Chapter 11 Questions

What cells have glycoalyx and how is it beneficial?

A sugar coating outside the plasma membrane of plant cells

What does glycoalyx form?

A sugar coating outside the plasma membrane of plant cells

What does the cytoskeleton add to the properties of the plasma membrane?

Cytoskeleton determines the shape and strength of the plasma membrane. - The cytoskeleton forms noncovalent interactions with integral attachment proteins (that are noncovalently linked to true transmembrane proteins)

What does a cell membrane do and how?

Due to its intracellular tethers, extracellular tethers, and intramembrane barriers, the cell membrane will selectively rearrange its macromolecule constituents into membrane domains with compartmentalized functions.

How does the arrangement of membrane lipids become asymmetrical?

Enzymes on E.R. distribute newly formed phospholipids into the extracellular monolayer. - Flippases then catalyze the redistribution of specific phospholipids into the cytosol-facing monolayer. - Concentration of types of phospholipids are uneven and monolayer specific.

What do scramblases do?

Enzymes that catalyze the random distribution of newly added phospholipids on the endoplasmic reticulum from the cytosol-facing monolayer to the ER lumen facing monolayer.

Where and how are phospholipids synthesized?

Enzymes within the endoplasmic reticulum catalyze the synthesis of phospholipids using fatty acids found in the cytosol.

What can we see in freeze-fracture replicas that are not visible via any other forms of microscopy?

Freeze-fracture replicas enable us to see the topographical structure of membranes, including integral membrane proteins, in high resolution

How do we know that membrane proteins are usually free to move in the plane of the membrane?

Human and mouse cell experiment - Human-specific and mouse-specific antibodies are labeled with rhodamine and fluorescin respectively. - The movement of anti-body binding proteins can be observed within the membrane - Initially, human-specific and mouse-specific exist in distinct halves. - Over time the spatial arrangement of membrane proteins becomes mixed.

What does the fact that the poison ricin is a lectin suggest about how it might exert its toxic effects (such as causing disseminated blood clotting)?

The bonding of lectin with proteoglycans and glycoproteins modifies the structures to bind nearby molecules. - For example, lectin bound red blood cells will clump and form clots in small blood vessels.

How does a lipid bilayer "self-seal" with a large tear?

The lipid bilayer will fold in on itself so as to form two distinct vesicles with their own energetically favorable bilayers.

Why do lipid bilayers form spontaneously?

- Bilayers are energetically favorable conformations

What affects the tightness of the packing of phospholipids in a monolayer?

- Dependent on the length and number of double bonds within the hydrocarbon tails - The shorter the hydrocarbon tail, the less non covalent interactions that can be established, which allows for more freedom and reduced tightness.

How do integral membrane proteins differ from peripheral membrane proteins? (think about linkage)

- Integral membrane proteins can only be removed with detergents that disrupt the bilayer because of they are linked to it via strong covalent interactions. - Peripheral membrane proteins can be excised without disrupting the bilayer due to their linkage consisting of noncovalent interactions.

How does a lipid bilayer "self-seal" with a small tear?

- Lipids will rearrange so as to minimize the unfavorable interactions between water molecules and the hydrophobic hydrocarbon tails.

How are phospholipids within a bilayer fluid? 2 ways

- Phospholipids can rotate around their long axis (noncovalent interactions are easy to disrupt) - Phospholipids can switch places within a monolayer dependent on the tightness of their packing

What explains the observation that poikilothermic (cold-blooded) organisms alter the lipid composition of the membranes according to the season?

- Temperature affects the cellular production of lipids so as to maintain fluidity.

What is lectin?

Both provide protection and structural support for the contents of a plant cell, yet glycoalyx also facillitates a cell's mobility through narrow spaces due to its slimy texture

Why do Phospholipids form bilayers? -What is their structure like? -How is a bilayer energetically favorable for the components of the structure? - Favorable?

