Chapter 11 Carbohydrates and Glycoproteins

personal part 2 w/o the stupid symbols

What is the general chemical formula for a monosaccharide?

The general chemical formula is (CH2O)n, where n = 3-7.

What are the three main components of a monosaccharide?

A carbon backbone, multiple hydroxyl groups (-OH), and a carbonyl group (C=O) (either aldehyde or ketone).

What functional groups are always found in monosaccharides?

Hydroxyl (-OH) and carbonyl (C=O) groups.

What determines whether a monosaccharide is an aldose or a ketose?

An Aldose has the carbonyl group at the end (C1)

How many carbons does glucose contain?

Glucose is a hexose and contains six carbons.

What does it mean when glucose is shown in “flat” Fischer projection form?

It represents the linear, straight-chain structure and shows the stereochemistry of the hydroxyl groups.

How is glucose represented in ring form?

As a cyclic hemiacetal (Haworth projection).

What is the bond formed when the ring structure of glucose closes?

A hemiacetal bond between the carbonyl carbon (C1) and an internal hydroxyl group.

What causes glucose to form a ring structure spontaneously in solution?

The carbonyl group reacts with an internal hydroxyl group to form a more stable, closed ring structure.

What is the difference between the alpha (α) and beta (β) forms of glucose?

They differ in the orientation of the hydroxyl (-OH) group on the anomeric carbon (C1). Alpha (α) = OH down

What is mutarotation, and how does it relate to glucose in solution?

Mutarotation is the spontaneous interconversion between the alpha (α) and beta (β) anomers through the temporary open-chain form.

Which ring form of glucose is the most stable in nature?

The beta-D-glucopyranose chair form.

How does glucose exist in equilibrium between open-chain and cyclic forms?

It constantly shifts between the linear, alpha, and beta cyclic forms via reversible reactions in aqueous solution.

What are the two types of ring forms that sugars can form?

Furanose (a five-membered ring) and pyranose (a six-membered ring).

What atom in the glucose molecule becomes the anomeric carbon when the ring forms?

Carbon 1 (C1), which was originally the carbonyl carbon in the linear aldose form.

What are structural isomers?

Compounds with the same molecular formula but different atomic connections (different bonding patterns).

What are stereoisomers?

Molecules with the same bonding pattern but different spatial arrangement of atoms (different 3D orientation).

What are enantiomers, and how are they related to D- and L- configurations?

Enantiomers are stereoisomers that are non-superimposable mirror images of each other (e.g., D- and L-sugars).

How is D-glucose different from L-glucose?

They are mirror opposites

What are diastereomers?

Stereoisomers that are not mirror images of each other

What are epimers?

Diastereomers that differ in configuration at only a single stereogenic carbon (e.g., glucose and galactose).

What are anomers?

The alpha (α) and beta (β) forms of a cyclic sugar, differing only at the anomeric carbon.

Which carbon in glucose determines whether it is alpha (α) or beta (β)?

The anomeric carbon (C1).

How can you identify a reducing sugar based on its structure?

It must have a free anomeric carbon that is not involved in a glycosidic bond, allowing the ring to open to the reactive aldehyde group.

What is the difference between the boat and chair forms of glucose?

The chair form is flat and staggered, while the boat form is folded and less stable.

Which form of glucose (boat or chair) is more stable, and why?

The Chair form is more stable because it minimizes steric hindrance and unfavorable axial group interactions.

What stabilizes the chair conformation of glucose?

The placement of most bulky groups (like the hydroxyls and the C6 group) in the equatorial position, minimizing crowding.

Why is D-glucose so important for most organisms?

It is the primary metabolic fuel used by cells, easily broken down via glycolysis for energy production.

How is D-glucose used in cellular metabolism?

It is broken down through glycolysis, followed by the citric acid cycle and oxidative phosphorylation, to produce ATP.

Why do organisms prefer D-glucose over other isomers?

Enzymes involved in metabolic pathways are stereospecific and have evolved to efficiently recognize and process the D-form of the sugar.

What pathways rely primarily on D-glucose?

Glycolysis, glycogen synthesis (glycogenesis), and the pentose phosphate pathway.

What is glycation?

The nonenzymatic, spontaneous attachment of glucose (or other sugars) to proteins or lipids.

How does glycation occur spontaneously in the body?

The aldehyde group of glucose reacts directly with amino groups (e.g., on lysine residues) of proteins.

Why is glycation important in diabetes?

Chronic hyperglycemia (high blood sugar) increases glycation, leading to the formation of Advanced Glycation End-products (AGEs) that cause tissue damage.

