Transport Across Cell Membranes Flashcards by Sophie Hurley

5 types of transport across a plasma membrane

Non-mediated transport
Mediated transport
Passive transport
Active transport
Vesicular transport

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What does non-medicated transport do?

Does not directly use transport protein

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What transport moves materials with help of a transport protein

Mediated transport

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Passive transport moves…

Moves substances down their conc. gradient or electrochemical gradients with only their kinetic energy

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What transport uses energy to drive substances against their conc. or electrochemical gradients

Active transport

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What does vesicular transport do?

Move materials across membranes in small vesicles either by exocytosis or endocytosis

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Non-mediated transport is diffusion through lipid bilayer… why is this transport type important?

Absorption of nutrients
Excretion of wastes

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What are these examples of O2, CO2, N2, fatty acids, steroids, small alcohols, ammonia and fat-soluble vitamins (A, D, E, and K)

Nonpolar, hydrophobic molecules via non mediated transport

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Diffusion requires gradient until reaches…

equilibrium

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Ion channels form ___ filled pore that ____ the ions from the _____ core of the ___ bilayer

Ion channels form (water) filled pore that (shield) the ions from the (hydrophobic) core of the (lipid) bilayer

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Water filled pores of ion channels are lined by…

Hydrophobic charged a.a

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What makes the ion channel transport rapid

Ions don’t bind to channel pore

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why are ions like “free diffusion”

through fluid filled pore

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Name the 3 properties of channels

Ionic selectivity
Gating
Electrical current

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What determines the selectivity of the channel to ions

Specific amino acids lining the pore

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How can channel harness the energy stored in the different ion gradients

Being selective to particular ions

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What contains ion selectivity filter

Channel core

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What do channel gates control

Opening and closing of the pore

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What controls channel opening and closing

Different stimuli control the gate

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Examples of stimuli that control gating

Voltage
Ligand binding
Cell volume (stretch)
pH
phosphorylation

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How to measure ion channel function

Patch clamp technique

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How can current flowing through individual channel be recorded

Patch clamp technique

What represents the opening and closing of single ion channels

Current fluctuations

What do current fluctuations represent

Conformational changes in channel structure that are associated with channel gating

The diffusion of over 1 ___ ions per ___ through a channel ____ a measurable current (~10-12 amp)

The diffusion of over 1 MILLION ions per SECOND through a channel GENERATES a measurable current (~10-12 amp)

What is carried mediated transport

Mode of action

What directly interacts with transporter protein in carrier mediated transport

Substrate to be transported

Why does substrate to be transported interacts with transporter protein in carrier mediated transport

Transporter undergoes conformational change transport rates slower than those obtained for channels

What are carrier mediated transport proteins have properties similar to…

enzymes

What carrier mediated transport proteins exhibit

1. Specificity 2. Inhibition 3. Competition 4. Saturation (transport maximum)

What transport proteins DON'T catalyse chemical reactions but mediate transport across cell membrane at faster than normal rate

Carrier mediated transport proteins

Is mediated transport passive (facilitated) or active

Mediated transport is BOTH passive (facilitated) or active

What display enzyme kinetics

Transporters

How long does glucose transport occur in transporter saturation

Occurs until all binding sites are saturated

3 steps of facilitated diffusion of glucose

1. Glucose binds to transport protein (GLUT) 2. Transport protein changes shape and glucose moves across cell membrane 3. Kinase enzyme reduces glucose conc. inside cell by transforming glucose to glucose-6-phosphate

What maintains conc. gradient for glucose entry

Conversion of glucose

Define active transport

An energy requiring process that moves molecules and ions against their conc. or electrochemical gradients

What are the 2 forms of active transport

1. Primary active transport 2. Secondary active transport

Primary active transport - ___ is directly derived from ____ of ____ - A typical cell uses 30% of its ___ (__) on ___ active transport

Primary active transport - (energy) is directly derived from (hydrolysis) of (ATP) - A typical cell uses 30% of its (energy/ATP) on (primary) active transport

What type of active transport "energy stored in an ionic conc. gradient used to drive active transport of a molecule against its gradient"

Secondary active transport

What are the primary active transporters

1. Na/KATPase 2. Na pump

4 steps of Na/KATPase transporters in primary active

1. Na+ binding 2. ATP split/Na+ pushed out 3. K+ binding/Phosphate release 4. K+ pushed in

What Na/KATPase transporters do

3 Na+ ions removed from cell and 2 K+ ions brought into cell so pump generates net current and electrogenic

Other examples of primary active transporters: Na/KATPase

- Ca/K - ATPase (muscle SR) - H/K ATPase (stomach)

What does Na pump maintain

Low concentration of Na+ and high conc. of K+ in cytosol

What is difference in ion conc. important for...

- Maintain resting membrane potential - Electrical excitability - Contraction of muscle - Maintenance of steady state cell vol. - Uptake of nutrients via secondary active transporters - Maintenance of intracellular pH by secondary active transporters

What is pump-leak hypothesis

Na and K continually leaking back into cell down their respective gradients so pump works continuously

Secondary active transport: ___ have many ___ active transporters which are powered by the ___ gradient initially established by the ___ pump

Secondary active transport: (cells) have many (secondary) active transporters which are powered by the (Na+) gradient initially established by the (Na) pump

Why secondary active transport uses stored energy in ion gradients created by active transporters

To move other subst. against their own conc. gradient

Do these secondary active transporters indirectly or directly use the energy obtained by hydrolysis of ATP

secondary active transporters INDIRECTLY use the energy obtained by hydrolysis of ATP

What happens in Na+ antiporter or exchangers

- Na+ ions rush inward - Ca2+ or H+ pushed out

What happens in Na+ symporters or cotransporters

Glucose/a.a rush inward together with Na+ ions

How is energy in ion gradients harnessed

Secondary active transporters use the energy store in ion gradients established by primary active transport