7.3 cell boundaries
DESCRIPTION
7.3 Cell Boundaries. Fluid compartments in our bodies are separated by membranes. Composition of body fluids. Greater number of osmotically active particles. Some organisms have a CELL WALL. Plants (cellulose) Algae (polysaccharide) Fungi (-chitin) Prokaryotes(peptidoglycan). - PowerPoint PPT PresentationTRANSCRIPT
7.3 Cell Boundaries
Fluid compartments in our bodies are separated by membranes
Composition of body fluids
Greater number of osmotically active particles
Distribution of Total body fluids
Some organisms have a CELL WALL
• Plants (cellulose)• Algae (polysaccharide)• Fungi (-chitin)• Prokaryotes(peptidoglycan)
Why have a cell wall?1. Mechanical support2. Protection3. Cell-cell communication4. Maintenance of structure (turgor)5. Prevent water loss
Membranes
2007-2008
Where are membranes located?
• Plasma membrane (double membrane)
• Membrane-bound organelles (single or double)
• Secret Universe• Introduction to cell
membrane
Why do we need plasma membranes made
Our cells inhabit an aqueous environment• …but they must let ‘stuff’ (nutrients, ions,
molecules,waste products) in and out• …..and they need to communicate with each
other…How is this achieved?....
Functions of the Cell membrane
1. Protective barrier2. Cell-Cell signalling3. Transport of nutrients, products and waste products4. Localisation of function within organelles5. Semi-permeable: controls entry and exit of
substances6. Self-sealing!7. Flexible, mobile fluid mosaicCell membrane function
Let’s meet the components of the cell membrane
• Phospholipid bilayer• Cholesterol• Carbohydrates
(glycoproteins)• Proteins• Let's build a membran
e from scratch…
Phospholipid bilayer
polarhydrophilicheads
nonpolarhydrophobictails
polarhydrophilicheads
Membrane lipid composition varies
Fat composition affects flexibility: membrane must be fluid & flexible% unsaturated fatty acids in phospholipids
– keep membrane less viscous– cold-adapted organisms, like
winter wheat increase % in autumn
– cholesterol in membrane
Membrane Proteins
• Proteins determine a membrane’s specific functions• Cell membrane &
organelle membranes each have unique collections of proteins
• Channels, pumps, receptors
NH2
H+
COOH
Cytoplasm
Retinalchromophore
Nonpolar(hydrophobic)a-helices in thecell membrane H+
Porin monomerb-pleated sheets
Bacterialoutermembrane
proton pump channel in photosynthetic bacteria
water channel in bacteria
function through conformational change (shape change)
Examples
Many Functions of Membrane Proteins
Outside
Plasmamembrane
Insidechannels forpassive transport
Cell surfacereceptor (pumps)
Immobilised Enzyme
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
Membrane glycoproteins (carbohydrates)
‘Chemical identification cards’Play a key role in cell-cell recognition• ability of a cell to distinguish
one cell from another– Antigens
• basis for rejection of foreign cells by immune system
Movement across the Cell Membrane
How are substances transported into and out of the cell?
1. Simple Diffusion(passive)2. Facilitated diffusion (Passive)
3. Osmosis4. Active transport
5. Endocytosis6. Exocytosis
Simple Diffusion2nd Law of Thermodynamics governs biological systems– universe tends towards disorder (entropy)
Diffusion movement from high low concentration
DiffusionMovement is from HIGH to LOW concentration• “passive transport”• no energy needed
diffusion osmosis
movement of water
Let’s watch some animations
• Diffusion animation 1• Diffusion animation 2
Diffusion through phospholipid bilayerWhat molecules can get through directly?• fats & other lipids
inside cell
outside cell
lipid
salt
aa H2Osugar
NH3
What molecules can NOT get through directly? polar molecules
H2O ions
salts, ammonia large molecules
starches, proteins
Facilitated DiffusionDiffusion through protein channels– channels move specific molecules across
cell membrane– no energy needed
open channel = fast transport
facilitated = with help
high
low
Channels through cell membraneMembrane becomes semi-permeable with protein channels – specific channels allow specific material across cell
membrane
inside cell
outside cell
sugaraaH2O
saltNH3
Which substances are transported by facilitated diffusion?
• Glucose• Urea• Amino acids• Animation
The Special Case of Water
Movement of water across the cell membrane
2007-2008
Osmosis is facilitated diffusion of water
Facilitated diffusion of water from
high concentration of water to low
concentration of water across a semi-permeable
membrane
Concentration of waterDirection of osmosis is determined by comparing total solute concentrations on either side of the membrane:• Hypertonic - more solute, less water• Hypotonic - less solute, more water• Isotonic - equal solute, equal water
hypotonic hypertonic
water
net movement of water
freshwater balanced saltwater
Water passes through special water pores - Aquaporins
Aquaporins
• Structure, function and dynamics of aquaporins
Peter AgreJohn Hopkins
Roderick MacKinnonRockefeller
Active Transport
Active Transport• Cells may need to move molecules against concentration
gradient– shape change transports solute from
one side of membrane to other – protein “pump”– “costs” energy = ATP
“The Doorman”
conformational change
ATP
low
high
symportantiport
Active transport• Many models & mechanisms
ATP ATP
Getting through cell membrane• Passive Transport– Simple diffusion
• diffusion of nonpolar, hydrophobic molecules– lipids– high low concentration gradient
– Facilitated transport• diffusion of polar, hydrophilic molecules• through a protein channel
– high low concentration gradient
• Active transport– diffusion against concentration gradient
• low high– uses a protein pump– requires ATP
ATP
Transport summarysimplediffusion
facilitateddiffusion
activetransport
ATP
Endocytosis and exocytosis
• ACTIVE processes for bulk transport• These processes are intimately dependent on lipid
bilayer fluid mosaic nature of the cell membrane• Endocytosis – internalisation• Exocytosis - externalisaton• Phagocytosis: the intake of large particulate
matter• Pinocytosis: intake of extracellular fluids
Endocytosis
• A simple one...• McGRaw Hill phagocytosis
Exocytosis• Protein produced by the ribosomes enter the lumen of the ER• Protein exits the ER and enters the cis or trans side of the Golgi
aparatus• Protein is modified through Golgi, and vesiculated• Vesicle moves to and fuses with the plasma membrane• Exocytosis
How about large molecules?• Moving large molecules into & out of cell– through vesicles & vacuoles– endocytosis• phagocytosis = “cellular eating”• pinocytosis = “cellular drinking”
– exocytosis
exocytosis
Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered bymolecular signal
Let’s look at membrane transport mechanisms in action…
Intravenous Fluid Therapy is often in the emergency room
• Hypertonic saline (7.2% NaCl)
• Isotonic glucose saline solution (5% glucose/ 0.45% NaCl)
• Isotonic saline (0.9% saline)
• (Blood, plasma, colloids)
Emergency Room therapy
Oxygen delivered by mask
0.9% isotonic saline
7.2% hypertonic saline
Oxygen crosses the alveolar membrane by diffusion
Explain how oxygen diffuses into cells
Cell (compared to beaker) hypertonic or hypotonicBeaker (compared to cell) hypertonic or hypotonicWhich way does the water flow? in or out of cell
.05 M .03 M
Osmosis…