T2 L2 Roles of ATP in living cells Flashcards
What happens to pyruvate in aerobic conditions?
It undergoes oxidation & complete degradation in the mitochondria
Where does glycolysis occur?
In the cytosol
What are the roles of pyruvate in metabolism?
Forms lactate using lactate dehydrogenase
Forms oxaloacetate using pyruvate carboxylase
Forms alanine using alanine aminotransferase
Forms acetyl CoA using pyruvate dehydrogenase complex
How is pyruvate transported into the mitochondria?
Via a specific carrier protein embedded in the mitochondrial membrane
What is the equation for oxidative decarboxylation of pyruvate
Pyruvate + CoA + NAD+ –> acetyl-CoA + CO2 + NADH + H+
The reaction is irreversible & forms the link between glycolysis & the citric acid cycle
What makes up the pyruvate dehydrogenase complex?
3 different enzymes
5 different co-enzymes
4 different vitamins
What are the 3 enzymes that make up the pyruvate dehydrogenase complex?
Pyruvate dehydrogenase
Dihydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase
What are the 5 different co-enzymes that make up the pyruvate dehydrogenase complex?
Thiamine pyrophosphate (TPP) NAD+ CoA Flavine adenine dinucleotide (FAD) Lipoic acid
What are the 4 different vitamins in the pyruvate dehydrogenase complex?
Thiamine - in TPP
Riboflavin - in FAD
Niacin - in NAD
Pantothenate - in CoA
What is the final pathway for the oxidation of fuel molecules?
Tricarboxylic acid cycle
What are the products of the TCA cycle?
3 NADH
1 FADH2
1 GTP (ATP)
2 CO2
What are the 4 ways that the TCA cycle is regulated?
1) Conversion of pyruvate to acetyl CoA
2) Entry of acetyl CoA into the TCA cycle
3) Isocitrate dehydrogenase reaction
4) Alpha-ketoglutarate dehydrogenase reaction
All 4 reactions are irreversible & all are activated by calcium. All are inhibited by ATP & NADH
What does high levels of ATP & NADH stimulate?
Signals a high energy status of the cell so there is no requirement for increased ATP synthesis
What are the products of glycolysis?
Pyruvate
NADH
What are NADH & FADH2 oxidised by?
The mitochondrial electron transport chain
Inner mitochondrial membrane is impermeable to NADH & there is no carrier
What are the 2 shuttles that transport electrons from NADH?
Glycerol-3-phosphate shuttle
Malate-aspartate shuttle
Both regenerate NAD+
Describe the glycerol-3-phosphate shuttle
In the brain & muscle
NADH reduces dihydroxyacetone-P (DHAP) to glycerol-3-phosphate
Catalysed by G-3-P dehydrogenase
G-3-P diffuses into the intramembrane space
Mitochondrial G-3-P 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 malate-aspartate shuttle
Present in liver & heart
Electrons of cytosolic NADH transfer to cytosolon oxaloacetate, yielding malate
Malate is transported into the matrix via the exchanger protein that transports alpha-KG in the opposite direction
NADH formed transfers its reducing power to the electron transport chain producing 2.5ATP
Oxaloacetate is converted to aspartate
Aspartate is transported to the cytosol via an exchanger protein that transports glutamate into the matrix
Cytosolic aspartate is transaminate to oxaloacetate
What are the multi-unit proteins that make up the electron transport chain?
Complex I Complex II Complex III Complex IV The proteins are intrinsic to the inner mitochondrial membrane complex
How is energy released from the electron transport chain?
Tightly coupled to the production of ATP
It is not released as heat
What are the complexes in the ETC linked by?
1) Ubiquinone
2) Cytochrome C
What is ubiquinone?
Coenzyme Q
Lipid soluble benzoquinone with a long isoprenoid tail
What is cytochrome C?
Not part of an enzyme complex
Moves between complex III & complex IV
