Question 1

What percentage of a healthy adult's energy need is met by metabolism of protein?

Accepted Answer

Proteins typically provide 10-20% of the total daily energy needs for a healthy adult, with fats and carbohydrates covering the majority of the remaining energy requirements.

Question 2

Two key amino acids in the catabolism of nitrogen atoms in amino acids are

Accepted Answer

Aspartate and glutamate are key amino acids in the catabolism of nitrogen atoms in amino acids. They are involved in the transamination reactions that transfer amino groups from amino acids to α-ketoglutarate, which is then converted to glutamate. Glutamate can then be further catabolized through the urea cycle to eliminate excess nitrogen from the body. Aspartate is also involved in the urea cycle and can accept an amino group from glutamate to form asparagine. Phenylalanine, tyrosine, alanine, and valine are not directly involved in the catabolism of nitrogen atoms in amino acids.

Question 3

The enzyme that removes an amine group from an amino acid and moves it to α-ketoglutarate is classified as a

Accepted Answer

The enzyme described in the question is performing transamination, which involves transferring an amine group from an amino acid to α-ketoglutarate. Therefore, the correct answer is C) transaminase.

Question 4

When the amino acid alanine is deaminated,it is converted to

Accepted Answer

When alanine is deaminated, it loses its amino group (-NH2) and the resulting molecule is pyruvate, which can enter into the Krebs cycle for energy production. Glutamate can also be formed from alanine deamination, but it requires the addition of a nitrogen atom from ammonia. Acetate and oxaloacetate are not direct products of alanine deamination. Urea is a waste product of amino acid breakdown in mammals, but it is not a direct product of alanine deamination.

Question 5

When an amine group is transferred to α-ketoglutarate,one product is always

Accepted Answer

When an amine group is transferred to α-ketoglutarate, the resulting compound is glutamate. This reaction is part of the process of transamination, which is important for the synthesis of many amino acids. While glycine, aspartate, and alanine are also amino acids, they are not necessarily produced when an amine group is transferred to α-ketoglutarate. Leucine, on the other hand, is not directly involved in the transamination reaction.

Question 6

If nitrogen is to be excreted from the body,it is converted to which chemical?

Accepted Answer

Nitrogen is converted to urea in the liver and is excreted through urine in mammals.

Question 7

The first step in amino acid catabolism is ________.

Accepted Answer

Transamination is the first step in amino acid catabolism, where an amino group is transferred from the amino acid to an alpha-keto acid, forming a new amino acid and alpha-keto acid.

Question 8

When α-ketoglutarate accepts an amine group,it is converted to

Accepted Answer

When α-ketoglutarate accepts an amine group, it becomes glutamate through transamination catalyzed by transaminase enzymes. Therefore, option A, glutamate, is the correct answer. Other options like pyruvate, acetyl, and urea are not involved in the transamination process. Transaminase is not a product but rather a class of enzymes that facilitate the transfer of amino groups from one molecule to another.

Question 9

α-ketoglutarate is converted to glutamate by

Accepted Answer

α-ketoglutarate is converted to glutamate by accepting an amine group, a process catalyzed by the enzyme glutamate dehydrogenase. This reaction is a key step in the synthesis of amino acids and involves the addition of an amine group to the α-ketoglutarate, forming glutamate.

Question 10

When the amine group of glutamate is replaced with a carbonyl group,the process is called

Accepted Answer

The process of replacing the amine group of glutamate with a carbonyl group is known as oxidative deamination, where the amine group is removed and converted to a keto group, typically producing α-ketoglutarate and ammonia.

Question 11

α-ketoacids are produced as a result of a transamination reaction with ________ acting as the donor molecule.

Accepted Answer

Glutamate is the most common amino acid acting as the donor molecule in transamination reactions, producing α-ketoacids as a result. Aspartate and oxaloacetate can also act as donors in some specific transamination reactions, but they are less common than glutamate. Urea and ornithine are not involved in transamination reactions.

Question 12

The amino acid pool is the collection of

Accepted Answer

The amino acid pool refers to all free amino acids in the body that are available for protein synthesis or other metabolic processes. It includes amino acids from dietary sources, those released during the breakdown of body proteins, and any synthesized by the body.

Question 13

Which of the following enzymes is not involved in the digestion of proteins?

Accepted Answer

Amylase is an enzyme that breaks down carbohydrates, not proteins. The other four enzymes listed are all involved in the digestion of proteins.

Question 14

One of the most important functions of amino acids is for the synthesis of

Accepted Answer

Amino acids are the building blocks of body proteins, making protein synthesis the most important function of amino acids. While amino acids can also be used for energy production and the synthesis of other molecules such as purines and pyrimidines, their primary role is in the formation of proteins.

Question 15

The process of oxidative deamination of an amino acid produces which of the following?

Accepted Answer

The answer of The process of oxidative deamination of an...

Question 16

The common features of catabolism of all amino acids include

Accepted Answer

The common feature of catabolism of all amino acids is the removal of the amine group in the form of ammonia or ammonium and the conversion of the carbon skeleton to intermediates which can enter the citric acid cycle. This process is known as deamination and is followed by transamination or transfer of the amine group to a suitable acceptor molecule. The carbon skeletons are then converted into intermediates which can be used for energy production or for gluconeogenesis. The waste products produced are ammonia or urea depending on the organism.

Question 17

The structural formula of glutamate is ________.

Accepted Answer

The answer of The structural formula of glutamate is ________.
...

Question 18

Which statement best summarizes the digestion of proteins?

Accepted Answer

The digestion of proteins involves the hydrolysis of peptide linkages, breaking down the protein into a mixture of amino acids. Amine groups may also be removed from some amino acids during this process, but this is not true for all amino acids. Denaturation by stomach acid may occur, but it is not a necessary step in digestion. The combination of amino acids to form proteins or enzymes is a process known as protein synthesis, which is not related to digestion.

Question 19

Which is the correct order for the steps in digestion and absorption of proteins?
I.hydrolysis by pancreatic lipases
II.denaturation by stomach acid
III.hydrolysis by pepsin
IV.active transport into the bloodstream

Accepted Answer

Proteins are denatured by stomach acid in the first step, followed by hydrolysis by pepsin in the stomach. The partially digested proteins then move to the small intestine where they are further hydrolyzed by pancreatic enzymes. The final step involves active transport of the absorbed amino acids into the bloodstream. Therefore, the correct order is II, III, I, IV. Choice D is the only option that follows this order.

Question 20

When glutamate acts as the source of an amino group,the enzyme involved is a

Accepted Answer

The answer of When glutamate acts as the source of...

Quiz 27: Protein and Amino Acid Metabolism