The Plasma Membrane – Gateway to the Cell 8/29/2018 The Plasma Membrane – Gateway to the Cell G. Podgorski, Biol. 1010

The Plasma Membrane is Semipermeable 8/29/2018 The Plasma Membrane is Semipermeable The physical properties of phospholipids account for membrane assembly and many of its properties. Small molecules and larger hydrophobic molecules move through. Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. G. Podgorski, Biol. 1010

Plasma Membrane Functions The Plasma Membrane 8/29/2018 Plasma Membrane Functions Maintain a high concentration of materials in the cell. Keep harmful materials out. Control the movement of materials into and out of the cell. Let the cell sense its environment. G. Podgorski, Biol. 1010

Membrane Components Phospholipids Proteins (peripheral and integral) The Plasma Membrane 8/29/2018 Membrane Components Phospholipids Proteins (peripheral and integral) Cholesterol Carbohydrates G. Podgorski, Biol. 1010

Proteins Are Critical to Membrane Function The Plasma Membrane 8/29/2018 Proteins Are Critical to Membrane Function G. Podgorski, Biol. 1010

Transport Processes - Diffusion The Plasma Membrane 8/29/2018 Transport Processes - Diffusion Solutes move down a concentration gradient until they are evenly distributed. This is diffusion. Another way of saying this is that solutes move from a region of higher concentration to a region of lower concentration until there is no difference in concentration. G. Podgorski, Biol. 1010

Three Forms of Transport Across the Membrane The Plasma Membrane Three Forms of Transport Across the Membrane 8/29/2018 G. Podgorski, Biol. 1010

Three Forms of Transport Across the Membrane The Plasma Membrane Three Forms of Transport Across the Membrane 8/29/2018 Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out. G. Podgorski, Biol. 1010

Three Forms of Transport Across the Membrane The Plasma Membrane Three Forms of Transport Across the Membrane 8/29/2018 Examples: Glucose or amino acids moving from blood into a cell. An nerve electrical impulse results from opening protein channels for ions that move by facilitated diffusion. G. Podgorski, Biol. 1010

Three Forms of Transport Across the Membrane The Plasma Membrane Three Forms of Transport Across the Membrane 8/29/2018 Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. G. Podgorski, Biol. 1010

The Plasma Membrane 8/29/2018 Moving the “Big Stuff” Large molecules move in via one of three forms of endocytosis. G. Podgorski, Biol. 1010

Pinocytosis This is the most common form of endocytosis. The Plasma Membrane 8/29/2018 Pinocytosis This is the most common form of endocytosis. Pinocytosis takes up most proteins and other large molecules. G. Podgorski, Biol. 1010

Pinocytosis mature transport vesicle pinocytic vesicles forming The Plasma Membrane 8/29/2018 Pinocytosis mature transport vesicle pinocytic vesicles forming Transport into a capillary cell (blue). G. Podgorski, Biol. 1010

Receptor-Mediated Endocytosis The Plasma Membrane 8/29/2018 Receptor-Mediated Endocytosis Receptor proteins make this a highly specific form of transport. Cholesterol is taken-up this way. G. Podgorski, Biol. 1010

Receptor-Mediated Endocytosis The Plasma Membrane 8/29/2018 Receptor-Mediated Endocytosis G. Podgorski, Biol. 1010

Endocytosis – Phagocytosis Transports Large Particles The Plasma Membrane 8/29/2018 Endocytosis – Phagocytosis Transports Large Particles G. Podgorski, Biol. 1010

In Preparation for Phagocytosis The Plasma Membrane 8/29/2018 In Preparation for Phagocytosis G. Podgorski, Biol. 1010

The Plasma Membrane 8/29/2018 The Threshold of Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) G. Podgorski, Biol. 1010

Moving the “Big Stuff” Exocytosis: moving things out. The Plasma Membrane 8/29/2018 Moving the “Big Stuff” Exocytosis: moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another. G. Podgorski, Biol. 1010

The Plasma Membrane 8/29/2018 Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. G. Podgorski, Biol. 1010

Exocytosis and Nervous System Function The Plasma Membrane 8/29/2018 Exocytosis and Nervous System Function A nerve cell communicates to another cell by releasing chemicals via exocytosis at the synaptic terminal. G. Podgorski, Biol. 1010

Exocytosis and Chemical Communication at the Synapse The Plasma Membrane 8/29/2018 Exocytosis and Chemical Communication at the Synapse The synapse is the region where a nerve cell and its target cell are closely apposed. G. Podgorski, Biol. 1010

Black Widow Spider Venom and Exocytosis The Plasma Membrane 8/29/2018 Black Widow Spider Venom and Exocytosis Black widow spider venom causes massive exocytosis of neurotransmitter into the synapse. G. Podgorski, Biol. 1010

Botulism and Exocytosis The Plasma Membrane 8/29/2018 Botulism and Exocytosis Botulism is caused by botulinim toxin – a protein produced by a bacterium that sometimes contaminates foods. Botulinim toxin blocks exocytosis at the synapse and causes paralysis. Mechanism of botulinum toxin. Mechanism of botulinum toxin web site. G. Podgorski, Biol. 1010

ENZYMES Definition: A protein that speeds up chemical reactions WITHOUT being changed. (catalyst)

Enzymes Speed Biochemical Reactions Energy and Enzymes 8/29/2018 Enzymes Speed Biochemical Reactions Enzymes are biological catalysts – substances that speed a reaction without being altered in the reaction. Most enzymes are proteins, some are RNA. Model of the surface of an enzyme. Enzymes are essential for life. G. Podgorski, Biol. 1010

Enzymes Lower a Reaction’s Activation Energy Energy and Enzymes 8/29/2018 Enzymes Lower a Reaction’s Activation Energy G. Podgorski, Biol. 1010

Energy and Enzymes 8/29/2018 Enzyme Action G. Podgorski, Biol. 1010

The Fit Between Enzyme and Substrate is Critical and Precise Energy and Enzymes The Fit Between Enzyme and Substrate is Critical and Precise 8/29/2018 Hexokinase, an enzyme (blue), binding its substrate, glucose (yellow). G. Podgorski, Biol. 1010

Substrate: Substance acted upon by the enzyme. ENZYMES Substrate: Substance acted upon by the enzyme.

Products: substances resulting from enzyme action. ENZYMES Products: substances resulting from enzyme action.

Substrate(s) + Enzymes Product(s)

Enzymes Lock and Key – Enzymes are like a key that can ONLY fit a certain lock or substrate.

Enzymes Active site – site on an enzyme molecule directly responsible for the chemical change.

Many Enzymes Work by Altering the Shape of Their Substrates Energy and Enzymes 8/29/2018 Many Enzymes Work by Altering the Shape of Their Substrates The active site of an enzyme is where substrate is bound. G. Podgorski, Biol. 1010

The “Nature of Life” – Coupling Favorable to Unfavorable Reactions Energy and Enzymes 8/29/2018 The “Nature of Life” – Coupling Favorable to Unfavorable Reactions G. Podgorski, Biol. 1010

ATP - Life’s Energy Currency Energy and Enzymes 8/29/2018 ATP - Life’s Energy Currency Energy is released when ATP is hydrolyzed (broken down) to ADP. ATP is restored from ADP and an input of energy. ATP’s energy is used to drive endergonic (energy-requiring) reactions. G. Podgorski, Biol. 1010