Biological molecules

Question 1

What about water gives its properties?

Answer 1

It is dipolar, meaning it can form hydrogen bonds.

Question 2

Properties of water

Answer 2

High specific heat capacity.
High latent heat of vaporisation.
Cohesion and surface tension

Question 3

What does high specific heat capacity mean for organsims?

Answer 3

Because of hydrogen bonding, water has a higher boiling point than usual so it is found as a liquid at common temps and can harbour life. Also water can act as a buffer against sudden temp variations so aquatic environments are stable and means water in terrestrial organisms are stable.

Question 4

What does high latent heat mean for organisms

Answer 4

Evaporation of water such as sweat is effective means of cooling (body heat used).

Question 5

What does cohesion mean for organisms

Answer 5

Allows water to be pulled up xylem vessels as water molecules stick together.

Question 6

Surface tension for organsims

Answer 6

Where water molecules meet air, they are pulled back into body of water, meaning water surface acts as skin and pond skaters can live on it.

Question 7

Water in metabolism role

Answer 7

Breaks down complex molecules via hydrolysis and produced in condensation reaction.
Chemical reactions happen in aqueous medium.
Raw material of photosynthesis.

Question 8

Water as solvent importance

Answer 8

Water dissolves O2 and CO2, wastes (urea and ammonia), inorganic ions, amino acids, monosaccharides and ATP and enzymes.

Question 9

Roles of inorganic ions

Answer 9

Fe used in haemoglobin.
Phosphate ions used in structure of DNA and stores energy in ATP.
Hydrogen ions determine pH.
Sodium ions are important in transport of glucose and amino acids across plasma membranes.

Question 10

General formula of monosaccharide

Answer 10

(C H2 O)n where 2 < n < 8

Question 11

Difference between alpha glucose and beta glucose

Answer 11

Arrangement of OH and H groups around carbon 1.

Question 12

Test for reducing sugar

Answer 12

Benedict’s test: Add Benedict’s reagent and then heat, positive result: green, yellow, red, brick red (increasing conc.)
Negative result: remain blue.

Question 13

Test for non-reducing sugar

Answer 13

Negative Benedict’s test (blue). Add HCl to hydrolyse solution to monosaccharide and then neutralise solution. Test with Benedict’s reagent again for orange-brown colour.

Question 14

Condensation reaction between two monosaccharides

Answer 14

Glyosidic bond

Question 15

How is maltose formed?

Answer 15

Condensation reaction between glucose and glucose.

Question 16

How is sucrose formed?

Answer 16

Condensation reaction between glucose and fructose.

Question 17

How is lactose formed?

Answer 17

Condensation reaction between glucose and galactose.

Question 18

How is glucose and starch formed

Answer 18

Condensation of alpha glucose

Question 19

How is cellulose formed

Answer 19

Condensation of beta glucose

Question 20

Test for starch

Answer 20

Changes iodine solution from yellow to blue-black.

Question 21

How is starch suited for storage

Answer 21

Insoluble, does not affect water potential (water not drawn in cells via osmosis).
Large and insoluble, does not diffuse out of cells.
Compact so can be stored in small place.
Forms a-glucose when hydrolysed, easily transported and used for respiration.
Branched form has many ends for enzymes to act on simultaneously, glucose released rapidly.

Question 22

How is glycogen suited for storage

Answer 22

Insoluble, does not draw water via osmosis and does not diffuse out of cells.
Compact, a lot stored in small space.
More highly branched than starch, can be acted on simultaneously by enzymes to break down rapidly, important for animals with higher metabolic rate than plants.

Question 23

How is cellulose suited for providing support and rigidity

Answer 23

Made up of B-glucose so forms long unbranched chains.
Chains run parallel and are crossed linked by H bonds to add strength.
Molecules are grouped to form microfibrils which are groups to form fibres to give strength.

Question 24

What are the main two types of lipids

Answer 24

Triglycerides and phospholipids.

Question 25

Structure of triglyceride

Answer 25

Three fatty acids that have formed ester bond each with glycerol.

Question 26

Structure of phospholipid

Answer 26

Two fatty acids that have formed ester bond each with glycerol and a phosphate molecule.
Hydrophilic head and hydrophobic tail.

Question 27

Roles of lipids

Answer 27

Source of energy (and release water).
Waterproofing (waxy cuticle layer)
Insulation
Protection

Question 28

What is a saturated fatty acid?

Answer 28

All carbon atoms linked to max number of H.

Question 29

Structure of triglyceride relating to properties

Answer 29

High ratio of high energy carbon-hydrogen bonds to carbon bonds - good source of energy.
Low mass to energy ratio, good storage molecule, reduces mass animal carries.
Insoluble in water, does not affect water potential of cells or osmosis.
High ratio of hydrogen to oxygen atoms, release water when broken down, good source of water in dry conditions.

Question 30

Structure of phospholipid to properties

Answer 30

Polar molecules, form bilayer in cell-surface membrane in aqueous environment, hydrophobic barrier.
Phosphate heads of phospholipids hold at the surface of cell-surface membrane.
Can emulsify.
Structure allows them to form glycolipids by combining with carbohydrates within cell-surface membrane (important for cell recognition).

