1.3a - Movement of Molecules Across Membranes Flashcards
The fluid mosaic model envisions the membrane as a mosaic of…
protein molecules in a fluid bilayer of phospholipids, held by hydrophobic R groups forming hydrophobic interactions in the phospholipid bilayer
Hydrophobic interactions hold the bilayer together which…
repels any water instantly
Only non-polar molecules can…
diffuse across the bilayer
Regions of hydrophobic R groups allow…
strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer
Integral membrane proteins interact extensively with…
the hydrophobic region of membrane phospholipid
Some integral membranes are…
transmembrane proteins
Peripheral membrane proteins have hydrophilic R groups on their surface, bound to their surface by…
mainly ionic and hydrogen bond interactions
Many peripheral membrane proteins interact with…
the surfaces of integral protein membranes
The phospholipid bilayer is a…
barrier to ions and the most uncharged polar molecules
Small molecules eg oxygen and carbon dioxide, pass through the bilayer by…
simple diffusion
Facilitated diffusion is…
the passive transport of substances across the membrane through specific transmembrane proteins
To perform specialised functions…
different cell types have different channel and transporter proteins
Most channel proteins in animal and plant cells are…
highly selective
Channels are…
multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane
Some channel proteins are gated and…
change conformation to allow or prevent diffusion
Ligand-gated channels are controlled by…
the binding of signal molecules
Voltage-gated channels are controlled by…
changes in ion concentration
Transporter proteins bind to…
the specific substance to be transported
Transporter proteins undergo…
a conformational change to transfer the solute across the membrane
Transporters alternate between two conformations so that…
the binding site for a solute is sequentially exposed on one side of the bilayer, then the other
Active transport uses pump proteins that transfer…
substances across the membrane against their concentration gradient
Pumps that mediate active transport are…
transporter proteins coupled to an energy source
What is required for active transport?
a source of metabolic energy
Some active transport proteins hydrolyse ATP directly to…
provide energy for the conformational change required to move substances across the membrane
What does ATPases do?
hydrolyse ATP
The class of R-groups that predominate in the transmembrane
regions of proteins is…
non-polar
