Unit 2 Exchange and Transport Flashcards
What are plasma membranes?
Plasma membranes are the combination of all membrane within the cell and the within organelles that have the same basic structure
Describe the cell-surface membrane?
The specific name given to the membrane that surrounds all the cells and its cell membrane as well as creating a barrier between the cytoplasm and the environment outside the cell
Describe the function of the cell-surface membrane?
It established different conditions inside and outside the cell as well as controlling the movement of substances inside and outside the cell
What are the component of the cell-surface membrane?
Phospholipids, proteins, cholesterol, glycolipids and glycoproteins
Give 2 reasons why phospholipids are important for the cell-surface membrane?
1) The hydrophilic heads of the phospholipids point outwards towards the cell-surface membrane attracted by water on both sides
2) The hydrophobic tails of the phospholipids point into the cell-surface membrane repelled by water on both sides
Through which portion do lipid-soluble substances enter the cell-surface membrane?
Lipid-soluble substances enter the cell-surface membrane via the phospholipid portion
What are the 3 functions of the phospholipids in the cell-surface membrane?
1) Allow the entry/exit of of lipid-soluble substances
2) Prevention of water-soluble substances entering or leaving the cell
3) Making the cell membrane flexible and self-healing
Where are proteins found within the cell-surface membrane?
They are interspersed throughout the whole cell-surface membrane
What is the 1st way proteins are interspersed throughout the cell-surface membrane?
Some proteins occur in the surface of the phospholipid bilayer and never extend across so they give mechanical support to the membrane, conjunctions with glycolipids and acts as cell receptors for hormones
What is the 2nd way proteins are interspersed throughout the cell-surface membrane? (1)
Other proteins completely span across the phospholipid bilayer. 1 type is called protein channels - water filled tubes to allow water-soluble ions to diffuse across the membrane
What is the 2nd way proteins are interspersed throughout the cell-surface membrane? (2)
2nd type is carrier proteins - bind to other molecules such as glucose and amino acids and these carrier proteins change in shape in order to move the molecules along the membrane
What are first 3 roles of the proteins along the membrane?
cp - carrier proteins
1) Provide structural support
2) Act as channels to transport water-soluble substances along the membrane
3) Allow active transport across membrane - cp
What are last 3 roles of the proteins along the membrane?
cp - carrier proteins
4) To form cell surface receptors for identifying cells
5) To help cells adhere together
6) Act as receptors for hormones
Where are the cholesterol molecules in the membrane?
Cholesterol molecules within the phospholipid bilayer of the cell-surface membrane
What does cholesterol add to the membrane?
Cholesterol adds strength to the membrane by pulling the hydrophobic tails of phospholipids together
What is the relation between cholesterol and water?
Cholesterol is a very hydrophobic molecule and so they help prevent loss of water and dissolved ions from the cell
What is an additional function of cholesterol in relation to structure?
Cholesterol also pulls together fatty acids tails of the phospholipid molecules which limits their movement as well as other molecules’ movement as well but at the same time allows the membrane not to be too rigid
What are the 3 main roles of cholesterol?
1) Reduces lateral movement of other molecules including the phospholipids
2) Makes the membrane less fluid-like at high temperatures
3) Prevent leakage of water and other dissolved ions
What is the definition of a Glycolipid?
Glycolipids are a carbohydrate covalently bonded with a lipid
Describe where the glycolipid is around the phospholipid bilayer?
Glycolipids portion extends from the phospholipid bilayer into the watery environment outside the cell in which acts as a cell-surface receptor for specific chemicals.
Give an example of a system that relies on the glycolipids on the cell-surface membrane as a receptor?
The human ABO system operates as a result of glycolipids on the cell-surface membrane
What are the 3 main roles of Glycolipids?
1) To act as a recognition sites
2) To help maintain the stability of the membrane
3) Help cells to attach to one another and form tissues
What are Glycoproteins?
Glycoproteins are Carbohydrate chains attached attached to many extrinsic proteins on the outer-surface of the cell membrane
What is a function of the Glycoproteins?
