Exam 3 Bio material

biological membranes

• phospholipid bilayer

  • amphipathic molecules

    • hydrophobic - water fearing region

    • hydrophilic - water loving region

• also contain proteins and carbohydrates

• amount of each vary

fluid-mosaic model

• mosaic - lipid, protein and carbohydrate molecules

• fluid - lipids and proteins can move

membrane proteins

• integral or intrinsic proteins

  • transmembrane proteins

  • lipid anchored protein

• peripheral or extrinsic proteins

  • noncovalently attached to integral membrane proteins or phospolipids

membranes are semifluid

• semifluid

  • lipids can rotate freely

  • move laterally within at leaflet

  • flipflop

    • movement of lipids from one leaflet to the opposite

    • does not occur spontaneously

    • flipase (requires ATP)

factors affecting fluidity

• length of fatty acyl tails

  • shorter acyl tails are less likely to interact

• presence of double bonds in the acyl tails

  • double bond creates a kink in the fatty acyl tail

• presence of cholesterol

  • cholesterol tends to stabilize membranes

not all integral membrane proteins can move

• may be bond to cytoskeleton

• may be attached to molecules that are outside the cell

  • extracellular

glycosylation

• glycolipid - carbohydrate to lipid

• glycoprotein - carbohydrate to protein

• role

  • recognition signals

  • protective effects

• protein glycosylation

  • n-linked - nitrogen atom of asparagine side chain to ER and Golgi

  • o-linked - oxygen atom of serine or threonine side chains - Golgi

membrane transport

• selectively permeable

• ensures

  • essential molecules enter

  • metabolic intermediates remain

  • waste products exit

ways to move across membranes

• passive transport

• does not require an input of energy

• down or with the gradient

  • simple diffusion - diffusion of a solute through a membrane without transport protein

  • facilitated diffusion - diffusion of a solute through a membrane with the aid of a transport protein

• active transport

  • requires energy

  • up or against the gradient

phospholipid bilayer barrier

• barrier to hydrophilic molecules and ions

• “you shall not pass”

cells maintain gradients

• homeostasis

• transmembrane gradient

  • concentrations of a solutes

• ion electrical gradient and chemical gradient

osmosis

• movement of water through a membrane from a region of low solute concertation to a region of high solute concentration

tonicity

• isotonic (same)

  • equal solute concentrations on either side of the membrane

• hypertonic (high)

  • solute concentration is higher 9and water concentration is lower) one one side of the membrane

• hypotonic (low)

  • solute concentration is lower (and water concentration is higher) or on one side of the membrane

• crenation - shrinking in the hypertonic solution

• cell wall

  • turgor plasma - pushed plasma membrane against the cell wall

  • plasmolysis - plants wilt because water leaves plant cells

transport protein

• transmembrane proteins

• provide a passageway

  • ions and hydrophobic molecules

• 2 classes based on manner of movement

  • channels

  • transporters

channels

• form an open passageway for diffusion

• most are gated

• aquaporins - how quickly osmosis occurs

transporters

• “carriers”

• conformational change transports solute

• principial pathway for the uptake of organic molecules, such as sugars amino acids and nucleotides

transporter types

• uniporter

  • single molecule or ion

• symporter/cotransporter

  • 2 or more ions or molecules transported in same direction

• antiporter

  • 2 or more ions or molecules transported in opposite directions

active transport

• movement of a solute across a membrance aganist its gradient

  • low concentration to higher concentration

• energetically unfavorable

• requires the input of energy

• primary active transport

  • directly use energy to transport solute

• secondary active transport

  • use pre-existing gradient to drive transport of solute

atp-driven ion pumps generate ion electrochemical gradients

• na plus/ k plus atpase

  • actively transports na plus and k plus against their gradients by using the energy from atp hydrolysis

  • 3 na plus exported for 2k plus imported into cell

    • anitporter

    • electrogenic pump - export one net positive charge