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Biology AS > Biological Molecules > Flashcards

Biological Molecules Flashcards

1
Q

Monomer

A

smaller unit from which larger molecules are made

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2
Q

Polymer

A

molecules made from a large number of monomers joined together

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3
Q

Name 3 types of monomer and polymer

A

Monosaccharides ⇒ polysaccharides (carbohydrates)
Amino acids ⇒ polypeptides ⇒ proteins
Nucleotides ⇒ polynucleotides (DNA, RNA)

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4
Q

Condensation reaction

A

joins 2 molecules together with the formation of a chemical bond and the elimination of a molecule of water.

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5
Q

Hydrolysis reaction

A

breaks a chemical bond between 2 molecules using a water molecule

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6
Q

Describe bonding in a polysaccharide

A

many monosaccharide monomers are joined together in condensation reactions - glycosidic bonds form

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7
Q

Disaccharide

A

formed by the condensation of 2 monosaccharides

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8
Q

Types + formation of disaccharides

A 
Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose = glucose + galactose
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9
Q

How are polysaccharides formed?

A

by the condensation of many glucose monomers.

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10
Q

Describe the 2 isomers of glucose

A

α-glucose and β-glucose

α has hydroxyl group below and β has hydroxyl group above on C4.

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11
Q

Describe the structure f starch

A

A polymer of α-glucose. Starch is formed of helical and branched chains of glucose.

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12
Q

Describe the function of starch

A

It is the main energy store found in plants.

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13
Q

Describe the adaptations of starch to its function

A
  • The helical and branched structure makes starch compact.
  • The many branched ends of starch allow it to be hydrolysed quickly to glucose by enzymes for use in respiration.
  • Starch is insoluble in water, so doesn’t affect water potential or diffuse out of cells.
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14
Q

Describe the function of glycogen

A

The main energy store in animals and bacteria - in liver and muscle cells

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15
Q

Describe the structure of glycogen

A

it has a similar structure to starch, with helical chains of α-glucose - but is more highly branched.

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16
Q

How is the structure of glycogen adapted to its function?

A

It is more highly branched, so the energy store is more compact and glucose can be released more quickly by hydrolysis. This is important as animals have a higher metabolic rate than plants.
(and same things as starch)

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17
Q

Describe the structure of cellulose and the formation of fibres

A

A polymer of β-glucose which has long, unbranched chains. Β-glucose molecules form straight chains when they bond as alternate monomers are rotated 180° so that OH groups line up for bonding. Hydrogen bonds between cellulose chains add strength collectively to form micro-fibrils, which associate to form fibres.

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18
Q

Name 3 polysaccharides

A

starch, glycogen, cellulose

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19
Q

Describe the role of cellulose and how it is adapted to this role.

A

It is a structural polysaccharide which adds strength to the cell walls of plant cells.

The strong fibres (due to the collective strength of hydrogen bonds) means cellulose provides structural support for cells, allowing them to become turgid without bursting.

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20
Q

Test for reducing sugars

A

Add blue benedict’s reagent to a sample and heat in a gently boiling water bath.
If a reducing sugar is present, a brick-red precipitate of copper(I) oxide forms.
The higher the concentration of reducing sugar, the further the colour change goes. You could filter the solution and weigh the precipitate to measure this.

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21
Q

Test for non-reducing sugars

A

If there is a negative result from the test for reducing sugars, a non-reducing sugar may still be present.
Add dilute HCl to a new sample of the test solution. Heat in a gently boiling water bath. Then neutralise the solution with sodium hydrogencarbonate. Carry out the Benedict’s test as you would for a reducing sugar.
If there is a positive result (coloured ppt) there was initially a non-reducing sugar, which has been hydrolysed to reducing sugars.

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22
Q

Test for starch

A

Add iodine dissolved in potassium iodide solution. If starch is present, there is a colour change from orange-brown to blue-black.

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23
Q

2 types of lipid

A

triglycerides and phospholipids

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24
Q

How are triglycerides formed?

A

by the condensation of 1 molecule of glycerol and 3 molecules of fatty acid (RCOOH)

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25
Q

Type of bond between glycerol and fatty acids in triglycerides/ phospholipids

A

ester bonds

-COO-

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26
Q

What can the R group of a fatty acid be?

A

saturated or unsaturated

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27
Q

what does saturated mean?

A

there are single C-C bonds only

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28
Q

What does unsaturated mean?

A

there are 1+ C=C bonds

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29
Q

Role of triglycerides

A

as an energy store

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30
Q

How are triglycerides adapted to their role as an energy store?

A
  • The long hydrocarbon tails of fatty acids release a lot of energy when they are broken down (more than carbohydrates!)
  • They are insoluble so don’t affect cell WP or cause water to enter or leave by osmosis.
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31
Q

Structure of phospholipids

A

Similar to triglycerides, but one of the fatty acids is substituted for a phosphate containing group.

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32
Q

Role of phospholipids

A

To form the phospholipid bilayer of cell membranes

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33
Q

Why do phospholipids form a phospholipid bilayer?

