Unit 1 - Intro to A&P II and Membrane Transport

Homeostasis

Maintenance of internal environment within physiological limits

Negative feedback

Reversal of stimulus

Positive feedback

Reinforcement of stimulus

Steps of homeostasis

1. Receptor: detects a stimulus and sends chemical signals to the control center

2. Control Center: receives the input from the receptor and initiates a response from the effector cell

3. Effector: the organ that acts in response to the signal sent by the control center

In the plasma membrane, describe the phospholipid bilayer

• Polar heads (Hydrophilic)

• Fatty acid tails (Hydrophobic)

Describe permeability of the plasma membrane/lipid bilayer

• selectively permeable

• Lipid bilayers is always permeable to small, nonpolar uncharged molecules

• Lipid bilayer is impermeable to ions or charged molecules

  • Need to use a transport protein

What do transmembrane proteins do

Act as channels or transporters that increase the permeability of the membrane

How are macromoleciles able to pass through the plasma membrae

vesicular transport

Concentration gradient

The difference in the concentration of a chemical between one side of the plasma membrane and the other

Describe concentration gradient for the plasma membrane

• O2 and Na ions are greater outside the cell (extracellular fluid)

• CO2 and K ions are greater inside the cell (cytosol)

What is the electrical gradient and describe it in terms of the plasma membrane

Difference in concentration gradient of ions between one side of the plasma membrane and the other

• Ion concentration is more negative inside the cell (cytosol) and more positive outside the cell (ECF)

What do electrical and concentration gradients together make up

the electrochemical gradient

What are the passive vs. active processes of transport across the plasma membrane

• Passive

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

• Active

  • Primary active transport

  • Secondary active transport

  • Vesicular transport

Differentiate between passive and active transport processes

• Passive

  • Doesn’t require ATP

  • Moves from high to low concentration (with the concentration gradient)

• Active

  • Requires ATP

  • Moves from low to high concentration (against the gradient)

Describe simple diffusion

• random mixing of particles in a solution as a result of the KE of those particles

• Both the solvent and solute can diffuse

• Moves from area of high to low concentration

What factors increase the rate of diffusion

• Increased temperature (adds to KE)

• Bigger difference between gradients

• Smaller particles (can spread more)

• Greater surface area

• Smaller diffusion distance

What kind of molecules pass thru the lipid bilayer in simple diffusion

AND why are these molecules important

• Nonpolar, hydrophobic molecules (respiratory gases, some liquids)

• Important for gas exchange, nutrient absorption, waste excretion

Name and describe the three types of ion channels

• Leakage channels

  • gates randomly alternate from open to closed (Na+ and K+)

• Voltage-gated channels

  • open in response to change in membrane potential (electrical charge)(Na+ and K+)

• Ligand-gated channels

  • open and close in response to a chemical stimuli like hormones, neurotransmitters, or other ions

  • ligand (chemical messenger) bounds to a channel and opens it up like a lock and key

Describe facilitated diffusion

• Solute binds to a specific binding site on a transporter protein

• The binding causes a shape change (conformational change) of the transporter protein

• The solute moves across the membrane and is released on the other side (with the concentration gradient)

What kind of solutes move through facilitated diffusion

• Larger, polar, and charged molecules

  • Glucose, urea, fructose, galactose, and some vitamins

What does facilitated diffusion’s speed depend on?

• Steepness of concentration gradient (the bigger the difference of the gradients)

• Number of transporter proteins

Describe osmosis

• The net movement of a solvent (usually water) through a selectively permeable membrane from an area of high solvent concentration to an area of low solvent (high solute) concentration

  • The solute cannot move but the solvent can

Hydrostatic pressure (osmosis)

Pressure that the water column exerts due to its weight (prevents water from diffusing thru a membrane)

Osmotic pressure (osmosis)

Pressure a solution exerts when its particles aren’t permeable to the membrane; proportional to solute particles that cannot cross the membrane

Tonicity

how the osmolarity of a solution affects the cell volume

Hypertonic solution

Tonicity of the solution is higher than the tonicity of the cell

• Higher concentration of solutes in the solution compared to inside the cell

  • This means that water’s concentration is higher inside the cell so water will move outside and into the solution where concentration is lower

• Water moves out of the cell, causing the cell to shrink

Hypotonic solution

Tonicity of the solution is lower than the tonicity of the cell

• The solution has a lower solute concentration than inside the cell

• Water has a higher concentration outside the cell so it rushes inside the cell where concentration is lower

• Water moves into the cell, causing it to expand

Isotonic solution

• tonicity of the solution is the same as the tonicity of the cell

  • same solute concentrations

  • No water will go into the cell and none will come out

How to remember what hypotonic means

Hypo = turns your cells into hippos (swells)

What is the most prevalent primary active transport mechanism and how does it work

the Na/K pump

• requires 40% of cellular ATP

• maintains low Na+ and high K+ in the cytosol

• Maintains cell volume

• How it works: Energy from ATP changes the shape of transporter protein to carry a substance across a membrane against its concentration gradient

Describe secondary active transport

• Instead of splitting ATP directly, this uses energy stored in an Na+ or H+ ion concentration gradient

  • This energy was created during primary active transport pumps

• As the driving ion moves naturally (with its concentration gradient), the released energy causes another substrate to go uphill (against the concentration gradient)

  • One follows concentration gradient, one uses that energy to go against the concentration gradient

Symporters (cotransporters)

Moves substrates in the same direction (Na/glucose, Na/K/Cl, Na/Cl)

Antiporters (exchangers)

moves substrates on opposite directions (Na/Ca exchanger, Na/H exchanger)

what is a vesicle

small membranous sac formed by budding off from an existing membrane

Describe the two types of transport in vesicles

• Endocytosis: bringing something into the cell

  • Phagocytosis: cell eating by macrophages and white blood cells

  • Pinocytosis: cell drinking of extracellular fluids

• Exocytosis: release something from cell

  • Vesicles form inside the cell and fuse to cell membrane

  • The vesicles release their contents

    • Ex. digestive enzymes, hormones, neurotransmitters, or waste products