Biochemistry 2: Metabolic Pathways Overview

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Questions and Answers

What is the primary function of the liver in relation to surplus amino acids?

Store surplus amino acids for later use.

Synthesize proteins using surplus amino acids to replace those degraded. (correct)

Convert surplus amino acids into glucose for energy production.

Decompose surplus amino acids into waste products for excretion.

What is the primary destination of surplus amino acids released from the liver?

Muscle tissue for energy production.

Brain tissue for neurotransmitter synthesis.

Other tissues for protein synthesis. (correct)

Adipose tissue for fat storage.

Which of the following is NOT a primary reason for amino acid degradation in the liver?

To eliminate excess amino acids from the bloodstream.

To generate precursors for other important molecules.

To synthesize essential amino acids that the body cannot produce. (correct)

To provide energy during periods of starvation.

What is the primary metabolic state during which amino acid degradation is elevated?

Post-absorptive state between meals. (A) Signup and view all the answers

Which of the following is a primary factor influencing the amount of surplus amino acids available for protein synthesis?

The amount of dietary protein consumed. (C) Signup and view all the answers

Which molecule directly stimulates phosphofructokinase-1 (PFK-1) in the liver, leading to increased glycolysis?

Fructose-2,6-bisphosphate (D) Signup and view all the answers

What effect does dephosphorylation have on most anabolic enzymes?

Activation (B) Signup and view all the answers

Which of the following enzymes is inhibited by dephosphorylation?

Glycogen phosphorylase (A) Signup and view all the answers

In the post-absorptive state, such as during fasting, which of these hormonal changes occurs?

Decreased insulin and increased glucagon (B) Signup and view all the answers

During the post-absorptive state, which of these processes is most prominent in the body?

Catabolism of TAGs, proteins and glycogen (D) Signup and view all the answers

If an enzyme is activated by phosphorylation, what is most likely to happen during a period of fasting?

The enzyme's activity will increase if it promotes catabolism. (B) Signup and view all the answers

During the fasting state, which of the following sources of substrates becomes most significant?

Catabolic breakdown of stored molecules. (B) Signup and view all the answers

When transitioning from a well-fed to a fasting state, what is the primary direction of change in substrate flow?

Substrate flow shifts towards catabolic processes. (A) Signup and view all the answers

Which of the following best describes the brain's primary substrate for energy production?

Glucose. (C) Signup and view all the answers

In the context of reciprocal changes between fasting and well-fed states, what would be the opposite effect of phosphorylation activating an enzyme that promotes substrate storage?

Dephosphorylation would activate the enzyme. (A) Signup and view all the answers

What is the primary reason the liver is considered a nutrient distribution center?

Its role in portal drainage and smoothing substrate fluctuations. (C) Signup and view all the answers

Which of the following best describes the liver's role in managing nutrient availability?

It maintains a steady state by smoothing changes in substrate availability. (D) Signup and view all the answers

What is a key function of the liver in relation to nutrient absorption?

It processes and distributes absorbed nutrients throughout the body. (C) Signup and view all the answers

Why is portal drainage essential for the liver's absorptive function?

It channels blood rich in nutrients directly from the digestive system to the liver. (C) Signup and view all the answers

What is meant by the liver 'smoothing fluctuations in the availability of substrates'?

It balances out high and low levels of nutrients, leading to a more consistent supply. (B) Signup and view all the answers

What is the process of converting deaminated amino acids primarily used for?

Oxidation and fatty acid synthesis (B) Signup and view all the answers

Which of the following compounds can result from the C-skeleton of deaminated amino acids?

Pyruvate (B) Signup and view all the answers

In addition to pyruvate, which other molecule is a product of deaminated amino acids?

Acetyl CoA (A) Signup and view all the answers

Which metabolic cycle is commonly associated with the intermediates derived from deaminated amino acids?

Krebs cycle (B) Signup and view all the answers

What is the main type of synthesis that can occur from the C-skeletons obtained from deaminated amino acids?

Fatty acid synthesis (C) Signup and view all the answers

What happens to the brain's energy source after several weeks of fasting?

It switches to using ketone bodies. (A) Signup and view all the answers

How does prolonged fasting affect the need for muscles proteolysis?

It decreases the need for muscle proteolysis. (A) Signup and view all the answers

What is the effect on gluconeogenesis after several weeks of fasting?

It decreases due to reduced demand from the brain. (C) Signup and view all the answers

What adaptation occurs in the brain during prolonged fasting?

Shift to utilizing ketone bodies for energy. (D) Signup and view all the answers

Which statement correctly describes the relationship between ketone bodies and gluconeogenesis after weeks of fasting?

Ketone bodies reduce the demand for both gluconeogenesis and muscle proteolysis. (A) Signup and view all the answers

Study Notes

Biochemistry 2

Metabolic Pathways (Well-Fed and Fasting States): Metabolic pathways involve the flow of intermediates, substrate availability, allosteric regulation of enzymes, reversible phosphorylation, and enzyme synthesis.
Absorptive State: Following a meal, glucose, amino acids, and TAGs (in chylomicrons) increase. Insulin promotes anabolic processes, activating liver glycolysis via F2,6BP and inhibiting gluconeogenesis.
Post-Absorptive State: During fasting, insulin levels decrease and glucagon increases. This shifts the body to a catabolic state, breaking down glycogen, fats, and proteins to maintain blood glucose levels.
Liver Function: The liver plays a central role, maintaining adequate glucose supply for the brain, mobilizing fatty acids and ketone bodies, and distributing nutrients. It acts as a crucial nutrient distribution center.
Carbohydrates (CHO): In the well-fed state, glucose is primarily phosphorylated to G6P, glycogen is synthesized, and glycolysis is upregulated. In the fasting state, glycogen is broken down (glycogenolysis), and gluconeogenesis produces glucose from other sources.
Fats (FAT): During the absorptive state, TAG synthesis increases and fatty acid synthesis occurs. During the post-absorptive state, lipolysis is activated, releasing fatty acids to be used for energy, and ketogenesis produces ketone bodies.
Proteins (PROTEIN): During the absorptive state, amino acids are used for protein synthesis. In fasting, protein degradation increases, providing amino acid carbon skeletons for gluconeogenesis.
Adipose Tissue: In the absorptive state, insulin promotes glucose uptake, glycogen synthesis, and TAG synthesis, while in the post-absorptive state, lipolysis increases, releasing fatty acids for energy needs.
Brain: The brain relies almost exclusively on glucose for energy during the well-fed state. During prolonged fasting, the brain can use ketone bodies alongside blood glucose.
Muscles: During the absorptive state, muscle glycogen synthesis is active, utilizing glucose as fuel. When glycogen stores are depleted, muscle shifts to fatty acids as energy source.

Summary of Different States

Fed State: Glucose is the main energy source, stored as glycogen, and excess glucose is converted to fat.
Fasting State: Ketones from fats provide energy. Gluconeogenesis makes glucose from non-carbohydrates. Glycogen breakdown is a way to boost glucose supply in the body. Proteins can be used for energy needs in very long periods of fasting.

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Description

This quiz covers key concepts in biochemistry related to metabolic pathways during well-fed and fasting states. It addresses the roles of insulin, glucagon, and the liver in maintaining metabolic balance, along with the processing of carbohydrates, proteins, and fats. Test your understanding of these crucial biochemical processes!