Why do cells divide? p. 51

Since we say family members are “blood” relatives, does that mean we share the same blood? You share no blood with anyone....not even your mother and father! Your family shares DNA. 1⁄2 of your DNA came from your mother (egg) and 1⁄2 from your father (sperm). The process that made this possible is MEIOSIS which makes the sperm and egg. A fertilized egg then grows into an organism by a different process of cell division called MITOSIS.

Cells divide to maintain a workable volume to surface area ratio

Write it if you need to… Volume is the amount of space inside of a cell. This would include the cytoplasm and all of the organelles.

Write it if you need to… Surface area is the total amount of exterior which is exposed to the environment around the cell. This would include the outside of the cell membrane.

Write it … Volume increases faster than surface area. As the cell gets larger, surface area decreases

Write it … The surface area must be large enough for a sufficient amount materials to enter the cell. The materials must enter quickly enough that all of the cell will get what it needs. Thus, a larger surface area: volume ratio is preferred.

Cells stay small to keep the rate of diffusion fast!

If it were a cell… EXPLAIN which of the cell sizes pictured is preferable.

Cells divide to make more cells Growth of a multicellular organism requires the addition of cells Larger organisms do not necessarily have bigger cells, but they will have more cells than smaller organisms. p. 52

Cells divide to make more cells Repair of damaged tissues by replacement of cells lost due to injury or cell death requires cell division. A healthy cell will divide to replace the lost cell(s). Mitosis

Fill It In … 2 reasons that cells need to divide: 1. 2.

Cells divide to make more cells Cell division occurs at different rates depending on the organism and the type of cell. Plant root cells would divide more rapidly because this is an area of active growth

Cell division occurs at different rates Some nerve cells enter a phase of no division Called G0 Why brain and nerve damage is often nonreversible

Cell division occurs at different rates Some bacteria cells divide very rapidly For example, E. coli can divide every 20 minutes in ideal conditions.

How do cells divide? Prokaryotic vs Eukaryotic Division

How do cells divide? The result of all cell division is the production of daughter cells. In order for daughter cells to contain enough DNA, the genetic material (DNA) of the parent cell must be copied. When does DNA need to be replicated? Before, during, or after cell division?

How do cells divide? Prokaryotic division differs from eukaryotic division because prokaryotic cells do not contain a nucleus or membrane-bound organelles.

How do cells divide? Eukaryotic division requires the replication of the nucleus and genetic material (DNA) as well as the allocation of the organelles into each daughter cell.

Fill It In … Reason that prokaryotic cell division is simpler than eukaryotic cell division …

Eukaryotic Cell Cycle & Mitosis Interphase is the “normal” part of the cell cycle. The cells spend most of the cycle (life of the cell) in interphase.

There are three stages in interphase G1 - Cell increases in size and synthesize new proteins and organelles “G” stands for Gap

There are three stages in interphase S - DNA is replicated During most of interphase, DNA exists in a “relaxed”, stringy form called chromatin After being copied, there are two complete copies of the DNA in the cell. These copies are attached to each other. S stands for “Synthesis” What is being synthesized during S phase?

There are three stages in interphase S - DNA is replicated Each copy of DNA is called a chromatid. The two chromatids are attached in a region celled the centromere. At this point in interphase, the chromatids are coiled/condensed The entire structure is called a doubled chromosome. (or duplicated chromosome)

DNA Replication in S Phase 2 duplicated chromosomes aka doubled chromosomes Made of 2 chromatids 2 chromosomes

There are three stages in interphase G2 - organelles and molecules required for cell division are produced (the cell is preparing for division)

Fill It In … Differentiate between … Chromatin - Chromatid - Chromosome -

Fill It In … On the diagram of the cell cycle, HIGHLIGHT the stages that are part of Interphase.

Mitosis: Amoeba Sisters! Fill in the “notes” as we watch.

Stages of Mitosis (Eukaryotic Cell Division) Prophase Coiled chromosomes become visible Nuclear membrane is broken down Spindles (protein fibers that attach to chromosomes and aid in chromosome movement) start to form

Stages of Mitosis (Eukaryotic Cell Division) Metaphase Spindle fibers attach to the centromere regions Chromosomes are moved to the Middle of the cell

Stages of Mitosis (Eukaryotic Cell Division) Anaphase Spindle fibers shorten Doubled chromosomes are separated into chromatids Chromatids begin to move to opposite poles/ends of the cell Anaphase – chromosomes move Apart

Stages of Mitosis (Eukaryotic Cell Division) Telophase Spindle fibers are broken down Nuclear membrane begins to form around the clusters of chromatids at each pole of the cell. (2 new nuclei are formed!) Telophase = Two

Cytokinesis Cytokinesis is the separation of the cytoplasm (including all organelles) into two identical daughter cells. “cyto” = cell “kinesis” = movement

Cytokinesis Animal cells constrict in the middle to pinch apart forming two different cells. Form a “cleavage furrow”

Cytokinesis Plant cells also produce a cell plate dividing the two cells. This cell plate will become the cell wall MITOSIS Animation

MITOSIS Animation

p. 53 Fill It In … Summary of the cell cycle Interphase . Mitosis

Mitosis & Cancer Typically, cell division is controlled by genes in the cell, contact with other cells, and available nutrients in the environment.

Mitosis & Cancer Cancer is a class of diseases characterized by uncontrolled cell division and the ability of these cells to invade other tissues (metastasis).

Mitosis & Cancer Cancer occurs when the genes that control cell division do not function properly. This may occur because of an 1) inherited genetic defect, a 2) spontaneous genetic mutation, or 3) mutation caused by environmental factors. Cancer Institute Cancer and the Cell Cycle Cancer

Fill It In … Cancer is caused by uncontrolled _______ ___________, which may occur because of 1. 2. 3.

Check Yourself! Name three reasons cells must divide. Why is eukaryotic cell division more complex than prokaryotic cell division? What are the three stages of the cell cycle? How is the genetic material “prepared” for cell division during interphase? How many daughter cells are produced as a result of mitosis, and how do these cells compare to the parent cell? How are mitosis and cancer connected?