Prokaryotic vs. Eukaryotic Cells Literally means “before the nucleus”. They do contain DNA but it is not organized into a nucleus. The DNA is circular and shorter The cell is much smaller in size. The only prokaryotic cells are bacteria.

Eukarytotic Means “true nucleus”, these cells all contain an organized nucleus containing DNA Eukaryotic DNA is linear and longer Cells will also contains many other membrane bound structures

Comparison of the 2 types of cells: Structure prokaryotic eukaryotic cell membrane chromosomes nuclear membrane, Golgi ER, lysosomes, vacuoles cell wall ribosomes mitochondria chloroplasts cytoskeleton http://learn.genetics.utah.edu/content/begin/cells/scale/

Endosymbiotic theory: Means “cell within a cell” One cell was engulfed by another cell or it entered as a parasite Instead of being destroyed it added energy to the cell and eventually evolved into a cell structure

Evidence for the endosymbiotic theory: 1. They kept their own membrane. These structures have a double membrane now. 2. They both contain their own DNA which is similar to bacterial DNA 3. Mitochondria and chloroplasts can divide independently in the same method as bacteria. 4. They have their own ribosomes.

A comparison of plant and animal cells: Plants have one large vacuole, animals have several small ones Plants contain plastids, animals don’t Plants have a cell wall, animals don’t Plants don’t have lysosomes, animals do Plants don’t use centrioles to divide, animals to

Specialized cells and tissues Tissue is Latin for “weave”, it is a group of cells with a common structure and function some are literally woven together some are held together with a sticky coating called a matrix

Cells form tissues which in turn form organs:

Fluid mosaic model of the cell membrane: The cell membrane is a bilayer of phospholipids embedded with proteins, with attached carbohydrate chains and cholesterol “fluid” means it is asymmetrical and changing-the materials making it up can move “mosaic” means it is made up of several different materials

A closer look at the mosaic parts: A. The proteins are of 2 types: 1.Transmembrane proteins go through the membrane and may project through the surface carriers-help carry materials across channels-allow substances to move through receptors-bind certain molecules enzymes-carry out metabolic reactions

2. Peripheral proteins-occur on the surface of the membrane Anchor to a carbohydrate or a lipid May link to cytoskeleton on inside or link to matrix on outside

C. Cholesterol-found within the bilayer B. Carbohydrates serve as fingerprints; sugars are recognized by other cells transplanted tissue may be rejected because the body doesn’t recognize the markers Examples: glycoproteins, glycolipids C. Cholesterol-found within the bilayer Acts to stabilize Reduces permeability to small molecules Found in animal cells only

D. Bilayer glycerol linked to 2 fatty acids and a phosphate hydrophobic ends face inside, hydrophilic end faces outside

Permeability-movement across the membrane The membrane is easily permeable to small, noncharged, lipid soluble molecules. Large polar molecules and ions do not pass freely. Membrane is said to be selectively permeable.

Types of transport: 1. Passive-requires no energy output by the cell a. diffusion-based on random motion of molecules molecules move from high to low concentration (down a concentration gradient) until equilibrium is reached speed is affected by gradient steepness temperature (faster at higher temperatures) pressure gradients (may differ in each side of membrane) molecule size (small move faster) electric gradients (charge differences)

How diffusion works:

b. Osmosis-diffusion of water across a membrane pressure develops on the side of the membrane that has a higher concentration of solutes examples-water absorbed by large intestines, water retention in kidneys, water taken up by blood

Differences in amounts of water inside and outside of cells creates tonicity: Isotonic-the solute concentration (and therefore the water concentration) is the same on both sides. Water moves equally in and out of the cell. Hypertonic-solution has more solute (and therefore less water) than the cell water leaves cell and it shrinks Called “crenation” in animals Called “plasmolysis” in plants Hypotonic-the solution has less solute than cell (therefore more water) water goes into cell causing it to swell and burst cell wall of plant prevents this (tugor pressure)

Animal cells Plant cells

c. Facilitated diffusion carrier proteins are used to move materials across the membrane. Proteins are specific-will combine with only one thing They can only move in the direction of the gradient (high to low) so no energy is used by the cell

2. Active transport-movement of molecules against the concentration gradient—requires energy. Protein pumps-proteins are used to bind to material and move it across the membrane sodium potassium pump

Endocytosis-taking in large materials by forming vessicles around them. 1. phagocytosis-”cell eating”– is the uptake of large particles. Can be seen in unicellular organisms or WBC. 2. pinocytosis-”cell drinking”– uptake of small particles or liquid. Seen in plant root cells

3. receptor mediated-receptor proteins in membrane fit to a particular molecule, bind it and indent to pull it in.

Exocytosis-release of materials (waste) from cell. Vessicles move to membrane and fuse with it. Membrane opens and contents spill out This is one way of secreting hormones (like insulin from pancreas into blood), plants use it to secrete material for the cell wall

Cell junctions: Neighboring cells interact and communicate with each other through junctions. Plant junctions: plasmodesma-channels in the cell wall of plants that allow cytoplasm to move through and into adjacent cells.

Animal cell junctions: 1. Tight junctions-found in cells like epithelial cells (linings). Prevents leaking of materials between cells 2. Desmosome (Adhering) junctions- joins cells of the skin and heart that need to stretch. Works like a rivet 3. Gap junctions-links cytoplasm of neighboring through membrane channels.