Biochemistry Glycolysis and β-Oxidation Quiz

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Questions and Answers

What is required for the oxidation of linoleic acid during β-oxidation?

NADPH-dependent 2,4-dienoyl-CoA reductase (correct)

Enoyl-CoA isomerase (correct)

Acetyl-CoA

Lysosomal enzymes

Which substrate is primarily used for glycolysis in animal cells?

Fructose

Sucrose

Glucose (correct)

Galactose

What forms the end product of glycolysis in plants?

Fructose

Acetyl-CoA

Glucose

Malate (correct)

What enzyme uses UDP to degrade sucrose in most plant tissues?

Sucrose synthase Signup and view all the answers

What is the true sugar substrate for plant respiration?

Sucrose Signup and view all the answers

Which products can directly enter the glycolytic pathway as triose phosphate?

Photosynthetic products Signup and view all the answers

What type of acids are generated as end products in the glycolytic pathways of plants?

Organic acids Signup and view all the answers

How many ATP molecules are consumed per sucrose unit in the reactions associated with the glycolytic pathway?

2 to 4 Signup and view all the answers

What happens to fatty acyl–carnitine once it enters the mitochondrial matrix?

The acyl group is transferred to mitochondrial coenzyme A. Signup and view all the answers

Which compound inhibits acyltransferase I, preventing simultaneous synthesis and degradation of fatty acids?

Malonyl-CoA Signup and view all the answers

During β oxidation, how many two-carbon units are removed from a 16-carbon fatty acid chain?

Seven Signup and view all the answers

What is the end product of the β oxidation of palmitate?

Eight acetyl-CoA molecules Signup and view all the answers

Which process occurs in the mitochondrial matrix during the second stage of fatty acid oxidation?

Citric acid cycle Signup and view all the answers

What is one of the primary outputs from the first two stages of fatty acid oxidation?

FADH2 Signup and view all the answers

In which process are electrons ultimately transferred to oxygen?

Mitochondrial respiratory chain Signup and view all the answers

How is energy conserved during fatty acid oxidation?

In the form of ATP via oxidative phosphorylation Signup and view all the answers

What is the primary energy yield from the oxidation of long-chain fatty acids in mammalian heart and liver?

80% Signup and view all the answers

What process converts fatty acids into acetyl-CoA?

β oxidation Signup and view all the answers

What is one of the alternative fates of acetyl-CoA in the liver?

Converted to ketone bodies Signup and view all the answers

How are free fatty acids transported in the bloodstream?

Bound to serum albumin Signup and view all the answers

What percentage of the biologically available energy of triacylglycerols is contributed by glycerol?

5% Signup and view all the answers

Where are the enzymes responsible for fatty acid oxidation located in animal cells?

Mitochondrial matrix Signup and view all the answers

Which enzyme phosphorylates glycerol released by lipase action?

Glycerol kinase Signup and view all the answers

What is the main function of acetyl-CoA in higher plants?

Biosynthetic precursor Signup and view all the answers

Which enzyme is primarily responsible for the conversion of malate to pyruvate in the plant citric acid cycle?

NAD+ malic enzyme Signup and view all the answers

Which of the following statements about succinate dehydrogenase is correct?

It is the only membrane-bound enzyme in the citric acid cycle. Signup and view all the answers

What is the role of anaplerotic reactions in the citric acid cycle?

They replenish intermediates used for biosynthesis. Signup and view all the answers

Which of the following intermediates is produced using pyruvate carboxylase?

Oxaloacetate Signup and view all the answers

What is transferred from cytosolic NADH to molecular O2 during aerobic respiration?

Electrons from NADH Signup and view all the answers

What does malonate do in relation to succinate dehydrogenase?

It is a strong competitive inhibitor. Signup and view all the answers

Which shuttle specifically functions in the liver, kidney, and heart mitochondria?

Malate aspartate shuttle Signup and view all the answers

In which specific type of tissue or organism does PEP carboxykinase operate?

Heart and skeletal muscle Signup and view all the answers

What does the mitochondrial glycerol phosphate dehydrogenase contain that distinguishes it from the cytosolic version?

FAD as a prosthetic group Signup and view all the answers

What is one of the products of the reaction catalyzed by malic enzyme?

NADH Signup and view all the answers

What distinguishes the citric acid cycle in aerobic organisms?

It acts as both a catabolic and anabolic pathway. Signup and view all the answers

How many ATP are yielded from one NADH through the electron transport chain?

2.5 ATP Signup and view all the answers

During which process is GTP produced instead of ATP in animals?

Citric acid cycle Signup and view all the answers

Which shuttle is associated specifically with skeletal muscle and brain?

Glycerol phosphate shuttle Signup and view all the answers

Where do the electrons from reduced flavin enter the respiratory chain?

