Cell membranes are gatekeepers. Every cell is bordered by a plasma membrane. 2

5.1 The Nature of the Plasma Membrane

Plasma membranes are complex structures They perform several critical functions. take in food & nutrients dispose of waste products build & export molecules regulate heat exchange regulate flow of materials in & out of cell 4

hydrophilic = water loving hydrophobic = water fearing Spilt Personalities…

The Plasma Membrane is a “Fluid Mosaic” Molecules embedded within the plasma membrane help it perform its functions. Membrane contains: Carbohydrates glycocalyx cell adhesion & binding Lipids cholesterol flexibility Proteins peripheral or integral The Plasma Membrane is a “Fluid Mosaic” 6

The Plasma Membrane glycocalyx phospholipids cholesterol proteins cell exterior cytoskeleton integral protein cell interior peripheral protein Phospholipid bilayer: a double layer of phospholipid molecules whose hydrophilic “heads” face outward, and whose hydrophobic “tails” point inward, toward each other. Cholesterol molecules that act as a patching substance and that help the cell maintain an optimal level of fluidity. Proteins, which are integral, meaning bound to the hydrophobic interior of the membrane, or peripheral, meaning not bound in this way. Glycocalyx: sugar chains that attach to proteins and phospholipids, serving as protein binding sites and as cell lubrication and adhesion molecules. Figure 5.1

Proteins (a) Structural support (b) Recognition (c) Communication (d) Transport cell exterior cell interior Membrane proteins can provide structural support, often when attached to parts of the cell’s scaffolding or “cytoskeleton.” Protein fragments held within recognition proteins can serve to identify the cell as “normal” or “infected” to immune system cells. Receptor proteins, protruding out from the plasma membrane, can be the point of contact for signals sent to the cell via traveling molecules, such as hormones. Proteins can serve as channels through which materials can pass in and out of the cell. Figure 5.3

The Plasma Membrane is a “Fluid Mosaic” of molecules Phospholipid bilayer Carbohydrates Lipids Proteins

Facilitated Diffusion Movement of Molecules Active Transport Primary Secondary Passive Transport Diffusion Osmosis Simple Diffusion Facilitated Diffusion

http://youtu.be/dPKvHrD1eS4 Crash Course

5.2 Diffusion, Gradients, and Osmosis

Facilitated Diffusion Movement of Molecules Active Transport Primary Secondary Passive Transport Diffusion Osmosis Simple Diffusion Facilitated Diffusion

Passive transport is the spontaneous movement of molecules across a membrane. 2 types: Diffusion – molecules move from an area of high concentration to an area of low concentration. 14

Diffusion, Gradients, & Osmosis Concentration gradient: difference btwn highest & lowest concentrations of a solute within a given medium. - In diffusion, compounds naturally move from high to low (down their concentration gradients) - Energy not needed High Low

Diffusion, Gradients, and Osmosis (a) Dye is dropped in. (b) Diffusion begins. (c) Dye is evenly distributed. water molecules dye molecules Figure 5.4

Diffusion, Gradients, and Osmosis Osmosis - net movement of water across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration Semipermeable - some compounds pass freely while others are blocked

2. Osmosis – diffusion of water molecules Cell will swell Cell will shrivel 18

Facilitated Diffusion Movement of Molecules Active Transport Primary Secondary Passive Transport Diffusion Osmosis Simple Diffusion Facilitated Diffusion

5.3 Moving Smaller Substances In and Out

Simple Diffusion vs Facilitated Diffusion Neither one requires Energy! Simple Diffusion – small molecules pass through membrane easily. Facilitated Diffusion – requires both a concentration gradient and a protein channel 21

ATP Passive transport Active transport simple diffusion facilitated diffusion ATP Materials move down their concentration gradient through the phospholipid bilayer. The passage of materials is aided both by a concentration gradient and by a transport protein. Molecules again move through a transport protein, but now energy must be expended to move them against their concentration gradient. Figure 5.7

Facilitated Diffusion - transport proteins work as channels for larger hydrophilic substances (b/c of size & electrical charge, can’t diffuse through the hydrophobic portion) cell exterior glucose plasma membrane cell interior 1.Transport protein has binding site for glucose open to the outside of the cell. 2. Glucose binds 4. Glucose passes into the cell & protein returns to its original shape. 3. This binding causes the protein to change shape, exposing glucose to the inside of the cell. Figure 5.8

Facilitated Diffusion Movement of Molecules Active Transport Primary Secondary Passive Transport Diffusion Osmosis Simple Diffusion Facilitated Diffusion

ATP Passive transport Active transport simple diffusion facilitated diffusion ATP Materials move down their concentration gradient through the phospholipid bilayer. The passage of materials is aided both by a concentration gradient and by a transport protein. Molecules again move through a transport protein, but now energy must be expended to move them against their concentration gradient. Figure 5.7

Active transport - cells use energy to move small molecules. Molecules can’t always move freely in and out of cells Some molecules need to maintain a high concentration – move against the gradient – membrane proteins act like motorized revolving doors 26

Active Transport example Cells surrounding Stomach H+ moving Against Concentration Gradient Inside Stomach 27

5.4 Moving Larger Substances In and Out

Moving Larger Substances In and Out Endocytosis Exocytosis Both mechanisms use vesicles the membrane-lined enclosures that alternately bud off from membranes or fuse with them

Exocytosis extracellular fluid protein plasma membrane transport vesicle cytosol a transport vesicle moves from the inside of the cell to the plasma membrane fuses with plasma membrane the contents of the vesicle are released Figure 5.10

Endocytosis There are two principal forms of endocytosis: pinocytosis and phagocytosis. http://www.buzzle.com/img/articleImages/609792-142329-45.jpg

Pinocytosis movement of moderate-sized molecules into a cell transport vesicles produced through infolding or “invagination” clathrin-mediated endocytosis (CME): cell-surface receptors bind to molecules - the protein clathrin becomes a vesicle

Phagocytosis Certain cells use pseudopodia or “false feet” to surround and engulf whole cells, fragments of them, or other large organic materials.

6.1 Energy Is Central to Life

Energy Conversions All life depends on capturing energy from the sun and converting it into a form that living organisms can use. Two key processes Photosynthesis Cellular respiration

6.2 The Nature of Energy

What is energy? The capacity to do work Work Moving matter against an opposing force

Energy has two forms. The energy of moving objects Heat energy Light energy

Potential Energy A capacity to do work that results from the location or position of an object Concentration gradients and potential energy Food, chemical energy, has potential energy

Energy Conversions Only ~1% of energy released by the sun that earth receives is captured and converted by plants. Converted into chemical bond energy What happens to the other 99%? reflected back into space (~30%) absorbed by land, oceans, & atmosphere (~70%), Mostly transformed into heat

The study of the transformation of energy from one type to another Thermodynamics The study of the transformation of energy from one type to another First Law of Thermodynamics Energy can never be created or destroyed. It can only change from one form to another. Second Law of Thermodynamics Every conversion of energy includes the transformation of some energy into heat. Heat is almost completely useless to living organisms.

Energy Tax! Every time energy is converted from one form to another the conversion isn’t perfectly efficient. Some of the energy is always converted to the least usable form of kinetic energy: heat.