Phisio Exam 1

In addition to functioning as structural support for the cell and a mechanical barrier, list several other roles of the plasma membrane (6)

1. Mechanical barrier – traps needed molecules inside cell

2. Selectively permits passage of specific substances

3. Controls import of nutrients & export of secretory products, wastes

4. Maintains different ion concentrations inside vs. outside (essential for electrical activity)

5. Cell junctions (tissue formation)

6. Respond to signals from chemical messengers

phospholipid

How are phospholipids in the membrane arranged?

Lipid bilayer with heads contacting the ECF and ICF

Are phospholipids linked into an interconnected network or floating loose?

Floating loose and in constant movement (like ping pong balls floating on a pool)

two seemingly opposing properties of the membrane are regulated by cholesterol?

Cholesterol regulates fluidity and stability. It prevents the phospholipid fatty acid tails from interacting and packing to the point of crystallization (like bacon fat solidifying) and thereby maintains the membrane’s fluidity. By intercalating between the phospholipids, cholesterol also contributes to the membrane stability.

Integral proteins

embedded in the phospholipid bilayer

Transmembrane proteins

an integral protein that crosses the entire thickness of the membrane

Peripheral proteins

proteins weakly anchored to a membrane surface (sometimes on the extracellular surface; very commonly on the intracellular surface)

List 7 different roles of membrane proteins

(1) Channels (e.g., leak channels, gated channels)

(2) Carriers (transporters)

(3) Docking-marker acceptors (essential for exocytosis)

(4) Membrane-bound enzymes

(5) Receptors

(6) Cell adhesion molecules (CAMs)

(7) Cell recognition (self-recognition)

Carbohydrate modifications are attached to which leaf of the membrane?

extracellular surface

To what molecules are carbohydrates attached, and what are the respective names of these carbohydrate-linked structures

To proteins= glycoproteins

To lipids= glycolipids

What major role do membrane carbohydrates serve?

“self-recognition” and cell-to-cell interactions

Fluid Mosaic Model

Membrane proteins floating freely amidst a constantly moving sea of phospholipids. Resembles buoys floating in a swimming pool covered with floating ping pong balls.

What does it mean for the membrane to be selectively permeable?

It permits certain particles to pass through it while others are excluded.

Two Route Determinants

1. Lipid solubility (aka polarity)

2. Size

Passive Transport

Passive transport does not require energy (ATP) expenditure

Active Transport

Active transport requires energy (directly or indirectly) to transport the molecule

Net Diffusion

Random movement down the concentration gradient

Where are steriod receptors

The steriod receptor is inside a cell because teh steriod nonpolar can diffuse through the lipid bylayer

In unassisted Transport What two forces drive this passive movement?

Concentration gradient and/or electrical gradient

[Simple] Diffusion

random movement of molecules as they “spread out” toward uniform distribution

Distinguish between net diffusion and dynamic equilibrium.

Net diffusion is the difference between random movement (diffusion) of molecules from area A-to-B vs. area B-to-A. When net diffusion is zero, the system is in dynamic equilibrium.

In diffusion, molecules move in what net direction?

Net diffusion of a solute occurs from its area of greater concentration to its area of lesser concentration

If there is no net diffusion, are molecules crossing the membrane?

Yes. When net diffusion is zero (dynamic equilibrium), molecules are still randomly crossing the membrane in both directions, but doing so in equal numbers each direction.

List the 5 factors the influence the rate of net diffusion. (Fick)

(1) Concentration gradient- directly

(2) Surface area of membrane- directly

(3) Lipid solubility- directly

(4) Molecular weight- inversely

(5) Distance (membrane thickness)- inversely

In terms of size and solubility, describe the type of molecules that directly permeate the membrane

Whether large or tiny, the molecules are uncharged, nonpolar, highly lipid soluble and can pass directly through the membrane

• Examples: O2, CO2, fatty acids, steroids

In terms of size and solubility, describe the type of molecules that could be allowed through the membrane using a protein channel.

These must be tiny (few atoms or less); They are polar or charged molecules (otherwise they’d pass directly)

• Examples: Water, Na+, K+, Ca2+

By what two routes does water enter/leave the cell?

(1) Aquaporins — very fast! (billion molecules/second per channel!)

