lecture 3 control of the cellular membrane Flashcards
- Explain how a single cell can survive and function in isolation. - Distinguish the main structures and functions of a cell and its main organelles. - Explain how cell membranes create compartmentalization which regulate the flow of substances into and out of cells. - Describe the passive diffusion of water across semi-permeable cell - membranes and the role of aquaporins - Describe how the cell uses the Na-K ATP base to create the electrochemical gradient that provides the energy for l (18 cards)
how can cells survive and live in isolation
because of homeostasis. they can also have genetic control, motility (flagella or cilia that allow them to move to nutrients of away from harmful conditions, and metabolis and have membrane transport as well as specialised cells.
plasma membrane
has a phospholipid layer with hydrophobic tail and hydrophilic tail. it is semi permeable and. It doesn’t allow glucose or large molecules like proteins and RNA they differ in size and can be physically connected at times
how do molecules move inside the cell
they can move either through
1. active transport: uses ATP and allows molecules to go against a concentration gradient
2. passive transport: simple diffusion and facilitated diffusion down a concentration gradient
simple diffusion vs facilitated diffusion
simple diffusion just means the molecules freely enters the membrane whilst facilitated diffusion needs channels or transporters but still doesn’t use energy
what is diffusion
the net movement of substance moving down a concentration gradient- high to low concentration. with time. Its random distribution of molecules leads to equal distribution.
factors that need to be considered when thinking about the rate of diffusion
-Distance (larger the area that the molecules need to travel, the slower the diffusion is),
-temperature the higher the temperature, the faster the rate of diffusion is,
-characteristics of the solvent
mass
how does water move through cells
osmosis: (movement of water to equilibrate concentrations of water. ) the more solute in a given volume, the higher the concentration of the solute and the lower amount of water. Water travels to where its concentration is lower to reach equilibrium.
tonicity
refers to the osmotic pressure gradient. its the difference in solute concentration between two solutions separated by a semi permeable membrane. its the measure of how much solute there is per volume of solvent.
hypertonic
higher concentration of solute particles outside the cell than inside. to reach equilibrium, water goes outside the cell causing it to shrink
hypotonic
there is more solute inside the cell than outside, causing water to flow inside and expand, soon bursting.
isotonic
equal concentration outside and inside the cell (dynamic equilibrium)
how do ions cross the phospholipid layer
they use membrane proteins which allow molecules to go through. Eg. potassium channels and sodium channels. they vary in shape and size, sodium channels are tighter, slowing down their movement (tortouos trajectory) while potassium channels allowing for faster rate of movement (straight trajectory)
two ways ions get transported into cells
1.channels: allow facilitated diffusion until equilibrium is reached. eg. aquaporins- allow diffusion of water. allow water to pass through quickly
2. transporters: transporters can be facilitated- moves molecules one by one rather than allowing it all to pass through. it opens and closes or active transport- use ATP to drive movement of the solute against its concentration gradient.
sodium potassium pump
an active transport. utilizes ATP hydrolysis to drive the expulsion of three sodium ions and the uptake of potassium ions. There is unequal distribution which is made possible by the ATP energy. This means that there will be a buildup of negative charges inside the cell at resting stage. The membrane potential is determined by the concentrations of charged and chemical equilibrium and where it sits (goldman-hodgkin-katz equation.
Goldman-hodgkin Katz equation
the membrane voltage depends on the conductance of an ion and its concentration inside and outside.
how do molecules move against they concentration gradient.
active transport or facilitate transport through sodium gradient (there is more costume outside the cell than in), it can be harnessed by the transporters to pull the amino acid through with the sodium ions, moving those amino acids against their concentration gradient. some ions are electronically charged, repelling against molecules and sometimes not reaching equilibrium
purpose of sodium potassium pump and how this works
- moves sodium ions out of the cell and potassium ions in the cell. this stabilises the cells membrane potential and allow neurons to fire an action potential. uses ATP.
- atp binds to the pump, promoting binding of 3 sodium ions and release of 2 previously bound potassium ions. ATP is broken down and transfers a phosphate group to the pump, causing it to change shape, releasing potassium into the intracellular space and sodium ions to the extracellular space.simultaneously, it binds 2 potassium ions which makes the pump close. this results into a net loss of positive ions, making the resting phase of the cell more negative.
