BIOCHEM
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Questions and Answers

What are enzymes?

Biological catalysts that speed up the rate of biochemical reactions

What is the region that binds substrates, cofactors and prosthetic groups in enzymes called?

Active site

Most enzymes are 3D globular proteins.

True

What are the two parts of the active site?

<p>Binding site and catalytic site</p> Signup and view all the answers

What is the function of a co-factor?

<p>Carries out chemical reactions that cannot be performed by standard 20 amino acids.</p> Signup and view all the answers

Which of these is NOT a characteristic of enzymes?

<p>Affect the nature and properties of end products</p> Signup and view all the answers

What is turnover number in relation to enzymes?

<p>Number of substrate transformed per minute, by one enzyme</p> Signup and view all the answers

Match the following enzyme classes with their reaction types:

<p>Oxidoreductases = Reduction-oxidation (redox) Transferases = Move chemical group Hydrolases = Hydrolysis, bond cleavage with transfer of functional group of water Lysases = Non-hydrolytic bond cleavage Isomerases = Intramolecular group transfer (isomerization) Ligases = Synthesis of new covalent bond between substrates using ATP hydrolysis</p> Signup and view all the answers

What are the two perspectives on how enzymes function?

<p>Thermodynamic changes and processes of the active site</p> Signup and view all the answers

Which of these is NOT one of the ways enzymes catalyze reactions?

<p>Transitional state</p> Signup and view all the answers

The lock-and-key model by Emil Fischer accurately depicts the dynamic nature of enzyme-substrate interactions.

<p>False</p> Signup and view all the answers

What is the study of the rate of enzyme-catalyzed reactions called?

<p>Enzyme kinetics</p> Signup and view all the answers

What are the three main factors that affect the rate of enzyme-catalyzed reactions?

<p>Temperature, hydrogen ion concentration (pH), and substrate concentration</p> Signup and view all the answers

What is inhibition in the context of enzymes?

<p>Prevention of an enzyme process as a result of interaction of inhibitors with the enzyme.</p> Signup and view all the answers

Which type of inhibition involves a molecule competing with the substrate for the active site?

<p>Competitive inhibition</p> Signup and view all the answers

What type of inhibition involves the covalent attachment of an inhibitor to the enzyme, completely eliminating its catalytic activity?

<p>Irreversible inhibition</p> Signup and view all the answers

Which of these is NOT a way enzymes can be activated?

<p>Activation by temperature increase</p> Signup and view all the answers

Pepsin is an example of an enzyme activated by proteolytic cleavage.

<p>True</p> Signup and view all the answers

What are the four main types of enzymes specificity?

<p>Bond specificity, group specificity, substrate specificity, and optical/stereo-specificity</p> Signup and view all the answers

Enzymes can function on multiple substrates with different reaction types.

<p>False</p> Signup and view all the answers

What is the common backbone structure of lipids?

<p>Glycerol</p> Signup and view all the answers

What is the basic structural unit of lipids that contains a carboxylic acid group?

<p>Fatty acid</p> Signup and view all the answers

Which of these is NOT a characteristic of saturated fatty acids?

<p>Low melting points</p> Signup and view all the answers

What are triacylglycerols?

<p>Storage form of fatty acids in organisms, typically found as fats or oils</p> Signup and view all the answers

Which of these is NOT a function of triglycerides?

<p>Structural component of cell membranes</p> Signup and view all the answers

What are complex lipids?

<p>Lipids containing additional components besides fatty acids and alcohol, such as proteins, carbohydrates, phosphates, sulfates, and nitrogen</p> Signup and view all the answers

What are the main functions of phospholipids?

<p>Structural and regulatory functions in cell membranes as well as absorption of fats and transport of lipids</p> Signup and view all the answers

Glycolipids are made up of fatty acids, an alcohol, and some carbohydrates.

<p>True</p> Signup and view all the answers

What are lipoproteins?

<p>Lipids combined with specific proteins, crucial for the transport of lipids around the body</p> Signup and view all the answers

Steroids are lipids containing a steroid nucleus, which consists of four fused rings.

<p>True</p> Signup and view all the answers

Cholesterol is the most common steroid in the body.

<p>True</p> Signup and view all the answers

What are the major reactions that lipids undergo?

<p>Hydrolysis, saponification, hydrogenation, iodination, and oxidation</p> Signup and view all the answers

What is the main function of lipids in terms of energy?

<p>Serving as a storage form of energy in the body</p> Signup and view all the answers

Cholesterol plays a role in stabilizing the fluidity of cell membranes.

<p>True</p> Signup and view all the answers

Which of these is NOT a type of membrane protein?

