cell division solves the problems of cell growth. KEY TERMS Cell Division DO NOW How do organisms grow?

2. Limits to Cell Growth • The larger a cell becomes, the more demands the cell places on its DNA. • Also, the cell has more trouble moving enough nutrients and wastes across the cell membrane.

3. Limits to Cell Growth • DNA “Overload” • Usually DNA does not make extra copies so as the cell gets bigger, the DNA is not enough to have enough information to meet the cell’s needs. • Exchanging Materials • The rate at which waste moves out and nutrients move in is dependent on the surface area of the cell membrane. • It is important to understand the relationship between the cell’s volume and surface area.

4. Ratio of Surface Area to Volume • Surface area= length x width x number of sides (imagine the cell is a cube) • Volume = length x width x height • Ratio of surface area: volume • Volume increases faster than surface area, causes the ratio of surface area to volume to decrease.

5. Divisions of the Cell • The process by which a cell divides into two new daughter cells is called cell division.

6. Homework • Complete laboratory report

7. Objective: Name the main events in the cell cycle and describe what happens during the four phases of mitosis KEY TERMS mitosis cytokinesischromatid Centromereinterphase cell cycle Prophase centriole spindle Metaphase anaphase telephase DO NOW Is it better for a cell to have a large or small surface area?

8. Cell Division • In eukaryotes cell division occurs in two parts • Mitosis: the division of the cell nucleus • Cytokinesis: division of the cytoplasm

9. Chromosomes • Contains the genetic information that is passed down in DNA • Not visible in most cells except during cell division • At beginning of cell division, chromosomes condense and is copied (replicated) • Consist of two identical sister chromatids • Each pair of chromatids is attached at an area called the centromere.

10. The Cell Cycle • Interphase: the “in-between” periods of growth • The cell cycle is the series of events that cells go through as they grow and divide • During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again.

11. Interphase • Divided into three phases: G1, S, G2 • G1 Is a period of activity in which cells do most of their growing. Increase in size and synthesize new proteins and organelles • S phase is when the chromosomes are replicated and the synthesis of DNA molecules take place. Key proteins are also synthesized. • G2 Is usually the shortest of the three phases of interphase. Many of the organelles and molecules required for cell division are produced

12. Mitosis • Divided into 4 phases • Prophase • Metaphase • Anaphase • Telophase

13. Prophase • The first and longest phase of mitosis • Can take as much as 50 to 60 % of the total time required to complete mitosis • The centrioles, two tiny structures located in the cytoplasm near the nuclear envelope, separate and take up positions on opposite sides of the nucleus. • Centrioles are in the centrosome and help organize the spindle

14. Prophase (continued) • Spindle- a fanlike microtubule structure that helps separate chromosomes. • Chromosome become attached to fibers in the spindle at a point near the centromere of each chromatid. • Plant cells do not have spindles but still have the chromosomes line up this way. • Towards the end chromosomes coil tightly, the nucleolus disappears, and the nuclear envelope breaks down

15. Homework • Finish notes on the last three phases of Metaphase