3.2.3 Transport across cell membranes Flashcards
What is the function of the plasma membrane?
-allows different conditions to be established inside + outside cell
-controls movement of substances in + out of cells
What are the main components of the fluid-mosaic model of the cell membrane?
-glycolipid
-glycoprotein
-phospholipid bilayer
-channel proteins
-extrinsic/ intrinsic proteins
-cholesterol
What are the functions of glycolipids?
-acts as recognition sites to bind to other receptors (e.g. hormones)
-maintains stability of membrane and adhesion of cells (formation of tissues)
What ae the functions of glycoproteins?
-acts as recognition sites
-helps adhesion of cells to form tissue
What is the function of a channel protein?
allows water soluble ions to diffuse across membrane
What is the function of a carrier protein?
binds to ions and molecule and changes their shape to move them across the membrane (allows active transport)
What is the general function of proteins in the membrane?
provides mechanical support and cell receptors for molecules
What are the functions of cholesterol in the membrane?
-adds strength to membrane (more cholesterol = less fluid membrane)
-prevents water loss (as very hydrophobic)
-pulls together fatty acid tails of phospholipids (limits movement, controlling fluidity)
What are the functions/ characteristics of the phospholipid bilayer?
ampiphatic: hydrophobic tails and hydrophilic heads
-allows lipid soluble substances to enter/ exit cell
-prevents water soluble substances entering/ exiting
-makes membrane flexible/ self sealing
-polar molecules/ ions cannot pass through membrane
Why is the membrane referred to as fluid?
phospholipid molecules can move relative to one another, giving membrane a flexible structure
Why is the membrane referred to as mosaic?
proteins imbedded in phospholipid bilayer vary in shape/ size/ pattern
What 3 factors effect membrane fluidity?
- temperature
- cholesterol
- saturated + unsaturated fatty acids
How does temperature effect membrane fluidity?
-effects phospholipid movement
-hot = phospholipids move further apart (more fluid)
How does cholesterol effect membrane fluidity?
-holds phospholipids together
-too little cholesterol = phospholipids separate, leaving large gaps so entrance/ exit of unwanted substances (more fluid)
How do saturated fatty acids effect membrane fluidity?
straight chains, easy to pack tightly = less fluid membrane
How do unsaturated fatty acids effect membrane fluidity?
‘kinks’ in chains (increases space between phospholipids), makes it hard for chains to pack tightly = more fluid membrane
What if the definition of simple diffusion?
net movement of molecules from an area of high concentration to an area of low concentration, until they are evenly distributed
What substances move across the membrane via simple diffusion?
-lipid soluble
-non-polar
-small molecules
What is the definition of facilitated diffusion?
diffusion of specific particles at specific points through transport proteins found in membrane; moves along/ down concentration gradient
What substances move across the membrane via facilitated diffusion?
-polar molecules
-ions
e.g. glucose, amino acids, Na+
How do channel proteins stimulate facilitated diffusion?
-has specific shape to ion/ molecule
-once ion/ molecule binds, protein changes shape
-protein closes on on side of membrane and opens on other side, transporting ion/ molecule across
How do carrier proteins stimulate facilitated diffusion?
-ion/ molecule binds to specific site on protein
-protein changes shape and ion/ molecule moves across membrane
What is the definition of active transport?
movement of molecules/ ions from an area of lower concentration, to an area of higher concentration using ATP and a carrier protein
How is energy provided for active transport to occur?
-ATP binds to carrier protein
-hydrolysis occurs
-ADP and Pi are released
-Pi remains attached to carrier protein, causing a change in shape of carrier protein
-this releases ion to other side of membrane