<p>Surface proteins</p> Signup and view all the answers

What are the two main types of membrane transport?

<p>Passive and active transport</p> Signup and view all the answers

Simple diffusion is a type of active transport.

<p>False</p> Signup and view all the answers

What are the two main categories of vitamins?

<p>Fat-soluble and water-soluble vitamins</p> Signup and view all the answers

Vitamin A is important for vision.

<p>True</p> Signup and view all the answers

What is the primary role of vitamin D in the body?

<p>Regulating calcium and phosphorus metabolism</p> Signup and view all the answers

What are the main functions of prostaglandins?

<p>Signaling molecules involved in various physiological processes, including inflammation, pain, and blood clotting</p> Signup and view all the answers

What is the primary role of leukotrienes?

<p>Signaling molecules involved in inflammation and immune responses</p> Signup and view all the answers

What is a carbohydrate?

<p>A polyhydroxyaldehyde, a polyhydroxyketone, or a substance that gives these compounds on hydrolysis</p> Signup and view all the answers

A monosaccharide can be hydrolyzed into a simpler carbohydrate.

<p>False</p> Signup and view all the answers

An aldose is a monosaccharide with an aldehyde functional group.

<p>True</p> Signup and view all the answers

What are the simplest monosaccharides?

<p>Trioses with three carbon atoms</p> Signup and view all the answers

How is the configuration of a monosaccharide determined in the Fischer projection?

<p>The position of the hydroxyl group (-OH) on the penultimate carbon atom</p> Signup and view all the answers

Epimers are stereoisomers that differ in the position of the hydroxyl group on only ONE chiral center.

<p>True</p> Signup and view all the answers

Enantiomers are mirror images of each other.

<p>True</p> Signup and view all the answers

Diastereomers are stereoisomers that are NOT mirror images of each other.

<p>True</p> Signup and view all the answers

What happens when a sugar forms a cyclic molecule?

<p>The carbonyl group reacts with a hydroxyl group on a distant carbon atom, forming either a hemiacetal or hemiketal.</p> Signup and view all the answers

The anomeric carbon is a new chiral center in a cyclic sugar.

<p>True</p> Signup and view all the answers

Haworth projections represent cyclic hemiacetals or hemiketals as planar pentagons or hexagons.

<p>True</p> Signup and view all the answers

A pyranose is a six-membered ring, while a furanose is a five-membered ring.

<p>True</p> Signup and view all the answers

In Haworth projections, an alpha anomer has the hydroxyl group on the anomeric carbon pointing up (above the plane of the ring), while a beta anomer has it pointing down (below the plane of the ring).

<p>False</p> Signup and view all the answers

Study Notes

Enzymes

  • Biological catalysts that speed up biochemical reactions.
  • Most are 3-dimensional globular proteins.
  • Some RNA molecules also act as enzymes (Ribozymes).

Enzyme Structure

  • Active site: Region that binds substrates, co-factors, and prosthetic groups.
    • Contains residues that help hold the substrate.
    • Has a specific shape due to the tertiary structure of the protein.
    • Divided into:
      • Binding site: Selects and binds the substrate.
      • Catalytic site: Performs the catalytic action of the enzyme.
  • Co-factors: Non-protein molecules essential for some chemical reactions.
    • Cannot be performed by standard 20 amino acids.
    • Activate the protein.

Types of Cofactors

  • Inorganic cofactors: Inorganic molecules needed for enzyme activity.
    • Example: Mg in Hexokinase.
  • Organic cofactors: Organic molecules needed for enzyme activity.
    • Prosthetic groups: Tightly bound organic cofactors.
      • Example: Flavins, heme group, biotin.
    • Coenzymes: Loosely bound organic cofactors.
      • Example: NAD+

Holoenzymes/Holoproteins

  • Complete enzymes, with the co-factor bonded.

Substrate

  • Reactant in a biochemical reaction.
  • Forms an enzyme-substrate complex when it binds to an enzyme.

NAD and NADH

  • NADH: Reduced form (gained electrons)
  • NAD: Oxidized form (lost electrons)

Enzyme Synthesis

  • Synthesized by ribosomes attached to the endoplasmic reticulum.
  • DNA carries information for enzyme synthesis.
  • Some enzymes are intracellular (used within the cell itself).
  • Some enzymes are extracellular (secreted for use outside the cell).
    • Example: Pancreatic digestive enzymes.

Enzyme Characteristics

  • Speed up reactions.
  • Do not alter the nature or properties of end products.
  • Highly specific.
  • Sensitive to changes.
  • Have a turnover number, which represents the number of substrate transformed per minute by one enzyme.
    • Example: Catalase turnover number = 6 x 10^7 /min.

