2.3 Transport Across Cell Membranes Flashcards
What are the 5 processes that movement across membranes occurs by?
Simple diffusion Facilitated diffusion Osmosis Active transport Co-transport
What is the cell surface membrane?
The plasma membrane around the cell
Give examples of organelles surrounded by two plasma membranes?
Mitochondria
Chloroplasts
What are the components of a cell membrane?
Intrinsic protein Extrinsic protein Hydrophilic phospholipid heads Hydrophobic phospholipid tail Glycoprotein Glycolipid Cholesterol Pore
Why is the term “fluid-mosaic” used to describe the arrangement of the cell membrane?
Fluid- molecules in the membrane are able to move (swap places with each other)
Mosaic- proteins float in phospholipid bilayer(stuck like mosaic tiles)
Define diffusion.
The net movement of molecules or ions from an area of high concentration to an area of lower concentration
No additional energy input required (the process is passive)
Is diffusion a passive or active process?
Passive
What properties are required for molecules in simple diffusion?
Insoluble in water Soluble in lipids (to pass across the phospholipid bilayer) (eg h2o, co2, o2) Small Non-polar
Describe facilitated diffusion with channel proteins.
Channel proteins form a water filled pore in the membrane Charged substances (usually ions) can then diffuse across the membrane Most channels can be gated which allows the cell to control entry and exit of ions
What does it mean if a membrane channel is gated?
It can be opened or closed
How do cell-surface membranes and the membranes around the cell organelles of eukaryotes relate?
The basic structure is the same
What do you call the structure comprised of hydrophobic phospholipid tails and hydrophilic phospholipid heads?
Phospholipid bilayer
What is a glycolipid?
Receptor site (eg for toxins)
Carbohydrate covalently bonded with a lipid
Maintain stability of the membrane
Helps cells to attach to one another to form tissues
What is a glycoprotein?
Receptor site (eg for hormones)
Carbohydrate attached to many extrinsic proteins
Help cells to attach to one another to form tissues
Allow cells to recognise each other (eg lymphocytes can recognise an organisms own cells)
Describe extrinsic proteins?
Only in one layer
Add more stability
Eg enzymes
Describe intrinsic proteins?
Cross the bilayer
Facilitate transport across the membrane
Eg carrier/channel proteins
How are hydrophobic phospholipid tails useful in the cell surface membrane?
Allow selectivity in what diffuses in and out
Stops the loss of water soluble/polar molecules from inside the cell
How are hydrophilic phospholipid heads useful in the cell surface membrane?
Small/ non-polar/ lipid soluble substances pass in/out here
Eg water/oxgygen
What three types of substance pass through the phospholipid bilayer without a facilitator?
Small
Non polar
Lipid soluble
How does cholesterol provide stability in cell surface membranes?
Binding phospholipid heads
Restricting movement of other molecules making up the membrane
Describe facilitated diffusion with carrier proteins.
Carrier proteins have a specific binding site for a specific solute
They constantly flip between two states so the site is alternately open to opposite sides of the membrane
The substance binds on the side where it is at high concentration and is released where it is at low concentration
Name a similarity between simple and facilitated diffusion?
Both high to low (down the concentration gradient)
Name a difference between facilitated diffusion and simple?
Facilitated needs a protein but simple doesn’t
Why does facilitated diffusion have a curved relationship on a graph and a maximum rate?
As the rate of diffusion is limited by the number of transport proteins
What is Fick’s Law?
Diffusion is proportional to surface area*difference in concentration/ length of diffusion path
Name a similarity between simple and facilitated diffusion?
Both high to low (down the concentration gradient)
Name a difference between facilitated diffusion and simple?
Facilitated needs a protein but simple doesn’t
Why does facilitated diffusion have a curved relationship on a graph and a maximum rate?
As the rate of diffusion is limited by the number of transport proteins
Define osmosis.
The net movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane
Define water potential.
The potential energy of water to move (the pressure created by water molecules)
What is the pressure of pure water?
0 kPa
Give an example of the pressure of a concentrated solution.
Anything below 0
Eg -500 kPa
Why does pure water have a higher pressure than a concentrated solution?
Water molecules hitting the container create a pressure
Adding a solute causes water to hang around the solute molecules
There’s now less collisions against the container
Define crenation.
