BIOL 305: Membrane Transport

molecules which readily diffuse across a membrane:

gasses

small uncharged polar molecules

passive transport:

does not require energy input and involves moving substances down a gradient

active transport:

required energy input to move at least one substance against its gradient

types of active transport:

primary- ATPase proteins

secondary- symporters and antiporters

symporters move two molecules in _________ direction

the same

antiporters move two molecules in __________ direction

opposite

classes of membrane transport proteins:

channels

transporters

pumps

channel definition:

proteins which form a pathway through a membrane

characteristics of channels:

utilize passive transport

are selective

gated

highest rate of transport

examples of channels:

aquaporins

ion channels

how is the nicotinic acetylcholine channel gated?

receptor ligand gated

how does the nicotinic acetylcholine channel work?

when acetylcholine is present the channel opens to allow Na+ into the cell for depolarization in muscle cells

how is the Na+ channel gated?

voltage gated

How does the Na+ channel work?

the depolarization from nicotinic acetylcholine channel induces a positive charge in the cell, causing the alpha helix voltage sensor to be pulled to the outside of the cell to open the channel and reinforce depolarization

where is the alpha helix of voltage sensor in Na+ channel at rest?

pulled towards the cytoplasmic face

transporter definition:

proteins which bind a substance with a specific binding pocket, which initiates a conformation change in the protein

types of transporters:

passive

secondary active

examples of transporter proteins:

GLUT

glucose transport is a __________ called ____

uniporter/GLUT

Vmax in respect to trabsporters:

the rate of transport when all substrate binding sites are filled

Km in respect to transporters:

the measure of affinity for a substrate

low Km=

high affinity

pump definition:

movement against a gradient which requires ATP hydrolysis

pumps have the ____ rate of transport:

slowest

subcategories of pumps:

P class

V class

F class

ABC superfamily

P-class protein pumps:

proteins which phosphorylate themselves during the pumping cycle

function of P-class pumps:

establish and maintain ion gradient, aspartate amino acid is phosphorylated

multiple ions are moved together

examples of P class proteins:

Ca+ pumps

Na+/K+ pumps

Ca+ pumps are required to allow Ca+ to bind ____________ for muscle contraction

troponin

E1 conformation in Ca+ pump:

has a high affinity bonding pocket on the cytosolic side for Ca+ and binds two at a time

___________ facilitates the switch from E1 to E2 conformations

ATP hydrolysis

E2 conformation of Ca+ pump:

low affinity binding pocket for Ca+ facing the sarcoplasmic reticulum

E1 conformation of Ca+ returns after ________________

phosphate group leaves

Na+/K+ pumps:

establish a resting state potential in neurons

Na+/K+ pumps move 3 Na+ ____ the cell and 2 Ca+ ______ the cell

out of/ into

inside is more negative than the outside

Switch between E1 and E2 conformations in Na+/K+ are facilitated by:

phosphorylation and dephosphorylation

E1 of Na+/K+ has a ______ affinity for Na+ and a _____ affinity for K+

high/low

E2 has a ____ affinity for Na+ and a ______ affinity for K+

low/high

V-class pumps:

pumps protons and is not self-phosphorylating to maintain pH

F-class pumps:

use the proton gradients to form ATP and is not technically a pump

only found in mitochondria and thylakoid membranes

ABC Superfamily:

ATP Binding Cassette is the largest family of pumps and moves a variety of substances

have 2 transmembrane domains and 2 cytosolic ATP binding domains

cotransport:

a transporter which moves two molecules where ne substance moves down a gradient and the energy produced is used to move a second substance against its gradient

types of cotransport:

symport

antiport

__________ is a symport movement

Na+/glucose

glucose moves ________ its gradient and sodium moves ________ its gradient into the cell

against/with

step one of Na+/glucose transport:

glucose is moved from the intestinal lumen into the cytosol of the intestinal cells

step two of Na+/glucose transport:

glucose moves via concentration gradient into the bloodstream

step three of Na+/glucose transport:

Na+ is pumped out of intestinal cells to form a gradient