(2) directly through momentary spaces between phospholipids — relatively slow

Hydrostatic pressure

pressure exerted by a standing fluid

Osmotic pressure

the pull of a water into a solution by osmosis; that is, the pull of water into a solution with higher solute concentration (“solutes suck”)

Isotonic

Solute Concentration (relative to the cell solute)- Equal

Osmosis- no net diffusion

Effect on Cell Volume- no change

Hypotonic

Solute Concentration (relative to the cell solute)- Less

Osmosis- into the Cell

Effect on Cell Volume- Cell swells

Hypertonic

Solute Concentration (relative to the cell solute)- More

Osmosis- Out of the Cell

Effect on Cell Volume- cell shrinks (crenates)

Osmosis

net flow of water across a membrane

Carrier mediated Transport

Binding site kenetics

• Specificity: What will fit

• Saturation: 1 thing at a time

• Competion: who will win

Cystinuria

A disease where you are missing one carrier protien, many kidney stones.

Passive Carrier-Mediated (properties)

• always DOWN concentration gradient (the Boyscout lending a arm to the old women)

• Large lipid-insoluble molecules (polar)

• “a” or “the” Facilitated Diffusion

Active Carrier Method

• Requires Energy! (“Pump”)

• Is independent of concentration

Primary Active Transport

Directly use ATP

Seconday Active Transport

Exploites gradient created by primary active transport to pump

The story of Glucoes

1. Glucose is to big and polar: No Channels, No passive transport

2. Fist we have good gradient→ but gets worse

3. SGLT→ Soduim Clucose cotransport: Active

4. GLUT→ glucose transport: passive carreir

5. Not all cells take in glucose all the time regulated by insulin

SGLT

Sodium Glucose co-transported

• Active transport

• Could be primary or seconday

• Need a sodium and potaisum pump

GLUT

Clucose Transport

• To get Glucose out of the cell the gradadient is always in our favore so we can use the PASSIVE CARREIR GLUT

Glocuse in the Cell

• Stored as Glycogin

• 1st step of Glycolis phospholoratoin

Counter-transport (Antiport)

One goes in the other goes out

VESICULAR Transport

Endocytosis

i. Phagocytosis

ii. Pinocytosis

iii. Receptor-mediated endocytosis

Endocytosis

movement into cel

• Phagocytosis: large chunks

• Pinocytosis: Water

• Receptor-mediated endocytosis: uses Recptors (more picky)

Exocytosis

movement out of cell

internal environment

Extracellular fluid ECF

ECF fluid can be further divided into two major components:

1. Plasma (Blood)

2. Interstitial fluid (ISF)

Define homeostasis

Maintenance of a relatively stable internal environment.

According to Sherwood, what 7 families of factors must be homeostatically maintained?

1. Concentration of nutrients

2. Concentration of O2 and CO2

3. Concentration of waste products

4. Concentration of hydrogen ions (pH)

5. Concentration of water, salts, and other electrolytes

6. ECF volume and pressure

7. Temperature

Which body system in not essential for homeostasis

Reproductive system

Intrinsic control system

a mechanism built into or inherent in an organ

• Systemic control

Extrinsic control system

mechanisms initiated outside an organ to alter its activity

What two body systems are responsible of extrinsic control

1. Nervous

2. Endocrine

Negative Feedback

restores homeostasis by generating a response that opposes or reverses the original stimulus (negates the deviation)

What is term for the desired value of a controlled variable?

Set point

Integumentary

Sweating

Positive Feedback

he response strengthens or reinforces the stimulus (increases the deviation).

What is uniquely defines a feedforward system

mechanisms designed to anticipate a deviation and respond in advance

• Insulin is the example of this

What are the Three Major players in Membrane potential

• Na+ / K+ ATPase pump

• Leak Current

• Trapped anions

What percent of all Calories power ATPase Pump

40% of all Caloric intake

What are the negatively charged anions inside of the Cell

Protiens

Nicleic acids

Phosphates

The Unstimulated cell Resting Memrane Potential

-70mV

ATPase Pump Maintains Steady state

Leak channels

Open at all times

• Potassium leaks out of the cell leading us to the -90mV difference

• Sodium leaks in making the -70mV

When Na+ leakage is High

we are producing more heat

so endotherms birds + Maamals have more Na+ leak channes

Seconday Active transport

use the gradient to pump something else

Graded Potentials

Small local changes in membrane potential

• Example of local potental triggers exocytosis

Action Potentials

Large Rapid changes and reset of membrane potential

Chemmically-Gated (Receptor- Channels)

