1.3 Flashcards
What make up membranes?
a bi layer of phospholipid molecules and a patchwork of protein molecules; fluid-mosaic model.
Describe the head region of a phospholipid molecule.
Is charged and therefore hydrophilic.
Describe the tail region of a phospholipid molecule.
is uncharged and non-polar so therefore hydrophobic.
What gives membranes fluidity?
The phospholipids are constantly changing positions.
What two types membrane proteins are there?
integral and peripheral.
How are integral proteins held within phospholipid bi layer?
Regions of hydrophobic R groups allow strong hydrophobic interactions.
integral Proteins…
are held firmly within the membrane.
What are transmembrane proteins?
Integral proteins (some); span the entire width of the membrane; e.g. channels, transporters and many receptors.
Peripheral proteins…
loosely associated with plasma membrane; hydrophilic R groups on surface so bound mainly by ionic and hydrophilic interactions; interact with surfaces of integral proteins.
transport across the membrane:
phospholipid bi layer barrier to ions and most uncharged polar molecules; small molecules such as O₂ and CO₂ pass through by simple diffusion; facilitated diffusion is positive transport of substances through transmembrane proteins.
Channel proteins:
different ones in different cell types due to specialisation; most in animal/plant cells are highly selective; multi sub-unit proteins arranged to form water filled pores extended across membranes; some gated, some free flowing.
How do gated channel proteins work?
change conformation to allow or prevent diffusion; respond to stimulus.
What are ligand gated channels?
they are gated channel proteins controlled by signal molecules; chemical.
What are voltage gated channels?
They are gated channel proteins controlled by ion concentration changes; electrical.
Transporter proteins…
allow specific substance to bind to be transported by undergoing conformational change.
