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Biology

Membranes

2015-10-28

www.njctl.org

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Vocabulary

active transport integral proteincarrier proteinchannel proteinconcentration gradientdiffusionenzymatic activityfacilitated diffusionfluid mosaichypertonichypotonic

isotonicmolarityosmosispassive transportperipheral proteinphospholipid bilayerselectively permeablesignal transduction

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Membranes Unit Topics

· Membranes, Diffusion

· Osmosis

Click on the topic to go to that section

· Plasma MembranesTransport through Proteins

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Membranes,Diffusion

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Membranes are an arrangement of phospholipids that gather together to enclose a volume.

Membranes act as a wall or a barrier separating the outside and the inside of that enclosed volume.

Membranes

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MembranesRemember we learned that a phospholipid has a hydrophilic and a hydrophobic end. When these phospholipids arrange to form a membrane that separates the inside and the outside of the shape, both the inside and the outside of the shape usually include water (think of a water balloon in a bathtub).

So how can these phospholipids arrange themselves so that their hydrophobic ends are not near the water? Move them into a bilayer.

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Phospholipid BilayerThe phospholipids do not form a single line, but instead form two parallel lines with their hydrophobic ends in between. Now the hydrophobic ends are protected from the water by the hydrophilic ends.

Phospholipids are amphiphilic molecules: meaning they contain both hydrophobic and hydrophilic regions.

We call this a phospholipid

bilayer.

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1 The section labelled A is:

A amphiphilic

B hydrophobic

C hydrophilic

A

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2 The sections labelled B are:

A amphiphilic

B hydrophobic

C hydrophilic

B

B

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Selective PermeabilityMembranes allow for the intake of nutrients and the elimination of waste because they are selectively permeable. This means they can let some molecules pass through and not others.

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The formation of a membrane was one of the first steps in evolution of cells.

The membrane separated the inside world and outside world but still allowed for the intake of nutrients and the elimination of waste.

Regulating the amount of nutrients and waste passing through the membrane is called maintaining homeostasis.

Homeostasis

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3 The basic component of all membranes is

A proteinsB fatsC starchesD phospholipids

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4 How many layers do plasma membranes have?A oneB twoC threeD four

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5 Phospholipids arrange themselves so that their

A hydrophilic ends contact each other

B hydrophobic ends ends contact each other

C hydrophilic end of one layer meets the hydrophobic end of the other layer

D hydrophobic ends contact the enclosed volume of fluid

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6 Plasma membranes allow all types of molecules to pass through.

TrueFalse

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7 A cell's regulation of its internal environment is called

A selective permeabilityB plasma membranesC phospholipidsD maintaining homeostasis

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Passive Transport

Some molecules pass through the membrane without the use of energy, this is called passive transport.

These molecules always move from areas of high concentration to areas of low concentration. This is referred to as moving "with the concentration gradient."

Which direction with the molecules move?

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Solutions Review

Solutions are defined as homogeneous mixtures of two or more pure substances.

The _______________ is the substance present in the greatest abundance.

All other substances are ____________.

___________ dissolves the ___________ .

In biology, the solvent is almost always ___________ .

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Molarity (M)

Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different.

Molarity is one way to measure the concentration of a solution.

Molarity (M) = moles of the solutevolume of solution in liters

Expressing Concentrations of Solutions

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Mass of Solute

Volume of Solvent

Concentration

5g C

10g C

20g NaCl

20g NaCl

100ml

100ml

100ml

200ml

___________

___________

___________

___________

Concentration Practice

Calculate the concentrations below.

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Diffusion

Osmosis

Facilitated Diffusion

Three Types of Passive Transport

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Diffusion is the process where solute molecules move from areas of high concentration to areas of low concentration. Membranes act as the barrier between these two areas. Molecules will continue to diffuse across the membrane until an equilibrium is reached.

Diffusion

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Which way will the O2 move?

8.3mM O2

9.5mM O2

Diffusion

No energy is required to move molecules with their concentration gradient.

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Concentration gradients are specific to each type of molecule meaning each type of molecule can diffuse in a different direction, some in and some out.

Diffusion

Which way will the O2 move?Which way will the CO 2 move?

9 mM O2

6 mM CO2

7.2mM O2

7.2mM CO2

Diffusion is a spontaneous process and each type of molecule diffuses at its own rate.

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8 Diffusion is the movement of molecules A against their concentration gradientB with their concentration gradientC in their concentration gradientD outside their concentration gradient

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9 All molecules diffuse from the inside of the membrane to the outside of the membrane.

