Cell Membrane

sWhat’s wrong with this

picture?

http://www.studyblue.com/notes/note/n/osmolality-and-osmo-gap/deck/1598495

The Plasma Membrane

Membranes• Cells separate “inside and outside” with

lipid barriers called membranes.• Organelle membranes separate too.• Limits passage of polar substances.• Protein channels allow specific passage.BILL: What is the difference between polar

and charged?

What passes freely?

• Small, uncharged polar molecules

• Small nonpolar molecules like N2

• Model simple diffusion

http://www.studyblue.com/notes/note/n/biology-172-lecture-7-flashcards/deck/124266

Cell Walls• Are outside the

membrane

• Structural

• Plant cell walls are made of cellulose

• Prokaryotes and fungi also have cell walls.

http://www.phschool.com/science/biology_place/biocoach/plants/walls.html

Phospholipid Bilayer•This represents a phospholipid-

•The tails are fatty acid, the head, phosphorylated alcohol

•These form a sheet two molecules thick.

Polar head-Hydrophilic-label

Nonpolar tail-Hydrophobic-label

http://en.wikipedia.org/wiki/Phospholipid

Why the embedded cholesterol?

Increase or decrease fluidity depending on temperature.(Decreases fluidity when warm, increases fluidity when cold…keeps membranes fluid at very cold temperatures)

What might a membrane in an arctic dweller look like?

Membrane ProteinsFunction in

•Transport-•Enzyme•Surface receptors•ID Markers•Cell-cell connection•Attachment

http://www.pc.maricopa.edu/Biology/pfinkenstadt/BIO201/201LessonBuilder/UnitOne/Membrane/index.html

Embedded Proteins

• Can be hydrophilic with charges and polar side groups or…

• Hydrophobic, with nonpolar

Place your proteins in the membrane.

http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect08.htm

Anchoring in the membrane

What could keep proteins in the membrane?

Transmembrane Proteins

•Carriers- change shape–Active and passive transport

–Sodium potassium pump

•Channels- –are tunnels through the hydrophobic core

•Receptors–Transmit information from the outside of the cell

–Hormone receptors, neurotransmitters.

What needs a channel?

Hydrophilic substance like large polar molecules and ions

http://www.cipsm.de/en/publications/researchAreaF/2007/index.html

Carrier proteins

•Holds ion or molecule•Changes shape•To move something across the membrane

Green ball is one K+ in

a potassium pump

Campbelll p 125 8th edition.

Have you seen shape changes before?

Aquaporins

•Channel Protein•Each aquaporin allows 3 billion water molecules per second to pass into the cell single file.

http://www.bio.miami.edu/~cmallery/150/memb/water.channels.htm

What might the positively charged region do?

Receptor Proteins

•Example:–G protein linked receptor

–neurotransmitter

Cell Surface Markers• Glycoproteins- a carbohydrate combined

with a protein. Add a carbohydrate chain to a protein embedded in the membrane. Add and label

Important in the self recognition.Recognized by the immune system.

• Glycolipid- a carbohydrate combined with a lipid . Add a carbohydrate to a lipid. Add and label.

Important in tissue recognition.Example is blood group marker.

Cell surface markersGlycocalyx- “Sugar coating”

•Glycoproteins- “self” recognition

The protein/carbohydrate chain shape is different person to person. For example, the major histocompatibility complex proteins are recognized by the immune system.

•Glycolipids-tissue recognition

The lipid/carbohydrate chain

shape is specific for a certain

tissue. For example blood group

markers.

Me You

Transport ModesThrough the cell membrane

• Passive - Down the concentration gradient-primary role in importing resources and exporting waste

1. Diffusion

2. Facilitated Diffusion- membrane proteins help charged and polar molecules pass.

3. Osmosis

• Active- Against the concentration gradient. Energy requiring. Requires membrane proteins.

1. Endocytosis/Exocytosis

2. Na+/K+ Pump

3. Proton Pump

Diffusion

•Often by Ion Channels•Direction of movement determined by

–Relative concentration

–Voltage

•Each channel is specific for one or a few ions•Nervous system

Facilitated Diffusion

•Carrier Proteins•Specific also•Bind/release•Moves things down the concentration gradient•Passive transport•Can become saturated

Active Transport

•Uses Energy •Moves things against the gradient•Na/K Pump•Coupled Transport

–Gradients created by one process can power another

Sodium Potassium Pump

• Cytoplasmic Na+ binds (high affinity in this shape).

• Na+ binding stimulates phosphorylation by ATP

• Phosphorylation causes shape change, lower Na+ affinity, now high K+ affinity.

• The K+ binding causes phosphate to be released

• Phosphate release causes shape to return. Now low K+ affinity,

Endocytosis and Exocytosis

•Exocytosis-internal vesicles fuse with the plasma membrane to release large macromolecules out of the cell.

•Endocytosis-cell takes in macromolecules and particulate matter by forming new vesicles from the plasma membrane.

Bulk Transport

•Endocytosis–Phagocytosis-particulate

–Pinocytosis-liquid

–Receptor-Mediated endocytosis

–Clathrin coated pits bind to specific molecules.

Bulk Transport

•Exocytosis–Neurotransmitter discharge

–Hormone secretion

–Digestion enzymes

http://www.kscience.co.uk/as/module1/pictures/endoexo.jpg

Explain the diagram.

Eukaryotic cells are compartmentalized By Membranes

These special areas let things happen by…

• Minimizing competing interactions

• Increasing surface area where reactions can occur

• Compartmentalizing metabolic processes and enzymatic reactions.

• Examples: Endoplasmic Reticulum, mitochondria, chloroplast, Golgi, nuclear envelope

• Archaea and Bacteria generally lack internal membranes and organelles.

Protein Pieces