Sec14

Key takeaways

Sec14 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sec14 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sec14 from memory before moving on to harder problems.

Reference excerpt

Sec14 is a cytosolic protein found in yeast (Saccharomyces cerevisiae) which plays a role in the regulation of several cellular functions, specifically those related to intracellular transport. Encoded by the Sec14 gene, Sec14p may transport phosphatidylinositol and phosphatidylcholine produced in the endoplasmic reticulum and the Golgi body to other cellular membranes. Additionally, Sec14p potentially plays a role in the localization of lipid raft proteins. Sec14p is an essential gene in yeast, and is homologous in function to phosphatidylinositol transfer protein in mammals. A conditional mutant with non-functional Sec14p presents with Berkeley bodies and deficiencies in protein secretion.

Structure Sec14p exhibits two distinct domains, made up of twelve ⍺-helices, six 𝛽-strands, and eight 310-helices. The phospholipid binding domain of Sec14p consists of a hydrophobic pocket within the carboxy-terminal domain.

Function The function of Sec14p has largely been determined through the phenotype presented in conditional Sec14p mutants. As Sec14p is an essential gene, Sec14p knockouts must be performed in yeast strains with several other mutations conveying viability without functional Sec14p. In this knockout mutant, certain proteins destined for export accumulate in non-vesicular compartments of the cell. From this, functional Sec14p likely plays a role in some pathway responsible for cellular export of certain proteins. Protein accumulation in a Sec14p knockout is also accompanied by the formation of Berkeley bodies, an organelle unique to yeast consisting of cytoplasm enclosed by a double membrane. The presence of Berkeley bodies in Sec14p knockouts suggests Sec14p regulates or is involved in the uptake and reabsorption of certain vesicles by other organelles, such as the Golgi body, or the plasma membrane of the cell. The accumulation of both Berkeley bodies and proteins in the cytosol indicate that Sec14p is involved in the formation and degradation of anterograde vesicles of certain proteins.

Molecular In vitro, Sec14p has been demonstrated to catalyze the transport of phosphatidylinositol (PtdIns) and phosphatidylcholine (PtdCho) between lipid membranes. It has been suggested that the ability to bind PtdIns and PtdCho aids the intracellular transport function and regulation of Sec14p. This property may arise from potential transport of membrane lipids between the endoplasmic reticulum (ER) and the Golgi body by Sec14p to maintain an equilibrium in the membrane lipid concentration. Sec14p is thought to achieve phospholipid transport through phospholipid exchange. The protein-phospholipid complex associates with a lipid bilayer, discharges the bound phospholipid into the bilayer, and upon recognition of another membrane bound phospholipid, extracts the phospholipid and disassociates with the lipid bilayer. Additionally, the PtdIns and PtdCho affinity of Sec14p has been suggested to act as a localizing force, bringing Sec14p into proximity to the ER or Golgi body where it may aid in the formation of transport vesicles.

Cellular In the cell, Sec14p plays an active and regulatory role in the intracellular transport of proteins. A good example of this function is the ability of Sec14p to both transport the phospholipids PtdIns and PtdCho between membranes as well as the inhibition of phospholipase D1 and phospholipase B1, which convert PtdCho to phosphatidic acid and choline or PtdCho to glycerophosphocholine, respectively. Sec14p and its homologs, some of which exhibit activation of phospholipase D1 and B1, aid in phospholipid metabolism regulation in vivo. Additionally, Sec14p is essential in the budding of vesicles from the Golgi body, as it is thought to serve a function related to preserving diacylglycerol concentration in the Golgi body, a compound essential to secretory vesicle biosynthesis. The influence of Sec14p in the localization of lipid rafts is inferred due to abnormal localization and transport of lipid raft localized proteins in mutant yeast strains with non-functional Sec14p. Upon restoration of Sec14p function in these mutant strains, the wayward lipid raft proteins localized to their wild-type location. Experimental evidence suggests Sec14p may play a role in sorting proteins for incorporation into lipid rafts at the Golgi body prior to transport to the plasma membrane.

Illustrations

Worked examples

Example 1 — a first encounter with Sec14

Start with the simplest possible case. Write down what Sec14 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sec14 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sec14 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sec14

In research: Sec14 appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sec14 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sec14 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Saccharomyces cerevisiae genes, so understanding it makes those chapters shorter.
In everyday life: Look for Sec14 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Sec14 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sec14 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sec14 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sec14 in simple terms?

Sec14 is a cytosolic protein found in yeast (Saccharomyces cerevisiae) which plays a role in the regulation of several cellular functions, specifically those related to intracellular transport. Encoded by the Sec14 gene, Sec14p may transport phosphatidylinositol and phosphatidylcholine produced in…

Why does Sec14 matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sec14?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sec14.