Chapter 5 Smartbook

What is the covalent attachment of a carbohydrate to a lipid or protein called?

Glycosylation

The structure that separates the internal contents of a cell from the extracellular environment is the plasma

membrane

What are the three main molecular components of cellular membranes?

Carbohydrates, phospholipids, proteins

The plasma membrane consists of a(n) bilayer.

phospholipid

Where are regions of the plasma membrane hydrophilic

a, c

Because the plasma membrane contains lipids, proteins, and carbohydrates, it is often described as a(n)

mosaic

What encloses the cytoplasm?

plasma membrane

Lipids and proteins can move relative to each other within a membrane. As such, we can say the membrane is

fluid

The three main types of macromolecules that comprise the plasma membrane are

lipids, proteins, carbohydrates

What is the basic structure of the plasma membrane?

Phospholipid bilayer

A lipid bilayer is composed of ______ leaflet(s).

2

The transmembrane segments of integral membrane proteins are ______ and interact with the ______ of the phospholipid bilayer.

non polar, hydrophoic tails

One layer, or half of a phospholipid bilayer, is termed a(n)

leaflet

Within the plasma membrane, where are glycolipids normally found?

On the extracellular leaflet

Transmembrane protein

Regions inserted into the hydrophobic interior are usually α helices.

Peripheral membrane protein

Not covalently bound to membrane

Lipid-anchored protein

Lipid tails are inserted into the hydrophobic portion of the membrane.

Most transmembrane segments of integral membrane proteins are folded into what type of secondary structure?

alpha-helix

Proteins that are non-covalently bound to the hydrophilic regions of integral membrane proteins or to the polar head groups of lipids are called

peripheral membrane proteins

Which of the following changes in lipid composition would be expected to increase the fluidity of a phospholipid bilayer?

Incorporating more unsaturated fatty acids

Incorporating more cholesterol at low temperatures

What property of biological membranes describes the ability of individual molecules to move within the membrane?

fluidity

Why do shorter tails make membranes more fluid?

Shorter tails interact less with each other

Most phospholipids move freely within a semifluid membrane ______.

laterally along the plane of the membrane in two dimensions

The presence of a double bond in a phospholipid tail makes the membrane more fluid because

it prevents phospholipids from packing tightly

The movement of lipids between leaflets is catalyzed by the enzyme _, which requires energy input in the form of _.

flippase, ATP

The fluidity of the plasma membrane can be increased by incorporating fatty acids with ______ (fatty acid) tails or by incorporating ______ lipids.

shorter, unsaturated

The short, rigid molecule produced by animal cells that is involved in membrane fluidity is called _

cholesterol

Phospholipids that have shorter tails are less likely to interact with each other, thus rendering the membrane more

fluid

The double bonds in unsaturated lipids create ______ in the acyl tails, making it more difficult for neighboring lipids to interact.

kinks

Why do shorter tails make membranes more fluid?

Shorter tails interact less with each other.

Most phospholipids move freely within a semifluid membrane ______.

laterally along the plane of the membrane in two dimensions

Phospholipids move from one leaflet to another in the bilayer by the enzyme

flippase

Building blocks of phospholipids

A glycerol molecule, phosphate, polar head group, two fatty acids

Where does lipid synthesis occur?

At the cytsolic leaflet of the smooth ER

N-linked glycosylation

1. Group of 14 sugars is built onto a lipid in the ER membrane

2. Oligosaccharide transferase removes the carbohydrate tree from the lipid and transfers it to an asparagine

3. Polypeptide synthesis is completed

Highly (O-linked) glycosylated proteins that are secreted from cells are called _. One of their main biological functions is to organize the extracellular matrix surrounding cells. 

proteoglycans

What is the target for N-linked glycosylation?

ER proteins

Glycolipids and glycoproteins that participate in cell surface recognition have carbohydrates that lie within the ______.

extracellular region

O-linked glycosylation occurs

in the Golgi apparatus

Diffusion

Movement of a substance from a region where its concentration is high to a region where its concentration is low

Facilitated Diffusion

Movement of a substance from a region where its concentration is high to a region where its concentration is low through a passageway provided by a transport protein

Active Transport

Movement of a substance from a region where its concentration is low to a region where its concentration is high with the aid of a transport protein and a source of energy

What is the biological relevance of proteoglycans?

They help organize the extracellular matrix and are a component of mucus

Identify the true statements comparing simple and facilitated diffusion

Facilitated diffusion, but not simple diffusion, requires a transport protein, both simple and facilitated diffusion require concentration gradients.

Why is the phospholipid bilayer an effective barrier to hydrophilic or polar molecules?

because of the hydrophobic interior of the bilayer

Membrane proteins that have undergone N-linked glycosylation are transported to what part of the eukaryotic cell?

the cell surface

Substance A diffuses less readily across the cell membrane than substance B. What can be concluded from this fact?

Substance A is polar, while substance B is nonpolar.

To move a substance through a membrane against a concentration gradient, which of the following are necessary?

Transport protein, source of energy

Which of the following can readily diffuse across a biological membrane?

Gases and small, uncharged molecules

Isotonic

The solute concentration outside a cell is equal to the solute concentration inside the cell.

Hypertonic solution

The solute concentration outside a cell is higher than the solute concentration inside the cell.

Hypotonic solution

The solute concentration outside the cell is lower than the solute concentration inside the cell.

Phospholipid bilayers are an effective barrier to many charged or polar solutes because of their _ interior region

Hydrophobic

What is osmosis?

Diffusion of water from an area of low solute concentration to an area of high solute concentration

What is the target for N-linked glycosylation?

Membrane proteins

Why can nitrogen gas diffuse through the lipid bilayer but a nitrogen ion cannot?

A nitrogen ion carries a charge

Small, uncharged molecules pass through the membrane via ______.

passive diffusion

Function of channel proteins

facilitated diffusion

Ions and hydrophilic molecules are able to cross the phospholipid bilayer via transmembrane proteins called _ proteins.

channel

What is the significance of being able to gate a channel protein?

Allows the cell to regulate the movement of solutes

Define aquaporin

Channel protein for water

When channel proteins are _, it means they can open and close to regulate the movement of ions and molecules across the cell membrane.

gated

Functions of transporter proteins

Uptake of hormones into animal cells, uptake of amino acids and sugars into cells, export of wastes from the cell

Transporters

Binds solutes and then undergoes a conformational change

Function of channel proteins

facilitated diffusion

How are transporter proteins classified?

By the direction of transport, by the number of solutes they bind

Which type of protein is the principal pathway for the uptake of sugars, amino acids, and nucleotides?

transporter proteins

Water diffuses through certain organs such as the kidneys and bladder much faster than would occur by passive diffusion through a lipid bilayer alone. What accounts for this more rapid rate of water transport in these organs?

The presence of aquaporin channels for facilitated diffusion of water

Antiporter

Binds two or more ions or molecules and transport them in opposite directions

Uniporter

Bind a single ion or molecule and transport it across the membrane in the same direction

Symporter

Binds two or more ions or molecules and transports them in the same direction

Transport involving a pump that uses energy from ATP to transport solutes against a gradient is called _ active transport.

primary

In both endocytosis and exocytosis, the transported substance is packaged into a ______.

vesicle

What do all three types of endocytosis involve?

The formation of a plasma membrane pocket around the target molecule

A process through which molecules can be imported into a cell after binding to specific cell surface proteins is called

receptor mediated endocytosis