Pack 3 - Transport Across Membranes Flashcards
What are the 2 functions of the cell surface membrane?
Control passage of molecules in and out of cells/organelles
Forms boundaries between organelles and the cytoplasm
What are the 5 main components of a plasma membrane?
Phospholpids Proteins Cholesterol Glycoproteins Glycolipids
What is the difference between an intrinsic and and extrinsic protein?
Extrinsic - sits on the outside or is slightly embedded
Intrinsic - runs through the whole membrane
What are the four molecules that make up a phospholipid?
Phosphate group
Glycerol
2 fatty acids
What are the bonds in the phospholipid called?
Ester bonds
Which end of a phospholipid is δ+?
Head (phosphate group)
How do phospholipids line up when they form a membrane?
o o
|| ||
|| ||
o o
What are the 6 functions of proteins within the plasma membrane?
Structural support
Help cells attach to each other
Channel proteins for water-soluble substances in facilitated diffusion
Carrier proteins for facilitated diffusion
Carrier proteins for active transport
Cell-surface receptors for
•eg. hormones
•cell recognition eg glucagon receptors in the liver (eg. hepatitis)
( )
What are the 4 functions of cholesterol?
Add strength to the membrane
Reduce movement of other molecules
Make the membrane less fluid at high temperatures
Prevent leakage of water and dissolved ions (through perforations)
0°oO0°o0
What are the 3 functions of glycoproteins?
Recognition sites - cell surface receptors for specific chemicals eg. neurotransmitters and hormones
Help cells attach to each other forming tissues
Allow cells to recognise each other eg. lymphocytes can recognise any organism’s own cells
Y
( )
What are the 3 functions of glycolipids?
Act as recognition sites - cell surface receptors for specific chemicals eg. ABO blood system
Help stability of the membrane
Help cells attach to each other forming tissues
Y
o
||
Explain the name fluid-mosaic model
Fluid
Molecules can move relative to each other
The membrane is flexible and constantly changing shape
Mosaic
Like the tiles in a mosaic, the proteins embedded in the phospholipid vary in size, shape and pattern
Why can’t most substances pass through the plasma membrane?
Not lipid soluble eg. water
Too large eg. glucose
Polar eg. Na+
List some properties of substances that can pass directly through the plasma membrane
Lipid-soluble eg. steroid hormones
Small molecules eg. O2
Non-polar molecules eg. CO2
Define passive (in exchange of substances)?
Does not require metabolic energy
Define active (in exchange of substances)?
Requires metabolic energy in the form of ATP
Define diffusion
The net movement of molecules or ions
From a region where they are highly concentrated to a region where they are less concentrated
Until evenly distributed
Is diffusion active or passive and why?
Passive as molecules move using their own kinetic energy therefore it does not require metabolic energy in the form of ATP
Why is meant by net flow?
The overall flow. Molecules of all substances will move in both directions.
When will net flow in diffusion stop?
When dynamic equilibrium is reached (there being equal concentrations on both sides)
What 6 factors affect the rate of diffusion?
1 Temperature
2 Difference in concentration gradient
3 Distance over which diffusion occurs
4 Area over which diffusion takes place
5 Nature of any structure across which diffusion occurs
6 Size of the diffusing molecule
How will temperature affect the rate of diffusion?
An increase in temperature will increase the kinetic energy of molecules and will therefore increase the rate of diffusion
How does a larger/steeper concentration gradient affect the rate of diffusion?
It will be faster
If the exchange surface for diffusion is relatively thick, what will happen to the diffusion rate?
The greater the distance, the slower the rate of diffusion
As the area over which diffusion takes place what will happen to the diffusion rate?
The greater the surface area over which diffusion takes place, the faster the diffusion rate
Why should a lipid-soluble molecule be able to get through a selectively permeable membrane more quickly?
Cell surface membranes are made primarily of lipids which allow lipids to pass through the membrane, between the phospholipids
Why should a small molecule be able to enter a cell faster than a large one?
Small molecules can pass through pores more easily than larger molecules
What is Fick’s law?
surface area × conc. distance
Diffusion rate ∝_____________________________
diffusion path length
Big × big
Small = Big
Why does facilitated diffusion require?
Transport or channel proteins
Give 4 properties of channel proteins and their use
Form water-filled hydrophilic channels across the membrane
Allow specific water soluble ions to pass through
Selective - only open in presence of a specific ion
The binding of specific ions changes the shape of the protein allowing the ions to pass
Give 4 properties of carrier proteins and their use
Span the plasma membrane
A molecule eg. glucose (with a specific, complementary shape) binds to the carrier proteins
This causes the protein to change shape
The molecule is released on the opposite side of the membrane
How would increased number of protein channels/carrier proteins in the same area of membrane affect the rate of diffusion?
