Phospholipid bilayer part 1 (aug 29th)

Question 1

Cytoplasm is the…

Answer 1

Cytosol and the organelles

Question 2

Plasma membrane

Answer 2

Outer most lipid bilayer

Question 3

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

Answer 3

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

Question 4

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

Answer 4

The Smooth endoplasmic reticulum.

Question 5

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

Answer 5

Covalent modification (glycosylation)

Question 6

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

Answer 6

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

Question 7

Lysosome is the ____ of the cell?

Answer 7

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

Question 8

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

Answer 8

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.

Question 9

What is autophagy?

Answer 9

The digestions of intracellular mass by the lysosome.

Question 10

What do centrosomes organize?

Answer 10

Mitotic Spindles?

Question 11

Where are endosomes most likely headed?

Answer 11

To a lysosome.

Question 12

Where did endosomes come from?

Answer 12

They are endocytosed material.

Question 13

Inclusions are?

Answer 13

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

Question 14

Proteasomes:

Answer 14

Degrade proteins marked with ubiquitin proteins.

Question 15

When would a protein be marked with ubiquitin?

Answer 15

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.

Question 16

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

Answer 16

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.

Question 17

Flagella are…

Answer 17

Found in sperm. Used for swimming.

Question 18

Where would microvilli be found? Why there?

Answer 18

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

Question 19

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

Answer 19

The cytoplasm by significant amount. Due to all organelles.

Question 20

What is a vesicle?

Answer 20

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.

Question 21

Name two functions of a peroxisome.

Answer 21

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

Question 22

Where is phosphatidylserine found?

Answer 22

In the cytosolic layer of the plasma membrane.

Question 23

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

Answer 23

Flipases actively maintain it on this one side.

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Phosphatidylserine and phosphatidyl-ethanolamine.

Question 26

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

Answer 26

Sphingomyelin and phosphatidyl-choline.

Question 27

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

Answer 27

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.

Question 28

Cholesterols main function in the membrane is to…

Answer 28

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.

Question 29

Micelles are?

Answer 29

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.

Question 30

Liposomes are what?

Answer 30

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

Question 31

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

Answer 31

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.

Question 32

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

Answer 32

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!

Question 33

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

Answer 33

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.

Question 34

Which of the four major phospholipids is negatively charged?

Answer 34

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

Question 35

The two factors that dictate membrane thickness are?

Answer 35

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?

Question 36

What is a lipid raft?

Answer 36

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.

Question 37

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

Answer 37

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

Question 38

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

Answer 38

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.

Question 39

Define glycoproteins and and glycolipids.

Answer 39

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

Question 40

Will lipid rafts form in the absence of cholesterol?

Answer 40

No. The presence of sphingolipids is also pivotal .

Question 41

What percentage of the membrane does phosphatidylinositol make up?

Answer 41

Less then 1 percent.

Question 42

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

Answer 42

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.

Question 43

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

Answer 43

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.

Question 44

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

Answer 44

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

Question 45

Diacylglycerol associates with what membrane bound kinase?

Answer 45

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