Chapter 13: Carbohydrates

Photosynthesis

Energy from the Sun is used to combine the carbon atoms from carbon dioxide and the hydrogen and oxygen atoms of water into the carbohydrate glucose.

respiration

In the body, glucose is oxidized in .

Respiration

A series of metabolic reactions which releases chemical energy to do work in cells.

Carbon Cycle

The combination of photosynthesis and respiration, in which energy from the Sun is stored in plants by photosynthesis and made available to us when the carbohydrates in our diets are metabolized.

Monosaccharides

• The simplest carbohydrate.
• These cannot be split or hydrolyzed into smaller carbohydrates.
• These have chains of three to eight carbon atoms, one in a carbonyl group and all the others attached to hydroxyl groups.

Aldopentose

A five-carbon monosaccharide that is an aldehyde.

Ketohexose

A six-carbon monosaccharide that is a ketone.

Disaccharides

These consist of two monosaccharide units joined together, which can be split into two monosaccharide units.

Polysaccharides

• These are carbohydrates that contain many polymers.

Stereoisomers

The atoms are bonded in the same sequence but differ in the way they are arranged in space.

non-superimposable

When the mirror images of organic molecules cannot be completely matched, they are .

chiral

Objects such as hands that have non-superimposable mirror images are ____

achiral

When the mirror image of an object is identical and can be superimposed on the original, it is .

Chiral Carbon

A carbon compound is chiral if it has at least one carbon atom bonded to four different atoms or groups.

Enantiomers

When stereoisomers cannot be superimposed.

Emil Fischer

He devised a simplified system for drawing stereoisomers that shows the arrangements of the atoms around the chiral centers.

Fischer Projection

It is used to represent a three-dimensional structure of enantiomers.

project backward

Vertical lines from the Fischer projection represent _ from a carbon atom.

project forward

Horizontal lines from the Fischer projection represent _ from a carbon atom.

farthest

The —OH group on the chiral carbon _ from the carbonyl group is used to determine the D or L stereoisomer.

Glucose

Also known as dextrose and blood sugar; mostly found in fruits, vegetables, corn, syrup and honey.

D-Glucose

A building block of the disaccharides sucrose, lactose, and maltose, and polysaccharides such as amylose, cellulose, and glycogen.

Galactose

• An aldohexose that is obtained from the disaccharide lactose, which is found in milk and milk products.
• It is important in the cellular membranes of the brain and nervous system.

Galactosemia

An enzyme needed to convert galactose to glucose is missing.

Fructose

A ketohexose; it is the sweetest of carbohydrates, almost twice as sweet as sucrose.

Haworth structures

These are the atoms rings produced from the reaction of a carbonyl group and a hydroxyl group in the same molecule.

Mutarotation

Each isomer converts to the open chain and back again.

aldohexose

Galactose is an that differs from glucose only in the arrangement of the —OH group on carbon 4.

carboxylic acid

In an aldose, the aldehyde group can be oxidized to a .

hydroxyl group

The carbonyl group in both an aldose and a ketose can be reduced to give a .

adjacent hydroxyl

An aldehyde group with an can be oxidized to a carboxylic acid by an oxidizing agent.

Reducing Sugar

A carbohydrate that reduces another substance.

alditols

The reduction of the carbonyl group in monosaccharides produces sugar alcohols — .

D-Sorbitol

D-Glucose is reduced to D-glucitol.

Disaccharide

It is composed of two monosaccharides linked together.

maltose

lactose

sucrose

Three most common disaccharides

Maltose

It is obtained from starch and is found in germinating grains.

Glycosidic Bond

An ether bond that connects two monosaccharides.

Lactose

A disaccharide found in milk and milk products.

Sucrose

• It consists of an ɑ-D-glucose and a β-D-fructose molecule joined by an ɑ, β-1, 2-glycosidic bond.
• The glycosidic bond in sucrose is between carbon 1 of glucose and carbon 2 of fructose.

Polysaccharide

A polymer of many monosaccharides joined together.

Starch

A storage form of glucose in plants is found as insoluble granules in rice, wheat, potatoes, beans, and cereals.

Amylose

It makes up about 20% of starch, and consists of 250 to 4000 ɑ-D-glucose molecules connected by ɑ-1,4-glycosidic bonds in a continuous chain.

Amylopectin

It makes up as much as 80% of starch, and is a branched-chain polysaccharide. The glucose molecules are connected by ɑ-1,4-glycosidic bonds.

Dextrins

Starches hydrolyze easily in water and acid to give smaller saccharides, which then hydrolyze to maltose and finally glucose.

Glycogen

A polymer of glucose that is stored in the liver and muscles of animals. It is hydrolyzed in our cells at a rate that maintains the blood level of glucose and provides energy between meals.

Cellulose

• The major structural material of wood and plants.
• The glucose molecules form a long unbranched chain similar to that of amylose.
• These are linked by β-1, 4-glycosidic bond.