Lipids + movement across membranes (Mid 1)

Structure of lipid

Amphipathic Molecule

Contains small polar hydrophilic region

Nonpolar hydrophobic region

Saturated Fatty Acid

Single bonds (saturated with hydrogen)

Long and straight

Solid at Room Temp.

Unsaturated Fatty Acids

One or more double bonds

Bent/kinked

Liquid at room temp

Fatty Acids

a hydrocarbon chain with 14-20 carbons bonded to a carboxyl (COOH) functional group

Phospholipids

Polar head and non polar tail (two fatty acid tails)

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Hydrophilic head

Hydrophobic tail

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Form micelles (one layer) or lipid bilayers (two layers)

Steroids

four ring structure

mostly function as hormones

Cholesterol ( a steroid) is a component of the cell membrane in animal cells

Peripheral proteins

proteins on surface

Integral Proteins

reside within the bilayer

Selective Permeability

Lipid bilayer has this

Small or non polar molecules cross easily

Charged or large polar substances cross slowly if at all

Phospholipid Bilayer

Forms spontaneously

Polar heads facing out

Nonpolar tails inside

also has steroids, proteins etc

Factors affecting Fluidity

More fluid= more permeabile

Less fluid= less permeable

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Number of double bonds-- increase permeability

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Saturated hydrocarbon chains have fewer spaces and are denser and less permeable

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Unsaturated hydrocarbon chains prevent the close packing(due to bent shape) -- more permeable

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Shorter tails have increased permeability

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Less cholesterol increases permeability

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Cold temp reduces permeabiloty

Hot temps increase permeability (motion increases)

Passive transport

substances diffuse across a membrane without an energy source

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Diffusion and Osmosis and Facilitated

Diffusion

movement across a membrane from high concentration regions to low concentration

Concentration Gradient

created by a difference in solute concentration

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When a gradient exists there is a net movement from high - low concentrations

Osmosis

movement of water across lipid bilayers

Fafrom low concentration to high concentration

Hypertonic

higher solute concentration (less water)

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water rushes out of cell when placed in this solution

Hypotonic

lower solute concentrations (more water)

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Water will rush in the cell when placed in this solution

Isotonic

inside and outside equal

water moves back and forth but no net change

Facilitated and Active Transport

Channel Proteins

facilitates diffusion

pass through a hole

Carrier Protein

changes shape (conformation)

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Facilitated Diffusion-- Spontaneous, doesn’t require energy

Voltage Gated Channel

can’t go across the channel until the charge is “correct”

Active transport

non spontaneous

Requires energy

Molecules pumped against the gradient (low-→ high)

Energy usually in form of ATP

Types of facilitated diffusion

Channels (passive)

Carriers (passive)

Pumps (active)

Facilitated diffusion

uses proteins for help

Does not need energy

type of passive transport

Secondary Active Transport

uses energy indirectly

Uses ions pumped against their gradient

Uses the established electrochemical gradient