every cell is bordered by a plasma membrane. cell membranes cell membranes are gatekeepers
TRANSCRIPT
Every cell is bordered by a plasma membrane.
Cell membranes are gatekeepers.
© 2011 Pearson Education, Inc.
5.1 The Nature of the Plasma Membrane
Plasma membranes are complex structures
They perform several critical functions.
• take in food & nutrients • dispose of waste products• build & export molecules • regulate heat exchange• regulate flow of materials
in & out of cell
hydrophilic = water lovinghydrophobic = water fearingSpilt Personalities…
Molecules embedded within the plasma membrane help it perform its functions.
The Plasma Membrane is a
“Fluid Mosaic”
Membrane contains:
• Carbohydrates• glycocalyx • cell adhesion & binding
• Lipids • cholesterol • flexibility
• Proteins • peripheral or integral
Figure 5.1
The Plasma Membrane
phospholipids cholesterol proteinsglycocalyx
cell exterior
cell interiorcytoskeleton peripheralprotein
integralprotein
Phospholipidbilayer: a doublelayer ofphospholipidmolecules whosehydrophilic “heads”face outward, andwhose hydrophobic“tails” point inward,toward each other.
Cholesterolmolecules that actas a patchingsubstance andthat help the cellmaintain anoptimal level offluidity.
Proteins, whichare integral,meaning bound tothe hydrophobicinterior of themembrane, orperipheral,meaning notbound in this way.
Glycocalyx: sugarchains that attachto proteins andphospholipids,serving as proteinbinding sites andas cell lubricationand adhesionmolecules.
Figure 5.3
Proteins
(a) Structural support (b) Recognition (c) Communication (d) Transport
cell exterior
cell interior
Proteins can serveas channelsthrough which materials can pass in and out ofthe cell.
Receptor proteins,protruding out from the plasma membrane,can be the point of contact for signals sent to the cell via traveling molecules, such as hormones.
Protein fragments held within recognition proteins can serve to identify the cell as “normal” or “infected” to immune system cells.
Membrane proteinscan provide structural support, often when attached to parts of the cell’s scaffolding or “cytoskeleton.”
• Phospholipid bilayer• Carbohydrates• Lipids • Proteins
The Plasma Membrane is a “Fluid Mosaic” of molecules
Movement of Molecules
Active Transport
Primary Secondary
Passive Transport
Diffusion Osmosis
Simple Diffusion
Facilitated Diffusion
http://youtu.be/dPKvHrD1eS4
© 2011 Pearson Education, Inc.
5.2 Diffusion, Gradients, and Osmosis
Movement of Molecules
Active Transport
Primary Secondary
Passive Transport
Diffusion Osmosis
Simple Diffusion
Facilitated Diffusion
2 types:1. Diffusion –
Passive transport is the spontaneous movement of
molecules across a membrane.
molecules move from an area of high concentration to an area of low concentration.
Diffusion, Gradients, & Osmosis
Concentration gradient: difference btwn highest & lowest concentrations of a solute within a given medium.
- In diffusion, compounds naturally move from high to low (down their concentration gradients)
- Energy not needed
High
Low
Figure 5.4
Diffusion, Gradients, and Osmosis(a) Dye is dropped in. (b) Diffusion begins. (c) Dye is evenly distributed.
water molecules
dye molecules
Diffusion, Gradients, and Osmosis
• Osmosis - net movement of water across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration
• Semipermeable - some compounds pass freely while others are blocked
Cell will swell
Cell will shrivel
2. Osmosis – diffusion of water molecules
Movement of Molecules
Active Transport
Primary Secondary
Passive Transport
Diffusion Osmosis
Simple Diffusion
Facilitated Diffusion
© 2011 Pearson Education, Inc.
5.3 Moving Smaller Substances In and Out
Simple Diffusion vs Facilitated Diffusion
Facilitated Diffusion – requires both a concentration gradient and a protein channel
Simple Diffusion – small molecules pass through membrane easily.