Water moves out of animal cell
Define plasmolysis.
Water moves out of plant cell
What is lysis?
Where a cell bursts because too much water has moved into it by osmosis
What sort of solutions encourage lysis of animal cells?
Pure water
Why don’t plant cells burst in a pure water solution?
The cell fills with with water but doesn’t burst Because the cell wall is strong and stops this
Cell becomes turgid instead
What is an isotonic solution?
Where the osmotic pressure is the same in and out of the cell
What happens to an animal cell in a isotonic solution?
Cells stays the same size
Amount of water moving in and out of the cell is the same
What happens to a plant cell in an isotonic solution?
The cell stays the same size
Amount of water moving into an out of the cell is the same
Why does an animal cell undergo crenation in a concentrated solution?
Too much water has moved out my osmosis
What happens when plant cells undergo plasmolysis in a concentrated solution?
Cell membrane pulls away from the cell wall
The cell wall maintains the shape of the cell and stops it from shrivelling up
Define active transport.
The net movement of water molecules or ions
From an area of lower concentration to an area of higher concentration
Using energy from the hydrolysis of ATP
Using carrier proteins
Describe the role of carrier proteins in active transport?
A molecule/ion binds to the receptor site in the carrier protein
Inside the cell, ATP binds to the protein and splits into ADP + Pi
The protein changes shape and opens to the other side of the membrane
The molecule/ion is carried to the other side
The Pi is released to which causes the protein to go back to its original shape
What’s the ratio of sodium to potassium in a sodium-potassium pump?
3Na+ : 2K+
Which direction do potassium and sodium go in a sodium-potassium pump?
Sodium leaves the cell
Potassium enters the cell
How does high temperature affect the rate of active transport?
Tertiary structure changed as hydrogen bonds are broken by increased kinetic energy
Less successful collisions
Less enzyme-substrate complexes formed
How does high oxygen concentration affect rate of active transport?
Facilitates aerobic respiration (in mitochondria)
More energy released
Works against the concentration gradient
How do respiratory inhibitors such as cyanide impact active transport?
Cyanide is an enzyme inhibitor in aerobic respiration
Less energy is released
Why do cells conducting active transport require large amount of mitochondria?
Facilitates aerobic respiration
Produces a lot of ATP
Needed for active transport
Why do cells carrying out active transport need a large surface area?
More membrane means more proteins
Proteins are needed for active transport
Why do cells carrying out active transport have a high concentration of ATP?
Broken down to release energy
Used for active transport
Name a structure you would expect to see in a cell that carries out active transport and why?
Ribosomes
Produce carrier proteins that facilitate active transport
Define co-transport.
Absorbing glucose into the blood
What are the three stages of co-transport?
Sodium-potassium pump
Facilitated diffusion with a channel protein
Facilitated diffusion with a carrier protein
Describe step 1 of co-transport.
Sodium moves out of the cell by active transport
Potassium moves in to the cell by active transport
Sodium ion concentration decreases inside the cell
Sodium ions are moved away by the blood stream
Describe step 2 of co-transport.
Sodium ions diffuse into the cell
The protein also moves glucose/amino acid molecules in
Describe step 3 of co-transport.
Bloodstream has low glucose concentration as it constantly carries it away
Glucose is high concentration in the cell
Facilitated diffusion out of the cell from high to low concentration
What are the functions of cholesterol in the membrane?
Reduce lateral movement of other molecules including phospholipids (stability)
Make the membranes less fluid at high temperatures
Prevent leakage of water and dissolved ions from the cell (cholesterol is hydrophobic)
What makes channel proteins selective?
They only open in the presence of a specific ion
Why do passive diffusion processes need no additional energy?
They rely on the kinetic energy of all molecules
How can haemolysis be prevented in cells?
By living in a liquid with the same water potential as the cell
Eg blood cells in blood plasma
How is active transport different form passive forms of transport?
Requires energy from ATP
Moves against concentration gradient
Only carrier proteins involves
Very selective
Why is co-transport important in the body?
Absorbs more glucose and amino acids into the blood
As diffusion only make concentrations either side of the intestinal epithelium equal
What makes co-transport an indirect form of active transport?
Is is the sodium ion concentration gradient that powers the movement of glucose and amino acids into cells (not ATP)
