Test 2 (Chapters 12-21) Flashcards
What is the major source of cellular energy?
Oxidation of carbon fuels
What is is the function of common intermediates, like NADH, in the oxidation of carbon fuels?
Electron carriers - higher affinity for activated group than carbon fuels, but a lower affinity for electrons than O2.
What is the ultimate electron acceptor in the oxidation of carbon fuels?
O2
What are five (5) common activated carriers in metabolism, and what is their activated group?
- ATP (phosphoryl)
- NADH (electron)
- NADPH (electron)
- FADH2 (electron)
- CoA (acyl)
What are three (3) mechanisms of metabolic regulation?
- the amount of enzymes
- their catalytic activities
- the accessibility of substrates
How is the amount of enzymes regulated?
Its rate of synthesis and its rate of degradation; adjusted primarily by its rate of transcription.
What are four (3) ways catalytic activity is regulated?
- Feedback inhibition (allosteric regulation of the first reaction in a pathway by the ultimate product)
- Reversible covalent modification (reduce catalytic activity by structural changes, such as phosphorylation)
- Energy status of the cell (measured by energy charge or phosphorylation potential), which is buffered (catabolic reactions take place when there is low amounts of ATP, anabolic reactions take place when there is high amounts of ATP)
What are the activated and deactivated forms of the nicotinamide adenine dinucleotide?
Deactivated: NAD+
Activated: NADH
NAD+ is an electron acceptor in what types of reaction? (3 components)
- a C-H hydride and a C-OH proton are removed forming a C=O bond
- NAD+ itself accepts a hydride, forming NADH, and a proton is added to the solvent.
- called dehydrogenation because protons accompany the electrons
What are the activated and deactivated forms of the flavin adenine dinucleotide?
Deactivated: FAD
Activated: FADH2
FAD is an electron acceptor in what types of reaction? (2 components)
- C-H hydrogens on adjacent carbons are removed along with two electrons (homolytic) forming C=C bond
- FAD accepts two electrons and two protons forming FADH2
What is the structural and functional difference between NADP+ and NAD+?
(1) NADP+ uses its electrons for the reductive biosynthesis (anabolism that creates fuels that can later be oxidated). (2) It contains an additional phosphoryl group tag, not on it’s active site, that tells enzymes that it should be used for reductive biosynthesis.
What are three molecules with a higher phosphoryl-transfer potential than ATP?
- 1,3-BPG (1,3-biphosphoglycerate)
- PEP (phosphoenolpyruvate)
3 Creatine Phosphate
What is Glycolysis?
The sequence of reactions that converts one molecule of glucose into two molecules of pyruvate while generating ATP.
What is gluconeogenesis?
The sequence of reactions that converts end products of biochemical pathways into glucose.
Where does glycolysis take place?
In the cytoplasm
What are three (3) factors that contribute to a high phosphoryl-transfer potential?
- Electrostatic repulsion of phosphoryl groups (ATP less stable than ADP)
- Resonance stabilization (inorganic phosphate resonance more stbale than ATP)
- Stabilization due to hydration (hydrogen bonds stabilize ADP and phosphate better than ATP)
How many reactions are in glycolysis?
Ten
What are the two stages of Glycolysis?
- Stage 1 cleaves glucose into two three-carbon aldehyde fragments
- Stage 2 oxidizes the each aldehyde to pyruvate while generating two ATP.
List the reactions, including substrates and products, of Stage 1 of glycolysis and the enzymes and cofactors involved.
- Glucose -> Glucose 6-phosphate [Hexokinase, ATP]
- Glucose 6-phosphate Fructose 6-phosphate [Phosphoglucose isomerase]
- Fructose 6-phosphate -> Fructose 1,6-biphosphate [Phosphofructokinase, ATP]
- Fructose 1,6-biphosphate -> Glyceraldehyde 3-phosphate + Dihydroxyacetone phosphate [Aldolase]
- Dihydroyacetone phosphate Glyceraldehyde 3-phosphate [Triose phosphate isomerase]
List the “big picture” steps of Stage 1 of Glycolysis
- Kinase phosphorylates glucose
- Isomerase prepares phosphorylated-glucose to be phosphorylated again
- Second phosphorylation occurs
- 6-carbon sugar is cleaved into a usable aldehyde and an unusable ketone
- Ketone product is converted to aldehyde product by an isomerase.
What is the important step that commits glucose to glycolysis?
Phosphorylation by Hexokinase
What irreversible reaction of Stage 1 of glycolysis uses a key regulatory enzyme?
Fructose 6-phosphate -> Fructose 1,6-biphosphate [Phosphofructokinase, ATP]
List the reactions, including substrates and products, of Stage 1 of glycolysis and the enzymes and cofactors involved.
