Ch 11 Molec Cell Smartwork Questions (Exam 2)

Where would LDL be found during internalization?

• bound to the receptor inside the transport vesicle

• bound to the receptor inside the endosome

LDL would be found bound to:

the receptor inside both the transport vesicle and the endosome

The cell membran is involved in:

• cell signaling

• cell recognition

• growth and motility

• the import of nutrients

• the export of wastes

The plasma membrane is NOT involved in

DNA replication and repair or in the gene-silencing technique of RNA interference

Why do phospholipids form bilayers in water?

the hydrophilic head is attracted to water while the hydrophobic tail shuns water

The hydrophilic head of a phospholipid can form

electrostatic attractions and hydrogen bonds with water

Phospholipids with shorter tails and unsaturated fatty acid chains

create a more fluid bilayer

A shorter chain length and double bonds both

reduce the tendency of a phospholipid tail to interact with one another which increases fluidity of the membrane

How does the inclusion of cholesterol affect animal cell membranes?

it tends to make the lipid bilayer less fluid

In eukaryotic cells, phospholipids are synthesized by enzymes bound to what?

the cytosolic face of the endoplasmic reticulum

New phospholipids are added to

the ER membrane asymmetrically

What type of protein moves randomly selected phospholipids from one monolayer of a lipid bilayer to the other?

scramblase

The action of the transporter scramblase distributes

phospholipids evenly between each monolayer of the ER, which allows symmetric growth of both halves of the bilayer

When a vesicle fuses with the plasma membrane, which way will the monolayer that was exposed to the interior of the vesicle face?

the cell exterior

The interior of the vesicle is

“equivalent” to the exterior of the cell

• neither come in contact with the cell cytosol

When grown at higher temperatures, bacteria and yeast maintain an optimal membrane fluidity by doing what?

producing membrane lipids with tails that are longer and contain fewer double bonds

Membrane fluidity increases with

temperature

• bacteria and yeast will add phospholipids with longer tails and fewer double bonds

The cytosolic monolayer will always face the

cytosol whether the vesicle is moving between organelles or fusing with the plasma membrane

During programmed apoptosis (cell death), the

scramblase that transfers random phospholipids from one monoloyer of the plasma membrane to the other is fully activated

• causes phosphatidylserine (initially deposited in the cytosolic monolayer) to become distributed to both halves of the bilayer

All of the carbohydrates in the plasma membrane face the cell exterior. Which direction do the carbohydrates on internal cell membranes face?

the lumen of the vesicle or organelle

Glycolipids and glycoproteins are located ONLY

in the noncytosolic half of the bilayer

The phosphate group is always

negatively charged

For all living cells, maintaining optimal membrane fluidity permits the

• diffusion of newly synthesized membrane lipids and proteins

• ensures that membrane molecules are distributed evenly when a cell divides

• allows membranes to fuse with one another and mix their molecules

Why must all living cells carefully regulate the fluidity of their membranes?

• to allow membranes under certain conditions to fuse with one another and mix their molecules

• to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell

• to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides

Phospholipids are inserted into the

cytoplasmic monolayer of the ER and then scramblase transfers the phospholipids between the two leaflets

Flippases specifically transfer the

phosphatidylethanolamine to the cytoplasmic monolayer

Glycosylation of membrane glycolipids occurs in the

golgi lumen

Membrane lipid orientation is maintained as the

lipids are transported between membranes by transport vesicles

New membrane lipids are synthesized by enzymes on the

cytosolic surface of the endoplasmic reiticulum

What are the functions of proteins in the plasma membrane?

• serve as anchors to attach the cell to the extracellular matrix

• allow specific ions to cross the plasma membrane, thereby controlling its electrical properties

• transmit extracellular signals to the cell interior

• transport molecules across the membrane

Bacteriorhodopsin is a membrane transport protein that uses sunlight to do what?

pump protons out of the cell to generate a proton gradient across the plasma membrane

What are the mechanisms for restricting the movement of proteins in the plasma membrane?

• tethering proteins to the cell cortex

• tethering proteins to the extracellular matrix

• tethering proteins to the surface of another cell

• using barriers such as tight junctions

On what side of the plasma membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located?

the extracellular side

The sugars on plasma membrane glycolipids, glycoproteins, and proteoglycans all face the

cell exterior where they form a carbohydrate layer or glycocalyx that coats the surfae of the cell

What is true of human red blood cells?

they possess no internal membranes

As a human red blood cell matures,

it ejects its nucleus and intracellular organelles

• they have no internal membranes

Red blood cells are an

attractive system for studying the structure and function of the plasma membrane

Small water-solube molecules can pass through

the water-filled pore formed by the hydrophilic side chains of the transmembrane helices

First step of leukocyte migration to the site of infection/inflammation

cytokines are released at sites of infection or inflammation and stimulate endothelial cells of blood vessels

Inhibiting selectins would lead to

fewer leukocytes adhering to the vessel and fewer red blood cells becoming trapped

A drug that inhibits selectin function will

rduce the adherence of leukocytes to the selectin expressed on the endothelial cells

Second step of leukocyte migration to the site of infection/inflammation

endothelial cells express selectins on their plasma membrane

Third step of leukocyte migration to the site of infection/inflammation

selectins bind to carbohydrates on the surface of leukocytes, causing them to stick

Fourth step of leukocyte migration to the site of infection/inflammation

leukocytes roll along vessel walls

Fifth step of leukocyte migration to the site of infection/inflammation

leukocytes crawl out of vessel into adjacent tissue

The plasma membrane is primarily made up of a

lipid bilayer with the fatty acid tails facing each other, andx membrane proteins are also found throughout the membrane

Both membrane lipids and proteins are frequently modified with

carbohydrate groups to form glycolipids and glycoproteins

Phospholipids, glycolipids, and triacylglycerol all consist of a

3-carbon glycerol molecule with fatty acids attached to two of its carbons

Where are new phospholipids made?

in the endoplasmic reticulum

Enzymes that are bound to the cytosolic face of the ER membrane make new

phospholipids and insert them into the ER membrane

Plasma membrane proteins that move ions in and out of cells using active transport are called

transporters

Transmembrane means

proteins can be directly associated with the membrane by being fully inserted into the membrane

Proteins that are associated with the membrane by noncovalent interactions with other membrane proteins are called

peripheral membrane proteins

Transmembrane, monolayer associated, and lipid-linked proteins are all

directly associated with the membrane and are called integral membrane proteins

If the backbone of a polypeptide is hydrophilic, how can a transmembrane alpha helix span the hydrophobic portion of the lipid bilayer?

because amino acid side chains in a transmembrane helix are hydrophobic and interact with the hydrophobic interior of the bilayer

Detergent molecules are

amphipathic in nature and bind with membrane proteins and membrane lipids to disrupt their interactions and release the proteins from the membrane

What is a NOT a way that cells restrict the lateral movement of membrane proteins?

reducing the temperature of the membrane

Cells restrict lateral movement of membrane proteins by

• tethering them to internal/external components

• creating barriers to their movement