A

The phosphate head is hydrophilic and the fatty acid tails are hydrophobic. Phospholipids form a double layer with the heads facing outwards into the aqueous solutions on each side. This is a phospholipid bilayer - forms the cell membrane.

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34
Q

Purpose of the phospholipid bilayer and how it is adapted for this

A

To control what enters and leaves the cell, water-soluble substances cannot easily pass through because the centre of the bilayer is hydrophobic

35
Q

The test for lipids

A

The emulsion test

1) Shake the test substance in a test tube with ethanol to dissolve and lipids present.
2) Add water.
3) If lipid is present, a cloudy white emulsion will form.

36
Q

How many common amino acids are there and how do they differ?

A

20, they differ only in their R group.

37
Q

Formation of a dipeptide

A

by the condensation of 2 amino acid to form a peptide bond

38
Q

Describe the structure of an amino acid

A

H atom, NH2, COOH and an R group all bonded to the same carbon atom

39
Q

Primary protein structure

A

the specific sequence of amino acids in a polypeptide chain

40
Q

Secondary protein structure

A

the twisting or folding of the polypeptide chain to form α-helices or β-pleated sheets due to hydrogen bonds between amino acids in the chain.

41
Q

Tertiary protein structure

A

the further coiling and folding of the polypeptide chain into a specific 3D shape.

42
Q

Quaternary protein structure

A

several polypeptide chains may be held together to produce the final protein. There may also be non-protein ‘prosthetic’ groups. E.g. haemoglobin.

43
Q

Formation of a polypeptide

A

by the condensation of many amino acids.

44
Q

Bond between 2 amino acids

A

peptide bond

- O=C - N-H -

45
Q

What are proteins?

A

polymers formed of many amino acids.

46
Q

What types of bonds maintain tertiary protein structure?

A

This is maintained by hydrogen bonds, ionic bonds between positively and negatively charged regions, and disulfide bridges between cysteine amino acids, which contain sulfur.

47
Q

The test for proteins

A

Biuret test

Add biuret reagent to the sample. If protein is present, there will be a colour change from blue to purple.

48
Q

The importance of protein structure

A

The tertiary (3D) structure is important in how a protein functions. The primary structure determines this tertiary structure, as it decides which types of bonds can form.

49
Q

Explain the role of phospholipids in the structure and functioning of cell membranes.

A
  • Phospholipid bilayer with hydrophilic phosphate heads pointing outwards and interacting with water in solutions either side of the bilayer.
  • Hydrophobic tails point inwards as they are repelled by water
  • The barrier is non-polar and will allow the passage of lipid soluble substances but not water-soluble.
  • The bilayer makes the membrane flexible.
50
Q

Starch structure related to function x 3

A
  • helical => compact storage molecule
  • insoluble => doesn’t affect WP of osmosis
  • large molecule => doesn’t diffuse or leave cell
51
Q

Polymerisation

A

the process by which a large molecule called a polymer is formed from many small monomers.

52
Q

Enzyme

A

Globular protein which acts as a biological catalyst, increasing the rate of a metabolic reaction.

53
Q

Catalyst

A

substance which increases the rate of a chemical reaction without being used up in the reaction.

54
Q

Properties of enzymes (3)

A
  • Unchanged by the reaction and not used up so can be repeatedly reused. This makes them effective in small amounts.
  • Catalyse intracellular and extracellular metabolic reactions.
  • Lower the activation energy of the reaction they catalyse so reactions can occur at lower temperatures than normal.
55
Q

Activation energy

A

The minimum amount of energy required by reactant particles for the reaction to occur.
Colliding particles won’t react unless they have enough energy.

56
Q

Active site

A

A small depression in an enzyme molecule which is where the substrate binds. The active site has a specific tertiary structure complementary to the enzyme.

57
Q

Substrate

A

the molecule upon which an enzyme acts

58
Q

Enzyme-substrate complex

A

The substrate binds to the enzyme active site to form the enzyme-substrate (E-S) complex. The substrate is held in place as it forms weak bonds with some groups from amino acids in the enzyme active site..

59
Q

What determines the specific tertiary structure of a protein?

A

the primary structure - the specific sequence of amino acids.

60
Q

The induced fit model of enzyme action

A
  • The enzyme active site is not complementary to the substrate initially
  • The active site changes shape and becomes complementary as the enzyme and substrate interact allowing an E-S complex to form.
  • The enzyme puts strain on the substrate as it changes shape, distorting some bonds in the substrate so the energy needed to break a bond (activation) is lowered.
61
Q

The lock and key model of enzyme action

A

The active site is a fixed shape which is already complementary to the substrate.

