Protein Degradation and Use of Amino Acids for Energy

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What is the main reason excess amino acids can be challenging for mammalian metabolism?

Ammonia production

Which part of the body is responsible for converting amino acid carbon skeletons into intermediates of the Krebs cycle for energy production?

Liver

Which enzyme in the small intestine is responsible for breaking down proteins into smaller peptides?

Trypsin

During which conditions are amino acids primarily used for energy production?

During fasting

Where are peptidases found in the body?

Small intestine brush border

What is the fate of ammonia produced from amino acid degradation in mammalian metabolism?

Converted to urea or other less toxic forms

Which biological role do amino acids play in immune function?

As building blocks of proteins

What happens to amino acids during dietary protein excess?

Used for energy production

Which enzymes are responsible for the breakdown of proteins into smaller peptides by cleaving peptide bonds?

Trypsin and chymotrypsin

What is the primary fate of amino acids under conditions of fasting or starvation when carbohydrates are not available?

Deaminated and used for energy production

What role do amino acids play as precursors in biological processes?

Precursors for synthesis of hormones and neurotransmitters

What is the purpose of a zymogen in enzyme regulation?

To prevent damage to cells and tissues

In the context of amino groups, what is the role of α-ketoglutarate?

Accepts an amino group to form glutamate

What distinguishes transamination from oxidative deamination in amino acid metabolism?

Formation of new amino acids vs. removal of ammonia

How is ammonia primarily transported to the liver for detoxification?

As glutamine or part of alanine in the glucose-alanine cycle

Which best describes the physiological function of the Glucose-Alanine Cycle?

Facilitating nitrogen removal from muscle to the liver

What is a characteristic excretory form of nitrogen in birds and reptiles?

Uric acid

What reaction is catalyzed by alanine transaminase?

Conversion of alanine and α-ketoglutarate to pyruvate and glutamate

How is the urea cycle related to the citric acid cycle?

Metabolically linked, forming the 'Krebs bicycle'

What activates carbamoyl phosphate synthase I, a key enzyme in the urea cycle?

N-acetylglutamate

Which category of amino acids can lead to ketone body formation during degradation?

Ketogenic amino acids

What can a carbon skeleton with 3 carbons from an amino acid be converted into?

Pyruvate for gluconeogenesis or energy production

What metabolite can glycine contribute to during its degradation through the glycine cleavage system?

Urea formation

Which enzyme is responsible for converting acyl-CoA to trans-enoyl-CoA during β-oxidation of fatty acids?

Enoyl-CoA hydratase

What is the role of carnitine in the β-oxidation of fatty acids?

Transferring the acyl group across the mitochondrial membrane

What is produced at the end of the β-oxidation cycle of fatty acids?

Propionyl-CoA

Which enzyme is involved in converting L-β-hydroxyacyl-CoA to β-ketoacyl-CoA?

β-hydroxyacyl-CoA dehydrogenase

During β-oxidation of fatty acids, what does β-ketothiolase do?

Converts β-ketoacyl-CoA to acetyl-CoA

What is the function of carnitine-palmitoyl transferase II during β-oxidation?

Converting acyl group back to CoA inside the mitochondrion

Which molecule is NOT a product of the β-oxidation cycle of fatty acids?

Glycerol

Which molecule inhibits fatty acid entry into mitochondria for beta-oxidation by inhibiting CPT I?

Malonyl-CoA

Where does fatty acid synthesis primarily occur?

Cytosol

Which enzyme catalyzes the synthesis of palmitate from acetyl-CoA and malonyl-CoA?

Fatty Acid Synthase (FAS)

In fatty acid synthesis, what provides the required NADPH?

Pentose Phosphate Pathway

Which molecule regulates Acetyl-CoA Carboxylase (ACC) that converts acetyl-CoA to malonyl-CoA?

Citrate and Palmitoyl-CoA

During periods of low carbohydrate availability, acetyl-CoA is converted to which compound in the liver?

Ketone bodies

'Ketone bodies serve as an alternative energy source for peripheral tissues' is particularly true during which physiological state?

Fasting

'Ketoacidosis' is a serious condition that can occur due to overproduction of which compounds?

'Ketone bodies'

Which enzyme converts arachidonic acid to prostaglandins during eicosanoid synthesis?

Cyclooxygenases (COX I and COX II)

Where are steroids synthesized from cholesterol?

Endoplasmic Reticulum (ER)

What is the key early step in cholesterol synthesis that is a major regulatory point?

HMG-CoA Reductase and Mevalonate

What is the specific role of carnitine in the β-oxidation of fatty acids?

Shuttling the acyl-carnitine across the outer mitochondrial membrane

Which enzyme is responsible for converting L-β-hydroxyacyl-CoA to β-ketoacyl-CoA in the β-oxidation of fatty acids?

Acyl-CoA dehydrogenase

What is produced during thiolysis in the β-oxidation cycle of fatty acids?

Trans-enoyl-CoA

In the final cycle of β-oxidation of fatty acids with an odd number of carbons, how many propionyl-CoA molecules are produced?

One

Which enzyme adds water across the double bond in the β-oxidation of fatty acids?

β-Hydroxyacyl-CoA dehydrogenase

During β-oxidation, what is the role of FAD-dependent acyl-CoA dehydrogenase?

Add water across the double bond

What is the primary fate of ketone bodies in the body during fasting or carbohydrate-restricted diets?

Utilization as an energy source by peripheral tissues

Which enzyme catalyzes the synthesis of prostaglandins from arachidonic acid during eicosanoid synthesis?

Cyclooxygenase (COX)

What is the key early step in cholesterol synthesis that serves as a major regulatory point?

Formation of HMG-CoA from acetyl-CoA

What role does malonyl-CoA play in regulating fatty acid metabolism?

Inhibiting fatty acid synthesis

Where does eicosanoid synthesis primarily occur within the cell?

Cell membrane

During which condition do glucagon and epinephrine decrease the activity of Acetyl-CoA Carboxylase (ACC), reducing fatty acid synthesis?

Low energy availability

What is the primary electron donor required for fatty acid synthesis?

NADPH

Which molecule is released from phospholipids by PLA2 during eicosanoid synthesis?

Arachidonic acid

What is the consequence of overproduction of ketone bodies leading to high blood acidity?

Ketoacidosis

What is the primary energy source for peripheral tissues, including the brain, during fasting or carbohydrate-restricted diets?

Ketone bodies

Which enzyme catalyzes the conversion of acetyl-CoA to acetoacetate and other ketone bodies in the liver?

HMG-CoA synthase

Which compound holds the growing fatty acid chain during fatty acid synthesis?

Acyl carrier protein (ACP)

Explore the biological roles of amino acids as building blocks for proteins, precursors for hormones and neurotransmitters, and contributors to immune function. Understand how amino acids can be utilized as an energy source during dietary protein excess, fasting, or starvation.

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