Biochemistry: Carbohydrates and Their Functions

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of carbohydrates in biochemistry?

Protein synthesis

Generating and storing biological energy (correct)

DNA replication

Membrane structure formation

Which of the following correctly describes a disaccharide?

A carbohydrate that cannot be further hydrolyzed

A polymer composed of multiple glucose molecules

A sugar containing two monosaccharide units (correct)

A simple sugar with a single monomer unit

How does carbon numbering begin in an aldose compared to a ketose monosaccharide?

Both start from the carbon opposite the functional group

Both start from the same end carbon

Aldoses start with the aldehyde carbon; ketoses start with the end carbon (correct)

Aldoses have no defined starting point

Which of the following statements about enantiomers is true?

They are nonsuperimposable mirror images Signup and view all the answers

Which carbohydrate is formed during the process of respiration?

Carbohydrates made by plants Signup and view all the answers

What is a common derivative of monosaccharides?

Amino sugars Signup and view all the answers

What characterizes D and L forms of monosaccharides?

They have different specific rotations Signup and view all the answers

Which carbohydrate is a polymer found in starch?

Amylose Signup and view all the answers

What does the notation (1→4) signify in the context of glycosidic bonds?

A bond between carbon 1 of one residue and carbon 4 of another residue Signup and view all the answers

Which of the following is an activated sugar molecule used in lactose biosynthesis?

UDP-galactose Signup and view all the answers

What type of reaction leads to the formation of glycosidic bonds in oligosaccharides?

Condensation reaction Signup and view all the answers

Which enzyme catalyzes the reaction transferring galactose to glucose during lactose formation?

Lactose synthase Signup and view all the answers

Which polysaccharides are considered principal storage polysaccharides in plants?

Amylose and amylopectin Signup and view all the answers

What is the main difference between amylose and amylopectin?

Amylose is linear, while amylopectin is branched Signup and view all the answers

Where is glycogen primarily stored in the human body?

In the liver and muscle tissue Signup and view all the answers

Which molecule is involved in the metabolic process of phosphorylating galactose during lactose synthesis?

ATP Signup and view all the answers

What is the most stable conformation of hexoses?

Chair conformation Signup and view all the answers

Which of the following describes configurational isomers?

Include isomers that differ in spatial arrangement Signup and view all the answers

What type of compounds are sugar phosphates considered in metabolism?

Activated intermediates Signup and view all the answers

The oxidation of an aldose can produce which type of acid when treated with alkaline Cu(II)?

Aldonic acid Signup and view all the answers

Which of the following best describes lactones?

Cyclic esters formed from aldonic acids Signup and view all the answers

What is a key structural difference between glycogen and amylopectin?

Glycogen branches are more frequent and shorter than those in amylopectin. Signup and view all the answers

What are alditols derived from?

Reduction of carbonyl groups on sugars Signup and view all the answers

What type of linkage characterizes cellulose structure?

b(1→4) linkages Signup and view all the answers

Which amino sugar is derived from glucose?

Glucosamine Signup and view all the answers

What type of bond is formed during the elimination of water between an anomeric hydroxyl and another hydroxyl group?

Glycosidic bond Signup and view all the answers

Which of the following is NOT a structural polysaccharide?

Glycogen Signup and view all the answers

Which sugars are commonly found in glycosaminoglycans?

N-acetylgalactosamine and N-acetylglucosamine Signup and view all the answers

What is the structure of heparin characterized by?

High sulfation and anticoagulant activity Signup and view all the answers

How does the organization of cellulose contribute to its function in the plant cell wall?

Cellulose forms microfibrils embedded in hemicellulose in a crosshatched pattern for strength. Signup and view all the answers

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

Gram-positive bacteria consist of a thick peptidoglycan layer. Signup and view all the answers

What is a function of glycosaminoglycans in connective tissue?

To serve as structural components Signup and view all the answers

What is the correct order of priority for groups in R–S nomenclature?

SH > OR > OH > NH2 Signup and view all the answers

Which configuration does the R designation in R-glyceraldehyde indicate?

Priority decreases clockwise Signup and view all the answers

What distinguishes diastereomers from enantiomers in monosaccharides?

They differ in orientation around one chiral carbon Signup and view all the answers

Which statement about the anomeric carbon in cyclic saccharides is correct?

It is the carbonyl carbon in the open-chain form Signup and view all the answers

Which of the following is NOT one of the possible ring forms for monosaccharides?

Four-membered lactone Signup and view all the answers

In which conformation of b-D-ribofuranose is C-2 above the defined plane?

C-2 endo Signup and view all the answers

What characterizes the two anomeric forms of cyclic saccharides?

Differing orientations at the anomeric carbon Signup and view all the answers

What is the configuration designation for L-glyceraldehyde?

S Signup and view all the answers

What is required for the biosynthesis of UDP-N-acetylglucosamine from glucosamine-6-phosphate?

