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AQA A Level Biology > ✅1 - Biological Molecules > Flashcards

✅1 - Biological Molecules Flashcards

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1
Q

What is metabolism?

A

All the chemical processes that take place in living organisms collectively

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2
Q

What is the general formula for monosaccharides?

A

(CH2O)n

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3
Q

Where is the ‘H’ on a-glucose?

A

At the top

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4
Q

Where is the ‘H’ on b-glucose?

A

At the bottom

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5
Q

What is the test for reducing sugars?

A

Add 2cm3 of the food sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water.
Add an equal volume of Benedict’s solution
Heat the mixture in a gently boiling water bath for 5 minutes

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6
Q

What will a positive test for reducing sugars show?

A

Will go from blue to a red precipitate

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7
Q

What is maltose?

A

Glucose + glucose

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8
Q

What is sucrose?

A

Glucose + Fructose

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9
Q

What is lactose?

A

Glucose + Galactose

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10
Q

What is the bond between two monosaccharides called?

A

A glycosidic bond

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11
Q

What is a condensation reaction?

A

When molecules are joined together and a molecule of water is removed

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12
Q

What is a hydrolysis reaction?

A

When a bond is broken using a molecule of water

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13
Q

What is the test for non-reducing sugars?

A

After a negative test for reducing sugars:
Add 2cm3 of food sample to 2cm3 of HCl and place in a water bath to hydrolyse any disaccharides to monosaccharides
Add sodium hydrogencarbonate to neutralise the HCl and test pH
Re-test the solution with Benedict’s

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14
Q

What is the test for starch?

A

Add 2cm3 of sample to a test tube
Add two drops of iodine solution and shake it
The presence of starch is indicated by a blue black solution

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15
Q

What is starch?

A

A polysaccharide

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16
Q

How can the structure of starch differ?

A

It can be branched or unbranched

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17
Q

What is the main role of starch?

A

An energy storage molecule

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18
Q

What are the properties of starch that make it suited to its function?

A

It is insoluble - doesn’t alter water potential of cell
Being large and insoluble, it does not diffuse out
It is compact, so a lot can be stored in a small space
When hydrolysed, it forms a-glucose which is easily transported and readily used in respiration
The branched form has many ends, which means it can be broken down quickly and easily

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19
Q

Where is starch found?

A

ONLY in plant cells, as starch grains

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20
Q

What is glycogen?

A

A similar structure polysaccharide to starch found in animal and bacteria cells

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21
Q

How is glycogen stored?

A

As small granules mainly in the muscles and liver

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22
Q

How is glycogen’s structure related to its function?

A

It is insoluble and so doesn’t draw water in by osmosis
Being insoluble, it does not diffuse out
It is compact so a lot can be stored
It is more highly branched so has more ends that can be acted on at the same time so can be broken down quickly

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23
Q

What is cellulose?

A

A polysaccharide of b-glucose

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24
Q

What is the structure of cellulose?

A

Straight, unbranched chains that run parallel to one another, allowing hydrogen bonds which form cross linkages between adjacent chains

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25
Q

What do groups of cellulose molecules form?

A

Microfibrils which are then arranged in parallel groups called fibres

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26
Q

How is cellulose’s structure related to its function?

A

Cellulose molecules are made up of b-glucose and so form long, straight, unbranched chains
These cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds which ass strength
These molecules are grouped to form microfibrils which in turn are grouped to form fibres which provides more strength

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27
Q

What is the function of cellulose?

A

To provide support and rigidity

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28
Q

What characteristics do lipids have?

A

The proportion of oxygen to carbon is smaller than in carbohydrates
They are insoluble in water
They are soluble in organic solvents such as alcohols and acetone

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29
Q

What are the roles of lipids?

A

Source of energy
Waterproofing
Insulation
Protection

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30
Q

What state are fats at room temperature?

A

Solid

31
Q

What state are oils at room temperature?

A

Liquid

32
Q

What does hydrolysis of triglycerides produce?

A

Glycerol and three fatty acids

33
Q

What is a saturated fatty acid?

A

One which has no double bonds in its chain

34
Q

What is an unsaturated fatty acid?

A

One which does have double bonds

35
Q

What is a fatty acid with one double bond called?

A

Mono-unsaturated

36
Q

What is a fatty acid with multiple double bonds called?

A

Polyunsaturated

37
Q

How does a triglyceride’s structure relate to its function?

A

High ratio of energy-storing carbon-hydrogen bonds to carbon atoms so good energy source
Low mass to energy ratio, so lots of energy stored in small molecule
Being large, non-polar, they are insoluble
High ratio of hydrogen to oxygen, release water when oxidised

38
Q

What are phospholipids?

A

Similar to lipids but one fatty acid is replaced by a phosphate

39
Q

Are fatty acids hydrophobic or hydrophillic?

A

Hydrophobic

40
Q

What are the two parts of a phospholipid molecule?

A

Hydrophillic head

Hydrophobic tail

41
Q

How does the structure of a phospholipid relate to its function?