Glycoproteins act as cell-surface receptors mainly for hormones and neurotransmitters
What are the 3 main roles for Glycoproteins?
1) To act as recognition sites
2) Helps cells to attach to each other and form tissues
3) Allows cells to recognise other cells that come from the same group eg lymphocytes recognising another lymphocyte
What are the use of Inorgnic phospahtes in the phospholipid bilayer?
They make hydrogen bonds with water and other molecules.
3 things affected by the hydrogen bonds?
pH temp and alcohol concentration
Definition of diffusion?
The net movement of particles from an area of high concentration to low concentration gradient (down the concentration gradient) until Equilibrium occurs
What are the 4 reasons why most molecules don’t freely diffuse across the cell-surface membrane?
1) The molecules may be non-lipid soluble and can’t pass through the phospholipid bilayer
2) The molecules are too large to pass through the channels in the membrane
3) Even if the molecules are smaller enough to pass they may have the same charge so they become repelled
4) The molecules may be electrically charged so polar which makes it difficult to pass through hydrophobic tails in the phospholipid bilayer
Why is the cell-surface membrane described as fluid?
The phospholipids can move relative to each other and gives the membrane flexibility since it constantly changes shape
Why is the cell-surface membrane described as mosaic?
The proteins are embedded in the phospholipid bilayer with different shapes, sizes and patterns
So what are the 5 general functions of the cell-surface membrane?
1) Controlled exit and entry of substances in organelles such as chloroplasts and mitochondria
2) It separates organelles from the cytoplasm to allow specific metabolic reactions to occur
3) To provide an internal transport system
4) To isolate enzymes which might damage the cell
5) To provide surfaces in which reactions can occur
Give an example in which the cell-surface membrane provides a surface for reactions to occur?
Protein synthesis using ribosomes on the endoplasmic reticulum
What are the 3 facts about the motion of particles?
1) All particles are in constant motion due to the kinetic energy they possess
2) There is no set of pattern in which the particles move around, so motion is random
3) Particles are constantly bouncing off one another and other objects around
What substances can easily pass across the membrane?
Small non-polar molecules because they are easily diffused across such as oxygen and carbon dioxide
What substances can’t easily pass across the membrane?
Large polar molecules because of their size and difficult interaction with the hydrophobic tails of the phospholipids
How can the polar large molecules pass across the membrane?
The large polar molecules can pass across a transmembrane channel such as a channel protein or carrier protein via facilitated diffusion
How does facilitated diffusion occur?
Facilitated diffusion is a passive process that relies on the inbuilt kinetic energy of the diffusing molecules
Describe what a protein channel is like?
These proteins form water-filled hydrophilic channels across the membrane and are selective allowing the entrance to a specific ion
What is the role of a protein channel and how does it work ?
Protein channels allow water-soluble ions to pass through and open accordingly to the specific ion present. If the particular ion is present it binds with the protein causing the protein to change shape so the protein is open at one side and closed at the other.
If the ion is not present the channel will remain closed
What is a simple description of a carrier protein?
A transport protein that tends to span across the plasma membrane
Describe how a carrier protein works?
The protein changes shape (tertiary structure of the protein) in a way that the molecule is released inside the molecule, so the molecules move from an area of high concentration molecules to an area of low concentration of molecules
What is osmosis?
The movement of water from an area of high water potential to an area of low water potential across a semi-permeable membrane
What does the Greek letter psi represent
Ψ?
Ψ = Water potential units are measured in psi
What are the 2 units of measurements that water potential uses?
Water potential is measured in psi and units of pressure kPa
What is water potential?
Water potential is the pressure created by water molecules
What are the normal conditions for the temperature and pressure of water?
The temperature of water is 25 C and the pressure of water is normally at 100 kPa so water has a water potential of zero
What happens to the water potential of water when a solute is added to water?
The water potential will decrease
What does the water potential of water + solute be?
Water + solute -> must always be less than zero so a negative number
So what in simple terms to water’s water potential happens when more solute is added to water?
The more solute added to water the more concentrated a solution becomes so lower the water potential is and the more negative its water potential becomes
What happens when water’s water potential lower when more solute is added?