Question 31

Test for lipids

Answer 31

Emulsion test: add sample, add ethanol, shake, then add water, white emulsion = positive, clear = negative.

Question 32

Structure of an amino acid

Answer 32

Central carbon, an amino group (NH2), carboxyl group COOH, hydrogen, R group (up to 20).

Question 33

Condensation reaction between two amino acid is which bond and how

Answer 33

Peptide bond, bond between nitrogen and carbon of carboxyl group, OH and H lost to form water.

Question 34

How does a change in one amino acid affect the protein?

Answer 34

A change in an amino acid changes the primary structure, changing the hydrogen bonds, altering tertiary structure.

Question 35

What is primary structure of protein?

Answer 35

The sequence of amino acids that form the polypeptide chain.

Question 36

Secondary structure of protein

Answer 36

C=O and NH can form hydrogen bonds to cause the long polypeptide chain to twist into 3D shape (alpha helix).

Question 37

Tertiary structure of protein and bonds involved

Answer 37

Alpha helix twists even more to form a specific 3D structure of protein.
Disulphide bridges (not easily broken).
Ionic bonds (easily broken).
Hydrogen bonds (easily broken).

Question 38

Why is the 3D structure of protein important?

Answer 38

It makes each protein distinctive and can be recognise and recognise other molecules and interact in specific ways.

Question 39

Quaternary structure of protein

Answer 39

Individual polypeptide chains linked with non-protein groups such as haem groups.

Question 40

Test for protein

Answer 40

Biuret test: sample in test tube and equal amount of sodium hydroxide at room temp.
Few drops of 0.05% copper (II) sulfate and mix.
Purple = positive and remains blue if no protein.

Question 41

What is an enzyme and how does it work?

Answer 41

Globular protein that acts as a catalyst by lowering activation energy for specific reaction it catalyses without undergoing permanent change.

Question 42

Enzyme structure

Answer 42

Active site made up of small number of amino acids that is a depression in the large molecule. The enzyme-substrate complex is formed here.
Amino acids that are not part of active site.

Question 43

Induced fit of enzyme action

Answer 43

Proximity of complementary substrate causes change in enzyme that forms functional active site. As enzyme changes shape, it puts strain on substrate molecule that distorts particular bonds in substrate to lower activation energy.

Question 44

Why is lock and key not used?

Answer 44

Proposes that enzyme has rigid structure when enzymes have been observed to have other molecules bind to places other than active site (suggested shape of enzyme was altered by molecule).

Question 45

Why does rate of enzyme controlled reaction slow down?

Answer 45

As reaction progresses, conc of substrate molecules decreases, meaning that there is less chance of a collision between enzyme and substrate molecules. Eventually no change in conc measured because so little substrate.

Question 46

Effect of temp on enzyme action

Answer 46

Temp up, kinetic energy up, enzyme and substrate move more rapidly and combine more often. More effective collisions, more enzyme-substrate complexes being formed, rate of reaction increases.
At around 45C, hydrogen in enzyme molecule breaks, meaning that substrate fits less easily into changed active site, slowing rate of reaction.
At ~60C, enzyme is denatured, permanent change in shape of active site and molecule.

Question 47

Why is body temp 37C if below optimum

Answer 47

Extra food to maintain high temp.
Other proteins would denature.
Illnesses that raise body temp would denature all enzymes.

Question 48

Effect of pH on enzyme action

Answer 48

Change of pH away from optimum reduces enzyme action, extreme change in pH denatures.
Change in pH affects charges on amino acids that make up active site, substrate can no longer attach and e-s complex cannot form, reducing action.
Can also break bonds maintaining tertiary structure and changes active site shape.

Question 49

How to find pH

Answer 49

pH = -log(H+)

Question 50

Effect of enzyme conc on enzyme action

Answer 50

Enzymes not used up, can work well in low conc. As long as there is excess of substrate, an increase in enzyme conc, increases enzyme action. Addition of further enzyme molecules has no effect as there are enough active sites to accommodate all available substrate molecules.

Question 51

Effect of substrate conc on enzyme action

Answer 51

Rate of reaction increases in proportion to conc of substrate. At low substrate concentration, limited number of substrate molecules to collide with and active sites not working at full capacity. As more subs added, active sites fill until all of them working at max capacity (when there is excess of substrate).

Question 52

Competitive inhibition of enzymes

Answer 52

Have molecular shape similar to complementary substrate so occupy active site of enzyme. Compete with substrate for available active sites. Is not permanent so increase substrate conc reduces effect of inhibitor until all substrate molecules will occupy active site.

Question 53

Non-competitive inhibitor

Answer 53

Attach to enzyme not at active site and alters shape of enzyme and active site so no substrate molecules can occupy and enzyme does not function. Increasing substrate concentration does not decrease effect of inhibitor.

Question 54

Use of non-competitive inhibitors in end-product inhibition of metabolic pathways.

Answer 54

To keep steady conc of chemical in cell, same chemical acts as inhibitor at the start of the metabolic pathway. If conc of end product increases beyond normal, less end product produced and conc returned to normal.
If conc decreases beyond normal, less inhibition and more end product produced.