Biomolecules: Functional Groups, Monomers/Polymers, and Carbohydrate Chemistry

Functional groups and their roles

  • Hydroxyl (OH) group
    • When attached to the main carbon skeleton, it acts as a functional group rather than an ion
    • Makes the region polar and capable of hydrogen bonding; helps define reactivity of the molecule
    • Earlier context: hydroxyl ions in water relate to acids/bases; presence on molecules affects interactions with water and other molecules
  • Carbonyl group (C=O)
    • Two main varieties: aldehydes and ketones
    • Ketone: carbonyl carbon bonded to other carbon(s) on both sides; typically located in the middle of a carbon chain
    • Aldehyde: carbonyl carbon bonded to at least one hydrogen; located at an end of the chain
    • Structure of carbonyl helps determine molecule’s class and reactivity
  • Carboxyl group (—COOH)
    • Very special case of carbonyl chemistry; carbon is double-bonded to oxygen and also bonded to a hydroxyl (OH)
    • Typically end of a molecule (the hydrogen is acidic and can dissociate); strongly influences molecule’s polarity and reactivity
    • Repeatedly seen in biology (especially in proteins, amino acids, and fatty acids)
  • Amino group (—NH₂)
    • Nitrogen can form three single bonds; here one bond to the main molecule and two to hydrogens
    • Functions as an endpoint group in amino acids; no other atoms typically bond to the amino group beyond its attachment to the main molecule
    • Central to amino acids, the building blocks of proteins
  • Thiol group (—SH)
    • Sulfur-containing group; sulfur is relatively electronegative and forms polar bonds
    • Can create slight negative charge on sulfur and positive region on hydrogen; facilitates hydrogen bonding and interactions with other R groups or water
    • Important for protein structure (e.g., forming disulfide bridges in some contexts) and overall folding
  • Phosphate group (—PO₄²⁻ or related forms)
    • Common shorthand: the phosphate group in biology is often shown as O–P(=O)(O⁻)₂–O (with a negative charge)
    • Net charge often −2 when attached to biomolecules; negative charges enable interactions with polar and ionic species
    • In nucleotides, phosphates form the backbone that links sugars; in ATP, three phosphates store energy
  • Methyl group (—CH₃)
    • Carbon with three hydrogens; hydrophobic, nonpolar
    • Commonly acts as a nonpolar junction or end-cap in molecules; ubiquitous in biomolecules
  • Summary note on functional groups
    • The arrangement and combination of these groups on a carbon skeleton determine the identity and function of biomolecules
    • Small changes in structure can dramatically alter function due to changes in polarity, hydrogen bonding, and reactivity

Building blocks and reactions that create biological macromolecules

  • Monomers and polymers
    • Monomer: a single unit that can be joined to others
    • Polymer: a long molecule built from many monomer units
    • Poly- means many; mono- means one; mer means part
  • Dehydration synthesis (condensation) vs hydrolysis
    • Dehydration synthesis: two monomers covalently bond and a molecule of water is released
    • General form: Monomer + Monomer → Dimer + H₂O (via covalent bond formation)
    • Hydrolysis: water is added to break a covalent bond between monomers
    • General form: Dimer + H₂O → Monomer + Monomer
    • Enzymes regulate dehydration synthesis and hydrolysis in biological systems
  • Enzymes
    • Special proteins that act as catalysts to speed up chemical reactions
    • In dehydration reactions, enzymes facilitate the removal of H and OH to form the covalent bond and release water
    • Hydrolysis requires enzymes to break bonds using water
  • Macromolecules and polymers
    • Macromolecule: large biomolecule (proteins, carbohydrates, lipids, nucleic acids)
    • Lipids are the notable exception: they are large but do not form regular repeating polymers like the other three classes
    • Polymers are built from repeating subunits called monomers
  • Why these concepts matter
    • Structure determines function: changing a functional group or bond can change biological activity
    • Small building blocks (amino acids, monosaccharides, nucleotides) assemble into large, functional macromolecules needed for life
  • Energy and metabolism link
    • Energy stored in covalent bonds (e.g., in ATP’s phosphates) can be released to power cellular work
    • Food provides the raw materials; organisms convert them into energy-bearing molecules (ATP) to power life processes

