Biological membranes Flashcards
roles of membranes
- partially permeable barriers between the cell and its environment, between organelles and the cytoplasm within organelles.
- site of chemical reaction
- site of cell signalling
- compartalisation: provides specific conditions for certain reactions to occur
fluid mosaic model
proposed that the fabric of the membrane consisted of a phospholipid bilayer with proteins floating in it making up a mosaic pattern. The lipid molecules can change places with each other, and some of the proteins may move, giving fluidity
role of components in the membrane
phospholipid bilayer- allows the membrane to be partially permeable
cholesterol- restricts the lateral (sideways) movement of other molecules in the membrane regulating the fluidity.
peripheral proteins - provides mechanical support, or are connected to proteins or lipids to make glycoproteins and glycolipids which function is cell recognition, as receptors.
integral proteins- protein carriers or channel proteins involved in the transport of molecule across the membrane.
how do drugs and hormones move into a cell
they bind to the membrane-bound receptors
why is it important that the membrane fluidity is controlled?
so that at high temperatures the membrane is less fluid therefore preventing water and dissolved ions leaking out of the cell.
How does an increase in temperature affect the cell membrane structure?
as temperature increases, the phospholipids gain kinetic energy meaning thy will move more. This causes gaps to appear between the phospholipids so the membrane will become more permeable. at high temperatures the proteins in the membrane will denature,
How does a decrease in temperature effect the cell membrane permeability?
when water freezes it expands and forms ice crystals which pierce and break the cell membrane
how does ethanol and detergents affect the cell membrane permeability?
they both dissolve the phospholipid bilayer making the membrane more permeable
passive transport
substances that can be exchanged across cell membranes without requiring metabolic energy from cells(no ATP)
diffusion
the net movement of molecules from an area of higher concentration to an area of lower concentration
facilitated diffusion
the net movement of molecules from an area of higher concentration to an area of lower concentration across a partially permeable membrane via protein channels or carriers
what happens at an equilibrium?
the particles are still moving freely and randomly but there is no net movement
factors that affect the rate of diffusion
temperature- as temperature increases, molecules have more kinetic energy so rate of diffusion increase visa versa.
diffusion distance- the thicker the membrane the slower the rate of diffusion
surface area-more diffusion takes place across larger surface areas
concentration gradient- the steeper the concentration gradient the faster diffusion
osmosis
the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
water potential of water
0Kpa
effects of osmosis on animal cells
when water diffuses into the cell it cannot withstand the hydrostatic pressure so swells and burst this is known as cytolysis.
when water diffuses out of the cell the cell shrinks (crenated)
effects of osmosis on plant cells
when water diffuses into the cell the hydrostatic pressure increases and the cell becomes turgid due to its strong cellulose walls.
when water diffused out of the cell it becomes plasmolysed as the cytoplasm shrinks.
active transport
the movement of substances against their concentration gradient from low to high concentration of the substance, using ATP and protein carriers.
endocytosis
how large particles and molecules are transported into the cell(bulk transport).
types of endocytosis
phagocytosis- solid molecules
pinocytosis-fluid molecules
exocytosis
-Cytoskeleton contracts; to move the vesicle to the plasma membrane;
- The membrane of the vesicle and plasma membrane fuse;
releasing the contents.
explain how cell surface membrane contribute the process of cell signalling
- they release signal molecules by exocytosis
- glycoproteins and glycolipids act as receptors that are specific
- the signal molecule attaches to the glycoprotein/lipid causing a change in shape
- cell surface membrane allow entry of some signal molecules,.
how do vesicles move from one organelle to another
they move along microtubules which are extended
What is cell signalling
-Communication between cells;
-Cells working together;
To trigger a response;
Why do phospholipids arrange themselves in a bilayer at the cell surface?
-The hydrophilic heads orientate themselves towards water and the hydrophobic tails orientate themselves away from water;
-There is water outside of the cell (extracellular fluid)
and inside the cell (cytoplasm/intracellul ar fluid);
Role of glucolipid and glycoprotein
- Cell recognition/identification;
-Cell signalling; - Act as antigens:
Carrier protein
- transport large and polar substances
Channel proteins
- transports polar substances
What do we controll in the beetroot experiment
- Mass/length of the beetro¢t;
- Same species of beetroot;
- Same volume of water;
- ensure you dry beetroot sample once cut to remove any excess pigment caused by damaging the membrane in the cutting process
Control variables of the osmosis experiment
-same length of potato
-same potato
- same volume of solution
-same length of time
Why is it important to use percentage change in the osmosis experiment
- it takes into consideration the starting masses
Why would the mass of potato increases when put in pure water
-There is a higher water potential in the solution/water;
-Therefore water moves into the potato, from the solution; by osmosis; down the water potential gradient;
so the mass of the potato increases:
Why would the mass of potato decrease in a sugar solution
-There is a higher water potential inside the potato;
-Therefore water moves out of the potato, into the solution; by osmosis; down the water potential gradient; so the mass of the potato decreases
