top of page

Biological Molecules

  • -  Elements that make up Biological Molecules:

    • -  Carbohydrates: Carbon, Hydrogen Oxygen

    • -  Lipids: Carbon Hydrogen, Oxygen

    • -  Proteins: Carbon, Hydrogen, Oxygen, Sulfur

    • -  Nucleic Acids: Carbon, Hydrogen, Oxygen, Phosphorus

  • -  Structure of Glucose:

    • -  Hexose sugar which has 2 forms

    • -  THINK: Alpha - Above Ahhhhhhhhhhh so in alpha the Hydrogen (ahhhhhh) is

      above and the hydroxyl group is below. NOTE: this is on the 1st carbon of the

      ring (far right)

    • -  In beta glucose the structure is the other way around

    • -  Roles:

      • -  Alpha - Energy source and a component of starch and glycogen which acts as an energy store

      • -  Beta - Energy source and a component of Cellulose which is for structural support (THINK: B for Builder → structural)

    • -  For the rest of the structure which is relatively constant think ohh hoh for the base of the Carbon-Carbon at the bottom, the next carbon on the left has H above and then there is the C bonded to the CH2OH

  • -  Structure of Ribose:

    • -  Pentose Sugar as 5 carbons

    • -  2 forms as there is ribose and deoxyribose

    • -  Deoxyribose is missing an Oxygen on the bottom right carbon of the drawn

      pentose sugar as the hydroxyl group is not just a hydrogen group, (carbon 2) so

      is C5H10O4 as opposed to rinse which is C5H10O5

    • -  THINK: use the name as DEOXY is without oxygen

    • -  General structure is a pencil (pentose) with the tip being an oxygen and the 4

      other points being carbons with there being a branch of CH2OH on the 4th

      carbon

    • -  Insert pic

  • -  Synthesis of Disaccharides:

    • -  Alpha glucose + Alpha glucose → maltose

    • -  Alpha glucose + Fructose → sucrose

    • -  Alpha glucose + Beta galactose → lactose (Link to lac operon)

    • -  Beta glucose + Beta glucose → cellobiose

- All bond via a glycosidic bond which forms due to a condensation reaction between the molecules forming a water molecule

- Structure of Starch (amylose and amylopectin), glycogen and cellulose
- Starch (amylose): 1,4 glycosidic bonds only in a long chain of alpha glucose

molecules, amylose will coil into a spiral with hydrogen bonds holding the spiral in shape between hydroxyl groups. As the hydrogen bonds are on the inside the molecule is made less soluble as no hydrogen bonds can form with water so

- Summary: tightly coiled no branches

  • -  Starch (amylopectin): glycosidic bonds between the 1 and 4 carbons in a coil but

    with the addition of branches formed from 1,6 there will be numerous branches stemming from the spiral.

    • -  Summary: Coil with branches caused by 1,6 bonds

    • -  THINK: Pecs are branched

  • -  Glycogen: Similar to amylopectin with 1,4-glycosidic bonds as well as

    1,6-glycosidic bonds by there is less tight coiling as shorter 1,4 chains and even more branched so easier to remove monomer units (as more metabolically active animals than plants)

- Structure and Function link:

  • -  Both compact and hold glucose in easy to hydrolyse chains by the

    enzyme glucosidase.

  • -  Not too soluble so assure that water potential in a cell does not

    decrease and lead to further osmosis causing cytolysis

- Cellulose;

  • -  Found in plant cell walls composed of a chain of beta glucose

  • -  Every other beta glucose is inverted to prevent spiralling and maintain a

    straight

  • -  This also assures hydrogen bonding between the straight chains to

    provide additional strength

  • -  The chains bundle together via these hydrogen bonds such that they form

    large structures, the process of this bundling is as follows

- Beta glucose chain → Microfibril → Macrofibril

  • -  The microfibrils run in different directions cross hatching to give the wall extra strength

  • -  Features:

    • -  High tensile strength

    • -  Difficult to digest because the glycosidic bonds between beta glucose are less easy to break

    • -  Also the tensile strength will prevent bursting of plant cells

    • -  Also the cell wall can be reinforced with lignin etc. if ever needed

- Triglycerides

  • -  Made of glycerol head and fatty acid acid tails

  • -  Glycerol is three carbon molecules with 3 hydroxyl groups

    (1,2,3-hydroxypropane) and fatty acids have a carboxyl (COOH) group at one end of a hydrocarbon tail thus they bond to each other via an ester bond between the COOH group and OH group in a condensation reaction

  • -  The tail is saturated if there are no carbon carbon double bonds but any double bonds may lead to kinks in that tail of an unsaturated tail

  • -  Functions:

    • -  Energy Source - can be broken down in respiration

    • -  Energy Store - as insoluble store energy with no effect on WP

  • -  Insulation - Mammals store lipids in adipose cells which can act as an insulator and in nerve cells (myelin sheath) to at as an electrical inhibitor

  • -  Buoyancy - Fat is less dense than water to can be used to assure we float

  • -  Protection - Lipid can be stored as fat around delicate organs to act as a shock absorber equally in bacteria there can be lipid to act as a protective layer

