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Biology AS > Biological molecules > Flashcards

Biological molecules Flashcards

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1
Q

What is the result for the test for reducing sugars?

A

A positive result forms an insoluble RED precipitate of copper oxide.

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2
Q

What is the test for reducing sugars?

A

Add 2cm^3 of the food sample to a test tube.
Grind it up with water if not in liquid form.
Add an equal volume of Benedict’s reagent.
Heat the mixture in a gently boiling water bath for 5 minutes.

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3
Q

What are reducing sugars?

A

All monosaccharides and some disaccharides. It is a sugar that can donate electrons to another chemical (- to Benedict’s reagent).

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4
Q

What is reduction?

A

A chemical reaction involving the gain of electrons.

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5
Q

What are examples of monomers?

A

Amino acids
Monosaccharides
Nucleotides

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6
Q

What are examples of polymers?

A

Protein
Polysaccharides
DNA

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7
Q

How do all living things have a similar biochemical basis?

A

Carbon atoms readily form bonds with other carbon atoms.
This means sequences of various lengths can be built up and allow other atoms to be attached.

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8
Q

What are monomers?

A

Smaller units that make up large chains of molecules.

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9
Q

What are polymers?

A

Long chains formed from a large number of monomers.

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10
Q

What 4 elements make up most polymers?

A

Carbon
Hydrogen
Oxygen
Nitrogen

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11
Q

How does a condensation reaction join two monomers?

A

A molecule of water is removed to make polymers.
The OH group is split leaving the oxygen with a spare electron to bond the 2 monomers together.

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12
Q

What is the bond formed by a condensation reaction?

A

It is a glycosidic bond.

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13
Q

How does a hydrolysis reaction break a chemical bond?

A

Water is added to a disaccharide and breaks the glycosidic bond.

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14
Q

What is the formula of a monosaccharide?

A

(CH^2O)n where n is any number from 3 to 7.

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15
Q

What are examples of monosaccharides?

A

Glucose
Fructose
Galactose

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16
Q

What are the types of carbohydrates?

A

A single monomer is a monosaccharide.
A pair of monosaccharides can form a disaccharide.
Monosaccharides can then combine in much larger numbers to form polysaccharides.

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17
Q

How are disaccharides formed from monosaccharides?

A

A condensation reaction occurs between two monosaccharides and removes a molecule of water.
The bond between the disaccharide is glycosidic.

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18
Q

What is maltose?

A

Maltose is a disaccharide formed by the condensation reaction of two α-glucose molecules.

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19
Q

What is sucrose?

A

A disaccharide formed from the condensation reaction between glucose and fructose.

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20
Q

What is lactose?

A

A disaccharide formed from the condensation reaction between glucose and galactose.

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21
Q

How does glucose have two isomers?

A

The atoms of carbon, hydrogen and oxygen can be arranged in many different ways. So glucose has α-glucose and β-glucose isomers.

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22
Q

What is the structure of α-glucose?

A

H |__ O H
\/ \ /
/ \ \ /
HO \____/ \OH

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23
Q

How are polysaccharides formed?

A

Many monosaccharides are joined by glycosidic bonds formed from condensation reactions.

24
Q

What is the structure of β-glucose?

A

H |__ O OH
\/ \ /
/ \ \ /
HO \____/ \H

25
Q

What is the function and structure of cellulose?

A

It provides support and rigidity because:
Cellulose molecules are made up of β-glucose so form long, straight, unbranched chains.
These cellular chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength.
These molecules are grouped to form microfibres which are grouped to form fibres - adding yet more strength.

26
Q

What is the function and structure of glycogen?

A

It is used for storage, because:
It is insoluble so does not draw water into the cells by osmosis.
It is insoluble so doesn’t diffuse out of cells.
It is compact so a lot can be stored in a small space.
It is more highly branched than starch so more ends can be simultaneously acted on by enzymes and therefore more rapidly broken down to form glucose, used in respiration.
This is important as animals have a higher metabolic and respiratory rate than plants.

27
Q

What is the function and structure of starch?

A

The main role is energy storage, suited to because:
It is insoluble so it doesn’t affect water potential - water is not drawn into the cells by osmosis.
It’s large and insoluble - doesn’t diffuse out of cells.
It is compact - so a lot can be stored in a small space.
When hydrolysed it forms α-glucose which is easily transported and readily used in respiration.
The branched form has many ends, which can each be acted on by enzymes simultaneously, meaning the glucose monomers are released very rapidly.

28
Q

What is the test for starch?

A

Place 2cm^3 of the sample to a test tube.
Add two drops of iodine solution and shake or stir.

29
Q

What is the positive result for the starch test?

A

The solution will turn a blue-black colour.

30
Q

What are the two types of lipids?

A

Phospholipids
Triglycerides.

31
Q

How are triglycerides formed?

A

From a condensation reaction between the carboxyl (COOH) group of each fatty acid and the hydroxyl (OH) group of the glycerol. The bonds between them are Ester bonds.