Conversion of glucosamine to UDP Signup and view all the answers

During asparagine-linked (N-linked) oligosaccharide synthesis, where must the asparagine residue be located on the polypeptide chain?

Next to a serine or threonine residue Signup and view all the answers

How does penicillin inhibit peptidoglycan synthesis?

Through forming a covalent complex with transpeptidase Signup and view all the answers

What are the major types of oligosaccharides that contain a common pentasaccharide core?

Asparagine-linked oligosaccharides Signup and view all the answers

What is the significance of the separate glycosyltransferases in the biosynthesis of lipid-linked oligosaccharides?

They catalyze different transfer reactions during synthesis Signup and view all the answers

Where do the initial reactions of O antigen biosynthesis occur?

In the inner membrane Signup and view all the answers

What is the final destination of the peptidoglycan once synthesized?

It is added to the cell wall Signup and view all the answers

Study Notes

Biochemistry I - CHM219

Course Instructor: Dr. Esra Aydemir
Class Time: 2:00 PM
Course Name: Biochemistry I
Course Number: CHM219

Carbohydrates: Sugars, Saccharides, Glycans

Carbohydrates play numerous roles in biochemistry.
They are involved in energy generation and storage.
They participate in cellular recognition and protection.
Carbohydrates contribute to cell signaling and adhesion.
They act as biological lubricants and regulate protein trafficking.
Carbohydrates maintain biological structure (e.g., cellulose).

Outline

Monosaccharides
Derivatives of Monosaccharides
Oligosaccharides
Polysaccharides
Glycoproteins
Oligosaccharides as Cell Markers
Biosynthesis of Glycoconjugates
Glycoconjugates of Interest

Monosaccharides

Monosaccharides are the simplest carbohydrates.
They consist primarily of carbon, hydrogen, and oxygen.
Glucose is a common monosaccharide.
They serve as building blocks (monomers) for oligosaccharides and polysaccharides.

Representative Carbohydrates

Glucose is a monosaccharide.
Maltose is a disaccharide composed of two glucose units.
Amylose is a glucose polymer found in starch.

The Energy Cycle of Life

Photosynthesis: Plants use sunlight to combine carbon dioxide and water to form carbohydrates, releasing oxygen.
Respiration: Plants and animals oxidize carbohydrates to release energy, forming carbon dioxide and water.

Trioses

Trioses are the simplest monosaccharides.
Triose tautomers illustrate the difference between aldoses and ketoses.
Carbon numbering in aldoses starts at the aldehyde carbon; in ketoses, it starts at the carbon closest to the ketone group.
The enediol intermediate is unstable and cannot be isolated.

Stereochemistry of Aldotetroses

Aldotetroses have two chiral carbon atoms, resulting in two diastereomeric forms (threose and erythrose).
Each diastereomer exists as a pair of enantiomers.
The prefixes D and L indicate enantiomeric configuration relative to the chiral carbon farthest from the carbonyl group.

Stereochemical Relationships of D-Aldoses

A branching diagram shows the relationship between D-aldooses based on their configuration at chiral carbons.

Stereochemical Relationships of D-Ketoses

A branching diagram displays the structures of D-ketoses.

Monosaccharides with Five or More Carbons

Existing predominantly in ring forms (five or six membered rings).
Ring structures formed via internal hemiacetal formation.
Two forms possible (α- and β-).
An epimer at the hemiacetal carbon, named the anomeric carbon because it formerly formed part of the carbonyl functional group (aldehyde or ketone) in the open-chain form.

Relative Amounts of Tautomeric Forms

Table provides the relative percentages of α- and β- forms of various monosaccharides at equilibrium in water.

Conformational Isomers

These isomers have identical stereochemical configurations.
Differences exist in three-dimensional conformations.
C-2 endo and C-3 endo are the two most common conformations in ribose/deoxyribose.

The Hexoses

The hexoses exist primarily in ring forms.
Two ring forms exist: furanose (five-membered ring) and pyranose (six-membered ring), each with possible α- and β- anomers.

Derivatives of Monosaccharides

Sugar phosphates are important metabolic intermediates.
They function as activated compounds in syntheses.
Addition of a phosphate group activates the molecule for further reactions.

Oxidation of Monosaccharides

Oxidation procedures can yield different products, depending on the oxidizing agent used.
Mild oxidation of an aldose with alkaline copper(II) (e.g., Fehling's solution) results in the formation of the corresponding aldonic acid.

Enzyme-Catalyzed Oxidation

Enzymes can catalyze the oxidation of monosaccharides, including the production of uronic acids.
This usually occurs at carbon 6 to produce an acid.

Free Aldonic Acids

Free aldonic acids (e.g., gluconic acid) are in equilibrium with lactones (cyclic esters).
Lactones are formed through the reaction of a carboxyl group with an alcohol group.

