Carbohydrates & Lipids (DP IB Biology)

A polymer is a molecule made from a large number of monomers joined together in a chain.

Polymerisation is the process by which monomers join to form polymers.

False.

Not all macromolecules are polymers; for example, lipids are macromolecules but not polymers.

A condensation reaction is a reaction where molecules combine together, forming covalent bonds and resulting in polymers or macromolecules, with water being removed as part of the reaction.

A glycosidic bond is a strong covalent bond formed between two hydroxyl (OH) groups on different monosaccharides.

A peptide bond is a strong covalent bond formed between two amino acid monomers in polypeptides.

A phosphodiester bond is a bond formed between nucleotides in nucleic acids, consisting of a phosphate group and two ester bonds.

Hydrolysis is a reaction where covalent bonds are broken when water is added, often used to break down macromolecules into their monomers.

False.

In hydrolysis reactions, water is added to break bonds, not produced.

The general formula for monosaccharides is C_nH_2nO_n, where 'n' is the number of carbon atoms in the molecule.

The molecular formula of glucose is C₆H₁₂O₆.

True.

Glucose exists in two structurally different forms: alpha (α) glucose and beta (β) glucose.

The two polysaccharides that make up starch are amylose and amylopectin.

Amylose typically makes up 10-30% of starch.

Amylopectin is a branched polysaccharide that makes up 70-90% of starch and contains both 1,4 and 1,6 glycosidic bonds between α-glucose molecules.

Glycogen is the storage polysaccharide of animals and fungi.

False.

Glycogen is more branched than amylopectin.

Cellulose is a structural carbohydrate found in the cell walls of plants.

Cellulose is made up of β-glucose monomers.

In β-glucose, the hydroxyl group on carbon 1 sits above the carbon ring, whereas in α-glucose, it sits below the ring.

Cellulose gains strength from hydrogen bonding between strands of β-glucose monomers.

Microfibrils are structures formed when several molecules of cellulose are linked by hydrogen bonds.

Starch and glycogen are effective storage polysaccharides because they are compact and insoluble.

This is a molecule of α-glucose as the hydroxyl group on carbon 1 is below the ring.

Glycoproteins are structures formed by the combination of carbohydrates and polypeptides via covalent bonds.

True.

Glycoproteins act as receptor molecules for cell recognition and identification.

Endocytosis is a process in which glycoproteins act as receptor molecules.

An antigen is a substance that can identify cells as either "self" or "non-self" and may trigger an immune response if recognised as non-self.

Glycoproteins can act as antigen.

A person's blood type is determined by the glycoprotein antigens on the surface of their red blood cells.

The two main categories of lipids are triglycerides and phospholipids.

True.

Lipids are hydrophobic, they repel water and do not dissolve in it.

Triglycerides are lipids composed of three fatty acids bonded to a glycerol molecule.

A triglyceride consists of a glycerol molecule and three fatty acid chains bonded by ester bonds.

These fatty acids can be either saturated (containing single carbon-carbon bonds) or unsaturated (containing double bonds).

Phospholipids consist of a glycerol molecule, two fatty acid tails, and a phosphate head. The tails are hydrophobic, while the head is hydrophilic.

An ester bond forms when the hydroxyl group of a glycerol molecule bonds with the carboxyl group of a fatty acid.

It occurs during the formation of triglycerides and phospholipids.

Amphipathic lipids have both hydrophobic and hydrophilic regions.

Phospholipids are an example of amphipathic molecules.

The hydrolysis of triglycerides releases glycerol and fatty acids, which can be used as respiratory substrates.

Three water molecules are taken in during this process as reactants.

True.

Lipids contain 2× more energy per gram than most carbohydrates due to their high number of C-H bonds.

In animals, lipids are stored in adipose tissue.

Subcutaneous fats are stored below the skin. Visceral fats are stored around the major internal organs.

Fatty acids occur in two forms: saturated and unsaturated.

Saturated fatty acids have single carbon-carbon bonds in their hydrocarbon tails.

Each carbon atom in the hydrocarbon tail (except the final carbon) is bonded to two hydrogen atoms in saturated fatty acids.

Saturated fatty acids can pack tightly together due to their straight structure, increasing their melting point.

Saturated fatty acids are present in fats found in meat and butter.

Unsaturated fatty acids have carbon-carbon double bonds in their hydrocarbon tails. They do not contain the maximum number of hydrogen atoms.

The double bonds cause the hydrocarbon tail of unsaturated fatty acids to bend, making them less straight than saturated fatty acids.

A monounsaturated fatty acid has one carbon-carbon double bond.

Polyunsaturated fatty acids have multiple carbon-carbon double bonds.

Unsaturated fatty acids cannot pack as tightly together as saturated fatty acids, due to their kinked structure, so fats containing unsaturated fatty acids have a low melting points are often liquids at room temperature.

Phospholipids form the basic structure of the cell membrane.

True.

Cell membranes consist of phospholipid bilayers.

The phosphate head is polar and soluble in water (hydrophilic), allowing it to orient towards water.

When placed in water, phospholipids can form a single layer (monolayer) on the water’s surface.

The nonpolar fatty acid tails prevent water-soluble molecules (such as sugars, amino acids, and proteins) from passing through the membrane.

Small, nonpolar molecules like O₂ and CO₂ can diffuse across the lipid bilayer.

Two examples of steroid hormones are oestradiol and testosterone.

Steroid hormones, such as oestradiol and testosterone, contain cholesterol (a type of lipid) in their structure, allowing them to cross the lipid bilayer.