32
Q

What is the emulsion test for lipids?

A

Take a completely dry and grease-free test tube.
Add 5cm^3 of ethanol to 2cm^3 of the sample.
Shake the tube to dissolve any lipid in the sample.
Add 5cm^3 of water and shake gently.

33
Q

What is the structure of saturated fatty acids?

A 
O H H H H H H H H H
\\ | | | | | | | | |
C- C - C -C-C -C- C-C-C-H
/ | | | | | | | | |
O H H H H H H H H H
34
Q

What is the structure of unsaturated fatty acids?

A 
O H H H H H
\\ | | | | | H
C-C-C-C-C-C- | H
/ | | | | C= | H
O H H H H C- | H
C- |
| C-
H | H
H
35
Q

Why are triglycerides hydrophobic?

A

There are no spare oxygen molecules for water to form hydrogen bonds with.

36
Q

What is the structure of triglycerides?

A

Three fatty acids combined with glycerol.
High ratio of energy-storing carbon-hydrogen bonds to carbon atoms so are a very good source of energy.
Low mass to energy ratio so good storage molecules as much energy can be stored in a small volume.
Large, non-polar molecules so are insoluble in water so don’t affect osmosis or the water potential in cells.

37
Q

What is the structure of phospholipids?

A

Similar to trigylcerides except: One of the fatty acid molecules is replaced by a phosphate molecule.
Hydrophilic ‘head’ - attracted to water but not fat.
Hydrophobic ‘tails’ - repels from water but readily mixes with fat.

38
Q

What are the properties of phospholipids?

A

Phosphate molecules are hydrophylic - because there are spare charges, it can form hydrogen bonds with water.
Fatty acids are hydrophobic.
Polar - so when the molecule is placed in water it forms a bilayer and positions itself so the hydrophilic head is the closest it can be to the water and the hydrophobic tails are as far away as possible.

39
Q

How are glycogen and starch formed?

A

The condensation of α-glucose.

40
Q

How is cellulose formed?

A

The condensation of β-glucose.

41
Q

What are examples of polysaccharides?

A

Starch
Cellulose
Glycogen

42
Q

What are the two polysaccharides starch are a mixture of?

A

Amylose
Amylopectin - branched.

43
Q

What is the test for non-reducing sugars?

A

Grind the sample up first if not already in liquid form.
Add 2cm^3 of the sample to 2cm^3 of Benedict’s reagent in a test tube.
Gently boil in a water bath for 5 minutes.
Add another 2cm^3 of the sample to 2cm^3 of hydrochloric acid in a test tube and boil in the water bath for 5 minutes.
Slowly add sodium hydrogencarbonate solution to the test tube to neutralise the acid. Test with pH paper to check the solution is alkaline.
Re-test this solution by heating it with 2cm^3 of Benedict’s in a gently boiling water bath for 5 minutes.

44
Q

What is the negative result for non-reducing sugars?

A

If, after the mixture is boiled in the water bath, the solution doesn’t change colour (stays blue).

45
Q

What does the hydrochloric acid do in the test for non-reducing sugars?

A

It will hydrolyse any disaccharide present into its constituent monosaccharides.

46
Q

Why is the hydrochloric acid neutralised?

A

The sodium hydrogencarbonate neutralises it because Benedict’s reagent does not work in acidic conditions.

47
Q

What is the positive result for non-reducing sugars?

A

The Benedict’s reagent will now turn orange/red/brown.
This is due to the reducing sugars that were produced by the hydrolysis of the non-reducing sugars.

48
Q

What is the positive result for lipids in the emulsion test?

A

The solution will a turn cloudy-white colour.

49
Q

What are the characteristics of lipids?

A

Contain carbon, hydrogen and oxygen.
Lower proportion of oxygen to hydrogen and carbon than in carbohydrates.
Insoluble in water - non-polar molecules (uncharged).
Soluble in organic solvents - alcohols and acetone.

50
Q

What is the function of lipids?

A

Source of energy
Waterproofing: both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion on the skin.
Insulation: Slow conductors of heat and when stored under the skin’s surface they retain body heat.
Protection - often stored around delicate organs.

51
Q

What are saturated fatty acids?

A

The hydrocarbon chain has only single bonds, the carbon atoms are linked to the maximum number of hydrogen atoms.

52
Q

What are unsaturated fatty acids?

A

The hydrocarbon chain has at least one double bond.

53
Q

Why are unsaturated fatty acids liquid at room temperature?

A

The double bonds cause the molecule to bend and cannot therefore pack closely together.

54
Q

What are fatty acids?

A

They consist of a long chain of hydrogens and carbons with a carboxyl group at one end.

55
Q

How does the structure of phospholipids relate to its properties?

A

The hydrophilic head help to hold at the surface of the cell-surface membrane.
It allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. Glycolipids are important in cell recognition.

Biology AS (20 decks)

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