McBride Lecture 6 BioTech2

Monosaccharide

A carbohydrate that is an aldehyde or ketone with two or more hydroxyl groups and 3–7 carbons in length.

Simple sugar

Another name for a monosaccharide

Carbohydrate

Carbon-based molecule high in hydroxyl groups

Empirical formula of carbohydrates

General formula often written as (CH2O)n for many simple sugars.

Triose

A monosaccharide containing three carbons in its backbone.

Tetrose

A monosaccharide containing four carbons in its backbone.

Pentose

A monosaccharide containing five carbons in its backbone.

Hexose

A monosaccharide containing six carbons in its backbone.

Heptose

A monosaccharide containing seven carbons in its backbone.

Aldose

A monosaccharide in which the most oxidized group is an aldehyde.

Ketose

A monosaccharide in which the most oxidized group is a ketone.

Glyceraldehyde

The simplest aldo-triose

Dihydroxyacetone

The simplest keto-triose

Ribose

A five‑carbon aldose (pentose) commonly found in cells

Deoxyribose

2‑Deoxy‑D‑ribose; a pentose lacking an OH at C‑2

Glucose

A six‑carbon aldose (hexose) that is the major fuel sugar in many organisms.​

Fructose

A six‑carbon ketose (hexose) that can form a five‑membered furanose ring.

Mannose

A C‑2 epimer of glucose

Galactose

A C‑4 epimer of glucose

Constitutional isomers

Molecules with the same molecular formula but different order of attachment (bonding) of atoms.

Stereoisomers

Molecules with the same bonding order but differing in spatial arrangement of atoms.

D configuration

Stereochemical designation in which the chiral center farthest from the carbonyl matches D‑glyceraldehyde configuration; most vertebrate sugars are D.​

L configuration

Stereochemical designation that is the mirror image of the D form

Enantiomers

Non‑superimposable mirror‑image stereoisomers

Diastereoisomers

Stereoisomers that are not mirror images of each other.

Epimers

Diastereoisomers that differ in configuration at only one of several asymmetric carbons

Asymmetric carbon

A carbon atom bonded to four different substituents

Number of possible stereoisomers

Equal to 2^n where n is the number of asymmetric carbon atoms.

Anomer

Isomer of a sugar that differs at the new asymmetric carbon formed upon ring closure (anomeric carbon).

Anomeric carbon

The carbonyl carbon (C‑1 in aldoses

Hemiacetal

Functional group formed when an aldehyde reacts with an alcohol group within the same molecule

Hemiketal

Functional group formed when a ketone reacts with an alcohol group within the same molecule

Pyranose

A six‑membered sugar ring structure (5 carbons + 1 oxygen)

Glucopyranose

The six‑membered ring form of glucose; can exist as α‑D‑glucopyranose or β‑D‑glucopyranose.

α‑anomer of glucose

Anomer where the OH on the anomeric carbon of D‑glucose is on the opposite side of the ring from the CH2OH group.

β‑anomer of glucose

Anomer where the OH on the anomeric carbon of D‑glucose is on the same side of the ring as the CH2OH group.

Furanose

A five‑membered sugar ring structure (4 carbons + 1 oxygen)

Fructofuranose

The five‑membered ring form of fructose (e.g.

Glycosidic Linkages

Determine polysaccharide structure: glucose storage in mammals and plants. Example:

Mammals: The α-1,4 linkages favor bent, helical structures, which are more suitable for storage.

Plants: The β-1,4 linkages favor straight chains, which are optimal for structural purposes.

O‑glycosidic bond

Covalent bond that links the anomeric carbon of one sugar to the hydroxyl oxygen of another molecule.

Oligosaccharide

Short polymer of two or more monosaccharides linked by O‑glycosidic bonds.

Disaccharide

Carbohydrate composed of exactly two monosaccharides linked by a glycosidic bond.

Reducing sugar

Sugar that has a free anomeric carbon capable of opening to the aldehyde (or ketone) form and reducing mild oxidizing agents.

