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AS and A level > Biology AS Chapter 1 - Biological Molecules > Flashcards

Biology AS Chapter 1 - Biological Molecules Flashcards

1
Q

What is covalent bonding?

A

Atoms share a pair of electrons in their outer shells. As a result the outer shell of both atoms is filled and a more stable compound, called a molecule, is formed

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2
Q

What is ionic bonding?

A

Ions with opposite charges attract one another. This forms an electrostatic attraction between the ions (the ionic bond).

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3
Q

What is weaker: ionic or covalent bonding?

A

Ionic

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4
Q

What is hydrogen bonding?

A

The electrons within a molecule are not evenly distributed and tend to spend their time more at one position, creating charged regions, and hence a polar molecule. The negative region is attracted to the positive region and a weak electrostatic bond is formed. Can only occur when hydrogen is bonded to F, O or N

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5
Q

What is polymerisation?

A

The process of linking monomers together to form a polymer

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6
Q

What is the basic sub-unit of a polysaccharide?

A

Monosaccharide

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7
Q

What are polynucleotides formed from?

A

Mononucleotide sub-units

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8
Q

How are polypeptides made?

A

By linking together peptides that have amino acids as their basic sub unit

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9
Q

Define the term condensation reaction

A

Chemical process in which two molecules combine to form a more complex one with the elimination/loss of water

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10
Q

Define the term hydrolysis

A

The breaking down of large molecules into smaller ones by the addition of water molecules

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11
Q

Define the term metabolism

A

All the chemical processes that take place in living organisms

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12
Q

What is a molar solution?

A

A solution that contains one mole of solute in each litre of solution

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13
Q

What is a reducing sugar?

A

A sugar that can donate electrons to (or reduce) another chemical. Monosaccharides and some disaccharides are examples of these

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14
Q

What is the test for a reducing sugar known as?

A

The Benedicts test because the sugar reduces Benedicts reagent

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15
Q

What is the test for a reducing sugar?

A
  1. Add 2cm3 of the food sample to be tested into the test tube. If the sample is not already in liquid form, first grind it up in water
  2. Add an equal volume of Benedicts reagent
  3. Heat the mixture in a gently boiling water bath for five minutes
  4. If a reducing sugar then the solution turns orange-brown
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16
Q

What forms maltose?

A

Glucose and glucose

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17
Q

What forms sucrose?

A

Glucose and fructose

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18
Q

What forms lactose?

A

Glucose and galactose

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19
Q

How is a glycosidic bond formed?

A

When monosaccharies join, a molecule of water is removed and it is a condensation reaction. The bond formed is a glycosidic bond

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20
Q

What is a non-reducing sugar, and what are some examples?

A

Sugars that do not change the colour of Benedicts reagent when heated with it. It must first be hydrolysed into its monosaccharide components. An example is sucrose

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21
Q

What is the test for a non-reducing sugar?

A
  1. If the sample is not already in liquid form, it must first be ground up in water
  2. Add 2cm3 of food sample being tested to 2cm3 of Benedicts reagent in a test tube and filter
  3. Place the test tube in a gently boiling water bath for 5 minutes. If there is no colour change then a reducing sugar is not present
  4. Add another 2cm3 of the food sample to 2cm3 of dilute hydrochloric acid in a test tube and place the test tube in a gently boiling water bath for 5 minutes. The dilute hydrochloric acid will hydrolyse any disaccharide present into its constituent monosaccharides
  5. Slowly add some sodium hydrogencarbonate solution to the test tube in order to neutralise the hydrochloric acid. Test with pH paper to check solution is alkaline
  6. Re-test by heating with 2cm3 of Benedicts reagent in a gently boiling water bath for 5 minutes
  7. If a non-reducing sugar was present in the original sample, the Benedicts reagent will now turn orange-brown. This is due to the reducing sugars produced from the hydrolysis of the non-reducing sugar
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22
Q

What are polysaccharides?

A

Polymers formed by combining many monosaccharide molecules

23
Q

What are monosaccharides joined by?

A

Glycosidic bond formed from condensation reaction

24
Q

Why are polysaccharides suitable for storage?

A

They are very large molecules and insoluble. However, some such as cellulose are used to give structural support to plants and other organisms

25
Q

What are the steps for the test for starch?

A
  1. Place 2cm3 of sample being tested into a test tube
  2. Add two drops of iodine solution and shake
  3. Starch is indicated by a blue-black colouration
26
Q

What is starch made up of?

A

Chains of alpha glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions

27
Q

How is the structure of starch suited for its function of energy storage?

A
  • Insoluble so doesn’t effect water potential and there is no water drawn into cells by osmosis
  • Large and insoluble so can’t diffuse out of our cells
  • Compact so lots can be stored in a small space
  • When hydrolysed it forms alpha glucose which is easily transported and readily used in respiration
  • Branched form has many ends which can be acted on by enzymes simultaneously meaning glucose monomers are released rapidly
28
Q

Where is starch found?

A

In plant cells as small grains. Never found in animal cells

29
Q

Where is glycogen found?

A

In animals and bacteria but never in plant cells. Found as granules in the muscles and the liver

30
Q

How do the structures of glycogen and starch differ?

A

Glycogen has shorter chains and is more highly branched

31
Q

What does glycogen store?

A

Carbohydrates. However, the mass stored is small because fat is the main storage molecule in animals

32
Q

How is the structure of glycogen suited to its function of storing carbohydrates?

