NOTES

• EVIDENCE FOR EVOLUTION

  • the variety of life is extensive but all living things share the same biological molecules. All have similar biochemical basis.
  • this supports the theory of evolution by indirect evidence that all organisms descended from one / a few common ancestors.
• MONOMER: simple, basic, molecular unit from which larger molecules / polymers are made from

  • eg. Monosaccharides, amino acids, nucleotides
• POLYMER: large, complex molecule made up of repeating monomers joined together

  • Eg. Starch, glycogen, cellulose, polypeptide ( protein), DNA, RNA
• MAKING POLYMERS: CONDENSATION REACTION

  • joins two monomers together
  • forms chemical bond
  • eliminating a water molecule
• BREAKING POLYMERS: HYDROLYSIS REACTION

  • separates two monomers
  • breaks chemical bond
  • requires addition of a water molecule
• CARBOHYDRATES CONTAIN:

  • carbon
  • hydrogen
  • oxygen
• CARBOHYDRATE FUNCTIONS:

  • energy
  • storage
  • strength
• MONOSACCHARIDE: simple sugars, monomers from which larger carbohydrates are made.

  EXAMPLES

  • fructose
  • galactose
  • glucose - alpha and beta

  all 3 examples have formula C6H12O6
• ISOMER: have the same molecular formula but different structure with atoms arranged in different ways.

  • Glucose - alpha and beta glucose.
  • OH group inverted on carbon 1

  
• DISACCHARIDES: forms when two monosaccharides join together by a condensation reaction forming a glycosidic bond. Hydroxyl group on one joins with a hydrogen from another to release a water molecule for each bond. One oxygen molecule joins the two sugars.

  • maltose = glucose + glucose
  • sucrose = glucose + fructose
  • lactose = glucose + galactose
  • lactulose = galactose + fructose

  
• POLYSACCHARIDES: when more than 2 monosaccharides join together via condensation reaction, releasing a water molecule for each glycosidic bond.

  EXAMPLES

  • starch
  • glycogen
  • cellulose
• STARCH FUNCTION:

  • found in many parts of a plant in the form of small grains.
  • especially large amounts occur in seeds and storage organs, such as potato tubers.
  • it forms an important component of food and is the major energy source in most diets.
• STARCH STRUCTURE:

  • made up of two polysaccharides of alpha glucose:
  • amylose (unbranched helical chains) contains C 1-4 glycosidic bonds.
  • amylopectin (branched every 20 monomers) contains C 1-4 and C 1-6 glycosidic bonds.
• STARCH STRUCTURE RELATED TO FUNCTION

  • helical because of angles on glycosidic bonds - compact, fit more in, good for storage - lots can fit in a small space
  • insoluble - doesn’t affect water potential / osmosis
  • branched chains - more efficient hydrolysis for respiration - increases surface area
  • large - can’t leave the cell
• GLYCOGEN FUNCTION

  • main storage of energy in animals, stored in muscle and liver cells.
• GLYCOGEN STRUCTURE

  • polysaccharide of alpha glucose
  • branched chains every 10 monomers
  • C 1-4 and C 1-6 glycosidic bonds
• GLYCOGEN STRUCTURE RELATED TO FUNCTION

  • branched - rapid hydrolysis into glucose to meet demands of cell
  • insoluble - doesn’t affect water potential / osmosis
  • Compact - good for storage
• CELLULOSE FUNCTION

  • provides structural strength in the cell walls of plants due to its strength which is a result of many hydrogen bonds between the parallel chains of microfibrils.
  • the high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure.
  • the strengthened cell walls provide support to the plant.
  • cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane.
• CELLULOSE STRUCTURE

  • polysaccharide of beta glucose monosaccharides joined together by C 1-4 glycosidic bonds.
  • they form straight chains.
  • due to the inversion of the beta glucose molecules many hydrogen bonds form between the long chains giving cellulose its strength. This forms microfibrils.
• CELLULOSE STRUCTURE RELATED TO FUNCTION

  • hydrogen bonds between chains - collective strength to the cell wall
• REDUCING SUGAR TEST

  • can donate electrons
  • glucose, fructose, galactose, maltose, lactose
  • add Benedict’s reagent (contains copper II sulfate) to the sample
  • place in a boiling water bath for 5 minutes
  • POSITIVE RESULT = blue —> green, yellow, orange, brick red
  • semi quantitive - depending on concentration.
  • reduces blue copper sulfate into red copper dioxide.
• NON-REDUCING SUGAR TEST

  • cannot donate electrons
  • sucrose (disaccharide)
  • if negative from first test for reducing sugars, needs hydrolysis into monosaccharides

