2007-2008

The Cell Membrane

BozemanOsmosis &

Diffusion Lab

BozemanThe plasma Membrane

BozemanDiffusion Lab

Arranged as a Phospholipid bilayer

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

• Serves as a cellular barrier / border= 8nm thickH2Osugar

lipids

salt

waste

impermeable to polar molecules

Amphipathic: both hydrophobic and hydrophilic regions.Cholesterol & Plasma Membrane

2007-2008

Why areproteins the perfect

molecule to build structures in the cell membrane?

Proteins domains anchor molecule

• Within membrane– nonpolar amino acids

• hydrophobic • anchors protein

into membrane

• On outer surfaces of membrane in fluid– polar amino acids

• hydrophilic

• extend into extracellular fluid & into cytosol

Polar areasof protein

Nonpolar areas of protein

Many Functions of Membrane Proteins

Outside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

“Antigen”

“Channel”

Membrane Proteins

• Proteins determine membrane’s specific functions– cell membrane & organelle membranes each have unique

collections of proteins

• Classes of membrane proteins:– peripheral proteins

• On the periphery of the cell

• ex: cell surface identity marker (antigens)

– integral proteins • penetrate lipid bilayer, usually across whole membrane

• transmembrane protein

• ex: transport proteins– channels, permeases (pumps)

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the

lipid bilayerExtracellular fluid

Cholesterol

Cytoplasm

Glycolipid

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model

Membrane carbohydrates • Play a key role in cell-cell recognition

– ability of a cell to distinguish one cell from another

• antigens

– important in organ & tissue development

– basis for rejection of foreign cells by immune system

– Blood type: codominanceUnderstanding

Cancer

Homeostasis and Transport

• How do substance enter and exit a cell?

• What is the difference between active and passive transport?

• How does the chemical make-up of the plasma membrane affect what can enter and exit the cell?

Cell SizeOverview

The plasma membrane only allows certain things to enter and exit the cell. What is this called?• Selectively permeable membrane or

selectively permeable

BozemanAP Lab 1

H2O Potential

What is passive transport? Name and describe the 3 types.

• Passive Transport- movement of substance of substances across the plasma membrane without the use of energy.

Passive Transport

Pearson's

The Three TypesDiffusion: movement of substances across the

plasma membrane from high to low concentration. aquaporins

Osmosis: diffusion of water across the plasma membrane from high to low concentration

Facilitated Diffusion: carrier molecules transport larger substances across the membrane from high to low.

Filtration: Using a pressure gradient to move particles through a plasma membrane.

What is active transport? Describe the two major types.

• Active Transport: uses energy and carrier molecules to move substances across the plasma membrane from low to high concentrations (against the concentration gradient)

Active Transport

Two Major types

• Bulk Transport• Endocytosis: process by which large particles

are brought into the cell– Pinocytosis– Phagocytosis– Receptor-mediated endocytosis

» familiar hypecholesterolemia causes high cholesterol levels. Caused by defective cholesterol receptors, can’t get it out of the blood. Receptor site binds to the ligand (in this case cholesterol) and ceates a vessicle.

• Exocytosis: process by which large particles leave the cell

– Contractile vacuoles• Solute Pumping/ Protein Carriers

Endo/Exocytosis

Types of Solute pumps/Protein Carriers

• Sodium-Potassium Pump (nerve cells)

• Plastoquinone (moves electrons in photosynthesis)

• Electron Transport Chain (mitochondria, photosynthesis)

Sodium Potassium Pump

symportantiport

Active transport• Many models & mechanisms

ATP ATP

There are 3 types of solutions a cell can be in.

• 1) Hypotonic

• 2) Hypertonic

• 3) IsotonicHypo/Hyper/

IsoScroll Down

Hypo/Hyper/Iso Sollutions

Describe a cell in an isotonic solution.

• Iso= the same. The concentration of the solution is the same inside and outside the cell.

• The cell stays the same size.

• There is no net movement across the plasma membrane (things enter and leave the cell at the same rate)

Describe a cell in an hypertonic solution.

• Hyper= above. The concentration of the solution is higher outside the cell than inside.

• The cell shrivels in size.

• Water leaves the cell at a faster rate then it enters.

Describe a cell in an hypotonic solution.

• Hypo= below. The concentration of solutions is lower outside the cell then inside.

• The cell swells or pops in size. hyPO=POP

• Water enters the cell at a faster rate than it leaves

Cell Signaling• Prokaryotic cells: Quorum sensing: bacteria

cells secrete molecules that allows them to respond to changes in population density.

• Eukaryotic cells: Helps maintain homeostasis

– Tight Junctions: epithelial cells, prevent leakage, Urinary bladder

– Desmosomes: spot welds rivet cells together, mechanical stress, Skin and Uterus

– Gap Junctions: cytoplasmic flow from one cell to another: heart (intercalated disks)

– Plasmodesmata: In Plants. Act as gap junctions.

Signal Transduction PathwaysSignal…Transduction…Responce

• Autocrine Signals: diffuse from one part of a cell to another part of the same cell.– Prostaglandins

• Synaptic Signaling: Used by nerves

• Paracrine Signals: Cells communicate with each other by diffusion– Prostaglandins

• Endocrine Signals: Hormones. (Hormone is a chemical that effects another cell. Produced at a specific site.)

Ligand= signaling molecule. Can be a hormone…. or not.

Signal Transduction Pathway

• Ligand: signaling chemical…(hormone)– Steroid: enters the nucleous becomes a transcription factor

switching genes on or off– Non-steroid: cAMP causes reaction to effect DNA

• Target cell: Where Ligand must travel to

• Receptor: Spot on the target cell that the ligand attaches to.(How cells know what proteins to make, apoptosis, what to become.) …receptor mediated endocytosis

Steroid effect

The cascade effect

• Both hydrophobic and hydrophilic signaling molecules may use a cascade effect because it amplifies the signal.

• Evolution: All kingdoms use the cascade effect and all steps/ proteins are similar. We all have a common ancestor.

• Highly specific. Regulated

• One molecule can cause thousands of other molecules to be made.

How do we control signals? • Negative and Positive Feedback systems

– Negative feedback: one organ or gland negates the effect of another. Maintains homeostasis.

– Positive feedback system: Amplifies the effect. Childbirth, blood clots, allergic reactions.