Carbohydrates Lecture Notes

Flashcards covering the classification, stereochemistry, cyclic structures, and chemical properties of carbohydrates based on the lecture transcripts.

Biochemistry

The study of the chemistry of biomolecules and living organisms.

Carbohydrates

Compounds that act as polyhydroxy aldehydes or ketones, or substances that produce such compounds upon hydrolysis.

Monosaccharides

The simplest carbohydrates containing a single polyhydroxy aldehyde or ketone unit, such as glucose or fructose.

Disaccharides

Carbohydrates consisting of two monosaccharide units connected by a covalent bond, such as sucrose.

Oligosaccharides

Carbohydrates that contain from $3$ to $10$ monosaccharide units.

Polysaccharides

Carbohydrates composed of very long straight or branched chains of hundreds or thousands of monosaccharide units.

Stereoisomers

Isomeric forms of a molecule, like glyceraldehyde, that are non-superimposable mirror images of each other.

Enantiomers

The two mirror-image forms of a chiral molecule that cannot be superimposed.

Chiral carbon

A carbon atom connected to four different groups, also known as a center of chirality.

$2^n$ Rule

A rule stating that if a molecule has $n$ chiral carbons, there are $2^n$ possible stereoisomers.

Fischer projections

A two-dimensional method used to represent the three-dimensional mirror images of chiral molecules.

D-isomer

A carbohydrate where the hydroxy group on the chiral carbon farthest from the carbonyl points to the right.

L-isomer

A carbohydrate where the hydroxy group on the chiral carbon farthest from the carbonyl points to the left.

Levorotatory ($-$)

A substance that rotates the plane of polarized light to the left.

Dextrorotatory ($+$)

A substance that rotates the plane of polarized light to the right.

Aldose

A monosaccharide that contains an aldehyde group.

Ketose

A monosaccharide that contains a ketone group.

Hexose

A monosaccharide containing $6$ carbon atoms.

Pentose

A monosaccharide containing $5$ carbon atoms.

Pyranose ring

A six-membered cyclic hemiacetal or hemiketal structure formed by monosaccharides.

Furanose ring

A five-membered cyclic hemiacetal or hemiketal structure formed by monosaccharides.

Anomers

Stereoisomers that differ only in the position of the hydroxy group at the anomeric carbon ($\text{α}$ is down, $\text{β}$ is up for D-sugars).

Anomeric carbon

The carbon atom (Carbon-$1$ in glucose) that becomes chiral when a monosaccharide closes into a ring.

Benedict’s reagent

A basic solution of $Cu^{2+}$ used to identify reducing sugars by forming a red-orange precipitate of $Cu_2O$.

Reducing sugars

Sugars that can be oxidized by Benedict's reagent; this includes all monosaccharides.

Glycosidic linkage

The new carbon-oxygen bond formed when a hemiacetal or hemiketal reacts with an alcohol to create an acetal (glycoside).

D-glucose

Also known as dextrose or blood sugar; an aldohexose used by the body for energy.

D-fructose

Also known as levulose or fruit sugar; the sweetest of the monosaccharides.

Maltose

A disaccharide known as malt sugar, consisting of two glucose units linked by an $\text{α}(1 \rightarrow 4)$ glycosidic bond.

Lactose

A disaccharide known as milk sugar, consisting of galactose and glucose linked by a $\text{β}(1 \rightarrow 4)$ glycosidic bond.

Sucrose

Table sugar; a non-reducing disaccharide where the anomeric carbons of glucose and fructose are joined by an $\text{α}, \text{β}-(1 \rightleftharpoons 2)$ linkage.

Amylose

A form of starch consisting of long, unbranched glucose chains connected by $\text{α}(1 \rightarrow 4)$ glycosidic linkages.

Amylopectin

A branched form of starch with $\text{α}(1 \rightarrow 4)$ chains and $\text{α}(1 \rightarrow 6)$ branch points every $24$ to $30$ glucose units.

Glycogen

Animal starch stored in the liver and muscles with $\text{α}(1 \rightarrow 6)$ branches occurring every $8$ to $12$ units.

Cellulose

An unbranched structural polysaccharide in plants with $\text{β}(1 \rightarrow 4)$ glycosidic linkages that humans cannot digest.

Mutarotation

The process where the optical rotation of a sugar solution changes as it reaches equilibrium between its open-chain and cyclic forms.

Maillard Reaction

A reaction between carbohydrates and proteins under heat, resulting in browning and the development of complex flavors.