Biological Molecules and Carbohydrates

Biological Molecules

• Biological molecules are essential for life, and are broadly categorized as organic and inorganic.
• Organic biomolecules include carbohydrates, lipids, proteins, and nucleic acids.
• Inorganic biomolecules include water and minerals.

Carbohydrates

• Carbohydrates are composed of carbon, hydrogen, and oxygen.
• They are an important source of energy, provide structural cell support, and facilitate cell communication.
• Carbohydrates are classified based on the number of sugar units they contain:
  • Monosaccharides: Single sugar unit (e.g. glucose, fructose, galactose)
  • Disaccharides: Two sugar units linked by a glycosidic bond (e.g. sucrose, lactose, maltose)
  • Polysaccharides: Many sugar units linked by glycosidic bonds (e.g. starch, glycogen, cellulose)

Monosaccharides

• Monosaccharides are simple sugars with multiple hydroxyl (OH) groups.
• Classified based on the number of carbons: triose (3C), tetrose (4C), pentose (5C), hexose (6C).
• Aldoses contain an aldehyde group and are reducing sugars.
• Ketoses contain a ketone group and are non-reducing sugars.

Glucose

• The primary fuel source for human cells.
• Concentration in blood is about 1 gram per cubic decimeter.
• Two glucose molecules react to form maltose (a disaccharide).
• Starch and cellulose are polysaccharides composed of glucose units.

Galactose

• Reacts with glucose to form lactose (a disaccharide).
• Cannot be used in respiration like glucose.

Fructose

• A hexose sugar.
• Reacts with glucose to form sucrose (a disaccharide).

Ribose and Deoxyribose

• Both are pentose sugars.
• Ribose is part of RNA nucleotides.
• Deoxyribose is part of DNA nucleotides.

Disaccharides

• Two monosaccharides react to form disaccharides.
• Disaccharides are soluble in water but too large to pass through cell membranes via diffusion.
• They are broken down in the small intestine during digestion to form smaller monosaccharides that can pass into the blood and into cells.

Hydrolysis Reaction

• The reverse of a condensation reaction.
• Releases energy.

Condensation Reaction

• Releases water and requires energy.
• Forms a glycosidic bond between two monosaccharides.

Polysaccharides

• Monosaccharides can undergo condensation reactions to form long chains of sugar units called polysaccharides.
• Important for energy storage and structure.

Starch

• Stored energy in plants.
• Exists in two forms:
  • Amylose: Unbranched polymer of α-glucose, coils into a helical structure, forms a colloidal suspension in hot water.
  • Amylopectin: Branched polymer of α-glucose, completely insoluble in water.

Glycogen

• A branched polymer of α-glucose, very similar to amylopectin.
• Acts as a carbohydrate energy store in humans.

Cellulose

• A polysaccharide composed of glucose units.
• Provides structural support for plant cell walls.
• Humans can’t digest cellulose due to lack of cellulase enzyme.
• Herbivores have cellulase enzymes in their stomachs which allows them to digest it.

Lipids

• A diverse group of molecules including fats, oils, waxes, and some steroids.
• Esters formed from fatty acids and alcohols (glycerol or alcohol chains).
• Primarily act as energy storage molecules.
• Triglycerides are fats if solid at room temperature and oils if liquid.
• Stored in fat cells (adipocytes), responsible for fat and lipid storage in animals.

Lipids: Properties

• Insoluble in water.
• Longer chains increase hydrophobicity and decrease solubility.
• Melting points are influenced by chain length and saturation, with unsaturated fats having lower melting points.

Importance of Lipids

• Main component of cell membranes (phospholipids).
• Heat and water insulation.
• Energy storage, protection, and cellular communication.

Proteins

• Made of amino acids linked by peptide bonds.
• 20 different amino acids, with proteins having unique combinations of these.

Protein Structure

• Primary Structure: Sequence of amino acids in a polypeptide chain. Directed by genetic information.
• Secondary Structure: Local three-dimensional structure of a protein chain, formed by hydrogen bonds between backbone atoms.
• Tertiary Structure: Overall three-dimensional shape of a protein, determined by interactions between R-groups.

Vitamins

• Many cannot be synthesized by the body and must be obtained through diet.
• Fat-soluble vitamins can be stored in the liver and fatty tissues.
• Water-soluble vitamins cannot be stored and need to be consumed regularly.

Water

• Composed of two hydrogen atoms covalently bonded to one oxygen atom.
• Essential for life, existing in gaseous, liquid, and solid states.
• Excellent solvent, allowing transportation of various substances.
• Polar molecule with unequal distribution of charges.

Minerals

• Inorganic compounds essential for building materials and metabolic functions.
• Iron is needed for hemoglobin synthesis, transporting oxygen in red blood cells.
• Calcium is important for bone formation and muscle and nerve function.
• Magnesium is a component of chlorophyll involved in photosynthesis.

Summary of Biological Molecules

• Carbon compounds are the building blocks of life.
• Large polymers are formed by joining smaller monomers.
• Four main types: carbohydrates, lipids, proteins, and nucleic acids.
• Monosaccharides are linked by glycosidic bonds to form disaccharides and polysaccharides.
• Peptide bonds join amino acids to form proteins.
• Lipids are esters of fatty acids and alcohols.