Alditols

Reduction of a carbonyl group on a sugar produces an alditol.
Important alditols include erythritol, mannitol, and sorbitol.

Amino Derivatives of Simple Sugars

Amino sugars (e.g., glucosamine and galactosamine) are widely found in natural polysaccharides.

Glycosidic Bonds

Glycosidic bonds link monosaccharides together to form oligosaccharides and polysaccharides.

Oligosaccharides as Cell Markers

Glycocalyx is a thick coating on animal cells composed of oligosaccharides.
Oligosaccharides interact with various substances, including bacteria and collagen.

Imaging Cell Surface Glycoproteins

Zebrafish embryos incorporate azido derivatives of GalNAc for imaging cell surface glycoproteins.

Glycoconjugates of Interest

This section describes the biosynthesis of lipid-linked oligosaccharide intermediates or other important aspects of glycan biosynthesis.

Biosynthesis of Glycoconjugates—Amino Sugars

Synthesis of UDP-N-acetylglucosamine.
The precursor is glucosamine-6-phosphate.

Biosynthesis of N-Acetylneuraminic Acid

The synthesis of sialic acid (N-acetylneuraminic acid) from UDP-N-acetylglucosamine is detailed.

Structures of Major Types of Asparagine-Linked Oligosaccharides

Common pentasaccharide core structures in N-linked oligosaccharides are highlighted.

Glycoconjugates of Interest-Biosynthesis of the Lipid-Linked Oligosaccharide Intermediate

Sequential mannosyl transfers from GDP-mannose.
Mannose transfers from dolichol phosphate.
Formation of the lipid-linked oligosaccharide intermediate.

Schematic Pathway of Oligosaccharide Processing on Newly Synthesized Glycoproteins

Glycoprotein processing pathway.

Synthesis of the Linear Peptidoglycan Molecule of S. aureus

Sequential steps in peptidoglycan synthesis.
Site-specific inhibition by antibiotics (e.g., bacitracin and vancomycin).

The Cross-Linking Reaction in Peptidoglycan Synthesis

The role of transpeptidase in the cross-linking reaction.
How penicillin inhibits this reaction.

Biosynthesis of the Repeating Oligosaccharide Unit of the O Antigen of Salmonella Typhimurium

The steps in the biosynthesis of the O antigen of Salmonella typhimurium.

Polysaccharides

Amylose, amylopectin, and glycogen are storage polysaccharides.
Glycogen is the primary storage polysaccharide in animals.
Amylose is a linear polymer; amylopectin and glycogen are branched.
Cellulose is a structural polysaccharide.
Its strands are parallel and linked by hydrogen bonds.

Organization of Plant Cell Walls

Microfibrils of cellulose are embedded in a matrix of hemicellulose.
Cross-hatching of the fiber pattern provides strength.

The Major Structural Polysaccharides in Vertebrate Animals

Glycosaminoglycans (formerly mucopolysaccharides) are major structural components.
Examples include chondroitin sulfates, keratan sulfates, dermatan sulfates, and hyaluronic acid.

Repeating Structures of Some Glycosaminoglycans

Repeating disaccharide units in glycosaminoglycans, illustrating the core structure.

A Highly Sulfated Glycosaminoglycan

Heparin is a highly sulfated glycosaminoglycan.
It functions as a natural anticoagulant.
It binds to antithrombin III to inhibit blood clotting.

The Cell Wall of a Gram-Positive Bacterium

Consists of a thick peptidoglycan layer.
Peptides are cross-linked by glycine.

The Cell Wall of a Gram-Negative Bacterium

Has a thin peptidoglycan layer and an outer lipid membrane.
Cross-links between tetrapeptides.

The Structure of a Lipoteichoic Acid

D-Alanyl and NAG groups in lipoteichoic acids are anchored in the membrane.

Glycoproteins

Oligosaccharides and proteins can be linked in two ways: O-linked and N-linked.
O-linked glycans are attached via threonine or serine hydroxyls.
N-linked glycans are linked via asparagines.

The ABO Blood Group Antigens

The O oligosaccharide does not elicit antibodies.
A and B antigens are formed by the addition of GalNAc or Gal, respectively.
Each antigen elicits a specific antibody.

Transfusion Relationships among ABO Blood Types

Table showing compatible blood types for transfusions.

The Structure of the Influenza Virus

RNA genome is packaged within a spherical structure.
Hemagglutinin and neuraminidase molecules form spikes on the virion surface.

Rational Design of Neuraminidase Inhibitors

Structures of sialic acid, zanamivir, and oseltamivir.
Model of the neuraminidase-inhibitor complex.

Note

This is a summary of a lecture; many details may be missing.
Additional details may be found in diagrams or specific structures.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the role of carbohydrates in biochemistry! This quiz covers various topics including disaccharides, monosaccharides, glycosidic bonds, and the processes of respiration and lactose biosynthesis. Understand the key characteristics and differences between storage polysaccharides and their derivatives.