Biological molecules

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Biological molecules by Mind Map: Biological molecules

1. Testing for biological molecules

1.1. Testing for biological molecules

1.1.1. Iodine Test Test for starch Iodine Solution is used Fit into the middle of the spiral starch molecules are curled up into Won't dissolve in water, so the iodide solution is iodine in Potassium iodide solution Procedure Add a drop of iodine solution to the solid or liquid substance to be tested Positive for starch- blue black colour Negative for starch- orange brown colour (as that is the colour of the iodine solution)

1.1.2. Benedict's test Test for Reducing sugars All monosaccharides (e.x: glucose) & some disaccharides (e.x: maltose) Called reduction sugars as they carry out a chemical reaction known as reduction (in the process the sugars are oxidised Benedict's reagent is used It's Copper (II) Sulfate in an alkaline solution Distinctive blue colour Procedure Add Benedict's reagent to the solution & heat it in a water bath Positive test Negative test Semi- quantitative test You can measure the concentration of reducing sugar by the intensity of the red colour (use excess Benedict's reagent) Can estimate concentration by using colour standards made by comparing the colour with another colour obtained in test with a known concentration Can also measure the time taken for the colour to change Can also use a colorimeter to measure precisely, subtle differences in colour

1.1.3. Non- reducing sugars Positive test Brick- red precipitate Test for disaccharides (Exs: sucrose) The disaccharide is first broken down into its two monosaccharides by hydrolysis (can be brought about by HCl) Hydrolysis is the removal of water Hydrolysis is the breakdown of dissacharides to monosaccharides The monosaccharides will be tested after HCl has been neutralized Procedure 1. Heat the sugar solution with HCl (this will release free monosaccharides 2. HCl needs to be neutralized as the Benedict's reagent needs alkali conditions to work (add alkali such as sodium hydroxide) 3. Add Benedict's reagent, heat again & look for any colour change If solution goes red now but not on first step, non- reducing sugar is present No change in colour= no sugars of any kind

1.1.4. Emulsion Test Test for lipids Lipids are insoluble in water, but soluble in ethanol (alcohol) Procedure 1. Substance shaken vigorously with some absolute ethanol (ethanol with little or no water in it) 2. Any lipids in substance dissolves in ethanol 3. The ethanol is then poured into a tube containing water Positive test- cloudy white suspension forms Negative test- Transparent (as if there is no lipids present, the ethanol mixes into the water)

1.1.5. Biuret Test Test for proteins Procedure 1. 1cm3 of protein solution 2. Add equal volume of dilute potassium or sodium hydroxide Add 2cm3 of copper sulphate Positive test- purple colour

1.2. Carbohydrates

1.2.1. Ring Structures Alpha- glucose Hydroxyl group (-OH) below the ring Beta- glucose -OH above the ring Isomers Same molecule can switch between the two forms; two forms of the same chemical Important biological consequences

1.2.2. Monomer Relatively simple molecule which is used as a basic building block for the synthesis of a polymer (by condensation reactions) Exs: Monosaccharides, amino acids & nucleotides

1.2.3. Polymer Giant molecule made from many similar repeating subunits joined together in a chain Exs: Polysaccharides, proteins & nucleic acids

1.2.4. Macromolecule Large biological molecule Exs: Protein, polysaccharide or nucleic acid

1.2.5. Monosaccharide A molecules consisting of a single sugar unit with the general formula (CH2O)n Exs: glucose (6C), galactose (6C) & ribose (5C) If classified according to the nº of Carbon atoms in each molecule, the main types are Trioses (3C) Pentoses (5C) Hexoses (6C) Are reducing Sugars Source of energy in respiration As glucose is a monosaccharide (very important in energy metabolism) Large nº of carbon- hydrogen bonds; these bonds are broken to release a lot of energy; transferred to help make ATP from ADP & phosphate

