lipids and proteins

[Lipids] Composition of a triglyceride

Three fatty acid molecules and one glycerol molecule.

[Lipids] Reaction forming a triglyceride

Condensation reaction.

[Lipids] Bonds present in a triglyceride

Ester bonds.

[Lipids] Hydroxyl groups in glycerol

Three $-\text{OH}$ groups.

[Lipids] Chemical classification of glycerol

An alcohol.

[Lipids] Basic structure of a fatty acid

A long hydrocarbon chain ending in a carboxyl group ($-\text{COOH}$).

[Lipids] Two main types of fatty acid

Saturated and unsaturated fatty acids.

[Lipids] Structural characteristic of unsaturated fatty acids

Contains at least one $\text{C}=\text{C}$ double bond.

[Lipids] Structural characteristic of saturated fatty acids

Contains no $\text{C}=\text{C}$ double bonds.

[Lipids] Chain shape: Saturated vs. Unsaturated fatty acids

Saturated fatty acid chains are straight, whereas unsaturated chains have bends or kinks caused by $\text{C}=\text{C}$ double bonds.

[Lipids] Ratio of $\text{H}:\text{C}$ in fatty acids

Saturated fatty acids have a higher $\text{H}:\text{C}$ ratio than unsaturated fatty acids.

[Lipids] Melting point comparison of fatty acids

Saturated fatty acids have higher melting points than unsaturated fatty acids.

[Lipids] Sources of saturated vs. unsaturated fatty acids

Saturated fatty acids are found in animal fats; unsaturated fatty acids are found in plant oils.

[Lipids] Energy storage advantages of triglycerides

They contain a high proportion of $\text{C}-\text{H}$ bonds and store more energy per gram than carbohydrates.

[Lipids] Biological roles of triglycerides

Thermal insulation (reduces heat loss), buoyancy (stored lipid is less dense than water), and metabolic water supply (produced via oxidation during respiration).

[Lipids] Components of a phospholipid

One glycerol molecule, two fatty acids, and one phosphate group.

[Lipids] Properties of phospholipid head vs. tails

The negatively charged phosphate head is hydrophilic, while the uncharged, non-polar fatty acid tails are hydrophobic.

[Lipids] Major cellular structure formed by phospholipids

The phospholipid bilayer of cell membranes.

[Lipids] Structure and role of cholesterol

Has a four-ring carbon lipid structure (different from triglycerides), does not provide energy, and regulates cell membrane fluidity.

[Proteins] Monomers of proteins

Amino acids (20 standard types exist).

[Proteins] Variable region of an amino acid

The R group (side chain), which determines its chemical properties and functions.

[Proteins] Functional groups on an amino acid central carbon

An amino group ($-\text{NH}_2$, basic), a carboxyl group ($-\text{COOH}$, acidic), a hydrogen atom, and a variable R group.

[Proteins] Bond formation and breakdown between amino acids

Peptide bonds are formed by condensation reactions and broken by hydrolysis reactions.

[Proteins] Products of amino acid bonding stages

Two amino acids form a dipeptide; many amino acids form a polypeptide.

[Proteins] Definition of essential amino acids

Amino acids that cannot be synthesized by the human body and must be acquired through diet.

[Proteins] Primary structure of a protein

The specific sequence of amino acids in a polypeptide chain, held together by peptide bonds.

[Proteins] Secondary structure of a protein

Regular coiling or folding of the polypeptide backbone into $\alpha\text{-helices}$ or $\beta\text{-pleated sheets}$, stabilized by hydrogen bonds between $-\text{NH}$ and $\text{C}=\text{O}$ groups.

[Proteins] Examples of secondary protein structures

Keratin contains $\alpha\text{-helices}$, while fibroin in silk contains $\beta\text{-pleated sheets}$.

[Proteins] Tertiary structure of a protein

Precise 3D folding of a single polypeptide, stabilized by hydrogen bonds, ionic bonds (disrupted by pH changes), hydrophobic interactions, and strong disulfide bridges (in cysteine).

[Proteins] Quaternary structure of a protein

The arrangement of multiple polypeptide chains and/or non-protein prosthetic components (e.g., haem groups).

[Proteins] Globular vs. Fibrous proteins: Structure & Solubility

Globular proteins are compact, spherical, and water-soluble (hydrophilic groups outside); fibrous proteins form long, insoluble strands.

[Proteins] Globular vs. Fibrous proteins: Functions & Examples

Globular proteins are functional (e.g., haemoglobin, enzymes, insulin, immunoglobulins); fibrous proteins are structural (e.g., collagen, keratin, myosin, actin, fibrin).

[Proteins] Structure of haemoglobin

A conjugated globular protein made of four chains (two $\alpha\text{-globin}$ and two $\beta\text{-globin}$), each bound to a haem group containing iron ($\text{Fe}$) that reversibly binds oxygen.

[Proteins] Structure of collagen

A fibrous protein composed of three polypeptide chains in a triple helix rich in glycine, proline, and hydroxyproline, held together by hydrogen bonds.

[Proteins] Definition and causes of protein denaturation

The loss of a protein's 3D tertiary structure caused by altered temperature or pH.