10 1 Cell Growth Why are cells small? This colorized scanning electron micrograph is showing a white blood cell undergoing cell division. This relates to cell theory because this is HOW all cells come from preexisting cells. As cells grow larger the two primary problems they face are: 1) having enough DNA 2) Their ability to transport nutrients in and wastes out. A cell s surface area is the primary physical factor that affects the rate or efficiency of a cell in transporting nutrients in and wastes out. A cells volume is the primary physical factor that affects the rate at which a cell requires nutrients and produces waste? The surface area to volume ratio (SA/V) is the geometric relationship between these two factors that govern how large cells can be...
10 1 Cell Growth Limits to Cell Growth As a cell gets larger, BOTH its surface area and volume INCREASE. The change in these two factors DO NOT happen at the same rate. VOLUME increases FASTER! The mathematical relationship between these factors is the surface area to volume RATIO (SA/V). Written as a fraction, the SA is the numerator (dividend) and the V is the denominator (divisor). As a cell gets larger the SA/V quotient gets smaller, because the denominator (V) increases faster than the numerator (SA)! As a cell grows, its DEMAND for nutrients INCREASES FASTER than its ability to transport them. Cells are small to keep their SA/V HIGH to transport enough nutrients to meet demands. Note: Surface area is a major factor affecting the function of all cells, tissues, organs and systems!
10 1 Cell Growth Division of the Cell Parent Cell Cytoplasm Parent Nucleus Mitosis Parent DNA (Replicated) Nuclear Envelope Cytokinesis Daughter Nuclei Daughter Cells Plasma Membrane This diagram shows a dividing eukaryotic parent cell. First the parent DNA replicates, then the parent DNA and nuclear envelope (nucleus) divide by mitosis, producing daughter nuclei. This is followed by the parent cytoplasm and plasma membrane dividing by cytokinesis leaving two identical daughter cells. The flaw in this diagram is that in most cells the nuclear envelope breaks down and reforms during mitosis.
The Cell Cycle Interphase S G1 C M Cell Division G2 The cell cycle is the cycle of growth and division of a cell. The major events are: 1) Growth/Function 2) Preparation to divide (x2) 3) Cell Division Interphase is the period of growth/function and preparation between cell divisions. The major events of G1 are growth and function. G stands for gap (but think growth). The major event of S is DNA replication (x2). S stands for synthesis. The major events of G2 are growth, enzyme synthesis, and organelle replication (x2). Mitosis (M) is division of the cell nucleus (not the whole cell). Cytokinesis (C) is the physical splitting of the cytoplasm and plasma membrane. This is a cycle because once cells divide, they enter G1.
Cytoplasm & Plasma Membrane Division Events of the Cell Cycle Growth & Function Cell Division Nuclear Division DNA Synthesis Growth, Enzymes & Organelles This diagram shows mitosis in greater detail. Inter = in between (cell divisions) Pro = first Meta = middle (chromosomes in the middle) Ana = away (chromosomes moving away) Telo = last
Chromosomes Interphase G1 S G2 uncondensed chromatin Mitosis - Prophase Mitotic Chromosome (condensed) Sister Chromatids Genetic information (DNA) is passed from one cell to another and from parents to offspring in the form of chromosomes through the process of cell division. One DNA molecule makes up each chromosome in the G1-phase of interphase. During this phase, they are uncondensed, unduplicated chromosomes, not visible under the microscope. Each chromosome (DNA molecule) replicates during the S-phase of interphase before a cell divides, so that each daughter cell can receive a copy. Following this phase (G2), they are uncondensed, duplicated chromosomes. Chromosomes condense and become visible under the light microscope (mitotic chromosomes) during prophase of mitosis. Following replication, each chromosome is made up of two DNA molecules, each one a sister chromatid, attached at the centromere. When a cell divides, the sister chromatids separate so that each daughter cell gets a copy. Six feet of DNA is packed into each and every nucleus of each and every human cell by the way it is organized with histones into nucleosomes and chromatin...
Chromatin/Chromosome Condensation The DNA double helix is 2nm wide. That s 2 billionths of a meter! But it is a long polymer. Nucleosome (8 histones + DNA) Histones are proteins that organize DNA. Eight histones make up each bead that DNA wraps around. Each bead + DNA is called a nucleosome. DNA is in the form of chromatin during interphase. During prophase of mitosis chromatin condenses into mitotic chromosomes visible under a light microscope. Chromatin condenses into chromosomes by wrapping, packing, folding and coiling. Two DNA molecules make up this chromosome, each a sister chromatid attached at the centromere. This is a duplicated chromosome. Sister Chromatids Duplicated Mitotic Chromosome