The Cell Cycle

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

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

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