Cell differentiation notes

Cell Cycle & Differentiation

Chapter 3

Unit 1

The Cell Cycle

• A set of events that occur during a cell’s lifetime– From the time a cell is “born” until it divides– Cycle is repeated for each cell– Includes:

• Growth• Preparation• Division

The Cell Cycle

The Cell Cycle

• Consists of three major stages:– Interphase*

– Mitosis*

– Cytokinesis

• *Each of these are broken into several distinct phases

The Cell Cycle

• Interphase– Cell’s spend about 90% of the cycle in here– Broken down into three phases

• Gap 1 • Synthesis• Gap 2

Interphase

• Gap 1– AKA “Growth” 1– Cells in this phase are growing in size– Producing lots of ATP– Dividing and reproducing cell organelles

Interphase

• Synthesis– Cells in this phase are copying all the DNA

found in the nucleus– Synthesis is referring to the building of new

DNA molecules– Necessary to ensure that both cells that

result from division have 100% of DNA

Interphase

• Gap 2– AKA “Growth” 2– Cells in the phase are checking to make

sure their DNA has been replicated correctly

– Check to make sure organelles are copied

The Cell Cycle

• Assuming everything is ready at the G2 phase, the cell will proceed to division– Cell division in humans is called mitosis– Has four phases

• Prophase• Metaphase• Anaphase• Telophase

Mitosis

• Prophase– Pro- means first– DNA thickens into chromosomes

• Remember, it has been replicated.• Look like X’s• Each side of the X is called a chromatid

– Nuclear membrane dissolves

Prophase

Mitosis

• Metaphase– Meta- means middle– Spindle Fibers form

• Attach to centromere of chromosome• Move chromosomes to cell’s equator

– Centrioles found at opposite ends of cell

Metaphase

Mitosis

• Anaphase– Spindle Fibers shorten, pulling

chromosomes in half• Sister chromatids split apart• Chromatids move toward opposite sides of cell• ***Chromatids are now called chromosomes

Anaphase

Mitosis

• Telophase– Chromosomes reach the cell’s poles– Two new nuclei form…one around each

set of chromosomes at opposite ends– Chromosomes unwind– Spindle fibers dissolve

Telophase

Cytokinesis

• The final stage of cell division

• Literally means “cytoplasm divides”– Cell pinches in half– The “pinch” is called

a cleavage furrow

Differentiation

• Humans are conceived when a sperm and egg unite, forming a single-celled zygote

• Zygotes are unspecialized

• When we are born, we have more than 260 specialized cell types

• How??? Differentiation

Differentiation

• Cells specialize by differentiating into certain cell types– They turn off parts of DNA that they don’t

need– Use only the parts of DNA that are needed

to become a specific cell– *Cells that are specialized generally

can’t change and become other cell types

Differentiation

• Stem Cells– Unspecialized cells that can can become

ANY type of cell in the body– Stem cells found in every organ in body– Stimulated to divide when…

• Growth is needed• Damage needs to be repaired

Differentiation

• When a stem cell divides…– Two cells are produced through mitosis– One cell is a new stem cell (unspecialized)– One cell is called a progenitor cell

• Somewhat specialized• Will divide many more times, with each

daughter cell become more and more specialized

– *Cells “decide” to become specialized at the end of the G1 phase of cell cycle

See Page 69 in textbook!!!

Apoptosis

• Defined as programmed cell death– Happens at the end of G1 in cell cycle– Occurs for many reasons

• Sculpting organs from overgrown tissue in the fetus

• Removes webbing between fingers as fetus• Destroys skin cells following a sunburn