At coenzyme A level Signup and view all the answers

What effect does the permeability of the mitochondrial membrane have on NADH?

It prevents NADH from entering directly, requiring shuttles Signup and view all the answers

What is the main function of external NAD(P)H dehydrogenases in plant mitochondria?

Oxidize cytosolic NADH and NADPH Signup and view all the answers

What distinguishes the alternative respiratory pathway in plant mitochondria?

It bypasses energy conservation sites. Signup and view all the answers

Which statement describes the role of the cyanide resistant terminal oxidase in plants?

It is inhibited by several compounds including SHAM. Signup and view all the answers

What occurs when complex I in plant mitochondria is overloaded?

The alternative pathway is utilized. Signup and view all the answers

What is the impact of adding cyanide to respiring animal tissue?

Cytochrome C oxidase is inhibited. Signup and view all the answers

Which of the following statements is true regarding plant mitochondrial electron transport?

There are multiple pathways for oxidizing matrix NADH in plant mitochondria. Signup and view all the answers

What percentage of respiration rate may plant tissues exhibit when cyanide is present?

10% to 25% Signup and view all the answers

What role does ubiquinone play in the alternative respiratory pathway?

Electrons branch off into the alternative pathway from it. Signup and view all the answers

Study Notes

Fatty Acid Catabolism

Fatty acid oxidation is a central energy-yielding pathway in many organisms and tissues, like the mammalian heart and liver.
Under physiological conditions, it provides up to 80% of energetic needs.
Electrons removed during oxidation pass through the respiratory chain, driving ATP synthesis.
Acetyl-CoA can be completely oxidized to CO2 via the citric acid cycle.

Fatty Acid Activation and Transport

Fatty acid oxidation enzymes are located in the mitochondrial matrix.
Fatty acids with 12 or fewer carbons directly enter mitochondria.
Those with 14 or more undergo the carnitine shuttle for transport.
The carnitine shuttle involves three enzymatic reactions.
Acyl-CoA synthetases catalyze the formation of a thioester linkage between the fatty acid and coenzyme A (CoA) via ATP hydrolysis.
Fatty acyl-CoAs are high-energy compounds; their hydrolysis is highly exergonic, driven by ATP hydrolysis.
The reaction is favorable as inorganic pyrophosphatase rapidly hydrolyzes the pyrophosphate, pulling the reaction forward.

β-Oxidation

β-oxidation is a four-step process to convert fatty acids into acetyl-CoA.
In the first step, acyl-CoA dehydrogenase removes hydrogen atoms, creating a double bond.
Enyol-CoA hydratase adds water across the double bond.
β-hydroxyacyl-CoA dehydrogenase oxidizes the alcohol to a ketone.
Acyl-CoA acetyltransferase (thiolase) cleaves off a two-carbon acetyl-CoA molecule.
The cycle repeats until the entire fatty acid chain is converted to acetyl-CoA.

Oxidation of Fatty Acids

Fatty acid oxidation occurs in three stages.
Stage 1: β-oxidation, which removes two-carbon fragments as acetyl-CoA.
Stage 2: Acetyl-CoA enters the citric acid cycle for further oxidation.
Stage 3: Reduced electron carriers (NADH and FADH2) donate electrons to the respiratory chain, generating ATP.

Saturated Fatty Acid Oxidation

Four enzymatic reactions form the first stage of fatty acid oxidation.
Dehydrogenation produces a trans-Δ²-enoyl-CoA.
Hydration creates L-β-hydroxyacyl-CoA.
Oxidation forms a β-ketoacyl-CoA.
Thiolysis releases acetyl-CoA and shortens the fatty acyl chain.

Glycolysis

Glycolysis converts carbohydrates into pyruvate.
In animals, the substrate is glucose, while in plants it is sucrose (plants often import sucrose rather than glucose).
The process produces NADH and ATP.
It is a crucial process for energy production.

Glycerol Metabolism

Glycerol, released from triacylglycerols, is converted to glycerol-3-phosphate.
This is oxidized to dihydroxyacetone phosphate.
Dihydroxyacetone phosphate easily enters glycolysis, or gluconeogenesis.

Additional Information

Plant tissues can undergo different fermentative pathways under anoxic conditions.
Fermentation can lead to lactic acid or ethanol production.
The glyoxylate cycle converts acetate to succinate, a precursor for glucose synthesis.
Vertebrate animals lack this cycle.
Alternative pathways exist for the oxidation of NADH in mitochondria that bypass the usual cytochrome pathway (i.e., cyanide-sensitive pathway)

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Description

Test your knowledge on the critical biochemical processes of glycolysis and β-oxidation. This quiz covers key substrates, enzymes, and end products associated with energy metabolism in plants and animals. Challenge yourself to understand the intricate pathways that sustain life.