Cells August 28th, 2007

Cell History Robert Hooke (1635-1703) Viewed slices of cork under a crude compound microscope He saw boxes which reminded him of cells that monks lived in Hence the name “cell”

Cell History Anton van Leeuwenhoek (1632-1723) Designed an early microscope First to see living organisms in a drop of water

Cell History Robert Brown (1773-1858) Used special stains and dye to view nucleus

Cell History Theodor Schwann, zoologist, (1810-1882) Rudolph Virchow, physician (1821-1902) Mathias Schleiden, botanist (1804-1881)

Cell Theory Schleiden, Schwann and Virchow each contributed to the cell theory (1838-1839): Cells are the basic unit of structure and function of all living things All living things are composed of one or more cells New cells are produced from existing cells

Cell Types Prokaryotic Eukaryotic First appear in fossil record 3.5 BYA No membrane bound organelles No Nucleus Bacteria Eukaryotic Evolved 1.5 BYA Have membrane bound organelles Have Nucleus Protists, fungi, animals, plants

Cell Structures Cell Membrane (AKA: Plasma Membrane) Selectively permeable Regulates what goes in and out Flexible Provides protection and support Made of a lipid bilayer

Phospholipids Fatty acid tails are non-polar Heads are polar Tails don’t want to be near water because water is polar so they are inside the bilayer.

Cell Membrane Lipid Bilayer Outside of cell Inside (cytoplasm) Proteins Protein channel Lipid bilayer Carbohydrate chains

Cellular Transportation The cell membrane is selectively permeable and allows some particles come into the cell and keeps some of them out.

2 Types of Transportation Passive Transport * The cell does not use any energy. * Materials flow down the concentration gradient from High concentration to low concentration Active Transport * Requires that the cell use energy. * Movement of solutes against a concentration gradient from Low concentration to High concentration.

The 3 most common types of Passive Transport: 1. Diffusion 2. Osmosis 3. Facilitated Diffusion

Diffusion The overall direction of the movement is referred to as the Gradient. In diffusion molecules usually move “down the concentration gradient”..... flow from high concentration to low concentration. A state of “equilibrium” is reached where molecules are uniformly distributed but continue to move randomly.

Direction of Diffusion Simple Diffusion Molecules Direction of Diffusion High Concentration Low Concentration Selectively Permeable Membrane

Osmosis The diffusion of WATER across a selectively permeable membrane is called OSMOSIS. Osmotic environments are classified by the concentration of the solutes in the solution.

Osmotic environments are classified as: 1. Isotonic 2. Hypertonic 3. Hypotonic

Isotonic Environment In an Isotonic solution, the concentration of solutes outside and inside the cell are equal. Water is moving in and out at an equal rate. 95% Water 5% Solutes 95% Water 5% Solutes

Hypertonic Environment Concentration of solutes is greater outside the cell than inside the cell. Water will move outside the cell… the cell will shrink and die. 97% Water 3% solute 95% Water 5% solute

Hypotonic Environment Concentration of solutes is greater inside the cell than outside the cell. Water will move inside the cell… the cell will swell, or burst, and die. 95% Water 5% solute 97% Water 3% solute

Facilitated Diffusion The diffusion of large particles through channel proteins in the plasma membrane. Example: Glucose moves in and out of cells through Facilitated Diffusion.

Types of Active Transport are: (Phagocytosis & Pinocytosis) Active Transport *Solutes flow against the concentration gradient. * The cell uses energy… usually ATP. *Requires Transport Proteins Types of Active Transport are: 1. Exocytosis 2. Endocytosis (Phagocytosis & Pinocytosis)

Exocytosis (exo = outside, Cyto = cell) Moving substances outside the cell Process of vesicles fusing with the plasma membrane and releasing their content to the outside of the cell.

Endocytosis (endo = inside, cyto = cell) The capture of substances outside the cell when the plasma membrane merges to engulf it.

Phagocytosis (phago = to eat, cyto = cell) Phagocytosis occurs when undissolved solids enter a cell. The plasma membrane wraps around the solid material and engulfs it, forming a vesicle. Phagocytic cells, such as white blood cells, attack and engulf bacteria in this manner.

Pinocytosis (pino = to drink, cyto = cell) Pinocytosis occurs when dissolved materials enter a cell. The plasma membrane folds inward to form a channel allowing the liquid to enter. The plasma membrane closes off the channel, encircling the liquid inside a vesicle.

Cell Structures The cytoplasm is a jelly-like substance that holds many other organelles such as: Endoplasmic Reticulum – transports lipids and proteins Ribosomes – produce proteins Golgi Apparatus – packages and delivers proteins Mitochondria – Transform energy into a chemical form that can be used by the cell. Lysosomes – Help with cell digestion Peroxisomes – House enzymes that speed up chemical reactions.

Cell Structures (cont.) Microfilaments/Microtubules – form cytoskeleton to help with cell movement. Centrosome – Contains centrioles that help during Mitosis. Cilia/Flagella – Cellular extensions that aid in cell movement. Vesicles – sacs that form to help particles come into and out of the cell.

Why are cells so small? Surface Area vs. Volume As a cell grows larger, the volume increases faster than the SA A bigger cell needs more nutrients, but has relatively less SA to take in those nutrients

Surface Area vs. Volume Cell Size 5 cm 10 cm Surface Area (l×w×6) Volume (l×w×h) 125 cm3 1000 cm3 SA to Volume Ratio 150/125 = 6:5 600/1000 = 6:10

Cell Cycle Cells divide before growing too large Before dividing, cells must prepare Preparation = Interphase G1 phase: Cell grows larger S phase: Cell makes new DNA for daughter cell G2 phase: Cell makes new organelles for daughter cell

Cell Cycle

Chromosomes Each chromosome is replicated during the S phase Centromere Sister Chromatids Each chromosome is replicated during the S phase A replicated chromosome has two identical sister chromatids connected by a centromere

Mitosis Four Stages: Prophase (pro- means first) Metaphase (meta- means middle/after) Anaphase (ana- means apart) Telophase (telo- means far away/end)

Prophase Chromatin condenses into chromosomes condensing Chromatin condenses into chromosomes Nuclear envelope and nucleolus disintegrate Centrioles migrate to opposite ends of the cell Spindle fibers form in foot ball shape across cell

Prophase

Metaphase Chromosomes line up in the middle (equator) of the cell Spindle fibers attach to centromeres

Metaphase

Anaphase Sister chromatids separate Spindle fibers shorten, pulling chromatids to opposite ends of cell Animal cells begin to pinch in Plant cells begin to form cell plate in the middle

Anaphase

Telophase Nuclear membrane built from ER around each set of chromosomes Nucleolus reforms in each nucleus Chromosomes become mass of chromatin

Two cells dividing into four Telophase Two cells dividing into four

Cytokinesis Final division of cytoplasm resulting in two daughter cells Animals – Cell Membrane pinches together Plants – Cell plate forms new Cell Membrane dividing into the daughter cells

Which phases can you see? Anaphase Prophase Metaphase Telophase Interphase

Knowing when to divide Cyclins Protein that regulates the cell cycle in eukaryotes Internal regulators – tell the cell when to enter mitosis External regulators – control the rate of the cell cycle

Cellular Response to Injury

Effect of Cyclins Cytoplasm is injected into a second cell in G2 phase Cytoplasm is removed from cell in mitosis Second cell enters mitosis

Cancer Cancer results when cells do not respond to cell cycle regulators Cells grow unregulated, forming a tumor Tumor damages surrounding tissue

Leukemia – Blood cancer

Mammary (Breast) Cancer

Skin Cancer