Review of Energetics Intro
Learning Check The First Law of Thermodynamics states that energy can be Created Destroyed Converted All of the above
Learning Check The second law of thermodynamics essentially says: heat is energy motion energy converts to heat energy at the atomic level, motion is continuous entropy increases
Learning Check In an exergonic reaction, the reactants contain less energy than the products the reactants contain more energy than the products catalysis cannot occur substrates outnumber enzymes
Learning Check An endergonic reaction could be described as one that will proceed spontaneously without energy input from the cell not be able to be catalyzed by enzymes produce products that have more energy stored in their bonds than the reactants release energy
Learning Check The synthesis of glucose from carbon dioxide and water. The burning of wood. The release of heat from the breakdown of glucose. Active transport through the membrane The breakdown of glucose Requires Energy Releases Energy
Protein Review
Formation of Macromolecules Made by joining together smaller subunits to make a long repeating chain Monomers à Subunits that serve as building blocks of a polymer (links) Mono = one Polymers à Large molecule made up of monomers linked together (chain) Poly = many monomer + monomer + monomer + monomer + monomer + monomer à polymer
Hydrolysis Dehydration
Protein (also called Polypeptide) Proteins macromolecule consists of C, H, O, N Amino acid protein building block (monomer) Two amino acids = dipeptide Many amino acids = polypeptide (polymer)
Protein Functions Structural Proteins Transport Proteins Keratin (hair and horns) In cell membranes Collagen (connective tissues) Silk in spider webs Storage Proteins Casein in milk Ovalbumin in egg whites Hemoglobin Defense Proteins Antibodies Enzymes Regulate rate of reactions Zein in corn seeds
Amino Acids: Formation of Protein Peptide bonds (covalent) hold amino acids together
Primary Structure unique sequence of amino acids
coils and folds along polypeptide chain caused by hydrogen bonds Secondary Structure
determined by interactions among various R group Tertiary Structure
interaction of two or more polypeptide chains. QUATERNARY STRUCTURE
Protein shape may be influenced by environmental factors Alterations in ph, salt concentration, temperature, or other factors can unravel or denature a protein. Disrupt the hydrogen bonds, ionic bonds, and disulfide bridges that maintain the protein s shape. Also caused by heat disrupts the weak interactions that stabilize conformation.
Learning Check Which of the following could be a function of a protein? speed up biochemical reactions. structure of the cell chemical messenger all of these could be functions of proteins
Learning Check A change in a protein's three-dimensional shape due to disruption of hydrogen bonds is termed hydrolysis condensation renaturation denaturation
Learning Check Do you think peptide bonds are broken when proteins unfold and become denatured?
Enzymes
Enzymes speed up metabolic reactions Spontaneous chemical reactions may occur so slowly as to be imperceptible Example: Sugar (sucrose) in water can sit for years without hydrolysis occurring Sucrase hydrolyzes it in seconds Catalyst: chemical agent that speeds up the rate of a reaction without being consumed by the reaction. Enzyme: a catalytic protein.
What do you notice? Sugar à Sucrose Hydrolysis Reaction Catalyzed by à Sucrase Sugar à Lactose Hydrolysis Reaction Catalyzed by à?
Activation Energy (E A ) Activation energy: amount of energy necessary to push the reactants over an energy barrier so that the reaction can proceed. Key ring example
Enzyme action Enzymes speed reactions by lowering E A. Enzymes do not effect energy change. Can t change exo to endo Enzymes are selective they determine which chemical processes will occur at any time.
Enzymes are substrate specific. Substrate: reactant that an enzyme acts on The enzyme binds to a substrate, or substrates, forming an enzyme-substrate complex. While the enzyme and substrate are bound, the catalytic action of the enzyme converts the substrate to the product or products.
Enzymes are substrate specific. Enzyme + Substrate à Enzyme-substrate Complex à Enzyme + Products Sucrase + Sucrose + H 2 O à Sucrase-Sucrose- H 2 O Complex à Sucrase + Glucose + Fructose
Enzyme specificity The specificity of an enzyme results from its threedimensional shape. Active site of an enzyme is typically a pocket or groove on the surface of the protein into which the substrate fits. The specificity of an enzyme is due to the fit between the active site and the substrate
Induced-fit model for enzyme action Review: Enzymes are? Made up of? Specific Amino Acids at Active Site Substrate enters active site interacts with these amino acids Held in place by weak bonds (h-bonds) Enzymes slightly changes shape, grasping substrate Like a hand shake Induced Fit: brings chemical groups in position to catalyze the reaction.
Enzymes are reusable A single enzyme molecule can catalyze thousands of reactions a second. Enzymes are unaffected by the reaction and are reusable.