Lipids and the big contrast among biomolecules

  • Lipids as hydrophobic and non-polymeric molecules
    • Do not have regular repeating subunits like proteins, carbohydrates, and nucleic acids
    • Exhibit a variety of structures (fats/triglycerides, phospholipids, steroids, etc.) but share a hydrophobic character
    • They are essential for membranes, energy storage, and signaling but are structurally and chemically distinct from the other three major polymer classes
  • Visual takeaway from lab examples
    • Lipids can be observed as oils that separate from water, illustrating their hydrophobic nature
  • Why lipids matter in the semester narrative
    • They provide contrast to the repeating-polymer architecture; they also participate in energy storage and membrane structure

Carbohydrates: monosaccharides, disaccharides, and polysaccharides

  • Monosaccharides (simple sugars)
    • General formula for a simple sugar: CnH{2n}O_n
    • Common example: glucose with formula C6H{12}O_6
    • Other monosaccharides include ribose (DNA/RNA sugar, C5H{10}O_5) and deoxyribose (RNA sugar, deoxygenated ribose)
    • Isomers: molecules with the same formula but different structures
    • Structural isomers example: glyceraldehyde (aldose) vs dihydroxyacetone (ketose)
    • Aldose vs ketose (carbonyl position determines classification)
    • Aldehyde: carbonyl group at the end of the chain (terminal carbonyl)
    • Ketone: carbonyl group in the middle of the chain
    • Ring vs linear forms
    • In dry form, monosaccharides can be linear; in aqueous solution, they cyclize to ring forms
    • Life predominantly uses ring forms in aqueous environments
    • Common 5- and 6-carbon sugars
    • 5-carbon: ribose
    • 6-carbon: glucose, fructose (glucose and fructose are isomers with same formula but different structures)
    • Important structural mnemonic
    • Ketones sugars contain the ketone in the middle; aldehyde sugars contain the aldehyde at the end
    • Examples of important monosaccharides
    • Glucose: central energy source; C6H{12}O_6
    • Fructose: found in many dietary sources (e.g., high-fructose corn syrup)
    • Ribose and deoxyribose: components of nucleic acids
  • Dissacharides (two monosaccharides linked)
    • Formed by dehydration synthesis: loss of water as two monosaccharides join via a glycosidic linkage
    • Examples:
    • Maltose: glucose + glucose (via glycosidic bond)
    • Sucrose: glucose + fructose
    • Lactose: glucose + galactose
    • Nomenclature and digestion
    • Glycosidic linkage: the covalent bond that links two monosaccharides; essential for the formation of larger carbohydrates
    • Digestion of disaccharides requires specific enzymes (e.g., lactase for lactose)
    • Lactose intolerance
    • Some individuals lack lactase; unable to break lactose into glucose and galactose
    • Evolutionary note: lactose tolerance arose in some human populations with dairy domestication
  • Polysaccharides (many monosaccharide units)
    • Functionally two broad roles:
    • Energy storage (easy to hydrolyze) – e.g., starch in plants, glycogen in animals
    • Structural support (difficult to hydrolyze) – e.g., cellulose in plants, chitin in some invertebrates
    • Key concepts:
    • Polymers formed by linking many monosaccharides via covalent glycosidic bonds
    • A polymer’s properties (build/enzymatic digestibility) depend on the type of glycosidic linkage (e.g., alpha vs beta) and the overall 3D structure
    • Alpha glycosidic link: a type of glycosidic bond in which the linkage is in the alpha orientation (example: starch components)
    • Specific examples mentioned
    • Starch: storage polysaccharide in plants; energy store
    • Glycogen: storage polysaccharide in animals; highly branched for rapid energy release
    • Cellulose: structural polysaccharide in plants; not easily digested by humans due to beta linkages
  • Blood groups and oligosaccharides
    • Blood type is determined by oligosaccharide patterns on red blood cells
    • A antigen and B antigen correspond to specific oligosaccharide extensions; type O has no A/B antigens
    • O blood type is often described as lacking surface markers that would be recognized as foreign by recipients with A or B antigens

