Cell Membrane Structure and Function Flashcards
(26 cards)
Glycolipids
lipid molecules attached to short chains of carbs
involved in cellular recognition, pay role in triggering immune responses.
Glycolipids are seen In blood types
Glycoproteins
Proteins attached to short chain of carbs
Roles include cell-cell recognition, binding of other molecules, strength, and stability (Finish)
How do molecules cross membranes?
Passive transport:
A. Diffusion
B. Facilitated diffusion
C. Osmosis
Active transport:
A.Transport by proteins
B. Bulk Transport (by membrane bound vesicles)
Passive transport
Happens normally or always with concentration gradient.
Does not require energy(ATP). Against - low to high
Active transport
Moving from low to high concentration, needs energy to do so.
Concentration gradient
The difference in concentration between two regions. This gradient allows cells to achieve homeostasis.
Extracellular fluid
Every cell in a multicellular organism is bathed in a thin layer of extracellular fluid.
This fluid consists of a mixture of water and other dissolved materials, including substances required by the cells and wastes excreted by the cells.
What molecules can pass through the hydrophobic interior
Non-polar gases such as O2, CO2
Fats, other lipids, hydrocarbons ex. benzene (C6H6)
Small uncharged molecules ex. urea, ethanol
Factors that affect diffusion
concentration. of particles (↑ conc., ↑ rate of diffusion)
temperature. of particles (↑ temp., ↑ rate of diffusion)
pressure (↑ pressure, ↑ rate of diffusion)
agitation (↑ movement, ↑ rate of diffusion)
Once molecules have diffused across the cell membrane, their rate of diffusion slows down abruptly.
Membrane pores
-Gaps between phospholipids
- Smallest nonpolar molecules pass through passively
Facilitated Diffusion
-These molecules are either too large to diffuse between the phospholipid molecules, or they are hydrophilic/charged ions.
- This is a type of passive transport which uses integral mb proteins to help/facilitate the movement of molecules across the plasma mb.
- Either channel proteins or carrier proteins are involved.
- A particular transport protein will recognize and help to move only one type of dissolved molecule or ion based on the particle’s shape, size, and electrical charge.
Two major types of proteins
-Carrier proteins and Channel proteins
Carrier proteins
-Transport medium-sized, uncharged molecules through the membrane.
-The proteins open at one end, allow the molecule to enter, and then open at the other end to allow for the passage of the molecule.
-These bind specific substances and change shape slightly, transporting the bound molecule across the membrane. Since movement is down/with the concentration gradient and does not use energy (ATP), this is passive transport.
Channel Proteins
-Transport medium-sized, charged molecules (ions) through the membrane.
-The ion must be small enough to fit through the protein, and must have the proper charge – a negatively charged channel attracts only positively charged ions, and vice versa.
-These act like a tunnel/slide and are specific for the substance being transported. Passage through the channel protein allows polar compounds ex. Na+, K+ to avoid the nonpolar hydrophobic tails that prevent them from crossing the lipid bilayer. Since movement is down/with the concentration gradient and does not use energy (ATP), this is passive transport.
Osmosis
Because water is so important to life on Earth, the movement of water is treated separately.
Water ONLY EVER moves passively, from high concentration to low concentration. There is no living organism on Earth that is able to move water against its concentration gradient (to do this, you would need a mechanical pump).
Since water is a molecule with polarity, it is unable to freely diffuse through the hydrophobic interior of the phospholipid bilayer. Water moves using special integral mb channels called AQUAPORINS.
3 types of solutions cells can be placed in
Hypertonic condition
Hypotonic condition
Isotonic condition
Hypertonic condition
-hyper means more/higher
-The concentration of water inside the cell is higher than outside the cell
Result: water moves OUT of the cell
Risk: plasmolysis (cell shrinking)
Animal cells shrivel and become crenated
plant cells lose turgor pressure and undergo plasmolysis
Hypotonic Condition
hypo means less/lower
the water outside the cell is higher than inside the cell
Result: water moves into cell
Risk: lysis (cell bursting)
Animal cells will expand and may lyse; plant cells will gain turgor pressure and not burst due to their cell wall
Isotonic Condition
iso means same/equal
the water on both sides of the cell is equal.
Not net movement of water across the membrane.
This is the goal of every cell. It is a state of dynamic equilibrium
Transport by Proteins
Process of moving substances against the concentration gradient is called active transport.
The transport protein directly involved in active transport is called the active transport pump.
In order to move molecules against the concentration gradient i.e. from low concentration to high concentration, a special integral mb protein pump must be used. This process requires energy (ATP). These integral mb proteins are all carrier proteins (never channel proteins).
The sodium-potassium (Na+/K+) pump is the best-understood example.
It is an integral membrane protein which transports Na+ and K+ ions against their concentration gradients.
The cell membrane of every cell in our bodies uses these pumps.
In the intestines, glucose can be transported against the concentration gradient from the gut (low conc of glucose) into the blood (high conc of glucose) using a protein pump.
Steps for moving glucose - Transport by proteins
1) Three Na+ ions bind to the receptor on the protein, from the inside of the cell.
2) Two K+ ions bind to the receptor on the protein from the outside of the cell.
3) This causes the protein to change shape, and taps into a form of cellular energy called ATP.
4) This allows Na+ to exit the cell, while K+
enters the cell. Once the switch has occurred, the protein returns to its original shape.
5) At this point, there is more Na+ outside the cell than inside, therefore, Na+ has created an artificial concentration gradient.
6) Sodium wants to re-enter the cell.
7) In doing so, it sneaks a glucose
molecule with it, since glucose is traveling against its own concentration, from low to high concentration (known as secondary active transport).
Bulk transport
For materials that are too big or too polar to pass through cell membrane via passive or active transport
Uses bulk transport so they don’t have to pass through the lipid bilayer.
Transport by vesicles due to the fluid nature of phospholipid bilayer. Large particles or large quantities of smaller particles dissolved in fluid can be transported by membrane-bound vesicles.
Allows cells to obtain nutrients by selectively grabbing extracellular fluid; export hormones and other proteins; release signaling molecules to communicate with neighbours.
Membrane folds in on itself creates a membrane enclosed vesicles that allows cell to fuse or bud off from plasma membrane and swallow or expel materials in or out.
Endocytosis
“Endo” means internal ex. endothermic, endodontist
Transport of material into a cell by means of vesicles
Cell engulfs material by folding a portion of its membrane around it, forming the vesicles
Energy is required
The vesicle floats through the cytoplasm and fuses with a lysosome, which will digest the contents.
3 main forms of endocytosis
Pinocytosis
Phagocytosis
Receptor-Mediated Endocytosis
