Physiology Flashcards
Wy are membranes important?
outer boundary
- controls entry and exit - maintains ion conc - functional differences in cells are to do with the composition of their plasma membrane
What are membranes mainly composed of?
- phospholipids - form complex structures in aqueous solution
- they can twirl vibrate and move about on their own
- cholesterol aids in the stiffening of the cell membrane
What are membranes impermeable to?
- water soluble substance - ions, proteins, sugars are insoluble in hydrophobic membrane core
- small uncharged polar molecules can cross fairly freely (O2 etc)
Why is the lipid bilayer important (3 things)
- forms basic structure of membrane
- hydrophobic barrier serves as a barrier - maintain diff in solute composition and concentrations inside and outside the cell
- responsible for fluidity of membrane - enables cell to change shape
What is the difference between peripheral and integral proteins?
p - not embedded within membrane, adhere tightly to surfaces of PM
I - transmembrane proteins (span lipid bilayer), embedded and linked to a lipid component of the membrane or a fatty acid that links into membrane
What are some functions of integral membrane proteins?
- ligand binding receptors - hormone receptors
- adhesion molecules - regulating cell shape and growth, pores and channels (conduits that allow ions to flow), carriers (facilitate or transport a molecule to other solutes) and pumps (energy from ATP to drive the transport)
can also be enzymes
docking marker acceptors - interact with secretory vesicles leading to exocytosis
What is the glycocalyx?
- a layer of glycoproteins and glycolipids
- small amount of membrane carb is located on the outer surface of cells (sugar coating)
Why is the glycocalyx important?
self identity markers - important in cell to cell interactions and in tissue growth - cancer cells have abnormal surface markings
What are some specialised cell junctions that are linked?
tight, desmosomes and gap junctions
- tight junctions - join lateral edges of epithelial cells near their lumen (tight or leaky)
- desmosomes - adhering junctions that anchor cells together especially in stretch - skin heart
- gap junctions - communicating junctions - allow movement of ions and small molecules between cells
What are the two things that influence whether a particle can permeate the plasma membrane or not
- solubility of particle
- the size
How can molecules or ions penetrate membrane passively?
- diffusion down a concentration gradient
- movement along an electrical gradient
What makes up fick’s law of diffusion?
- magnitude of concentration gradient
- surface area of the membrane across which the diffusion is taking place
- lipid solubility of the substance
- molecular weight of the substance
- distance through which diffusion must take place
How are ions affected by electrical charge?
- move passively along their electrochemical gradient
- electrical gradient is created when there is a difference in charge in two areas, moves towards area of opposite charge
- move through ion-specific channel proteins (leak or gated)
Define osmosis:
- net diffusion of water down its own concentration gradient through a selectively permeable membrane
- permeate more than expected through aquaporins (water channels)
What is osmolarity?
concentration of osmotically active particles in a solution
tonicity?
what is hypotonic
what is hypertonic
- effect a solution has on cell volume - (iso, hypo, hypertonic) eg isotonic saline that have the same electrolytes as the plasma in the human body
- hypotonic - water diffuses into the cell and causes swelling
- hypertonic - water diffuses out of cell and the cell starts to shrink
What are some passive transport mechanisms?
- diffusion down concentration gradients (simple diffusion)
- movement along electrical gradients (ion channels)
- osmosis - dependant on size and lipid solubility
poorly lipid soluble polar molecules - glucose + amino acids - iosn have to be transported against conc gradient
- What are the two different mechanisms for selective transport
carrier-mediated transport or vesicular transport
What is carrier mediated transport and state 3 important characteristics of this
- substance binds onto a specific carrier which undergoes a conformational change to transport the substance
- can take 2 forms active or passive (facilitated)
- faciliated uses a carrier to help move the substance down a conc gradient
- active transport requires energy
- 1 - specificity
- 2 - saturation (transport maximum)
- 3 - competition
how does facilitated diffusion work?
- enters protein and binds
- flips protein 180 so binding site is facing the low conc - goes back to normal
How does active transport work?
- primary - direct use of energy
- carrier splits up ATP into ADP and P, P binds to carrier to increase affinity, ions binds to carrier which flips the site and releases the ion and the P
- secondary - uses second hand energy from ion concentration gradients
What is the energy used to drive Na+ potassium pump also used for?
energy used to drive pump indirectly serves as the energy source for secondary active transport
What is the definition of secondary active transport?
The transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force
what are the mechanisms involved?
- symport - solute and NA move in the same direction
- antiport - solute and Na move in opposite directions
How does vesicular transport work?
endocytosis and exocytosis?
- requires energy for vesicle formation and movement within the cell
- endocytosis - pinching off of membrane to engulf substance
- exocytosis - vesicle fuses with the membrane releasing its contents into the ECF - (secretion of enzymes, ways of adding carrier or channels into membrane)
What is membrane potential?
- separation of opposite charges across the membrane
- plasma membranes of all cells are electrical polarised
What is responsible for potential across a membrane?
separated charges at each side of the membrane that form a layer along the plasma membrane
Is the membrane charged? what does Em refer to?
- no
- Em = difference in charge between thin layers of ECF and ICF located next to the outside and inside of the membrane, respectively
- What cells have the ability to produce rapid transient changes in membrane potential?
nerve or muscle cells - when they are excited they produce something called action potentials
Why does Em exist?
differences in the concentration and permeability of key ions in the ECF and ICF
Describe the flow of potassium and sodium (conc gradient)
- potassium is outward
- sodium is inward
- both cations the electrical gradient will always be towards the negatively charged side of the membrane
- when at rest membrane is 100x more permeable to potassium
Describe the equilibrium potential for potassium ions
- electrical gradient is moving the potassium back into the cell
- concentration gradient is moving the potassium out of the cell
- (equilibrium potential for K+ = Ek)
- membrane potential at Ek = -90mV (negative inside the cell)
What is the nernst equation used for?
calculate equilibrium potentials for any given ion
What is the general resting potential for a membrane? why is this
- -70mV
- because K leaves the cell more than sodium leaves the cell therefore a lack of positive charge in the cell leaves the resting membrane potential to be negative
What is the goldman-hodgkin katz equation used for?
calculate resting membrane potentials
What is the sodium potassium pump used for?
- it has a hyperoplarizing current
- potassium gradient is the most important thing in setting the membrane potential
What is the difference between depolarisation and hyper
- when the membrane potential becomes less negative
- when the membrane potential gets more negative
what does the direction of change in potential depend upon?
- the charge carried by the moving ion
- the direction of the moving ion
Why does sodium travel into the cell?
- conc gradient is inward and so is electrical gradient
- it moves due to cell membrane sodium selective channels
- the driving force when negative causes inward movement of sodium
Why does potassium move out of the cell
conc gradient is outwards and has an energy that exceeds the electrical gradient which is pointing into the cell
what are some types of ion channels?
opened - gated
- membrane voltage activated
- chemical substances - ligand gated ion channels
- physical stimuli - mechanical or thermal
Which are responsible for action potentials in neurones?
Voltage activated Na and K channels