Roles of ATP in living cells Flashcards
What is anabolism?
synthesis of complex molecules from simpler ones (necessary energy usually derived from ATP)
What is catabolism?
breakdown of energy- rich molecules to simpler ones (CO2 H2O and NH3)
What is energy used for?
Motion (muscle contraction)
Transport (of ions/molecules across membranes)
Biosynthesis of essential metabolites
Thermoregulation
Why are storage forms required?
Because feeding times and usage times do not coincide all the time
Where is free energy gained from?
Food
What is gibbs free energy?
Energy capable of doing work at constant temperature and pressure
The energy derived from the oxidation of dietary fuels
When does entropy increase?
Breakdown
When does enthalpy increase?
When energy is put into the system
What is an exergonic reaction?
One which releases energy
When is free energy negative?
When the reaction releases energy
When is free energy positive?
When reaction is endergonic and require energy to begin
Give an example of an exergonic reaction?
Catabolism
Give an example of endergonic reactions
Anabolism
Describe coupling of reactions
An endergonic reaction can be driven in the forward direction by coupling it to an exergonic reaction through a common intermediate
When is phosphate group transfer used?
When ATP is used
What can magnesium deficiency do?
Interfere with metabolism
Describe substrate level phosphorylation
Formation of ATP by phosphoryl group transfer from a substrate to ADP
Respiration-linked phosphorylation involve…
Membrane-bound enzymes and transmembrane gradients of protons and require oxygen
How do enzymes interfere with gibbs free energy?
They do not
What are coenzymes derived from?
Vitamins
What is a prosthetic group?
Non-protein cofactor that is covalently bound to the enzyme
Acts as a temporary store for e- or intermediates
What is NAD formed from?
Niacin
What is FAD formed from?
B2 Riboflavin
In each redox case how many electrons and protons are transferred?
2 electrons
Various protons
What is NAD+ reduced to?
NADH
What is FAD reduced to?
FADH2
What is the functional group of NAD+
Nicotinamide
What are priming reactions?
Where ATP is put into the reaction to begin it
Where does glycolysis occur in the cell?
Cytoplasm
What continues to the next stage of the glycolysis reaction
G3P
How many times do the payoff reactions occur per molecule of glucose?
Twice
What is the product of glycolysis?
Pyruvate
What is the priming stage?
investment of ATP at the hexokinase and PFK-1 reactions
What is the payoff stage?
recovery of ATP by SLP using the 1,3 - bisphosphate kinase and pyruvate kinase reactions
What are the two possible fates of pyruvate?
Under aerobic conditions, oxidation and complete degradation
In hypoxic conditions, it can be reduced to lactate
Under aerobic conditions where does pyruvate get degredated?
Mitochondria
Describe how pyruvate is transported into the mitochondria?
Occurs via by specific carrier protein embedded in the mitochondrial membrane
How does pyruvate form acetyl CoA?
Pyruvate undergoes oxidative decarboxylation by the pyruvate dehydrogenase complex to form Acetyl CoA:
Describe the structure of the pyruvate dehydrogenase complex?
Three different enzymes
Five different coenzymes
List the vitamins essential for the pyruvate dehydrogenase complex
Thiamine (in TPP)
Riboflavin (in FAD)
Niacin (in NAD)
Pantothenate (in CoA)
What is the TCA cycle?
Krebs cycle/Tricarboxylic acid cycle/Citric acid cycle
Final common pathway for the oxidation of fuel molecules
In 8 steps, acetyl residues (CH3-CO-) are oxidised to CO2
What does 1 turn of the TCA cycle produce?
3 NADH
FADH2
GTP
2 CO2
Describe the 3 ways TCA cycle is regulated
Entry of acetyl-CoA into the TCA cycle (citrate synthase reaction)
Conversion of pyruvate to acetyl-CoA (PDH reaction)
Also regulated at isocitrate dehydrogenase and -ketoglutarate dehydrogenase reactions
Name some other sources of Acetyl coA
Fatty acids
Amino acids
How are the TCA intermediates replenished?
By anaplerotic reactions
What happens to the NADH and FADH2 after the TCA and glycolysis? State the problem here
Oxidised by the mitochondrial ETC
The inner mitochondrial membrane is impermeable to NADH!
There is no carrier in the membrane to transport it across
Describe how NADH is transported?
It is not!
The shuttles transport the electrons across the membrane
Describe the two shuttles stating where they are prevalent and what they do
The glycerol-3-phosphate shuttle, especially prevalent in brain and muscle
The malate-aspartate shuttle, in liver and heart
Both shuttles act to regenerate NAD+ and make 1.5 or 2.5 moles of ATP
Describe the action of the glycerol-3-phosphate shuttle
NADH reduces dihydroxyacetone-P (DHAP) to glycerol-3-phosphate (G-3-P)
Catalysed by G-3-P dehydrogenase
G-3-phosphate diffuses into the intramembrane space
A mitochondrial G-3-P dehydrogenase (called flavoprotein dehydrogenase) uses FAD to oxidise it to DHAP
FADH2 carries electrons to ubiquinone in the electron transport chain eventually producing 1.5 ATP
Describe the action of the malate aspartate shuttle
Electrons of cytosolic NADH transfer to cytosolic oxaloacetate yielding malate
Malate is transported into the matrix via an exchanger protein that transports α-KG in the opposite direction
In the matrix, malate is oxidised back to oxaloacetate
NADH formed transfers its reducing power to the electron transport chain producing 2.5 ATP
Oxaloacetate is converted to aspartate
Aspartate is transported to the cytosol via an exchanger protein that transports glutamate into the matrix
Cytosolic aspartate is transaminated to oxaloacetate
Describe the electron transport chain
Comprises four large multi-unit proteins intrinsic to the inner mitochondrial membrane
State the reaction the electron transport chain catalyses
NADH + H+ + 1/2O2 = NAD+ + H2O
Energy released from this reaction not released as heat but tightly coupled to the production of ATP
The 4 complexes are linked by 2 soluble proteins. What are they?
Ubiquinone (coenzyme Q) – a lipid soluble benzoquinone with a long isoprenoid tail
Cytochrome C - These are free to move in the membrane by diffusion (they are not part of the complexes)
Which complex does NADH pass its electrons to in the electron transport chain?
Complex 1
Which complexes move protons in the electron transport chain?
1,3,4
