T2: Transport across Cell Membranes Flashcards
what are the functions of the cell surface membrane?
Forms the boundary between the cell and its environment
Controls the movement of substances in and out of the cell
phospholipid structure
hydrophilic head - interacts with water
hydrophobic tail - orientates itself away from water
fatty acid molecules repel water (non-polar/hydrophobic)
phosphate molecules attract water (polar/hydrophilic) - because of the charge on the phosphate
one fatty acid tail is saturated and the other is unsaturated
describe how phospholipids are arranged in a plasma membrane
in a phospholipid bilayer
hydrophobic fatty acid tails to inside
hydrophilic phosphate heads to outside
what is the ‘fluid mosaic’ model of the cell membrane?
‘fluid’ - phospholipid and proteins can move around within each layer so the membrane is flexible
‘mosaic’ - studded with proteins, arrangement varies
what are the 2 types of proteins found in cell membranes?
intrinsic - within the bilayer from one side to the other, have hydrophobic portions in contact with hydrophobic tails
extrinsic - found on the surface of one side, hydrophillic
what is the function of membrane proteins?
provide structural support
act as receptors for molecules (ext)
enzymes (ext)
act as channel and carrier proteins (intrinstic)
what is the function of cholesterol in the membrane?
ONLY found in animal cell membranes
prevents loss of water and dissolved ions from the cell, stops the cell from being too leaky
adds strength and rigidity to the membrane, pulls together fatty acid tails of phospholipid reducing movement
structure and function of glycoproteins and glycolipids
carbohydrate chain attached to a protein/lipid
provide membrane stability
act as cell-surface receptors for binding of molecules or recognition sites (cell-recognition)
also help cells to attach to each other (to form tissues)
glycolipids on the cell surface of RBC’s determine ABO blood groups
define simple diffusion
the net movement of particles from an area of higher concentration to a region of lower concentration gradient (down the conc gradient)
doesn’t require energy
partially permeable
how does concentration gradient affect diffusion?
the greater the concentration gradient, the faster the rate of diffusion
how does particle charge + size affect diffusion?
the cell membrane contains a hydrophobic core so charged particles CANNOT pass through (water is an exception, small)
generally the smaller the particle the greater the rate of diffusion
how does temperature affect diffusion?
the higher the temperature the faster the rate of diffusion because particles have more KE
how does surface area of the membrane affect diffusion?
diffusion takes place faster if the membrane has a larger SA
how does distance affect diffusion?
the shorter the diffusion distance, the faster the rate of diffusion
name all the factors affecting diffusion
temperature
concentration gradient
particle charge + size
SA of the membrane
diffusion distance
define facilitated diffusion
hydrophilic substances diffuse across the cell membrane via protein molecules
allowing them to cross without interacting with the hydrophobic centre of the phospholipid bilayer
define osmosis
the diffusion of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
how does water potential gradient affect osmosis?
the higher the water potential gradient, the faster the rate of osmosis
as osmosis occurs the water potential gradient decreases so the rate of osmosis levels off over time
how does thickness of membrane affect osmosis?
the thinner the membrane, the faster the rate of osmosis
how does SA of membrane affect osmosis?
the bigger the SA the faster the rate of osmosis
define active transport
the movement of particles into/out of a cell from a region of lower concentration to a region of higher concentration (against the conc gradient) using ATP and protein pumps
requires ATP
involves water soluble molecule (ions and polar)
carrier proteins act as pumps
what are all the factors affecting osmosis
water potential gradient
thickness of membrane
SA of membrane
how is active transport similar to facilitated diffusion?
a molecule attaches to the carrier protein
the protein changes shape moving the molecule across the membrane
the molecule is released
how is active transport different to facilitated diffusion?
active transport requires energy from the hydrolysis of ATP
active transport moves substances from low to high concentrations, facilitated diffusion does the opposite
both use carrier proteins, only f.diffusion uses channel proteins
what are co transporter proteins?
a type of carrier protein
bind to 2 molecules at once, the conc gradient of one of the molecules is used to move the other against the concentration gradient
describe the co transport system for glucose and amino acids
Sodium ions are actively pumped out by the Na+K+ATPase pump using ATP.
Sodium ions inside the cell are at a lower concentration than in the lumen.
Sodium moves into the cell from the lumen down its concentration gradient through a carrier protein.
Glucose moves in with it against its concentration gradient, creating a high concentration inside the cell.
Glucose moves into the blood by facilitated diffusion from a high concentration inside to a low concentration in the blood where it is quickly removed by the flow, maintaining a concentration gradient.
what factors affect active transport?
speed of individual carrier proteins
number of carrier proteins
the rate of respiration in a cell (availability of ATP), if respiration is inhibited then active transport can’t take place