Water will move from an area of higher water potential (less negative) to an area of lower water potential (more negative) via osmosis
What are the numerical values given to less negative water potential and more negative water potential?
Less negative water potential = -20 kPa
More negative water potential = -30 kPa
How is it possible to determine the different water potentials around the cell or tissue?
Different water potentials can be determined by using different concentrations of solute and observing whether the solute goes into or out of the cell
Describe what happens when there is a high concentration of solute on the right an a low concentration of solute on the left?
1) Both the solute and the water molecules are moving at random motion due to their inbuilt kinetic energy
2) The selectively permeable plasma membrane only allows water molecules and not solute molecules
3) So the water molecules diffuse from a high water potential on the left to a lower water potential on the right which means they travel down a concentration gradient
4)They diffuse from left to right until the water potentials on both sides of the semi-permeable membrane are equal
When the water potential is equal on both sides of the semi-permeable membrane what does this mean?
Water potential equal on both sides means that there is no net movement of water and also there is a dynamic equilibrium established
What is different about the red blood cell cytoplasm?
Red blood cell cytoplasm contains a wide number of different solutes.
What happens when a red blood cell is place in pure water?
Hypotonic solution
The red blood cell will absorb the water by osmosis because it has a higher water potential outside the cell compared to within the red blood cell also since the cell membrane is very thin at 7nm so when too much water is absorbed the cell becomes swollen and the cell breaks resulting in the contents of the cell breaking out (Haemolysis)
How do the animals prevent their cells bursting out of overload of water?
Animal cells are usually placed within a liquid that has the same water potential as the cells such as the cells in the blood plasma in humans
What happens when a red blood plasma is placed in a solution with a lower water potential than the water potential inside itself? Hypertonic solution
The high water potential within the cell osmoses outside the cell where there is a lower water potential allowing the cell to shrink and become shrivelled
What happens when a red blood cell is put in a liquid with the same solute concentration as itself? Isotonic Solution
There is no net movement of water as a result of both sides of water potential being equal so the red blood cell stays the same
What happens when plant cells are placed in a solution of normal water?
Plant cells absorb the water due to the vacuole within the plant that contains dissolved sugars and ions which all have different solutes which means inside the plant cell there is a lower water potential and outside the cell there is a higher water potential so the water moves into the plant cell allowing it become swollen and turgid.
What is active transport?
The movement of molecules or ions unto or out of a cell from a low concentration to a high concentration using ATP and carrier proteins
What are 2 things that Atp is used to do?
Directly move molecules
Individually move molecules using a concentration gradient set up by active transport also known as co-transport
How does active transport differ from passive processes?
1) Metabolic energy is needed in the form of ATP
2) Substances are moved from a low conc to high conc against the concentration gradient
3) Carrier proteins acts as pumps are used
4) The process is selective which only specific substances being involved
What are the first 3 steps of using active transport on a molecule or ion?
1) The carrier proteins span the plasma membrane and bind to the ion or molecule to be transported to it
2) The molecule or ion binds to the receptor site on the carrier protein
3) Inside cell/organelle ATP binds to the protein splitting it into ADP and a phosphate molecule allowing the protein to change shape and open to opposite sides of the membrane
What are the last 2 steps of the active transport process?
4) The molecule or ion is released to the other side of the membrane
5) The phosphate molecule is released from the protein allowing the protein to revert to its original shape so the process can be repeated. The phosphate and ADP are combined together during respiration to form ATP
What are the binding sites of the carrier proteins different to?
They are different to enzyme active sites
Usually how many molecules are involved in active transport?
Sometimes more than one molecule or ion are moved in the same direction via active transport
Often there are more than one molecule or ion being moved into an cell/organelle while one is taken out
Give an example of more ions and molecules moving into a cell while an ion or molecule is removed?
The sodium potassium pump, the sodium ions are being removed from the cell/organelle while the potassium ions are taken in from the surroundings.
What is the sodium potassium pump useful for?
