IB Biology SL - Carbohydrates, Lipids, & Proteins

Why is carbon essential for life?

Carbon can form four covalent bonds, allowing it to build diverse and complex molecules needed for life, including carbohydrates, lipids, proteins and DNA.

What makes carbon compounds so diverse?

Carbon can form single, double and triple bonds, as well as chains, branches and rings.

What is a monomer?

A small molecule that can join with other monomers to form a polymer.

What is a polymer?

A large molecule made of many repeating monomers joined together.

What is a condensation reaction?

A reaction that joins two molecules by forming a covalent bond and releasing a molecule of water.

What is hydrolysis?

A reaction that breaks a molecule into smaller units by adding water.

What is the difference between condensation and hydrolysis?

Condensation joins molecules and releases water; hydrolysis breaks molecules apart using water.

What is a monosaccharide?

A single sugar molecule that acts as a building block for larger carbohydrates.

Give three examples of monosaccharides.

Glucose, fructose and galactose.

What is the general formula of many monosaccharides?

(CH2O)n, where n is commonly 3–7.

What are the main functions of monosaccharides?

They provide an immediate energy source and act as building blocks for larger carbohydrates.

How are disaccharides formed?

Two monosaccharides join through a condensation reaction, forming a glycosidic bond.

What is a glycosidic bond?

A covalent bond that joins two monosaccharides.

What are polysaccharides?

Large carbohydrates made of many monosaccharides joined by glycosidic bonds.

What are the main functions of polysaccharides?

Energy storage and structural support.

What is starch?

A plant storage polysaccharide made of alpha-glucose.

What are the two components of starch?

Amylose and amylopectin.

What is amylose?

An unbranched, coiled polymer of alpha-glucose joined by alpha-1,4 glycosidic bonds.

What is amylopectin?

A branched polymer of alpha-glucose with alpha-1,4 and alpha-1,6 glycosidic bonds.

Why is starch suitable for energy storage?

It is compact, insoluble and does not significantly affect the cell's water potential.

What is glycogen?

A storage polysaccharide made of alpha-glucose, found in animals and fungi.

Where is glycogen stored in humans?

Mainly in the liver and skeletal muscles.

Why is glycogen suitable for energy storage?

It is compact, insoluble and highly branched, allowing glucose to be released rapidly.

What is cellulose?

A structural polysaccharide made of beta-glucose that forms plant cell walls.

How are glucose molecules arranged in cellulose?

Beta-glucose molecules are joined by beta-1,4 glycosidic bonds, with alternate molecules rotated 180 degrees.

What gives cellulose its strength?

Hydrogen bonds form between parallel cellulose chains, creating strong microfibrils.

Why is cellulose suitable as a structural material?

Strong microfibrils provide rigidity, support and resistance to stretching.

What is the difference between starch and cellulose?

Starch is made of alpha-glucose for energy storage; cellulose is made of beta-glucose for structural support.

What is a glycoprotein?

A protein with carbohydrate chains attached to it.

What is the role of glycoproteins in cell-cell recognition?

Carbohydrate chains act as identification markers, allowing cells to recognize one another.

What does hydrophobic mean?

Repelled by water or unable to mix with water because a substance is non-polar.

Why are lipids hydrophobic?

They contain mainly non-polar hydrocarbon regions that do not form hydrogen bonds with water.

What is a triglyceride made of?

One glycerol molecule bonded to three fatty acid molecules.

How are triglycerides formed?

Three condensation reactions form three ester bonds between glycerol and fatty acids, releasing three water molecules.

What is an ester bond?

A covalent bond formed between the hydroxyl group of glycerol and the carboxyl group of a fatty acid.

What is a fatty acid?

A molecule consisting of a carboxyl group attached to a hydrocarbon chain.

What is a saturated fatty acid?

A fatty acid containing no carbon-carbon double bonds.

What is a monounsaturated fatty acid?

A fatty acid containing one carbon-carbon double bond.

What is a polyunsaturated fatty acid?

A fatty acid containing two or more carbon-carbon double bonds.

How does saturation affect fatty acid structure?

Saturated chains are relatively straight; double bonds in unsaturated chains create bends or kinks.

How does saturation affect the melting point of fats?

Saturated fats generally have higher melting points than unsaturated fats because their straight chains pack more closely.

What are the functions of triglycerides in adipose tissue?

Long-term energy storage and thermal insulation.

Why are triglycerides effective energy stores?

They contain many energy-rich C-H bonds and release large amounts of energy when oxidized.

Why are triglycerides suitable for long-term energy storage?

They are insoluble in water, compact and have a high energy content per gram.

What is adipose tissue?

Connective tissue containing cells called adipocytes that store triglycerides.

How do triglycerides provide thermal insulation?

Fat beneath the skin reduces heat loss from the body.

What is a phospholipid made of?

One glycerol, two fatty acids and one phosphate-containing group.

How are phospholipids formed?

Condensation reactions form ester bonds between glycerol and two fatty acids.

What is the structure of a phospholipid?

A hydrophilic phosphate head and two hydrophobic fatty acid tails.

What does amphipathic mean?

Having both hydrophilic and hydrophobic regions within the same molecule.

Why do phospholipids form bilayers in water?

Hydrophilic heads face the watery environments while hydrophobic tails face inward, away from water.

What is the structure of a phospholipid bilayer?

Two layers of phospholipids with heads facing the aqueous surroundings and tails facing each other.

Why are phospholipid bilayers important?

They form the basic structure of cell membranes and create a barrier between the cell and its surroundings.

What are steroids?

A type of lipid characterized by four fused carbon rings.

Why can non-polar steroids pass through the phospholipid bilayer?

Their non-polar nature allows them to dissolve in the hydrophobic interior of the membrane and diffuse across it.