57. Biochemistry - Lipid Metabolism IV Phosphoglycerol & Sphingolipid Metabolism

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Questions and Answers

What is the significance of the mannose-6-phosphate (M6P) tag in sphingolipid storage diseases?

It regulates the synthesis of sphingolipids in the cytoplasm.

It enhances the activity of acid-stable hydrolases in the ER.

It marks the enzymes for export to the plasma membrane.

It directs vesicle traffic to transport hydrolases to lysosomes. (correct)

Which of the following best describes the inheritance pattern of sphingolipidoses?

Mitochondrial inheritance.

X-linked dominant inheritance.

Autosomal recessive inheritance. (correct)

Dominant inheritance in both genders.

What occurs as a result of a genetic mutation in sphingolipid-specific hydrolases?

Decreased synthesis of mannose-6-phosphate.

Enhanced breakdown of neutral sugars.

Production of excess sphingolipids in lysosomes. (correct)

Increased activity of acid-stable hydrolases.

Which feature characterizes Fabry’s disease in relation to sphingolipidoses?

Caused by a mutation in an X-linked gene. Signup and view all the answers

What mechanism makes reactions between sugars and nucleoside triphosphates (NTPs) irreversible during sugar activation?

Pyrophosphatase-catalyzed cleavage of pyrophosphate (PPi). Signup and view all the answers

What is the primary precursor to all glycerolipids?

Phosphatidate Signup and view all the answers

Which lipid class is derived from ceramide?

Sphingolipids Signup and view all the answers

What is the main role of phospholipases in phosphoglycerol metabolism?

To hydrolyze phosphoglycerols Signup and view all the answers

Which statement about sphingolipid storage diseases is accurate?

They are linked to deficiencies in enzymes responsible for sphingolipid breakdown. Signup and view all the answers

What kind of fatty acids are included in the structure of ceramide?

N-acyl fatty acids Signup and view all the answers

Which of the following is an activated intermediate used in the synthesis of sphingomyelin?

Ceramide Signup and view all the answers

Which lipid type is NOT classified as a phosphoglycerol?

Sphingomyelin (SM) Signup and view all the answers

What role does 1,2-diacylglycerol (DAG) play in lipid synthesis?

It serves as a substrate for the synthesis of phosphoglycerol membrane lipids. Signup and view all the answers

Which statement accurately describes the reaction involving phosphatidate?

It couples with CMP to create a chemically-reactive metabolite. Signup and view all the answers

What is the precursor for phosphatidylinositol (PI) synthesis?

CDP-DAG Signup and view all the answers

Which lipids are synthesized from PE through a reaction with serine?

PS and TAG Signup and view all the answers

What activates the phosphorylated alcohol in the synthesis process?

The transient attachment of CMP Signup and view all the answers

How is CDP-choline involved in lipid synthesis?

It is used to synthesize phosphatidylcholine. Signup and view all the answers

Which metabolite is formed by the coupling of DAG with a phosphorylated alcohol?

CDP-DAG Signup and view all the answers

What is the primary outcome of the synthesis involving CDP-DAG and inositol?

Production of phosphatidylinositol Signup and view all the answers

In the context of lipid synthesis, what does PS refer to?

Phosphatidylserine Signup and view all the answers

What is the primary product formed when phosphatidylglycerol condenses with the phosphatidate component of another CDP-DAG?

Cardiolipin Signup and view all the answers

Which enzyme catalyzes the conversion of CDP-choline and DAG into phosphatidylcholine?

Cytidyl transferase Signup and view all the answers

What is the primary role of S-adenosylmethionine (SAM) in the biosynthesis of phosphoglycerols?

Serves as a methyl donor for trimethylation reactions Signup and view all the answers

What product results from the decarboxylation of phosphatidylserine (PS)?

Phosphatidylethanolamine Signup and view all the answers

Which process leads to the formation of lysophosphatidate?

Hydrolysis by phospholipase A1 Signup and view all the answers

Which phospholipase specifically hydrolyzes the bond to the phosphorylated alcohol at glycerol C3?

Phospholipase C Signup and view all the answers

Which of the following lipids can be produced through isoenergetic exchange with serine replacing ethanolamine?

Phosphatidylserine Signup and view all the answers

What type of reaction is used to convert phosphatidylethanolamine (PE) to phosphatidylcholine (PC)?

Trimethylation Signup and view all the answers

Which component is released when phosphatidylcholine is formed from CDP-choline and DAG?

CMP Signup and view all the answers

What type of derivatives are created by the action of downstream kinases on phosphatidylinositol (PI)?

Polyphosphorylated derivatives Signup and view all the answers

What initiates the metabolic pathway for ceramide synthesis?

Attachment of an acyl component of palmitoyl-CoA to serine Signup and view all the answers

Which component is common among all sphingolipid biosynthesis pathways?

Ceramide Signup and view all the answers

What is one reason ceramide is also called N-acyl sphingosine?

It features a fatty acid attached to the nitrogen of the amino group Signup and view all the answers

Which reaction type is crucial for interconverting ceramide and sphingosine?

