1. Biological Molecules Flashcards
Polymer
Definition + Examples
A polymer is a macro-molecule, composed of many repeated subunits known as monomers.
Examples:
- Polymer: polysaccharides (starch, glycogen, cellulose); monomer: monosaccharides (glucose).
- Polymer: protein/polypeptides; monomer: amino acids.
- Polymer: polynucleotides; monomer: nucleotides.
Lipids are not polymers because they are not composed of repeating units of the same molecules or atoms.
Condensation Reaction
Definition
Condensation is a chemical reaction whereby two or more small, simple molecules are joined together to form a larger, complex biological molecule with the removal of water molecules.
Hydrolysis
Definition
Hydrolysis is the splitting up of a large, complex biological molecule into its component units with the addition of water molecules.
Carbohydrates
Component elements + Solubility
Made up of carbon, hydrogen, oxygen with the general formula Cm(H2O)n.
Hydrogen and oxygen atoms are present in the ratio 2:1.
Monosaccharides and disaccharides are soluble in water but insoluble in organic solvents, hence they are able to lower water potential of solutions.
Polysaccharides are insoluble in both water and organic solvents.
Monosaccharides
What they are + General formula + Examples
Simplest form of carbohydrates - cannot be hydrolysed further.
All the same general formula (C6H12O6), but arranged in different structures, hence they are structural isomers.
e.g. glucose, fructose, galactose
Disaccharides
What they are + General formula + Examples
2 monosaccharides joined through condensation reaction.
Glycosidic bond is formed between the monosaccharides.
All the same general formula (C12H22O11), but arranged in different structures, hence they are structural isomers.
e.g.
Maltose - glucose + glucose
Lactose - glucose + galactose
Sucrose - glucose + fructose
Formula is because of the addition of 2 C6H12O6 with removal of 1 H20
Polysaccharides
What they are + Types + Examples
Many monosaccharides joined through condensation reaction.
Glycosidic bond is formed between the monosaccharides.
Storage polysaccarides:
- Starch and glycogen
Structural polysaccharide:
- Cellulose
Glycosidic Bond
What it is + Structure
Bond between 2 monosaccharides formed through condensation reaction.
[Photo of Glycosidic Bond in Sucrose]
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Starch
What it is + How it is formed + Structure + Where it is found + Function
Starch is a storage polysaccharide:
- Formed from the condensation reaction of large numbers of glucose molecules
- Can be in long straight chains (amylose) or branched chains (amylopectin)
- Found only in plants
- Function is to store energy
Glycogen
What it is + How it is formed + Structure + Where it is found + Function
Glycogen is a storage polysaccharide:
- Formed from the condensation reaction of large numbers of glucose molecules
- In highly branched chains
- Found mainly in animals - stored in the liver and muscles of mammals
- Function is to store energy
Why are starch and glycogen suitable as storage materials?
4 reasons
- They are insoluble in water. So, they do not affect the water potential in cells.
- They are too large to diffuse through the cell membranes. So, they stay in the cells.
- They have compact shapes. So, they occupy lesser space than all the individual glucose molecules that make up a starch or glycogen molecule.
- They can be easily hydrolysed to glucose when needed.
Cellulose
What it is + How it is formed + Structure + Function
Cellulose is a structural polysaccharide:
- Formed from the condensation reaction of large numbers of glucose molecules
- In straight chains
Functions as the main component of the cellulose cell wall in plant cells:
- Consists of cellulose fibres embedded in a polysaccharide matrix
- Fully permeable structure
- Provide mechanical support for the plant cell and to the plant
- Resist expansion when water enters by osmosis, ensuring integrity of plant cell and to provide turgidity
What are the 5 general functions of carbohydrates?
- Glucose - As a substrate for respiration, to release energy for all cell activities
- Deoxyribose sugar/Ribose sugar - Used for the formation of nucleic acids (e.g. DNA)
- Forms lubricants (e.g. mucus which consists of a carbohydrate and a protein)
- Forms nectar in some flowers
- Cellulose - To form supporting structures (e.g. cellulose cell walls in plants)
Benedict’s Test
Purpose + Steps + Observations
Benedict’s Test - to test for the presence of reducing sugar
Steps:
- To 2 cm3 of food solution to be tested, add an equal volume of Benedict’s solution.
- Shake the mixture.
- Place test tube in boiling water bath for a maximum of 5 minutes.
- Observe precipitate formation and colour changes, if any.
Presence of reducing sugars based on colour of precipitate formed:
Blue (absent) => Green (little concentration) => Yellow (moderate concentration) => Orange/Brick red (large concentration)
Presence of sucrose cannot be tested with Benedict’s test bcs sucrose is a non-reducing sugar
Iodine Test
Purpose + Steps + Observations +
Iodine Test - to test for the presence of starch
Steps:
- Place food substance on a white tile. Solid foods may need to be chopped up to smaller pieces.
- Add 2 - 3 drops of dilute iodine solution to substance to be tested.
- Observe colour changes, if any.
Presence of starch based on colour change:
Remains yellow-brown (absent) => Blue-black coloration oberserved (present)