Chapter 6 Flashcards
Give 4 general properties of membrane
- Made up of a continuous bilayer of phospholipid molecules with protein molecules embedded in it
- Is a boundary that separates the living cell from its nonliving surroundings
- Has a 8nm thin barrier which controls traffic in and out of the cell
- Selectively permeable
What is a phospholipid?
- Makes up the cell membrane
- Contains 2 fatty acid chains that are nonpolar, in which the head is polar and contains a phosphate group
Who proposed the first plasma membrane model?
H. Davson and J. Danielli proposed a sandwich model in 1935 where the phospholipid bilayer lies in between two layers of globular proteins
Who created the revised model of the phospholipid bilayer?
S.J. Singer and G. Nicolson presented a reviewed model in 1972 where it was proposed that the membrane proteins are dispersed and individually inserted into the phospholipid bilayer
What influences the membrane fluidity?
- Temperature - As temperatures cool, membranes switch from a fluid state to a solid state, where the phospholipids are more closely packed
- Saturated and unsaturated fatty acids - More unsaturated fatty acids equal to a more fluid membrane because the double bonds in the fatty acid tails prevent tight packing
- Cholesterol - At warm temperatures, cholesterols wedged between phospholipid molecules restrains the movement and reduces fluidity
What does the proteins in the plasma membrane do?
- As transport proteins
- As enzymatic activity
- For intercellular joining
- Cell-cell recognition
Explain transport proteins
- Have much in common with enzymes
- May have specific binding sites for the solute
- Can become saturated when they are translocating passengers
Give two examples of transport proteins
- Channel protein - allows for fast transport and provides corridors allowing for specific molecules to pass through
- Carrier proteins - opens or close depending on the presence or absence of a physical or chemical stimulus and holds their passengers and changes their shape to move a target molecule from one side of the membrane to the other
What is passive transport?
- The movement of particles across a cell membrane down its concentration gradient without using energy
Osmosis: the diffusion of water molecules through a semi-permeable membrane
Diffusion: The movement of small molecules from an area of high concentration to low concentration
Give two examples of osmosis
- Diffusion of water molecules from a region of lower osmotic pressure to a region of a higher osmotic pressure through a selectively permeable membrane
- Diffusion of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane
What happens to a cell immersed in a hypotonic environment?
Water diffuses into the cell, and therefore causes it to swell and burst
What happens to a cell immersed in a hypertonic environment?
Water diffuses out from the cell, causes it to shrivel and undergo crenation
Explain diffusion
In the absence of other forces, a substance will randomly diffuse from concentrated to less concentrated down its concentration gradient and it requires no energy from the cell
Give two types of diffusion
- Simple diffusion: Diffusion of small substance without assistance of transport proteins such as uncharged molecules and non-polar molecules
- Facilitated diffusion: Diffusion of small substance with assistance of transport proteins such as charged molecules and polar molecules
What is the meaning of active transport?
- The movement of particles against the concentration gradient and requires the use of energy
- Uses cellular energy obtained from ATP
- Requires the cell to expend its own metabolic energy
- Performed by highly specific proteins embedded in the membranes
