TRANSPORT ACROSS THE CELL MEMBRANE Flashcards
what is the function of the cell?
ability to move ions and organic molecules across membranes selectively
How do things move in/out PM?
Simple diffusion
Facilitated diffusion
Active Transport
(Endocytosis, Exocytosis)
is the PM selectively permeable?
Allows controlled passage of substances & ions
what kind of things are transported in/out of the cell?
Macromolecules eg.DNA, RNA, protein
Solutes eg.Ions, metabolites, amino acids
what is simple diffusion?
Unaided net movement of solute molecules through the lipid bilayer from [high] to [low]
what can move by simple diffusion?
Small non-polar molecules move across PM: O2, Co2
how is O2 transported by simple diffusion?
[O2] is high in lungs and [O2] is low in RBCs
O2 is taken up by RBCs in circulatory system and released in body tissues
why is facilitated diffusion necessary?
Large and polar substances cannot cross PM
what is used to allow facilitated diffusion to occur?
transport proteins
what do transport proteins allow?
provide a path through the hydrophobic lipid bilayer facilitating the diffusion
what type of gradient do uncharged molecules have?
conc gradient
what type of gradient do ions have?
electrochemical gradient
give an example of facilitated diffusion?
Glucose movement across the PM
how is glucose transported across the PM?
Glucose conc is higher in blood than in RBC
Transport protein in required
what are transport proteins?
integral membrane proteins containing trans-membrane segments
what are the 2 main types of transport proteins?
Carrier proteins
Channel proteins
what do carrier proteins do?
Facilitate traffic in either direction (inward/outward)
Bind one/more solute molecules on one side of the PM, then undergo a conformational change
how are carrier proteins categorised?
based on the number of solutes transported and the direction they move
what are the 3 types of carrier proteins?
Uniport: Single solute
Symport: 2 solutes / simultaneously
Antiport: 2 solutes / opposite directions
why doesn’t glucose move by simple diffusion?
Too large and too polar to diffuse across unaided
how does glucose transport occur?
Erythrocytes: Glucose transporter GLUT 1 (uniport)
integral membrane protein
Where are other glucose transporters located?
Liver & Muscle
what do channel proteins do?
Form hydrophilic transmembrane channels
Allow specific solutes to pass PM/no change in shape
what are the 3 types of channel protein?
Ion channels
Porins
Aquaporins
what are ion channels?
Small pores lined with hydrophilic AA side chains
what do ion channels allow?
Allow rapid passage of specific ions
Na+, K+, Ca2+, and Cl-
are ion channels gated?
yes, pore opens/closes in response to stimulus
what are the 3 kinds of ion channels?
Voltage gated: change in memb potential
Ligand gated: binding of specific molecules
Mechano-sensitive: mechanical forces
why are ion channels important?
Play a vital role in cellular communication via regulation of ions passage across memb
what do ion channels maintain+example?
maintain salt balance in cells
eg. a specific Cl- ion channel maintains conc in lung epithelial cells (airways)
why is maintaining salt balance in the lungs important?
Defects: excessive mucus build up in lungs -> Cystic Fibrosis
what is active transport?
Movement of solutes against conc or electrochemical gradient
requires ATP
what are the 3 major functions of active transport?
Uptake of nutrients when conc higher inside cell
Secretory products & waste materials removed
Enables cells maintain intracellular conc inorganic ions
what does active transport involve?
membrane proteins: pumps
transport system / exergonic reaction
how do solutes move in active transport?
moved in one direction: unidirectional process
what is a result of active transport?
a non-equilibrium steady state
what is the role of Na+/K+ pump present on PM?
Maintains electrochemical ion gradients
increase [ K+] [ Na+] =inside
decrease[K+] increase[Na+] =outside
what does the activation of ATPase allow?
K+ pumped inward & Na+ outward
How are large materials transported across PM ?
Exocytosis and Endocytosis
what is Exocytosis and Endocytosis involved in?
in the delivery, recycling and turnover of membrane proteins
what is exocytosis?
Process by which the contents of secretory granules (intracellular molecules) are released to the exterior of the cell
Vesicle fuse with PM in releasing process
What kind substances released by exocytosis?
Peptides and protein hormones
Enzymes
Neurotransmitters
what is endocytosis?
Process by which external materials are internalised by cells
what happens in endocytosis?
A small segment of PM progressively folds inward
It pinches off to form an endocytic vesicle containing ingested substances or particles
what is endocytosis important in?
Ingestion of nutrients by some organisms
Defence against microorganisms by WBC
give examples of endocytosis
Phagocytosis ‘cellular eating
Pinocytosis ‘cellular drinking’
what happens in phagocytosis?
Large and solid particles are ingested
give examples of phagocytes
Macrophages
Neutrophils
what is pinocytosis?
Liquids containing soluble molecules are taken up
what happens in pinocytosis?
Nonspecific in the substances that it transports
An invagination into the cell
Pinching off inside the cell to form coated vesicles (clathrin)
