Transport Across Membranes Flashcards
What is a plasma membrane
All membranes sighing and around all cells and organelles
Structure of plasma membrane
Phospholipid bilayer with hydrophilic heads facing outside and tails facing each other Proteins (extrinsic and intrinsic) Cholesterol in animal cells Glycolipids Glycoproteins
Cell - surface membrane is —— membrane
Plasma
Mitochondria membrane called/is
Two plasma membranes wrap around organelle
Phospholipid in plasma membrane purpose
Allows lipid soluble substances to enter and leave cell
Prevent water soluble substances entering and leaving cells
Make the membrane flexible and self sealing
Purpose of proteins in plasma membrane
Extrinsic - give mechanical support, or as cell receptors for hormones or in conjunction with glycolipids
Intrinsic - Protein channels or Carrier proteins for allowing water soluble molecules to pass or for active transport
Also help dells adhere together
What characteristics of molecules allow it to pass through phospholipid membrane by simple diffusion
Small,non polar apart from water which is small hence passes through
Extrinsic proteins means
Proteins that do not extend through bi layer/ on surface
Intrinsic proteins mean
Extend all the way through membrane
Phospholipid has
Single phosphate head and two fatty acid tails
Cholesterol purpose in bilayer only in animal cells k
Pulls fatty acid tails together, limiting movement
Reduces lateral movement of molecules including phospholipid
Less fluid membrane at high temperature
Prevents the leakage of water and dissolved ions from cells
Glycolipids made of
Carbohydrate covalently bonded to a lipid
Carbohydrate extends out of bi layer into watery environment where it acts as a receptor for specific chemicals
Blood type depends on
Type of receptor glycolipids
Glycolipids function
Recognition sites
Stability of the membrane
Help cells to attach to one and other and form tissues
Glycoproteins are
Carb chains are attached to extrinsic proteins on the outer surface more for hormones and neurotransmitters
Glycoproteins function
Recognition sites for neurotransmitters and hormones
Helps cells attach to each other and form tissues
Allows cells to recognise each other for example lymphocytes can recognise an organisms own cells
Why cholesterol only in animal cell membrane
Because animal cells don’t contain cell walls so need added protection and strength from cholesterol
Why can water pass through plasma membrane
Small enough
Fluid mosaic model of plasma membranes
Large macromolecular proteins floating in a sea of phospholipids
Why are plasma membranes described as adhering to the fluid mosaic model? 2 marks
The glycoproteins are embedded within the phospholipid hence like a mosaic and float and move within a sea of phospholipids hence fluid
Factors that affect the fluidity of plasma membranes
Saturated/unsaturated more flows if saturated
Temperature if higher more random movement so more fluid but then becomes disordered
Length
Osmosis definition
The passage of water from a region of high water potential to a region of low water potential, through a selectively permeable membrane.
Water potential
Psi = trident like symbols
Measures in kilopascals
Pressure created by water molecules
Under standard conditions (25°C and 100kPa) water potential is 0.
Increase in solute causes an —— in water potential
Decrease
Increase in solute and concentration cause an —— in water potential
Decrease
In terms of positive/ negative how does water move
Less negative to more negative
Water potential is equal inside cells and outside in solution when
There is no net movement of water
Osmosis will continue till
Enough H2O molecules will pass through the selectively permeable membrane for dynamic equilibrium to be obtained.
What is the highest value of water potential = only when water is pure.
0
A hypotonic solution
Higher concentratation in solution than in cell
A hypertonic solution
Higher concentration of solute in cell than solution
If RBC is in a solution with a higher water potential (hence less negative) then what happens
Absorbs water, then cell surface membrane will break (haemolysis)
A lower water potential
Means a less negative solution hence the cell will absorb water
A lower water potential of solution means
Means more negative hence water leaves cell
RBC in a soo with lower water potential hence more negative
Water leaves cell and cell shrinks
Haemoglobin is more concentrated hence darker
Cell shrivels and becomes cremated
Blood plasma and RBC have the same
Water potential
Plant cell places in a sol with higher water potential hence less negative
Water enters the cell
Protoplast swells
Cell is turgid
Wall of protoplast pushed against cell wall is
Turgid
Plant cell in sol with equal water potential
No change
Incipient plasmolysis when protoplast is beginning to pull away from the cell
Incipient plasmolysis
When protoplast begins to pull away from the cell
When plant cell is place in a solution with lower water potential hence more negative
Water leaves cell
Cell shrinks
Protoplast pulls complexity away from cell wall
Plasmolysis
Plasmolysis
Protoplast has been complete pulled away from cell wall
A hypotonic sol will have a —— water potential
Higher
A hypertonic sol will have a —— water potential
Lower
Diffusion definition
The net movement of molecules/ions from a region of high concentration to a region of low concentration until they are evenly distributed.
