Bio 1000- 2nd midterm

cellular resp stuff

what is the plasma membrane’s main purpose?

1. acts as a selective barrier and chooses what gets to move in and out of the cell interior.

• allows small, uncharged, non-polar molecules to diffuse through 

• doesn’t allow polar, charged, large particles to go through

what is the plasma membrane made of?

phospholipid bilayer

• fluid

• embedded with proteins for transport and signaling

how does the plasma membrane maintain ion gradients?

1. ion pumps

2. ion channels

3. electrochemical gradient

how is the membrane involved in signalling?

embedded in the phospholipid bilayer is the receptors and proteins involved in transmitting and detecting signals

what is the term used for a phospholipid referring to their different polarity of head and tail?

amphipathic

• hydrophilic head (polar)

• hydrophobic head (non-polar)

what are the 3 groups that made up the polar head of a phospholipid?

1. choline

2. phosphate

3. glycerol

phospholipid bilayers hold these 3 properties.

1. flexible: cells can change their shape

2. repairable: lipids move to reform a continuous surface

3. expandable: cells increase surface area by adding new membrane lipids

what happens when the membrane increases its fluidity?

• phospholipids separate slightly

• membrane becomes more permeable for small molecules

what specific factors increase fluidity?

• increase temp

• more unsaturated FA compared to saturated FA

• shorter FA tails

what does the membrane do when there is too much fluidity?

• hydrogenation (adding H-bonds to increase number of single bonds)

• add cholesterol

what does the membrane do when it is too rigid?

• desaturation via desaturase enzyme (takes away H-bonds to create more double bonds)

• add cholesterol

how is cholesterol able to embed itself into the membrane?

is amphipathic (hydrophilic head, hydrophobic tail)

what is the main role of cholesterol at the membrane?

Buffer effect

• prevents too much fluidity

• prevents overpacking

In a cold environment what would the membrane of an organism look like in terms of its FA composition?

• more unsaturated FA

• shorter FA tails

define passive simple diffusion

movement of substances down their concentration gradient without energy, happens spontaneously.

define passive facilitated diffusion

uses a membrane protein to take larger charged molecules across the membrane down their concentration gradient without energy

what are the 3 types of membrane proteins?

1. transmembrane

2. integral

3. peripheral

• integral and transmembrane proteins are amphipathic and are embedded into the membrane. make them difficult to remove without damaging them

how are the amino acids of a transmembrane protein arranged?

into alpha helices 

what side of the membrane are most peripheral proteins found on?

intracellular

how do peripheral proteins attach to the outside of the membrane?

• non-covalent bonds

• attach to integral proteins

• directly with phospholipids

• lipid anchor

  • all interactions are weak and reversible