Learning Check When an enzyme catalyzes a reaction: It lowers the activation energy of the reaction It raises the activation energy of the reaction It becomes a product It is used once and discarded It acts as a reactant
Learning Check What will happen to the rate at which a chemical reaction proceeds if the activation energy is increased? The reaction rate will not change The reaction will happen slower The reaction will happen faster
Learning Check What are enzymes, substrate, and product?
Learning Check What is the active site of an enzyme?
Learning Check Two substrates lactose and a short protein are shown on the left. Two enzymes are shown on the right, labeled A and B. Which of the two enzymes is lactase?
Learning Check The complete structure of an antibody is shown on the left. The part of the antibody that is circled is the antigen binding site of the antibody. Protein (antigens) from the cell surface of four harmful bacteria (A, B, C, D) are shown on the right. Which of the four will bind more effectively to the antibody?
Learning Check What surface antigen would you expect to see on a bacteria that was effectively destroyed by the antibody?
Learning Check are molecules that bind to an enzyme, which are then converted to
Factors affecting enzyme activity Substrate concentration Temperature ph Cofactors Inhibitors
Substrate Concentration At low substrate concentrations, an increase in substrate concentration speeds binding to available active sites. At high substrate concentrations, the active sites on all enzymes are engaged. The enzyme is saturated. The rate of the reaction is determined by the speed at which the active site can convert substrate to product.
Temperature As temperature increases, collisions between substrates and active sites occur more frequently as molecules move more rapidly. As temperature increases further denaturation may occur Each enzyme has an optimal temperature. Most human enzymes have optimal temperatures of about 35 40 C.
ph Each enzyme also has an optimal ph. Maintenance of the active conformation of the enzyme requires a particular ph. This falls between ph 6 and 8 for most enzymes. However, digestive enzymes in the stomach are designed to work best at ph 2, while those in the intestine have an optimum of ph 8.
Environmental Factors Affecting Enzyme Activity
Learning Check For each statement below indicate if the reaction pathway will proceed faster or slower. More enzymes More substrates More product
Learning Check All of the following statements are true of enzymes except Enzymes function best at a particular ph. Enzyme function is dependent on the threedimensional structure of the enzyme. Most enzymes are proteins. Enzymes increase the amount of activation energy required for a reaction to occur.
Learning Check In the human stomach, proteins are digested by pepsin, an enzyme that requires an acidic ph for its optimal function. Antacids are medications that increase stomach ph. Examples include Alka-Seltzer, Tums, and Rolaids. If a person overuses antacids, how do you think this might affect that person's digestive process?
Learning Check Which of the following curves best represents the activity of a human enzyme as a function of temperature? (The temperature scale is in Fahrenheit; normal body temperature is 98.6 degrees F).
Cofactors Many enzymes require nonprotein helpers, called cofactors, for catalytic activity. Cofactors bind permanently or reversibly to the enzyme. Some inorganic cofactors include zinc, iron, and copper. Organic cofactors are called coenzymes. Many vitamins are coenzymes.
Inhibitors Binding by inhibitors prevents enzymes from catalyzing reactions If inhibitors attach to the enzyme by covalent bonds, inhibition may be irreversible. If inhibitors bind by weak bonds, inhibition may be reversible.
Competitive inhibitors Some reversible inhibitors resemble the substrate and compete for binding to the active site. These molecules are called competitive inhibitors. Competitive inhibition can be overcome by increasing the concentration of the substrate.
Noncompetitive inhibitors Noncompetitive inhibitors impede enzymatic reactions by binding to another part of the molecule. Binding by the inhibitor causes the enzyme to change shape, rendering the active site less effective at catalyzing the reaction. Toxins and poisons are often irreversible enzyme inhibitors.
Feedback inhibition A common method of metabolic control is feedback inhibition in which an early step in a metabolic pathway is switched off by the pathway s final product. The product acts as an inhibitor of an enzyme in the pathway. Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed.
Learning Check What is likely to happen if there is more than enough of some product in an otherwise healthy cell? The pathway producing it will continue doing so at the same rate The pathway producing it will slow down The pathway producing it will speed up
Learning Check The binding of compound C to enzyme E1 in this pathway would be an example of what type of Noncompetitive inhibition Feedback inhibition Competitive inhibition Enzyme modification
Learning Check What would happen to the amount of compound A that is converted to compound C if there was an increase in E 2? It decreases No change It increases
Learning Check An increase of E2 would be what type of regulation? Noncompetitive inhibition Feedback inhibition Competitive inhibition Enzyme availability
Putting it All Together Sort the following terms into two categories. Anabolic/Catabolic Endergonic/Exergonic Increase/Decrease in entropy Delta G>0/G<0 Increase/Decrease in stability Photosynthesis/Respiration ADP Phosphorylation/ATP hydrolysis