IB Bio Test 3.6 7.6

Metabolic Pathways consist of chains and cycles of enzyme-catalyzed reactions

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Explain that enzymes lower the activation energy of the chemical reactions that they catalyze

All reactions require some energy to get started which is called activation energy. Enzymes are protein catalysts that speed up chemical reactions by lowering the amount of energy needed. They do this by putting the reactants in the correct orientation to react and by helping break the reactant bonds. Once the reactant bonds are broken, the reactant can proceed quickly.

State four functions of proteins, giving a named example of each.

Antibodies are defensive proteins Hemoglobin is a transport protein Keratin is a structural protein Casein is a storage protein

Outline how enzymes catalyze biochemical reactions

Bring substrates close together in active site, forms enzyme-substrate complex, substrates bind to active site, lowers activation energy for the reaction, weakens bonds in substrate.

Explain the difference between competitive and non-competitive inhibition

Competitive Inhibition: An inhibiting molecule that is structurally similar to the substrate molecule will bind to the active site, preventing the substrate from entering the active site. If you increase substrate concentration, the substrates can kick out the competitive inhibitor. Non-Competitive Inhibition: An inhibiting molecule attaches to the allosteric site on the enzyme. This causes a shape change in the active site which blocks the substrate. An increase in substrate concentration has no effect on non-competitive inhibitors.

Define Denaturation

Denaturation is a structural change in a protein that results in the loss(usually permanent) of its biological properties(function).

Explain Enzyme-Substrate specificity

Enzyme-Substrate specificity means, the active site has a particular shape and chemical makeup that matches its substrate(s). The active site of an enzyme binds to a specific substrate. The shape of the active site and substrate fit each other. The lock and key fit means only the correct shapes will fit together.

Define Enzyme

Enzymes are protein catalysts that speed up chemical reactions by lowering the amount of activation energy needed.

State why each step in a biochemical pathway often require a separate enzyme

Enzymes are specific for their substrate, lock and key fit, the energy requirements for reactions with substrates vary, each step of the pathway is unique.

Explain effects of temperature, pH, and substrate concentration on enzyme activity.

Enzymes have an active site that fits precisely, change in environment can lead to shape change. Increasing temp. will increase the rate of reaction until the optimal temp. is reached. After that, the rate will decrease quickly until the enzyme denatures. Increasing temp. can increase molecular motion leading to disruption of intermolecular interactions. The maximum rate is at the optimal pH.The rate increases as you go toward the optimal pH and decreases as you go away from the optimal pH. If the pH is too high or low the enzyme will denature. The optimal pH is where the enzyme will work the fastest. As substrate concentration increases the number of enzyme -substrate complexes formed increases.

Outline the difference between fibrous and globular proteins

Fibrous proteins: long, narrow, coiled chains. Usually insoluble in water, have repeated amino acid sequence, often form structural elements for the cell. Globular proteins: Compact and round. Usually soluble in water, have irregular amino acid sequences, metabolic, often enzymes or hormones.

Induced Fit

Induced fit means an enzyme changes shape of enzymes active site slightly as the substrate binds, which allows for a perfect fit. The induce fit brings the amino acid side chains into the right position to catalyze the reaction. It is also accountable for the ability of several enzymes to bind to several substrates.

Explain the use of lactose in the production of lactose-free milk

Lactose is the sugar found in milk. Lactase is the enzyme that breaks down lactose. In order to help lactose intolerant people, milk products are treated with lactase before consumption.

Explain the control of metabolic pathways by end-product inhibition, including the role of allosteric sites

The end product of the last reaction of the metabolic pathway will bind to the allosteric site. When it binds, it acts as a non-competitive inhibitor and changes the shape of the active site. Metabolic pathways need to be controlled so the cell doesn't make excess materials. The final product is the inhibitor for one of the enzymes earlier in the pathway.

Explain the four levels of protein structure, indicating the significance of each level

The primary structure(1 ) is an amino acid sequence. Determines the type/function of the other structures. Secondary structure(2 ) are specific shapes that form in small sections of the amino acid sequence as it folds. These shapes are held together by H-bonds between side chains. Includes Beta sheets and alpha helix's. Tertiary structure(3 ) , the polypeptide continues to fold up into its final shape, but is only functional in this shape. Proteins are held in this shape by H-bonds, hydrophobic/hydrophilic interactions, disulfide bridges, and ionic bonds. Quaternary structure(4 ) takes several polypeptides to form the final protein. Sometimes proteins require the binding of a prosthetic group.

Define Active Site

The site to which substrate(s) bind, the site on the enzyme where it catalyzes a chemical reaction.

Explain the significance of polar and non-polar amino acids.

When a protein forms its tertiary structure, the polar and non-polar amino acids may be very important to the proteins function. A protein with non-polar amino acids on the outside may be a protein bound in a phospholipid membrane.