L9: Lipids and Membranes

phospholipids

main lipid found in cell membrane; amphipathic

amphipathic

contains both hydrophobic and hydrophilic regions; ex: phospholipids & cholosterol

hydrophilic part on phospholipids

polar head

hydrophobic part on phospholipids

fatty acid tails (can be saturated or unsaturated)

how do phospholipids arrange themselves in an aqueous environment

spontaneously depending on head group size

types of phospholipid structures

micelles, bilayer, liposomes

micelles

large head group with 1 hydrophobic tail

bilayer

small head group with 2 hydrophobic tails

liposomes

multiple phospholipids spontaneously form enclosed bilayers in test tube

primary mechanism by which phospholipids interact with one another

van der waal forces

what are van der waal forces

weak interactions that allow phospholipids to move in plane of membrane

are saturated or unsaturated fatty acids more flexible

unsaturated, double bonds increase flexibility

membranes are ___ because they are fluid and flexible

dynamic

are saturated or unsaturated fats more stable

saturated

do organisms in warmer climates have more or less saturated fatty acids in their membranes compared to organisms in colder climates

more

properties of cholesterol

amphipathic with four interconnected carbon rings

the amphipathic structure of cholesterol allows it to _____ with phosopholipids

pack tightly

function of cholesterol

restricts phospholipid movement at warmer temps and prevents tight packing at colder temps

does cholesterol cause membrane fluidity to increase or decrease in warmer temps

decrease

classes of proteins that associate with plasma membrane

transporters, enzymes, receptors, anchors

transporters

move ions/molecules across membrane

receptors

allow cell to receive signals from environment

enzymes

catalyze chemical reactions

anchors

interact with proteins on inside and outside of cell to provide structure

integral membrane proteins

permanently span plasma membrane (integrated)

peripheral membrane proteins

temporarily associate with membrane through weak non-covalent interactions (in or out of membrane)

what do lipids and proteins form when they coexist in the membrane

mosaic

what does the fluidity of the mosaic model contribute to

maintaining homeostasis in cells

plasma membrane

defines the space of the cell

main functions of a plasma membrane

• separate internal contents from surrounding environment

• maintain homeostasis by keeping internal environment within a persistent and narrow window of conditions

what type of barrier is a cell membrane

selective barrier

which process requires energy in order to transport molecules across plasma membrane

primary active transport

simple diffusion

aka passive transport- the simplest movement into and out of cells

• movement of molecules from high to low concentration

  • mainly gasses and small lipids

facilitated diffusion

the movement of most molecules with the help of a transporter (channel or carrier); no energy required

osmosis

diffusion of water from a low concentration of solute to a high concentration for solute

• water levels decrease

what are the protein channels used to move water into and out of cells by facilitated diffusion

aquaporins

primary active transport

movement of substances against the concentration gradient

• REQUIRES ENERGY

• low concentration to high concentration

  • ex: sodium pump

secondary active transport

uses the energy from primary active transport to move a difference substance across a concentration gradient creating an electrochemical gradient

hypertonic cells

shrunk; concentration of solute in < concentration of solute out

isotonic cells

normal; concentration of solute in = concentration of solute out

hypotonic cells

swollen; concentration of solute in > concentration of solute out

very hypotonic cells

lysed (burst); concentration of solute in >> concentration of solute out

what form of transport is used to keep intracellular fluid isotonic

active transport

when plants lose water, the size of the vacuoles ___ and the turgor pressure against cell walls ___

decrease, decrease

cell wall

rigid structure that surrounds plasma membrane and resists cell expansion when cell take in water

turgor pressure

force exerted by water pressing against cell wall