62
Q

6 factors that affect enzyme action

A

Temperature, pH, enzyme concentration, substrate concentration, inhibition by competitive and non-competitive inhibitors

63
Q

Roles of proteins in living organisms

A
  • enzymes
  • antigens
  • hormones
  • transport proteins
  • CSM receptors
  • Structural function - e.g. in cartilage and tendons
  • protein filaments in muscle contraction
64
Q

Limitations of the lock and key model of enzyme action

A

the enzyme is considered to be a rigid structure, which is not true as other molecules can bind to enzymes at places other than their active site and change active site shape - so structure is flexible.

65
Q

How can rate of reaction be found from a graph curve of an enzyme-controlled reaction?

A

Rate of reaction = gradient.
Draw a tangent to the curve.
Rate/ gradient = change in Y/ change in X.
Be careful of units.

66
Q

How can the progress of an enzyme catalysed reaction be determined?

A

by measuring the rate at which the substrate is used up or the rate at which the product is formed.

67
Q

Why does rate of an enzyme controlled reaction change over its course?

A

as substrate concentration is highest at the start and decreases over the course of the reaction, so fewer E-S complexes form per unit time and rate decreases. Plateau occurs when all the substrate has been converted to product (or denaturation)

68
Q

How and why does increasing temperature up to the optimum alter rate of reaction?
(enzymes)

A

Rate increases
Molecules have more kinetic energy at a higher temperature, so more collisions occur and more E-S complexes form in a given time.

69
Q

What happens as temperature rises past the optimum in an enzyme controlled reaction?

A
  • initially, hydrogen bonds in the enzyme break and the shape of the enzyme changes. The substrate fits less easily into the changed active site.
  • At a higher temperature, the shape of the enzyme has changed so much that it no longer functions at all. E-S complexes cannot form and the enzyme is denatured - this is permanent.
70
Q

What is pH? How can it be calculated?

A

A measure of hydrogen ion content of a solution. Every enzyme has an optimum pH.
Can be calculated using the formula pH = -log10[H+]

71
Q

What happens when pH changes from the optimum in an enzyme controlled reaction?
(small and large change)

A
  • A pH change alters the charges on amino acids that form the enzyme’s active site. The substrate may not be able to bind to the enzyme active site as effectively. Fewer E-S complexes form in a given time and the rate of reaction decreases.
  • If there is a large pH change, bonds maintaining tertiary protein structure can break. This causes the active site to change shape and the enzyme becomes denatured.
72
Q

Describe the graph for rate of reaction against enzyme concentration.

A

Initially rate increases as enzyme concentration increases . Gradient of curve decreases and the curve plateaus after the saturation point.

73
Q

How and why does an increase in enzyme concentration increase rate of reaction when there is excess substrate?

A

an increase in enzyme concentration will lead to a proportionate increase in rate of reaction. This is because there are not enough enzyme molecules to allow all substrate molecules to occupy an active site at one time.

An increase in enzyme concentration means more enzyme active sites are available and more E-S complexes form in a given time, so the rate of reaction will increase.

74
Q

What happens to rate if enzyme concentration is further increased past the saturation point?

A

Rate doesn’t further increase as there are already enough active sites for all available substrate molecules.

75
Q

What is an enzyme inhibitor?

A

a substance which directly or indirectly interferes with the functioning of an enzyme’s active site and so reduces its activity.

76
Q

2 types of enzyme inhibitor

A

competitive and non-competitive

77
Q

How does a competitive enzyme inhibitor work?

A

Have a similar molecular structure to the substrate so can occupy the enzyme active site. The inhibitor competes with the substrate for active sites, so fewer E-S complexes form in a given time and rate of reaction decreases.

78
Q

How does a non-competitive enzyme inhibitor work?

A

Bind to enzyme at a site other than its active site (allosteric site). This changes the tertiary structure of the enzyme and active site, which is no longer complementary to the substrate and E-S complexes cannot form. This binding is permanent, and the enzyme can no longer function.

79
Q

How does the affect of a competitive enzyme inhibitor depend on substrate concentration?

A

Increasing substrate concentration increases rate of reaction and reduces the effect of the inhibitor - eventually maximum rate + plateau is reached.

80
Q

How does the affect of a non-competitive enzyme inhibitor depend on substrate concentration?

A

The substrate and inhibitor are not competing for the same site, so altering substrate concentration doesn’t decrease the effect of the inhibitor.

81
Q

Describe how substrate concentration affects rate of reaction when substrate concentration is low and up to the saturation point.

A

At a low substrate concentration, there are too few substrate molecules to occupy all available active sites. Rate of reaction is less than maximum for number of enzyme molecules.
As substrate concentration further increases, all active sites can be occupied at one time. Rate of reaction is at its maximum.

82
Q

Describe how substrate concentration affects rate of reaction when substrate concentration is above the saturation point.

A

The addition of further substrate molecules does not further increase the rate of reaction as all active sites are already occupied at one time. There is an excess of substrate.

83
Q

Why are enzymes specific to 1 substrate and reaction?

A

Enzymes have an active site with a specific tertiary structure which is complementary only to the substrate upon which they act.

84
Q

polymerisation

A

the process by which a polymer is formed from many small molecules called monomers.

Biology AS (10 decks)

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