Biological Molecules Flashcards
Define nutrients
Chemical substances in food that provide energy and materials needed by the body
What are monomers and polymers of carbohydrates
Monomer: Glucose
Polymer: Starch, glycogen, cellulose
Define condensation
A chemical reaction whereby two or more simple molecules are join to form a larger biological molecule with the removal of water
Define hydrolysis
The splitting up of complex biological molecule into its component units with the addition of water molecules
What are the characteristics of carbohydrates
Made of carbon, hydrogen and oxygen with hydrogen and oxygen atoms present in the ratio 2:1
What are properties of monosaccharides
Same general formula C6H12O6 but atoms arranged differently, different chemical and biological properties
Still generally sweet-tasting, soluble in water, lower water potential of solutions
What is the bond formed in disaccharides and polysaccharides
Glycosidic bond, -O-
Describe the three types of disaccharides(in syllabus)
All have formula C12H22O11, different structure and properties
Maltose = glucose + glucose
Lactose = glucose + galactose
Sucrose = glucose + fructose
Describe structure of starch
Formed from condensation reaction of large numbers of glucose molecules, can be in long straight chains or branched chains
Describe structure of glycogen
Formed from condensation reaction of large number of glucose molecules, joined up in highly branched chains and found in liver and muscles of mammals
Why are starch and glycogen suitable as storage materials
Insoluble in water so do not affect water potential in cells
Too large to diffuse through cell membrane
Compact shape, occupy less space than individual glucose molecules
Easily hydrolysed to glucose
Describe structure of cellulose
Formed from condensation reaction of large numbers of glucose molecules, bonded differently compared to starch. Insoluble in water
Describe structure and function of cellulose cell wall
Consists of cellulose fibres embedded in polysaccharide matrix. Fully permeable structure. Provides mechanical support for plant cell and plant, resist expansion when water enters by osmosis, ensuring integrity of plant cell and provides turgidity
What are the general functions of carbohydrates
Glucose - substrate for respiration to release energy for cell activities
Deoxyribose sugars - formation of nucleic acids
Forms lubricants (e.g. mucus)
Forms nectar in flowers
Cellulose - supporting structure
Ready source of energy that can be easily utilised
Describe Benedict’s test
It is test for reducing sugar
To 2cm^3 of food solution to be tested, add equal volume of BS
Shake mixture
Place test tube in boiling water bath for maximum of 5 minutes
Observe precipitate formation and color changes, if any
Describe iodine test
It is test for starch, blue-black coloration observed in presence of starch
Place food substance on white tile. Solid foods may need chopping
Add -3 drops of dilute iodine solution to substance
Observe color changes, if any
Describe structure of lipids
Organic compounds containing carbon, hydrogen and oxygen, with much less oxygen compared to carbon and hydrogen
Lipids insoluble in water but soluble in organic solvents
Describe formation of triglyceride
Condensation reaction of 3 molecules of fatty acids and 1 molecules of glycerol with removal of three molecules of water. Fatty acids can be same or different
Describe bond in triglyceride
Bond formed is ester bond
O
||
- O - C –
How to differentiate fats and oils
Depends on state at 20degC
Solids for fats, liquid for oils
Describe difference between oil and fats
Oil has unsaturated fatty acids but fat has saturated fatty acids
Presence of at least one carbon-carbon double bond in carbon atoms, relatively shorter fatty acid chains in oil
Lower melting point and molecular weight
What are characteristics of fat and oil
Insoluble in water(both)
Fat stored as droplets inside specialised fat cells, adipose cells, as they are insoluble and do not affect water potential in cells
What are functions of triglycerides
Energy storage, heat insulator, buoyancy in aquatic animals, protective layer, important component of myelin sheath, provides metabolic water, can act as a solvent for fat-soluble vitamins and other vital substances
Describe energy storage of triglycerides
One gram of triglyceride yields twice as much energy as one gram of carbohydrate, half the mass for equivalent amount of energy stored, is light-weight energy source
Carbohydrates still most direct source of energy as they can be metabolised quickly
Describe production of metabolic water by triglycerides
Oxidation of triglycerides release twice as much water as carbohydrates when oxidised. Metabolic water produced from respiration. Hydrogen atoms are used in formation of metabolic water during oxidation and triglycerides contain more hydrogen atoms than carbohydrates
Describe phospholipids
Compound lipids containing two molecules of fatty acids, one molecule of glycerol and phosphate group. Hydrophilic phosphate group(face aqueous environment) attracted to water molecules and hydrophobic fatty acid tails(face inside of bilayer) repelled by water molecules. Major component of biological membranes
Describe ethanol emulsion test
White emulsion will be formed in presence of fats
Add food solution/chopped food
Add 2cm3 of ethanol and shake thoroughly
(Allow solid particles to settle)
Decant ethanol mixture into another test tube containing 2cm^3 of water
Describe structure of proteins
Made of elements carbon, hydrogen, oxygen and nitrogen
Each protein has unique 3D shape
When heated, weak bonds in protein are broken, denatured
What are components of protein
At least one amino group(NH2)
A carboxyl group (COOH)
A hydrogen atom
A variable/R group
Describe formation of polypeptide
Condensation reaction with removal of water molecules. Amino group one amino acid reacts with carboxyl group of another amino acid, with removal of water, covalent bond is formed is peptide bond
O=C-N-H
Describe functions of proteins
Synthesis of new cells, growth and repair of worn-up cells
Biological catalysts - enzymes
Chemical messenger - hormones
Transport proteins - haemoglobin
Structural proteins - collagen-skin and bones, keratin-hair and nails
Defence of body - antibodies
Source of energy during starvation
Describe kwashiorkor
A form of protein deficiency disease. Children with disease caused by malnutrition will have swollen stomachs, skins crack and become scaly
Describe biuret’s test
In presence of copper(II) ions in alkaline solution, compound containing peptide bonds will form violet colouration
2 cm3 of food solution, add 1cm3 of sodium hydroxide solution
Shake thoroughly
Add 1% copper(II) sulfate solution, drop by drop until color change
