Biochemistry: Amino Acids - Nitrogen Disposal (Part 1)

Questions and Answers

What percentage of liberated amino acids is typically recaptured for biosynthesis of new tissue protein in adults?

60-70%

75-80% (correct)

80-90%

50-60%

What is the effect of glucocorticoids on muscle tissue protein?

Increase protein synthesis

Increase protein degradation (correct)

No effect on protein levels

Cause protein denaturation

Which of the following represents a consequence of lysosomal activation?

Decreased intracellular proteolytic rate

No change in protein turnover

Increased intracellular proteolytic rate (correct)

Increased extracellular protein synthesis

In normal physiological conditions, how does the rate of protein synthesis compare to the rate of protein degradation?

Synthesis equals degradation Signup and view all the answers

Which hormone is primarily associated with increasing protein turnover?

Thyroid Hormone Excess Signup and view all the answers

What is the primary fate of the remaining 20-25% of liberated amino acids after protein degradation?

Converted to urea Signup and view all the answers

During the degradation process, what happens to the carbon skeletons of amino acids?

Degraded to amphibolic intermediates Signup and view all the answers

What is the primary role of protein degradation in adults?

To recycle amino acids for new proteins Signup and view all the answers

What influences the half-life of a protein like trypsinogen?

The nature of the N-terminal residue Signup and view all the answers

What is the half-life of a protein with serine as its N-terminal amino acid?

More than 20 hours Signup and view all the answers

What is one of the main consequences of diets low in protein?

Undigested protein in the feces Signup and view all the answers

What does trypsin do besides activating itself?

Activates other pancreatic zymogens Signup and view all the answers

What is the recommended dietary allowance for protein for a 70 kg individual?

56 gm protein/day Signup and view all the answers

What condition could lead to pancreatic secretion deficiency?

Chronic pancreatitis Signup and view all the answers

Which of the following is classified as a pancreatic zymogen?

Chymotrypsin Signup and view all the answers

What can result from a deficiency in pancreatic secretion?

Steatorrhea Signup and view all the answers

What is the primary function of active transport systems in relation to amino acids?

To facilitate the uptake of amino acids against their concentration gradient Signup and view all the answers

Which amino acids have the highest gradient size in active transport systems?

Glutamate and Glutamine Signup and view all the answers

What is the role of Na+ in the luminal transport process regarding amino acids?

It is essential for Na+-dependent transport of amino acids Signup and view all the answers

Which of the following accurately describes the COAL system?

It is involved in transporting Cystine and dibasic amino acids Signup and view all the answers

Which product results from the peptic hydrolysis of proteins?

Large polypeptides and some free amino acids Signup and view all the answers

How does pepsin function in the stomach?

It denatures proteins to aid in digestion Signup and view all the answers

What primarily drives the active transport of amino acids?

Hydrolysis of ATP Signup and view all the answers

Which statement about contraluminal transport is accurate?

It operates independently of sodium ions Signup and view all the answers

What are the primary elements that make up amino acids?

Carbon, Hydrogen, Oxygen, Nitrogen Signup and view all the answers

What is the end product of the removal of alpha-amino groups during the first phase of amino acid catabolism?

Ammonia Signup and view all the answers

How are alpha-ketoacids relevant to amino acids?

They serve as energy-producing intermediates. Signup and view all the answers

What byproduct of amino acid catabolism is primarily used for urea synthesis?

Ammonia Signup and view all the answers

What process is involved in the hydrolysis of polypeptides to free amino acids?

Proteolysis Signup and view all the answers

Which of the following are common dietary sources of amino acids?

Meat and Legumes Signup and view all the answers

What is the approximate daily intake of dietary protein that provides amino acids?

70-100 grams Signup and view all the answers

What occurs to excess amino acids that cannot be stored in the body?

They undergo degradation immediately. Signup and view all the answers

Which statement accurately describes the process of transamination?

It involves the transfer of an amino group from an amino acid to a keto acid. Signup and view all the answers

In which of the following conditions would you expect increased plasma levels characterized by ALT < AST?

Myocardial infarction Signup and view all the answers

Which organ primarily facilitates oxidative deamination, resulting in the release of free ammonia?

Liver Signup and view all the answers

What is the initial step in amino acid catabolism?

Transamination Signup and view all the answers

What characterizes nonhepatic disease in terms of plasma enzyme levels?

Increased AST and decreased ALT levels Signup and view all the answers

Study Notes

Overview of Amino Acids and Nitrogen Disposal

Amino acids are composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) atoms.
Excess amino acids cannot be stored; they are rapidly degraded.
Amino acids are derived from dietary intake, de novo synthesis, and normal protein degradation.

Catabolism of Amino Acids

First Phase:
- Involves the removal of alpha-amino groups via transamination and oxidative deamination.
- Products are ammonia and corresponding alpha-ketoacids.
- Ammonia primarily contributes to urea synthesis, excreted in urine.
- Alpha-ketoacids serve as carbon skeletons for amino acids.
Second Phase:
- Carbon skeletons of alpha-ketoacids are intermediates in energy metabolism.
- Daily dietary input: 70-100 grams of dietary protein and 35-200 grams of endogenous protein.
- Proteins are hydrolyzed to free amino acids for absorption, aided by proteolytic enzymes.

Protein Denaturation and Turnover

Adults degrade 1-2% of total body protein daily, mostly from muscle.
75-80% of liberated amino acids are recaptured for new tissue protein synthesis; remaining 20-25% is converted to urea.
Loss of native protein configuration leads to increased proteolytic breakdown.

Factors Influencing Protein Turnover

Glucocorticoids: Increase degradation of muscle tissue protein.
Thyroid Hormone Excess: Enhances protein turnover rate.
Insulin: Affects protein half-life based on the N-terminal residue of proteins.

Role of Dietary Protein

Provides energy secondarily after carbohydrates and fats.
Recommended Dietary Allowance (RDA) for protein is 56 grams per day for a 70 kg individual.
Low protein diets can lead to incomplete protein digestion and absorption issues, leading to steatorrhea.

Digestion of Proteins

Pepsin, secreted in inactive form (pepsinogen) by stomach serous cells, is an acid-stable endopeptidase that denatures proteins.
Main products from peptic hydrolysis include large polypeptides and some free amino acids.

Amino Group Handling and Deamination

Nonhepatic diseases can cause increased plasma levels of transaminases, especially after myocardial infarction or muscle disorders.
Transamination transfers amino groups from amino acids to α-keto acids.
Oxidative deamination liberates amino groups as free ammonia, primarily in the liver and kidney.

Transport Mechanisms

Active transport systems drive amino acids from lower to higher concentration areas, utilizing ATP.
Variability in amino acid transport gradients; highest for glutamate and glutamine.
COAL System mediates uptake of cystine and dibasic amino acids like ornithine, arginine, and lysine.
Na+-dependent and Na+-independent transport mechanisms operate for luminal and contraluminal transport, respectively.

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Description

This quiz covers key concepts in biochemistry focusing on amino acids and their nitrogen disposal mechanisms. It highlights their elemental composition, sources of amino acids, and introductory phases of catabolism. Perfect for students looking to understand the foundational aspects of amino acids.