B1.1 Carbohydrates and Lipids 2.0

• The chemical properties of carbon allow it to form the macromolecules found in all living organisms such as: carbohydrates, lipids, proteins and nucleic acids
• carbons have four valence electrons in its' outer shells allowing them to form four covalent bonds with other carbon atoms or non-metal elements
• the covalent bonds that carbons form can be single bonds or a combination of single and double bonds
• covalent bonds are bonds that form when valence electrons are shared between two non-metal elements
• there is a wide diversity of carbon compounds, they can be;

  • unbranched chains such as fatty acids
  • branched chains such as triglycerides
  • single rings such as glucose
  • multiple rings such as cholesterol
• monomers are molecules which join to other similar molecules to form polymers
• the macromolecules of life are polymers built out of monomers
• monomer -> polymer -> macromolecule ->

  • glucose -> polysaccharide -> amylose and amylopectin in starch or cellulose
  • amino acid -> polypeptide -> proteins
  • nucleotide -> polynucleotide -> DNA and RNA
  • fatty acids and glycerol -> triglycerides -> fats and oils
• condensation reactions include the combining of two molecules together and the release of a water molecule
• many repeated condensation reactions with monomers produce macromolecule polymers
• hydrolysis reactions include the addition of a water molecule to break down a large molecule into smaller molecules
• macromolecules are digested (broken down) during hydrolysis to their monomers through a series of hydrolysis reactions
• in hydrolysis:

  1. water causes a monomer to break of from a polymer
  2. water separated into -H and -OH
  3. -H attaches to one molecule and -OH attaches to the second molecule
• carbohydrates are a large group of organic compounds present in foods and living tissues and include sugars, starch and cellulose.
• carbohydrates contain hydrogen and oxygen in the same ratio as water (2:1) and can be typically broken down to release energy in the animal body
• carbohydrates are classified based on the number of sugar monomers in the molecule:

  • monosaccharides - 1 sugar molecule i.e. glucose, ribose, fructose
  • disaccharide - 2 sugar molecules i.e. sucrose, maltose, lactose
  • polysaccharide - many sugar molecules i.e. starch, glycogen, cellulose, chitin
• pentose sugars are monosaccharides that contain 5 carbons i.e. ribose and deoxyribose
• hexose sugars are monosaccharides that contain 6 carbons i.e. alpha glucose and beta glucose (where bonds usually form between carbon 1 and carbon 4 during the formation of polysaccharides)
• glucose is a typical monosaccharide that possess the following properties:

  • soluble in water - it is a polar molecule which readily dissolves in water
  • transportability - since it is soluble, it can be transported within body fluids, such as the bloodstream in humans
  • chemical stability - it is a relatively stable compound so it doesn't degrade as it's being transported
  • energy yield - it is the primary fuel for respiration in cells. it is repeatedly oxidized to produce net gains of up to 36ATP molecules
• polysaccharides are composed of many sugar molecules combined through a series of condensation reactions
• polysaccharides such as starch in plants and glycogen in animals serve as stores of energy and are composed of long chains of glucose molecules
• glucose molecules can be added to the polysaccharides (starch or glycogen) by condensation reactions or can be removed by hydrolysis reactions
• starch and glycogen are compact polysaccharides due to the coiling and branching as they are formed and this compact nature of polysaccharides allow the storage of many glucose molecules making them excellent storage compartments
• starch is composed of two polysaccharide molecules:

  • amylose - long chains of alpha glucose molecules
  • amylopectin - long chains of alpha glucose with branching chains of alpha glucose
• amylose and amylopectin are large polysaccharide molecules and are not very soluble in water. this allows compact storage of starch grains in plant cells, without impacting osmotic pressure in cells.
• amylose consists of long chains of alpha glucose with glycosidic bonds between carbon-1 and carbon-4.

  glucose molecules can be added to amylose by condensation reactions or removed by hydrolysis reactions.
• amylopectin consists of long chains of alpha glucose with glycosidic bonds between carbon-1 and carbon-4, however, at every 20th glucose molecule an additional glucose molecule binds at carbon-6 and this is what results in amylopectin's branched structure
• glycogen is a polysaccharide used for short-term energy storage in animals
• glycogen, a polysaccharide, is composed of chains of alpha glucose with bonds between carbon-1 and carbon-4
• in glycogen, many branches of alpha glucose chains are present with alpha glucose binding to carbon-6
• glycogen is an insoluble compact molecule, due to its many branches and coiling during polymerization
• cellulose is an unbranched polysaccharide composed of beta glucose molecules - which are found in the cell walls of plants
• cellulose molecules consist of long chains of beta glucose molecules bonded between carbon-1 and carbon-4.

  note that every 2nd beta glucose is flipped, resulting in straight chains of cellulose molecules
• cellulose molecules form groups known as microfibrils which are held together by hydrogen bonds
• cellulose microfibrils have high tensile strength which allows them to maintain the structural integrity of cell walls in plants
• four cellulose molecules can be held together by hydrogen bonds
• glycoproteins are integral proteins located within the phospholipid bilayers of cells
• glycoproteins always have a chain of carbohydrates attached and these carbohydrates have a specific shape and can act as an antigen
• roles of glycoproteins include:

  • cell to cell adhesion - glycoproteins interact with other glycoproteins allowing the formation of tissues
  • receptors - for hormones. when a hormone binds to a specific glycoprotein receptor, it changes the metabolism of the cell
  • cell to cell communication - neurotransmitters bind to glycoproteins allowing communication between cells
  • immune response - they act as markers on cells allowing the immune system to distinguish between self and non-self
• glycoproteins act as antigens if the glycoprotein is not recognized as itself by the immune system