What is hemoglobin A1C, and why is it clinically significant?

Glycated hemoglobin

What does a high A1C value indicate about blood glucose levels?

It indicates prolonged hyperglycemia (high average blood sugar).

Why does glycation damage proteins?

It alters the protein's structure and function through chemical changes, crosslinking, and oxidation, leading to loss of biological activity.

What are advanced glycation end-products (AGEs)?

Stable, irreversible, and harmful products resulting from long-term, persistent glycation that cause oxidative stress, inflammation, and cellular aging effects.

What is a glycosidic bond?

A covalent bond linking the anomeric carbon of one sugar to a hydroxyl (-OH) or amine (-NH2) group of another molecule (sugar, protein, or lipid).

How is a glycosidic bond formed between two monosaccharides?

Through a condensation (dehydration) reaction, where a molecule of water is released as the two sugar units join.

What is the difference between an O-glycosidic linkage and an N-glycosidic linkage?

An O-linked bond connects the sugar to an oxygen atom (usually a hydroxyl group)

What functional group is involved in an O-glycosidic bond?

A Hydroxyl (-OH) group (an alcohol group) on another molecule.

What type of molecule typically forms an N-glycosidic bond?

The Amino groups from proteins (like asparagine) or the nitrogen bases found in nucleotides.

How does the position of the glycosidic bond determine whether it is alpha (α) or beta (β)?

It is determined by the starting position of the hydroxyl (-OH) group on the anomeric carbon of the first sugar: alpha if the bond points down, beta if it points up.

What enzyme catalyzes the formation of glycosidic bonds in biological systems?

Glycosyltransferases.

Why is the phosphorylation of sugars relevant in metabolism?

It serves two key purposes: activates the sugar for subsequent metabolic reactions, and traps the sugar inside the cell.

How does phosphorylation affect the charge and reactivity of sugars?

It adds a negative charge, which increases polarity and makes the sugar more reactive for enzyme processing.

What is the metabolic purpose of trapping phosphorylated sugars inside the cell?

The large, charged phosphate group prevents the sugar from undergoing passive diffusion and leaking out of the cell's membrane.

What is a disaccharide?

A carbohydrate composed of two monosaccharide units linked together by a single glycosidic bond.

What determines whether a disaccharide has a reducing end?

It has a reducing end if the anomeric carbon of one of the sugar units is free (not involved in the glycosidic bond).

What does it mean for a sugar to be “reducing”?

It has a free aldehyde or ketone group (due to a free anomeric carbon) that is capable of reducing (donating electrons to) other molecules, meaning the saccharide is oxidized.

What is a nonreducing sugar?

A sugar in which both anomeric carbons are involved in a glycosidic bond, so no free aldehyde or ketone group is available to reduce other compounds.

What determines the reducing or nonreducing nature of a disaccharide?

If both anomeric carbons are linked, the disaccharide is nonreducing (e.g., sucrose). If one anomeric carbon is free, it is reducing (e.g., maltose, lactose).

What are the monosaccharide components of sucrose?

Glucose + Fructose.

What are the monosaccharide components of lactose?

Glucose + Galactose.

What are the monosaccharide components of maltose?

Glucose + Glucose.

What type of glycosidic linkage is found in sucrose?

alpha 1 -> beta 2 glycosidic bond.

What type of glycosidic linkage is found in lactose?

beta 1 -> 4 glycosidic bond.

What type of glycosidic linkage is found in maltose?

alpha 1 -> 4 glycosidic bond.

Which disaccharides are reducing sugars and which are not?

Reducing = maltose and lactose (they have a free anomeric carbon)

What enzyme hydrolyzes maltose to glucose?

Maltase (a digestive enzyme).

Why is lactose intolerance related to enzyme deficiency?

It is caused by a deficiency of the enzyme lactase in the intestinal lining, which is needed to hydrolyze the beta 1 -> 4 linkage in lactose.

What is a polysaccharide?

Large carbohydrates composed of long chains of repeating monosaccharide units joined by glycosidic bonds.

How are polysaccharides formed from monosaccharides?

By repeated condensation reactions (releasing water) that form numerous glycosidic linkages.

What is the primary function of glycogen?

It serves as the main glucose storage form in animals (primarily in the liver and muscles).

What type of glycosidic bonds are found in glycogen?

alpha 1 -> 4 linkages for the linear chains and alpha 1 -> 6 linkages for the branch points.

What is the difference between glycogen and starch?

Both store glucose, but glycogen (animal storage) is more highly branched than starch (plant storage).

What are the two components of starch?