TrueFalse

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10 Each type of molecule diffuses at a different rate.TrueFalse

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11 The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to the sucrose. Which solute(s) will exhibit a net diffusion into the cell?

A sucroseB glucose

C fructose

D sucrose, glucose, and fructose

E sucrose and glucose

Cell:0.05M sucrose0.02M glucose

environment0.01M sucrose0.01M glucose0.01M fructose

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12 Which solute(s) will exhibit a net diffusion out of the cell?

A sucrose

B glucose

C fructose

D sucrose, glucose, and fructose

E sucrose and glucose

Cell:0.05M sucrose0.02M glucose

environment0.01M sucrose0.01M glucose0.01M fructose

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13 When diffusion has occurred until there is no longer a concentration gradient, then _______________ has been reached.

A equilibriumB selective permeabilityC phospholipid bilayerD homeostasis

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14 When equilibrium is reached, what is the concentration of fructose outside the cell?

Cell:0.05M sucrose0.02M glucose

environment0.01M sucrose0.01M glucose0.01M fructose

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Osmosis

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OsmosisOsmosis is the diffusion of free water molecules across a selectively permeable membrane.

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Two ways to Describe Osmosis

The water is moving with its concentration gradient from an area with lots of free water molecules to an area with fewer free water molecules.

The water moves from areas of low solute concentration to areas of high solute concentration until the solute concentrations are in equilibrium.

OR

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Osmosis

If the solution on the outside of the membrane has a higher solute concentration than the solution inside, we say that the outside solution is hypertonic. This means that water will diffuse from the inside solution to the outside solution.

solute molecule

water molecule

H2 O

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If too much water leaves the cell, due to its being in a hypertonic solution, it can shrink or shrivel up.

solute molecule

water molecule

H2 O

Osmosis

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If the solution on the outside of the membrane has a lower solute concentration than the solution inside the membrane we say that the outside solution is hypotonic. This means that water will diffuse from the outside solution to the inside solution.

solute molecule

water molecule

H2 O

Osmosis

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If too much water enters a cell due to its being in a hypotonic solution it can swell, and if it swells too much it can _________, or burst.

H2 O

solute molecule

water molecule

Osmosis

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If the solution on the outside of the membrane has an equal solute concentration to the solution inside the membrane we say that the outside solution is isotonic to the inside solution.

This means that water will diffuse equally across the membrane in either direction.

H2 O

solute molecule

water molecule

Osmosis

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15 The diffusion of water molecules across a selectively permeable membrane is called what?

A diffusionB isotonicC osmosisD hypotonic

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16 Water molecules diffuse fromA inside the plasma membrane to outside onlyB outside the plasma membrane to inside only

C from areas of high solute concentration to areas of low solute concentration

D from areas of low solute concentration to areas of high solute concentration

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17 Diffusion and osmosis are both types of active transport.

TrueFalse

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18 What type of environment has a higher concentration of solutes outside the plasma membrane than inside the plasma membrane?

A hypertonicB isotonicC normalD hypotonic

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19 What type of environment has an equal amount of solute on the inside and outside of the plasma membrane?

A hypertonicB isotonicC normalD hypotonic

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20 What type of solution has a greater flow of water to the inside of the plasma membrane?

A hypertonicB isotonicC normalD hypotonic

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21 The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to the sucrose. Is the solution outside the cell isotonic, hypotonic, or hypertonic?

A HypertonicB HypotonicC Isotonic Cell:

0.03M sucrose0.03M glucose

environment0.02M sucrose0.04M glucose0.01M fructose

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22 In which direction will there be a net osmotic movement of water?

A InB OutC No net osmosis

Cell:0.05M sucrose0.03M glucose

environment0.02M sucrose0.04M glucose0.01M fructose

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Plasma Membrane of Cells,Transport through Proteins

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Plasma Membrane of Cells

Early cells were simple lipid bilayers, relying only on passive transport.

Later cells developed more complex membranes that included proteins. These proteins act as doorways to allow for more molecules to enter and leave the cell.

Most small molecules can diffuse without membrane proteins.

Larger molecules need to be facilitated (helped) to diffuse across a membrane by these proteins.

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Phospholipid BilayerRemember that membranes are made up mostly of phospholipids.

Phospholipids are __________________ molecules, containing hydrophobic and hydrophilic regions.

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2 Types of Membrane Proteins

Peripheral proteins are not embedded in the membrane, but instead stay on only one side of the membrane.

Integral proteins pass through the hydrophobic core and often span the membrane from one end to the other, also called transmembrane proteins.

