From Molecules to Organisms: Membrane Structure … · Membrane Structure and Function ......

Structure & Function (LS1A) Membrane Structure and Function

Copyright © Rebecca Rehder Wingerden

From Molecules to Organisms: Structure & Processes

LIFE SCIENCE DISCIPLINARY CORE IDEAS

5.10 - 5.20, 25.5

Membrane Structure and Function

Copyright © 2014 Rebecca Rehder Wingerden

Epithelial cells

Paramecium

Elodea leaf cells

•All cells have similar structures and those structures have similar functions.

•Cell membranes:-separate living cells from their non-living environment,-are made of a phospholipid bilayer, -and are selectively permeable.

Non polar tails

Polar head

Phospholipid

Hydrophobic environment

Hydrophilic environment

Hydrophilic environment

Plasma Membrane

The hydrophobic interior prevents charged substances (ions, polar molecules) from passing through the membrane, therefore membranes are selectively permeable.


•Cell membrane structure is described as a fluid mosaic.-Fluid- lateral movement of molecules-Mosaic- diverse protein molecules embedded in a framework of phospholipids

Fibers of the extracellular matrix

Glycoprotein

Carbohydrate (of glycoprotein)

Microfilaments of the cytoskeleton

Phospholipid

CholesterolProteins

CYTOPLASM

Glycolipid

OUTSIDE CELL

Cholesterol which is wedged into the bilayer, it helps stabilize the phospholipids at body temperature but also helps keep the membrane fluid at lower temperature. Carbohydrate bound to proteins (glycoprotein) and to lipids (glycolipid) serve as identification tags. Membrane proteins attach the membrane to the cytoskeleton and external fibers, provide identification tags, form junction between adjacent cells, function as enzymes, cell receptors and facilitate signal transduction, as well as facilitate the movement of materials across the cell membrane.


•Movement of substances across cell membranes can occur through both passive transport and active transport.

-Passive transport substances diffuse through membranes without cellular work, no ATP (diffusion, osmosis, facilitated diffusion).

EQUILIBRIUMMolecule of dye High Concentration Membrane

EQUILIBRIUMMembraneHigh Concentration

1. Diffusion is the tendency for particles to spread out spontaneously to regions where they are less concentrated. A substance diffuses down a concentration gradient, from areas of high concentration to areas of lower concentration.No energy (ATP) required.

ATP


2. Osmosis is the diffusion of water across a selectively permeable membrane. Hypertonic- solution have a high solute concentrationHypotonic- solution have a low solute concentrationIsotonic- solution have equal concentrationsNo energy (ATP) required.

ATP

Hypotonic

Solute molecule

HYPOTONIC SOLUTION

Hypertonic

HYPERTONIC SOLUTION

NET FLOW OF WATER

Solute molecule with cluster of water molecules

Selectively permeable membrane

Selectively permeable membrane

Water molecule

Isotonic






3. Facilitated diffusion is the movement of a molecule across a biological membrane by a specific transport protein.The transport protein provides a pore for the passage of a particular solute (sugars, amino acids, atomic ions and water).No energy (ATP) required.

ATP

Solute molecule

Transportprotein


1. Active Transport requires that a cell expend energy to move molecules a crossed a membrane.Transport proteins actively pump specific solute across a membrane against the solute’s concentration gradient.Energy (ATP) required.

ATP

Transportprotein

FLUID OUTSIDE CELL

First solute

Phosphorylated transport protein

2 ATP transfers phosphate to protein

3 Protein releases solute outside cell

4 Second solute binds to protein

Second solute

5 Phosphate detaches from protein

6 Protein releases second solute into cell

First solute, inside cell, binds to protein

1


-Active transport requires energy from the cell, ATP required (active transport, exocytosis, endocytosis).




2. Exocytosis is the process by which large molecules (such as proteins) are exported outside the cell.A membrane-enclosed vesicle filled with macromolecules (green) moves to the plasma membrane and fuses with the plasma membrane, spilling the contents of the vesicle outside the cell. Energy (ATP) required.

ATP

FLUID OUTSIDE CELL

CYTOPLASM

Tears Insuline- glucose regulation




1. Endocytosis is the process by which large molecules are imported into the cell.A cell takes in macromolecules or other particles by forming vesicles or vacuoles from it plasma membrane.Energy (ATP) required.

ATP

FLUID OUTSIDE CELL

CYTOPLASM

Pseudopod of amoeba

Food being ingested

Plasma membrane

Material bound to receptor proteins

PIT

Cytoplasm

Phagocytosis Pinocytosis Receptor-mediated endocytosis


•Osmoregulation is the active regulation of the level of water in an organism.

•Water balance problems are somewhat different for plant cells and animal cells.

ISOTONIC SOLUTION

HYPOTONIC SOLUTION

HYPERTONIC SOLUTION

(1) Normal

(4) Flaccid

(2) Lysing

(5) Turgid

(3) Shriveled

(6) Shriveled

ANIMALCELL

PLANTCELL

Plasma membrane

Animal cells prefer isotonic environments, where the net flow of water into the cell is equal to the flow of water out of the cell. Plant cells prefer a hypotonic environment, which creates a net flow of water into the cell. The plant’s cell wall prevents the cell membrane from bursting, creating turgid pressure.


•Osmoregulation in organisms

Uptake of water and some ionsin food

Osmotic water gain through gills and other parts of body surface

Uptake ofsalt ions by gills

Excretion of large amounts of water in dilute urine from kidneys

Gain of water and salt ions from food and by drinkingseawater

Osmotic water loss through gills and other parts of body surface

Excretion of saltions from gills

Excretion of salt ions and small amounts of water in scanty urine from kidneys

Freshwater fishes gain water by osmosis and tent to lose solutes. It takes the work of three organ systems (digestive, respiratory, excretory) to achieve the proper water and solute balance.

Saltwater fishes internal fluids are lower in total solutes than seawater, therefore it loses water by osmosis through its body surfaces. It takes the work of three organ systems (digestive, respiratory, excretory) to achieve the proper water and solute balance.


Paramecium are Protozoans (single celled animals that live in fresh water and have contractile vacuoles. Why would this type of organisms need contractile vacuoles to survive?

Terrestrial animals obtain most of their water from food and drink. They lose water by urination, defecting, and evaporation as they breathe and perspire. Why is it not healthy to drink salt water?

•Osmoregulation in organisms

hypotonic

hypertonic

Contractile vacuoles pump water out to prevent the cell from bursting.

Saltwater is hypertonic to human blood and fluids. So, if you drank saltwater you would actually lose more water than you gained, effectively dehydrate your body.

water

From Molecules to Organisms: Membrane Structure … · Membrane Structure and Function ......

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