Reducing end

End of a sugar or polysaccharide that has a free anomeric carbon and can interconvert with the open‑chain form.

Nonreducing end

End of a sugar or polysaccharide where the anomeric carbon is in a glycosidic linkage and cannot open to the linear form.

Sucrose

Nonreducing disaccharide of glucose and fructose linked via an α‑1

Maltose

Disaccharide of two glucose units joined by an α‑1

Lactose

Disaccharide of galactose and glucose linked by a β‑1

Polysaccharide

Large polymeric carbohydrate (glycan) formed by linkage of multiple monosaccharides; used for energy storage and structural roles.

Glycan

General term for large

Homopolymer

Polymer in which all of the monosaccharide units are the same (e.g.

Glycogen

Highly branched homopolymer of glucose serving as the major storage form of glucose in animals

α‑1

4‑glycosidic linkage

α‑1

6‑glycosidic linkage

Role of branching in glycogen

Branching increases surface area and enzyme accessibility

Glycogen phosphorylase

Enzyme that cleaves glycogen to produce glucose‑1‑phosphate during glycogen breakdown. Breaks down gylcogen when cells need more glucsoe

Short‑term energy storage

Role of glycogen which is stored in the liver and the muscles as a storage form of glucose that can sustain about a day of normal energy demands in humans.

Longer‑term energy storage

Role of fat (triacylglycerols) as a more concentrated energy reserve lasting weeks.

Fatty acid

Carboxylic acid with a long hydrocarbon chain; major fuel molecule and building block for lipids.

Saturated fatty acid

Fatty acid with no double bonds in the hydrocarbon chain; straight. Have higher energy density than unsaturated fatty acids

Unsaturated fatty acid

Fatty acid with one or more double bonds in the hydrocarbon chain; double bonds introduce kinks. Less stackable

Four roles of fatty acids

1. Fuel molecules

2. Building blocks for phospholipids and glycolipids

3. Many proteins are modified by the covalent attachment of fatty acids, which

functions to target proteins to membrane locations.

4. Fatty acid derivatives serve as hormones and intracellular messengers.

Triacylglycerol (TAG)

Neutral fat composed of three fatty acids esterified to glycerol; major storage form of fatty acids. Stored in the Adipose Tissue.

Simple triglyceride

Triacylglycerol in which all three fatty acid chains are identical.

Mixed triglyceride

Triacylglycerol in which the three fatty acid chains are different.

Adipose tissue

Fuel‑rich tissue composed of adipocytes that store triacylglycerols

Adipocyte

Specialized fat cell that synthesizes

Lipid droplet

Large intracellular globule of triacylglycerols surrounded by a phospholipid monolayer and associated proteins.

Lipase

Enzyme that hydrolyzes triacylglycerols into free fatty acids and glycerol

Lipolysis

Metabolic process of triacylglycerol degradation to release free fatty acids and glycerol.

Energy yield of fat

Oxidation of one gram of fat releases about twice as much energy as oxidation of one gram of glycogen.

Phospholipid

Major membrane lipid composed of glycerol

Phosphatidylcholine (PC)

Common phospholipid with choline as the head group attached to the phosphate.

Phosphatidylethanolamine (PE)

Phospholipid with ethanolamine as the polar head group.

Phosphatidylserine (PS)

Phospholipid with serine as the polar head group

Phosphatidylinositol (PI)

Phospholipid with inositol head group

Diphosphatidylglycerol (CL)

Phospholipid composed of two phosphatidic acid units linked by glycerol

Micelle

Spherical aggregate of fatty acids where hydrophobic tails face inward and polar heads face outward in water.

Lipid bilayer

Double‑layered sheet of phospholipids and glycolipids with hydrophobic tails inside and hydrophilic heads outside; basis of biological membranes.

Steroid

Class of lipids with a characteristic four‑ring fused hydrocarbon structure (steroid nucleus).

Cholesterol

Steroid with a hydrocarbon tail and a single hydroxyl group; aligns with phospholipid fatty acid chains and interacts via its OH with head groups in membranes.