The plasma membrane also contains two types of proteins:

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Fluid MosaicThe plasma membrane is sometimes referred to as a fluid mosaic.

Fluid because the phospholipids can move sideways within the membrane and do not stay in one stationary position.

Proteins can also move around in the membrane but they are much larger than lipids and move more slowly.

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Fluid MosaicThe plasma membrane is sometimes referred to as a fluid mosaic.

Mosaic means the membrane contains many different proteins spread throughout.

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23 Which of the following statements about the role of phospholipids in forming membranes is correct?

A They are completely insoluble in water.B They form a single sheet in water.

C They form a structure in which the hydrophobic portion faces outward.

D They form a selectively permeable structure.

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24 Which best describes the structure of a cell's plasma membrane?A proteins sandwiched betweeen two layers of

phospholipids

B proteins embedded in two layers of phospholipids

C phospholipids sandwiched between two layers of proteins

D a layer of protein coating two layers of phospholipids

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25 The fluid-mosaic model of membrane structure refers to _____.

A the fluidity of phospholipids and the pattern of proteins in the membrane

B the fluidity of proteins and the pattern of phospholipids in the membrane

C the ability of proteins to switch sides in the membranes

D the fluidity of hydrophobic regions, proteins, and the mosaic pattern of hydrophillic regions

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Proteins serve several important functions in the cell membrane.

Transport

Signal transduction

Cell-cell recognition

Enzymatic activity

Membrane Protein Functions

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Transport

Proteins can act as doorways for nutrients and waste.

There are two types of transport which require proteins:

· Facilitated Diffusion (a type of passive transport)

· Active Transport (requires energy)

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Small molecules like O2 and CO2 readily diffuse through all plasma membranes because they are small and non-polar; they can

squeeze between the phospholipids.

However......

Facilitated Diffusion

Larger molecules and ions, charged particles, cannot squeeze between the phospholipids, they need the help of a transport

protein. This is called Facilitated Diffusion .

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Just like regular diffusion, particles in Facilitated Diffusion move from an area of high to low concentration.

Unlike regular diffusion these particles move through the membrane with the help of a integral protein.

Since the substances are going with their concentration gradient, this is a type of Passive Transport: no energy is needed.

Facilitated Diffusion

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Examples of Transport Proteins

Channel proteins are one type of transmembrane transport protein that provide corridors that allow a specific molecule or ion to cross the membrane.

Carrier proteins are another type of transmembrane transport protein that change shape slightly when a specific molecule binds to it in order to help move that molecule across the membrane.

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Examples of Transport Proteins

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26 Which of the following molecules is most likely to diffuse freely across the lipid bilayer of the plasma membrane without the involvement of a transport protein?

A carbon dioxideB glucoseC sodium ionD DNAE all of the above

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27 Which of the following processes includes all others?

A osmosisB diffusion of a solute across a membraneC facilitated diffusionD passive transport

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28 Facilitated diffusion moves molecules _____.

A against their concentration gradients using energy

B against their concentration gradients without the use of energy

C with their concentration gradients using energy

D with their concentration gradients without the use of energy

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29 Carrier proteins are an example of integral proteins.

TrueFalse

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Active Transport

Active Transport uses energy to move solutes through a transport protein against their concentration gradients.

Carrier proteins can be used in active transport for specific molecules.

energy

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Comparing Facilitated Diffusion and ActiveTransport

Passive Transport

Active Transport

(REQUIRES ENERGY)

Click here for a comparison of the different forms of membrane transport

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30 Which one of the following is not in some way involved in facilitated diffusion?

A a concentration gradientB a membraneC a proteinD an energy sourceE all of the above are components of facilitated

diffusion

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31 Active transport moves molecule _____.A against their concentration gradients using energy

B against their concentration gradients without the use of energy

C with their concentration gradients using energyD with their concentration gradients without the use of energy

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32 Which protein can be used for both active and passive transport?

A carrier proteinB channel proteinC any integral proteinD any transmembrane protein

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Transport

Membrane Protein FunctionsProteins serve several important functions in the cell membrane.

Click here for an animation about Membrane Proteins

Enzymatic activitySome proteins are used to catalyze (speed up) reactions.

Cell-cell recognitionSome proteins are used to recognize viruses, bacteria, or other cells that have attached to the cell they are in.

Signal transductionSome proteins are used to gather information about the cell's surrounding environment.

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Diffusion Facilitated Diffusion Active Transport

No EnergyEnergy RequiredTransmembrane Protein

High Low

Carrier Protein Channel ProteinLow High

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