A
  • Insoluble so doesn’t tend to draw water into the cells by osmosis
  • Being insoluble, it does not diffuse out of cells
  • It is compact so lots can be stored in a small space
  • Highly branched so many enzymes can act at the same time, so rapidly broken down into glucose monomers used in respiration
33
Q

How does cellulose differ from starch and glycogen?

A

It is made up of beta glucose, rather than alpha

34
Q

What is the structure of cellulose?

A

It has straight, unbranched chains which run parallel to each other, allowing hydrogen bonds to form cross linkages between adjacent chains. The number of hydrogen bonds male the molecule very strong

35
Q

What is the function/role of cellulose?

A

Provides rigidity to a plant cell. It prevents the cell from bursting as water enters by osmosis and does so by exerting an inward pressure that stops any further influx of water.

36
Q

How is the structure of cellulose suited to its function?

A
  • made up of beta glucose so form long, straight, unbranched chains
  • these cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength
  • these molecules are grouped to form microfibrils which are then grouped to form fibres, providing more strength
37
Q

What are the 5 roles of lipids?

A
  • in cell membranes to contribute to the flexibility and to transfer lipid soluble substances across them
  • source of energy as when oxidised they produce twice as much energy as the same mass of carbohydrate
  • waterproofing as insoluble in water
  • insulation as slow conductors of heat when stored beneath body surface to help retain heat
  • protection as fat is often stored around delicate organs
38
Q

Describe the structure of a triglyceride

A

Three fatty acids combined with glycerol. Each fatty acid forms an ester bond with glycerol in a condensation reaction

39
Q

What is the difference between a saturated and non-saturated triglyceride?

A

Saturated - contains no carbon carbon double bonds
Unsaturated - contains carbon carbon double bonds

40
Q

How is the structure of triglycerides related to their function?

A
  • They have a high ratio of energy storing carbon hydrogen bonds to carbon atoms so are an excellent source of energy
  • Low mass to energy ratio so good storage molecules as much energy can be stored in a small volume
  • Large and non-polar so are insoluble in water, meaning their storage does not effect osmosis or water potential
  • High ratio of hydrogen to oxygen atoms, so release water when oxidised, providing an important source of water
41
Q

What is the structure of a phospholipid?

A

Glycerol is bonded to 2 fatty acids and one phosphate molecule. They are made up of:
- a hydrophilic head which is attracted to water
- a hydrophobic tail which orientates itself away from water

42
Q

How is the structure of a phospholipid related to its function?

A
  • They are polar molecules so in an aqueous environment they form a bilayer within cell surface membranes, forming a barrier between the inside and outside of a cell
  • The heads help to hold at the surface of the membrane
  • They can form glycolipids by combining with carbohydrates
43
Q

What is the test for lipids?

A

Emulsion test:
1. Take a dry and grease free test tube
2. To 2cm3 of the sample, add 5cm3 of ethanol
3. Shake to dissolve any lipid
4. Add 5cm3 of water and shake gently
5. A cloudy white colour indicates a lipid

44
Q

What is the structure of an amino acid?

A

The central carbon atom is attached to 4 different chemical groups:
- amino group (NH2)
- carboxyl group (COOH)
- hydrogen atom (H)
- R group –> a variety of different chemical groups which makes amino acids different

45
Q

How is a peptide bond formed?

A

A condensation reaction. Water is made my combining an OH from the carboxyl group of one amino acid and the H of another. The 2 amino acids then become linked by a peptide bond between the C of one amino acid and the N of the other

46
Q

Describe the structure of a protein (6 marks)

A
  • Primary structure is determined by the sequence of amino acid
  • Which are linked by peptide bonds
  • These are wound to produce the secondary structure –> alpha helices or beta pleated sheets
  • Which are held by hydrogen bonds
  • Folded again to produce the tertiary structure
  • Held by hydrogen bonds, disulfide bridges and ionic bonds
  • Quaternary structure is a number of tertiary structures combined, with a prosthetic group
47
Q

What is the test for proteins?

A

Biuret test:
- Place a sample of the solution to be tested into a test tube and add an equal volume of sodium hydroxide solution
- Add a few drops of dilute copper sulfate solution and mix gently
- A purple colouration indicates peptide bonds and hence a protein. If no protein present, solution remains blue

48
Q

What are fibrous and globular proteins?

A

Fibrous - proteins with structural functions
Globular - proteins that carry out metabolic functions

49
Q

What are enzymes?

A

Globular proteins that act as biological catalysts

50
Q

What conditions must be satisfied for reactions to occur naturally?

A
  • Reactants must collide with sufficient energy to alter the arrangement of their atoms to form the products
  • The energy of the products must be less than that of the substrates
  • The activation energy must be overcome
51
Q

What is the induced fit model of enzyme action?

A

It proposes that the active site forms as the enzyme and substrate interact. Th proximity of the substrate leads to a change in the enzyme that forms the functional active site. The enzyme is flexible and can mould itself around the substrate. They have to be mostly complementary in the first place to do this

52
Q

What is a competitive inhibitor?

A

They have a shape similar to the substrate. This allows them to occupy the active site of an enzyme, thereby competing with the substrate for an available active site

53
Q

What is a non-competitive inhibitor?

A

They attach themselves to the enzyme at a binding site which is not the active site. This alters the shape of the enzyme so the substrate molecules are no longer complementary and cannot occupy it, meaning the enzyme cannot function

AS and A level (30 decks)

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