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AQA - A level Biology > Topic 1 - Biological Molecules > Flashcards

Topic 1 - Biological Molecules Flashcards

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1
Q

What is a monomer?

A

Smaller units from which larger molecules are made

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1
Q

What 4 carbon-based compounds are all living things made of?

A

Lipids, carbohydrates, proteins, nucleic acids

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2
Q

By which process do monomers join to form polymers?

A

Polymerisation

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2
Q

What is a polymer?

A

Molecules made from a large amount on monomers joined together.

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3
Q

Name 3 examples of monomers.

A

Monosaccharides (e.g. glucose)
Amino acid
Nucleotides (e.g. A,T,C,G,U)

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4
Q

Which biological molecule does not form ploymers?

A

Lipids

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5
Q

By what process are polysaccharides split into monosaccharides?
What is needed for this reaction?

A

Hydrolysis reaction
A water molecule

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5
Q

Monomers join to form polymers by what reaction? What is removed during this reaction?

A

Condensation reaction
Water is removed

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6
Q

What three chemical elements make up carbohydrates?

A

Carbon, Hydrogen, Oxygen

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7
Q

What are the main 2 functions of carbohydrates?

A

To store energy
Structured role in plant cell walls (cellulose)

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8
Q

What are the three groups of carbohydrate?

A

Monosaccharides, disaccharides, polysaccharides

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9
Q

Glucose and fructose have the same chemical formula. How can they exist as two different monosaccharides?

A

They have a different atomic structure

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10
Q

Draw a-glucose.

A

Look up answer

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11
Q

Draw b-glucose.

A

Look up answer

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12
Q

What are reducing sugars?

A

Sugars that reduce Benedict’s reagent.

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13
Q

Which disaccharide is not a reducing sugar?

A

Sucrose

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14
Q

What is another name for Benedict’s reagent / solution?

A

Copper (II) sulphate

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15
Q

Why does Benedict’s Reagent turn red when heated with a reducing sugar?

A

Reducing sugar donates its electrons from their reducing centres to the blue copper (II) sulphate. This forms copper (I) oxide which makes a brick-red precipitate.

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16
Q

Describe the stages in the Benedict’s test.

A

Add Benedict’s reagent to a sample solution in a test tube
Heat the test tube in a water bath for a few minutes.
If a reducing sugar is present, a coloured precipitate will form as copper (II) sulfate is reduced to copper (I) oxide which is insoluble in water.
It is important that an excess of Benedict’s solution is used so that there is more than enough copper (II) sulfate present to react with any sugar present.
A positive test result is a colour change somewhere along a colour scale from blue (no reducing sugar), through green, yellow and orange (low to medium concentration of reducing sugar) to brown/brick-red (a high concentration of reducing sugar)

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17
Q

Name 3 monosaccharides?

A

Glucose
Fructose
Galactose

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17
Q

What is the test for non-reducing sugars?

A

Add dilute hydrochloric acid to the sample and heat in a water bath.
Neutralise the solution with sodium hydrogencarbonate.
Complete the Benedict’s test and if there is a positive result, a non-reducing sugar is present.

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18
Q

What bond is formed between two monosaccharides?

A

Glycosidic bond

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19
Q

Name 3 disaccharides.

A

Sucrose
Maltose
Lactose

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20
Q

What two monosaccharides does sucrose form when hydrolysed?

A

glucose and fructose

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21
Q

What two monosaccharides does lactose form when hydrolysed?

A

glucose and galactose

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22
Q

What are the products of a condensation reaction between two monosaccharides?

A

Disaccharide and a water molecule

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22
Q

What is formed when two molecules of a-glucose join together?

A

Maltose

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22
Q

Name 3 polysaccharides.

A

Starch, cellulose and glycogen

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23
Q

What glycosidic bond do two molecules of a-glucose form?

A

1-4 glycosidic bond

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24
Q

A polysaccharide containing 101 monosaccharides monomers contains how many glycosidic bonds?

A

100

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25
Q

Starch is made from what monomer?

A

a-glucose

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26
Q

Cellulose is made from what monomer?

A

b-glucose

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27
Q

Glycogen is made from what monomer?

A

a-glucose

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28
Q

What glycosidic bond/s is present in starch?

A

1-4 and 1-6

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29
Q

What glycosidic bond/s is present in cellulose?

A

1-4

30
Q

What glycosidic bond/s is present in glycogen?

A

1-4 and 1-6

31
Q

What is the basic structure of starch, cellulose and glycogen?

A

Starch - branched, helical and compact
Cellulose- unbranched, straight
Glycogen - highly branched

32
Q

What is the helical structure of starch called and what forms this?

