Cell Membrane Structure and Transport

What are cell membranes made of

Phospholipid bilayer, carbohydrates, glycolipids, glycoproteins, integral membrane protein, peripheral membrane proteins

Where is cholesterol found in

Animal cells

How are phospholipids arranged

Leaflets

Asymmetrical distribution

Selectively permeable barrier

How many different phospholipids are in the cell membrane

Variety

Are phospholipids in one leaflet different than the other?

Yes

Where is ergosterol found

Plant cells

Where are hopanoids found

Bacteria

Are hopanoids sterols?

No! They have a 5-ring structure

What type of structure do sterols have

4-ring

What do sterols do in the cell membrane

Regulate fluidity

What are the proteins not embedded in the cell membrane called?

Peripheral

What are the proteins embedded in the lipid bilayer but specifically in the extracellular bilayer

Transmembrane

What are the proteins whose tail is attached into the membrane called

Lipid anchored

What do you call lipids that can rotate and move laterally within the cell membrane?

Semi-fluidR

How do lipids move within a cell membrane?

Rotate and move laterally

What are lipid rafts

Collection of phospholipids and sterols moving as one

What is an example of lipid rafts

Fungi

Why do lipids “flip”

To maintain symmetry

Does lipid flipping require energy?

Yes!

What affects fluidity

Length of fatty acid chains

Degree of saturation

Amount of sterol

How long should fatty acid chains be to have an increase in fluidity?

Shorter

How long should fatty acid chains be to have a decrease in fluidity

Longer

How many bonds do saturated fatty acids have

Single bonds

How many bonds do unsaturated fatty acids have

One or more

What would a cooler temperature do to cell membrane fluidity

Would stay fluid

What would a warmer temperature do to cell membrane fluidity

Would become solid

Can cell membrane proteins move?

Kinda. Some can rotate and move laterally

Can cell membrane proteins flip?

No!

Why can’t some cell membrane proteins move?

Proteins are polar, needs too much energy to flip

What is a flippase?

Catalyzes movement from one leaflet to another

What is diffusion

The movement of molecules from an area of high concentration to an area of low concentration

Is energy required for diffusion?

No!

What affects the rate of diffusion

Size of solute

Difference in concentration

Temperature

How will smaller solutes diffuse across a membrane?

Will diffuse faster

How will larger solutes diffuse across a membrane?

Will diffuse slower

What does a high concentration mean for the rate of diffusion

Will have an initial fast rate

What factors affect the diffusion across a phospholipid bilayer?

Size

Polarity

Charge

How long does diffusion continue?

Until equilibrium

What is diffusion

Movement of a solute down a gradient

Does diffusion require energy

No!

What is facilitated diffusion

Movement of a solute down a gradient with the aid of a transport protein

What is active transport

Movement of a solute against a gradient with the aid of a transport protein

What solutes have high permeability

Gases, small uncharged molecules

What solutes have moderate-low permeability

Water, urea

What solutes have low permeability

Polar organic molecules (sugars)

What solutes have very low permeability

Ions, charged polar molecules, charge macromolecules

What is membrane potential

Difference in charge across a membrane

What is osmosis

The diffusion of water

How does water move through a membrane

Aquaporins

What is osmosis an example of

Facilitated diffusion

What are aquaporins

Transmembrane protein

What is an isotonic solution

Equal solute concentrations

How does water move in isotonic solutions

Moves equally in both direction

What is a hypotonic solution

Lower solute concentration

How does water move in hypotonic solutions

Water flows into of cell

What is a hypertonic solution

Higher solute concentration

How does water move in hypertonic solutions

Water flows out of the cell

How would an animal cell react to being placed in a hypertonic solution?

Cell will shrink (aka crenation)

What happens to the water in the cell after being placed in a hypertonic solution

Water leaves the cell

How would an animal cell react to being placed in a hypotonic solution

Animal cell will swell and may rupture (aka osmotic lysis)

What happens to the water in the cell after being placed in a hypotonic solution?

Water enters the cell

How would a plant cell react to being placed in a hypertonic solution

The plasma membrane shrinks but the cell wall keeps the cell from shriveling (plasmolysis)

What happens to the water in a plant cell after being placed in a hypertonic solution

The water exits the cell

How would a plant cell react to being placed in a hypotonic solution

Central vacuole fills with water, pushing cytoplasm against the cell wall, causing turgor pressure

What does the transport of solutes across a cell membrane require?

Transport proteins

What type of transport proteins are needed to transport solutes

Transmembrane proteins

What types of proteins are used to transport solutes

Channels and transporters

Which direction do channel proteins transport solutes

Down a gradient

How do channel gates open and close

In response to ligands/changes in membrane potential

Which direction do transporter proteins transport solutes

Against a gradient (active transport)

Where do transporter proteins bind molecules

In a hydrophilic pocket

What are the types of transporters

Uniporter

Symporter

Antiporter

How do uniporters transport?

A single solute moves in one direction

How do symporters transport

Two solutes move down a gradient

One moves in providing the second molecule energy to move out

How do antiporters transport

Two solutes move in opposite directions

What does active transport help with

Conformational change

What are the types of active transport

Primary and Secondary

What is primary active transport

Direct use of energy to transport against a concentration gradient

What is secondary active transport

Use of pre-existing gradient to drive active transport

What energy does secondary active transport use

Electrochemical gradient

What is secondary active transport an example of

Symport

What would happen if active transport continues

High concentration of hydrogen ions outside membrane than inside

Creates electrochemical gradient

What is primary active transport an example of

Primary active transport

What are gap junctions

Small gaps between cell membranes of adjacent cells

How are gap junctions formed

Integral membrane proteins called connexins or innexins

Where are connexins found?

Animals

Where are innexins found?

Invertebrates

How many connexins is one connexon made of

6 Connexins

How many innexins is one innexon made of

8 innexins

What is the function of connexons/innexons

Allows transport of ions and small signaling molecules

What is the plasmodesmata

Connects the cytoplasm of the adjacent cells

In plants (a plant gap junction)

What is exocytosis

Secretion of proteins

What is endocytosis

Absorption of proteins

What is the process of exocytosis

Vesicle loads with cargo—>protein coat forms—>vesicle released from golgi—>protein coat sheds near cytosol—>vesicle fuses with plasma membrane—>cargo released

What is the process of endocytosis

Cargo binds to receptor—>receptor causes coat proteins to bind and surround membrane—>Vesicle released in cell—>Protein coat is shed—>Vesicle fuses with a lysosome—>cargo released in cytosol