Exam1 Part 2 Flashcards
What is an enzyme?
Large polymers made of amino acids that act as catalysts, speeding up chemical reactions necessary for life
Enzymes change the chemical structure of small organic molecules, known as substrates.
What are enzymes made of and how do they work?
Made of amino acids linked by peptide bonds; they lower the activation energy of reactions
This allows reactions to occur at a rate consistent with life.
How are enzymes synthesized in the cell?
Through the central dogma: DNA → RNA → Protein
Genes are transcribed into mRNA, which is translated into protein by ribosomes.
What is a metabolic pathway?
A series of enzyme-catalyzed reactions that transform a substrate into another compound
Functions include energy production, detoxification, or synthesis of necessary molecules.
What is the difference between anabolic and catabolic reactions?
Anabolic reactions build complex molecules; catabolic reactions break down molecules to release energy
Examples include protein synthesis for anabolic and glycolysis for catabolic.
What does Gibbs free energy indicate?
Indicates whether a reaction is spontaneous; a negative ΔG signifies a spontaneous process
This is important in determining the direction of metabolic reactions.
What is coupling in relation to metabolism?
Energy-releasing reactions are coupled with energy-requiring reactions
This drives biological processes.
What is the role of oxygen in human metabolism?
Final electron acceptor in the electron transport chain, essential for ATP production in aerobic respiration
What is the primary energy source for most cells?
Glucose
It is absorbed in the intestines and transported through the bloodstream to various tissues.
How is glucose transported upon absorption?
Facilitated by GLUT transporters and sodium-dependent glucose transporters (SGLTs)
For example, GLUT4 is insulin-dependent and located in muscle and adipose tissues.
What are the consequences of defects in glucose transporters?
GLUT1 deficiency causes developmental delays; GLUT2 deficiency leads to Fanconi-Bickel syndrome
What are the basic reactions of glycolysis?
Consists of 10 enzymatic steps converting glucose to pyruvate while producing ATP and NADH
What is the net gain of ATP and NADH in glycolysis?
2 ATP and 2 NADH molecules per glucose molecule
What is allosteric regulation in glycolysis?
ATP and citrate inhibit, while AMP activates key enzymes like phosphofructokinase (PFK1)
How does hormonal regulation affect glycolysis?
Insulin promotes glycolysis, while glucagon inhibits it
What happens to pyruvate under limited oxygen conditions?
Converted to lactate to regenerate NAD+ and sustain glycolysis
The Cori cycle transports lactate to the liver, where it is converted back to glucose.
What is the difference between glycolysis and gluconeogenesis?
Glycolysis breaks down glucose; gluconeogenesis synthesizes glucose from non-carbohydrate precursors
Irreversible steps in glycolysis are bypassed in gluconeogenesis.
What is the overall reaction of the pyruvate dehydrogenase reaction?
Pyruvate + CoA + NAD+ → Acetyl-CoA + CO2 + NADH
What inhibits and activates pyruvate dehydrogenase?
Inhibited by acetyl-CoA, NADH, and ATP; activated by ADP and pyruvate
What vitamins are required for the pyruvate dehydrogenase reaction?
Requires TPP (B1), FAD (B2), NAD (B3), CoA (B5), and lipoic acid
How does pyruvate dehydrogenase relate to the TCA cycle?
Links glycolysis to the TCA cycle by converting pyruvate to acetyl-CoA
What are important TCA cycle intermediates?
- Citrate (fatty acid synthesis)
- α-ketoglutarate (amino acid synthesis)
- Succinyl-CoA (heme synthesis)
- Oxaloacetate (gluconeogenesis)
How does fructose enter glycolysis?
Via fructose-1-phosphate; galactose enters as glucose-6-phosphate
What defects are associated with fructose and galactose metabolism?
- Fructokinase deficiency causes essential fructosuria
- Aldolase B deficiency leads to hereditary fructose intolerance
- Galactokinase or galactose-1-phosphate uridyltransferase deficiencies cause galactosemia
What are the major products of the pentose phosphate pathway?
- NADPH
- Ribose 5-Phosphate
What is the role of NADPH in the body?
Used in fatty acid synthesis, antioxidant defense, and immune response
What is the function of ATP synthase?
Uses the proton gradient to synthesize ATP from ADP and Pi
What enzymes are involved in glycogen breakdown?
- Glycogen phosphorylase
- Debranching enzyme
- Phosphoglucomutase
What hormones regulate glycogen metabolism?
Glycogen breakdown is promoted by glucagon and epinephrine; insulin stimulates synthesis
What condition can high insulin levels in infants lead to?
Neonatal hypoglycemia due to maternal hyperglycemia
What is McArdle’s Disease?
A deficiency in muscle glycogen phosphorylase causing exercise intolerance, muscle cramps, and rhabdomyolysis