A

Amylose
Made from straight unbranched chains with 1-4 glycosidic bonds. The hydroxyl groups point inwards on a-glucose and these form the hydrogen bonds that keep the helix in place.

33
Q

What is the structure of amylopectin?

A

a-glucose molecules joined by 1-4 and 1-6 glycosidic bonds. Lots of branches.

34
Q

Describe the structure of cellulose.

A

Straight unbranched chains that run parallel to each other allowing hydrogen bonds to form cross-linkages between adjacent chains.

34
Q

Describe the structure of glycogen.

A

Similar structure to amylopectin but more highly branched and forms 1-4 and 1-6 glycosidic binds.

35
Q

How is starch suited for its function?

A

Insoluble so does not affect water potential.
Does not diffuse out of cells as its insoluble.
Compact so a lot can be stored in a small space.
When hydrolysed it forms a-glucose, which can be transported and used in respiration.
Branched ends so enzymes can act simultaneously on multiple ends.

36
Q

How is cellulose suited to its function?

A

Chains run parallel to each other and are cross-linked by hydrogen bonds for strength.
Molecules grouped to form microfibrils which are grouped to form fibres providing more strength.
Made of b-glucose so form long straight unbranched chains.

37
Q

How is glycogen suited to its function?

A

Does not diffuse out of cells as its insoluble.
Compact so a lot can be stored in a small space.
More branched than starch so has more ends so more enzymes can act simultaneously.
Insoluble so doesn’t tend to draw water into the cell.

38
Q

What are the two types of lipids?

A

Triglycerides and phospholipids

39
Q

Describe lipid solubility.

A

All soluble in water and in some solvents (e.g. alcohol)

40
Q

Describe the roles of lipids.

A

Energy source - provide twice as many calories as the same mass of carbohydrate or protein.
Waterproofing - Plants and animals have a waxy cuticle. Mammals produce sebum.
Insulation - lipids are poor conductors, but good insulators.
Protection - delicate organs such as kidneys have fat around them.
They form part of the plasma membrane - phospholipids.

41
Q

What are triglycerides made from and how are these joined?

A

One glycerol and 3 fatty acids joined by condensation reactions.

42
Q

What is the difference between an unsaturated and saturated fatty acid?

A

A saturated fatty acid has no carbon to carbon double bonds.
All of the carbon atoms are linked to the maximum number of hydrogen atoms in saturated.
Saturated fatty acids solid at room temp.
Unsaturated liquid at room temp as double bond between 2 carbons doesn’t allow it to pack together.

43
Q

What makes up a phospholipid?

A

Two fatty acids - the hydrophobic tail.
One glycerol molecule
One phosphate group - hydrophillic.

44
Q

What bonds are formed between fatty acids and glycerol molecules?

A

Ester bonds

45
Q

What will a positive result for a lipid show?

A

Milky white emulsion

45
Q

What are the monomers that form proteins called?
What do these monomers form?

A

Amino acids
They form a polypeptide

45
Q

What main things make up the structure of an amino acid?

A

An ‘R’ group (variable group)
A carboxyl group
An amino group

46
Q

After the condensation reaction of two amino acids, what bond forms?

A

A peptide bond

46
Q

Where does the bond between two amino acids form?

A

After the first ‘NCC’ and after the carbonyl group.

47
Q

Describe the primary structure of a protein.

A

A particular sequence of amino acids.

48
Q

Describe the secondary structure of a protein.

A

Hydrogen bonds form between the ‘R’ groups of amino acids causing coiling (alpha helix) or folding (beta sheets).

49
Q

Describe the tertiary structure of a protein.

A

The secondary structure can be folded again to form the tertiary structure. Disulphide bridges, hydrogen bonds and ionic bonds form.

50
Q

Describe the quaternary structure of a protein and give an example.

A

Proteins with multiple polypeptide chains fold again to form the final, 3D quaternary structure. Haemoglobin is an example of a protein with a quaternary structure.

51
Q

How will a change in one amino acid change the function of a protein?

A

A change in the sequence of amino acids will change the primary structure and therefore the position of the hydrogen bonds when folded into a beta sheet or coiled into an alpha helix.
This in turn will change the position of the ionic bonds, disulphide bridges and hydrogen bonds in the tertiary structure.
This will change the function of the protein.

52
Q

What are fibrous and globular proteins?

A

Fibrous - have structural functions. Long chains which run parallel to each other. Linked by cross-bridges.

Globular - have metabolic functions

53
Q

What is the test for proteins?

A

Add buiret solution.
Turns violet to show a positive result.

53
Q

What are enzymes?

A

Biological catalysts.

