Biological Macromolecules: Carbohydrates and Lipids

Comprehensive review flashcards covering biological macromolecules, focusing on the structures, classifications, chemical reactions, and biological functions of carbohydrates and lipids based on Dr. Aya El-Hanafy's biochemistry lecture.

What are the four major classes of large biological molecules (macromolecules) that make up living organisms?

Carbohydrates, lipids, proteins, and nucleic acids.

How does a condensation (dehydration) reaction synthesize a polymer from monomers?

Two monomers bond together through the loss of a water molecule, linking them with a covalent bond while requiring an input of energy.

How does hydrolysis break down polymers into monomers, and what happens energetically during this reaction?

Hydrolysis adds a water molecule to break the covalent bonds between monomers, liberating energy that was contained during condensation.

What general chemical formula do most carbohydrates follow?

$C_n(H_2O)_n$ (commonly written as $(CH_2O)_n$).

What are the three defining chemical characteristics of carbohydrates?

1. Composed of Carbon, Hydrogen, and Oxygen ($C, H \& O$).\n2. Contain more than one hydroxyl group (poly-hydroxyl).\n3. Contain a free active carbonyl group: either an aldehyde ($HC=O$) or a ketone ($C=O$).

What is the ratio of Carbon, Hydrogen, and Oxygen in a molecule of glucose ($C_6H_{12}O_6$)?

A $1:2:1$ ratio.

How do simple carbohydrates differ from complex carbohydrates in terms of providing energy to tissues?

Simple carbohydrates provide fast-acting energy, whereas complex carbohydrates provide long-lasting energy.

In what form and locations do humans and animals store excess dietary carbohydrates?

Excess carbohydrate is converted into glycogen and stored in the liver and muscle tissue to meet immediate energy demands.

How are carbohydrates classified based on the number of sugar units they contain?

1. Monosaccharides: 1 sugar unit (e.g., glucose, fructose, galactose)\n2. Disaccharides: 2 sugar units (e.g., maltose, sucrose, lactose)\n3. Oligosaccharides: 3–10 sugar units (e.g., raffinose, sesamose)\n4. Polysaccharides: > 10 sugar units (e.g., starch, glycogen, fibers)

How are monosaccharides classified based on their carbon atom count and active carbonyl groups?

By carbon number: Trioses ($3\text{ carbons}$), Tetroses ($4\text{ carbons}$), Pentoses ($5\text{ carbons}$), and Hexoses ($6\text{ carbons}$).\nBy active group: Aldoses containing an aldehyde group ($HC=O$) and Ketoses containing a ketone group ($C=O$).

What type of covalent bond connects two monosaccharide units to form a disaccharide?

An O-glycosidic bond formed via a dehydration reaction.

What specific pairs of monosaccharide subunits make up sucrose, maltose, and lactose?

• Sucrose: fructose + glucose\n- Maltose: glucose + glucose\n- Lactose: glucose + galactose

What are the primary biological roles of the polysaccharides starch, glycogen, cellulose, and chitin?

• Starch: energy storage in plants\n- Glycogen: energy storage in animals (liver and muscle)\n- Cellulose: structural support in plant cell walls\n- Chitin: structural component in arthropod exoskeletons and fungal cell walls

Why are lipids unique compared to other classes of macromolecules?

Lipids are the one class of large biological molecules that do not form polymers.

Why are lipids hydrophobic and relatively insoluble in water?

Water molecules form hydrogen bonds with each other and exclude fats, leaving lipids with little or no affinity for water.

How does the energy yield of lipids compare to that of carbohydrates or proteins?

Lipids yield twice the energy produced by the same weight of carbohydrates or proteins.

What chemical components constitute a triacylglycerol (fat molecule), and what linkage joins them?

One glycerol molecule joined to three fatty acids by ester linkages.

How do saturated fatty acids differ from unsaturated fatty acids in terms of chemical bonds and physical state at room temperature?

Saturated fatty acids have no double bonds and are solid at room temperature (e.g., stearic acid in most animal fats); unsaturated fatty acids have one or more double bonds (where cis double bonds cause bending) and are liquid at room temperature (e.g., oleic acid in plant and fish fats).

What is the process of hydrogenation, and what health concern is associated with its products?

Hydrogenation converts unsaturated fats into saturated fats by adding hydrogen; it creates trans fats, which may contribute more than saturated fats to cardiovascular disease through plaque deposits.

What is the structural organization of a phospholipid molecule?

A glycerol molecule attached to two hydrophobic fatty acid tails and a hydrophilic head composed of a phosphate group and its attachments (such as choline).

What class of lipids is characterized by the carbon skeleton of four fused rings shown in this diagram, and what is a primary animal example?

Steroids; an important example is cholesterol, a critical component of animal cell membranes.

What specialized insulating functions do lipids perform in the nervous system and under the skin?

Lipids in the myelin sheath of nerve fibers serve as electrical insulators, while lipids stored under the skin serve as thermal insulators.