MEMBRANES
Fluid mosaic of phopholipid bilayer, cholesterol, protein
Singer – Nicolson Fluid Mosaic Model, 1970’s
Selectively permeable
Allows some substances, and not others, to pass
Built in EM System
95
Phospholipids
Glycerol, two fatty acids, hydrophobic tails, hydrophilic heads
Can have CHO chains, glycolipids
Form the basis of the fluidity in the fluid mosaic
Plipids move ~2um/sec
Proteins
Peripheral, held in place by cytoskeleton
Integral, move in fluid mosaic, hydrophilic and –phobic regions
Can have CHO chains, glycoproteins, externally
Proteins make membrane more absorbent than w/o protein
Glycoproteins form Glycocalyx
Provides for cellular recognition in animals
Basis for immune responses, organ transplant rejections, blood typing
oligosaccharides
Channel Proteins: pass compounds to opposite side of membrane
Carrier Proteins: interactively aids in movement through membrane
Recognition Proteins: Glycoproteins recognizing pathogens
Receptor Proteins: receive hormone signals from elsewhere in organism
Enzymes: catalyze specific reactions
Cholesterol (lipid, steroid) providing rigidity , lowers freezing pt.
Fluid Mosaic demonstrated by Mouse / Human protein mixing
Permeability, Selective Permeability
Substances can be moved by exocytosis and endocytosis
Small, uncharged molecules generally pass freely through membranes
These molecules follow concentration gradients
e.g. O2, CO2, H2O (polar but small)
99 Fig 5.4
Diffusion, Osmosis, Facilitated and Active Transport
Entropy
Solution = Solute (solid) in a Solvent (liquid)
100 Table 5.1
102
Fig 5.6
Diffusion moves solute from area of high concentration to areas of low concentration
Rate of diffusion is a function of concentration gradient, temp, and pressure
Selective Permeability allows select substances to cross membrane by diffusion
The gases and water mentioned above, e.g.
103 Fig 5.7
Osmosis is selective diffusion due to concentration differentials across a membrane
Osmotic Pressure is a measure of the concentration differential
104 Fig 5.8
Function of total [solute]
Isotonic: Solute (solid) concentration equal on both sides of membrane
0.9% salt solution is isotonic with blood (saline solution)
Hypotonic: greater solute concentration w/in cell and water enters cell
Turgor: seen in neglected house plants
Contractile Vacuoles: as seen, or not, in Paramecium
Cytolysis: bursting of cells due to Osmotic differential
Hypertonic: greater solute concentration outside cell
RBC’s can be “crenated” in a salt solution
Plasmolysis: vacuole and cytoplasm shrink due to water loss
113
Note that “hypo” and “hyper” depend on observer’s point of view
It’s the cell’s point of view regarding the solution
The environs are hypotonic to the cytoplasm, water enters cell
- “ - hypertonic to cytoplasm, water leaves cell
Consider metabolic consequences of osmotic pressure on aquatic organisms
Marine animals must work to retain water
FW animals must work to eliminate water
What about salmon and eels that move between the two
What about estuarine animals that deal with daily saline fluctuations
Facilitated Transport or Diffusion: movement down concentration gradient but with help
Carrier Proteins aid movement of, e.g. glucose and aa down gradient
Active Transport: facilitated movement against concentration gradient
Requires not only Carrier Proteins, but also E in form of ATP
In what class of macromolecule is ATP
Because cells involved in Active Transport need E, they have what
organelle in abundance?
K+ / Na+ Pump important in nerves and muscles
Carrier protein specific to movement of these two ions
Against conc gradient
107
Transport by Vesicle
Macromolecules are too big to be moved by Carrier Proteins
Exocytosis and endocytosis are cross-membrane transports by vesicle
Hormones are often delivered by Exocytosis
108
Insulin laden Secretory Vesicles accumulate in Pancreatic Cells and are
released following an increase in blood sugar
Endocytosis – Phagocytosis, Pinocytosis, Receptor-Mediated Endocytosis
109
Phagocytosis: remember Amoebas and Monocytes
Applies to bigger particles, cells, viruses, Greek: to eat
Pinocytosis: applies to liquids and very small (0.1um) particles, Greek: to drink
R-M Endocytosis: Receptor Proteins in membrane recognize specific molecules
external to cell. Receptor Proteins are found in a Coated Pit, coated with the proteins
Junctions
110
Allow for coordination between cells
Anchor Junctions attach adjacent cells, but w/o intracellular transport, in one of two ways
Adhesion Junction: adjacent cells together with intercellular filaments
bladder
Desmosome: cytoskeleton attachment between cells
Tight Junction: adjacent membrane proteins attach to each other
Intestine, kidney, blood – brain barrier
Gap Junction: channel proteins of adjacent cells align, strength and communication
Cardiac and smooth muscle requiring coordination
Extracellular matrix
Composed of substances with specialized structure and function, just as w/in cell
Cell Walls
112
Porous, cellulose microfibrils in plants
Pectin for flexibility, other polysaccharides to harden
Middle lamella between adjacent Walls
Secondary Cell Wall in some plants, interior to Primary, fibrils lie crossways
Plasmodesmata: membrane lined channels allowing molecular comm’n between cells
METABOLISM
Living things require Energy
Energy
Potential: stored E, ball at top of hill
Kinetic: E of motion, ball rolling down hill
Food consumed is chemical E as Potential converted to Kinetic as mechanical
Laws of Thermodynamics
First: E cannot be created or destroyed but can be converted from one form to another
Second: changing forms of E results in a loss of E – increasing disorganization
= Entropy
Cellular E transformations (e.g. Na / K pump) result in loss of E
Diffusion releases E as solute becomes randomly distributed
Glucose hydrolysis results in more, smaller, and more stable molecules
Energy Transformation
Exergonic Reaction: E released, negative delta G
Reaction will happen spontaneously
Endergonic Rxn: E required, positive delta G
Protein synthesis, muscle contraction
ATP: the universal E currency of Biology
Which class of macromolecules does this belong to?
Adenine (N base), Ribose, 3 Phosphates
Used in many rxns, provides the required amount of E for many biological functions
Used to:
Chemical: synthesize macromolecules for cell function
Transport: of compounds across membranes
Mechanical: contraction, movement
Metabolic Pathways