Module 2.1.2- Biological molecules

• The chemical elements that make up biological molecules (in carbohydrates, lipids, proteins and nucleic acids)

  Carbohydrates- C , H , O

  Lipids- C , H , O

  Proteins- C , H , O , N , S

  Nucleic acids- C , H , O , N , P
• Condensation reaction


  a chemical reaction in which two or more molecules combine to produce water

  
• Hydrolysis reaction


  A chemical reaction that breaks apart a larger molecule by adding a molecule of water
• Bonding and structure of water

  Water is polar as the oxygen is more electronegative than hydrogen Therefore it is able to form hydrogen bonds with other water molecules

  Hydrogen bonds are relatively weak interactions

  
• Explanation for the high boiling point of water

  this is due to the (high amount of) hydrogen bonding between the water molecules which requires a lot of energy to overcome
• Explanation for ice being less dense than liquid water

  when water freezes, the water molecules are held in an open rigid lattice with the hydrogen bonds fixed in position. This, therefore, holds the molecules further apart causing it to become less dense

  
• Explanation for water's cohesive properties


  moves as one mass and molecules are attracted to each other through hydrogen bonding

  uses: in plants it allows water to be drawn up the roots
• Explanation for water's adhesive properties

  water molecules are attracted to other materials
• Explanation for water's high specific heat capacity


  water requires a lot of energy to prevent the formation of hydrogen bonds and overcome them to increase the temperature of water
• Uses of water: universal solvent


  It is a polar molecule and so it can act as a solvent for many solutes

  It can also act as a medium for chemical reactions
• Uses of water: efficient transport medium

  cohesion between water molecules allows molecules to stick together

  adhesion allows water molecules stick together to other molecules

  the result of these 2 properties result in capillary action where water moves up a tube against gravity
• Uses of water: buffer


  due to waters high specific heat capacity it is able to act as a coolant

  this helps to maintain the temperature which is essential for enzymes
• Uses of water: aquatic organisms

  because ice floats it forms an insulating layer below

  also allows organisms such as polar bears to inhabit the area

  surface tension is strong enough for small insects such as pond skaters to inhabit the surface of the water

  has a high specific heat capacity
• Monosaccharide


  A single sugar molecule such as glucose or fructose, is the simplest type of sugar.

  
• Properties of glucose


  polar and soluble in water due to hydrogen bonding

  
• Alpha glucose vs. Beta glucose structure

  the reversal of the H and OH on the first carbon

  H is above for alpha and its below for beta

  
• In a condensation reaction between 2 glucose monomers a disaccharide is formed with a 1,4-_____________ bond

  (1,4)-glycosidic

  
• Fructose + Glucose ->

  Sucrose
• Galactose + Glucose ->

  Lactose
• Glucose + Glucose ->

  Maltose
• Pentose monosaccharides


  Sugars that contain five carbon atoms for example ribose (in RNA) and deoxyribose (in DNA)

  
• What are the 2 polysaccharides that form starch and what is their function

  Amylose and amylopectin

  Glucose made by photosynthesis in plant cells is stored as starch.

  It is a chemical energy store
• Structure of amylose (starch in plants)


  Alpha glucose molecules joined together only by 1,4-glycosidic bonds

  The long chain of glucose twists to form a helix stabilised by hydrogen bonding

  Makes it compact and much less soluble

  
• Structure of amylopectin (starch in plants)


  Alpha glucose molecules joined together by 1,4-glycosidic bonds and 1,6-glycosidic bonds

  Branched structure, side branches allow the enzymes that break the molecule down to access the bonds easily (by hydrolysis) meaning glucose can be released quicklyIt is insoluble and compact
• Glycogen (animals)


  An extensively branched glucose storage polysaccharide found in the liver and muscle of animals.

  More branched than amylopectin and so is more compact.

  Many free ends where glucose molecules can be added or removed by hydrolysis

  It is insoluble and compact
• Structure of cellulose


  β-glucose arranged in a straight chain (each alternative β-glucose is rotated 180 degrees) = cellulose straight chainmany cellulose chains are cross linked by hydrogen bonds to form microfibrils many microfibrils are cross linked to form macrofibrils which combine to form fibres strong and insoluble material (prevents plant cell from bursting or shrinking)
• Reducing sugars


  saccharides (sugars) that donate electrons resulting in the reduction (gain of electrons) of another molecule.

  examples are: all monosaccharides and some disacharrides such as lactose and maltose

  
• Test for reducing sugars (Benedicts test/ CuSO4)


  1) Place sample in a boiling tube. Grind up or blend it if need be to have it in the liquid form

  2) Add an equal volume of benedicts reagent

  3) Heat the mixture gently in a boiling water bath for 5 minutes

  4) brick-red precipitate formed in presence of a large amount of reducing sugars

  In the presence of reducing sugars, Cu2+ will get reduced to brick red Cu+

  See diagram to deduce the result

  
• Example of a non-reducing sugar


  sucrose
• Testing for a non-reducing sugar

  1) boil mixture with dilute HCl (to hydrolyse non-reducing sugar)

  2) carry out the original benedicts test
• Testing for starch (iodine)

  1) Put iodine into the substance

  2) Iodine turns blue/black (starch present)
• Testing for protein (Biuret reagent)


  1) Add biuret reagent to the substance

  2) Turns violet/purple (protein present)
• Testing using reagent strips


  Manufactured reagents test strips can be used to test for the presence of reducing sugars

  Use colour-coded chart
• Testing for lipids (emulsion test)


  1) Add a few drops of ethanol to the test tube

  2) Add water to the test tube and then shake well

  3) Turns white cloudy emulsion (lipids present)

  
• Using a colorimeter


  Measures absorbance of light by a substance.

  Filter was placed in the colorimeter

  Calibrate using distilled water (zero it)

  Benedicts reagent performed on a range of known concentrations of glucose

  The resulting solutions were filtered to remove the precipitate

  The % transmission of each of the solutions of glucose was measured using the colorimeter

  Plot calibration curve
• Using a biosensor


  A device that combines a biomolecule, such as an enzyme, with a transducer, to produce an electrical signal which measures the concentration of a chemical

  
• Triglycerides


  made by combining one glycerol molecule with three fatty acids

  
• How are triglycerides formed and broken down


  To form triglycerides, a condensation reaction takes place between glycerol and 3 fatty acids forming 3 ester bonds. 3 moles of water is formed as a result To hydrolyse a whole triglyceride molecule, you add 3 moles of water to break the ester bonds

  
• Saturated triglycerides


  composed of saturated fatty acids-typically have high melting points as they can closely pack tight with eachother-tend to be hard at room temp e.g. butter-animal fats
• Monounsaturated and polyunsaturated triglycerides


  in fatty acids

  1 double bond- monounsaturated

  1+ double bonds- polyunsaturated causes molecule to kink/bend and so cannot pack closely togethertherefore is liquid at room temperature or an oil