Amide formation Signup and view all the answers

Which sphingolipid is synthesized through the transfer of phosphocholine to ceramide?

Sphingomyelin Signup and view all the answers

What is the role of sphingosine-1-phosphate (S1P) in cellular signaling?

Ellicits responses by binding to S1P receptors Signup and view all the answers

Which type of reaction is responsible for synthesis of sphingolipids?

Transfer of phosphocholine or monosaccharides to ceramide Signup and view all the answers

Which amino acid is a precursor for ceramide synthesis?

Serine Signup and view all the answers

What is the result of the attachment of a second fatty acid during ceramide formation?

Conversion into a ceramide Signup and view all the answers

Which component indicates the acidic nature of certain sphingolipids?

Ganglioside Signup and view all the answers

Study Notes

Phosphoglycerol & Sphingolipid Metabolism

Learning Objectives:
- Outline glycerolipid biosynthetic pathways, focusing on tissue-specific glycerol-3-phosphate origin, pathway bifurcations from phosphatidate, and activated intermediates for different lipids (TAG, PC, PE, PS, PI, PG/CL).
- Recall phosphoglycerol phospholipase names and actions.
- Outline sphingolipid biosynthetic pathways, emphasizing relationships between ceramide and sphingosine, and activated intermediates for SM and glycolipids.
- Explain sphingolipid storage disease mechanisms.
- Identify specific sphingolipid storage diseases from enzyme or accumulated material names.
Outline (Phosphoglycerol):
- Overview of membrane lipids and phosphoglycerol nomenclature/structure
- Anabolic pathways for phosphoglycerols (glycerol-3-phosphate origin, phosphatidate synthesis bifurcation, DAG synthesis)
- Review of phospholipase names and cleavage sites
Outline (Sphingolipids):
- Anabolic pathways for sphingolipids (ceramide synthesis, activated donor production for sphingomyelin and glycolipids)
- Sphingolipid catabolism and storage diseases
Membrane Lipids (Review):
- Cholesterol constitutes ~35-40% of membrane lipids in humans, mostly in plasma membranes.
- Glycerolipids (containing glycerol) and sphingolipids (containing sphingosine) are sub-classes of fatty acid lipids that form membrane bilayers.
Phosphoglycerol Nomenclature and Structure:
- Phosphoglycerols/phospholipids are named based on the alcohol residue attached (e.g., choline—phosphatidylcholine, ethanolamine—phosphatidylethanolamine).
Phosphatidate:
- A key precursor for a variety of glycerolipids, including triacylglycerols and phospholipids.
- Its activation leads to different pathways, producing various glycerolipids.
Phospholipases:
- Hydrolyze phosphoglycerol bonds, releasing sub-components.
- Specific types are PLA1, PLA2, PLC, and PLD, each cleaving at different points.
Sphingolipids:
- Derivatives of ceramide (sphingosine + N-acyl fatty acid).
Sphingolipid Biosynthesis:
- Ceramide synthesis starts with serine and fatty acyl-CoA.
- It's a key intermediate for other sphingolipids.
Sphingolipid Storage Diseases:
- Genetic mutations in sphingolipid-specific hydrolases lead to accumulation of specific sphingolipids.
- This causes lysosomal storage diseases like Tay-Sachs, Gaucher, Niemann-Pick, Krabbe's, etc.
- Common characteristics: neurological deficits, poor prognosis, often fatal in early life, and accumulating lysosomal metabolites.
Anabolic Pathways (Glycerolipids):
- Glycerol-3-phosphate is derived from glycolysis for creating glycerolipids.
- Tissues can use glycerol kinase to attach phosphate from ATP, when needed.
- Pathway bifurcates at phosphatidate to make storage lipids (TAG) and phosphoglycerols (PC, PE, PS).
- Phosphatidate is activated using CTP, creating CDP-DAG for further synthesis (PI and PG).
Anabolic Pathways (Sphingolipids):
- Ceramide is the central molecule in sphingolipid synthesis.
- Synthesized from serine and fatty acyl groups, often involving reactions involving redox reactions.
- Sphingolipids are synthesized by attaching various sugars/phosphocholine to ceramide.
Specific Diseases (Examples):
- Niemann-Pick: Lack of sphingomyelinase
- Tay-Sachs: Deficiency in hexosaminidase A; build-up of ganglioside GM2
- Gaucher's: Deficiency in glucocerebrosidase; build-up of glucocerebroside.

Sphingolipid Structure

Sphingomyelin (SM): Ceramide + phosphocholine
Cerebrosides: Ceramide + monosaccharide
Globosides: Ceramide + neutral polysaccharide
Gangliosides: Ceramide + acidic polysaccharide (containing sialic acid)

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Description

This quiz focuses on the metabolic pathways of phosphoglycerol and sphingolipids. It covers glycerolipid biosynthesis, enzyme actions on phospholipids, and the mechanisms behind sphingolipid storage diseases. Test your knowledge on the key intermediates and relationships within these important lipid molecules.