Leyland 3 intro to metabolism

Question 1

METABOLISM

Answer 1

• linked series of chemical reactions, whereby one molecule is converted to another molecule(s) in a defined way.
  • Lots of pathways
  • Many interdependent.
  • Lots of reactions BUT limited number of types of reactions. (eg redox, hydrolysis).

Question 2

Why use metabolism

Answer 2

⇒ need more than 1 pathway to control mechanisms

• Metabolic pathways can be divided into 2 classes.

Question 3

Plants use:

Answer 3

photosynthesis

Question 4

Animals use:

Answer 4

chemotrophs – macromolecules for movement, active transport, membrane potential etc

Question 5

Types of reaction:

Answer 5

1 Substitution
2 Addition
3 Elimination
4 Condensation

Question 6

catabolic

Answer 6

• breakdown of complex molecules to produce energy –usually oxidative
  Fuel → CO2 + H2O + useful energy

Question 7

anabolic

Answer 7

formation of complex molecules from simple ones, utilising energy – usually reductive
energy + simple precursors → complex molecules

Question 8

Exergonic reactions:

Answer 8

spontaneous, release energy. ΔG –ve.

Question 9

Endergonic reactions:

Answer 9

non-spontaneous, need energy to occur. ΔG +ve.

Question 10

Amphybolic:

Answer 10

pathways that do both

Question 11

energy of a reaction is defined as :

Answer 11

ΔG = ΔH - TΔS

Question 12

ΔH enthalpy change:

Answer 12

heat exchange with surroundings
heat released, Δ H is –ve (exothermic).
heat absorbed, ΔH is +ve (endothermic).

Question 13

ΔS entropy change:

Answer 13

measure of the order/disorder
decrease in disorder, ΔS is -ve.
increase in disorder, ΔS is +ve.

Question 14

ΔG (Gibbs) free energy change of a reaction

Answer 14

energy available to do work.
Δ = ‘change in’
T = temperature in K (0C + 273

Question 15

standard conditions

Answer 15

(1M concentrations of reactants and products, 25oC, pH7)
Standard free energy change = ΔGo’
• NB Actual free energy change in cells is usually different (370C in mammals & reactants/products not 1M concentration).

Question 16

A thermodynamically unfavourable reaction can be driven by a favourable reaction

Answer 16

+/ve unlikely to happen spontaneously

pathways= lots of reactions together & individual steps may not happen, but overall reaction will.

Question 17

C6H12O6 + 6O2 →

Answer 17

6CO2 + 6H2O ΔG = - 2870 kJmol-1

Oxidation of glucose releases energy that can be used by cells

Question 18

Energy supplied

Answer 18

to organism as food. Broken down (catabolism) to produce energy.

Question 19

Energy used for :

Answer 19

synthetic processes (anabolism) for growth and renewal
•	 mechanical work (cell movement, muscle contraction)
•	 active transport of molecules and ions

Question 20

Dietary requirements

Answer 20

Sources of energy : Energy currency - ATP
• carbohydrate, lipid, protein
Also need :
• Water, Source of elements (Mg, Ca, Fe etc), Vitamins (fat & water soluble), Essential amino acids and fatty acids (biosynthesis)

Question 21

ATP

Answer 21

mononucleotide
containing an adenine base, a ribose sugar & 3 phosphate groups
ATP-> ADP -> AMP
Hydrolysis of phosphoanhydride bonds releases lots of energy

Question 22

ATP releases lots of energy because of :

Answer 22

1) Resonance stabilisation of orthophosphate favours ATP hydrolysis.
2) Electrostatic repulsion
4 negative charges à electrostatic repulsion which is reduced when ATP is hydrolysed.
3) Stabilisation due to hydration
- Water binds more effectively to ADP and Pi, than ATP, thus stabilising ADP/Pi > ATP.

ATP + H2O → ADP + Pi ΔGo’ = - 31 kJ/mol

Question 23

intermediate phosphoryl transfer potential allows …

Answer 23

ATP to act as a carrier of phosphate groups

Question 24

ATP is a carrier of energy, not a store:

Answer 24

• Limited amount of ATP/ADP in cells
• Constant recycling between ATP and ADP (40 kg ATP turnover /day in resting adult !!)
• Some ATP produced directly from catabolic reactions substrate level phosphorylation (discussed later)
• Most ATP produced by oxidative phosphorylation using reduced coenzymes (NADH, FAD2H) generated by catabolic pathways

Question 25

Redox

Answer 25

• one is oxidised, other is reduced

* fuel molecules (e.g. A-2H) are oxidised, Hydrogen atoms & electrons are transferred to another molecule (B)

Question 26

Carrier molecules

Answer 26

• number of small molecules have important roles in passing electrons (and protons)
• finite quantity of these molecules in cells => recycled
• control rate through coenzymes

Question 27

AH2 + NAD+ ->

Answer 27

A + NADH + H+

• ATP produced when NADH reoxidised at a later stage; oxidative phosphorylation

Question 28

Major Carrier molecules

Answer 28

• NAD+ Nicotinamide Adenine Dinucleotide
• NADP+ Nicotinamide Adenine Dinucleotide Phosphate
• FAD Flavin Adenine Dinucleotide
• FMN Flavin MonoNucleotide

Question 29

NAD

Answer 29

dinucleotide 
•	 1 nicotinamide base
•	 1 adenine base
•	 2 ribose sugars
•	 2 phosphate groups

Question 30

During catabolic processes, intermediates are oxidised and

Answer 30

coenzyme (NAD+) is reduced in REDOX reactions.

Question 31

During anabolic processes, intermediates are reduced and

Answer 31

coenzyme (often NADPH) is oxidised in REDOX reactions.