Y1S2 002 III Biochem: Structure of Biopolymers

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Questions and Answers

What is the characteristic of D-a.a. in proteins?

They are not present in proteins (correct)

They are present in bacterial cell walls

They are present in polypeptide antibiotics

They are present in proteins

What determines the kind of amino acid?

The kinds of amino acids present (correct)

The number of carbon atoms

The order in which they are linked together

The spatial relationship of one amino acid to another

What is the classification of aspartate?

Monoaminodicarboxylic acid (correct)

Polar amino acid

Diaminomonocarboxylic acid

Non-polar amino acid

What is the characteristic of glycine?

It has no optical activity Signup and view all the answers

What is the α–carbon in an amino acid?

The carbon bearing the C=O and NH2 groups Signup and view all the answers

What is the function of biocatalysts in living cells?

Enzymes Signup and view all the answers

What is the primary consequence of α–KG depletion in the TCA cycle?

Reduced production of ATP Signup and view all the answers

What is the consequence of a complete block in any of the steps of the urea cycle?

Incompatibility with life Signup and view all the answers

What is the role of α-keto analogues in the treatment of hyperammonemia?

To convert NH3 to glutamate Signup and view all the answers

What is the outcome of a high concentration of NH4+ in the brain?

Shift of equilibrium of GDH reaction to the formation of glutamate Signup and view all the answers

What is the outcome of glutamate formation in the brain?

Depletion of α-keto glutarate Signup and view all the answers

Which enzyme is responsible for funneling amino groups from a variety of compounds to Glutamate for conversion to Ammonia?

Glutamate Transaminase Signup and view all the answers

What is the byproduct of the transamination reaction between Glutamate and α-Ketoglutarate?

Keto acid and NH4+ Signup and view all the answers

What is the characteristic of Portal System Encephalopathy (PSE)?

Acquired type of hyperammonemia Signup and view all the answers

Which two amino acids are the primary donors of amino groups to the urea cycle?

Aspartate and Glutamate Signup and view all the answers

What is the role of Glutamate-Aspartate Aminotransferase in amino acid metabolism?

It interconverts Glutamate and Aspartate Signup and view all the answers

What is the end product of the degradation of most amino acids in amino acid metabolism?

Urea Signup and view all the answers

What is the enzyme that precedes the urea cycle in amino acid metabolism?

Glutamate Dehydrogenase Signup and view all the answers

What is the result of a defect in the enzyme phenylalanine hydroxylase?

Phenylketonuria Signup and view all the answers

What is the byproduct of the reaction catalyzed by the enzyme homogentisate oxidase?

Fumarate Signup and view all the answers

What is the precursor molecule to melanin synthesis?

Tyrosine Signup and view all the answers

What is the result of a defect in the enzyme dihydropterin reductase?

Hyperphenylalaninemia Signup and view all the answers

What is the enzyme that catalyzes the conversion of phenylalanine to tyrosine?

Phenylalanine hydroxylase Signup and view all the answers

What is the result of a defect in the enzyme tyrosinase?

Albinism Signup and view all the answers

Which amino acid is converted to oxAA through transamination with α-KG?

Aspartate Signup and view all the answers

What is the biochemical defect in individuals with Maple Syrup Disease?

Absence of α-keto acid decarboxylase enzyme Signup and view all the answers

Which of the following amino acids is not a member of the C5 Family?

Aspartate Signup and view all the answers

What is the result of the blockage of oxidative decarboxylation of branched-chain amino acids?

Elevated levels of corresponding α-keto acids Signup and view all the answers

What is the characteristic feature of the urine of individuals with Maple Syrup Disease?

Sweet odour like maple syrup Signup and view all the answers

What is the consequence of the absence of α-keto acid decarboxylase enzyme in individuals with Maple Syrup Disease?

Elevated levels of branched-chain amino acids Signup and view all the answers

Study Notes

Biopolymers and Monomer Units

Biopolymers are constructed from distinct monomer units/building blocks.
For nucleic acids, the monomer units are nucleotides.
For proteins, the monomer units are L-α-amino acids.

Amino Acids

α-amino acids have both an amino and a carboxylic acid function attached to the same carbon atom.
There are different classes of amino acids, including:
- Diaminomonocarboxylic acid (positively charged, e.g., lysine)
- Monoaminodicarboxylic acid (negatively charged, e.g., aspartate)
- Polar or non-polar (hydrophilic/hydrophobic)
Glycine, with R=H, has no optical activity.
Although D-amino acids occur in cells and in polypeptides, they are not present in proteins.

Amino Acid Structure and Classification

Amino acids have trivial names (e.g., glycine, tryptophan) and systematic chemical names.
The carbon bearing the C=O and NH2 groups is the α–carbon, and the next is β-carbon.

Urea Cycle and Hyperammonaemia

Inherited hyperammonaemia is caused by genetic defects of various enzymes of the urea cycle.
High levels of NH3 are toxic to humans and can lead to coma or death.
Treatment involves a low protein diet and α-keto analogues.

Transamination Reactions

Transamination reactions involve the transfer of amino groups from a variety of compounds to glutamate for conversion to ammonia.
Alanine transaminase and glutamate dehydrogenase funnel amino groups from various compounds to glutamate.
These reactions are reversible.

Amino Acid Metabolism

Amino acid metabolism involves the degradation of amino acids to glutamate or aspartate, which are interconverted by glutamate-aspartate aminotransferase.
The amino group of most amino acids is funneled into the formation of glutamate or aspartate, which are then converted to ammonia.

Inborn Errors of Phenylalanine Metabolism

Phenylketonuria is caused by a lack of phenylalanine hydroxylase, leading to the accumulation of phenylalanine.
Tyrosinemia is caused by a defect of tyrosine transaminase, leading to the accumulation of tyrosine.
Albinism is caused by a defect of tyrosinase, leading to the accumulation of tyrosine.
Alcaptonuria is caused by a defect of homogentisate oxidase, leading to the accumulation of homogentisate.

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Description

Test your understanding of biopolymers, including proteins and nucleic acids, and their composition of distinct monomer units. Learn about the structure of these biomolecules and their role in living cells.