54
Q

How do enzymes increase the rate of a reaction?

A

Provides an alternate pathway with a lower activation energy

55
Q

At what level of protein structure is an enzyme?

A

tertiary

55
Q

Where does the substrate bind on an enzyme?

A

The active site

56
Q

What are enzymes denatured by?

A

High temperatures and extreme pH.

57
Q

What forms when a complementary substrate binds to an enzyme?

A

An enzyme-substrate complex

57
Q

Describe the ‘Lock and Key’ model of enzyme action.

A

The substrate will bind to the active site of one particular enzyme.

58
Q

Describe the ‘Induced Fit’ model of enzyme action.

A

Suggests the active site is flexible and changes shape slightly when the substrate molecules bind to the active site.

58
Q

Why are enzymes highly effective in small quantities?

A

They can be reused quickly and catalyse more reactions.

58
Q

Describe the advantages/disadvantages of the ‘Lock and Key’ model.

A

Limitations:
Suggests an enzyme is a rigid shape.
Suggests enzymes can’t bind to other sites other than the active site.
Doesn’t show that enzymes are flexible.

58
Q

Describe the advantages/disadvantages of the ‘Induced Fit’ model.

A

Advantages:
Shows how enzyme activation can be affected by other molecules (inhibitors). This explains how strain is placed on the substrate as the enzyme changes shape.

58
Q

How does temperature affect the rate of enzyme action?

A

As temperature increases, the kinetic energy of both substrates and enzymes increase.
This increases the number of collisions, which means more enzyme-substrate complexes form.
Generally temperatures above 45 degrees cause enzymes to denature.

58
Q

How does a temperature of above 45 degrees cause an enzyme to denature?

A

Heat causes molecules to vibrate.
Vibrations cause the hydrogen bonds, ionic bonds and disulphide bridges in the tertiary structure of the enzyme to break..
This causes the active site to lose its shape so no enzyme-substrate complexes can be made.

59
Q

What is pH?

A

pH is the measure of hydrogen ion (H+) concentration of a solution.

59
Q

Describe the effects of pH on enzyme activity?

A

At optimum pH, the concentration of H+ ions gives the tertiary structure the best overall shape.
As pH changes, the concentration of H+ ions change.
This affects the bonds in the tertiary structure and changes the shape of the active site.
No/less enzyme-substrate complexes can form.

60
Q

Describe the affect of enzyme concentration on the rate of reaction.

A

At the beginning, there are too few enzyme molecules to allow all the substrate molecules to find an active site at one time.
The rate of reaction is therefore half the maximum possible for the number of substrate molecules available.
As enzyme concentration continues to increase, the rate of reaction will continue to increase until it eventually plateaus.
This is because all the substrate molecules can occupy an active site at the same time.
The reaction has reached its maximum rate.

61
Q

Describe the affect of substrate concentration on rate of reaction.

A

At a low substrate concentration there are too few substrate molecules to occupy the available active sites.
The rate of reaction continues to increase until there are more substrate molecules than enzyme molecules so rate plateaus.

62
Q

What are enzyme inhibitors?

A

Molecules that have an altering effect on the active site of an enzyme.
This reduces the activity of an enzyme and therefore the rate of an enzyme controlled reaction.

63
Q

How does a competitive inhibitor work?

A

They bind directly to the active site.
They compete with the substrate for active sites so have a complementary shape to the substrate.

64
Q

How does a non-competitive inhibitor work?

A

They bind to a position other than the active site.
The substrate can still fit the active site but no it a way that allows the reaction to proceed.

65
Q

In a reaction with a fixed quantity of substrate, describe what would happen to the rate of reaction if you increased the concentration of a competitive inhibitor?

A

The competitive inhibitor has a shape similar to the substrate.
It competes with the substrate for the enzymes active site.
Fewer active sites would be available to catalyse the reaction.
Fewer enzyme-substrate complexes would form.
This therefore decreases the rate of reaction

66
Q

In a reaction with a fixed quantity of competitive inhibitor present, describe and explain what would happen to the rate of reaction if you increased the concentration of the substrate?

A

The inhibitor is not permanently bound to the active site.
When the inhibitor leaves the active site the likelihood of collision between substrate and enzymes active site is increased.
This means the rate of reaction increases.

67
Q

In an enzyme controlled reaction, what would happen to the rate of reaction if you increased the concentration of the following? Explain each answer.
i) non-competitive inhibitor
ii)substrate

A

i) The rate would decrease because the active site will change shape meaning the substrate cannot fit the active site. This means less enzyme-substrate complexes form.
ii) The rate would stay the same

AQA - A level Biology (5 decks)

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