Biomolecules

• Important elements in living systems: C, H, O, N, P, S, K, Ca, Na, Cl, Mg, Fe, Cu, I, Mo, Zn
• By dry mass, the percentage composition of elements in living systems:

  • O: 63%
  • C: 20%
  • H: 10%
  • N: 2.5%
  • Ca: 2.5%
  • P: 1.1%
  • Cl, Fe, S, K, Na: <0.2%
  • Mg, Cu, I, Mo, Zn: <0.1%
• All important biological molecules contain carbon

  • Molecules with carbon are called organic (except for CO2)
  • Carbon forms 4 covalent bonds, allowing for diverse shapes of molecules
• Most biological molecules have a core of carbon and hydrogen

  • Molecules differ in structure and function due to different functional groups
• Major classes of biological molecules:

  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
  • Large biological molecules are called macromolecules, built from smaller building blocks into polymers
• Carbohydrates:

  • Compounds made of C, H, and O
  • Used for energy storage and structures
  • Caloric value of 4.1 kilocalories/gram
• Simplest class of carbohydrates: monosaccharides

  • All have 3 to 6 carbons
  • Six-carbon sugars have the chemical formula C6H12O6
  • Monosaccharides are building blocks of more complex carbohydrates
• Disaccharides:

  • Formed by dehydration synthesis
• Polysaccharides:

  • Polymers of monosaccharides
  • Starches are polymers of glucose
  • Starches are used for energy
  • Different properties of glucose stereoisomers: Starch (α-glucose) is digestible, Cellulose (β-glucose) is indigestible
• Chitin:

  • Structural polysaccharide
  • Polymer of β-glucose with a nitrogen-containing functional group
  • Used in cell walls of fungi and exoskeletons in arthropods
• Lipids:

  • Chemically diverse organic molecules
  • Major classes: fatty acids, neutral fats, phospholipids, steroids
  • Functions include energy storage, cell membrane structure, vitamins, and hormones
• Fatty acids:

  • Long-chain carbon molecules with carboxyl group
  • Saturated (no C=C bonds) and unsaturated (C=C bonds) varieties
• Neutral fats:

  • Composed of glycerol and fatty acids
  • Used for long-term energy storage
  • Saturated fats are solid at room temperature, unsaturated fats are liquid
• Phospholipids:

  • Structural lipids integral to cell membranes
  • Structurally similar to triglycerides with a choline group replacing a fatty acid
  • Have hydrophilic heads and hydrophobic tails
• Steroids:

  • More complex structure and diverse functions
  • Cholesterol is important in cell membranes
  • Vitamin D is necessary for biochemical reactions
• Proteins:

  • Most functionally diverse biological molecules
  • Protein diversity is the basis of functional diversity
• Proteins are the most functionally diverse class of biological molecules
• Proteins serve as enzymes, for defense, transport, support, motion, regulation, and storage
• Proteins have a gross caloric value of 5.7 kcal/g, but the metabolism of proteins creates toxic nitrogenous waste that must be processed for excretion from the body
• Proteins have a net caloric value of 4.8 kcal/g
• Proteins are polymers of amino acids
• There are 20 different amino acids used in proteins, each with a central carbon, an amino group (NH2), a carboxyl group (COOH), and a different R group
• Proteins are polymers of amino acids joined through peptide bonds, forming polypeptides
• Proteins are classified at different levels of structure: primary, secondary, tertiary, and quaternary
• Hemoglobin (Hb) is a protein that carries oxygen in blood, has quaternary structure, and is sensitive to changes in pH
• Nucleic acids are the repositories and carriers of information
• DNA and RNA are polymers of nucleotides
• DNA contains the information that makes living things what they are and is passed from parent to child through sperm or egg
• RNA is responsible for protein synthesis and mediates the expression of genetic information
• DNA and RNA have different sugars (ribose for RNA, deoxyribose for DNA) and different nitrogenous bases (A, T, G, C for DNA; A, U, G, C for RNA)
• The linkage between nucleotides in DNA and RNA is called a phosphodiester bond
• RNA is a single-stranded polymer of nucleotides, while DNA is a double-stranded molecule with two strands wrapping around each other in a helix
• ATP (Adenosine Triphosphate) is a high-energy molecule used for important energy transfer reactions
• NAD (Nicotinamide Adenine Dinucleotide) is composed of two nucleotides and is used in oxidation-reduction reactions to accept or donate high-energy electrons
• 1. Hydroxyl (-OH): Found in alcohols and phenols.
  2. Carbonyl (C=O):

  • Ketone: Carbonyl group bonded to two carbon atoms.
  • Aldehyde: Carbonyl group bonded to at least one hydrogen atom.

  1. Carboxyl (-COOH): Found in carboxylic acids.
  2. Amino (-NH2): Found in amines and amino acids.
  3. Sulfhydryl (-SH): Found in thiols.
  4. Phosphate (-PO4): Found in nucleotides, ATP, and phospholipids.
  5. Ether (-O-): Commonly found in ethers.
• The methyl group is a common functional group in organic chemistry, consisting of one carbon atom bonded to three hydrogen atoms (-CH3).
• Proteins are large, complex molecules composed of amino acid subunits. They perform a wide range of functions in cells such as catalysis, transport and support. Some of example of this are hemoglobin, myosin and collagen.
• Nucleic acids are polymers of nucleotides and are involved in the storage and transmission of genetic information. These function for encoding genes and for gene expresion. Some examples are chromosomes and messenger RNA.
• Lipids are a diverse group of hydrophobic molecules that include fats, oils, phospholipids, and steroids. The building blocks of lipid are the fatty acids, phosphate groups (for phospholipid) and glycerol. They serve as energy storage molecules, structural components of cell membranes, and signaling molecules.
• Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen atoms, usually in a ratio of 1:2:1. They serve as a major source of energy for organisms and also play structural roles. The building blocks of this is the monosaccharides. Examples include sugars, starches, and cellulose.