Proteins and amino acids

  • Amino acids: building blocks of proteins
    • Core structure: central carbon (alpha carbon) bound to four groups
    • Amino group (—NH₂)
    • Carboxyl group (—COOH)
    • Hydrogen atom (H)
    • R group (side chain that varies among amino acids)
    • When an amino acid is built as described, the side chain (R) distinguishes one amino acid from another
    • Formation of amino acids into proteins via peptide bonds involves dehydration synthesis: removal of water to form a covalent bond between the carboxyl group of one amino acid and the amino group of the next
  • Importance of proteins
    • Proteins are essential for structure (muscle, enzymes, etc.) and function in biology
    • Without proteins, life as we know it would not exist
  • Enzymes (special case of proteins)
    • Enzymes catalyze chemical reactions; many dehydration reactions in biology require enzyme activity
    • Enzyme-regulated dehydration ensures bonds form in a controlled manner

Nucleic acids and energy carriers

  • Phosphate backbone and nucleotides
    • Nucleic acids (DNA and RNA) have a backbone made of sugar-phosphate-sugar-phosphate
    • Phosphate groups are key to linking nucleotides; phosphates contribute negative charges and polarity to the backbone
  • ATP: adenosine triphosphate
    • Structure: adenosine + three phosphate groups
    • Adenosine consists of adenine (a nitrogenous base) attached to ribose (a sugar)
    • Energy storage and release
    • Bond between the last two phosphates is high-energy due to charge repulsion; breaking this bond releases energy used for cellular work
    • The last phosphate bond is particularly important for energy release
    • Important context about energy use
    • The body’s ATP supply is finite; a person has roughly a few minutes of ATP-ready energy at any moment (the lecture cites about four minutes)
    • Relevance to metabolism
    • ATP is produced in processes like photosynthesis and aerobic respiration and acts as a universal energy currency
  • Nucleotides and nucleic acids as backbones
    • Phosphates are integral to DNA and RNA backbones; the phosphate group is not just an energy carrier but a structural component of genetic material

Energy and metabolism in context

  • Photosynthesis and respiration link to glucose
    • Glucose production in photosynthesis uses energy from sunlight to form carbon-carbon bonds; carbon in glucose ultimately comes from CO₂ in the air
    • Glucose stores high-energy bonds that can be broken down to harvest energy (via cellular respiration) to form ATP
    • The rate and efficiency of ATP production depend on oxygen availability (aerobic vs anaerobic conditions)
  • Energy flow summary
    • Food provides substrates; biosynthetic pathways assemble energy-rich molecules (e.g., glucose, amino acids, nucleotides)
    • Energy is captured in ATP and used for cellular work (muscle movement, breathing, heart function, etc.)
  • The big picture: structure-function-energy
    • The transcript emphasizes building blocks, how they connect, and why their arrangements matter for life processes

Quick recap of key terms and concepts

  • Monomer vs. polymer; dehydration synthesis; hydrolysis; enzyme regulation
  • Major functional groups: hydroxyl, carbonyl (aldehyde vs ketone), carboxyl, amino, thiol, phosphate, methyl
  • Carbohydrate hierarchy: monosaccharides → disaccharides → polysaccharides
  • Ring vs linear forms of sugars; aldose vs ketose classification
  • Glycosidic linkage (including α-glycosidic bonds) and its role in forming complex carbohydrates
  • Major carbohydrate roles: energy storage (starch, glycogen) vs structure (cellulose)
  • Lipids: hydrophobic, diverse structures, not polymers like other macromolecules
  • Amino acids and protein structure; dehydration synthesis forming peptide bonds
  • Nucleotides and nucleic acids; phosphate backbone; ATP as energy currency
  • Blood types and oligosaccharides as reference to complex carbohydrate roles on cell surfaces

Connections to broader biology themes

  • The same functional groups recur across biomolecules, enabling a cohesive language to describe structure and function
  • The way atoms bond and the 3D arrangement determine how molecules behave in water and in biological environments
  • Energy flow underpins all life processes; understanding ATP formation and hydrolysis helps explain metabolism, exercise, and cellular needs
  • The concept of polymers vs. non-polymers (lipids) highlights diversity in biomolecule architecture and function
  • Evolutionary context for human traits (e.g., lactose tolerance) illustrates how chemistry intersects with biology and history