Many processes but mainly for the creation of a nerve impulse
Explain and describe what feature the epithelial tissue has along the ileum
The epithelial tissue along the ileum has microvilli which are finger-like projections of the cell-surface membrane, 0.6 micrometers in length, they seem like a brush under a light microscope
How do microvilli help along the epithelial tissue in the ileum?
Microvilli provide more SA for carrier proteins insertions through diffusion, facilitated diffusion and active transport.
They also help to increase transport across membranes increasing the number of protein carriers and protein channels in a given area of a membrane. Therefore increasing the density of carrier proteins and protein channels
How does diffusion involve in the absorption of molecules?
Diffusions allow there to be concentrations in either sides of the intestinal epithelium being equal so not all available glucose and amino acids can be absorbed and some may even pass out the body
Why is it that the glucose and amino acids don’t always pass out of the body?
The glucose and the amino acids are absorbed via active transport so all the glucose and amino acids are absorbed into the blood
Where does co-transport occur in the body?
When glucose and amino acids are drawn from the small intestine
Why is the term co-transport not diffusion used during the absorption of molecules/ions from the small intestine?
The glucose and amino acids are drawn into the cells along with the sodium ions that have been actively transported by the sodium potassium pump
Explain how the glucose and molecules are absorbed from the small intestine at the same time? First 2 steps only
1) Sodium ions are transported out of epithelial cells into the blood this happens in a one-type of protein-carrier molecule in the cell-surface membrane of epithelial cells
2) This maintains a much higher conc of sodium ions in the lumen of the intestine than inside the epithelial cells
Why in another way is it called co-transport not diffusion of sodium ions and glucose/amino acids?
Sodium ions and glucose molecules move into the cell but while the sodium ions are moving down the concentration gradient the glucose/amino acids are moving against the concentration gradient.
So the sodium ion conc gradient not the ATP directly powers the movement of glucose/amino acids into the cell. Making it in an indirect form of active transport
Explain how the glucose and molecules are absorbed from the small intestine at the same time? Last 2 steps only
3) Some ions diffuse into the epithelial cells down this conc gradient through a co-transport protein in the cell surface membrane as these sodium ions diffuse they carry either amino acids or glucose molecules into the cell with them
4) The glucose/amino acids then pass into the blood plasma via facilitated diffusion using another carrier
What is diarrhoea and what are its 3 causes?
Diarrhoea is an intestinal disorder where watery faeces are produced frequently due to:
1) Damage to epithelial cells lining the intestine
2) Loss of microvilli due to toxins
3) Excessive secretion of water due to toxins such as cholera toxins so little or more water is taken leading to dehydration
So how is diarrhoea relieved?
The pateint is given a rehydration solution that contains lots of sodium ion so that the cell’s water potential fall so the absorbtion of water will increase in the intestine via osmosis as there is more than one type of carrier protein in the plasma membrane of epithelial cells that takes up sodium ions
What does the rehydration of a solution contain?
Water - rehydrate the tissues
sodium ions - optimising the use of glucose-sodium pathways and allow the absorbtion of sodium ions that were already lost from the epithelium of the intestine
Glucose - stimulates the uptake of sodium ions from intestine and provides energy
pottassium ions - to stimulate uptake of potassium ions and increase apetite
other electrolytes - to prevent electrolyte imbalance and metabolic acidosis (preventing acid build up in body fluids)
Phosphorylation process?
The phosphate group is attached to the carrier protein so that ATP is converted into ADP which means that there is a change in tertiary structure which allows a substance to pass through
Phosphorylation process 2?
The hydrolysing of ADP + inorganic phosphate group can be recombined to form ATP in the releasing of a substance within the carrier proteins
Why does T and A as well as C and G bond together?
A and T has 3 hydrogen bonds
C and G has 2 hydrogen bonds
Explain how ADP is hydrolysed ?
ATP = ADP +Pi which means there is 3 phosphates and 1 ribose sugar as it converts to 1 ribose sugar with 2 phosphates and 1 ribose sugars
Sodium pottasium pumps ratio of Na : K?
3 Na+ out of pump to blood
2 K+ in to cell
Good blood supply of Sodium
