Cellular Reproduction

Question: Does an organism get larger because of the cells increase in size or because they increase in number?

Limits to Cell Growth: There are three reasons why cells divide instead of continually grow larger. A. DNAOverload B. Exchanging Materials C. Surface Area to Volume Ratio  

A. DNAOverload: How does this limit cell growth? If a cell gets too large, there is too great a demand on the genetic information. The making of cell products slows way down; it is inefficient. Open-book test analogy Cookbook restaurant analogy

B. Exchanging Materials: How does this limit cell growth? Nutrients, oxygen, and waste products are exchanged through the cell membrane. Larger cells need more nutrients AND produce more waste and their cell membranes become “congested”. Wal Mart check-out lines analogy HRBT analogy

C. Surface Area to Volume Ratio *Surface area = length x width x number of sides *Volume = length x width x height *Ratio compares the surface area to the volume. 1. What happens to the ratio as the cube gets bigger?____________ *To maintain life, and carry-out cellular functions, materials must be able to move into and out of the cell. Also, material needs to be able to move within the cell.  

2. What might be the advantage of having a large surface area?  Easier to exchange materials 3. What might be the disadvantage of having a large volume? Increased demand for nutrients and oxygen AND producing more wastes  4. How could this apply to a cell? Surface area is like the cell membrane of the cell. Volume is like the cytoplasm of the cell. As a cell gets larger its volume increases much more quickly than its surface area. A larger cell will have more cellular metabolism going on, but relatively less cell membrane to work through. 5. How might this affect a cell’s ability to get food or dump wastes?

D. To solve the problem of DNA overload and exchanging of materials, a cell makes a copy of its DNA and divides into two daughter cells. Specific examples of when cells divide in living organisms. A. Growth   B. Repair of damaged tissue C. Reproduction

Chromosomes: A single piece of coiled DNA containing many genes, found in the nucleus of all cells.   Histones: Protein spools that chromatin winds around. Chromatin: DNA in its unwound state. 

Sister chromatids: Two identical copies of a single chromosome that are connected by a centromere.   Centromere: The part of a chromosome that links sister chromatids. During mitosis, spindle fibers attach to the centromere.  

Centriole: Cylindrical structures that are composed of groupings of microtubules. Centrioles are found in animal cells and play a role in cell division.    Spindle fiber: Groups of microtubules that move chromosomes during cell division.   Spindle apparatus: Collection of all of the spindle fibers.

CELL CYCLE

Cell Cycle: Cells divide in stages A. Interphase: Interphase is a phase when the cell prepares for cell division. During interphase, the cell obtains nutrients, grows and matures, and duplicates its genetic material.   1. G1 phase- Period of growth.  2. S phase- DNA is duplicated. G2 phase- Period of growth. Double checks DNA **G0 phase- Non-dividing state (nerve cells for example)

B. Mitosis: Mitosis is nuclear division, in which the sister chromatids separate and are distributed to each of the new daughter cells to generate two, identical cells.    1. Prophase: Chromosomes coil up, centrioles move to the poles, nuclear membrane breaks down, spindle forms.  2. Metaphase: Spindle fibers pull chromosomes to the metaphase plate (equator of the cell).  3. Anaphase: Sister chromatids are separated and pulled to opposite sides of the cell.  4. Telophase: Chromosomes uncoil, nuclear membranes reforms, spindle disappears.

PROPHASE METAPHASE ANAPHASE TELOPHASE

Mitosis VidClip

C. Cytokinesis: Cytokinesis divides the cytoplasm and cell membrane.  1. Cleavage Furrow in animals/humans: The cell membrane is drawn inward until the cytoplasm is pinched into two equal parts.  2. Cell plate in plants: Vesicles from the Golgi body deposit cellulose midway between the two daughter nuclei forming a divider which eventually becomes the cell wall.

Animal Cells Undergoing Mitosis

Plant Cells Undergoing Mitosis

MEIOSIS: GAMETE PRODUCTION Vocabulary: asexual reproduction: Offspring formed by a single parent; no genetic recombination  sexual reproduction: Offspring formed by two parents and are genetically unique  gametes: Reproductive cells that join during fertilization; sperm and egg  homologous chromosomes: Duplicate, but not identical, copies of the same chromosome; one from mother and one from father  5. diploid: A cell that contains both sets of homologous chromosomes; body cells; (2n)  

6. haploid: A cell that contains only one set of chromosomes; gametes; (n)  7. meiosis: The production of gametes where the number of chromosomes is cut in half through the separation of homologous chromosomes.   8. tetrad: The pairing of homologous chromosomes in their sister form. 9. crossing over: Exchange of genes between homologous chromosomes.

Haploid vs Diploid

Interphase: G1, S, G2 (same as in mitosis)  2. Meiosis: 2 Nuclear Divisions Meiosis 1 – Homologous chromosomes separate Prophase 1 Nuclear membrane breaks down. Centrioles move to the poles. Homologous chromosomes line up next to each other to form a tetrad. Crossing over takes place. Adds all of the diversity. Spindle fibers form. Metaphase 1 Tetrads line up on the metaphase plate (50 yard line of the cell). Anaphase 1 Spindle fibers separate the homologous pairs. Telophase 1 Nuclear membrane reforms resulting in 2 haploid daughter cells. Cytokinesis: Cytoplasm divides between the 2 haploid dgt. cells.

Meiosis 2 – Sister chromatids separate forming 4 haploid daughter cells; looks just like mitosis. Prophase 2 Metaphase 2 Anaphase 2 Telophase 2   3. Cytokinesis: Cytoplasm divides between the 4 gametes.

Meiosis VidClip

Meiosis 1 Meiosis 2

DO THE COMPARE AND CONTRAST OF MITOSIS AND MEIOSIS