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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 - PowerPoint PPT Presentation
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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– 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 than 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
– 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
Interphase
Interphase
Interphase
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
Prophase
Prophase
Prophase
Prophase
Prophase
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.
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Mitosis• Anaphase
– The centromeres split apart and the sister chromatids separate from each other
– The spindle fibers pull the chromatids toward the poles
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Mitosis• Telophase
– Chromatids reach the poles– Chromosomes unwind– Spindle fibers break down– Nucleus reforms– Cell begins to split
• Cleavage furrow
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
After Mitosis…
• Cytokinesis– Cells Separate
Cytokinesis
The Cell Cycle
