Lipid Metabolism during Fasting

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Questions and Answers

What happens to peroxisomes as more proteins are imported into them?

They become non-functional.

They undergo fission. (correct)

They shrink in size.

They alter their membrane composition.

Which of the following is true about Zellweger syndrome?

It is an autosomal recessive disorder. (correct)

Patients typically have normal peroxisome function.

It can be treated effectively with diet alone.

It is caused by dominant mutations in peroxin genes.

What compounds accumulate in individuals with impaired peroxisome function?

Saturated fatty acids

Short-chain fatty acids

Triglycerides

Very long chain fatty acids and branched chain fatty acids (correct)

Which proteins are required for the normal assembly of peroxisomes?

Peroxins Signup and view all the answers

Where do the receptor proteins involved in peroxisomal function primarily interact?

In the cytosol Signup and view all the answers

What is one of the consequences of mutations in peroxin genes?

Impaired peroxisome function Signup and view all the answers

Which mutation pattern is most common among patients with Zellweger syndrome?

Mutations that inactivate both copies of specific PEX genes Signup and view all the answers

What is the initial cellular response to the accumulation of fatty acids due to peroxisome impairment?

Cellular apoptosis Signup and view all the answers

What is a characteristic facial abnormality associated with peroxisomal disorders?

High forehead Signup and view all the answers

Which condition is related to impaired neuronal development and function as a result of peroxisomal disorders?

Hypomyelination Signup and view all the answers

What is a consequence of the accumulation of lipids in peroxisomal disorders?

Impaired organ function Signup and view all the answers

Which statement is true about the developmental effects of peroxisomal disorders?

Mental retardation is common. Signup and view all the answers

What must occur before fatty acids can be oxidized in the mitochondria?

They must be activated Signup and view all the answers

Which statement about fatty acid oxidation is correct?

It generates more ATP per carbon than sugars. Signup and view all the answers

What neurological issue is commonly reported in patients with Zellweger syndrome?

Progressive loss of vision and hearing Signup and view all the answers

What physiological characteristic is commonly observed in children affected by peroxisomal disorders?

Floppy appearance due to hypotonia Signup and view all the answers

What significant role do peroxisomes play in cellular metabolism?

Breaking down hydrogen peroxide into water Signup and view all the answers

How are peroxisomes different from lysosomes in terms of origin?

Lysosomes are formed in the Golgi complex, whereas peroxisomes self-replicate. Signup and view all the answers

Which process is primarily associated with the detoxification function of peroxisomes?

Oxidation of toxic compounds Signup and view all the answers

What distinguishes peroxisomes from mitochondria in terms of genetic material?

Peroxisomes lack internal DNA molecules. Signup and view all the answers

What was the original term replaced by 'peroxisomes' as per De Duve's naming?

Microbodies Signup and view all the answers

What is the main mechanism involved in the importation of proteins into peroxisomes?

Active transport using specific targeting signals Signup and view all the answers

Which function is NOT associated with peroxisomes?

Production of ATP Signup and view all the answers

What cellular process is triggered by the discovery of firefly luciferase's targeting to peroxisomes?

Peroxisome biogenesis understanding Signup and view all the answers

What is produced during each round of fatty acid oxidation?

One NADH, one FADH2, one Acetyl-CoA, and a fatty acid shortened by two carbons Signup and view all the answers

Which enzyme is responsible for catalyzing the reverse reaction in beta oxidation when the R-group is a hydrogen?

Thiolase Signup and view all the answers

Which of the following statements about beta oxidation reactions is true?

The third reaction resembles the malate dehydrogenase reaction of the citric acid cycle. Signup and view all the answers

Where is Acetyl-CoA released during fatty acid metabolism and where is it utilized?

In the matrix of the mitochondrion, where it is oxidized in the citric acid cycle Signup and view all the answers

What is the significance of an enzyme's role in the medium form concerning Sudden Infant Death Syndrome (SIDS)?

Its deficiency can lead to improper fatty acid oxidation, potentially linked to SIDS. Signup and view all the answers

What role do free fatty acids (FFAs) play during normal starvation and sepsis?

