Biology, Membranes

Raven Biology, CH5

Membrane Strucuture

Phospholipid Bi-layers

Globular protines

fluid Mosaic model

Phospholipid Bi-layer

Structure of Membranes

Include Glycerol Phosoplipids and Sphingolipids

Fluid Mosaic Model

Structure of membranes

Mosaic of proteins float in or on the fluid lipid bi-layer

EX: Boats on a pond

Boats on a pond are a example of what?

Fluid Mosaic model

Fluid Mosaic model of Cell membranes

Components of Cellular membranes

Phospholipid bilayer

Transmembrane Proteins

Interior Protein Network

Cell Surface Markers

Cellular membranes- Phospholipid Bilayer

Flexible Matrix, barrier to permeability

Cellular membranes- Transmembrane Proteins

Integral membrane proteins

Cellular membranes- Interior Protein Network

Peripheral or intracellular membrane proteins

Cellular membranes- Cell Surface Markers

Glycoproteins and Glycolipids

Studying the cell membrane- TEM

Transmission electron microscope (TEM), one method of TEM is to embed specimen in epoxy

less than 1 micro meter thick of of speciman can be imaged

Studying the cell membrane- SEM

Scanning electron microscope (SME)

Freeze Fracture Microscopy

Membrane lipids

Lipidomics

Glycerol phospholipids

sphingolipids

sterols

3 Classes of the 1000 distinct lipids in cells

Glycerol phospholipids

sphingolipids

sterols

Lipidomics

Defines the number and biological function of lipids

Sphingolipid Structure

Phospholipids

Amphipathic structure ( bi-layer forms spontaneously)

Head is Polar, Hydrophilic, and has Phospate group attached

2 fatty acids, are non polar and hydrophobic

Phospholipid structure

Physiology of Phospholipid Bilayer

Bilayers are fluid

Hydrogen bonding holds layers together

unanchored proteins and individual phospholipids move through membrane

Bilayers are

fluid

what holds phospholipid bilayers together

Hydrogen bonds of: H2O -H2O and H2O-polar heads

Hydrophillic and Hydrophobic bonds

Saturated Fatty Acids affect on fluidity

Cause membrane to be less fluid compared to unsaturated fatty acids

How dose temperatures affect membranes fluidity

Warm temps make the membrane more fluid, cold makes them more viscous

Cold tolerant bacteria are possible by fatty acid desaturases

what compositions of lipids affect fluidity, thickness, and shape of membrane?

lipid composition of the ER membrane, Golgi stack and plasma membrane

Endolpasmic reticulum (ER)

Plasma Membrane (PM)

Functions of Membrane Proteins

Transport
Enzymes
Cell-surface receptors
Cell-surface ID Markers
Cell-Cell adhesion Proteins
Attachment to Cytoskeleton
Affect on membrane structure

Membrane Protein Function

Membrane Structure relates to Function

Diverse Function form Diverse structure of membrane proteins

Common Structural features relate to role of membrane Protein

Diverse Function form Diverse structure

Membrane Proteins

Anchor Molecules

Attach to membrane protein, to the membrane surface

modified by lipids

anchor molecules moded by lipids

by nonpolar intersecting regions of the internal portion of the lipid bilayer

Chemical bonding domains, linking directly to proteins

Transmembrane proteins

Span Lipid bilayer

Non polar regions of proteins are embedded interior of bilayer

Alpha Helices and Beta sheets

Polar regions of proteins protrude form both sides of bilayer

Affect of non polar and polar regions on Transmembrane Proteins

Non Polar embed inside bilayer

Polar protrude form both sides of bilayer

Transmembrane Domain

membrane spanning region

Hydrophobic amino acids form Alpha helices

one domain need to be anchored in Membrane for proteins

may have more than one domain

Class of receptors is based on # of Domains present

how are hydrophobic amino acids arranged in Transmembrane domains

Alpha Helices

how many trans membrane domains needed in proteins to anchor in Membrane?

A single TM domain needed, but may have more than one of the same domain with the amount domain based on class of receptor type.

