Chemotrophic Energy Metabolism: Glycolysis and Fermentation

Flashcards covering key concepts from the lecture on Chemotrophic Energy Metabolism, Glycolysis, and Fermentation, including metabolic pathways, ATP, redox reactions, details of glycolysis, fermentation types, gluconeogenesis, and their regulation.

What is the collective term for all the reactions in a cell?

Metabolism

Which type of metabolic pathway synthesizes cellular components, creates polymers, involves an increase in order, and is endergonic?

Anabolic pathways

Which type of metabolic pathway breaks down cellular constituents, often involves hydrolysis, results in a decrease in order and increase in entropy, and is mostly exergonic?

Catabolic pathways

What is the most common energy molecule in the biological world?

Adenosine triphosphate (ATP)

Besides ATP, what are some other high-energy molecules that store chemical energy?

GTP, creatine phosphate, and reduced coenzymes like NADH

Is the hydrolysis of ATP to ADP and Pi an exergonic or endergonic process?

Exergonic

What defines chemotrophic energy metabolism?

The reactions and pathways by which cells catabolize nutrients and conserve the released energy in the form of ATP

In biological systems, what does oxidation typically involve the removal of?

Both electrons and hydrogen ions (dehydrogenation)

What is reduction?

The addition of electrons

What are the enzymes involved in reduction called?

Dehydrogenases

What is the role of coenzymes like NAD+ in biological oxidations?

They serve as electron acceptors and carriers of electrons or small functional groups.

What is the main energy source for most cells in the body?

Glucose

Describe obligate aerobes.

Organisms that have an absolute requirement for oxygen.

Describe obligate anaerobes.

Organisms that cannot use oxygen as an electron acceptor and for which oxygen is toxic.

Describe facultative organisms.

Organisms that can function under both aerobic and anaerobic conditions.

What is glycolysis?

A ten-step reaction sequence that converts one glucose molecule into two molecules of pyruvate, producing both ATP and NADH.

Where are the enzymes for glycolysis typically found in most cells?

In the cytosol

What happens to pyruvate in the absence of oxygen?

It undergoes fermentation to regenerate NAD+.

What is the primary role of ATP hydrolysis in Phase I of glycolysis?

It is the driving force that makes the phosphorylation of glucose and fructose-6-phosphate exergonic and irreversible.

Which enzyme catalyzes the addition of a phosphate to the sixth carbon atom of glucose in the first reaction of glycolysis?

Hexokinase (and glucokinase in liver cells)

What is the net energy yield of Phase 1 of glycolysis?

Negative, as two molecules of ATP are consumed per molecule of glucose.

What process occurs in Gly-7 when ATP is generated by transferring a phosphate group directly to ADP from a phosphorylated substrate such as 1,3-bisphosphoglycerate?

Substrate-level phosphorylation

Which high-energy compound is generated in Gly-9 by the removal of water from 2-phosphoglycerate?

Phosphoenolpyruvate (PEP)

What is the net yield of ATP for the glycolytic pathway per molecule of glucose?

Two molecules of ATP

What is the main purpose of fermentation?

To regenerate NAD+ from NADH so that glycolysis can continue in the absence of oxygen.

In lactate fermentation, what enzyme directly transfers electrons from NADH to pyruvate to form lactate?

Lactate dehydrogenase

What is gluconeogenesis?

The process of glucose synthesis from three- and four-carbon precursors, such as pyruvate and lactate.

Which organisms typically carry out alcoholic fermentation under anaerobic conditions?

Plant cells, yeasts, and bacteria

What are the final products of alcoholic fermentation from pyruvate?

Ethanol and carbon dioxide (CO2)

What are the common starting materials for gluconeogenesis?

Pyruvate and lactate

Why is gluconeogenesis not a simple reversal of glycolysis?

Because key exergonic steps of glycolysis (Gly-1, Gly-3, and Gly-10) are thermodynamically difficult to reverse and are accomplished by other means.

What type of regulation involves the interconversion of an enzyme between two forms, one catalytically active and the other inactive, depending on the binding of an effector?

Allosteric regulation

Name two key regulatory enzymes for glycolysis.

Hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase

Name two key regulatory enzymes for gluconeogenesis.

Fructose-1,6-bisphosphatase and pyruvate carboxylase

How do AMP and acetyl CoA reciprocally regulate glycolysis and gluconeogenesis?

AMP activates glycolysis and inhibits gluconeogenesis, while acetyl CoA activates gluconeogenesis and inhibits glycolysis.

What is considered the most important regulator of both glycolysis and gluconeogenesis?

Fructose-2,6-bisphosphate (F2,6BP)

Why is phosphofructokinase-2 (PFK-2) called a bifunctional enzyme?

Because it has two separate catalytic activities: phosphofructokinase activity (synthesizes F2,6BP) and fructose-2,6-bisphosphatase activity (removes phosphate from F2,6BP).

How does an increase in cAMP concentration, mediated by hormones like glucagon and epinephrine, affect F2,6BP levels and gluconeogenesis?

cAMP inactivates PFK-2 kinase activity and stimulates F2,6BP phosphatase activity, decreasing F2,6BP concentration and thereby stimulating gluconeogenesis.