Transporters, Pumps and Channels

What is the purpose of the selective permeability of the cell membrane?

The selective permeability of the cell membrane allows a cell to maintain its internal composition at necessary levels.

Why is Active Transport named so?

- Active transport moves a molecules AGAINST a concentration gradient - It therefore requires ENERGY (ATP). - Active transporters are called PUMPS. - Active transporters exhibit specificity, competition, saturation (SCS).

What are aquaporins?

- Aquaporins are integral membrane proteins - they serve as channels in the transfer of water

How does a Transporter work to carry molecules across the membrane?

- Binds to specific molecules (substrates) - Carry molecule across membrane by *changing configuration* - NEVER forms direct connection b/w ECF and ICF

How does water cross a cell membrane?

- By diffusion through the lipid bilayer - Through water channels called *aquaporins*

What is SECONDARY active transport?

- Energy that drives molecule against concentration gradient it NOT from ATP. - Energy comes from another gradient that was created using ATP. - *Called SECONDARY Active Transport b/c ATP does not fuel the pump DIRECTLY*

What is a Transport Protein?

- Integrated proteins, that span the membrane. - Involved in the movement of ions and small molecules *Transport proteins are classified as either:* - Transporters - Channels

How does water interact with the cell membrane?

- It is small molecule, therefore can pass through C.M -H/e, phospholipid bilayer is hydrophobic in centre! - Therefore, water CAN pass through, but it passes very slowly.

How are Channels in the membrane gated? Is this transport Simple, Facilitated or Active?

- LIGANDS (CHEMICALLY GATED) - ELECTRICALLY GATED (VOLTAGE GATED) - BY TENSION (MECHANICALLY GATED) Transport is *FACILITATED*.

What is facilitated diffusion?

- Membrane impermeable molecules have restricted entry - Occurs with the help of a *transport protein* - No energy required! - One kind of molecule moved a time - Process exhibits Specificity, competition, saturation (SCS) - GLUCOSE enters most cells this way!

What is passive transport?

- Movement of molecular substances across cell membranes without energy input. - Driven by movement of molecules DOWN a concentration gradient

What is net flux determined by?

- Net flux is determined by concentration gradients - i.e. movement of material is determined by concentration.

What is diffusion? How many types of diffusion are there?

- Passive movement of materials *down* concentration gradient - Two: Simple diffusion and facilitated diffusion

What does a Gap Junction do?

- Permits diffusion of ions between coupled cells - Also calle *nexus*

What are the three main types of passive transport?

- Simple Diffusion - Facilitated diffusion - Osmosis

What molecules pass easily through the phospholipid bilayer?

- Small, non-polar molecules pass via simple diffusion - I.e. GASES : O2 and Co2

What is a phospholipid bi-layer?

- The basic structure of the cell membrane - Bi layer of lipids (Hydrophilic heads and hydrophobic tails)

What does hydophilic mean?

- Water "loving" - Will interact well with water - Can sometimes be dissolves in water.

What does hydrophobic mean?

- water "fearing" - Will not interact with water

What are the six characteristics of Simple diffusion?

1) Occurs down concentration gradient 2) No energy required! 3) Continues until equilibrium is reached 4) Occurs rapidly over short distances and slowly over long 5) Is directly related to temperature (molecules move faster at higher temperatures) 6) is related to the size of the molecule (larger molecules move slower)

Fatty acids enter the cells that line the small intestine via: A. Simple diffusion B. Facilitated diffusion C. Active transport

ANSWER: A. Simple diffusion

Channels and supporters are alike because they facilitate diffusion or effective solutes across membranes as well as: A) Exhibit solute specificity B) Use ATP C) Exhibit saturation and solute specificity D) exhibit saturation, solute specificity and use ATP

ANSWER: C) Exhibit saturation and solute specificity

The PepT is a H+/peptide *antiporter* located in the small intestine. It has which of the following characteristics? A) requires ATP for activity B) exhibits maximal transport when saturated C) requires H+ and peptides for activity D) B and C E) A, B, and C

ANSWER: D) B and C

Why does material dominantly move down concentration gradient from the ECF?

Because there is a high concentration of material in ECF and low in ICF.

What types of molecules CANNOT cross through the cell membrane?

CANNOT CROSS PHOSPHOLIPID BI-LAYER: - Large, polar molecules (hydrophilic) - Charges molecules, Ions (Na, Cl, K), Amino acids

Tranport proteins are classified as Transporters or ____________.

CHANNELS - Create a water filled passageway that connects ECF & ICF - Channels are GATED.

What creates chemical gradients?

Concentration differences between ECF and ICF.

What is the difference between Passive Transport and Diffusion?

Diffusion is a Form of Passive Transport

True or false: A Transporter can only ever bind to a single molecule.

FALSE - Some transporter bind to a single substrate, HOWEVER... - *CO-TRANSPORTERS* can bind to two or more.

TRUE OR FALSE: Facilitated Diffusion requires energy in the form of ATP to transport molecules across the cell membrane.

FALSE: ACTIVE transport requires energy in the form of ATP to move substrates across cell membrane. In facilitated diffusion, molecules move DOWN the concentration gradient, therefore NO ENEGRY INPUT NEEDED.

What is the most important quality of the cell membrane?

Most important property of the cell membrane is selective permeability - I.e. some substances can pass through freely, but others cannot.

Can molecules that are hydrophilic cross the cell membrane visa Simple Diffusion?

NO. - Molecules that are hydrophilic are charged/polar - Therefore NOT soluble in phospholipid bilayer - Therefore CANNOT cross the plasma membrane visa simple diffusion

What facilitates Active Transport?

PUMPS facilitate active transport. - Active transport moves solute form [High] to [Low]. - Pumps ALWAYS use energy (ATP)

What types of molecules can cross the cell membrane via simple diffusion?

SIMPLE DIFFUSION RESERVED FOR: - Small, non-polar molecules (O2, Co2) - Tiny polar molecules (H2O) - Large non-polar molecules (Benzene)

Tranport proteins are classified as Transporters or Channels... Transporters can bind single substrates or be *co-transporters* and bind two and more... Co-transporters are further classified into ________________ and _________________.

SYMPORTERS: Move two or more substances in the *same* direction across the membrane ANTIPORTERS: Move two or more substances in *opposite* direction across membrane.

What is Osmosis?

The diffusion of water. - Usually water is a *solvent*, in the context of a semi-permeable membrane, where the *solute* CANNOT travel through the membrane. - Osmosis is FACILITATED diffusion

What does it mean for a molecule to move "down a concentration gradient"?

The molecule moves from an area of higher concentration to an area of lower concentration.

What are the two classifications of transport proteins?

Transport proteins are classified as either: - Transporters - Channels

What is PRIMARY active transport?

When protein pump uses energy taken DIRECTLY from ATP to transport molecules against their concentration gradient.