3.1 Biological Molecules💧 Flashcards
What are monomers
Smaller units from which larger molecules (polymers) are made
What are polymers
Molecules made from a large number of monomers joined together
Three examples of monomers
• Monosaccharides (polysaccharides)
• Amino Acids (polypeptides)
• Nucleotides
How are polymers formed
Polymerisation through a condensation reaction
Outline a condensation reaction
Joining two molecules together with the formation of a chemical bond, releasing water from the -OH group of one molecule and an -OH group on another
How are monomers formed
The hydrolysis of a polymer through a hydrolysis reaction
Outline a hydrolysis reaction
Breaks a chemical bond between two molecules and involves the use of a water molecule
What’s covalent bonding
Atoms share a pair of electrons in their outer shells, so both atoms have full outer shells forming a more stable compound
What’s ionic bonding
Electrostatic attraction where ions with opposite charges attract each other
• These are weaker than covalent bonds but stronger than hydrogen bonds
What’s hydrogen bonding
• A weak electrostatic bond forming important forces that alter the physical properties of molecules.
• The electrons within a molecule are polarised (not evenly distributed) but tend to spend more time at one position
What are monosaccharides
Smaller units (monomers) from which larger carbohydrates are made
What’s the formula for monosaccharides
(CH2O)n where n=3-7
Outline characteristics of monosaccharides
They’re sweet tasting and soluble and can be pentose sugars (ribose, deoxyribose) or hexose sugars (glucose, galactose, fructose)
State three common hexose monosaccharides
• Glucose
• Galactose
• Fructose
(C6 H12 O6)
What’s an isomer
Two molecules with the same molecular formula but differ structurally, so contain the same number of atoms of each element, but the atomic arrangement differs
What are the two types (isomers) of glucose
• Alpha glucose
• Beta glucose
Outline the characteristics of alpha glucose
• Found in food
• Hydrolysed from starch
• Used in respiration
• Has an -OH group below the hydrogen
Outline the characteristics of beta glucose
• Can’t be broken down by the human body
• Made in photosynthesis
• Produced by plants
• Has an -OH group above the hydrogen
What type of bonds joins carbohydrates
1,4 or 1,6-Glycosidic bond (from a condensation reaction)
What’s a glycosidic bond
A type of covalent bond that joins a carbohydrate molecule to another group (that may not be carbohydrate)
How are disaccharides formed
A condensation reaction of two monomers joined by a glycosidic bond
State three common disaccharides, where they’re produced and their monomers
• Maltose (2x alpha glucose)
• Sucrose (fructose and alpha glucose) produced
by plants
• Lactose (galactose and alpha glucose) produced
by mammals
(C12 H22 O11)
How are polysaccharides formed
By the condensation of many monosaccharides units
State three common polysaccharides
• Glycogen
• Starch
• Cellulose
Outline the characteristics of glycogen
• Polymer of alpha glucose
• Used in animals to store glucose
• Highly branched so has increased surface area
for fast breakdown and enzyme action
• 1,4-glycosidic bonds and 1,6-glycosidic bonds
Outline characteristics of starch
• Polymer of alpha glucose
• Used in plants to store glucose
• Large molecule that cannot leave the cell
• Insoluble in water (doesn’t affect water potential)
• Found in two forms; amylose and amylopectin
Why is starch a good storage molecule
• Large so it can’t cross the cell membrane
• Insoluble in water so doesn’t affect water potential
• Polymer of alpha glucose so provides glucose for respiration
• Branched so it makes the molecule compact and can fit many molecules in a small area
• Branched so has increased surface area for fast breakdown and enzyme action
Outline the characteristics of amylose
• Carbon 1,4-glycosidic bonds
• Compact helical structure to store lots of glucose
in a small space
• Hydrolysed into maltose by amylase enzyme
Outline the characteristics of amylopectin
• Carbon 1,4 and 1,6-glycosidic bonds
• Branched, so has increased surface area for enzyme action and releases glucose molecules faster than amylose
Describe the test for starch
Iodine/potassium iodine test:
- Add iodine solution, a positive result is a colour change from orange to blue-black
Outline the characteristics of cellulose
• Polymer of beta glucose
• Provides structure and support in plant cell
walls, preventing bursting under turgor pressure
and holds the stem up
• 1,4-glycosidic bonds
• Alternating glycosidic bonds due to the differing
-OH group placement in beta glucose than
alpha glucose, so it’s found in long straight chains
• These chains are joined together by hydrogen
bonds to form bundles of cellulose fibres
(microfibrils) that have high tensile strength
Differences between the structure of starch and cellulose
• Starch formed from alpha glucose, cellulose from beta glucose
• Position of hydrogen and hydroxyl groups on Carbon atom one are inverted
What biochemical test is used to test for carbohydrate/sugar
Benedict’s solution test
Outline the method of a Benedict’s test for reducing sugars
• Add an equal volume of Benedict’s solution to a
sample and heat in a water bath for 5 minutes
• A positive results indicated by a colour change of
the Benedict’s reagent from blue to brick red
What’s Benedict’s reagent
An alkaline solution of Copper (II) sulphate
How can the concentration of sugar be approximated in the Benedict’s test
Semi-quantitative use can approximate the concentration of sugar present by the colour of the Benedict’s reagent
Why can’t the Benedict’s test be used for non-reducing sugars, providing examples
• They can’t be oxidised as they can’t donate electrons, so must be hydrolysed into monosaccharides by breaking any glycosidic bonds
• Eg. Sucrose and all polysaccharides
Outline the method for testing for non-reducing sugars
• Negative Benedict’s test, reagent remains blue
• Add dilute hydrochloric acid and heat in a water
bath for 5 minutes and neutralise the solution with sodium hydrogen carbonate (NaHCO3)
• Can use an indicator (eg red litmus paper to
ensure neutralisation)
• Carry out Benedict’s test as normal