Metabolic Pathways Overview

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Questions and Answers

What is the primary cause of increased hemolysis with jaundice in certain patients?

Defect in aldolase A enzyme

Enzyme defect affecting erythrocytes (correct)

Absence of the M gene in muscle

Lack of functional L subunit in erythrocytes

Which gene is expressed in mature muscle that relates to PFK enzyme activity?

P gene

L gene

ALDOA gene

M gene (correct)

What is the predominant isoform of aldolase in skeletal muscle and erythrocytes?

Aldolase A (correct)

Aldolase B

Aldolase C

Aldolase D

What is the result of isomerization by triose phosphate isomerase?

Conversion of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate Signup and view all the answers

What condition is caused by autosomal recessive mutations in the ALDOA gene?

Glycogen storage disease type 12 Signup and view all the answers

What is indicated by the high rates of protein turnover in the liver and gut tissues?

There is rapid synthesis and degradation of proteins. Signup and view all the answers

Which enzyme is primarily responsible for initiating carbohydrate digestion in the mouth?

Amylase Signup and view all the answers

What happens to the substrates of defective enzymes in genetically altered organisms?

They accumulate and are excreted. Signup and view all the answers

What role does chloride ion (Cl-) play in the function of salivary amylase?

It is necessary for enzyme activation. Signup and view all the answers

Why do muscle and brain tissues have a slower protein turnover compared to liver and gut tissues?

They do not participate in metabolic adjustments. Signup and view all the answers

How did the early 20th-century discovery relate to metabolic errors?

It illuminated hereditary conditions linked to enzyme defects. Signup and view all the answers

What types of carbohydrates primarily compose dietary intake?

Polysaccharides and disaccharides. Signup and view all the answers

What is the optimum pH range for salivary amylase activity?

6-7 Signup and view all the answers

What is the role of glucose 6 phosphate in metabolic pathways?

It is a key intermediate in several pathways. Signup and view all the answers

Which enzyme is primarily responsible for the phosphorylation of glucose in liver cells and pancreatic beta cells?

Glucokinase Signup and view all the answers

How does glucokinase differ from hexokinase in terms of glucose concentration?

It functions only at elevated glucose concentrations. Signup and view all the answers

Which regulatory mechanism does glucokinase utilize?

Indirect inhibition by fructose 6-phosphate. Signup and view all the answers

What is a major clinical consequence of hexokinase deficiency?

Nonspherocytic Hemolytic Anemia Signup and view all the answers

What is the clinical significance of glucose 6-phosphate accumulation in tissues?

It reduces further metabolism and inhibits hexokinase. Signup and view all the answers

Why is hexokinase considered a regulatory enzyme in glycolysis?

It phosphorylates glucose and other hexoses. Signup and view all the answers

Which factor does NOT contribute to glucokinase's effectiveness after a carbohydrate-rich meal?

Direct inhibition by glucose 6-phosphate. Signup and view all the answers

What is the primary reason that NADH cannot be oxidized directly in the electron transport chain?

NADH is oxidized to NAD+ through lactate conversion. Signup and view all the answers

Under anaerobic conditions, how does the energy yield from glucose compare to aerobic conditions?

Less energy is produced per glucose molecule. Signup and view all the answers

Which enzyme specifically catalyzes the phosphorylation of glucose in liver cells?

Glucokinase Signup and view all the answers

Why is the glycolytic pathway crucial for cells without mitochondria?

It produces energy in the form of ATP without mitochondria. Signup and view all the answers

During the initial phase of glycolysis, what is primarily occurring?

Phosphorylation of intermediates at the expense of ATP. Signup and view all the answers

In what tissues is glucose taken up via 'active' transport?

Kidney tubules and intestinal mucosa. Signup and view all the answers

What is the overall net gain of ATP from one glucose molecule during glycolysis?

Two molecules of ATP. Signup and view all the answers

How does ATP function during the phosphorylation of glucose in glycolysis?

It donates a phosphate group in the presence of Mg. Signup and view all the answers

What is the mode of inheritance for conditions caused by genetic changes in the HK1 gene?

Autosomal recessive Signup and view all the answers

What role does glucokinase play in the liver?

It aids in the storage of glucose as glycogen. Signup and view all the answers

What is associated with homozygous mutations of the glucokinase gene?

Permanent neonatal diabetes mellitus Signup and view all the answers

What is the consequence of impaired glucokinase activity in the liver in patients with GCK-MODY?

Mild hyperglycemia Signup and view all the answers

What proportion of MODY cases does GCK-MODY account for?

30%–60% Signup and view all the answers

Which enzyme catalyzes the isomerization of glucose 6-phosphate to fructose 6-phosphate?

Phospho glucose isomerase Signup and view all the answers

In which cell type does glucokinase function primarily as a glucose sensor?

Pancreatic β-cells Signup and view all the answers

What happens to glucose-stimulated insulin secretion in individuals with mutated glucokinase?

It occurs at higher serum glucose levels. Signup and view all the answers

What is the primary function of phosphofructokinase-1 (PFK-1) in glycolysis?

