biological membranes Flashcards
describe the structure of a phospholipid
phosphate head- soluble in water, hydrophilic and polar
fatty acid tails- insoluble, hydrophobic and non-polar
give 3 roles of cell membranes
barrier between internal and external environment
location of chemical reactions
protection
why hydrophobic molecules (e.g. steroids) pass through the membrane easily
phospholipid bilayer is hydrophobic
why can water molecules pass through easily even though they are polar
they are extremely small
why does cholesterol increase the strength of the cell surface membrane
polar, hydrophilic group attracts polar phosphate heads in the phospholipids
non-polar, hydrophobic groups attracts non-polar fatty acid tails in the phospholipids
give 2 advantages of cholesterol
maintains fluidity of membrane
maintains strength
reduces the movement of water soluble chemicals
why is it called the fluid mosaic model
fluid- phospholipids can move around (flexible and can change shape)
mosaic- arrangements of proteins vary
what are intrinsic proteins
embedded in the membrane from one side to the other
how are intrinsic proteins hydrophobic
they have hydrophobic amino acid groups on the outside surface of the protein which interact with the hydrophobic fatty acid tails
what are the 2 types of intrinsic proteins
channel proteins
carrier proteins
what is the role of channel proteins
allow water soluble molecules and ions to diffuse through
why do channel proteins allow water soluble molecules to diffuse through
the central pore is lined with hydrophilic amino acids
what is the role of carrier proteins
they change tertiary shape or position to transfer ions or molecules from one side of the membrane to another side
give 3 roles of extrinsic proteins
structural role
act as enzymes
receptors (e.g. hormones)
how are extrinsic proteins different to intrinsic proteins
extrinsic don’t span the membrane whereas intrinsic proteins do
what are glycoproteins
carbohydrate molecule attached to the protein
give 3 roles of glycoproteins
allow cells to attach to each other (to make tissues)
present antigens
receptors for hormones
what are glycolipids
carbohydrate molecule attached to the phospholipid
give 3 roles of glycolipids
antigens
recognition
define diffusion
the net movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient
why is diffusion a passive process
no metabolic energy is required to take place
give 6 factors that affect the rate of diffusion
concentration gradient
particle size/charge
temperature
surface area
distance
presence of carrier/channel proteins
why does particle charge affect the rate of diffusion
ions with a charge will not pass through the membrane due to the hydrophobic core
why does temperature affect the rate of diffusion
particles have more kinetic energy
what happens in facilitated diffusion
hydrophilic substances pass through the cell membrane through intrinsic proteins (carrier and channel proteins)
give 2 key facts about protein channel
they are selective of the chemical it passes through
some are constantly open and others open via a trigger
is facilitated diffusion passive?
yes
what protein is used in active transport
carrier proteins
define active transport
the net movement of molecules from a region of low concentration to a region of high concentration against a concentration gradient
is active transport passive
no
how is metabolic energy is required
ATP
how does active transport work
molecule attaches to a receptor site on a carrier protein
ATP undergoes hydrolysis creating ADP and phosphate ATP binds to the carrier protein causing it to change shape
the changing of shape causes it to transport the molecule so it can leave via the other end of the membrane where it is released
what are product after ATP is hydrolysed
ADP and phosphate
why do we find a lot of mitochondria in cells that perform a lot of active transport
active transport uses a lot of ATP
define 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
what water potential is pure water
0
what is the unit of water potential
kPa
what is water potential a measure of
pressure
what is the highest possible water potential
0
define hypertonic
lower solute concentration in the inside than on the outside, causing water to leave the cell to a higher concentration of water
what can hypertonic lead to
plasmolysis (shrivelled up)
define hypotonic
higher solute concentration in the inside than the outside, water enters cells where there is a higher concentration of water
what can hypotonic lead to
cytolysis
define isotonic
equilibrium
what do both endocytosis and exocytosis transfer
large quantity of material (bulk transport)
what is phagocytosis
when solid materials are taken in by endocytosis
what is pinocytosis
when liquid materials are taken in by endocytosis
what is endocytosis
material into the cell
what is exocytosis
material out of a cell
are endocytosis and exocytosis passive
no- they require energy
