Cell Growth and Division
Stress on DNA Where is DNA held in eukaryotic cells? Does the amount of DNA increase as the cell increases? Why is this stressful? As the cell increases in size, which increases faster: the volume or the surface area?
How do you calculate surface area: volume ratios? Surface area of a cube: length x width x 6 (6 faces on a cube) Volume of a cube: length x width x height Ratio can be represented with a colon or as a fraction, such as 1:2 or 1/2
1x1x 6 = surface area of 6 square mm 1x1x1 = volume of 1 cubic mm 2x2x6 = surface area of 24 square mm 2X2X2 = volume of 8 cubic mm 4x4x6 = surface area of 96 square cm 4X4X4 = volume of 64 cubic mm
So what are their surface area to volume ratios? First cell 6:1 Second cell 24:8, which reduces to 3:1 Third cell 96:64, which reduces to 1.5 :1 …so there is less and less surface area available to support the volume of the cell
The Cell Cycle
The Cell Cycle an overview What must happen to a cell before it can divide? Copy DNA and grow in size (interphase) Nucleus will divide (Mitosis) Cytoplasm divides (Cytokinesis) and the two daughter cells enter Interphase
The Importance of Mitosis Many unicellular organisms reproduce this way (asexual reproduction) Multicellular organisms use mitotic cell division for numerous reasons Growth Development Repair NOT FOR SEXUAL REPRODUCTION (that is meiosis)
How does the DNA copy itself DNA replication Chromosomes copied Sister chromatids remain connected by a centromere Eventually, they will be separated into the two daughter cells
Interphase First and longest stage of cell cycle Subdivided G1: grow S: synthesis of DNA G2: grow organelles used in mitosis
Mitosis Prophase, Metaphase, Anaphase, Telophase During Mitosis, the nucleus will be divided into two Prophase Metaphase Anaphase Telophase
Prophase (preparation) Chromosomes Centrioles Spindle fibers
Metaphase (middle) Chromosomes Spindles
Anaphase (apart) Centromeres split Sister chromatids separate to poles
Telophase (two) Chromosomes uncoil Nuclear envelope reforms Spindle breaks apart Mitosis is now complete, but the rest of the cell still needs to divide
Cytokinesis the end of the M phase Two nuclei Cytokinesis is the division of the cytoplasm, and usually occurs simultaneously with telophase cleavage furrow vs. cell plate
Cytokinesis Cleavage furrow in animal cells Cell plate in plant cells
Test Yourself Mitosis and Meiosis A. You will be shown images of cells in various stages of the cell cycle. Identify each stage. B. We will go over the answers. C. You will identify the stages individually and turn your papers in.
Test Yourself –Part A A B C D E F G H
We’ll go over the answers now Everyone Done? We’ll go over the answers now
Test Yourself-Part B A. Telophase B C D E F G H
Test Yourself A. Telophase B Metaphase C D E F G H
Test Yourself A. Telophase B Metaphase C Anaphase D E F G H
Test Yourself A. Telophase B Metaphase C Anaphase D Prophase E F G H
Test Yourself A. Telophase B Metaphase C Anaphase D Prophase E Anaphase F G H
Test Yourself A. Telophase B Metaphase C Anaphase D Prophase E Anaphase F Interphase G H
Test Yourself A. Telophase B Metaphase C Anaphase D Prophase E Anaphase F Interphase G Metaphase H
Test Yourself A. Telophase B Metaphase C Anaphase D Prophase E Anaphase F Interphase G Metaphase H Prophase
One last practice—can you find each stage?
Any Questions? Quiz Time! Number your paper 1-5 Identify the stage of the cell cycle shown in each image
Question 1 Identify the stage shown below Metaphase
Question 2 Identify the stage shown below Prophase
Question 3 Identify the stage shown below Telophase
Question 4 Identify the stage shown below Anaphase
Question 5 Put these words in chronological order Anaphase Cytokinesis Interphase Metaphase Prophase Telophase Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis
Parson, LRCHS, 2007