To phosphorylate fructose 6-phosphate to fructose 1,6-bisphosphate Signup and view all the answers

What is the consequence of phosphofructokinase deficiency in patients?

Accumulation of abnormal glycogen in muscle tissue Signup and view all the answers

Which substrate concentration directly influences the activity of phosphofructokinase-1?

Fructose 2,6-bisphosphate Signup and view all the answers

What structural characteristic is noted in the abnormal glycogen present in patients with PFK deficiency?

Diastase-resistant and filamentous Signup and view all the answers

Which of the following describes the regulation of phosphofructokinase-2?

It is an enzyme responsible for the formation of fructose 2,6-bisphosphate. Signup and view all the answers

What is true about the reaction catalyzed by phosphofructokinase-1?

It produces fructose 1,6-bisphosphate and is rate-limiting. Signup and view all the answers

Which condition is not commonly associated with phosphofructokinase deficiency compared to myophosphorylase deficiency?

Renal failure Signup and view all the answers

What is the impact of glucose 6-phosphate (G6P) accumulation in PFK deficiency?

It maintains glycogen synthase in its active form. Signup and view all the answers

Study Notes

Metabolic Pathways Study Notes

Two main reasons for studying metabolic pathways:
- Describe chemical changes catalyzed by enzymes in the pathway.
- Describe intracellular controls regulating pathway rate.
Whole organism/organ studies show substance conversion and tissue localization. For example, urea is exclusively formed in the liver. However, these studies don't reveal enzyme details.
Four methods to identify/understand enzymatic steps:
- Accumulation of metabolites: Stress or disease can lead to metabolite buildup (e.g., lactic acid during intense exercise). These observations do not confirm metabolic intermediates but may suggest likely intermediates.
- Metabolic poisons: Administering poisons like fluoroacetic or fluorocitric acid leads to metabolite accumulation, revealing enzyme inhibition (e.g., citric acid accumulation suggests inhibition of citrate oxidation).
- Isotopic labeling: Administering a labeled nutrient (with an isotope) allows tracking the nutrient's fate and chemical group/atom movement.

Carbohydrate Metabolism Study Notes

Digestion in the mouth: Saliva containing amylase hydrolyzes starch/glycogen into smaller molecules (maltose, glucose, maltotriose). Amylase activity ceases with changing stomach pH.
Digestion in the stomach: No carbohydrate-splitting enzymes, however HCl may hydrolyze sucrose.
Digestion in the duodenum: Pancreatic amylase (α-amylase) further hydrolyzes polysaccharides, similar to salivary amylase.
Digestion in the small intestine: Pancreatic amylase, lactase, and other enzymes complete digestion. Lactase acts on lactose, breaking it down into glucose and galactose.

Lactose Intolerance Study Notes

Lactose intolerance: Symptoms can arise from difficulty digesting lactose, a dairy sugar. Symptoms include abdominal pain, bloating, diarrhea, gas, and nausea. Symptoms appear typically 30 minutes to 2 hours after lactose ingestion.
Primary lactose intolerance occurs with age-related lactase decline.
Secondary lactose intolerance develops with small intestine damage (e.g., infection, celiac disease).
Developmental lactose intolerance is seen in premature babies and can resolve over time.
Congenital lactose intolerance: Rare genetic disorder with little to no lactase production from birth.
Management: Reducing lactose intake, lactase supplements, or treatment of the underlying cause are options.

Liver Metabolism Study Notes

Liver: First organ to process nutrients, storage/release of glucose, protein and fat metabolism occur here.
Fed conditions: Blood glucose levels rise after a carbohydrate-rich meal; liver takes up glucose and produces glycogen for storage.
Glucose absorption: Glucose enters the portal vein with a high concentration, allowing the liver high glucose uptake.

Glycolysis Study Notes

Glycolysis: The conversion of glucose to pyruvate, crucial for energy generation. This process occurs in all tissues; erythrocytes/nervous tissues using glycolysis only.
Glycolysis Stages:
- Energy investment phase: First five reactions, use ATP to phosphorylate intermediates..
- Energy generation phase: Subsequent reactions produce a net gain of ATP via substrate-level phosphorylation. Two ATP molecules per glucose molecule are produced.
Aerobic glycolysis: Pyruvate is converted into Acetyl CoA that enters the Krebs Cycle in the presence of oxygen to generate ATP.
Anaerobic glycolysis: In the absence of oxygen, pyruvate is converted to lactate. This process produces a lower yield of ATP.
Key Enzymes: Hexokinase, Glucokinase, Phosphofructokinase, Aldolase, and others, are important in these processes.

Other Important Metabolic Pathways

Pentose phosphate pathway: Links to other metabolic pathways and produces NADPH and pentose sugars.
Glycogen metabolism: Glycogen storage, breakdown, and synthesis pathways are vital for glucose homeostasis.

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Description

This quiz covers the study of metabolic pathways, focusing on the chemical changes facilitated by enzymes and the regulation of these pathways within cells. It also explores methods for identifying enzymatic steps and understanding how various factors influence metabolite accumulation.