Molecules of life

• Carbohydrates

  One of the four classes of large biological molecules
• Elements necessary for life

  • Water
  • Small molecules
  • Four classes of large biological molecules: Carbohydrates, Lipids (fats), Proteins, Nucleic acids
• All living things are made up of the compounds listed
• Covalent bonding

  Bonding of non-metals by sharing electrons
• Covalent bonding examples

  • H2O = water
  • CH4 = methane
  • NH3 = ammonia
• Ionic bonding

  Electrostatic attraction by oppositely charged ions
• Ionic bonding example

  • NaCl = salt
• Hydrogen bonding

  Weak electrostatic bonding due to uneven distribution of electrons in some atoms
• Monomer

  Smaller unit from which larger molecules are made
• Polymer

  Molecule made from a large number of monomers joined together in a chain
• Biological monomers and polymers

  • Carbohydrates: Monosaccharides -> Polysaccharides
  • Proteins: Amino acids -> Polypeptides and proteins
  • Nucleic acids: Nucleotides -> Nucleic acid
• Monosaccharide

  Single monomer, simple sugar (e.g. glucose, fructose)
• Oligosaccharide

  1. 20 monomers
• Disaccharide

  2 monomers (e.g. sucrose)
• Polysaccharide

  More than 20 monomers
• Polysaccharides

  • Starch
  • Glycogen
  • Cellulose
• Carbohydrates

  • Major energy source and components of nucleic acids and many lipids
  • Serve structural and regulatory roles and are associated with proteins and lipids
  • Structural and storage role in all organisms
• Alpha-glucose

  Forms starch when joined chemically via glycosidic bonds
• Beta-glucose

  Forms cellulose when joined to form a polymer
• Condensation reaction

  1. Two molecules combine to form a single molecule by removal of water molecule

  2. A covalent bond is formed following the removal of water, glycosidic bond
• Hydrolysis reaction

  Water is used to break down the bonds of a particular substance
• Amylopectin

  Branched chains of glucose
• Amylose

  Linear chains of glucose, in a helix
• Starch

  • Stored as granules in chloroplasts
• Glycogen

  • Amylose chain is shorter with more branches
  • Stored in liver and muscle cells
  • More compact than starch
  • Break down to release energy
• Cellulose

  • Chains of beta glucose, different from amylose chains
  • Do not form helices, beta pleated sheets
  • Stronger
  • Cross linked to form microfibrils of the cell wall via H bonds
• Lipids (Fats)

  Constructed from two types of small molecules: glycerol and fatty acids
• Glycerol

  A three-carbon alcohol with a hydroxyl (OH) group attached to each carbon
• Fatty acid

  Consists of carboxyl group (COOH) attached to a long carbon skeleton
• Saturated fat

  No double C=C bond present
• Unsaturated fat

  Contains one or more double C=C bonds
• Phospholipid

  • Hydrophilic head
  • Hydrophobic tails
  • Self-assemble into double-layered structures called bilayers
  • Hydrophobic tails point toward the interior
  • Existence of cells depends on phospholipids
• Cell membrane components

  • Channel protein
  • Glycoprotein
  • Glycolipid
• Triglyceride

  • Three fatty acids joined to glycerol via ester linkage
  • Major component of blood
  • Adipose tissue is primarily present in the form of triglycerides
  • Covers the internal organs and protects them from physical 'trauma' or 'shock'
• Cholesterol

  • A type of steroid, component in animal cell membranes and precursor from which other steroids are synthesized
  • Synthesised in liver - also obtained from eating animal products
  • Needed for cell membranes, brain and nerve tissue, steroid hormones and Vitamin D
  • A high level of cholesterol in blood clogs arteries, by forming plaques, may contribute to cardiovascular disease
• Proteins

  • After water, proteins are most abundant molecules in body
  • A diverse group of large complex polymers made up of amino acids
• Functions of proteins

  • Structural
  • Catalytic
  • Signalling
  • Transport and Storage
  • Defense
• Amino acid

  The only difference between each one is the nature of the R group
• There are 20 common amino acids encoded by the universal genetic code, plus 1 additional amino acid (selenocysteine) found in eukaryotes, and 1 more (pyrrolysine) found only in prokaryotes
• Peptide bond formation

  Condensation reaction: OH- from carboxylic group of one amino acid, and H- from second amino acid amine group form covalent peptide bond and release a water molecule