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

Lectures 17/18: Introduction to Metabolism Flashcards

1
Q

Cellular metabolism (3)

A

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
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2
Q

Catabolism

A

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

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3
Q

Anabolism

A

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

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4
Q

Macromolecules (3)

A
  1. Energy storage (carbohydrates, fat, proteins)
  2. Energy transport
  3. Energy release
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5
Q

Oxidation

A

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

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6
Q

Reduction

A

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

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7
Q

Oxidation state

A

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

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8
Q

Highest redox energy yield

A

Most reduced to most oxidized: full oxidation to CO2 and H2O

Catabolism of fatty acids provides more energy than catabolism of carbohydrates

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9
Q

Metabolic pathways

A

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

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10
Q

Redox-active cofactor

A

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

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11
Q

Oxidation of cofactors

A

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

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12
Q

Oxidative phosphorylation

A

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

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13
Q

FAD/FADH2

A

Cofactor that is usually directly complexed to an enzyme

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14
Q

Ubiquinone (Co-enzyme Q)

A

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

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15
Q

Essential

A

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

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16
Q

Thermodynamics

A

Energy changes in metabolic pathways

17
Q

Directionality

A

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

18
Q

Flux

A

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

19
Q

Enthalpy

A

H
Energy
Reaction is favoured if deltaH is negative

20
Q

Gibbs Free Energy

A

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

21
Q

Entropy

A

S
Disorder
Reaction is favoured if delta S is positive

22
Q

Dynamic equilibrium

A

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
Q

Equilibrium constant Keq

A

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

24
Q

Standard Free Energy Change

A

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

Biochemistry 2300 (10 decks)

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