Transport Across Cell Membranes Flashcards
5 types of transport across a plasma membrane
- Non-mediated transport
- Mediated transport
- Passive transport
- Active transport
- Vesicular transport
What does non-medicated transport do?
Does not directly use transport protein
What transport moves materials with help of a transport protein
Mediated transport
Passive transport moves…
Moves substances down their conc. gradient or electrochemical gradients with only their kinetic energy
What transport uses energy to drive substances against their conc. or electrochemical gradients
Active transport
What does vesicular transport do?
Move materials across membranes in small vesicles either by exocytosis or endocytosis
Non-mediated transport is diffusion through lipid bilayer… why is this transport type important?
- Absorption of nutrients
- Excretion of wastes
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
Diffusion requires gradient until reaches…
equilibrium
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
Water filled pores of ion channels are lined by…
Hydrophobic charged a.a
What makes the ion channel transport rapid
Ions don’t bind to channel pore
why are ions like “free diffusion”
through fluid filled pore
Name the 3 properties of channels
- Ionic selectivity
- Gating
- Electrical current
What determines the selectivity of the channel to ions
Specific amino acids lining the pore
How can channel harness the energy stored in the different ion gradients
Being selective to particular ions
What contains ion selectivity filter
Channel core
What do channel gates control
Opening and closing of the pore
What controls channel opening and closing
Different stimuli control the gate
Examples of stimuli that control gating
- Voltage
- Ligand binding
- Cell volume (stretch)
- pH
- phosphorylation
How to measure ion channel function
Patch clamp technique
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
- Specificity
- Inhibition
- Competition
- 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
- Glucose binds to transport protein (GLUT)
- Transport protein changes shape and glucose moves across cell membrane
- 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
- Primary active transport
- 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
- Na/KATPase
- Na pump
4 steps of Na/KATPase transporters in primary active
- Na+ binding
- ATP split/Na+ pushed out
- K+ binding/Phosphate release
- 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
