transport across cell membranes Flashcards
what are the 4 functions of cell membranes ( plasma membranes)
1) control the movement of substances into and out of cells
2) to keep the cells contents together and seperate from other cells
3) to allow communication between cells
4) membranes allow cellular compartments to have different conditions
describe the cell membrane
cell membranes are complex structures made up of two layers of lipids called a phospholipid bilayer. the phospholipid bilayer consists of phospholipids , cholesterol, glycolipids , glycoproteins and proteins scattered throughout
what is the head of the phospholipid
hydrophillic head - polar and soluble
what is the tail of the phospholipid
hydrophobic , non polar and insoluble
explain why phospholipids form a bilayer in plasma membrane
phospholipids have a phosphate group which are hydrophillic and will face the solution . the fatty acid tails which are hydrophobic will move away from aqeuous enviroment . phospholipids will form two layers with the hydrophobic fatty acid tails facing inwards and phosphate groups outward towards the solution
what is the cell surface membrane
the plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the enviroment
what are the functions of phospholipids in the plasma membrane
allow lipid - soluble substances to enter and leave the cell
prevent water soluble substances leaving and entering the cell
make the membrane flexible and self healing.
what is the fluid mosaic model
fluid - moving , phospholipids can move around within each layer so membrane is flexible
mosaic - made of pieces eg proteins
where is the model from
the agreed structure is based upon experimental and chemical evidence and so is classed as a model
what are the two types of proteins in the membrane
extrinsic or intrinsic
what are the functions of the proteins in the cell membrane
provide structural support , act as channels supporting water soluble substances across the membrane , allow active transport across the membrane through carrier proteins , form cell- surface receptors for identifying cells , help cells adhere together , act as receptors for example for hormones
what does the cholesterol do
cholesterol molecules occur within the phospholipid bilayer of the cell - surface membrane . they add strength to the membranes . cholesterol molecules are very hydrophobic and therefore play an important role in preventing loss of water and dissolved ions from the cell . furthermore cholesterol pull together the fatty acid tails limiting their movement without making the membranes as a whole too rigid
describe glycolipids
glycolipids are made up of a carbohydrate covalently bonded with a lipid . it extends from the bilayer into the watery enviroment where it acts as a cell surface receptor for specific chemicals their functions are too
act as recognition sites
help maintain the stability of the membrane
help cells attach to one another and so form tissues
describe glycoprotiens
carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane . these glycoproteins also act as cell - surface receptors more specifically for hormones and neutrotransmitters .
the function of glycoproteins are too
act as recognition sites
help cells to attach to one another and so form tissues
allows cells to recognise one another , for example lymphocytes can recognise organisms own cells
in general why do most molecules not freely diffuse across the membrane
because many are
not soluble in lipids and therefore cannot pass through the phospholipid bilayer
too large to pass through the channels in the membrane
of the same charge as the charge on the protein channels and so even if they are small enough to pass through , they are repelled
what is the definition for simple diffusion
simple diffusion is the random net movement of ions or molecules down their concentraion gradient from regions of higher concentration to regions of lower concentration until they reach an equilibrium. it doesnt require energy from ATP
what is facilitated diffusion
the cell membrane is not readily permeable to molecules . some larger molecules eg amino acids glucose and ions cannot diffuse directly through the cell membrane due to the hydrophobic nature of the fatty acids . instead they are ‘ facilitated’ and diffuse though carrier proteins or channel proteins . ( particles still move down a concentration gradient and it doesnt require energy from ATP)
describe facilitated diffusion through protein channels
small ions are able to diffuse passively through protein channels down a concentration gradient . the channel is selective , each opening in the presence of a specific ion . the ion binds causing the protein to change shape and opens it
describe facilitated diffusion through carrier proteins
a large molecule attaches to a carrier protein , then the protein changes shape , this releases the molecule on the oppositte side of the membrane
What is the definition for osmosis
Osmosis is the net movement of water molecules from a solution with a higher concentration of water to a solution with a lower concentration of water through a partially permeable membrane
What is the definition for osmosis in terms of solute
Osmosis is the net movement of water molecules from a solution with a lower concentration of solute to a solution with a higher concentration of solute through a partially permeable membrane
What is a hypotonic solution
A solution that surrounds the cell and has a lower concentration of solutes on the outside of the cell when compared with the inside of the cell
What is a hypertonic solution
A hypertonic solution is a solution that surrounds the cell and has a higher concentration of solutes on the outside of a cell when compared with the inside of a cell
What is an isotonic solution
A solution that surrounds the cell that has equal amounts of water and solute particles
What is water potential
Water potential is the pressure created by water molecules under standard conditions of temperature and pressure . Pure water is said to have a water potential of zero
The water potential of a solution always is less than zero
Water will move from a region of ……………. Water potential to one of a …….. water potential
High (less negative ) , lower (more negative )
When does osmosis happen the fastest
When the concentration gradient is the biggest
what is the definition for active transport
active transport is the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
what are the needs for direct active transport
- required metabolic energy(ATP)
-against concentration gradient
-
How does direct active transport work
The molecule or ion to be transported attaches to a receptor site on the carried protein , the molecule of ATP binds to the carrier protein and ATP undergoes hydrolyisis . Shape change which allows the carrier protein to transport the molecule or ion to the other side of the membrane
Why would a cell have a lot of mitocondria
Because active transport uses a lot of ATP
What 2 other notes is there for active transport
Active process
Each carrier protein is specific
What is the role of the ileum
To absorb the molecules produced by digestion , this includes glucose
Describe the mechanism for the absorption of amino acids in the ileum
-Facilitated diffusion of amino acid into epithelial cell when there is a higher concentration in lumen of ileum
-co transport
-sodium ions are actively transported from the cell to the bloodstream , creating sodium ion concentration gradient
-facilitated diffusion of amino acid into blood . The energy for the transport comes indirectly from the concentration gradient of the sodium ion
what are co - transporters
co transporters are a type of carrier protein , they bind 2 molecules at a time and the concentration gradient of one molecule is used to move the other molecule against its own concentration gradient
what are the factors that affect the rate of active transport
- the speed of the individual carrier proteins - the faster they work , the faster the rate of active transport .
- the number of carrier proteins present , the more proteins there are the faster the rate of active transport
- the rate of respiration in the cell and the availibility of ATP
what molecules can and cannot pass through the membrane
water soluble , large , polar substances cannot pass through they have to be passed through by facilitated diffusion
lipid soluble , non -polar , small substances can pass through by simple diffusion
