Membrane Transport Flashcards
Types of membrane transport: small molecules
Passive transport
- simple diffusion
- facilitated diffusion
Active transport
- ATP- driven
- Ion- driven
Simple diffusion
- no metabolic energy required
- small molecules
- no specificity
- rate of diffusion proportional to concentration gradient
Facilitated diffusion
- occurs down concentration gradient
- no energy required
- depends on integral membrane proteins
- proteins are specific
- similar kinetics to enzymes- dependent on temp, pH,
Ionphores
Example of facilitated diffusion Ionophore= ion carrier
Often produced by bacteria as antibiotics to discharge ion gradients of target cell
Ion channels
FD example
- allow rapid and gated passage of anions and cations
- highly selective
- allow ions to flow across membrane down conc. gradient
Essential for:
- osmotic balance
- signal transduction
- nerve impulses
GLUT
-Glucose transporter into the blood and from the blood
- Aquaporine- transmembrane protein that filtrate, absorb and secrete fluids
Uniport
Transport one specific molecule
Symporter
Transport two molecules in the same direction across the cell membrane
Antiporter
Cotransporter
Transport of two molecules in opposite directions
Active transport
ATP driven
Transport against concentration or electrochemical gradient= need energy
Ion- driven active transport
-Secondary active transporter that transport of a molecule is coupled to the movement of an ion
- Energy stored in the electrochemical gradient is used to drive the transport
Exocytosis
Excretion/ secretion
Constitutive
- all cells
- secreted proteins and plasma membrane proteins
Regulated
- specialised cells
- Ca2+ dependent
Endocytosis
Ingestion/ uptake
Types of endocytosis
- Phagocytosis
- Pinocytosis
- Receptor- mediated endocytosis
What is Pinocytosis?
Cell drinking
Uptake of fluid
Phagocytosis
Professional phagocytes are found in the immune system
- macrophages, neutrophils and dendritic cells
What is receptor mediated endocytosis
- selective (receptor recognition)
- involves Clathrin- coated pits & vesicles
- good for concentrating low levels of macromolecules
Example of receptor mediated endocytosis
Cholesterol uptake (LDL receptor)
Can be exploited by viruses to gain entry to cells
Glucose transporter
Transport of glucose into erythrocytes
- Facilitated diffusion
- Integral membrane protein- glucose transporter
Intestinal epithelial cells
- line the lumen of small intestine
- large surface area for absorption
- absorb nutrients from digested food
- transfer nutrients into the blood
- similar cells found in kidney tubules
FD- aquaporins
- water channel proteins required for the bulk flow of H20 across cell membranes
- 28kDa protein, 6 transmembrane alpha helices
- tetramer with 4 pores through which H20 can pass
- Abundant in erythrocytes, kidney cells
NaKATPase- ATP driven transporter
High (K+), low (Na+) in cell= Na+/ K+ gradient:
- controls cell volume
- makes nerve and muscle cells electrically excitable facilitates ion driven active transport of amino acids and sugars
Maintained by Na+/K+ ATPase
ATP driven AT
- pumps 3 Na+ ions out and 2K+ into the cell
- polarises the cell membrane= important for pathogen protection
- ATP hydrolysis induces conformational changes, pumping Na+ & K+ against their conc gradients
- Coupled system= ATP is not hydrolysed unless Na+ & K+ are transported and vice versa
Cardiac glycosides
Use of foxglove (digitalis) for treatment of dropsy- congestive heart failure
Strengthens the heart beat of patients with congestive heart failure
How do cardiac glycosides work?
Inhibit Na+/K+ATPase
- increases concentration of Na+ inside cell
- Decreases Na+ gradient across membrane
- Decreases Ca2+/Na+ exchange across membrane
- Increases concentration of Ca2+ inside cell
- Enhances strength of contraction of heart muscle
