1 Exams Questions Flashcards
Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.
Give two named examples of monomers and their associated monomers to illustrate your answer. [5]
A condensation reaction joins monomers and forms a bond and releases water
A hydrolysis reaction breaks a bond between monomers and uses water
eg1. Amino acids join by peptide bonds to form polypeptide/protein
eg2. Alpha glucose joined by glycosidic bonds to form starch
What is a monomer? [1]
A monomer is a smaller repeating unit from which larger molecules (polymers) are made
Suggest a method, other than
using a colorimeter, that a student could use to measure the quantity of reducing sugar in a solution. [3]
Carry out Benedict’s test
Filter and dry the precipitate
Find mass/weight
Use of a colorimeter in this investigation would improve the repeatability of the student’s results.
Give one reason why. [1]
Quatitative - colour change is subjective
Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule. [2]
Cellulose has straight chain, glycogen is branched
Cellulose is made up of beta glucose monomers and glycogen is made up of alpha glucose monomers
Starch is a carbohydrate often stored in plant cells.
Describe and explain five features of starch that make it a good storage molecule. [5]
Insoluble so doesn’t affect water potential
Branched so can be compact
Branched so enzyme action faster
Polymer of alpha glucose so provides glucose for respiration
Large so can’t cross cell membrane
Describe the structure of glycogen. [2]
Polysaccharide of alpha glucose
Joined by glycosidic bonds
Suggest how glycogen acts as a source of energy. [2]
Hydrolysed to glucose
Glucose used in respiration
Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above. [2]
Starch formed from alpha glucose but cellulose formed from beta glucose
Position of hydrogen and hydroxyl groups on carbon inverted
Explain how cellulose molecules are adapted for their function in plant
cells. [3]
Long and straight chains
Become linked by many hydrogen bonds to form fibrils
Fibrils provide strength to cell wall
Describe how you would test for the presence of a lipid in a liquid sample of food. [2]
Add ethanol then add water and shake
White/milky emulsion if positive
Describe how a triglyceride molecule is formed. [3]
One glycerol and three fatty acids
Condensation reactions and removal of three water molecules
Ester bonds formed
Describe how an ester bond is formed in a phospholipid molecule. [2]
Condensation reaction
Between glycerol and fatty acid
Describe how you would test a piece of food for the presence of lipid. [2]
Dissolve in alcohol then add water and shake
White emulsion if positive
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. [3]
Substrate binds to active site
Active site changes shape slightly so it is complementary to substrate
Reduces activation energy
Explain the change in ATP concentration with increasing inorganic phosphate concentration. [2]
With increasing Pi concentration, more enzyme-substrate complexes form
When all active sites are occupied, enzyme concentration is a limiting factor
A competitive inhibitor decreases the rate of an enzyme-controlled
reaction.
Explain how. [3]
Inhibitor similar shape to substrate
Binds to active site
Prevents ES complex forming
Describe how the structure of a protein depends on the amino acids it contains. [6]
Structure determined by position of amino acid
Primary structure is sequence of amino acids
Secondary structure formed by hydrogen bonding between amino acids
Tertiary structure formed by interactions between R groups
Creates active site in enzymes
Quarternary structure is more than 1 polypeptide chain bonded
Explain how the active site of an enzyme causes a high rate of reaction. [3]
Lowers activation energy
Induced fit causes active site of enzyme to change shape
So enzyme-substrate complex causes bonds to break
Describe a biochemical test to confirm the presence of protein in a
solution. [2]
Add biuret agent
Positive result is purple/lilac
Describe three ways in which all dipeptides are similar and two ways in which they might differ. [5]
All consist of two amino acids joined by a peptide bond
All contain C and H and N and O
All have two R groups
May differ in type of amino acids they contain
May differ in R group
Describe how a non-competitive inhibitor can reduce the rate of an
enzyme-controlled reaction. [3]
Attaches to enzyme not at active site
Changes tertiary structure of active shape
Active site is no longer complementary to substrate so can’t bind
Describe how a peptide bond is formed between two amino acids to form a dipeptide. [2]
Condensation reaction
Between amine and carboxyl
The secondary structure of a polypeptide is produced by bonds between amino acids.
Describe how. [2]
Hydrogen bonds
Forming beta pleated sheets/alpha helix
