Midterm Flashcards
What is glycolysis?
The metabolic process that breaks down glucose into two molecules of pyruvate
It occurs in the cytoplasm and generates ATP and NADH.
This pathway provides energy for both aerobic and anaerobic conditions
What is the importance of the Krebs cycle?
Essential for energy production, generating NADH and FADH₂
It occurs in the mitochondrial matrix and oxidizes Acetyl-CoA to CO₂
This cycle provides intermediates for biosynthsis and ATP generation
How does the electron transport chain function?
Transfers electrons from NADH and FADH₂, creating a proton gradient
This proton gradient drive ATP synthesis via ATP synthase
Oxygen is the final electron acceptor, forming water.
Define oxidative phosphorylation.
Process where ATP is synthesized using ETC and chemiosmosis
Electrons pass through the ETC, pumping protons into the intermembrane space
ATP synthase utilizes the proton gradient to generate ATP
Describe the significance of gluconeogenesis.
Synthesizes glucose from non-carbohydrate sources like amino acids and lactate
It mainly occurs in the liver and kidneys during fasting or low glucose levels
It ensures a continuous glucose supply for the brain and the RBCs
What are the key enzymes of glycolysis?
Hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase
Hexokinase: phosphorylates glucose, committing it to glycolysis
PFK-1: regulated glycolysis
Pyruvate kinase: catalyze the final ATP-producing step
Explain the function of hexokinase in glucose metabolism.
Phosphorylates glucose into glucose-6-phosphate in the 1st step of glycolysis
This prevents glucose from diffusing out of the cell
It has a curial role in regulating glucose utilization
What is the Cori cycle?
Recycles lactate produced by anaerobic glycolysis in muscles back to glucose
Lactate is converted into glucose in the liver and returned to muscles
This prevents lactic acid buildup and maintains glucose supply
How does the pentose-phosphate pathway work?
Generates NADPH and ribose-5-phosphate
NADPH is used for biosynthesis, while ribose-5-phosphate is essential for nucleotide synthesis
It consists of oxidative and non-oxidative phases
Describe the regulation of glycolysis.
Regulated by allosteric control of hexokinase, PFK-1, and pyruvate kinase
ATP and citrate inhibit PFK-1, while AMP and fructose-2,6-bisphosphate activate it
Insulin promotes glycolysis while glucagon inhibits it
What is the role of NADH in metabolism?
Electron carrier that donates electrons to the ETC for ATP production
Generated during glycolysis, Krebs cycle, and beta-oxidation
it is crucial for oxidative phosphorylation and energy metabolism
Define substrate-level phosphorylation.
Direct synthesis of ATP from ADP and a phosphorylated substrate
Occurs in glycolysis and the Krebs cycle
Unlike oxidative phosphorylation, it doesn’t require oxygen
How does insulin regulate glucose metabolism?
Stimulates glucose uptake, glycolysis, and glycogenesis
It inhibits gluconeogenesis and glycogenolysis
It lowers blood glucose levels by increasing glucose utilization
What are the key differences between aerobic and anaerobic respiration?
Aerobic requires oxygen and produces more ATP
38 ATP per Glucose
Anaerobic occurs without oxygen 2 ATP per Glucose and generates lactate as a byproduct.
Explain the metabolic fate of pyruvate.
Enters the Krebs cycle as Acetyl-CoA under aerobic conditions; converted to lactate under anaerobic conditions
Can also serve as a precursor for gluconeogenesis.
What is the role of glycogen phosphorylase in glycogenolysis?
Breaks down glycogen into glucose-1-phosphate
Activated by glucagon in the liver and epinephrine in muscles
It ensures glucose availability during fasting or exercise
How is the HMP pathway linked to nucleic acid synthesis?
Provides ribose-5-phosphate for nucleotide biosynthesis
Also generates NADPH, essential for DNA synthesis
it is crucial for rapidly dividing cells
Describe the biochemical significance of the TCA cycle.
Central to aerobic metabolism and ATP generation
Produces NADH and FADH₂, driving oxidative phosphorylation
Provides intermediates for biosynthetic pathways
What are the key regulatory steps of glycolysis?
Involves hexokinase, PFK-1, and pyruvate kinase
These enzymes are subject to allosteric regulation and hormonal control
ATP inhibits PFK-1, insulin promotes glycolysis
Explain the process of glycogenesis.
Synthesis of glycogen from glucose
Glycogen synthase elongates chains, while the branching enzyme introduces branches
It is promoted by insulin
What is the significance of the malate-aspartate shuttle?
Transfers NADH electrons into mitochondria
Helps maintain NAD+/NADH ratio in glycolysis
Increases ATP yield in aerobic respiration
How does lactate accumulation affect metabolism?
Leads to acidosis and muscle fatigue
Cleared via the Cori cycle in the liver
It is converted back into glucose by gluconeogenesis
Describe the structure and function of ATP synthase.
Enzyme in the mitochondrial membrane that synthesizes ATP using the proton gradient from ETC
Consists of F₀ (proton channel) and F₁ (ATP-producing unit).
What are the consequences of glucose-6-phosphatase deficiency?
Leads to glycogen storage disease type I (Von Gierke’s disease)
The liver cannot release glucose, causing hypoglycemia
Excess glycogen accumulates, leading to liver enlargement
How does the citric acid cycle contribute to amino acid metabolism?
Provides intermediates like alpha-ketoglutarate for amino acid synthesis
Facilitates amino acid degradation
Intermediate link protein and carbohydrate metabolism
MCQ: What is the primary function of gluconeogenesis?
Synthesis of glucose from non-carbohydrate sources
Mainly occurs in the liver and kidney
MCQ: Which enzyme is NOT bypassed in gluconeogenesis?
