1 Exams Questions Flashcards

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1
Q

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

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

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2
Q

What is a monomer? [1]

A

A monomer is a smaller repeating unit from which larger molecules (polymers) are made

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3
Q

Suggest a method, other than
using a colorimeter, that a student could use to measure the quantity of reducing sugar in a solution. [3]

A

Carry out Benedict’s test
Filter and dry the precipitate
Find mass/weight

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4
Q

Use of a colorimeter in this investigation would improve the repeatability of the student’s results.

Give one reason why. [1]

A

Quatitative - colour change is subjective

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5
Q

Glycogen and cellulose are both carbohydrates.

Describe two differences between the structure of a cellulose molecule and a glycogen molecule. [2]

A

Cellulose has straight chain, glycogen is branched
Cellulose is made up of beta glucose monomers and glycogen is made up of alpha glucose monomers

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6
Q

Starch is a carbohydrate often stored in plant cells.

Describe and explain five features of starch that make it a good storage molecule. [5]

A

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

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7
Q

Describe the structure of glycogen. [2]

A

Polysaccharide of alpha glucose
Joined by glycosidic bonds

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8
Q

Suggest how glycogen acts as a source of energy. [2]

A

Hydrolysed to glucose
Glucose used in respiration

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9
Q

Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above. [2]

A

Starch formed from alpha glucose but cellulose formed from beta glucose
Position of hydrogen and hydroxyl groups on carbon inverted

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10
Q

Explain how cellulose molecules are adapted for their function in plant
cells. [3]

A

Long and straight chains
Become linked by many hydrogen bonds to form fibrils
Fibrils provide strength to cell wall

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11
Q

Describe how you would test for the presence of a lipid in a liquid sample of food. [2]

A

Add ethanol then add water and shake
White/milky emulsion if positive

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12
Q

Describe how a triglyceride molecule is formed. [3]

A

One glycerol and three fatty acids
Condensation reactions and removal of three water molecules
Ester bonds formed

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13
Q

Describe how an ester bond is formed in a phospholipid molecule. [2]

A

Condensation reaction
Between glycerol and fatty acid

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14
Q

Describe how you would test a piece of food for the presence of lipid. [2]

A

Dissolve in alcohol then add water and shake
White emulsion if positive

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15
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. [3]

A

Substrate binds to active site
Active site changes shape slightly so it is complementary to substrate
Reduces activation energy

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16
Q

Explain the change in ATP concentration with increasing inorganic phosphate concentration. [2]

A

With increasing Pi concentration, more enzyme-substrate complexes form
When all active sites are occupied, enzyme concentration is a limiting factor

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17
Q

A competitive inhibitor decreases the rate of an enzyme-controlled
reaction.

Explain how. [3]

A

Inhibitor similar shape to substrate
Binds to active site
Prevents ES complex forming

18
Q

Describe how the structure of a protein depends on the amino acids it contains. [6]

A

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

19
Q

Explain how the active site of an enzyme causes a high rate of reaction. [3]

A

Lowers activation energy
Induced fit causes active site of enzyme to change shape
So enzyme-substrate complex causes bonds to break

20
Q

Describe a biochemical test to confirm the presence of protein in a
solution. [2]

A

Add biuret agent
Positive result is purple/lilac

21
Q

Describe three ways in which all dipeptides are similar and two ways in which they might differ. [5]

A

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

22
Q

Describe how a non-competitive inhibitor can reduce the rate of an
enzyme-controlled reaction. [3]

A

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

23
Q

Describe how a peptide bond is formed between two amino acids to form a dipeptide. [2]

A

Condensation reaction
Between amine and carboxyl

24
Q

The secondary structure of a polypeptide is produced by bonds between amino acids.

Describe how. [2]

A

Hydrogen bonds
Forming beta pleated sheets/alpha helix

25
Q

Two proteins have the same number and type of amino acids but different tertiary structures.

Explain why. [2]

A

Different sequence of amino acids
Forms ionic/hydrogen/disulfide bonds in different places

26
Q

Formation of an enzyme-substrate complex increases the rate of reaction.

Explain how. [2]

A

Reduces activation energy
Due to bending bonds

27
Q

Suggest two variables the biochemist controlled when investigating the effect of temperature on the rate of breakdown of a protein by the protease. [1]

A

Initial substrate concentration
Enzyme concentration
pH

28
Q

Describe the structure of DNA. [5]

A

Polymer of nucleotides
Each nucleotide formed from deoxyribose, a phosphate group and an organic base
Phosphodiester bonds between nucleotides
Double helix held by hydrogen
Hydrogen bonds between adenine, thymine and cytosine, guanine

29
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. [3]

A

Condensation reaction
Between phosphate and deoxyribose
Catalysed by DNA polymerase

30
Q

Describe how the separation of strands occurs. [2]

A

DNA helicase
Breaks hydrogen bonds between base pairs

31
Q

Describe the role of DNA polymerase in the semi-conservative replication of DNA. [3]

A

Joins adjacemt DNA nucleotides
Catalyses condensation reactions
Catalyses formation of phosphodiester bonds between adjacent nucleotides

32
Q

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. [2]

A

Two strands so both can act as templates
Complementary base pairing allows accurate replication

33
Q

Describe the role of two named enzymes in the process of semi-conservative replication of DNA. [3]

A

DNA helicase causes breaking of hydrogen bonds between strands
DNA polymerase joins the DNA nucleotides
Forming phosphodiester bonds

34
Q

Contrast the structures of ATP and a nucleotide found in DNA to give three differences. [3]

A

ATP has ribose and DNA nucleotide has deoxribose
ATP has 3 phosphate groups and DNA nucleotide has 1
ATP base always adenine and DNA nucleotide base can be different

35
Q

Describe how an ATP molecule is formed from its component molecules. [3]

A

Adenine, ribose, three phosphates
Condensation reaction
ATP synthase

36
Q

ATP is an energy source used in many cell processes.

Give three ways in which ATP is a suitable energy source for cells to use. [3]

A

Releases relatively small amount of energy as heat
Releases energy instantly
Can be rapidly resynthesised

37
Q

Describe how ATP is resynthesised in cells. [3]

A

Form ADP and phosphate
By ATP synthase
During respiration

38
Q

Give two ways in which the hydrolysis of ATP is used in cells. [2]

A

To provide energy for other reactions
To add phosphate to substances

39
Q

Explain the properties that make water important for organisms. [6]

A

A metabolite so takes part in metabolic reactions
A solvent for metabolic reactions and transporting substances
High specific heat capacity so buffers changes in temperature
Large latent heat of vapourisation so provides a cooling effect through evaporation
Cohesion between water molecules so supports columns of water
Cohesion between water water molecules so produces surface tension supporting small organisms

40
Q

Describe the roles of iron ions, sodium ions, and phosphate ions in cells. [6]

A

Iron
Haemoglobin binds with oxygen

Sodium
Sodium moved out by active transport by Na K pump
Cotransport of glucose/amino acids into cells

Phosphate
Joins nucleotides in backbone of DNA
Used to produce ATP
Part of phospholipid bilayer

41
Q

Describe the test for a non-reducing sugar. [3]

A

Heat with acid and neutralise
Heat with Benedict’s solution
Red precipitated formed if positive