Cell Membrane

Diffusion and Water

Membrane structure

Made up of Phospholipids, proteins, and carbohydrates

The membrane creates the protective outer layer of the cell

Creates boundaries in a watery environment

Hydrophilic head

Phosphategroup

Symbol

Hydrophobic tails

Phospholipid bilayer

The cell membrane is called a bilayer because it has two layers together to create the boundary

Due to the hydrophobic nature of the lipids, the center of the membrane hates water and charged molecules

Hydrophilicheads

Hydrophobictails

Water

Water

Membrane Proteins

Membrane proteins are found embedded in the membrane and have specific function:CommunicateTransport materialsEnzyme activity

Messenger molecule

Receptor

Activatedmolecule

TransportSignal transductionEnzyme activity

ATP

Extracellularmatrix

Glycoprotein

Carbohydrate

Plasmamembrane

Microfilamentsof cytoskeleton

Phospholipid

Cholesterol

Proteins

Cytoplasm

Glycolipid

Diffusion

Molecules inside of cells are in constant motion (Brownian motion)

The result of Brownian motion is diffusionDiffusion= movement of particles from

high concentration to low concentrationDiffusion leads to equilibrium

LE 5-14

Molecules of dye Membrane Equilibrium

Equilibrium

Passive transport

Selectively permeable membrane= allows some (small, non-polar) substances across.

Passive transport = When there is movement (diffusion) across a membrane without energy.

Molecules of dye Membrane Equilibrium

Facilitated diffusion

Some molecules (larger, polar) can not pass through the membrane without help

Facilitated diffusion= movement of larger, or polar molecules through a membrane protein (tunnel)

LE 5-15

Solutemolecule

Transportprotein

Active transport

Some molecules are needed in high concentrations in the cell.

These molecules go against diffusion and need help

Active Transport= The movement of molecules across the membrane using energy and a protein to move.

LE 5-18a

Transportprotein

Solute

Solute binding Phosphorylation

ATPADP

P

Osmosis

Water is in constant movementOsmosis= The movement of water across

a selectively permeable membrane. Water moves from high concentration to

low concentration.

LE 5-16

Watermolecule

Selectivelypermeablemembrane

Solutemolecule

H2O

Lowerconcentration

of solute

Higherconcentration

of solute

Equalconcentration

of solute

Solute molecule withcluster of water molecules

Net flow of water

Tonicity

Solute= substance being dissolvedSolvent= Substance dissolvingHypertonic= a solution with a higher

concentration of soluteHypotonic= a solution with a lower

concentration of soluteIsotonic= a solution with equal amounts of

solute

LE 5-17 Isotonic solution Hypotonic solution Hypertonic solution

H2O H2O

(1) Normal (2) Lysed

H2O

H2O H2O H2O

Animalcell

Plantcell

(4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed)

(3) Shriveled

Plasmamembrane

H2O

H2O

Movement of molecules

Endocytosis= materials being engulfed into the cellEndocytosis=Enter

Exocytosis= materials being released from the cell. Exocytosis=Exit

LE 5-19

Vesicle

Fluid outside cell

Protein

Cytoplasm

Vesicle forming

(a)

Molecules crosscell membranes

polar moleculesand ions

(e)(b)

(d)

(c)

ofof

uses

uses

by by

passivetransport

may be movingdown

movingagainst

requires

diffusiontransportproteins