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#cholesterol

11 public questions tagged with this topic.

Paracrine Factor

What role does cholesterol play in Hedgehog protein processing?

Hedgehog proteins undergo unique autoprocessing requiring intein-like activity and lipid modifications for gradient formation. C-terminal domain cleaves N-terminal signaling peptide, covalently attaches cholesterol to C-terminus, and palmitate attaches to N-terminal cysteine via Skinny hedgehog HHAT acyltransferase in endoplasmic reticulum. Cholesterol moiety anchors Hedgehog to membranes of producing cells, restricts diffusion, enables multimeric sterol-rich puncta for long-range gradient and facilitates secretion via Dispatched transporter RND protein requiring sterol sensing domain. Without

Ref: Porter et al., Science 1996: Cholesterol modification of Hedgehog required for secretion, multimerization and gradient.

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Plasma Membrane

Which of the following is NOT a function of cholesterol in the plasma membrane?

Cholesterol's structure with rigid tetracyclic ring system and short iso-octyl tail allows it to insert into phospholipid bilayers with hydroxyl near phospholipid carbonyls and ring system interacting with upper acyl chains. At low temperatures it disrupts tight packing of saturated chains, preventing transition to gel phase and preserving lateral diffusion essential for protein function, while at high temperatures its rigid ring restricts chain motion, decreasing permeability to small polar molecules, protons, and sodium ions, maintaining electrochemical gradients. Within membranes cholestero

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Cholesterol Functions and Steroidogenesis.

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Plasma Membrane

Which component of the membrane forms lipid rafts?

Lipid raft genesis requires cooperative interaction two distinct lipid classes rather than single component protein scaffold alone driven thermodynamics enthalpy. Sphingolipids sphingomyelin glycosylceramide ganglioside with amide linked saturated acyl chains eighteen to twenty four carbons sphingosine backbone capable hydrogen bond donor acceptor network adopt extended conformation high melting temperature promoting condensation ordered domain formation. Cholesterol planar rigid ring three beta hydroxyl inserts voids between chains increasing order parameter thickness three point seven to fou

Ref: Sezgin et al., Biochim Biophys Acta 2017, Cholesterol sphingolipid cooperation forms lipid rafts domains and phase separation.

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Plasma Membrane

Which of the following stabilizes the plasma membrane by modulating its fluidity?

Modulation membrane order cholesterol textbook example fluidity homeostasis buffering mechanism dual action concentration dependent. Cholesterol inserts three beta hydroxyl near phospholipid ester carbonyl forming hydrogen bond rigid tetracycle parallel upper ten carbons acyl chains restricting trans gauche isomerization high temperatures decreasing lateral diffusion coefficient from one to zero point five micrometer squared per second and passive permeability small solutes two to three fold measured calcein leakage assays. Low temperatures cholesterol disrupts all trans crystalline lattice in

Ref: Krause & Regen, JACS 2005, Cholesterol regulates fluidity stability buffering phase transition mechanism.

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Glycolipid and Phospholipid

Which sterol is abundant in plant membranes?

Plant membranes replace cholesterol phytosterols where stigmasterol and sitosterol are prominent structurally related functionally overlapping but distinct regulation. Both derive cycloartenol via CYP51 SMT1 SMT2 sterol methyltransferases, with sitosterol bearing twenty four alpha ethyl group dominating sixty percent free sterols stigmasterol bearing additional trans double bond C22 C23 introduced CYP710A comprising ten to thirty percent campesterol ten percent remainder. In most crops soybean Arabidopsis tomato sitosterol quantitative major but stigmasterol characteristic marker plasma membra

Ref: Schaller H., Plant Physiol 2003, Plant sterols stigmasterol sitosterol biosynthesis and membrane functions.

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Glycolipid and Phospholipid

Which lipid component is most abundant in lipid rafts?

Detergent resistant membrane fractions shotgun lipidomics consistently show enrichment sphingolipids relative glycerophospholipids quantitative evidence rafts composition bias and lateral organization. Sphingomyelin ceramide cerebrosides gangliosides share sphingosine backbone hydrogen bonding capacity amide hydroxyl groups predominantly saturated very long chains eighteen to twenty four carbons promoting all trans extended conformation high Tm above thirty seven degrees favoring condensation cholesterol into liquid ordered phase where acyl packing tight yet laterally mobile diffusion moderate

Ref: Lingwood et al., Nature Chem Biol 2008, Sphingolipid enrichment rafts quantification and sorting.

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Glycolipid and Phospholipid

Which of the following best describes cholesterol’s role in lipid rafts?

Liquid ordered raft stability arises favorable packing between sphingolipid and sterol driven enthalpy entropy compensation. Cholesterol small polar hydroxyl rigid planar tetracycle inserts into voids between long saturated amide linked acyl chains sphingosine backbone maximizing van der Waals contacts permitting hydrogen bond between sphingosine C3 hydroxyl cholesterol hydroxyl and amide carbonyl to amide donor. This promotes condensed complex formation increasing bilayer thickness four angstroms decreasing permeability solutes and creating diffusion distinct from liquid disordered with FRAP

Ref: Simons & Sampaio, Cold Spring Harb Perspect Biol 2011, Cholesterol sphingolipid stabilization rafts formation.

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Properties of Plasma Membrane

What happens when cholesterol is added to a membrane at high temperature?

Dual effect of cholesterol on membrane order described as condensing and fluidity buffering arises from rigid steroid ring system intercalating among phospholipid acyl chains. At temperatures above phospholipid Tm chains highly disordered with many gauche conformers large area per lipid fluid low order. Cholesterol hydroxyl moiety positioned near phospholipid carbonyl oxygen forms hydrogen bond, rigid tetracyclic rings restrict chain isomerization reducing number gauche kinks order parameter S increases from zero point two to zero point five measured deuterium NMR, lateral diffusion coefficien

Ref: Ohvo-Rekila et al., Cholesterol Interactions and Membrane Fluidity Biphasic Effect, Prog Lipid Res 2002.

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Endocrinology

Which hormone is derived from cholesterol?

Answer: B) Estrogen. For Endocrinology, once you lock onto the key mechanism or definition, Estrogen is the clear fit. If you restate the concept in your own words, Estrogen is the option that correctly names the structure, process, or principle asked for in Endocrinology. So Estrogen is the clean, accurate selection. If a similar stem appears later, start from the same core fact and you will land on the same kind of answer. In class notes, highlight this same phrase next to the related diagram so the wording and the picture reinforce each other. When you practise, cover the choices first, wri

Ref: Animal physiology is Unit 7 of the CSIR NET Life Science Syllabus, covering core body systems. It accounts for roughly 10% of the total marks in Sections B and C.

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