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]
— O —
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)
Lipids
Component elements + Solubility
Made up of carbon, hydrogen, oxygen,
with much lesser oxygen compared to carbon and hydrogen.
Lipids are insoluble in water but soluble in organic solvents.
Triglycerides
What they are + How are they formed + Structure
Triglycerides are simple lipids:
- Formed by condensation reaction of 3 molecules of fatty acids and 1 molecule of glycerol with the removal of 3 molecules of water.
- 3 ester bonds are formed between the fatty acids and glycerol.
Fatty Acids
What it is + Types of fatty acids
A fatty acid is a long hydrocarbon chain that has a carboxyl functional group (COOH).
The hydrocarbon chain can be:
- Unsaturated (contain 1 or more carbon-carbon double bonds, C=C, which causes a kink in the chain) ~ less hydrogen
- Saturated (lack of carbon-carbon double bond) ~ more hydrogen
Glycerol
What it is + Chemical formula + Structure
Glycerol is an alcohol.
The chemical formula of glycerol is C3H8O3.
Has 3 hydroxyl functional groups.
Ester Bond
What it is + Structure
Ester bond is the bond formed between 1 fatty acid and glycerol through condensation reaction.
O–C=O
Fats and Oils
Classification of Triglycerides
Triglycerids can be classified as fats or oils, depending on their state at 20°C.
Fats (triglycerides with saturated fatty acids):
- Solid at 20°C
- Absence of carbon-carbon double bond
- Relatively longer fatty acid chains
- Higher melting point
- Higher molecular weight (heavier)
Oils (triglycerides with unsaturated fatty acids):
- Liquid at 20°C
- Presence of at least 1 carbon-carbon double bond
- Relatively shorter fatty acid chains
- Lower melting point
- Lower molecular weight (lighter)
How are fats stored in mammals?
+ Why are they stored this way?
Fats are stored as droplets inside specialised fat cells, known as adipose cells.
This is because fats are insoluble in water and do not affect the water potential in cells.
Adipose cells are grouped together to form adipose tissue.
What are the 7 general functions of triglycerides?
- Energy storage - one gram of triglycerides yields about twice as much energy as one gram of carbohydrates
- Heat insulator - Fats conduct heat slowly
- Buoyancy in aquatic mammals - Fats are less dense than water
- Protective layer - Fats are able to absorb shock
- Important component of myelin sheath - Fats act as an electrical insulator, allowing rapid tramsission of electrical impulses along myelinated neurons
- Provides metabolic water - Triglycerides release twice as much water as carbohydrates when oxidised during respiration
- As a solvent - for fat-soluble vitamins and vital substances
Why do triglycerides yield more energy than carbohydrates?
Because triglycerides contain a greater number of carbon-hydrogen (C-H) bonds per gram than starch or glycogen.
Therefore, one gram of triglyceride yields about twice as much energy than one gram of carbohydrates.
Why are triglycerides used as storage in fast moving or flying animals and speeds dispersed by wind or insects?
Because triglycerides have about half the mass of carbohydrates for an equivalent amount of energy stored.
It is therefore a lightweight energy source.
Why are carbohydrates the most utilised energy source and not lipids?
Because carbohydrates are still the most direct source of energy in living things.
They can be metobolized quickly, both in aerobic and anaerobic conditions.
Why do triglycerides produce more metabolic water than carbohydrates?
Because triglycerides contain more hydrogen atoms than cabohydrates.
Hydrogen atoms are used in the formation of metabolic water during oxidation.
Therefore, triglycerides release twice as much water as carbohydrates when oxidised during respiration.
Phospholipids
What they are + Structure
Phospholipids are compound lipids:
- Contains 2 molecules of fatty acids, 1 molecule of glycerol & a phosphate group
- 2 ester bonds are formed between the fatty acids and glycerol
Phosphate group is hydrophilic, while fatty acid tails are hydrophobic
What gives the phospholipid bilayer its unique structure?
The hydrophilic phosphate group is attracted to the water molecules in their environment
and the hydrophobic fatty acid tails are repelled by the water molecules.
Hence, the hydrophilic heads face the aqeuous environment
while the hydrophobic tails face the inside of the bilayer, away from water in their environment, forming the interior of the membrane.
Function of Phospholipids
Phospholipids are a major component of biological membranes.
Due to the nature of phospholipids, the cell membrane is made up of two layers of phospholipids, the phospholipid bilayer.
Ethanol Emulsion Test
Purpose + Steps + Observations
Ethanol Emulsion Test - to test for fats
Steps (for liquid food mixture):
- Add 2 cm3 of ethanol to 2 cm3 of food solution in a test-tube.
- Shake the mixture thoroughly.
- Decant the ethanol mixture into another test tube containing 2 cm3 of water.
Steps (for solid food mixture):
- Chop solid food into small pieces and place them into a dry test tube.
- Add 2 cm3 of ethanol and shake the mixture thoroughly.
- Allow the solid particles to settle.
- Decant the ethanol mixture into another test tube containing 2 cm3 of water.
Presence of fats based on observation:
No visible change (absent) => White emulsion formed (present)
Proteins
Component elements + Solubility
Made up of carbon, hydrogen, oxygen, nitrogen.
Sulfur is sometimes present.
Proteins are generally soluble in water, some are insoluble in water.
Proteins are polymers made up of monomers - amino acids.
Structure of Proteins
Peptide bonds join amino acids to form a polypeptide chain.
The polypeptide chain folds as a result of 4 other types of bonds: disulfide bridges, ionic bonds, hydrogen bonds, hydrophobic interactions.
Each protein has a unique 3-dimensional shape, giving it its unique function.
Amino Acids
What they are + Structure
Monomers of proteins.
Structure consists of:
- a central carbon atom
- an amino group (-NH2)
- a carboxyl group (-COOH)
- hydrogen atom
- a variable group, R group (also known as the side chain)
Different amino acids have different R groups, giving them different properties and functions
Peptide Bond
What it is + Structure
Bond between 2 amino acids formed through condensation reaction:
- Amino group (-NH2) of one amino acid reacts with the carboxyl group (-COOH) of another amino acid, removing 1 water molecule
O=C—N–H
What are the 7 Functions of Proteins?
- Used in the synthesis of new cells, for growth, and repair of worn out cells
- Biological catalysts - enzymes, to speed up chemical reactions
- Chemical messenger - hormones, to stimulate target organs to perfom a certain function (e.g. insulin)
- Transport proteins - (e.g. haemoglobin to transport oxygen in red blood cells)
- Structural proteins (e.g. collagen is a component of skin, keratin is a component of hair, nails, and feathers)
- Defence of body - antibodies are used to help fight infections in body
- Source of energy during stavation - only oxidised after all the carbohydrates and lipids are used up
Biuret’s Test
Purpose + Steps + Observations
Biuret’s Test - to test for proteins
Steps:
- To 2 cm3 of food solution, add 1 cm3 of sodium hydroxide solution.
- Shake the mixture thoroughly.
- Add 1% copper(II) sulfate solution, drop by drop, shaking after each drop until a colour change is observed
Presence of proteins based on colour change:
Remains blue (absent) => Violet colouration (present)
In the presence of copper(II) ions in alkaline solution, a compound containing peptide bonds will form violet colouration, which develops slowly without heating
Kwashiorkor
What it is + Symptoms
Kwashiorkor is a form of protein deficiency disease.
Children with this disease, caused by malnutrition (non-infectious), will have swollen stomachs. Their skin crack and become scaly.
