Do Now & Homework Check

Miss Pollack

A key part of cell division is to create copies of the genetic material. There are different names for the genetic material depending on the form it takes. It’s important to know the differences between these terms. FILL IN THE BLANKS in your notebook for #1-4

1.___________________• When DNA is not

dividing it is sitting in the nucleus, and so the DNA is not tightly coiled yet

• Loosely packed• Not condensed

*SPAGHETTI*

3._______________• DNA condensed into a transportable form after it has replicated; humans have 46 individual and 23 pairs of these

2._______________• The identical

halves of a chromosome; each half is attached by the centromere

_________________chromosomes

• A pair of 2 chromosomes that are the same size, shape & contain the same genes,with each parent contributing one of the chromosomes in the pair

Cell Reproduction/Cell Division• Cells in your body are constantly reproducing

– Approximately 25 million cells per second • Why do our cells do this?

– Part of growth and maturing as a human/organism– Cells in your body may be dying or damaged and we need to replace

them• As we know from the cell theory, all cells come from preexisting

cells

–Get 2 new cells from 1 original cell

Cell Division: Prokaryotes• Prokaryotes have a single,

circular chromosome• Do binary fission– 3 steps– End result: Get 2 new cells

from 1 original cell

• Binary fission has 3 steps:– 1. DNA is replicated so that there are 2 identical chromosomes.

– 2. The 2 chromosomes separate and move to opposite ends of the cell.

– 3. Cytokinesis: a new membrane grows at the center of the cell and the cytoplasm splits apart, forming 2 new daughter cells

• End result: 2 new cells that are genetically identical to each other and to the 1st original cell

Cell Division: Eukaryotes

• Eukaryotic cells = humans, mammals, fish– do NOT go through binary fission

• Go through a cell cycle= period from the beginning of one division to the beginning of the next; life cycle of a cell– Cell cycle has 2 periods:• 1. Interphase = a cell spends MOST OF its life here• 2. Mitosis = shorter period for the cell to be in

Period 1- Interphase• Interphase = the time between cell divisions; also is the

longer period compared to mitosis• cell has not yet started to divide but is doing its regular

activities like making the proteins/ enzymes it will need later on– 3 subphases:

• 1. G1: cell grows• 2. S phase: (synthesis) each chromosome is copied (DNA

copied)• 3. G2: prepares for cell division, growing again

– G0: cells do not copy their DNA and do not prepare for cell division in a resting stage, just hanging out after they go through G1• Ex: Nerve cells, or other mature cells that do not need more

development

G0

CELL CYCLE ALIVE!

Cell Cycle

Think- Pair- Share

• Give evidence…that the eukaryotic cell is more complex than the prokaryotic cell

– Think and explain your reasoning in your CW ntbk– Pair up with your neighbor– Share as a class

MONDAY- Do NOW

• 1. What are autosomes?– How many pairs of autosomes do humans have?

• 2. What are sex chromosomes?– How many pairs of sex chromosomes do humans

have?

So what is the purpose of mitosis?

• Produce daughter cells that are identical copies of the parent cell for all the cells in the body, except sex cells/gametes

• Maintain the correct number of chromosomes from generation to generation

Period 2: Mitosis

• Now that the chromosomes have been copied in the S phase of interphase…

• Can now go through mitosis:– Division of the nucleus to give the cell’s copied

DNA to new cells• The cell is dividing in 4 steps:

– PMAT– Prophase, metaphase, anaphase, telophase– cytokinesis

Mitosis: Prophase• 1st • Chromosomes thicken and

coil, condense– Allows them to be visible for

first time• Nuclear envelope

disappears• Centrioles move to

opposite ends of the cell• Spindle fibers/strings attach

to chromosomes

Metaphase

• 2nd • Spindle fibers are

attached to centromere of chromosome

• Chromosomes line up at the equatorial plane or metaphase plate– Middle

Anaphase

• 3rd

• Sister chromatids of each chromosome separate at the centromere– Go to opposite poles, pulled apart– Each half of a pair of sister chromatids now moves

to opposite ends

Telophase

• 4th (reverse of prophase)• Spindle fibers disappear• Chromosomes uncoil to become chromatin• Nuclear membrane forms around each set of

chromosomes

Cytokinesis• Split the cytoplasm, done in the middle too– Get the 2 DISTINCT DAUGHTER CELLS

• Animals form a furrow to pinch off • Plants form a cell plate

In mitosis…

• … what happens if this does not go as planned? What happens if we do not get identical copies of the parent cell? What happens if you do not get the correct number of chromosomes?