Lectures 17/18: Introduction to Metabolism Flashcards Preview

Biochemistry 2300 > Lectures 17/18: Introduction to Metabolism > Flashcards

Flashcards in Lectures 17/18: Introduction to Metabolism Deck (39):
1

Cellular metabolism (3)

The chemical processes occurring within a living cell or organism that are necessary for maintaining life
1. Provide energy, macromolecules, bioactive molecules from intermittent supply of nutrients
2. Prevent build up of toxic materials in wrong place
3. Breakdown of xenobiotics

2

Catabolism

Breakdown of large molecules to release energy and small molecules
Of amino acids, monosaccharides and fatty acids: involves oxidizing carbon

3

Anabolism

Synthesis of large molecules for storage or biomass using energy
Of amino acids, monosaccharides and fatty acids: involves reducing carbon

4

Macromolecules (3)

1. Energy storage (carbohydrates, fat, proteins)
2. Energy transport
3. Energy release

5

Oxidation

Loss of electrons from an atom or molecule
The atom/molecule that loses electrons is being oxidized and is an electron donor
Oxidative, exergonic

6

Reduction

Gain of electrons by an atom/molecule
The atom/molecule that gains the electron is being reduced and is an electron acceptor
Reductive, endergonic

7

Oxidation state

Most: CO2, carboxylic acid, aldehyde/ketone, hydroxyl, hydrocarbon: least
Most: triple bond, double bond, single bond: least

8

Highest redox energy yield

Most reduced to most oxidized: full oxidation to CO2 and H2O
Catabolism of fatty acids provides more energy than catabolism of carbohydrates

9

Metabolic pathways

Interconverted network of metabolites
Several major metabolic pathways share a few common intermediates
Series of sequential reactions, each catalyzed by a specific enzyme

10

Redox-active cofactor

When a metabolite is oxidized in catabolic reaction, electron is passed on to cofactor (reduced)
Cofactors can be oxidized again by giving up an electron in anabolic reactions
Many derived from vitamins
Includes NAD/NADH, FAD/FADH2, NADP/NADPH, Q/QH2

11

Oxidation of cofactors

Occurs during anabolic reaction (NADPH) or during oxidative phosphorylation (NADH, FADH2)

12

Oxidative phosphorylation

NADH and FADH2 are oxidized, oxygen is reduced to water, and ATP is produced

13

FAD/FADH2

Cofactor that is usually directly complexed to an enzyme

14

Ubiquinone (Co-enzyme Q)

Cofactor that accepts two electrons in a stepwise manner to become ubiquinol

15

Essential

A required nutrient that the human body cannot synthesize de novo
The human body cannot synthesize vitamins

16

Thermodynamics

Energy changes in metabolic pathways

17

Directionality

Many pathways are overall reversible, but at any given time, only one direction is active

18

Flux

Rate of overall pathway
Described how many molecules of substrate are converted to product
Controlled through activity of enzymes catalyzing irreversible reactions

19

Enthalpy

H
Energy
Reaction is favoured if deltaH is negative

20

Gibbs Free Energy

A reversible process moves spontaneously in the direction that lowers the systems Gibbs' Free Energy

21

Entropy

S
Disorder
Reaction is favoured if delta S is positive

22

Dynamic equilibrium

Rates of the forward and reverse reactions are the same
Nothing changes in the total amount
The concentrations of products and substrates are not necessarily equal

23

Equilibrium constant Keq

Defined by the concentrations of the reactants and substrates at equilibrium
Inherent property of reaction

24

Standard Free Energy Change

DeltaG*' = -RTlnKeq
Described driving force of equilibrium at standard conditions, when all reactants are present at equal concentrations
Set characteristic of a reaction

25

Actual Free Energy Change

DeltaG= DeltaG*' + RTln([C][D])/([A][B])
Depends on actual equilibrium concentrations and reflects how far the system is from equilibrium
Spontaneous, favourable systems move towards equilibrium and have a negative deltaG
At equilibrium, deltaG=0

26

Positive deltaG

Reaction is not spontaneous
Reaction is endergonic and unfavourable
Free energy is required to perform the reaction

27

Negative deltaG

Reaction is spontaneous
Reaction is exergonic and favourable
Free energy becomes available during the reaction
Unfavourable reactions can be coupled with favourable reactions to make them possible

28

Exergonic

Energy releasing
DeltaG is negative
Final state is lower energy than starting state

29

Endergonic

Energy requiring
DeltaG is positive
Final state higher energy than staring state
Often coupled to ATP hydrolysis to make overall reaction favourable and possible

30

Glucose phosphorylation

Highly unfavourable reaction
DeltaG=+13.8Kj/mol
ATP hydrolysis provides the energy for glucose phosphorylation
DeltaG of each reaction added to give deltaG of coupled reaction

31

ATP

Energy currency
Drives unfavourable reactions to completion
Made my two exergonic processes: glycolysis and oxidative phosphorylation
Not membrane permeable
Short lived (seconds), must be constantly replenished
Turned over at very high rate

32

Thioester hydrolysis

To give carboxylic acid ion and CoA-SH
Thioesters have less resonance stability than oxygen esters
Hydrolysis is more exergonic than oxygen ester hydrolysis

33

Futile cycle

At least one step in a catabolic/anabolic pathway must differ to avoid a futile cycle
All metabolic pathways must be directional and overall irreversible
Directionality is conferred by one or a few irreversible steps

34

Steady state

Levels and concentrations of metabolites
Does not give information about flux of a reaction

35

Forward enzyme

Stimulation causes forward reaction
Reverse enzyme is inactive

36

Reverse enzyme

Stimulation causes reverse reaction
Forward enzyme is inactive

37

Reversible reactions

Small deltaG
Forwards and reverse rate are similar
Reaction is near equilibrium and cam easily go in either direction: relative ratio of substrate and product determine the direction of the reaction
Increased enzyme activity increases rate of both direction: steady state is reached faster but no change in direction of overall rate

38

Irreversible reactions

Large deltaG: one side of the reaction is much more stable
Reacts towards products even if there is little substrate available, and changes in reactants have little effects
Forward rate much higher than reverse rate
In metabolic pathways: reverse reaction requires a different enzyme and can have different side products

39

Homeostasis

Living systems are thermodynamically open and do not reach equilibrium
Work towards maintaining a steady state: flow through system is adjusted so overall system does not change over time
Levels of metabolites are kept relatively constant by adjusting the rates of different pathways
Flus is regulated to maintain homeostasis