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The Cell Cycle. Why are cells so small??. What limits the size of a cell?? Most cells are between .002 - .2 millimeters. What limits the size of a cell?. Diffusion Very fast and efficient over short distances Becomes slow and inefficient as the distances become larger
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Why are cells so small?? • What limits the size of a cell?? • Most cells are between .002 - .2 millimeters
What limits the size of a cell? • Diffusion • Very fast and efficient over short distances • Becomes slow and inefficient as the distances become larger • Cells would die before nutrients could reach the organelles if the cell was too big
What limits the size of a cell?? • Surface Area – to – Volume Ratio • As cell size increases, its volume increases much faster than surface area • Example: If cell size doubles, the cell would require 8 times more nutrients, but the cell membrane would only increase by 4 times. This would mean that the cell doesn’t have enough room (cell membrane) to diffuse.
What limits the size of a cell?? • DNA • There’s a limit to how fast DNA can make proteins • If you have a large cell then the DNA can’t make proteins fast enough for the cell.
The Cell Cycle • Cell Reproduction • One cell (parent cell) reproduces to make 2 identical cells (daughter cells) • 5 steps in this process
What is Mitosis • Mitosis is…THE PROCESS BY WHICH A CELL’S NUCLEUS DIVIDES!
Before Mitosis… • Interphase • This phase is broken down into 3 subphases • G1 = Cell grows in size and organelles replicate • S = DNA duplicates itself (DNA Replication) • Chromatin duplicates – long coily strands of DNA that become wrapped up • G2 = Rapid Growth before dividing • Cells spend most of their time in this phase
Mitosis • Prophase • A.) Chromatin organizes itself into chromosomes made up of 2 sister chromatids attached by a centromere • Sister Chromatids – A chromosome and its duplicated twin • Centromere – rubber band structure that joins the 2 sister chromatids together
Prophase • B.) Nuclear membrane breaks down • Nucleus dissolves • C.) Centrioles move to opposite ends of the cell (poles) • Centrioles – cylinder structures that will reel in the chromatids • D.) Spindle fibers form • Spindle fibers – football shaped set of ropes that will attach to the centrioles and the chromatids • Made of microtubules
Mitosis • Metaphase • Spindle fibers attach to centrioles and sister chromatids at their centromeres. • Chromosomes line up in the middle of the cell • Line up on the metaphase plate/equator.
Mitosis • Anaphase • The centromeres split apart and the sister chromatids separate from each other • The spindle fibers pull the chromatids toward the poles
Mitosis • Telophase • Chromatids reach the poles • Chromosomes unwind • Spindle fibers break down • Nucleus reforms • Cell begins to split • Cleavage furrow
