Carbohydrates, Lipids, and Plasma Membrane Structure: Study Notes for General Biology

Carbohydrates

Introduction to Carbohydrates

Carbohydrates are a major class of biological macromolecules that serve as energy sources and structural components in living organisms. They are composed of carbon, hydrogen, and oxygen, and include sugars and their polymers.

• Definition: Carbohydrates are organic molecules consisting of carbon, hydrogen, and oxygen, typically in a ratio of 1:2:1.

• Monomers: The simplest units of carbohydrates are monosaccharides (single sugars).

• Polymers: Carbohydrate polymers include disaccharides (two sugars), oligosaccharides (few sugars), and polysaccharides (many sugars).

• Key Elements: All carbohydrates contain carbon, hydrogen, and oxygen.

• Examples: Glucose (monosaccharide), sucrose (disaccharide), starch (polysaccharide).

Monosaccharides

Structure and Properties of Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as building blocks for more complex sugars. They have general formulas that are multiples of CH2O.

• General Formula: $C_nH_{2n}O_n$ (e.g., glucose is $C_6H_{12}O_6$)

• Functional Groups: Each monosaccharide contains a carbonyl group (either an aldehyde or ketone), multiple hydroxyl groups, and many C-H bonds.

• Classification: Monosaccharides are classified by the number of carbon atoms (triose, tetrose, pentose, hexose, etc.) and by the position of the carbonyl group (aldose or ketose).

• Example: Glucose is a hexose (six-carbon sugar) and an aldose (carbonyl group at the end).

Additional info: Monosaccharides can exist in linear or ring forms, and their structure determines their chemical reactivity and biological function.

Disaccharides and Polysaccharides

Formation and Types of Carbohydrate Polymers

Disaccharides and polysaccharides are formed by linking monosaccharide units through glycosidic bonds. These polymers serve various roles, including energy storage and structural support.

• Disaccharides: Composed of two monosaccharide units (e.g., sucrose = glucose + fructose).

• Oligosaccharides: Short chains of 3-10 monosaccharide units, often involved in cell recognition.

• Polysaccharides: Long chains of hundreds to thousands of monosaccharide units (e.g., starch, glycogen, cellulose).

• Glycosidic Bond: The covalent bond formed between monosaccharides via a dehydration reaction.

• Functions: Energy storage (starch in plants, glycogen in animals), structural support (cellulose in plants, chitin in fungi and arthropods).

Additional info: The type of glycosidic linkage (e.g., α or β) affects the digestibility and function of the polysaccharide.

Summary Table: Types of Carbohydrates

Type	Number of Sugar Units	Example	Main Function
Monosaccharide	1	Glucose	Energy source
Disaccharide	2	Sucrose	Transport/storage
Oligosaccharide	3-10	Cell surface oligosaccharides	Cell recognition
Polysaccharide	Hundreds-thousands	Starch, cellulose	Storage/structure