Enzyme Nomenclature

  • Enzymes are classified by the International Enzyme Commission.
  • Classified based on the reaction type.

Enzyme Action Mechanism

  • Thermodynamic changes: Chemical reactions have energy barriers.
    • The difference between the transition state and substrate is the activation barrier.
  • Active site processes: Enzymes facilitate reactions differently.
    • Covalent catalysis: Covalent linkages form between the enzyme and substrate. The enzyme is released unaltered after the reaction.
    • Acid-base catalysis: Histidine residues often participate as both a proton donor and acceptor.
    • Catalysis by proximity: Enzymes bring molecules close together so reactions can occur faster.
    • Catalysis by bond strain: Causes reorientation, and the bond between substrate is broken into product.

Enzyme Kinetics and Inhibition

  • Enzyme kinetics: Studies the rate of enzyme-catalyzed reactions.
  • Factors that affect enzyme reaction rates:
    • Temperature
    • pH
    • Substrate concentration
  • Inhibition: Prevention of an enzyme process due to interactions with inhibitors.
    • Reversible: Inhibitor associates and dissociates from the binding site. Some subtypes include:
      • Competitive: Inhibitors compete with the substrate for the active site.
      • Uncompetitive: Inhibitors bind to another site on the enzyme.
      • Mixed: Inhibitors bind to either the enzyme or the enzyme–substrate complex
      • Non-competitive: Inhibitor has equal affinity for the enzyme and the enzyme–substrate complex.
    • Irreversible: Inhibitor forms a covalent bond with the enzyme, permanently inhibiting its activity.

Enzyme Activation

  • Enzyme activation: Conversion of an inactive form of an enzyme to an active form to process metabolic activity.
    • Types:
      • Activation by cofactors: Often a non-protein (inorganic or organic) molecule.
      • Conversion of an enzyme precursor (inactive form of an enzyme): Zymogen is converted to an active enzyme through a proteolytic cleavage process, such as enteropeptidase acting on trypsinogen to produce trypsin.

Enzyme Specificity

  • Enzymes are highly specific, interacting with one, or very few types of substrates.
    • Bond specificity: Enzyme acts on similar substrates (e.g., with a 1,4-glycosidic bond)
    • Group specificity: Enzyme is specific to the surrounding structure.
    • Substrate specificity: Enzyme acts on only one substrate.
    • Optical/stereo-specificity: Enzyme is specific for optical configuration(e.g., D-amino acid oxidase).
    • Dual specificity: Enzyme acts on one substrate via two reactions (e.g. isocitrate dehydrogenase).

Lipids

  • Diverse group of chemicals, including fats and oily substances.
  • Hydrophobic (water-repelling).
  • Amphipathic : polar (water-loving) and nonpolar (water-repelling) regions
  • Backbones include glycerol (C3H8O3).
  • Classes include:
    • Simple lipids: Esters of fatty acids with alcohols.
      • Fats: Solid at room temperature; rich in saturated fatty acids.
      • Oils: Liquid at room temperature; rich in unsaturated fatty acids.
      • Waxes: Esters of long-chain fatty acids and long-chain alcohols.
    • Complex lipids: Lipids containing other components in addition to fatty acids and alcohols.
      • Phospholipids: Include phosphoric acid and nitrogenous bases and are major components of cell membranes.
      • Glycolipids: Have carbohydrates attached and are part of many cell membranes.
      • Lipoproteins: Conjugates of lipids and proteins that transport lipids in blood.
    • Derived lipids: Obtained by hydrolysis of other lipids
      • Fatty acids
      • Steroid
      • Cholesterol - common steroid building block.

Carbohydrates

  • Polyhydroxyaldehydes or polyhydroxyketones.
    • Can be broken down (hydrolyzed) into simple sugars.
      • Monosaccharides: Simplest sugars that can't be hydrolyzed further.
        • Aldoses: Have an aldehyde group (e.g., glucose).
        • Ketoses: Have a ketone group (e.g., fructose).
        • Trioses: Simplest monosaccharides (e.g., glyceraldehyde).
        • Examples of monosaccharides: glucose, fructose, ribose.
      • Disaccharides: Two monosaccharides joined together (e.g., sucrose).
      • Oligosaccharides: Three to ten monosaccharides joined together.
      • Polysaccharides: Many monosaccharides joined together (e.g., starch, glycogen).

Nucleic Acids

  • Biopolymers containing three types of monomer units:
    • Bases (derived from purines or pyrimidines)
    • Monosaccharides (pentose, typically deoxyribose in DNA)
    • Phosphate groups. Nucleotides are monomers of nucleic acids.

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