1 - Intro Flashcards
How do you calculate the respiratory quotient? What is it?
Moles CO2 over moles O2
the ratio of the volume of carbon dioxide expelled to that of oxygen consumed by an organism, tissue, or cell in a given time.
How many kJ does per mole glucose does it take to produce one mole of ATP?
-30.5 kJ per mole glucose.
What makes ATP a high energy phosphate compound?
ATP is considered a high energy phosphate compound because the hydrolysis of its two phospoanhydride bonds proceeds with the release of a large negative ΔG*’ (standard free energy)
The hydrolysis of phosphocreatine to creatine and phosphate has a standard free energy of -43.1 kJ/mole. Write the individual reactions and net reaction for the coupling of phosphocreatine hydrolysis and ATP synthesis from ADP. Is the synthesis of ATP thermodynamically favoured? Why or why not?
Phosphocreatine + H20 -> creatine + Pi (deltaG = -43.1 kJ/mole)
ADP + Pi -> ATP + H20 (delta G = +30.5 kJ/mole)
Phosphocreatine + ADP -> creatine + ATP (delta G = -12.6 kJ/mole)
What is facilitated diffusion across a membrane?
The rate is not limited by the energy state of the cell.
(also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.
Describe the formation of mixed micelles in the small intestine during the digestion of dietary fat. What dietary components would be decreased in a person with a defect in bile salt secretion into the gut?
Bile salts are cholesterol derivateives that are synthesized in the liver. Stored in the bile and released into the small intestine. In the presence of bile salts and the mechanical agitation that occurs inthe intestine, traicylglycerols in the diet are emulsified to form emulsions with the amphiphatic bile salts at the triacylglycerol-water interface. Triacylglycerol lipase and other lipases act on the droplet at the interface to hydrolyze the fatty acid componentns of the traicyglycerol. These fatty acids are also amphipathic and are incorporated into the micelle surface. Forming a mixed micelle. A person with a defect in bile salt secretion would be unable to form micelles efficiently and would therfefore have inefficient digestion and absorption of fats from the diet. In addition, the absorption of the fat soluble vitamins (A, E, D, K)
How can you determine the rate determining step by thermodynamic criteria?
Often early in the pathway, the RLS has a very high negative ΔG*’, indicating its irreversibility.
What is the rate determining step in glycolysis?
The phosphofructokinase reaction that converts fructose-6-phosphate to fructose-1,6-bisphosphate
What is the rationale for the unusual regulation of glycolysis?
- The first reaction in glycolysis is catalysed by hexokinase (AKA glucokinase), this is not a suitable control point for the overall pathway of glycolysis because significant amounts of sugar ENTER the pathway as glucose-6-phosphate, the product of the hexokinase reaction. For example, galactose is converted to glucose-6-phosphate to enter glycolysis. In addition, mannose and fructose enter glycolysis as fructose-6-phosphate.
Therefore the phosphofructokinase reaction is the most effective point for regulation of glycolysis as it is the first committed step in the pathway.
What enzymes do the brain and muscle tissues lack that precludes the secretion of glucose derived from glycogen?
Which tissue does contain this enzyme and in which organelle?
glucose-6-phosphatase
Glucose 6-phosphatase is an enzyme that hydrolyzes glucose-6-phosphate, resulting in the creation of a phosphate group and free glucose. Glucose is then exported from the cell via glucose transporter membrane proteins. This catalysis completes the final step in gluconeogenesis and glycogenolysis and therefore plays a key role in the homeostatic regulation of blood glucose levels.
Liver, in the endoplasmic reticulum.
What is the metabolic advantage to breaking down glycogen to phosphoglucose (phosphorolysis) rather than glucose (hydrolysis)?
Phosphorolysis saves energy expenditure by producing glucose-1-phosphate instead of glucose. The energy required to convert glucose to glucose-6-phosphate via hexokinase (eses ATP) is avoided by phosphorolysis
UDP-glucose pyrophosphorylase catalyses the synthesis of UDP-glucose in the glycogen biosynthetic pathway.
The ΔG*’ for the reaction is near zero. Where does the energy to drive the reaction to UDP-glucose come from?
The energy to drive this reaction is obtained from the hydrolysis of pyrophosphate by the ubiquitous enzyme pyrophosphatase (ΔG*’ = -33.5 kJ/mole)
UDP-glucose pyrophosphorylase catalyses the synthesis of UDP-glucose in the glycogen biosynthetic pathway.
[γ32P]UTP was used as a tracer to monitor the reaction in hepatocytes. Where is the radioactivity at the completion of the reaction?
This enzyme converts glucose-1-phosphate to uridine diphosphate (UDP)-glucose, which is the step before glycogen synthase and branching enzyme.
A by product of this reaction is pyrophosphate (from the hydrolysis of UTP to UDP - by attaching uridine and the alpha phosphate to the already phosphorylated glucose). Pyrophosphate (the leaving beta and gamma phosphates) is then converted by pyrophosphatase to inorganic phosphate.
The radioactivity will be found in inorganic phosphate after completion of the reaction.
The CO2 produced in one round of the citric acid cycle does not originate in the acetyl carbons that entered that round. If acetyl-CoA is labeled with 14C at the carbonyl carbon, how many rounds of the cycle are required before 14CO2 is released?
- Acetyl from Acetyl-CoA becomes the terminal (C4) carbon of succinyl-CoA (which becomes succinate, a symmetrical 4 carbon diprotic dicarboxylic acid from alpha-ketoglutarate).
- Succinate becomes fumerate, fumerate becomes malate and malate becomes oxaloacetate.. Because succinate is symmetrical, the oxaloacetate can have the label at C1 or C4.
- When these condense with acetyl-CoA to begin the second round of the cyle, both of these carbons are eliminated as CO2 during the isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase reactions (formation of alpha ketoglutarate and succinyl-CoA respectively).
So in short, 14 CO2 will be released in the second turn of the cycle.
Although animals cannot synthesize glucose from acetyl-CoA, if a rat is fed 14C-labeled acetate, some of the label appears in glycogen extracted from its muscles. Explain.
Animals cannot carry out the net synthesis of glucose from acetyl-CoA (which is the fate of fed acetate). However, 14C labeled acetyl-CoA enters the citric acid cycle and is converted to oxaloacetate.
Some of this oxaloacetate may be converted to glucose via gluconeogenesis and converted to glycogen by muscle.