• A type of Ion Gated Channel

• taste, small

• neurotransmitter

Mechanically-Gated

• A type of Gated Ion Change

• Distortion of the plasma memnrane

• Touch

• Hearing

• Stretch (pressure)

Thermally-Gated Channels

Temp gated

Voltage-Gated channel

• a type of Gated Ion Channel

• However action potential not graded potential

Example of a Gated Na+ Channel Triggering a Graded Potential

1. Stimulus Opens channel (like a nuerotransmitter)

2. Na+ rapidly flows IN down both the chemical and electrical gradiant

3. Membrane potential shift Causigng dexrease in potential membrane becomes less negative= DEPOLARZATION

4. Depolarrization spreads locally causing LOCAL CURRENT

Example of a Gated K+ Channel

1. k+ channel open

2. k+ radidly out of cell

3. Shifts membrane potantial increase becoming extra negative= HYPERPOLARZING

4. 
   

Gated Cl- Channels

1. Cl- rapidly flows into the cell

2. Shifts the membraine potantial to become even more negative also HYPERPOLIZING

Graded or Local

• Local because only affects whats around it Rember lanas chair

• Grade because can vary depending on what

Propoerties of Graded Potential

• Graded- Vary in magnitude

• Local- Decline in strength over short distance

• Short-lived- membrane quickly returns to resting potential

• Either Excitiory or inhibitory

Why are Graded potentals short lived

Pumps do help but the LEAK channels help restore quicly

Fuctions of Graded Potentials

1. Stimulate specific cell functions like exocytosis

2. Trigger an Action potential in cells with Excitable Membranes

EPSPs

Excitatory Post-synaptic potentials

IPSPs

Inhibitory Post-synaptic Potentials

EPPs

End-Plate Potentials

What is important to rember about Diffusion

IT IS SLOW!!!!

so we need something better

Excitable Membrane

Can Generate electrical signals (or action potentials)

• Neurons

• Muscle Cells

ONLY

What things define Excitable Membrane

• Voltage-gated Na+ channel

• Voltage gated K+ Channel

basic anatomy of Neuron

Action Potential

Radin, large, depolarization PROPEGATED across/down the entire membrane

8 Steps in the action potential

1. Threshold is reached -50 to -55 mV

2. two events at threshold ( gates open +close)

3. Depolarixation phase Na+ comes in reaches +30mV

4. Repolarization Phase (K+ out gets to -7mV)

5. returened to Resting Membrane Potental k+ slowly starts closing)

6. Afterhyperpolarization Phase Membrane potental now less that -70mV

7. Resetting the gradent pump resets chemical gradient

8. Refactory Period

When are Action Potentail triggered

ONLY IF THRESHOLD IS REACHED -50 or 055 mV

Axon Hillick

Is where the dendrites turn into axons

3 things that happen when threshold is reached

1. Voltage gated Na+ channels, open rapidly,

2. inactivation gates begin to close slowly (NOT STOPABLE)

3. Voltage gated K+ channels Befin to open slowly

Dpolarization phase of teh Action potential

a. Na+ rushes in → triggering more Na+ channels to open

In 0.5 msec delay before the inactivation gate shuts ( in this time poteital has reached (+30 mV)

Repolariarization Phase

a. K+ rushes out

membranse potantial resturns to -70mV

Events at Return to Resting Membrane Potental

Voltagegated Na+ chanes

• Activation gates now close

• Inactivation gates reopen

Volage gated K+ channels becgin closing

Afterhyperpolariztion Phase (ONE WORD)

Voltage-gated Na+ channels ready to go again

Membrane Potential dips below Resting Membrane Poteintal

Resetting the Gradient (step 7)

Electical gradient - is reset already YAY

Chemail gradient needs to be corrected

Refractory Periods

the local membrane cannot be stimulated to fire another action potential

Absolute Refactory Period

due to inactive Na+ channels

Duration entire action potental to reactivation: so threshold to closing of K+ channels