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

✅1 - Biological Molecules Flashcards

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

An orange-brown precipitate will form of copper (I) oxide

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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
What do groups of cellulose molecules form?
Microfibrils which are then arranged in parallel groups called fibres
26
How is cellulose's structure related to its function?
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
27
What is the function of cellulose?
To provide support and rigidity
28
What characteristics do lipids have?
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
29
What are the roles of lipids?
Source of energy Waterproofing Insulation Protection
30
What state are fats at room temperature?
Solid
31
What state are oils at room temperature?
Liquid
32
What does hydrolysis of triglycerides produce?
Glycerol and three fatty acids
33
What is a saturated fatty acid?
One which has no double bonds in its chain
34
What is an unsaturated fatty acid?
One which does have double bonds
35
What is a fatty acid with one double bond called?
Mono-unsaturated
36
What is a fatty acid with multiple double bonds called?
Polyunsaturated
37
How does a triglyceride's structure relate to its function?
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
What are phospholipids?
Similar to lipids but one fatty acid is replaced by a phosphate
39
Are fatty acids hydrophobic or hydrophillic?
Hydrophobic
40
What are the two parts of a phospholipid molecule?
Hydrophillic head | Hydrophobic tail
41
How does the structure of a phospholipid relate to its function?
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
What is the test for lipids?
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
Which polymer are amino acids the monomers for?
Polypeptides
44
What is the structure of an amino acid?
``` An amino (NH2) group A carboxyl (COOH) group A hydrogen atom A variable R group ```
45
How do peptide bonds form?
Through condensation reactions
46
Which atoms are peptide bonds formed between?
The carbon of one amino acid and the nitrogen of another
47
The sequence of amino acids forms...
...the primary structure
48
What does primary protein structure determine?
The ultimate shape and function of a protein
49
What is the secondary structure of a protein?
Hydrogen bonding between amino acids to form alpha helices or beta pleated sheets
50
What is tertiary protein structure?
Further twisting and folding to form a 3D structure maintained by different bonds
51
Which bonds are involved in tertiary protein structures?
Ionic bonds Hydrogen bonds Disulfide bridges
52
What are the ionic bonds in tertiary structures between?
Any carboxyl and amino groups not involved in peptide bonds
53
What is quaternary protein structure?
A number of individual polypeptide chains linked in various ways often with non protein prosthetic groups attached
54
What is the test for proteins?
The Biuret test
55
How would you perform the Biuret test?
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
What type of proteins are enzymes?
Globular
57
What is the structure of an enzyme?
A specific 3D shape with an active site, the functional region. Small number of specific amino acids forming a small depression in molecule
58
What is an enzyme-substrate complex?
When the substrate binds with the enzyme
59
How is the substrate held into the enzyme?
By bonds that temporarily form between certain amino acids and groups on the substrate
60
What is the induced fit model?
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
How does the induced fit model lower activation energy?
As it changes shape, the enzyme puts strain on the substrate molecule, distorting particular bonds in the substrate and lowering activation energy
62
What are the two most frequently measured changes for enzyme catalysed reactions?
The formation of products | The disappearance of the substrate
63
How does temperature affect enzyme action?
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
What is the most common optimum temperature for human enzymes?
40 degrees
65
Why has the body temperature evolved to be 37 degrees?
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
How does pH affect enzyme action?
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
Why does pH cause the active site to change shape?
The arrangement of the active site is determined by ionic bonds between NH2 and COOH. The change in H+ affects this bonding.
68
How does enzymes concentration affect rate of reaction?
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
How does substrate concentration affect enzyme action?
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
What are competitive inhibitors?
Ones which bind to the active site of the enzyme
71
What are non-competitive inhibitors?
Ones which bind to the enzymes at a position other than the active site
72
How do competitive inhibitors work?
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
What is an example of competitive inhibition?
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
How does not competitive inhibition work?
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

A-Level Biology - AQA (22 decks)

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