Membrane And Transport Flashcards
Describe the structure of the cell membrane
The cell membrane is in a bilayer shape formed by phospholipids , which have phosphate hydrophilic heads immersed in the water pointing to the outside of the cell membrane, and fatty acid hydrophobic tails pointed to the inside away from water. In addition, there are protein scattered along the membrane of different types, including peripheral proteins, glycoproteins and gated channel. Lastly, there are cholesterol molecules in the cell membrane usually between the phospholipids, this cause the bilayer shape of the cell membrane
Explain what is meant by fluid mosaic model
Fluidity of the cell memrbane due to thw ability of the phospholipids in the membrane to move, and it also refers to the fact that there are scattered proteins along the cell membrane
Factor affecting membrane structure
Temperature
As increase temperature
kinetic energy - increase of phospholipid
(Vibrate more -> hydrogen bond break)
- > break H bond between tail
- more permeable
Denatures protein
Channels/carriers
- effect permeability
Solvent factor affecting membrane structure
(Lipid soluble substance)
Non polar solvent sit between tails
-> ethanol will denature membrane protein by replacing hydrogen bind between amino acid with new bond between ethanol & amino acid
- break H bond -> disrupt bilayer
- dissolve the phospholipid
- increase permeability +more fluid
(I.e alcohol -ethanol)
Phospholipid
Made of a glycerol molecules two fatty acid chains and a phosphate group (attached to the glycerol)
Via two condensation reactions resulting in two ester bonds
Properties of phospholipids
Hydrophilic head of a phospholipid can attract with water as it is charged
Due to the phosphate being charged it repels other fats
The fatty acid chain is not charged
It is known as the hydrophobic tail and it repels water, but will mix with fats
Cholesterol
Parts of a family of lipids called sterols
The hydroxyl group is hydrophilic however the rest of the molecule is hydrophobic
Cholesterol can insert into the cell membrane
The hydrophilic hydroxyl group on the cholesterol molecule can interact with head group of phospholipid
While the rest of the cholesterol molecule can interact with the hydrophobic fatty acid
Cholesterol actually plays a key role in controlling the fluidty of cell membrane
Cholesterol & phospholipid
It increases strength of the cell surface membrane -> more stable
Cholesterol reduces the sideway movement of phospholipid
-regulate (control) fluidity
Help reduce the movement of water -soluble chemicals across the cell surface membrane
Intrinsic proteins
Fully embedded in the membrane from one side to the other
Protein channel ( intrinsic proteins)
Selective ( some have gated channel) (this allows the channel proteins to control the exchange of ions)
- channel lined with hydrophilic amino acids & filled with water molecule
- > allow water soluble molecules & ions to diffuse through
Facilitated diffusion
Carrier protein (selective) cell membrane
Move large molecules into or out of the cell down their concentration gradient
Protein undergo a confronational change
This release the molecule on the opposite side of the membrane
—> facilitated diffusion & active transport
Extrinsic protein
Structural role
Act as enzyme
Cell receptors
Glycoproteins
Protein attached to a carbohydrates
Carbodrates part help them hold lots of water - harder for protease to break them down
—> muscus & synovial fluid are glycoprotein
Define diffusion
Net movement of particels from a region of higher concentration to a region of lower concentration down the concentration gradient
—> No ATP
—> passive process
Define facilitated diffusion
Not all substances diffusion at the same rate due to the centre of cell membrane is hydrophobic
- due to the fatty acid tails of teh phospholipid molecule
Steroid molecule can diffuse rapidly across the memrbane
Hydrophilic substance ions/polar molecules cant diffuse across the membrane
Molecules
Small uncharged
I.e. - CO2, O2
Passive diffusion
Charged / ions
Facilitated diffusion
Small dipole
osmosis
I.e water
Define endocytosis
The movement of large molecule into cells through vesicle formation
Define exocytosis
The movement of large molecule out of cell by the fusing of a vesicle containing the molecule with the surface cell membrane, the process requires ATP
Define isotonic
When the solite conc is balanced woth the concentration inside the cell
Water movement still mores between the solution
Define hypotonic
Solute concentration is lower than concentration inside the cell
- water moves in the cell and cause the cell to swell; cell that dont have cell wall (animal cell) burst
Define hypertonic
Solute concentration is higher than concentration inside the cell
-water move out of the cell & cause the cell to shrivel
Why do red blood cells burst when placed in water
First of all water molecules will move into the cell from high water potential to low water potential through a partially permeable membrane by osmosis. This cause pressure on the cell membrane of the red blood cell causing it burst
What happens to a red blood cell when it is placed in a salt solution
Water will move out of the cell and into the solvent from high water potential to low water potential by osmosis through a partially permeable membrane , in order to equalize the salt concentration. This cause the cell to shrivel and become flaccid
What happens to a plant cell when it is placed in water
Water will move into the cell from high water potential to low water potential by osmosis through a partially permeable membrane , bit not indefinietly , vacuole will he too full and will start to cause hydrostatic pressure on the cell membrane. The cell wall will then reply with potential pressure until no more water can enter the cell, and the plant will be in state called turgor where it is rigid
What happen to a plant cell when it is placed in a salt solution
Water will move out of the cell from hgih water potential to low water potential by osmosis through a partially permeable membrane, causing the vacuole and the cell membrane to shrink in a state called incipient plasmolysis however, the cell wall is not affected
Endocytosis process
Some molecule ae way too large to be taken into a cell by carrier proteins eg proteins, lipids and some carbohydrates
2) instead a cell can surround a substance with a section of its cell membrane
3) the membrane then pinches off to form a vesicle inside the cell containing the ingested substance - endocytosis
4) some cells also take in much larger object by endocytosis
Ex. White blood cell (called phagocytes) use endocytosis to take in things like microorganism and dead cells so that they can destroy them
5) like active trasnport, this process also use ATP for energy
Exocytosis process
1) some substance sproduced by the cell (eg digetsive enzyme, hormones , lipid) need to be released the cell - exocytosis
2) vesicles containing these substances pinches off from the sacs of the golgi apparatus and move towards the cell membrane
3) the vesticles fuse with cell membrane and release their content outside the cell
4) some substance arent released outside the cell - instead they are inserted straight into the cell membrane
5) exocytosis use ATP as an energy source
