The Cell is the smallest structural and functional unit of life functions are dictated by their specific structures/organelles Continuity of life has a cellular basis All cells have some common structures and functions Human cells have three basic parts: Plasma membrane—flexible outer boundary Cytoplasm—intracellular fluid containing organelles Nucleus—control center 105 Lab 2-Cell, Plasma Memb, Transport 1 Lab 2, BIO 105

Cytoplasm Located between plasma membrane and nucleus Site where most cellular activities accomplished Cytoplasmic Organelles Membranous Mitochondria Peroxisomes Lysosomes Endoplasmic reticulum Golgi apparatus Nonmembranous Cytoskeleton Centrioles Ribosomes 105 Lab 2-Cell, Plasma Memb, Transport 2

Plasma Membrane Phospholipid bilayer and proteins in a constantly changing “fluid mosaic “ small amount of cholesterol and glycolipids Plays a dynamic role in cellular activity Is selectively permeable Determines what can enter and exit cell 105 Lab 2-Cell, Plasma Memb, Transport 3

Membrane Lipids Phospholipids (lipid bilayer) heads: polar (carries an electric charge) and attracted to water (hydrophilic) heads form the inner and outer surface of PM tails: nonpolar and hydrophobic so they form the interior area of the PM small amount of cholesterol to i ncrease membrane stability and fluidity Glycolipids--role is to provide energy and as markers for cellular recognition. Carbohydrates are found on the outer surface of cell membranes. 105 Lab 2-Cell, Plasma Memb, Transport 4

Plasma Membrane Proteins Integral proteins Firmly inserted into the membrane (most span the width of the PM) Many float in the lipid bilayer to form a changing “mosaic pattern” Functions: Transport proteins (form channels and carriers), enzymatic activities, or receptors Peripheral proteins Loosely attached to integral proteins Include filaments on intracellular surface and glycoproteins on extracellular surface Functions: Enzymes, motor proteins, cell-to-cell links, provide support on intracellular surface, and form part of the glycocalyx (carbohydrate rich area on PM surface) Lab 2-Cell, Plasma Memb, Transport

Functions of Membrane Proteins 1.Transport 2.Binding site for chemicals (i.e. hormones) 3. Enzymatic activity 4.Intercellular joining 5.Cell-cell recognition: glycolipids identify your cells as “yours” so foreign cells can be recognized by a lack of a “self” ID tag 105 Lab 2-Cell, Plasma Memb, Transport 6

Membrane Transport Plasma membranes are selectively permeable Some molecules easily pass through the membrane; others do not Types of Membrane Transport Passive processes No cellular energy (ATP) required Substance moves down its concentration gradient Active processes Energy (ATP) required Substances typically move against the concentration gradient 105 Lab 2-Cell, Plasma Memb, Transport 7

Cell Transport Passive Processes occur because of kinetic energy of molecules Substances move down the concentration gradient — from an area of high concentration to an area of lower concentration o Simple diffusion — o movement of solute throughout a solution (solvent) o Facilitated diffusion— o Carrier-mediated-- moves through PM through a carrier protein o Channel-mediated -moves through PM via a water channel Osmosis—movement of the solvent (water) – Filtration Usually across capillary walls 105 Lab 2-Cell, Plasma Memb, Transport 8

Osmosis Movement of solvent (water) across a selectively permeable membrane Water diffuses through plasma membranes down the concentration gradient : Through the lipid bilayer Through water channels called aquaporins (AQPs) Water concentration is determined by solute concentration because solute particles displace water molecules Water moves by osmosis until hydrostatic pressure (back pressure of water on membrane) and osmotic pressure (tendency of water to move into cell by osmosis) equalize osmosis occurs until equilibrium is reached 105 Lab 2-Cell, Plasma Memb, Transport 9

Importance of Osmosis When osmosis occurs, water enters or leaves a cell Change in cell volume disrupts cell function 105 Lab 2-Cell, Plasma Memb, Transport 10

Active Transport Energy to do work comes from splitting the bonds within the ATP molecule OR from the energy formed in the ionic gradient pumps create and used by the splitting of the ATP bonds to move substances – Think of water being pumped uphill by an energy source; as some of the water leaks back downhill, it can carry substances with it; it co-transports substances Examples: – Vesicular transport—endocytosis and exocytosis 105 Lab 2-Cell, Plasma Memb, Transport 11

– Types of Endocytosis: Phagocytosis—cell engulfs a relatively large or solid material i.e. bacteria Pinocytosis—cell engulfs a small amount of extracellular fluid containing dissolved molecules – Allows cell to “taste” extracellular fluids Receptor-mediated endocytosis —plasma membrane proteins which only bind certain substances 105 Lab 2-Cell, Plasma Memb, Transport 12

LAB: TO DO 1. Describe the phospholipid bilayer and how it functions as a semipermeable membrane. 2. Describe process of diffusion and perform diffusion and dialysis experiments. 3. Describe process of osmosis and how it can affect the cell. Perform the osmosis experiment. 4. Describe process of filtration (as it pertains to function of human cells and tissues). Perform filtration experiment Lab 2-Cell, Plasma Memb, Transport