every cell is bordered by a plasma membrane. cell membranes cell membranes are gatekeepers

Every cell is bordered by a plasma membrane.

Cell membranes are gatekeepers.

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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

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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

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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

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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.

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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

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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.