Pores

Created by extensive non polar regions in a TM Protein

Beta barrel are secondary protein structure

polar interior allows water and small polar molecules to pass through membrane

polar interior that allows water and small polar molecules to pass through membrane

Pore

Passive transport

movement of molecules through membrane

no energy required, move in response to concentration gradient

diffusion

Diffusion

movement of molecules high to low concentration

continues till conc. is same in all regions

Diffusion

transport Across membranes

major barrier is hydrophobic interior, only repels polar molecules

nonpolar molecules function like diffusion

only small polar molecules

limited permeability to larger polar molecules & ions

Protein affect on membrane diffusion

-Facilitate diffusion:

Molecules can use proteins as gateways

Channel proteins are hydrophillic when open

Carrier proteins assist membranes when binded

-Membrane is selectively permeable due to channels and carriers

Channel Proteins

-Ion channels: passage of ions through non polar interior of plasma membrane

Gated channels, open or close to stimuli

direction dependent on concentration, voltage difference, Gate channels open or closed

direction in protein channels are dependent on

Relative Concentration on eather side of membrane

Voltage Difference across membrane

Gated Channels opened or closed

Facilitated Diffusion of Ions

Carrier Proteins

Required to bind to molecule they transport

Transport both Ions and other solutes

Move by diffusion

Saturation in Carrier Proteins

Rate of transport limited by # of transporters

Facilitated diffusion by carrier proteins

Osmosis

Net diffusion of water across membrane to higher solute conc.

Cytoplams of cell is an Aqueous solution

Cytoplasm of cell

Aqueous solution

Water

is a solvent

solute

dissolved substances

Osmosis Across a Semipermeable Membrane

Osmotic concentration

Hypertonic solution- higher solute conc.

|Hypotonic solution- lower solute conc.

Isotonic solution- equal conc.

Aquaproins facilitate osmosis

Aquaporins

Channles for water in cells membrane

Facilitate Osmosis

Osmotic pressure

Force to stop osmotic flow

Cells swelling can create pressure

Hydrostatic pressure, balances pressure by driving water out

Plasma membrane are weak and may burst

Cell Swelling

In a hypotonic solution cells gain water causing swelling, that creates pressure

Hydrostatic Pressure

aids in reaching osmotic pressure, by driving water out

used by Prokarytoes, Fungi, Plants, and many Protists

Isotonic Environments

Animal cells must be in these environments to avoid bursting plasma membranes

Solutes and Osmotic Pressure in cells

Maintaining Osmotic Balance

Extrusion- injects water through contractive vacuoles

Isosmotic regulation- used by marine organisms and terrestrial animals

Turgor pressure- used by plants

Active Transport

Req. Energy ATP directly or indirectly used to fuel

Moves substance low to high concentration

Req. use of Highly Selective carrier proteins

Carrier Proteins used in Active Transport

Uniporters- move one molecule

Symporters- move 2 molecules, same direction

Antiporters- move 2 molecules, opposite direction

Uniporters

carrier proteins that move one molecule at a time

Symporters

carrier proteins, move 2 molecules in same direction

Antiporters

Move 2 molecules in opposite directions

Na+-K+ Pump

Sodium-Potassium Pump

What type of transport is the Na+-K+ Pump

Active transport, uses ATP to change the conformation of carrier protein

what type of carrier protein is used for the Na+-K+ pump

Antiporter’s to move 3 Na+ out of cell and 2K+ in to cell

they move against the concentration gradient

How dose the Na+-K+ function

To change ions so they can be carried across the membrane, by moving 3 Na+ out of cell and 2K+ into cell using antiporter’s that have a affinity for Na+ or 2 K+

What is the Na+-K+ Pump ratio

3 Na+ out of cell and 2 K+ into cell

NA+-K+ Pump Function (Diagram)

How Coupled Transport Use ATP

Indirectly

How Coupled Transport Use Energy

Uses energy released when a molecule moves by diffusion to supply energy to activate transport of different molecule

Carrier Proteins in Coupled Transport

Symporter or Aniporter

Coupled Transport: Glucose-Na+ symporter

Captures energy form Na+ diffusion to move Glucose against a concentration gradient

Coupled Transport Via Membrane Proteins

Bulk Transport

Endocytosis & Exocytosis

Active transport

Endocytosis

Movement of Sub into cell

Requires Energy

Phagocytosis

Pinocytosis

Receptor’s

Phagocytosis

Cell takes in Particulate Matter

Pinocytosis

Cell only takes in FLUID

Endocytosis Receptor

Mediate endocytosis

specific molecules are taken in after binding to receptor

Exocytosis

Movement of substance OUT of cell

Requires energy

Endocytosis (Diagram)

Example of Receptor mediate Endocytosis

In The disease Hypercholertolemia, The LDL receptors lack tails, therefor never fastened in the clathrin-coated pits and as a result do not trigger vesicle formation. The cholesterol stays in the blood stream of affected individuals, accumulating as plaques inside arteries, leading to heart attacks.

Example of Receptor mediate Endocytosis (Diagram)

Exocytosis (Diagram)

Exocytosis Function

Discharge of materials out of cell

Plants use to export cell wall material

Animals use to secrete Hormones, neurotransmitters, Digestive enzymes