Diffusion is passive
Energy comes from the natural inbuilt motion of particles rather than an external source like ATP
Facilitated diffusion
movement of large/charged/polar molecules/ion through the plasma membrane vis transmembrane channels and carriers - no energy required
Why do charged/polar molecules not diffuse essily through plasma membrane
Due to Hydrophobic fatty acid tails
Protein channels are/do
Water filled hydrophilic proteins, hence allow water soluble molecules to pass
Very selective - only opens up in the presence of a specific ion
Ion bonds to protein causing a change of shape that closes one side of the membrane and opens up the other
Carrier proteins
When s molecule like glucose binds with its specific protein, a change in shape causes the glucose to be released to the inside of the membrane
What is the active transport def
The movement of molecules/ions from a region of low concentration to a region of high concentration (into/out of cell) using ATP and carrier proteins (also know as pumps)
Direct Active Transport Process
Intrinsic carrier proteins are specific to substrate
Molecule/ion binds to the receptor sited on the protein
On the insides of the carrier protein, ATP binds to the protein causing it to split into ADP and a phosphate molecule, hence protein shape changes and it opens to the opposite side
Molecule/ion is released as is the phosphate, which allows the protein to revert to its original shape
Phosphate molecule recombined with ADP to form ATP during respiration
4 ways direct active transport differs from passive transport methods
Metabolic energy in the form of ATP is needed
Against the concentration gradient whereas passive is down the concentration gradient
Carrier proteins/pumps are needed
Very selective (so is facilitated though!)
Explain the purpose of ATP in active transport (2 marks)
Directly moves molecules in direct active transport
Induvidually moves molecules using a concentration gradient already set up by active transport hence in co-transport.
Co - transport
More than one molecule is moved in the same direction by active transport
Sodium-Potassium Pump
Sodium ions are actively removed from cell/organelle, whilst potassium ions are actively taking in from the surroundings
NOT SAME DIRECTION OF TRAVEL
NOT CO-TRANSPORT
Use of sodium-potassium pump
Many processes including, the creation of nerve impulses.
Co-Transport of a glucose molecule full steps
1) Na+ ions moved out of epithelial cells, via sodium-potassium pump, which lowers intracellular concentration.
2) hence higher concentration of Na+ in blood than epithelial cell in lumen
3) Na+ ions diffuse from the lumen (cavity of ileum) into epithelial cells, down the concentration gradient. During this diffusion, glucose (or amino acids) are pulled in against glucose’s (or amino acids’) concentration gradient (in order to get the most of those molecules in the cell)
4) Glucose molecules leave the cell into blood plasma via facilitated diffusion using a third carrier protein.
Sodium potassium pump is — transport
Active
How does sodium leave the epithelial cell?
State the concentration gradient
Active transport via sodium - potassium pump
Low concentration to high concentration
How does glucose leave the epithelial cell?
State the concentration gradient
Via facilitated diffusion
High concentration to low concentration
How does sodium enter the epithelial cell?
State concentration gradient
Co - transport
High concentration to low concentration
How does glucose enter the epithelial cell?
Co - transport
Low concentration to high concentration
In the co - transport of a glucose molecule, how many proteins are used?
Three
One for sodium- potassium pump
One for sodium and glucose entering cell
One for glucose leaving cell
Rate of movement improve in ileum
Microvilli on villi greatly increase SA
Capillary = short diffusion distance
Constant circulation of blood and constant respiration maintains the concentration gradient (higher in the ileum than blood)
Active transport
Dilution series production
S
Concentration formula (osmosis)
V1= (C1xV2)/C2 1= stock solution 2= new solution
