Animal PhysiologyChapter 2

Chapter 2 Opener Two slow-moving predators that use molecular weapons to capture fast-moving prey

Four Topics in Chapter 2

1. Cell membranes and intracellular membranes2. Epithelia-the sheets of tissue that line body

cavities and form the outer surfaces of organs

3. Enzyme function, diversity and evolution4. Mechanisms by which cells receive and act

on signals

Cell membranes and intracellular membranes

Figure 2.1 The structure of a cell membrane

Terminology

• Polar – electrons are unevenly distributed• Nonpolar – electrons are evenly distributed,

no charge imbalance• Amphipathic-each molecule consists of a

polar part and a nonpolar part (head group of phospholipid)

• Leaflets – two layers of the membrane

Figure 2.2 The structure of membrane phospholipid molecules

Figure 2.2 The structure of membrane phospholipid molecules

Membrane Fluidity

• RBC’s have >150 kinds of phospholipids• Phospholipids can travel (by diffusion) around

the whole cell in a matter of minutes• Temperature: lowerlower fluidity• Fluidity depends on chemical saturation of the

hydrocarbons in the tails– Saturated-non double bonds– Unsaturated – one or more double bonds, creates

bends higher fluidity

Figure 2.3 The degree of chemical unsaturation of the hydrocarbon tails of brain phospholipids in fish varies with habitat temperature

Arctic fish have high levels of unsaturated

phospholipids

Proteins Endow Membranes with Numerous Functional

Capacities

Two structural designations for membrane proteins

1. Integral – parts of the membrane, can’t be removed, usually transmembrane (span the

whole membrane)2. Periperal – can be removed, bonded

noncovalently to membrane components, on one side of the membrane or the other

Five functional designations for membrane proteins

Fluid Mosaic Model of Membranes

A membrane consists of a mosaic of protein and lipid molecules, all of which move about in directions parallel to the membrane faces

because of the fluid state of the lipid matrix

Box Extension 2.1 Figure A The structural hierarchy of proteins

Box Extension 2.1 Figure B Three ways to diagram the tertiary structure of one protein. All three diagrams represent lysozyme

Box Extension 2.1 Figure C Types of weak, noncovalent bonds that are important in protein structure

Figure 2.4 The structure of a transmembrane protein—a voltage-gated Na+ channel—illustratingseveral modes of presentation

Four Topics in Chapter 2

1. Cell membranes and intracellular membranes2. Epithelia-the sheets of tissue that line body

cavities and form the outer surfaces of organs

3. Enzyme function, diversity and evolution4. Mechanisms by which cells receive and act

on signals

• Epithelia compartmentalize the body by forming boundaries between body regions

• Also form a boundary between an animal and its external environment

Figure 2.5 Simple epithelia-single layer of cells (squamous, cuboidal, columnar)

Figure 2.6 Tubules and follicles formed by simple epithelia (Part 1)

Figure 2.6 Tubules and follicles formed by simple epithelia (Part 2)

The cuboidal cells of this epithelium

display two signature

properties of high metabolic activity:

microvilli on the apical surfaces and

abundant mitochondria

Figure 2.6 Tubules and follicles formed by simple epithelia (Part 3)

Squamous cells (no microvilli), can’t see all nuclei in a

cross section since cells are quite long

Figure 2.7 Types of junctions between cells

Figure 2.8 The organization of epithelial cells into apical and basolateral regions

Figure 2.9 Transcellular and paracellular paths across an epithelium

Four Topics in Chapter 2

1. Cell membranes and intracellular membranes2. Epithelia-the sheets of tissue that line body

cavities and form the outer surfaces of organs

3. Enzyme function, diversity and evolution4. Mechanisms by which cells receive and act

on signals

Metabolism

• The set of processes by which cells and organisms acquire, rearrange and void commodities in ways that sustain life.

• Can be described by commodities – nitrogen metabolism

• Or energy metabolism-how energy is acquired, transformed, channeled and dissipated.

• Mediated by enzymes

Metabolism-type of transformation

• Catabolism-complex chemical compounds are broken down to release energy, create smaller building blocks or prepare chemical constituents for elimination

• Anabolism – synthesize larger or more complex chemical compounds from smaller building blocks

Figure 2.10 Two amphibians with different jumping capabilities based in part on different levels of a

key enzyme, lactate dehydrogenase

Amphibians can’t make a lot of ATP by aerobic mechanisms due to simple lungs. LDH lets the frog use anaerobic mechanisms

Figure 2.11 The reaction catalyzed by lactate dehydrogenase (LDH)

Substrate Product

Cofactor

Enzyme Catalysis

E + S ↔ E-S complex ↔ E-P complex ↔ E + P

Kinetics

• Kinetics: velocity properties of rxns• Saturation kinetics: limited to a maximum

velocity because of a limited supply of a molecule (enzyme)– Hyperbolic (Michaelis-Menten): enzyme has one

substrate binding site or multiple sites that behave independently

– Sigmoid: Multiple substrate binding sites that influence each other

Figure 2.12 Reaction velocity as a function of substrate concentration

V= Vmax [S][S] + Km

V: velocity[S]: substrate conc.Vmax: max velocityKm: Michaelis constant

Figure 2.12 Reaction velocity as a function of substrate concentration

Catalytic Effectiveness of an Enzyme

• Kcat: turnover number – number of substrate molecules converted to product per second by each enzyme molecule when saturated

• Depends partly on activation energy– Substrate must pass through a transition state to form a product– Must gain energy by random collisions with other molecules– Enzymes lower activation energy– Also depends on how fast an enzyme can go through its

conformational change

Figure 2.13 Enzymes accelerate reactions by lowering the needed activation energy

Enzyme-substrate affinity affects the reaction velocity

The enzyme and substrate might bounce apart when they collide or form the necessary

complex (enzyme-substrate affinity)

Figure 2.14 The approach to saturation depends on enzyme–substrate affinity

Figure 2.14 The approach to saturation depends on enzyme–substrate affinity

Michaelis constant Km=1/2Vmax:

[substrate] required to attain one-half of

the maximal reaction velocity

Low affinity=higher Km

Reaction Velocities in Cells Therefore Depend On:

1. Number of active enzymes present2. Catalytic effectiveness of each enzyme

3. Affinity of enzyme for its substrate

Molecular flexibility is important for enzyme function

Active Site for

substrate binding

Ligand: any molecule that binds an enzyme (substrate or nonsubstrate)

Cooperativity

Positive cooperativity: ligand binding at one site facilitates the binding of other

sites on the same molecule

Negative cooperativity: binding at one site inhibits binding at other sites on the same

molecule

Cooperativity continued

Homotropic cooperativity: the binding of a ligand facilitates or inhibits binding of

other molecules of the same ligand to the same enzyme molecule

Heterotropic cooperativity: the binding of one type of ligand to an enzyme molecule

influences the binding of other types of ligands

Cooperativity continued

• Allosteric modulation: the modulation of catalytic properties of an enzyme by

the binding of nonsubstrate ligands (allosteric to regulatory/allosteric sites

Cooperativity continued

• Allosteric activation: the binding of an allosteric modulator increases the affinity

of the active site for its substrate or increase catalytic activity of the enzyme

• Allosteric inhibition: the binding of an allosteric modulator impairs catalytic

activity of an enzyme