Biochemistry Basics: Carbohydrates, Lipids, Proteins and Nucleic Acids

Chemical Elements and Basic Biomolecules

Elements:

Carbohydrates: C, H, O

Lipids: C, H, O (P, S)

Proteins: C, H, O, N, S

Nucleotides and ATP: C, H, O, N, P

Mineral Elements

K (potassium): maintains osmotic pressure and the water balance, supports the heartbeat, plant seed germination and muscle contraction.

Na (sodium): regulates osmotic pressure, supports membrane permeability and stimulates nerve activity.

Ca (calcium): needed for healthy growth, strengthens bones and teeth, supports blood clotting and stimulates muscle contraction.

Fe (iron): essential for chlorophyll synthesis, acts as a catalyst and is a component of hemoglobin.

Water

H₂O: takes part in chemical reactions, supports cell functions, maintains the water balance and is resistant to heat.

Carbohydrates

Carbohydrates are classified into monosaccharides, disaccharides and polysaccharides.

Monosaccharides

• Ribose
• Deoxyribose
• Glucose
• Fructose
• Galactose

Disaccharides

• Sucrose: glucose + fructose
• Lactose: glucose + galactose
• Maltose: two glucose units

Polysaccharides

• Starch: the main plant storage carbohydrate
• Glycogen: the animal storage carbohydrate
• Cellulose: the main component of plant cell walls
• Chitin: made of glucose and amino groups; forms the cell walls of fungi

Monosaccharides and disaccharides are sweet and soluble in water. Polysaccharides are not sweet and are insoluble in water.

Functions of carbohydrates: energy source, energy storage and structural function.

Nucleic Acids

Nucleic acids (deoxyribonucleic acid and ribonucleic acid) are polymers made of nucleotide monomers.

DNA

DNA is made of a phosphate group (phosphoric acid residue), the sugar deoxyribose and nitrogenous bases: adenine (A), guanine (G), cytosine (C) and thymine (T).

A and G are larger purines; C and T are smaller pyrimidines. A pairs with T, and G pairs with C.

RNA

RNA is made of a phosphate group, ribose and nitrogenous bases: adenine (A), guanine (G), cytosine (C) and uracil (U). RNA is responsible for protein synthesis and is formed from long polymer chains. There are three types:

• Messenger RNA (mRNA): copies DNA and carries information about protein structure to the ribosome.
• Transfer RNA (tRNA): transports amino acids to the ribosome.
• Ribosomal RNA (rRNA): forms ribosomes, which produce proteins.

ATP

Adenosine triphosphate (ATP) is a nucleotide monomer consisting of a nitrogenous base, three phosphate groups and ribose. ATP is the universal energy carrier of all living organisms.

Proteins

Proteins are polymers made of amino acid monomers linked into long chains.

Amino acids join through peptide bonds, which form between the carboxyl group of one amino acid and the amino group of another.

Levels of Protein Structure

1. Primary structure: a chain of amino acids linked by peptide bonds.
2. Secondary structure: the chain folds into a helix or pleated sheet, stabilized by hydrogen bonds between its parts.
3. Tertiary structure: the polypeptide folds further into a three-dimensional globular configuration.
4. Quaternary structure: several polypeptide chains join together, held by hydrogen and ionic bonds.

Protein Denaturation

Denaturation is the disruption of the natural spatial structure of a protein caused by changes in temperature, pH or solvent.

When denaturation occurs, the protein can no longer perform its biological function. Denaturation can be a reversible process.

Functions of Proteins

• Structural: collagen forms intercellular substances, tendons, ligaments and cartilage; keratin is the main component of skin, nails and hair and is insoluble in water.
• Protective: fibrinogen forms blood clots; antibodies support the immune system.
• Transport: hemoglobin carries oxygen.
• Movement: myosin and actin enable the movement of the organism.
• Energy: casein in milk and albumin in egg whites can serve as an energy source.
• Catalytic: enzymes take part in chemical reactions.

Lipids

Lipids are included in the basic biomolecules and contain carbon, hydrogen and oxygen, with phosphorus and sulfur in some types.