BSCI 170: Membranes, Osmosis, Facilitated/Active transport

Exam 2 material

Whats the current model of the plasma membrane?

fluid mosaic model

What are the membranes mostly composed of?

lipids, proteins, & carbohydrates

Membrane lipids are mostly ______.

Phospholipids

• lipids in fluid state

• mostly unsaturated fatty acids

Proteins are ____ in the membrane & are ____ in the lipid fluid

• dispersed

• free to float

both lipids and proteins are ____

amphipathic (partly hydrophilic and partly hydrophobic)

Movement of lipids in membrane

• free to move in 2-D plane of membrane

• move sidways (laterally) very frequently (10^7x per s)

• flip flop across membrane rarely (once a month)

  • bc its harder for hydrophilic head to travel through hydrophobic part

3 predictions of the fluid mosaic model

1. movement of lipids

2. proteins exists as discrete particles

3. Proteins should be able to move in membrane —> proven that they move laterally

Transition temperature (T_m)

temperature at which the membrane undergoes fluid to solid phase change

• like the melting point

• affected by changes in lipid structure

membrane fluidity varies with ____

temperature

relationship between saturation levels of lipids and fluidity

more kinks = more fluid membranes:

• increased number of C=C, decresed T_m

What does cholesterol do to the membrane?

• reduces membrane fluidity at moderate temperature but it hinders solidification at low temperatures (makes it a lil more fluid)

• acts as fluidity buffer

• alters interactions between adjacent fatty acids

  • interacts with hydrophobic tails

Cholesterol

• lipids that are soluable in hydrophobic core of membrane bilayer

• have one polar region

number and types of proteins depend on ____

function of the membrane

Intergral membrane proteins

• integrated into the membrane

• penetrate the hydrophobic core

• removed only by solubilizing the membrane

• many are transmembrane

• amphipathic: function of both sides of membrane

Anchored membrane proteins

• covalently attached to lipids that insert into membrane

• no exposed hydrophobic regions

Peripheral Membrane proteins

• loosely bind to intergral proteins or lipids

• removed w/o destroying membrane

• differ on each side of membrane

• only function on one side of membrane

membrane carbohydrates

• short chains of monosaccaraides added to protein/lipid

  • glycoprotein or glycolipid

• attachment in rough ER or golgi

  • glycosylation

• found in outer membrane layer

Functions of membrane carbohydrates

1. defense: immune system, recognizing self from non-self

2. protection; cell lining of GI, respiratory, & reproductive trats

3. cell sorting: during embryogenesis

• I don’t think we have to know the specifics but just in case 😎

functions of proteins

• transport

• enzyme activity

• signal transduction

• cell-cell recognition

• intercellular joining

• attachment to cytoskeletom & extracellular matrix

are cells able to create and maintain different environments?

• selective permeability & regulated transport

Diffusion

movement from region of higher concentration to lower concentration

What molecules are able to diffuse across the membrane more rapidly?

smaller and hydrophobic ones

Rank these based on their ability to diffused across the membrane: ions, hydrophobic molecules, small polar molecules, & large polar molecules

What allows polar or charged molecules to diffuse through the membrane?

intergral (transmembrane) proteins

Channel proteins

• hydrophilic pores; no specific binding

• allow rapid movement of ions and water

• can transport millions/billions per second

Carrier proteins

• specific binding of solute

• requires conformation/shape change

• transports 100s-1000s per sec (slower than channels)

Passive vs Active transport

Passive:

• no energy added

• [higher] to [lower]

• driving force determined by direction of electrochemical gradient

Active:

• energy is added

• [lower] to [higher]

• driving force is inout of energy

Osmosis

passive movement of water across a membrane

water uses special channels called ____

aquaporins

Isotonic vs Hypertonic vs hypertonic

isotonic: solution around cell has same [solute] as inside the cell (equilibrium)

hypertonic: solution around cell cell has higher [solute] than inside the cell

• net movemnet OUT of cell

• shriveled cell

hypotonic: solution around cell cell has lower [solute] than inside the cell

• net movement INTO the cell

• swollen cell

In osmosis: water moves from region of ___ to ___

lower [solute] to higher [solute]:

• hypo to hyper

• more water to less water

Why does water go from regions with less solute to more?

some water bounds to solute, forming a hydration shell, so when the more solute there is the less unbound water there is that is able to move freely

Facilitated diffusion

passive transport that is aided by proteins (both channels and carriers)

• uniporter

In facilitated diffusion, in what ways can channels be “gated” to control transport

• ligand gated

• electrically gated

• mechanically gated

what happens when carrier proteins are saturated?

rate of diffusion slows down because all carrier proteins are occupied

uniport vs symport vs antiport

uniport: moves 1 substance at a time

Cotransport systems:

symport: can move 2 things together

antiport: move things in opposite directions

In active transport, substances are transported ___ their concentration gradients

against

active transport allows cells to generate & maintain ___

different concentrations of across a membrane (gradient)

active transport only uses ____

carriers

stored potential energy

when you have a bunch of (+) charged things on one side and (-) on the other

• in this example, h+ wants to move down its chemical gradient but also wants to move down the electrical gradient towrads (-)

secondary active transport

stored potential energy can drive the active transport of another solute with a separate cotransport portein

Bulk transport

movement of LARGE molecules like proteins & polysaccharaides

• exocytosis

• endosytosis

Exocytosis

secretion of material

endocytosis

uptake of materials

what are the 3 types of endocytosis

phagocytosis: cellular eating

• cell engulfs particle into vesicle like a fatty

pinocytosis: cellular drinking

• gulp of fluid taken to vesicle

receptor mediated: bringing in SPECIFIC receptors

• ligands bind to specific receptors

• transferred to lysosome for digestion