- Glyceraldehyde 3-phosphate 1,3-Biphosphoglycerate + NADH [inorganic phosphate, NAD+, glyceraldehyde 3-phosphate dehydrogenase]
- 1,3-Biphosphoglycerate 3-Phosphoglycerate + ATP [ADP, Phosphoglycerate kinase]
- 3-Phosphoglycerate 2-Phosphoglycerate [Phosphoglycerate mutase]
- 2-Phosphoglycerate Phosphoenolpyruvate + H2O [Enolase]
- Phosphoenolpyruvate -> Pyruvate + ATP [Pyruvate kinase]
List the “big picture” steps of Stage 1 of Glycolysis
- 3-carbon aldehyde transfers electrons to NAD+ and gains a highly active phosphate group
- 1,3-BPG phosphorylates ADP to make ATP
- remaining phosphate group is moved to a middle carbon so water can be removed from adjacent carbons
- water removed from adjacent carbons, forming highly active phosphate group
- phosphoenolpyruvate phosphorylates ADP to make ATP and pyruvate remains.
What are the three fates of pyruvate so as to balance the redox potential of the cell? (i.e. replenish NAD+ that is consumed)
Pyruvate must be oxidized (1&2 are anaerobic, 3 is aerobic):
- Lactic acid fermentation, in which pyruvate is reduced by NADH using lactate dehydrogenase.
- Alcoholic fermentation, in which pyruvate is converted to acetaldehyde by pyruvate decarboxylase, which is reduced by NADH using alcohol dehydrogenase.
- Combustion of pyruvate into CO2 and H2O by O2
What is the molecular entry-point of the aerobic respiration?
Pyruvate is oxidized to (1) acetyl CoA and (2) carbon dioxide by NAD+
What are two (2) ways Fructose enters glycolysis?
- In most tissues, Fructose is phosphorylated to Fructose 6-phosphate
- In the liver (where most fructose metabolizatin occurs), fructokinase phosphorylates to Fructose 1-phosphate, which is split into Glyceraldehyde and Dihydroxyacetone phosphate [which enters glycolysis] and Glyceraldehyde is phorphorylated to Glyceraldehyde 3-phosphate [which enters glycolysis]
What are the four steps that Galactose takes to enter into Glycolysis?
- Galactose converted to Galactose 1-phosphate
- Galactose 1-phosphate converted to UDP-Galactose
- UDP-Galactose converted to UDP-Glucose
- UDP-Glucose converted to Glucose
What three enzymes are regulated in Glycolysis?
- Hexokinase
- Phosphofructokinase
- Pyruvate kinase
What is a committed step?
The first irreversible reaction unique to a metabolic pathway.
What is the committed step of glycolysis?
Phosphorylation of fructose 6-phosphate to fructose 1,6-biphosphate by phosphofructokinase
What is the most important control element in a metabolic pathway?
The enzyme of the committed step.
What are four (4) ways glycolysis helps pancreatic beta cells regulate glucose?
- Increase ATP concentration
- Closing K+ Channel
- Opening Calcium Channel
- Releasing Insulin
What three irreversible reactions are bypassed in Gluconeogenesis?
- Glucose -> Glucose 6-phosphate
- Fructose 6-phosphate -> Fructose 1,6-biphosphate
- Phosphoenolpyruvate -> Pyruvate
How is glucose -> glucose 6-phosphate bypassed in gluconeogenesis?
Glucose 6-Phosphotase: Glucose 6-phosphate -> Glucose
How is Fructose 6-phosphate -> Fructose 1,6-biphosphate bypassed in gluconeogenesis?
Fructose 1,6-biphosphatase: Fructose 1,6-biphosphate -> Fructoes 6-phosphate
How is Phosphoenolpyruvate -> Pyruvate bypassed in gluconeogenesis? (two steps)
- Pyruvate carboxylase: pyruvate + ATP -> oxaloacetate + ADP
- Phosphoenolpyruvate carboxykinase (PEPCK): oxaloacetate + GTP -> phosphoenolpyruvate + GDP
What are (2) differences between Glycolysis and Gluconeogenesis?
- Irreversible steps of glycolysis are bypassed by new reactions in gluconeogenesis
- Not all reactions in gluconeogenesis occur in cytoplasm
Which enzymes of gluconeogenesis are located outside of cytoplasm, and where are they?
- Pyruvate carboxylase (mitochondria)
2. Glucose 6-phosphatase (membrane in ER, ONLY IN LIVER! Otherwise, this is used to make glycogen)
What happens to oxaloacetate while it is shuttled from mitochondria to cytoplasm?
- It is reduced to malate
2. then reoxidized, also generating NADH
What are three allosteric regulators of glycolysis/gluconeogenesis
- ATP/AMP (energy state)
- Citrate (status of citric acid cycle)
- High alanine and acetyl CoA
What enzymes are reciprocally regulated between glycolysis and gluconeogenesis, and by what signal molecule?
- Phosphofructokinase and fructose 1,6-biphosphatase are regulated by fructose 2,6-biphosphate (high concentration favor glycoclysis)
- Pyruvate kinase and pyruvate carboxylase regulated by other effectors
Describe the Cori cycle
Lactate generated by glycolysis in muscle is released into bloodstream, absorbed by liver and converted into glucose by gluconeogenesis.