S13 - Urea Cycle: Amino Acid Catabolism in Mammals

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Questions and Answers

What is a source of amino acids for catabolism?

Excess sugars from diet

Fat stored in adipose tissue

DNA from dead cells

Leftover amino acids from normal protein turnover (correct)

All amino acids can undergo gluconeogenesis.

False

What is the purpose of the ubiquitin tagging system in protein degradation?

To recognize and tag proteins that need to be degraded.

Proteins are continuously synthesized and degraded, with half-lives ranging from ___________ to weeks.

minutes Signup and view all the answers

What is the primary function of proteasome in protein degradation?

To hydrolyze ubiquitinated proteins Signup and view all the answers

Match the following protein types with their characteristic half-lives:

Structural proteins (such as collagen) = Digestive enzymes Months or years = Minutes to weeks Signup and view all the answers

Lysosomal hydrolysis degrades all proteins in the body.

False Signup and view all the answers

What is the significance of protein turnover in tissues undergoing structural rearrangement?

High rates of protein degradation occur in tissues undergoing structural rearrangement, such as uterine tissue during pregnancy. Signup and view all the answers

What is the fate of the nitrogen atom after deamination of an amino acid?

It is incorporated into other compounds Signup and view all the answers

Amino acid degradation occurs mainly in the kidneys.

False Signup and view all the answers

What is the purpose of deamination in amino acid catabolism?

To remove the nitrogen atom from the amino acid, allowing the carbon skeleton to enter the metabolic mainstream. Signup and view all the answers

The α-keto acids resulting from deamination are further metabolized to enter the _____ mainstream.

metabolic Signup and view all the answers

How do different animals excrete excess nitrogen?

Through ammonia, uric acid, or urea Signup and view all the answers

Match the following compounds with their role in nitrogen excretion:

Ammonia = Excreted by some aquatic animals Uric acid = Excreted by birds and reptiles Urea = Excreted by mammals Signup and view all the answers

What is the role of N-acetyl-glutamate in the urea cycle?

To activate carbamoyl phosphate synthetase I Signup and view all the answers

Amino acids are classified as either glucogenic or ketogenic, but not both.

False Signup and view all the answers

What is the difference between glucogenic and ketogenic amino acids?

Glucogenic amino acids yield pyruvate or intermediates of the citric acid cycle, while ketogenic amino acids yield acetoacetate or one of its precursors. Signup and view all the answers

Carbamoyl phosphate synthetase I is the main enzyme that ______________ the urea cycle.

starts Signup and view all the answers

Match the following amino acids with their classification as glucogenic, ketogenic, or both:

Tyrosine = Both Threonine = Both Soleucine = Ketogenic Tryptophan = Both Signup and view all the answers

What is the result of the catabolism of ketogenic amino acids?

Ketone body production Signup and view all the answers

Essential amino acids can be synthesized by the human body.

False Signup and view all the answers

What is the role of arginine in the urea cycle?

Arginine activates carbamoyl phosphate synthetase I Signup and view all the answers

Amino acids are classified as glucogenic, ketogenic, or ______________ based on the intermediates produced during their catabolism.

both Signup and view all the answers

What is the result of the catabolism of glucogenic amino acids?

Glucose production Signup and view all the answers

Study Notes

Amino Acid Catabolism in Mammals

Sources of amino acids for catabolism: leftover amino acids from normal protein turnover, dietary amino acids that exceed body's protein synthesis needs, and proteins broken down to supply amino acids for energy when sugars are scarce (starvation, malnutrition, diabetes mellitus).
Not all amino acids can undergo gluconeogenesis, and only ketogenic ones can do so.

Protein Turnover

Proteins are continuously synthesized and degraded (turnover), including digestive enzymes and plasma proteins.
High rates of protein degradation occur in tissues undergoing structural rearrangement, such as uterine tissue during pregnancy.
Structural proteins, such as collagen, are metabolically stable and have half-lives measured in months or years.
Lysosomal hydrolysis degrades some proteins.

Protein Degradation

Some proteins are targeted for degradation by a covalent attachment of ubiquitin (Ub) at the C-terminus.
Proteasome hydrolyzes ubiquitinated proteins.
Ubiquitin tagging system recognizes proteins that need to be degraded.

Deamination

The α-amino group must be removed from amino acids, as there are no nitrogenous compounds in energy transduction pathways.
Deamination is an obligatory step in catabolism of all amino acids.
Once removed, nitrogen can be incorporated into other compounds or excreted.

Urea Cycle

The major site of amino acid degradation in mammals is the liver.
Carbamoyl phosphate synthetase I is the main enzyme that starts the urea cycle.
This enzyme is activated by N-acetyl-glutamate, which is formed when glutamate and acetyl-CoA concentrations are high.

Amino Acid Classification

Amino acids are classified as glucogenic, ketogenic, or both based on the intermediates produced during their catabolism.
Glucogenic amino acids yield pyruvate or citric acid cycle intermediates, while ketogenic amino acids yield acetoacetate or acetyl-CoA.

Amino Acid Degradation

Different amino acids have different degradation pathways.
Some amino acids, such as phenylalanine, tyrosine, and tryptophan, are both glucogenic and ketogenic.

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Description

This quiz covers the sources of amino acids for catabolism, including leftover amino acids from normal protein turnover and dietary amino acids exceeding body's protein synthesis needs. It also explores the breakdown of proteins in the body.

S13 - Urea Cycle: Amino Acid Catabolism in Mammals

Podcast Beta

Questions and Answers

What is a source of amino acids for catabolism?

All amino acids can undergo gluconeogenesis.

What is the purpose of the ubiquitin tagging system in protein degradation?

Proteins are continuously synthesized and degraded, with half-lives ranging from ___________ to weeks.

What is the primary function of proteasome in protein degradation?

Match the following protein types with their characteristic half-lives:

Lysosomal hydrolysis degrades all proteins in the body.

What is the significance of protein turnover in tissues undergoing structural rearrangement?

What is the fate of the nitrogen atom after deamination of an amino acid?

Amino acid degradation occurs mainly in the kidneys.

What is the purpose of deamination in amino acid catabolism?

The α-keto acids resulting from deamination are further metabolized to enter the _____ mainstream.

How do different animals excrete excess nitrogen?

Match the following compounds with their role in nitrogen excretion:

What is the role of N-acetyl-glutamate in the urea cycle?

Amino acids are classified as either glucogenic or ketogenic, but not both.

What is the difference between glucogenic and ketogenic amino acids?

Carbamoyl phosphate synthetase I is the main enzyme that ______________ the urea cycle.

Match the following amino acids with their classification as glucogenic, ketogenic, or both:

What is the result of the catabolism of ketogenic amino acids?

Essential amino acids can be synthesized by the human body.

What is the role of arginine in the urea cycle?

Amino acids are classified as glucogenic, ketogenic, or ______________ based on the intermediates produced during their catabolism.

What is the result of the catabolism of glucogenic amino acids?

Study Notes

Amino Acid Catabolism in Mammals

Protein Turnover

Protein Degradation

Deamination

Urea Cycle

Amino Acid Classification

Amino Acid Degradation

Studying That Suits You

Description

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