Enzymes Classification Quiz: Identify Reaction Catalyst Classes

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Questions and Answers

What is the diagnostic significance of elevated LDH-1 levels compared to LDH-2 levels in serum?

A higher level of LDH-1 than LDH-2 in serum suggests myocardial infarction (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream).

Describe the subunit composition of the five lactate dehydrogenase (LD) isoenzymes.

LD-1 (HHHH; H4), LD-2 (HHHM; H3M), LD-3 (HHMM; H2M2), LD-4 (HMMM; HM3), LD-5 (MMMM; M4)

What is the major diagnostic use of serum creatine kinase (CK) levels?

Serum CK activity is greatly elevated in all types of muscular dystrophy. Exercise and muscle trauma will also increase serum CK levels.

Explain the significance of elevated serum aminotransferase levels in the context of liver disease.

In viral hepatitis and other forms of liver disease associated with acute hepatic necrosis, serum AST and ALT concentrations are elevated even before the clinical signs and symptoms of disease appear. Signup and view all the answers

What are the major isoenzyme forms of lactate dehydrogenase (LD) found in skeletal muscle and heart muscle?

The major isozyme of skeletal muscle is M5 (with four muscle (M) subunits), while H4 is the main isozyme for heart muscle. Signup and view all the answers

Explain the role of creatine kinase (CK) in muscle contraction and energy production.

Creatine kinase catalyzes the reversible phosphorylation of creatine by ATP. When muscle contracts, ATP is converted to ADP, and CK catalyzes the rephosphorylation of ADP to ATP using creatine phosphate as the phosphorylation reservoir. Signup and view all the answers

Describe the subunit composition of creatine kinase (CK) and the different isoenzyme forms.

CK is a dimeric enzyme composed of two subunits, B and M. There are three different isoenzyme forms: BB (CK-1), MB (CK-2), and MM (CK-3). Signup and view all the answers

Which enzyme class does creatine kinase (CK) belong to, and what is the general function of this class?

Creatine kinase belongs to the class of transferases, which catalyze the transfer of moieties such as glycosyl, methyl, or phosphoryl groups. Signup and view all the answers

Explain the significance of the tissue distribution of creatine kinase (CK) activity.

CK activity is greatest in striated muscle and heart tissue, which are tissues with high energy demands. Other tissues like the brain, gastrointestinal tract, and urinary bladder contain significantly less CK activity. Signup and view all the answers

In the context of enzymatic reactions, what are substrates and products? Provide an example specific to the creatine kinase reaction.

In enzymatic reactions, substrates are the molecules at the beginning of the process, and products are the different molecules formed by the enzyme's action. For the creatine kinase reaction, the substrates are ATP and creatine, and the products are ADP and creatine phosphate. Signup and view all the answers

Study Notes

Enzymes

Enzymes are biomolecules that catalyze and increase the rates of chemical reactions.
Almost all enzymes are proteins.
Enzymatic reactions involve substrates, which are converted into products by the enzyme.

Enzyme Classification

Oxidoreductases: catalyze oxidations and reductions.
Transferases: catalyze the transfer of moieties such as glycosyl, methyl, or phosphoryl groups.
Hydrolases: catalyze hydrolytic cleavage of C-C, C-O, C-N, and other bonds.
Lyases: catalyze cleavage of C-C, C-O, C-N, and other bonds by atom elimination, leaving double bonds.
Isomerases: catalyze geometric or structural changes within a molecule.
Ligases: catalyze the joining together of two molecules, coupled with the hydrolysis of ATP.

Creatine Kinase (CK)

CK is a dimeric enzyme that catalyzes the reversible phosphorylation of creatine by ATP.
Physiologically, CK catalyzes the rephosphorilation of ADP to ATP using creatine phosphate as the phosphorylation reservoir.
CK activity is greatest in striated muscle and heart tissue.
CK is composed of two subunits: B and M.
There are three different pairs of subunits: BB (CK-1), MB (CK-2), and MM (CK-3).
Serum CK activity is elevated in muscular dystrophy, cardiac conditions, and muscle trauma.

Lactate Dehydrogenase (LD)

LD is a hydrogen transfer enzyme that catalyzes the oxidation of lactate to pyruvate with the mediation of NAD.
LD is composed of four peptide chains of two types: M (or A) and H (or B).
There are five isoenzymes: LD-1 (HHHH), LD-2 (HHHM), LD-3 (HHMM), LD-4 (HMMM), and LD-5 (MMMM).
Serum LD elevations occur in various clinical conditions, including myocardial infarction, hemolysis, and disorders of the liver, kidneys, lung, and muscle.
LDH-1 is significantly elevated in myocardial infarction, while LDH-2 is the predominant form in the serum.
Diagnostic use of LDH:
- Myocardial infarction: significant elevation of LDH-1 (LDH-1 > LDH-2).
- Hemolysis: LDH is abundant in red blood cells.
- Cancer: predominant elevation of LDH-2 and LDH-3 occurs in leukemia.
- LDH activity is elevated in plasma following an infarction, peaking 36-40 hours after the onset of symptoms and remaining elevated for up to 10 days.

Other Enzymes

Aminotransferases:
- Catalyze the interconversion of amino acids to 2-oxo acids by transfer of amino groups.
- Examples include aspartate aminotransferase (AST) and alanine aminotransferase (ALT).
Other enzymes include γ-glutamyltransferase (GGT), alkaline phosphatase (ALP), 5′-nucleotidase (NTP), serum cholinesterase (CHE), and glutamate dehydrogenase (GLD).
Serum AST and ALT concentrations are elevated in viral hepatitis and other forms of liver disease associated with acute hepatic necrosis.

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Test your knowledge on enzymes and their classification based on their functions. Learn about how enzymes catalyze chemical reactions, from substrates to products. Explore categories like Oxidoreductases, Transferases, and Hydrolases.

Enzymes Classification Quiz

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