Neither one requires Energy!
Passive transport Active transport
simple diffusion facilitated diffusion
Materials move downtheir concentration gradient through the phospholipid bilayer.
The passage of materials is aided both by aconcentration gradient and by a transport protein.
Molecules again move through a transport protein, but now energy must be expended to move them against their concentration gradient.
ATP
Figure 5.7
Figure 5.8
Facilitated Diffusion - transport proteins work as channels for larger hydrophilic substances (b/c of size & electrical charge,
can’t diffuse through the hydrophobic portion)
cell exterior
plasmamembrane
cell interior
glucose
1.Transport protein has binding site for glucose open to the outside of the cell.
2. Glucose binds
4. Glucose passes into the cell & proteinreturns to its original shape.
3. This binding causes the protein to change shape, exposing glucoseto the inside of the cell.
Movement of Molecules
Active Transport
Primary Secondary
Passive Transport
Diffusion Osmosis
Simple Diffusion
Facilitated Diffusion
Passive transport Active transport
simple diffusion facilitated diffusion
Materials move downtheir concentration gradient through the phospholipid bilayer.
The passage of materials is aided both by aconcentration gradient and by a transport protein.
Molecules again move through a transport protein, but now energy must be expended to move them against their concentration gradient.
ATP
Figure 5.7
Active transport - cells use energy to move small molecules.
• Molecules can’t always move freely in and out of cells
• Some molecules need to maintain a high concentration – move against the gradient
– membrane proteins act like motorized revolving doors
Active Transport example
Inside Stomach
Cells surrounding Stomach
H+ movingAgainst Concentration Gradient
© 2011 Pearson Education, Inc.
5.4 Moving Larger Substances In and Out
Moving Larger Substances In and Out
• Endocytosis• Exocytosis• Both mechanisms use
vesicles– the membrane-lined
enclosures that alternately bud off from membranes or fuse with them
Figure 5.10
Exocytosis
extracellular fluid protein
transport vesicle cytosol
plasma membrane
1. a transport vesicle moves from the inside of the cell to the plasma membrane
2. fuses with plasma membrane3. the contents of the vesicle are released
Endocytosis
• There are two principal forms of endocytosis: pinocytosis and phagocytosis.
Pinocytosis• movement of moderate-sized molecules into a cell• transport vesicles produced through infolding or
“invagination”
clathrin-mediated endocytosis (CME):- cell-surface receptors bind to
molecules - the protein clathrin becomes a vesicle
Phagocytosis
• Certain cells use pseudopodia or “false feet” to surround and engulf whole cells, fragments of them, or other large organic materials.
© 2011 Pearson Education, Inc.
6.1 Energy Is Central to Life
Energy Conversions All life depends on capturing energy from
the sun and converting it into a form that living organisms can use.
Two key processes• Photosynthesis• Cellular respiration
© 2011 Pearson Education, Inc.
6.2 The Nature of Energy
What is energy?
The capacity to do work
Work• Moving matter against
an opposing force
Energy has two forms.
• The energy of moving objects
• Heat energy• Light energy
A capacity to do work that results from the location or position of an object
Concentration gradients and potential energy
Food, chemical energy, has potential energy
Potential Energy
Energy Conversions Only ~1% of energy released by the sun that
earth receives is captured and converted by plants.
• Converted into chemical bond energy What happens to the other 99%?
reflected back into space (~30%)
absorbed by land, oceans, & atmosphere (~70%),
Mostly transformed into heat
ThermodynamicsThe study of the transformation of energy from one
type to another
First Law of Thermodynamics Energy can never be created or destroyed. It can only change from one form to another.
Second Law of Thermodynamics Every conversion of energy includes the
transformation of some energy into heat. Heat is almost completely useless to living
organisms.
Energy Tax!
Every time energy is converted from one form to another the conversion isn’t perfectly efficient.
Some of the energy is always converted to the least usable form of kinetic energy: heat.