cell differentiation notes
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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
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