They accumulate in the blood and organs due to compromised breakdown. Signup and view all the answers

Which transcription factor is primarily responsible for the induction of genes involved in β-oxidation of fatty acids?

PPAR-α Signup and view all the answers

What happens to peroxisomal PPAR-α levels during sepsis?

They are downregulated, impairing fatty acid metabolism. Signup and view all the answers

Which process in the peroxisomes is essential for lipid metabolism?

Breakdown of very long chain fatty acids Signup and view all the answers

What is a significant consequence of the accumulation of free fatty acids in organs during sepsis?

Lipotoxicity and mitochondrial damage Signup and view all the answers

How are FFAs affected by insulin during sepsis?

Insulin resistance allows for increased levels of FFAs in the blood. Signup and view all the answers

What is the primary function of catalase in the peroxisomes?

To decompose hydrogen peroxide to oxygen and water Signup and view all the answers

What can be inferred about the relationship between adipose tissue lipolysis and energy availability during sepsis?

Lipolysis is inhibited, resulting in decreased energy availability. Signup and view all the answers

Study Notes

Lipid Utilization During Fasting

Hormonal pathways, substrates, organelles, key enzymes, and signaling molecules all promote lipid utilization during fasting.

Adipose Tissue Lipolysis

Adipose tissue lipolysis is a crucial process during fasting.
Key enzymes like ATGL and HSL break down triglycerides (TGs) into free fatty acids (FFAs).
Glycerol is another byproduct of this process.
Hormones like epinephrine and glucagon stimulate lipolysis.
FFAs are transported to other tissues for energy production.

Cellular Lipid Metabolism

Extracellular signal molecules, such as AMPK and ACC, activate the process.
Lipid Fatty Acids (LCFAs) are transported into the mitochondria.
CPT1 and CPT2 facilitate the transfer of acylcarnitine into the mitochondrial matrix for beta-oxidation.
Beta-oxidation breaks down fatty acids, creating Acetyl-CoA, which then enters the citric acid cycle (TCA).

Starvation/Sepsis

Starvation and sepsis trigger similar responses for lipid utilization.
Both increase lipolysis in adipose tissue, leading to increased free fatty acids in the blood.
PPAR-α is a key transcription factor induced by FFAs, promoting further fatty acid oxidation and ketone body production.
Sepsis can result in decreased PPAR-α levels and impaired fatty acid breakdown.

Peroxisomes

Peroxisomes contain various enzymes, including catalase, to break down toxic substances, primarily hydrogen peroxide.
They also handle the breakdown of very long-chain fatty acids via beta oxidation, converting them to medium-chain fatty acids for further mitochondrial processing.

Peroxisomes (Microbodies)

Peroxisomes were first described by Rhodin (1954) and identified as organelles by De Duve (1967).
Peroxisomes contain enzymes for hydrogen peroxide metabolism, such as catalase
Import targeting signals, usually composed of specific amino acid sequences, are important for transporting proteins to peroxisomes.

Mitochondria vs. Peroxisomes

Mitochondria are double-membrane-bound organelles that contain mtDNA and play a crucial role in oxidative phosphorylation.
Peroxisomes are single-membrane-bound organelles lacking DNA and are essential for the breakdown of very long-chain fatty acids.

Zellweger Syndrome

Zellweger syndrome is an inherited disorder caused by mutations in PEX genes.
This results in inefficient peroxisome function, leading to the accumulation of very long-chain fatty acids (VLCFA) and other abnormal lipids
Symptoms include characteristic facial deformities, hypotonia, developmental delays, and impaired brain and lung function.

Fatty Acid Oxidation (Beta Oxidation)

Fatty acid oxidation breaks down fatty acids into acetyl-CoA, generating ATP.
The process occurs in both mitochondria and peroxisomes
Different enzymes catalyze each step in the beta-oxidation process.
Four steps are involved in generating FADH2, NADH, and Acetyl-CoA.

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Description

Explore the intricacies of lipid utilization, particularly during fasting. This quiz covers key processes like adipose tissue lipolysis, hormonal pathways, and the role of enzymes in lipid metabolism. Learn how these mechanisms respond to conditions such as starvation and sepsis.