Cell Structure and Function Chapter 4 and 5

Cell Theory 1. All Living things are made of cells 1838 – Matthias Schleiden – plants are made of cells. 1839 – Theodor Schwann – animals are made of cells. 1. All Living things are made of cells 2. Cells are the basic unit of life 1855 – Virchow – studied cell division and… 3. All cells come from preexisting cells.

plasma membrane Fig. 5-23a, p.88

Cell Membrane Structure Phospholipid Bilayer Phosphate head towards the water (hydrophilic) Lipid tails towards each other (hydrophobic)

Fluid Mosaic Model of the Cell Membrane Fluid (dynamic) Phopholipids are not rigid Proteins also move around within the membrane Mosiac A network of many proteins/molecules/cholesterol Some proteins go through the membrane (integral) Others stay on one side of the membrane (peripheral)

Function of the Cell Membrane Protects the cells from surroundings and Selectively allows substances to pass through the membrane (what kind of substances?) Enzyme activity, cell recognition, cell signaling, cell transport

glucose and other large, polar, water-soluble molecules; ions (e.g., oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules glucose and other large, polar, water-soluble molecules; ions (e.g., H+, Na+, K+, Ca++, Cl–); water molecules Fig. 5-15, p.82

Passive Transport Flow of solutes down their concentration gradients: High to low conc. Can move both ways Does not require any energy input Ex. Diffusion, Osmosis and facilitated diffusion

Passive Transport Diffusion Small molecules move from a region of high concentration to a region of low concentration till they are equally dispersed (equilibrium is reached) Ex. Oxygen, carbon-dioxide Fig. 5-16, p.82

Passive transport Osmosis Diffusion of water molecules across a selectively permeable membrane Direction of net flow is determined by water concentration gradient Side with the most solute molecules has the lowest water concentration

Tonicity and Osmosis Passive Transport Osmosis 2% sucrose Tonicity and Osmosis water 10% sucrose 2% sucrose Hypotonic: lower conc. solutes outside the membrane High conc. of water outside – more water flows in Hypertonic: higher conc. solutes outside the membrane So lower conc. of water outside – more water flows out Isotonic: equal conc. solutes across the water flows across in equal amounts

Passive transport- Facilitated Diffusion glucose transporter solute (glucose) high low Passive transport- Facilitated Diffusion Stepped Art Fig. 5-18b, p.84

Active transport

Against the concentration gradient Needs energy (ATP) Active transport Against the concentration gradient Needs energy (ATP) Uses membrane proteins Example: Sodium and potassium pumps in nerve cells

Bulk Transport Endocytosis (vesicles in) Exocytosis (vesicles out) Fig. 5-17b, p.83

Cells need energy to live and work What is cell work? Transport of substances across and within the cell Breakdown and build up of compounds Chromosomes in nucleus duplicates In most ecosystems the ultimate form of energy is from ____ Used to form the bonds of energy in _____ Breaking bonds releases energy to form ATP ATP does the actual work in cell

Energy Cycle in Cells

Energy Flow First Law of Thermodynamics Second Law of Thermodynamics Energy cannot be created or destroyed Can be converted from one form to another Ex. Energy is released when burning wood Second Law of Thermodynamics During energy conversions, some forms of energy cannot be used for work Entropy or disorder

Energy Flow in Ecosystems Photosynthesis transfers the energy from light to… Energy in the chemical bonds of sugars Cell respiration breaks the bonds of the sugars to make ATP Metabolism = sum total of all the reactions in a cell. Catabolism (break down) Anabolism (build up)

Nature of Metabolism Most reactions occur controlled stepwise fashion Reactants > Intermediates > products These reactions can also happen in reverse Example: Glucose + Glucose > Maltose + Maltose > Starch etc. Reverse Starch > Glucose + Glucose + Glucose ……

Metabolic reaction rate Must happen very quickly Need catalysts to speed up reactions which would otherwise happen slowly Ex glucose will degrade into CO2 and H2O but would take a long time Biological catalysts –ENZYMES speed up this reaction so cells can use the energy

How do enzymes work? For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller

Enzyme - Catalase

How do enzymes work?

Enzymes Biological catalysts – Proteins Lowers activation energy needed to begin a reaction Have an active site where the reactants attach Remain unchanged at the end of the reaction Can be reused Specific to the reaction it catalyzes Each reaction has its own specific protein

Factors effecting enzyme activity pH Temp changes Salt concentrations Cofactors Inhibitors – competitive and noncompetitive

Cell transport review Go to: http://www.wiley.com/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm