Enzyme Regulation and Catalytic Mechanisms

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Questions and Answers

What is the primary functional role of hyaluronic acid in cartilage?

To form rigid structures

To transport nutrients across cell membranes

To provide lubrication and hydration (correct)

To serve as a water-soluble hormone

What distinguishes the cell wall structure of gram-positive bacteria from gram-negative bacteria?

Incorporation of glycolipids in the structure

A higher concentration of lipopolysaccharides

Absence of peptidoglycan components

Presence of thicker peptidoglycan layers (correct)

Which statement accurately describes peptidoglycans?

They consist of heteroglycans linked to small peptides (correct)

They are solely composed of amino acids

They possess a uniform structure across all bacterial species

They lack carbohydrate components

What is the effect of penicillin on bacterial cells?

It irreversibly inhibits bacterial cell wall synthesis Signup and view all the answers

How are glycoproteins primarily structured in relation to proteins?

They include oligosaccharides covalently linked to proteins Signup and view all the answers

What is the correct term for the stereoisomers that differ at one chiral center?

Epimers Signup and view all the answers

In monosaccharides, which configuration is predominantly used by living cells?

D-sugars Signup and view all the answers

How many possible stereoisomers exist for a monosaccharide with 3 chiral carbons?

6 Signup and view all the answers

Which hemiketal or hemiacetal is unstable when formed between two different molecules?

Intermolecular hemiacetal Signup and view all the answers

What configuration does -OH stick to in the Haworth projection of an alpha-sugar?

Sticks downwards Signup and view all the answers

Which sugar structure can be classified as pyranose?

Alpha-D-Glucopyranose Signup and view all the answers

What distinguishes enantiomers from other stereoisomers?

They differ at every chiral center Signup and view all the answers

What is the process by which an aldehyde or ketone reacts with an alcohol group in monosaccharides called?

Cyclization Signup and view all the answers

What is the correct description of a diastereomer?

They differ in configuration at multiple chiral centers Signup and view all the answers

What bond formation occurs when a cyclic hemiacetal constantly reverts to an open configuration?

Anomeric bond Signup and view all the answers

What is true regarding the structure of maltose?

Maltose is a hexose disaccharide formed from two glucose units. Signup and view all the answers

Which characteristic is associated with sucrose?

Sucrose is commonly found in sugar cane and sugar beets. Signup and view all the answers

What function do starch and glycogen primarily serve in living organisms?

They act primarily as energy storage molecules. Signup and view all the answers

What role does cellulose play in plants?

Cellulose provides rigidity and structure to the plant cell wall. Signup and view all the answers

Which property describes lactose?

Lactose is a disaccharide that is hydrolyzed by lactase. Signup and view all the answers

Which statement regarding chitin is accurate?

Chitin provides structural support in the exoskeletons of arthropods. Signup and view all the answers

What distinguishes the function of starch from that of cellulose?

Starch provides energy storage, whereas cellulose provides structural integrity. Signup and view all the answers

In terms of energy utilization, how do glycogen and starch differ?

Glycogen is primarily found in animals while starch is found in plants. Signup and view all the answers

What type of glycosidic bond connects the two glucose molecules in maltose?

Alpha(1,4) Signup and view all the answers

Which of the following describes sucrose?

It consists of glucose and fructose with an alpha,beta (1,2) linkage. Signup and view all the answers

What is the primary function of glycogen in animals?

Acting as a storage form of glucose. Signup and view all the answers

How are cellulose and chitin structurally similar?

Both are linear polymers connected by beta (1,4) glycosidic linkages. Signup and view all the answers

What characteristic of lactose makes it a reducing sugar?

There is a free hemiacetal group in its glucose unit. Signup and view all the answers

What is the main structural feature of cellulose that contributes to its strength?

Extensive hydrogen bonding between chains. Signup and view all the answers

In what way does the structure of starch differ from that of glycogen?

Glycogen has fewer branches and smaller residues. Signup and view all the answers

Why can't humans metabolize cellulose effectively?

Humans lack enzymes to break Beta(1,4) linkages. Signup and view all the answers

Which of the following best characterizes the polysaccharides starch and glycogen?

Both serve as major forms of energy storage. Signup and view all the answers

Which specific monosaccharide is involved in the structure of chitin?

N-acetyl-D-glucosamine Signup and view all the answers

What is the primary reason that glucose can form either a pyranose or furanose structure?

The ability of the hydroxyl group on C-4 to react with the aldehyde on C-1 Signup and view all the answers

What distinguishes reducing sugars from non-reducing sugars?

Reducing sugars have a free aldehyde or ketone group in open configuration Signup and view all the answers

Which of the following statements about anomers is true?

Anomers are isomers that differ only at the anomeric carbon Signup and view all the answers

What is the resulting product when the carbonyl group of a sugar is oxidized?

Carboxylic acid Signup and view all the answers

Which component is crucial for the formation of glycosides from sugars?

Reactivity of the anomeric -OH group with alcohols Signup and view all the answers

What is the equilibrium mixture percentage of beta-D-glucopyranose in a solution of D-glucose?

62% Signup and view all the answers

Which structural feature causes the anomeric carbon to become chiral?

Cyclization leading to the formation of a ring structure Signup and view all the answers

What is formed when an aldehyde on C-1 reacts with a hydroxyl group on C-4 in D-glucose?

Glucofuranose Signup and view all the answers

In which context can disaccharides and polysaccharides be considered reducing sugars?

If they possess an 'unlocked' anomeric carbon Signup and view all the answers

What distinguishes N-glycosides from standard glycosides?

N-glycosides contain an amine at the anomeric carbon Signup and view all the answers

Study Notes

Catalytic Mechanisms and Enzyme Regulation

Reaction occurs between electron-deficient (electrophiles) and electron-rich (nucleophiles) atoms.
Chemical bond formation involves a nucleophile donating an electron pair to an electrophile.
Enzymes stabilize transition states, short-lived intermediates between reactant and product with energy maxima.
Enzymes bind transition states with high affinity, stabilizing them and reducing the activation energy required.
Catalyst lowers the energy of activation (∆G≠) and the rate increases, reaction proceeds faster.

Catalytic Mechanisms

Active sites of the enzyme are structured to lower the activation energy (∆G≠) of the reaction,
Key mechanisms involved include:
- Proximity and strain effects.
- Electrostatic effects.
- Acid-base catalysis.
- Covalent catalysis.

Proximity and Strain Effects

Substrate fits the active site with the correct orientation between enzyme and substrate functional groups.
Enzyme conformation changes to create a strained enzyme-substrate (ES) complex.

Electrostatic Effects

Substrate binding site prevents water molecules (H₂O).
This reduces the dielectric constant, strengthening electrostatic interactions between the enzyme (E) and substrate (S).

Acid-Base Catalysis

Important factor in various chemical reactions like hydrolysis of esters.
Certain amino acids in the active site act as either proton donors (general acid) or acceptors (general base).
Examples: Hydrolysis of esters can be catalyzed by free hydroxide ion (HO-).

General Base Catalysis

Involves an active site amino acid accepting a proton from the substrate.

Covalent Catalysis

A nucleophilic side chain forms a temporary covalent bond with the substrate.
Examples include serine proteases, like chymotrypsin involved in polypeptide digestion.
Oxygen or serine attacks the carbonyl group of a peptide bond causing an acyl-enzyme ester to form, and the peptide bond breaks.
The resulting intermediary is subsequently hydrolyzed by water.

Mechanism of Chymotrypsin

Breaks peptide bonds next to large nonpolar amino acids (Phe, Tyr, Trp).
Ser195 (a serine residue), His57, and Asp102 (an aspartate residue) work together to activate the enzyme.
His57 removes a proton from Ser195, making it a better nucleophile.
Ser195 attacks the peptide bond, forming a temporary covalent bond with the peptide chain.
The acyl-enzyme intermediate undergoes hydrolysis, releasing the peptide fragment.

Mechanism of Triose Phosphate Isomerase

Catalyzes the isomerization of dihydroxyacetone phosphate (DHAP) to glyceraldehyde 3-phosphate (GAP).
Involves two enediolate transition states (TS1 and TS2) and an enediol intermediate.
Crucial amino acid residues involved in the reaction are Glu 165 and His 95.

2-Phosphoglycolic Acid (PGA) inhibition

Resembles enediolate 1 intermediate, thus inhibits triose phosphate isomerase.

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Description

Explore the intricate world of catalytic mechanisms and enzyme regulation in this quiz. Understand how enzymes interact with substrates to stabilize transition states and lower activation energy, enhancing reaction rates. Delve into key concepts like acid-base catalysis and the role of proximity and strain effects in enzymatic activity.