3.2.3 Transport Across Cell Membranes Flashcards
Why do we need membrane?
Separating cell content from the outside world
Separating cell component from cytoplasm
Cell recognition and signalling
Holding component for some metabolic pathways (protein channel)
Regulating transport of substances in and out of the cell
What is on the cell membrane?
Extrinsic protein
Intrinsic protein
- channel protein
- Carrier protein
Cholesterol (lipid)
Glycoprotein
Glycolipid
Why do we need protein on the cell membrane?
Only lip at syllabus substance, nonpolar molecule to pass through phospholipid bilayer
Structure and function of cholesterol
Making sex hormone
Essential part of the cell membrane, giving rigidity and make it stronger
Steroid : four ring structure, hydrophobic
HydroPhobic : prevent loss of water and the sofa ions from cell, prevent burst/ lysis is due to water potential
exam ans : stablize the membrane by restricting the movement of phospholipid
function of glycoprotein
Act as a cell surface receptor for hormone and neurotransmitter
Help cell attached to one another to form tissues
Allowed so to recognise each other (lymphocytes recognise, organism own cell)
Functional structure of glycolipid
Carbon hydrate portion extend from the phospholipid bilayer into the watery environment outside the cell
Act as cell surface receptor for specific chemical
Maintain stability of membrane by forming hydrogen bonds with water surrounding each cell
Help so attached to one another to form tissue
Exam Q: why phospholipid are important component in cell surface membrane
It’s can from bilayer, hydrophobic tail facing inside of bilayer, hydrophilic head facing outside
It’s allowed lipidsoluble molecule across, but not water soluble molecules due to the control of water potential
It makes the membrane flexible and self sealing
The model for cell membrane, why do we need the model?
Fluid mosaic model
To visualise what we can’t see
Describe fluid Mosaic model
Fluid- phospholipid can move freely in relation to one another
Mosaic - phospholipid and protein embedded in the membrane are vary in size, shape and pattern
How does High temperature damage the membrane?
Higher temperature, the phospholipid move faster, spread out, further
become more permeable, less stable
Protein, denatured
Definition of diffusion
Diffusion is substance like gas and liquid, moving across the cell membrane down a concentration gradient from high to low until equilibrium
Definition of osmosis
The net movement of water from a region of high water potential to a region of lower water potential across selectively permeable membrane
Factor affecting the rate of diffusion
Temperature- more vibration, more kinetic energy
Concentration gradient : steeper more net movement
Surface area : more movement of substances at one moment
Diffusion distance
Size of molecule : larger is harder to gain kinetic energy harder to get through bilayer
Stirring /moving of molecule - higher kinetic energy
describe all types of transport
Passive transport (do not require external energy)
Simple diffusion [Small, lipids soluble ,uncharge that molecules]
Facilitate diffusion by channel protein/ carrier protein [Small, water soluble molecules]
- charged / Polar molecule , down a concentration gradient (exam)
Active transport (ATP) by carrier protein
- use of ATP
- bind to carrier protein
- against concentration gradient
Describe the process of active transport
- The molecule or ion to be transferred to across the membrane bind to specific area of protein on one side of the membrane at the binding site.
- On the inside of the membrane, ATP binds to the carrier protein, ATP binding site, causing it to split (bond break) and hydrolysed into ADP and Pi releasing the ADP.
- Energy released Costa carrier protein to change, shape and open to the opposite side of the membrane, releasing the molecule or ion to the opposite side.
- The inorganic phosphate is released from the carrier protein, causing it to revert back to original shape.
- The process can then be repeat.
Co- transport (sodium, ion and glucose)
Indirect active process (ATP)
1. Sodium potassium pump the sodium to blood and potassium to cell against a concentration gradient to prepare a steep gradient for cotransport.
2. Sodium ion decrease in cell so it moves from lumen to cell passively down the concentration gradient set up concentration gradient for sodium ion.
3. Sodium move from high to low concentration gradient. Provide energy for glucose to move against its concentration gradient.
4. Glucose move down a concentration gradient through, facilitated diffusion through carrier protein.
Exam Q: Glucose from the lumen of the small intestine into epithelial cell transport of sodium ion is involved in the absorption of glucose by epithelial cell
The concentration of sodium ion is lower in the cell than lumen
Glucose is absorbed with sodium ion down a concentration gradient by facilitate diffusion and co-transport by carrier protein
Before that sodium ion is being transported through active transport out of the cell to bloodstream
What is water potential?
Ability to move from one to another area
Down water potential gradient
Measure in the unit of pressure (kilopascal ) kPa
Explain water potential
Water is dipolar molecule, attract to positive or negative molecule
Only the water not attached it could be moved by osmosis. The one attached it to ions are polar molecule cannot.
So the water is less freely, move and devil, reduce potential to move of water if there’s more ion attached
3 level of water potential, is it good for animal cell or plant cell?
Hypotonic (lysis) [turgid]
Isotonic (good) [incipient plasmolysis]
Hypertonic (shrinks) [plasmolysis]
How can animal cell keep in isotonic solution?
Homeostasis by urine concentration
