4. Cell Membranes and Transport Flashcards
Draw and label a cell surface membrane (11)
glycoprotein, glycolipid, glycocalyx, phosphate head, fatty acid tail, phospholipid (bilayer), hydrophobic core, carrier protein, channel protein, cholesterol, glycoprotein
What is the fluid mosaic model?
fluid: phospholipids and proteins can move about by diffusion; phospholipids can move sideways in their layers, and proteins can move within the bilayer
mosaic: scattered protein molecules when viewed from above
What affects fluidity?
1) fatty acid tails: the more saturated, the less fluid
2) presence of cholesterol
3) length of fatty acid tails: longer = less fluid
4) temperature: lower temp. = less fluid
What are the functions of cholesterol in the cell surface membrane? (3)
1) responsible for mechanical stability and strengthens the membrane
2) hydrophobic regions prevent ions or polar molecules from passing through
3) maintains fluidity by preventing phospholipid tails from packing too closely together at low temperatures, so that cells can withstand colder pressures
What are the functions of carbohydrate chains glycolipid and glycoprotein? (2)
1) act as receptor molecules
– bind with particular substances at the cell surface
2) cell to cell recognition
– bind to complementary sites on other cells
What are the functions of protein in the cell surface membrane? (2)
1) act as enzymes
2) some proteins on the inside are attached to a system of protein filaments – cytoskeleton: helps to maintain and decide the shape of the cell
3) act as transport proteins: carrier or channel
5 types of movement of substances across membranes
1) diffusion
2) osmosis
3) bulk transport
4) active transport
5) facilitated diffusion
List 3 points about water potential
1) high water potential to low water potential
2) highest water potential is 0, then it goes into the negatives
3) equal water potential on both sides = no net movement
Unit for osmosis?
psi, trident shape
What is a hypotonic solution?
water moves from solution into the cell
What is a isotonic solution?
both solutions have a same water potential
What is a hypertonic solution?
water moves from the cell to the solution
What is it called when cells burst from osmosis?
lysis
What is it called when cells shrivel from osmosis?
crenation
What is incipient plasmolysis?
when 50% of the cells are plasmolysed, occurs when the surrounding solution has the same water potential as the plant cells
The gaps caused by plasmolysis are filled with what?
the surrounding solution, NOT AIR
What affects the rate of diffusion?
1) steepness of concentration gradient
2) temperature
3) nature of molecules or ions
– large molecules need more energy to move
– non-polar molecules diffuse easier through cell membranes than polar molecules
4) surface area where diffusion takes place
Which 2 proteins are used in facilitated diffusion?
channel proteins and carrier proteins
What are aquaporins?
a part of facilitated diffusion, proteins that increase water movement across the cell surface membrane
Function of channel protein
has water-filled pores that allow hydrophilic ions or molecules to pass
Function of carrier protein
have specific shape for a particular type of ion or molecule, opens to allow a passage in and out the cell
What is active transport?
movement of molecules or ions through transport proteins against their concentration gradient, with the use of ATP
it requires intrinsic carrier proteins (pumps)
What is the function of the receptor site on the pump?
it is a receptor site for ATP, and acts as an ATPase enzyme which hydrolyses ATP into ADP
What is endocytosis?
engulfs material into cell
a form of bulk transport; by the infolding of the cell surface membrane to form vesicles containing the substance being transported
What is exocytosis?
material removed from cell
a form of bulk transport; by the fusion of vesicles containing the substance being transported with the cell surface membrane
What are phagocytosis and pinocytosis?
2 forms of endocytosis
phagocytosis: solid material
pinocytosis: liquid
Which processes require ATP?
active transport, exocytosis, endocytosis