It would increase as more can be passed through the membrane at one time
Define osmosis
The passage of water
Where it has a higher water potential to a region where it has a lower water potential
Through a selectively-permeable membrane
Is osmosis a specialised form of diffusion?
Yes
What is a solute?
Something that dissolves in a solvent to form a solution
What is the water potential of pure water?
0
Which would water move from and to?
- 300kPa
- 200kPa
-200 to -300 as there is a higher water potential in -200
Which is more concentrated?
- 300kPa
- 200kPa
-300 as it has a lower water potential (further from pure water)
What will happen if you place RBCs in pure water?
They will lyse Cell Ψ < H20 Ψ Net flow of water into the cell By osmosis To even the Ψs Which will keep filling the cells until they burst
What happens if you place RBCs in strong NaCl solution?
They will shrivel NaCl Ψ < Cell Ψ Net flow of water out of the cell By osmosis To even the Ψs Which will shrivel the cells
What happens if you place plant cells in pure water?
They will become turgid but not lyse Due to strong cellulose cell wall Cell Ψ < H20 Ψ Net flow of water into the cell By osmosis To even the Ψs Protoplast swells until pressing against the cell wall Cell wall is rigid and cannot expand more Therefore resists entry of more water
What happens if you place plant cells in strong NaCl solution?
They will become plasmolysed NaCl Ψ < Cell Ψ Net flow of water out of the cell/protoplast By osmosis To even the Ψs Causing cell to become plasmolysed
Define plasmolysis
When the protoplast shrivels due to a loss of water from the cell
Describe incipient plasmolysis
When the corners of the vacuole are pulling away from the membrane
(The first sign of plasmolysis hence incipient [slight])
Define hypertonic (solution)
When the solute concentration is greater outside the cell than inside the cell
Define hypotonic (solution)
When the solute concentration is greater inside the cell than outside the cell
Define isotonic (solution)
When the solute concentration is the same outside of the cell as inside the cell
Which way will the water flow?
-500kPa -1100kPa
-500kPa -> -1100kPa
Define active transport
Movement of molecules/ions into or out of a cell
From a region of lower concentration to a region of higher concentration
Using metabolic energy and carrier molecules (protein pump/carrier protein)
Give an example of active transport in the human body
The sodium - potassium pump
Explain the sodium - potassium pump
1) Na+ ions bind to specific receptor sites on the carrier protein
2) ATP binds to the protein and splits into ADP and a phosphate molecule
3) Energy is released the phosphate molecule remains bound to the carrier
4) The carrier protein changes shape. Na+ is released on the opposite side of the membrane
5) K+ ions now bind to their receptor sites. This causes the carrier protein to change shape again
6) K+ and phosphate are released on the original side of the membrane leaving the carrier protein ready to pick up more Na+
What are the similarities between active transport and facilitated diffusion?
Both use protein carriers
Specifically binding sites for the molecules or ions being transported are present
What are the differences between active transport and facilitated diffusion?
FD AT
High -> Low Low -> High
No metabolic energy needed ATP needed
How do microvilli help to maximise absorption in the small intestine?
They increase the surface area
What is starch broken down into in the small intestine?
Amylase Maltase
Starch -> Maltose -> a Glucose
What are proteins broken down into
Amino acids (Using protease or trypsin)
After a meal, will the concentration of molecules/ions be higher or lower in the lumen of the ileum than in the blood?
Higher in lumen
What role does the circulatory system play in maintaining the concentration gradient between the lumen and the blood?
Carries away products of digestion
Over time what will happen to the relative concentrations of glucose etc. in the lumen of the ileum and the blood?
Will reach equilibrium/lower in ileum
Explain co transport across the wall of the ileum
1) Na+ ions are pumped out of the cell into the blood by the sodium potassium pump. This requires energy from ATP and is therefore active transport
2) This maintains a concentration gradient of sodium ions from the blood (high) to the cells/lumen (low)?
3) Sodium ions diffuse into the cell along their concentration gradient through the carrier protein. For this to happen glucose also has to bind to the protein and is therefore brought in with the sodium ions.
4) Glucose molecules pass into the blood plasma by diffusion using another type of carrier protein.
In co transport across the wall of the ileum, is glucose moving into the cell down its concentration gradient or against it?
Down
In co transport across the wall of the ileum, what’s effectively causes the movement of glucose into the cell?
Facilitated diffusion
What usually happens at the start of movement of ions and molecules in and out of cells?
Active transport / ATP usage
