BIO Chapter 5.1

Hepatitis virus attacks

liver cells

The tail of the phosphipid is

(the fatty acids), which has no charge

carbohydrate chains may consist of ________monosaccharide units and can be either straight or branched

2-60

What is a phospholipid?

A phospholipid is a molecule consisting of glycerol, two fatty acids, and a phosphate-linked head group.

What is cholesterol?

Cholesterol, another lipid composed of four fused carbon rings, is found alongside the phospholipids in the core of the membrane.

What is the primary function of carbohydrates attached to the exterior of cell membranes?

Identification of the cell

What is a less obvious function of the plasma membrane?

In addition, the surface of the plasma membrane carries markers that allow cells to recognize one another, which is vital for tissue and organ formation during early development, and which later plays a role in the "self" versus "non-self" distinction of the immune response.

Can the hydrophilic head of a phospholipid form hydrogen bonds?

No.

What is the second major component of the plasma membrane?

Proteins

Why is it advantageous for the cell membrane to be fluid in nature?

The fluid characteristic of the cell membrane allows greater flexibility to the cell than it would if the membrane were rigid. It also allows the motion of membrane components, required for some types of membrane transport.

Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?

The hydrophobic, nonpolar regions must align with each other in order for the structure to have minimal potential energy and, consequently, higher stability. The fatty acid tails of the phospholipids cannot mix with water, but the phosphate "head" of the molecule can. Thus, the head orients to water, and the tail to other lipids.

What is the main fabric of the membrane composed of?

The main fabric of the membrane is composed of amphiphilic, phospholipid molecules.

What are the principal components of the plasma membrane?

The principal components of a plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrates attached to some of the lipids and some of the proteins.

Does the plasma membrane need to be flexible?

Yes in order to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries.

When placed in water, hydrophobic molecules tend to form

a ball or cluster.

Lipid bilayer

a barrier composed of a double layer of phospholipids that separates the water and other materials on one side of the barrier from the water and other materials on the other side.

The fluid mosaic model of the plasma membrane describes the plasma membrane as

a fluid combination of phospholipids, cholesterol, and proteins. Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membran​

A phospholipid molecule consists of

a three-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate-containing group attached to the third carbon.

What is the third major component of the plasma membrane?

carbohydrates

What is the plasma membrane also called?

cell membrane

glycolipids

combination of carbohydrates and lipids

glycoproteins

combination of carbohydrates and proteins

fluid mosaic model

describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids, respectively), resulting in a fluid character (fluidity)

Which characteristic of a phospholipid contributes to the fluidity of the membrane?

double bonds in the fatty acid tail

Peripheral proteins, along with integral proteins, may serve as

enzymes, as structural attachments for the fibers of the cytoskeleton, or as part of the cell's recognition sites. These are sometimes referred to as "cell-specific" proteins. The body recognizes its own proteins and attacks foreign proteins associated with invasive pathogens.

Carbohydrates are present only on _______________ surface of the plasma membrane and are attached to proteins, forming *glycoproteins*, or attached to lipids, forming *glycolipids*.

exterior

They are always found on the ____________surface of cells and are bound either to________ or ___________

exterior; proteins (glycoproteins) or lipids (glycolipids)

These plasma membrane receptors provide

extracellular attachment sites for effectors like hormones and growth factors, and they activate intracellular response cascades when their effectors are bound.

The glycocalyx (glycolipids + glycoproteins) is

highly hydrophilic and attracts large amounts of water to the surface of the cell. This aids in the interaction of the cell with its watery environment and in the cell's ability to obtain substances dissolved in the water.

The hydrophilic regions of the phospholipids tend to form

hydrogen bonds with water and other polar molecules on both the exterior and interior of the cell.

Thus, the membrane surfaces that face the interior and exterior of the cell are ____________. In contrast, the interior of the cell membrane is _________________ and will not interact with water.

hydrophilic; hydrophobic

Single-pass integral membrane proteins usually have a

hydrophobic transmembrane segment that consists of 20-25 amino acids.

Amphiphillic

molecule possessing a polar or charged area and a nonpolar or uncharged area capable of interacting with both hydrophilic and hydrophobic environment

Hydrophobic

molecule that does not have the ability to bond with water; "water-hating"; the tails of the phospholipid; generally non-polar and interact with other non-polar molecules and NOT polar ones

Hydrophillic

molecule with the ability to bond with water; "water-loving"; the head of the phospholipid

The hydrophilic head of the phospholipid is the

phosphate-containing group which has a polar or negative charge

Which plasma membrane component can be either found on its surface or embedded in the membrane structure?

protein

What are the proportions of the plasma membrane for the typical human cell?

protein accounts for about 50 percent of the composition by mass, lipids (of all types) account for about 40 percent of the composition by mass, with the remaining 10 percent of the composition by mass being carbohydrates.

peripheral protein

protein found at the surface of a plasma membrane either on its exterior or interior side; these proteins can be removed (washed off of the membrane) by a high-salt wash

Integral Proteins

protein integrated into the membrane structure that interacts extensively with the hydrocarbon chains of membrane lipids and often spans the membrane; these proteins can be removed only by the disruption of the membrane by detergents

The plasma membrane is able to transmit signals by means of complex, integral proteins called

receptors

Why is the glococalyx important?

the glycocalyx is also important for cell identification, self/non-self determination, and embryonic development, and is used in cell-cell attachments to form tissues.

What is the function of the plasma membrane?

the most basic one is to define the borders of the cell and keep the cell functional. The plasma membrane is selectively permeable. This means that the membrane allows some materials to freely enter or leave the cell, while other materials cannot move freely, but require the use of a specialized structure, and occasionally, even energy investment for crossing.