1.2.6. Disaccharide A sugar molecule consisting of two monosaccharides joined together by a glycosidic bond maltose (glucose+glucose) Sucrose (glucose+ fructose) Lactose (glucose+ galactose) Are not reducing sugars Joining of two monosaccharides to make disaccharides takes place by a process known as condensation Condensation is the removal of H2O molecule Sucrose is made from an alpha- glucose and a beta- fructose

1.2.7. Polysaccharide A polymer whose subunits are monosaccharides joined together by a glycosidic bond Starch Glycogen Cellulose They are made by joining many monosaccharide molecules by condensation (loss of H2O molecule)

1.2.8. Hydrolysis Adding H2O molecule reverse process of condensation Used to break the large molecules back into smaller molecules From disaccharide to monosaccharide Polysaccharide to monosaccharide

2. Lipids

2.1. Diverse group of chemicals

2.2. Triglycerides (Fats & Oils)

2.2.1. Made by condensation between 3 fatty acids & glycerol

2.2.2. Hydrophobic (do not mix with water)

2.2.3. Is an ester formed by a fatty acid combining with the alcohol glycerol (Acid+ alcohol= ester)

2.3. Functions

2.3.1. Energy storage compounds in animals

2.3.2. Insulation & buoyancy in marine mammals

2.4. Phospholipids

2.4.1. Have a hydrophilic phosphate head & two hydrophobic fatty acid tails

2.4.2. Inportant in formation of membranes (as the hydrophobic part does not allow water in, & the hydrophilic does)

3. Proteins

3.1. Long chains of amino acids which fold into precise shapes

3.2. Linkages that join a.a are called peptide bonds

3.2.1. One loses -OH from its carboxylic acid group, other loses a hydrogen atom from its amine group

3.2.2. C atom of the first a.a free to bond with Nitrogen atom of the second

3.2.3. Break down of peptide bonds Hydrolysis reaction Happens in the stomach & small intestine during digestion (to form a.a for absorption)

3.3. Primary structure

3.3.1. sequence of amino acids in a polypeptide or protein

3.4. Secondary structure

3.4.1. structure of a protein molecule resulting from the regular coiling or folding of a polypeptide chain Alpha- helix Hydrogen bonding between the oxygen of the -CO- group of one a.a & the Hydrogen of the -NH- group of a.a 4 places ahead of it beta- pleated sheet H bonds Easily broken by high temperatures and pH changes

3.5. Tertiary structure

3.5.1. compact structure of a protein molecule resulting from the three- dimensional coiling of the already- folded chain of a.a Very precise & held in place by Hydrogen bonds Disulfide bonds Ionic bonds Hydrophobic interactions

3.6. Quartenary structure

3.6.1. Different polypeptide chains held by the 4 types of bonds in the tertiary structure

3.7. Globular protein

3.7.1. Roughly spherical

3.7.2. Ex: Haemogoblin Contains a non- protein group (haem group), which contains iron Iron combines with oxygen and delivers to cells for cellular respiration Composed of 2 alpha and 2 beta chains (4 polypeptide chains)

3.7.3. Most are soluble & metabolically active

3.8. Fibrous protein

3.8.1. less folded & forms long strands

3.8.2. Ex: Collagen Has high tensile strength Most common animal protein (found in a lot of tissues, ex: tendons, teeth & skin) triple helix Held by H2 bonds & some covalent

3.8.3. Are insoluble & often have a structural role

4. Water

4.1. Acts as a solvent for ions & polar molecules, & causes non- polar molecules to group together

4.2. Has a high specific heat capacity

4.2.1. Makes water more resistant to changes in temperature Temp within cells constant Lakes, oceans (etc) slow to change temp, so more stable habitat for aquatic animals

4.3. High latent heat of vaporisation

4.3.1. Evaporation can be used as a cooling mechanism (sweating), and large amount of heat can be loss without a big loss of water

4.4. Acts as a reagent in photosynthesis as a source of hydrogen

4.5. Negatively charged oxygen of one molecule is attracted to a positively charged hydrogen of another- HYDROGEN BOND