-Phospholipids are amphipathic with a hydrophilic phosphate group and one or two hydrophobic hydrocarbon tails. - They form bilayers because the hydrophobic hydrocarbon tails will be shielded from interacting with water and will form noncovalent interactions. - The hydrophilic phosphate groups will form hydrogen bonds and electrostatic attractions with water - Energetically favorable

If reading the amino acid sequence of a known transmembrane protein, how would you recognize in the sequence the portion that traversed the membrane?

29 to 33 residues - side chains are hydrophobic and nonpolar and would face the hydrophobic hydrocarbon tails of the amphipathic phopholipids, thus forming noncovalent interactions

What does a cell membrane define?

A cell's functions in respect to its cytosolic material, intracellular activities, and intramembrane fluidity.

Which Lipids become parts of membranes?

Amphipathic Lipids ex, Cholesterol

How do transport proteins create hydrophilic channels?

B-barrels create hydrophilic channels due to their conformation. - Backbone of polypeptide and small amount of side chains are hydrophilic and polar and they border the inner core of the barrel. - This allows for hydrophilic, polar molecules to interact with the core of the membrane while they diffuse through the channel.

How is a b-pleated sheet an energetically favorable conformation for an integral membrane protein?

Backbone of polypeptide chain can fold onto itself in an antiparallel fashion - Hydrophobic side chains interact with lipids of bilayer - Hydrophilic phospholipids interact with the core of the barrel

How is an alpha-helix an energetically favorable conformation for an integral membrane protein?

Backbone of polypeptide chain can fold onto itself in an antiparallel fashion - Hydrophobic side chains interact with lipids of bilayer - Hydrophilic phospholipids interact with the core of the barrel

What are the three types of integral membrane protein? What is the other type of membrane protein?

Integral membrane proteins include - transmembrane - associated with a lipid monolayer - lipid linked - Protein attached proteins are peripheral membrane proteins

What would prevent an integral membrane protein from diffusing in the plane of the membrane?

Intracellular tethers such as the cell cortex - Extracellular tethers, such as molecules on the extracellular bilayer - Intramembrane barriers, such as those that form tight junctions that divide the membrane domains within epithelial cells

Which Lipids do not become parts of membranes?

Lipids that are not amphipathic, need to have both hydrophobic and hydrophilic composition.

Why do lipids in a bilayer interact with one another?

Nonpolar/uncharged lipids will aggregate into compact molecules so as to reduce their interactions with the water molecules

How are plant cell walls and glycoalyx alike?

Share structural and functional features - Structural features include specific proteins such as proteoglycans and glycoproteins and carbohydrates including various sugars

How are plant cell walls and glycoalyx dissimilar?

Share structural and functional features - Structural features include specific proteins such as proteoglycans and glycoproteins and carbohydrates including various sugars

What does SDS stand for? What are SDS and Triton-X?

Sodium dodecyl sulfate - Detergents (amphipathic with one hydrocarbon tail)

Why might it be important to restrict the freedom of movement of proteins in the membrane?

Specialized regions called membrane domains can form within the bilayer. Each domain has multiple integral membrane proteins.

The more unsaturated carbons in the hydrocarbon tails....

The more fluidity of phospholipids in a bilayer.

Why do integral membrane proteins contain a-helices or b-pleated sheet structures within those portions of the protein which reside in the lipid bilayer?

These conformations are energetically favorable for the relationship between integral memraben proteins and phospholipid bilayer

How do SDS and Triton-X interact with the bilayer? Why is this beneficial for the amphipathic detergent?

They disrupt the noncovalent interactions between lipids of the bilayer and the hydrophobic side chains of the integrating protein. - The unfavorable interaction between the tails of the detergent monomers and the water molecules are reduced - The hydrophilic head of the amphipathic detergent can form hydrogen bonds with water and pull the integral membrane protein out of the membrane.

What happens to detergents in solution?

They form micelles so as to minimize the unfavorable interactions between the hydrocarbon tail and water molecules.

What is a cell membrane?

bilateral structure composed of amphipathic lipids integrated with various proteins (that are asymmetrically distributed) that combine to compartmentalize and interact with the contents of an aqueous environment.