    - Phospholipids

  • -  Same structure as a triglyceride but with one fatty acid being a phosphate

    group and the condensation reaction between the OH group of a phosphoric acid molecule and hydroxyl group from the glycerol molecule leads to a phospholipid forming

  • -  THE PHOSPHATE GROUP COMES FROM A PHOSPHORIC ACID MOLECULE

  • -  Forms bilayer etc. - Cholesterol

  • -  Is a steroid alcohol as not made of glycerol of fatty acids but instead carbon rings

  • -  Hydrophobic so sits in the bilayer and regulates fluidity

  • -  Made in the liver for animals

  • -  Plants hae stigmasterol and has a double bond between the 22nd and

    23rd carbon

  • -  Fibrous Proteins:

    • -  Regular repeated sequence and are insoluble in water so form fibres and thus have structural function

    • -  This is as opposed to globular which is a non-protein component that forms a part of the functioning molecule

    • -  Fibrous Proteins:

      • -  Collagen - artery walls prevents bursting and withstands pressure,

        tendons are formed of collagen, bones are collagen based and reinforces

        with calcium and cartilage is made of collagen

      • -  Keratin - lots of disulfide bridges so very strong and thus forms finger and

        toenails, hoofs, horns, scales and hair

      • -  Elastin - Cross linking makes it strong and extensible found in skin, lungs

        and blood vessels to enable stretching etc.

    • -  Globular Proteins:

      • -  Conjugated Haemoglobin - 2 alpha 2 beta globin chains with haem prosthetic group for oxygen transport

      • -  Insulin - section of alpha and section of beta with shape complementary to receptors to reduce blood glucose

      • -  Pepsin: Digests protein in the stomach, made of single polypeptide chain and is very stable in acidic conditions as very few basic groups

  • -  Inorganic Ions:

- Positive:

  • -  Calcium: increases bone and teeth rigidity, aids blood clotting, can

    activate several enzymes (ATPase) stimulates muscle contraction (neuromuscular junction) and regulates cell membrane permeability also important for plant cell wall development

  • -  Sodium: Regulation of osmotic pressure, absorption of carbohydrate, Contributes to action potential generation, constituent of vacuole in plants

  • -  Potassium: Involved in control of water level and pH of the blood, aids active transport across the cell membrane, involved in protein synthesis and breakdown of glucose. Contributes to nervous transmission and part of the vacuole in plants

  • -  Hydrogen photosynthesis and respiration, transport of oxygen and carbon dioxide in blood and blood pH regulation

  • -  Ammonium (NH4+): Component of amino acids, proteins, vitamins and chlorophyll, and thus can be a part of hormones, aids the maintenance of blood pH and component of nitrogen cycle

    - Negative:

  • -  Nitrate (NO3-): Component of amino acids, proteins, vitamins and

    chlorophyll, and thus can be a part of hormones as well as nucleic acids

    and plays a role in the nitrogen cycle

  • -  Hydrogencarbonate (HCO3-): regulation of blood pH and transport of

    CO2

  • -  Chloride: Helps in urine production, transport of CO2 and haemoglobin

    affinity for oxygen regulation, for HCl production in the stomach and pH

    regulation in blood and stomach

  • -  Phosphate (PO4 3-): Rigidity of bone, teeth, cartilage and component of

    the exoskeleton etc. Component of phospholipids, ATP, nucleic aids and

    enzymes as well as blood pH regulation and growth of plant roots

  • -  Hydroxide: Blood pH

- Biological Tests:

  • -  Biuret Test:

    • -  For Protein

    • -  LIGHT BLUE - LILAC colour change

    • -  Add biuret A and biuret B (sodium hydroxide and copper sulphate)

    • -  The cu2+ forms a complex with protein causing change

  • -  Benedict's Test: Reducing Sugars

    • -  Reducing sugars

    • -  BLUE TO GREEN TO YELLOW TO ORANGE/RED colour change

    • -  Colour intensity proportional to concentration so colourimetry can be used

    • -  Precipitate may form

    • -  Method is simple addition

  • -  Benedict's Test: Non-reducing sugar

    • -  Non reducing sugar

    • -  After reducing sugar test done and no result

  • -  Take a separate sample and BOIL with HCl to hydrolyse the nonreducing sugar

  • -  Cool the solution and add sodium hydrogencarbonate until neutral (test with pH strip)

  • -  Test for reducing sugar

  • -  Same positive

  • -  Iodine Test for Starch:

    • -  For starch

    • -  Add iodine solution

    • -  YELLOW/BROWN - BLUE/BLACK colour change

    • -  The iodide forms a triiodide which slips into the amylose helix and causes

      the colour change

  • -  Emulsion Test for lipids:

    • -  For Lipids

    • -  Mix with ethanol

    • -  Filter

    • -  Pour into a clean test tube

    • -  CLOUDY WHITE EMULSION OF LIPID forms for a positive result

- To make a result quantitative do colourimetry and use a known absorbance grid or table to gain an idea of possible concentration if required

bottom of page