Phosphoglycerate kinase
MCQ: What is the role of fructose-1,6-bisphosphatase in gluconeogenesis?
Converts fructose-1,6-bisphosphate to fructose-6-phosphate
MCQ: Which pathway is closely linked to gluconeogenesis for lactate recycling?
Cori cycle
MCQ: Why can’t Acetyl CoA contribute to gluconeogenesis?
It cannot be converted back to pyruvate
MCQ: Which enzyme catalyzes the conversion of pyruvate to oxaloacetate in gluconeogenesis?
Pyruvate carboxylase
MCQ: What is the end product of anaerobic glycolysis?
Lactate
MCQ: What is the function of aldolase in glycolysis?
Cleaves fructose-1,6-bisphosphate into two 3-carbon molecules
MCQ: What inhibits enolase activity?
Fluoride
MCQ: What happens in pyruvate kinase deficiency?
Hemolytic anemia
MCQ: What is the major regulatory hormone of glycolysis?
Insulin
MCQ: What is another name for the Krebs cycle?
Citric acid cycle / TCA cycle
MCQ: Where does the Krebs cycle occur?
Mitochondria
MCQ: Which enzyme catalyzes the conversion of pyruvate to acetyl CoA before entering the Krebs cycle?
Pyruvate dehydrogenase
MCQ: What is the first step of the Krebs cycle?
Condensation of acetyl CoA with oxaloacetate to form citrate
MCQ: What is the main function of the Krebs cycle?
Oxidation of acetyl CoA to produce ATP and reducing equivalents
MCQ: Which enzyme is responsible for the production of FADH₂ in the Krebs cycle?
Succinate dehydrogenase
MCQ: How many ATP molecules are generated per cycle of the Krebs cycle?
12 ATP (or 10 ATP as per recent evidence)
MCQ: How many molecules of NADH are produced per turn of the Krebs cycle?
3
MCQ: Which of the following inhibits citrate synthase?
ATP, NADH, Acetyl CoA, and Succinyl CoA
MCQ: Which of the following enzymes is the rate-limiting step of the Krebs cycle?
Isocitrate dehydrogenase
MCQ: What is the total number of CO₂ molecules released per acetyl CoA in the Krebs cycle?
2
MCQ: Which enzyme is activated by ADP and inhibited by ATP in the Krebs cycle?
Isocitrate dehydrogenase
MCQ: What is the fate of NADH and FADH₂ produced in the Krebs cycle?
They enter the electron transport chain to generate ATP
MCQ: The complete oxidation of one glucose molecule produces how many ATP molecules via glycolysis, Krebs cycle, and oxidative phosphorylation?
38 ATP (or 36 ATP in some cases)
MCQ: Why is the Krebs cycle considered an amphibolic pathway?
It has both catabolic and anabolic roles
MCQ: What is glycogenesis?
The synthesis of glycogen from glucose
MCQ: Where is glycogen primarily stored?
Liver and muscles
MCQ: What is the key enzyme in glycogenesis?
Glycogen synthase
MCQ: What is the role of UDP-glucose in glycogenesis?
It acts as an activated donor of glucose residues
MCQ: Which enzyme creates the branching points in glycogen synthesis?
Branching enzyme
MCQ: What is the primer required for glycogen synthesis?
Glycogenin
MCQ: What type of bonds are formed during glycogenesis?
α-1,4 and α-1,6 glycosidic bonds
MCQ: Which hormone stimulates glycogenesis?
Insulin
MCQ: What is glycogenolysis?
The breakdown of glycogen into glucose
MCQ: What is the key enzyme for glycogenolysis?
Glycogen phosphorylase
MCQ: Which enzyme removes the α-1,6 linked branches in glycogen?
Debranching enzyme
MCQ: What is the fate of glucose-6-phosphate in the liver after glycogenolysis?
It is converted into free glucose by glucose-6-phosphatase
MCQ: What happens to glucose-6-phosphate in muscles after glycogenolysis?
It enters glycolysis and produces ATP
MCQ: Which hormone stimulates glycogenolysis?
Glucagon
MCQ: What is the primary purpose of glycogenolysis in muscles?
To provide energy for muscle contraction
MCQ: What is another name for the HMP pathway?
Pentose phosphate pathway
MCQ: Where does the HMP pathway occur in the cell?
Cytoplasm
MCQ: What are the two phases of the HMP pathway?
Oxidative and non-oxidative
MCQ: What is the key enzyme in the oxidative phase of HMP shunt?
Glucose-6-phosphate dehydrogenase
MCQ: What is the main product of the oxidative phase of the HMP pathway?
NADPH
MCQ: What is the significance of NADPH produced in the HMP shunt?
It is used in biosynthesis reactions like fatty acid and nucleotide synthesis
MCQ: Which enzyme is involved in the non-oxidative phase of HMP shunt?
Transketolase
MCQ: Which vitamin is essential for transketolase activity?
Vitamin B1 (Thiamine)
MCQ: What are the two key intermediates generated in the non-oxidative phase?
Ribose-5-phosphate and fructose-6-phosphate
MCQ: What is the function of ribose-5-phosphate in the cell?
Nucleotide and nucleic acid synthesis
MCQ: How is the HMP pathway linked to glycolysis?
Through glucose-6-phosphate, which can enter either glycolysis or the HMP pathway
MCQ: What is the clinical significance of glucose-6-phosphate dehydrogenase (G6PD) deficiency?
Hemolytic anemia due to oxidative stress
MCQ: Which enzyme deficiency is used to diagnose thiamine (Vitamin B1) deficiency?
Transketolase
MCQ: Why is the HMP pathway called a “shunt” ?
It diverts glucose-6-phosphate from glycolysis to produce NADPH and ribose-5-phosphate
MCQ: In which type of cells is the HMP pathway particularly active?
Red blood cells and liver cells
