Phospholipid bilayer part 1 (aug 29th) Flashcards Preview

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Flashcards in Phospholipid bilayer part 1 (aug 29th) Deck (45):

Cytoplasm is the...

Cytosol and the organelles


Plasma membrane

Outer most lipid bilayer


Why is the Rough Endoplasmic reticulum called the rough endoplasmic reticulum?

It is covered with ribosomes. It is the site of protien synthesis


What organelle is predominately involved in lipid biosynthesis and calcium storage, release, and reuptake?

The Smooth endoplasmic reticulum.


What form of modification does the golgi apparatus perform on proteins?

Covalent modification (glycosylation)


Why are the mitochondria and chloroplast encased in two lipid bilayers instead of just one, like the rest?

They were, theoretically, originally endocytosed, but not digested. They therefore had their membrane and the hosts membrane around them.


Lysosome is the ____ of the cell?

The stomach. It is filled with hydrolytic enzymes, and is involved in autophagy and endocytosis.


Hydrolytic enzymes are activated at a pH of ~5. Why is this important? Where are these enzymes found?

It is important because hydrolytic enzymes decay cellular debris and endocytosed material. While hydrolytic enzymes are enclosed in the lysosome, if the lysosome ruptured they would digest the cell. But they can't digest the cell, because the cellular pH is too basic for them. So happy day.


What is autophagy?

The digestions of intracellular mass by the lysosome.


What do centrosomes organize?

Mitotic Spindles?


Where are endosomes most likely headed?

To a lysosome.


Where did endosomes come from?

They are endocytosed material.


Inclusions are?

Material in the cell not enclosed in a lipid bilayer. This includes glycogen granules. Fat droplets, ribosomes, proteasomes.



Degrade proteins marked with ubiquitin proteins.


When would a protein be marked with ubiquitin?

If it was misfolded (which is fairly common surprisingly), this is a type of quality control. This marking would also be done if the protein was no longer needed.


Primary cilia have been noted in what types of cells? What is their purpose?

Every cell type. They have a sensory function. In the kidney the primary cilia may stick into urine to determine flow rate. In the eye it has been modified to be the sight of light recognition for rods and cones.


Flagella are...

Found in sperm. Used for swimming.


Where would microvilli be found? Why there?

The small intestine. To maximize surface area for maximal absorption of nutrients.


Does the cytoplasm of the cell, or the plasma membrane contain more lipid bilayer?

The cytoplasm by significant amount. Due to all organelles.


What is a vesicle?

In biology, it is a package inclosed with a lipid bilayer. It could be filled with something to secrete, a secretory vesicle. Or being used as a form of transportation.


Name two functions of a peroxisome.

Production of H202, the reduction of H202 via copious amounts of catalase.


Where is phosphatidylserine found?

In the cytosolic layer of the plasma membrane.


How is phosphatidylserine maintained in only the cytosolic (inner) layer of the plasma membrane?

Flipases actively maintain it on this one side.


Scramblase is switching phosphatidylserine from the cytosolic side to the extracellular side of the cell. What is the significance of this for the cell?

Switching of the negatively charged phosphatidylserine to the extracellular side of the cell is a signal to macrophages to kill the cell.


Which of the four most abundant phospholipids are concentrated on the cytosolic side of membrane?

Phosphatidylserine and phosphatidyl-ethanolamine.


Which of the four most abundant phospholipids are found on the extracellular monolayer (outer layer of plasma membrane?)

Sphingomyelin and phosphatidyl-choline.


What are glycolipids, where are they found? What does this imply about their function?

Glycolipids are sugar fat complexes. They are concentrated on the extracellular side of the membrane. This implies that they are likely involved with extracellular processes, such as intercellular signaling, and attachment.


Cholesterols main function in the membrane is to...

Decrease the membrane's permeability to small hydrophilic molecules, by filling gaps between phospholipid molecules, and forming tighter interactions. It also appears to be a bidirectional regulator of fluidity? But my professor does not think this is true.


Micelles are?

made of phospholipids with a single non polar chain (can be made of ones with multiple chains as well). They are little balls with no water in the middle and polar ends out, nonpolar ends in.


Liposomes are what?

Liposomes are naturally occurring spheres made by phospholipid bilayers to minimize entropy unfavorable interactions.


What is a black membrane? How where they used by scientists?

Black membranes where made by 'painting' a phospholipid bilayer over a pin size hole which separates two water filled chambers. After the bilayer seperates the chambers cells can be ran into this bilayer, joining it, and placing their proteins in it. The properties of these proteins and the bilayer can then be studied by varying the ion concentrations, and the voltage between chambers.


What are the three possible motions of a phospholipid that exists in a bilayer?

Lateral diffusion: movement throughout the lipid bilayer.
Flexion: Imagine fixing the polar head in place and moving the nonpolar tails back and forth like a joystick. This is flexion.
Rotation: it can turn!


What movement is not performed by a phospholipid normally without aid? What provides the aid?

Flipping from one side of the membrane to another is very very rare. Flipases are enzymes which catalyze flipping of phospholipids from one side of the membrane to another.


Which of the four major phospholipids is negatively charged?

phosphatidylserine. (who chills on the cytosolic side with phosphatidyl-ethanolamine)


The two factors that dictate membrane thickness are?

Unsaturations, if bent by a double bond the chains won't reach as far. The other factor is length, is it a c16 or a c18 fatty acid?


What is a lipid raft?

It is a thicker microdomain in the membrane. It contains longer lipid tails, from sphingolipids like sphingomyelin. These thicker areas of the membrane attract preferentially proteins with longer transmembrane domains, as the thicker membrane width will cover more of this nonpolar region.


Sphingolipids have longer nonpolar tails. How does this apply to lipid rafts?

Lipid rafts are thicker regions of the membrane. Therefor they must be occupied predominately by lipids with longer nonpolar tails.


Name several of the interactive forces which help hold lipid rafts separate from the rest of the membrane.

Protein-protein, lipid-protein, and lipid-lipid interactions. Additionally glycolipids, glycoproteins, cholesterol, glycophosphatidylinositol with protein association, sphingolipids and transmembrane proteins are in higher concentrations in lipid rafts.


Define glycoproteins and and glycolipids.

Glycoproteins are proteins with carbohydrates attached, glycolipids are fats with carbohydrates attached.


Will lipid rafts form in the absence of cholesterol?

No. The presence of sphingolipids is also pivotal .


What percentage of the membrane does phosphatidylinositol make up?

Less then 1 percent.


How many times can a phosphatidylinositol be phosphorylated by a kinase? What is the significance of this?

Three times. It is common for it to be already phosphorylated twice. An extracellular molecule can bind to a transmembrane protein and catalyze kinase addition of phosphate to a phosphatidylinositol. The three phosphates act as a docking point for other proteins. Which can now bind to the signal relaying proteins in the cell which directly perform further phosphorylation/activation or deactivation of other cells.


What does phospholipase do, how does this apply to phosphatidylinositol?

Phospholipase catalyzes the cutting of phospholipids into smaller pieces. In the case of phosphatidylinositol it will only be able to bind once it has all three of inositol's phosphates on it. It will cleave it into IP3 which can interact with molecules in the cytoplasm causing further signal amplification, and into diacylglycerol (DAG) can activate membrane bound kinases.


IP3 is what? Is associated with the release of what?

Inositol triphosphate. It is associated with release of intracellular calcium.


Diacylglycerol associates with what membrane bound kinase?

Phosphokinase C. PKC. Which can further amplify signal, to activate or deactivate proteins.