The _______ ___________ is a boundary between what's inside and outside of the cell.

plasma membrane

until about 1970 the ____________ model was widely accepted. It had a layer of ______________ in the middle between two layers of ___________.

sandwich, phospholipids, proteins

Today we use the ________ __________ model which has ________ embedded into the phospholipid bilayer

fluid mosaic, proteins

What does semi-permeable mean?

Passage from one side of the membrane to the other is restricted due to multiple factors.

What is the most common molecule in the membrane according to the fluid mosaic model?

Phospholipids

Why do phospholipids form a bilayer?

Because they orientate their hydrophobic tails together and shield them from surrounding water with their hydrophilic heads.

Phospholipids are __________ molecules, containing hydrophobic and hydrophilic regions

amphipathic

What are the hydrophobic and hydrophilic regions of phospholipids made of?

Fatty acid tails and phosphate group heads

If you transposed part of a dog cell's membrane into a cat cell's membrane would they stay separate or would they mix? Why?

They would mix because the molecules of the membrane will move around

A membrane rich in unsaturated fatty acids will be more (fluid/viscous) than
those rich in saturated fatty acids. Why is this?

Fluid

The bends in unsaturated fatty acids prevent close packing of the membrane

How does cholesterol affect the membrane?

At warm temperatures, it restrains movement of phospholipids and at cool temperatures, it
maintains fluidity

__________ proteins are bound to the surface of the membrane

Peripheral

____________ proteins penetrate the hydrophobic core, and are embedded in the membrane

Integral

What are transmembrane proteins and are they integral or peripheral, why?

Integral, despite not reaching both sides of the bilayer they still penetrate the hydrophobic core of the membrane.

What does the hydrophobic regions of an integral protein consist of?

One or more stretches of nonpolar amino acids, often coiled into alpha helices

In the membrane, proteins have six major functions. What are they?

Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)

Which protein function does HIV take advantage of in order to enter the cell?

Extracellular surface molecules, often containing carbohydrates, do what?

Allow Cell-Cell Recognition when they bind to each other.

Membrane carbohydrates may be covalently bonded to ______ or more commonly to __________. The resulting molecules are called...?

lipids, proteins

glycolipids, glycoproteins

The Carbohydrates of plasma membranes vary among species, individuals, and cell types in an individual, true or false?

True

Does the plasma membrane have sidedness?

Yes

(nonpolar/polar) molecules can dissolve in lipid bilayer and pass through membrane rapidly.

nonpolar

___________ proteins allow hydrophilic substances to pass across membrane

Transport

_________ proteins have hydrophilic tunnel that certain molecules or ions can use as a tunnel

channel

Which channel protein is used to specifically transport water?

aquaporins

______ proteins bind molecules and change shape to shuttle them across membrane

carrier

A transport protein is specific for the substance it moves, true or false?

True

_________ is the tendency for molecules to spread out evenly into available space

Diffusion

In diffusion each molecule moves randomly, true or false?

True, however diffusion of a population
of molecules may be directional

Explain dynamic equilibrium.

When the total movement of molecules both directions across the membrane is net 0.

Substances diffuse (up/down) their concentration gradient

down

Diffusion of a substance across a biological membrane is ________ transport

passive

________ is the diffusion of water across a selectively
permeable membrane

Osmosis

Water diffuses across a membrane from the region of _____ solute concentration to the region of _____solute concentration

lower, higher

When does water stop diffusing across a membrane?

When the solute concentration is equal on both
sides

_______ is the ability of a surrounding solution to cause cells to gain or lose water

Tonicity

What happens to a cell in an isotonic, hypotonic and hypertonic solution?

no net water movement across the plasma
membrane, cell gains water, cell loses water

Define Osmotic concentration

total solute concentration of a
solution

Which three terms are used to describe an animal cell in the three types of tonicity? What kind of solution do they prefer?

Shrivelled, normal and lysed

Prefer isotonic

Which three terms are used to describe a plant cell in the three types of tonicity? Which do they prefer?

Plasmolyzed, turgid, flaccid

Prefer hypotonic

Define Osmoregulation

the control of solute concentrations and
water balance

In __________ ___________, transport proteins aid the passive movement of molecules across the plasma membrane

facilitated diffusion

___ channels are a type of channel protein which facilitate the diffusion of ions

ion

Some ion channels are _________ _________, which open or close in response to a stimulus

gated channels

_______ proteins undergo a subtle change in shape
(___________) that translocate the solute-binding site across the membrane

Carrier, conformation

Active transport requires _______, usually in the form of ________

energy, ATP

________ ___________ is the voltage difference across a membrane

Membrane potential

What is membrane potential caused by?

Voltage is created by differences in the distribution of positively and negatively charged ions across a membrane

Two combined forces, collectively called electrochemical gradient, drive diffusion of ions across a membrane. What are they?

A chemical force, An electrical force

An ___________ ______ is a transport protein that generates voltage across a membrane. The sodium-potassium pump is the major __________ ______ of
animal cells

electrogenic pump, electrogenic pump

The main electrogenic pump of plants, fungi, and bacteria is a _________ pump

proton

Electrogenic pumps help store energy that can be used for ___________ ______

cellular work

________ occurs when active transport of a solute indirectly drives transport of other solutes

Cotransport

Large molecules, such as polysaccharides and proteins, cross membrane via __________

vesicles

Does bulk transport require energy?

Yes

Describe exocytosis

transport vesicles migrate to the membrane, fuse
with it, and release their contents to the outside of the cell

Describe endocytosis

cell takes in macromolecules by forming
vesicles from the plasma membrane

What are the three types of endocytosis?

Phagocytosis, Pinocytosis, Receptor-mediated endocytosis

In Phagocytosis what fuses to the newly made vesicle to digest its contents?

lysosome

In receptor-mediated endocytosis, binding of ________ to receptors triggers vesicle formation

ligands

Human cells use receptor-mediated endocytosis to take in __________ for synthesis of membranes and other steroids

cholesterol