A

Polar molecules, so form a bilayer in an aqueous solution
Hydrophillic phosphate heads help to hold the surface of the cell membrane
The phospholipid structure allows them to form glycolipids by combining with carbohydrates at the cell surface membrane. Important in cell recognition

42
Q

What is the test for lipids?

A

Take a dry and grease-free test tube
To 2cm3 of the sample being tested, ass 5cm3 of ethanol
Shake tube thoroughly to dissolve any lipid in sample
Add 5cm3 of water and shake gently
A cloudy white colour indicates the presence of a lipid
Repeat with water as a control

43
Q

Which polymer are amino acids the monomers for?

A

Polypeptides

44
Q

What is the structure of an amino acid?

A 
An amino (NH2) group
A carboxyl (COOH) group
A hydrogen atom
A variable R group
45
Q

How do peptide bonds form?

A

Through condensation reactions

46
Q

Which atoms are peptide bonds formed between?

A

The carbon of one amino acid and the nitrogen of another

47
Q

The sequence of amino acids forms…

A

…the primary structure

48
Q

What does primary protein structure determine?

A

The ultimate shape and function of a protein

49
Q

What is the secondary structure of a protein?

A

Hydrogen bonding between amino acids to form alpha helices or beta pleated sheets

50
Q

What is tertiary protein structure?

A

Further twisting and folding to form a 3D structure maintained by different bonds

51
Q

Which bonds are involved in tertiary protein structures?

A

Ionic bonds
Hydrogen bonds
Disulfide bridges

52
Q

What are the ionic bonds in tertiary structures between?

A

Any carboxyl and amino groups not involved in peptide bonds

53
Q

What is quaternary protein structure?

A

A number of individual polypeptide chains linked in various ways often with non protein prosthetic groups attached

54
Q

What is the test for proteins?

A

The Biuret test

55
Q

How would you perform the Biuret test?

A

Place a sample of solution in a test tube and add an equal volume of NaOH
Add a few drops of very dilute copper (II) sulfate solution and mix
A purple coloration indicates the presence of peptide bonds, if none, solution remains blue

56
Q

What type of proteins are enzymes?

A

Globular

57
Q

What is the structure of an enzyme?

A

A specific 3D shape with an active site, the functional region. Small number of specific amino acids forming a small depression in molecule

58
Q

What is an enzyme-substrate complex?

A

When the substrate binds with the enzyme

59
Q

How is the substrate held into the enzyme?

A

By bonds that temporarily form between certain amino acids and groups on the substrate

60
Q

What is the induced fit model?

A

Proposes that the active site forms as the enzyme and substrate , the proximity of the substrate leads to a change in the enzyme which forms a functional active site

61
Q

How does the induced fit model lower activation energy?

A

As it changes shape, the enzyme puts strain on the substrate molecule, distorting particular bonds in the substrate and lowering activation energy

62
Q

What are the two most frequently measured changes for enzyme catalysed reactions?

A

The formation of products

The disappearance of the substrate

63
Q

How does temperature affect enzyme action?

A

A rise in temperature increases kinetic energy, so move around more rapidly and collide more often, so enzymes and substrates collide more and more collisions are effective, rate of reaction increases

64
Q

What is the most common optimum temperature for human enzymes?

A

40 degrees

65
Q

Why has the body temperature evolved to be 37 degrees?

A

Additional food would be needed to maintain it
Other proteins may be denatured at high temperatures
A further rise in temperature during illness may denature enzymes

66
Q

How does pH affect enzyme action?

A

A change in pH alters the charges on the amino acids in the active site and so the substrate can no longer bind
The bonds in the tertiary structure may also break if pH change is significant enough

67
Q

Why does pH cause the active site to change shape?

A

The arrangement of the active site is determined by ionic bonds between NH2 and COOH. The change in H+ affects this bonding.

68
Q

How does enzymes concentration affect rate of reaction?

A

Once the active site of an enzyme has acted, it is free to repeat the action on another substrate, as they are catalysts and not used up. As long as there is excess substrate, an increase in enzymes will increase rate f reaction

69
Q

How does substrate concentration affect enzyme action?

A

If the enzyme concentration is fixed and substrate concentration increased, the rate of reaction increases in proportion to the concentration of substrate. When there is excess, the rate levels off.

70
Q

What are competitive inhibitors?

A

Ones which bind to the active site of the enzyme

71
Q

What are non-competitive inhibitors?

A

Ones which bind to the enzymes at a position other than the active site

72
Q

How do competitive inhibitors work?

A

They have a molecular shape similar to the substrate, allowing them to occupy the active site. They compete with the substrate and it is the difference between the concentration of the inhibitor and concentration of the substrate that determines effect.

73
Q

What is an example of competitive inhibition?

A

An important respiratory enzyme which acts on succinate. Malonate can inhibit enzyme because it is very similar to succinate, therefore binds with active site

74
Q

How does not competitive inhibition work?

A

Attach themselves to the enzyme at a binding site which is not the active site. Alters shape of enzyme and thus its active site in such a way that substrates can no longer occupy it

AQA A Level Biology (22 decks)

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