Topic 1.5-7 Biological molecules

Question 1

Describe the structure of enzymes

Answer 1

Globular proteins

Specific tertiary structure determines shape of acitve site, complementary to specific substrate

Question 2

Explain the function of enzymes

Answer 2

Biological catalysts for intra (e.g. DNA polymerase) and extra cellular (e.g. digestive enzymes in tears) reactions.

Formation of enzyme-substrate (ES) complexes lowers activation energy of metabolic reactions.

Question 3

Explain the lock and key hypothesis

Answer 3

The active site of an enzyme is very specific and only one substrate or type of substrate will fit in it, this is called specificity.

1. Random movement causes the enzyme and substrate to collide, the substrate enters the active site
2. An enzyme-substrate complex forms. Charged groups attract, distorting the substrate and aiding bond breakage or formation
3. Products are released from the active site, leaving the enzyme unchanged and ready to accept another substrate molecule

Question 4

Explain the induced fit hypothesis

Answer 4

Shape of active site is not directly complementary to substrate and is flexible.

Conformational change enables ES complexes to form.

This puts strain on substrate bonds, lowering activation energy.

Question 5

Name five factors that effect the rate of enzyme-controlled rates of reactions

Answer 5

• Enzyme concentration
• Substrate concentration
• Concentration of inhibitors
• pH
• Temperature

Question 6

How does substrate concentration affect rate of reaction?

Answer 6

Given that the enzyme conc. is fixed, rate increases proportionally to substrate conc..

Rate levels off when maximum number of ES complexes form at any given time.

Question 7

How does enzyme concentration effect rate of reaction?

Answer 7

Given that the substrate is in excess, rate increases proportionally to enzyme conc..

Rate levels off when maximum number of ES complexes form at any given time.

Question 8

How does temperature effect rate of reaction in an enzyme controlled reaction?

Answer 8

Rate increases as kinetic energy increases and peaks at optimum temperature.

Above optimum temperature, ionic and hydrogen bonds in 3^o structure break = active site no longer complementary to substrate (denaturation).

Question 9

How does pH affect rate of reaction in an enzyme controlled reaction?

Answer 9

Enzymes have a norrow optimum pH range.

Outside range, H⁺/OH^- ions interact with hydrogen and ionic bonds in 3^o structure = denaturation.

Question 10

How do enzymes lower activation energy?

Answer 10

• By bringing substances close together in the active site so bonds are easier to form
• By putting strain on bonds in the substrate to break them appart

Question 11

Why do organisms need enzymes?

Answer 11

Without enzymes biochemical reactions happen to slowly at the temperature at which living things can survive

Question 12

How do competitve inhibitors work?

Answer 12

Bind to active site since they have similar shape to substrate. Temporarily prevent ES complexes from forming until released.

Increasing substrate concentration decreases their effect.

Question 13

How do non-competitive inhibitors work?

Answer 13

Bind to allosteric site.

Trigger conformational change of active site.

Increasing substrate conc. has no impact on their effect.

Question 14

What is end product inhibition?

Answer 14

One of the products of a reaction acts as a competitive or non-competitive inhibitor for an enzyme involved in the pathway. Prevents further formation of products.

Question 15

Why is it advantageous to calculate initial rate?

Answer 15

Represents maximum rate of reaction before conc. of reactants decreases and end-product inhibition.

Question 16

Explain the effect of a competitive inhibitor on a rate of reaction against substrate conc. graph

Answer 16

Initially rate of reaction is lower than without the inhibitor, eventually conc. of substrate outcompetes the inhibitor and rate of reaction will be the same as without the inhibitor

Question 17

Explain the effect of a non-competitive inhibitor on a rate of reaction against substrate conc. graph

Answer 17

Excess substrate conc. has no effect on rate of reaction, so rate of reaction will always be lower than without the inhibitor

Question 18

Explain the role of nitrate ions in plants

Answer 18

Used to make:
* DNA
* amino acids
* NADP for photosynthesis
* NAD for respitation

Question 19

Explain the role of calcium ions in plants

Answer 19

Used to make calcium pectate, which adds stability to middle lamella of cell wall (layer that joins adjacent cells)

Question 20

Explain the role of magnesium ions in plants

Answer 20

Component of chlorophyll, which absorbs light energy for photosynthesis

Question 21

Explain the role of phosphate ions in plants

Answer 21

Component of:
* ADP and ATP, which are involved in energy release for metabolic reaction
* NADP for photosynthesis

Question 22

State 5 biologically important properties of water

Answer 22

• Reaches maximum denstiy at 4^oC
• High specific heat capacity
• High surface tension
• Acts as a polar solvent
• Incompressible

Question 23

Why does water have a permanant dipole?

Answer 23

Oxygen is more electronegative than hydrogen, so attracts the electron density in the covalent bonds more strongly.

Forms O δ- (slight negative charge) and H δ+ (slight positive charge)

Question 24

Describe the intermolecular bonding that between water molecules

Answer 24

Hydrogen bonds form between lone pair on oxygen of one molecule and H δ+ on neighboring molecule.

Question 25

Why is the high specific heat capacity of water important for organisms?

Answer 25

Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity.

Question 26

Why is water an important solvent for organisms?

Answer 26

Polar universal solvent dissolves and transports charged particles involved in intra and extracellular reactions.

Question 27

Why is high surface tension of water important for organisms?

Answer 27

Slows water loss due to transpiration in plants.

Water rises unusually high in narrow tubes, lowering demand on root preasure.

Some insects can “skim” across the surface of water.

Question 28

Why is the incompressible nature of water important for organisms?

Answer 28

Provides turgidity to plant cells.

Provides hydrostatic skeleton for some small animals - e.g. earthworms

Question 29

Explain why ice floats on water. Why is this important for organisms?

Answer 29

Ice is less dense than water because hydrogen bonds hold water molecules in fixed positions further away from each other.

Insulates water in artic climates so aquatic organisms can survive