Transcript Why does a cell need to divide?

Why does a cell need to divide?
Agenda for Thursday March 3rd
1. Go over homework
2. Mitosis
All late work is due TOMORROW!!
Quiz – words 56-60
Cellular Growth
Cell Size limitations
• Ratio of surface area to volume
– Difficulty providing nutrients and expel waste
– Lower ratio = easier to maintain
Cellular Growth
Cell size limitations
• Transport of Substances
– Diffusion over a large area is slower & less
efficient
• Cellular communication
– Too large means too hard to communicate
The Cell Cycle
• Cell reaches max size it stops growing or divides
– Cells reproduce by growing and dividing = cell cycle
• 3 main stages of cell cycle
– Interphase – cell grows, replicates DNA
– Mitosis – cell nucleus and nuclear material divide
– Cytokinesis – cell’s cytoplasm divides
3 Stages of Interphase
Gap 1 (G1)
• Right after cell divides, cell carries out normal
functions, prepares to replicate DNA
Synthesis (S)
• Cell copies DNA
– Chromosomes are structure that contain genetic
material that is passed on
– Chromatin is the relaxed form of DNA
Gap 2 (G2)
• Cell prepares for mitosis
Mitosis
• Cell’s DNA separates
– Creates 2 identical daughter cells
– Same DNA
– Same Number of Chromosomes in each cell
• Increases number of cells as organisms grow
• Replace damaged cells
• 4 Stages – Prophase, Metaphase, Anaphase,
Telophase
1. Prophase
• Longest phase
• Chromatin condenses into
chromosomes (X – shaped)
– Chromosomes consist of two chromatids
– identical copies of DNA
– Chromatids are connected at a
centromere
1. Prophase
• Spindle fibers appear between poles
• Centrioles appear at the ends of each cell
• Aster fibers come out of the centrioles
• Spindle fibers, centrioles, and aster fibers are
called spindle apparatus
– Helps move chromosomes
2. Metaphase
• Chromatids are pulled by motor proteins along
spindle apparatus
• Line up at center of cell
3. Anaphase
• Chromatids pull apart
• Spindle fibers start to shorten – causes
chromosomes to move to end of cells
4. Telophase
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Chromosomes arrive at the poles
Chromosomes start to unwind
Two nuclear membranes begin to form
Spindle apparatus disappears
Cytokinesis
• Divides cytoplasm
• Animal Cells
– Microfilaments constrict/pinch the cytoplasm
• Plant Cells
– Cell plate forms between two daughter nuclei
– Cell walls then form on either side of cell plate
Cell Cycle Regulation
• Proteins called cyclins bind to enzymes called
cyclin dependent kinases (CDK) to start different
cell activities
List the stages of the Cell Cycle
Agenda for Friday March 4th
1. Quiz
2. Mitosis stuff
Describe the stages of Mitosis.
Agenda for Monday March 7th
1. Mitosis review
2. Review
FINAL ON WEDNESDAY!!
Homework
• Page 253 – 257
• Questions 1 – 7 on page 257