  1. add hydrochloric acid then neutralise with sodium hydrogen carbonate.
  2. then add Benedict’s solution and put in boiling water bath for 5 minutes
  3. POSITIVE RESULTS: blue —> brick red
  4. high concentration of sugars now as there’s two monosaccharides
• TEST FOR STARCH

  • add iodine in potassium-iodide solution to the sample
  • POSITIVE RESULT - orange —> blue/black
• LIPIDS

  contain elements:

  • C
  • H
  • O
• TRIGLYCERIDE STRUCTURE

  • 1 molecule of glycerol attached to 3 fatty acids
  • non-polar
  • hydrophobic

  
• TRIGLYCERIDE FORMATION

  • condensation reaction where a H from OH group on glycerol joins with the OH group on the COOH to release a water molecule.
  • this forms an ester bond
  • repeats for the other 2 fatty acids

  
• TRIGLYCERIDE FUNCTION

  • mainly used as storage molecules
• TRIGLYCERIDE PROPERTIES

  • insoluble in water - due to hydrophobic fatty acid tails facing inwards, glycerol outwards - water potential unaffected
  • long hydrocarbon tails, lots of C-H, little O - when oxidised releases energy

  
• PHOSPHOLIPID STRUCTURE

  • 1 glycerol, 1 phosphatase group, 2 fatty acid tails
  • glycerol + phosphate group are head = PO4^2- charged, polar, hydrophilic (attracts water), soluble
  • 2 fatty acid tails = non-polar, insoluble in water, hydrophobic (repels water)
  • amphipathic - both hydrophobic and hydrophilic regions
• PHOSPHOLIPID FORMATION

  • condensation reactions between glycerol and phosphate group forming phosphodiester bond
  • reaction between glycerol and fatty acids forming an ester bond, releasing water molecule per bond
• PHOSPHOLIPID FUNCTION

  • phospholipid bilayer
  • micelles
• PHOSPHOLIPID PROPERTIES

  • bilayer - hydrophilic heads attract water, tails repel, tails inwards shielded, heads outwards.
  • barrier - in cell membrane to water soluble molecules, ions, charged/polar molecules
  • electrical insulator - ions can’t enter as they are charged and repel fatty acid hydrophobic tails
  • stability/fluidity - saturated fatty acids less fluid, can move past each other to keep membrane fluid to change shape and move but never expose hydrophobic fatty acid tails.
• FATTY ACIDS: all consist of a carboxyl group (COOH) and a hydrocarbon tail which can vary (R)

  • can be saturated - no double bonds, saturated with hydrogen
  • unsaturated - contains C=C double bond, which causes the chain to kink.
  • if on the double bond the H are on the same side, it is Cis, if the H’s are on opposite sides, it is a trans unsaturated fatty acid.

  
• TEST FOR LIPIDS

  1. Add ethanol to the sample
  2. then add water
  3. shake

  • POSITIVE RESULT: white/milky emulsion
  • HAZARDS: ethanol is flammable, don’t test near open flames
• PROTEINS

  • monomers are amino acids

  CONTAINS:

  • carbon
  • hydrogen
  • oxygen
  • nitrogen
  • sometimes - sulfur
• AMINO ACID STRUCTURE

  • NH2 = amine group
  • COOH = carboxyl group
  • R = variable group
  • 20 amino acids
  • only vary in R group
  • Glycine - H in R group

  
• DIPEPTIDE AND POLYPEPTIDE FORMATION

  • condensation reaction between OH on carboxyl group and H on amine group, releasing a water molecule and forming a peptide bond.
  • 2 amino acids = dipeptide
  • 2 + amino acids = polypeptide
  • 1 or more polypeptide chains is a protein

  
• PRIMARY STRUCTURE OF PROTEINS

  • PRIMARY STRUCTURE: sequence of amino acids in a polypeptide chain
  • DNA of a cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence.
  • this affects the shape and therefore the function of the protein.
  • the primary structure is specific for each protein (one alteration in the sequence of amino acids can affect the function of the protein)
• SECONDARY STRUCTURE OF PROTEINS

  • hydrogen binds form between amino acids close together (weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms between carboxyl group and amine group).
  • this causes the polypeptide chain to be coiled into an alpha helix or folded into a beta pleated sheet.
  • BONDS: peptide and hydrogen bonds.

  
• TERTIARY STRUCTURE OF PROTEINS

  • further conformational change of the secondary structure, coiled or folded further, leads to additional bonds forming between the R groups (side chains).

  BONDS:

  • hydrogen bonds - between R groups
  • disulphide bridges - only occurs between cysteine amino acids
  • ionic bonds - occurs between charged R groups
  • hydrophobic interactions - between non-polar R groups
  • final 3D structure for proteins of only one polypeptide chain.