Amylose (the unbranched, linear component) and Amylopectin (the branched component).

What type of linkage connects glucose units in amylose?

alpha 1 -> 4 glycosidic linkages (linear).

What type of linkage connects glucose units in amylopectin?

alpha 1 -> 4 (linear) and alpha 1 -> 6 (branch points) linkages.

How does the branching structure of glycogen affect its function?

The high degree of branching increases solubility and provides many nonreducing ends, allowing for the rapid release of glucose when needed.

What enzyme releases glucose from glycogen?

Glycogen phosphorylase.

What is chitin composed of?

Repeating units of N-acetylglucosamine (GlcNAc).

What kind of linkage is found in chitin?

beta 1 -> 4 glycosidic bonds.

How does the structure of chitin differ from cellulose?

Chitin has an N-acetylamino group on each glucose unit, whereas cellulose does not.

Why can humans digest starch but not cellulose or chitin?

Humans possess enzymes (like amylase) that can hydrolyze the alpha 1 -> 4 linkages in starch, but we lack the enzymes to break the beta 1 -> 4 linkages in cellulose and chitin.

What is soluble fiber?

Fiber that dissolves in water to form a gel-like substance, which slows down digestion (e.g., pectin).

What is insoluble fiber?

Fiber that does not dissolve in water

How does soluble fiber affect digestion and blood sugar levels?

It delays gastric emptying, which slows the absorption of glucose and helps reduce blood glucose spikes.

How does insoluble fiber affect bowel movement and health?

It increases stool bulk and softens it, which helps prevent constipation and promotes regular digestion.

Why is fiber important for maintaining cholesterol levels?

Soluble fiber binds to bile acids in the gut, which reduces cholesterol reabsorption and forces the body to use more cholesterol to make new bile acids.

How does fiber contribute to gut health?

It is fermented by gut microbiota to produce important metabolites, such as short-chain fatty acids, which are beneficial for colon health.

What is a glycoprotein?

A molecule consisting of a protein with one or more oligosaccharide (glycan) chains covalently attached.

What are the three major classes of glycoproteins?

Glycoproteins, proteoglycans, and mucins.

How do glycoproteins differ from proteoglycans and mucins?

Glycoproteins have shorter, often branched glycans

What types of sugars are commonly attached to glycoproteins?

Common monosaccharides include glucose, galactose, mannose, fucose, N-acetylglucosamine, N-acetylgalactosamine, and sialic acid.

What roles do glycoproteins play in the body?

Functions include cell signaling, molecular recognition (like blood groups), immune defense (antibodies), and providing structural support.

What are examples of glycoproteins discussed in class?

Collagen, erythropoietin (EPO), and antibodies (immunoglobulins).

How do proteoglycans differ structurally from glycoproteins?

They consist of a core protein linked to long, unbranched chains of repeating disaccharide units called Glycosaminoglycans (GAGs).

What is the function of mucins?

They provide lubrication and form a thick, protective barrier for epithelial surfaces (e.g., in the respiratory and digestive tracts).

What is the overall structural pattern seen in the three classes (glycoproteins, proteoglycans, mucins)?

All contain carbohydrate-protein linkages, but they differ significantly in the length, complexity, and density of the attached carbohydrate chains.

What is an N-linkage in glycoproteins?

A glycosidic bond where the sugar is linked to the amide nitrogen of the amino acid asparagine (Asn).

What is an O-linkage in glycoproteins?

A glycosidic bond where the sugar is linked to the hydroxyl (-OH) group of the amino acids serine (Ser) or threonine (Thr).

What amino acids are commonly linked to sugars in O-linked glycoproteins?

Serine and threonine.

What amino acid residues are used for N-linked glycosylation?

Asparagine (Asn).

What does post-translational modification mean?

Covalent modification of a protein after it has been fully translated (synthesized) from the mRNA, often to add functional groups or alter structure.

Where does glycosylation occur in eukaryotic cells?

It occurs sequentially in the rough endoplasmic reticulum (RER) and the Golgi apparatus.

What role does the rough endoplasmic reticulum (RER) play in glycoprotein processing?

The initial steps of N-linked glycosylation (attachment of the core sugar block) occur on proteins as they enter the RER lumen.

What role does the Golgi apparatus play in glycoprotein processing?

It is responsible for the extensive modification, trimming, and fine-tuning of the carbohydrate chains, as well as directing the modified proteins to their final destinations.

How are proteins sorted for secretion or membrane localization after modification?

Specific sorting signals (like carbohydrate labels) added in the Golgi direct the proteins into vesicles that transport them to the plasma membrane or for secretion outside the cell.