Establishing an Excitable Membrane Flashcards
1
Q
Cellular Specialization
A
- refers to special set of functions or activities that a specific cell or tissue can perform
- Individual nature of different cells
- Protein Synthesis – how the cell controls its internal environment and how it controls enzymatic activity, etc
- Boils down to nucleus and protein synthesis
2
Q
Membrane structure
A
- phospholipid bilayer oriented with heads exterior and interior, tails are on the inside of membrane
- Creates external hydrophilic part and inner hydrophobic part
- Helps control access to the cytoplasm
- Membrane Proteins (Fluid Mosaic Model) – the proteins are relatively free to float around in the membrane, concentrate in certain areas, etc.
3
Q
simple vs. facilitated
A
- Simple: diffusion (no energy is spent) – all you need is a channel to allow flow
- Facilitated: diffusion can be facilitated (you need a transport molecule to bind and translocate a substance)
- We think glucose moves this way
4
Q
Factors that affect diffusion rate
A
- Permeability (P) – cell membrane is selectively permeable (some cells will be permeable to specific molecules and others will not be)
- Area: D = P x A
- Concentration Difference D(Co-Ci)
5
Q
when does diffusion stop
A
- Diffusion proceeds to equilibrium, NOT equal concentrations
- Equilibrium means that all of the forces at play are in balance and at that point then there is no net diffusion
- The pressure, concentration, and electrical gradients are balanced to keep the status quo
- If there’s only one substance in the media, it will stop at equal concentrations, but there’s never just one substance
6
Q
Nernst Potential
A
- Formula for electromotive force (voltage) across a membrane that will balance a given concentration of univalent ions
- When you have a charged ion on either side of the membrane, you have a charged membrane because there is a voltage difference
- This equation determines how much electrical charge you have to apply given a certain concentration gradient to directly oppose the movement of that ion
- In other words: what is the electrical charge at which point the system will be in equilibrium
- Also called the reversal potential
- EMF = electric motor force – opposes the diffusion of a given ion
- ONLY APPLIES TO UNIVALENT IONS (i.e. doesn’t apply to Ca2+)
7
Q
osmosis
A
- Net movement of water
- Osmotic pressure
- Non-diffusable particles – if you don’t have non-diffusible particles, you don’t have osmotic pressure
- Osmole – molar content of non-diffusible elements
8
Q
primary active transport
A
- Source of Energy – ATP
- Example: Sodium/potassium pump – establishes concentration gradient needed to establish voltage across a membrane
- Phosphorylation: “the meaning of life”
- Need ATP to phosphorylate enzymes, glucose (to trap inside cells), etc.
9
Q
Na/K ATPase critical functions
A
- Osmotic balance – so that the cell doesn’t shrink or swell
- Electrogenic – separates charge unevenly and creates an electrical current across the membrane
- These are the two critical and essential functions of this pump
- Net movement of positive ions to the outside of the cell that maintains slightly negative electrical potential inside
- The volume of these cells is massive compared to the membrane
10
Q
secondary active transport
A
- Source of Energy – concentration gradient used to run this pump occurs elsewhere
- If you are using a Na/K pump to create a gradient and then using the Na gradient to move something somewhere else
- Versions: Co- (together) or Counter (opposite)
11
Q
factors effecting diffusion potential
A
- Polarity of each ion involved is important – can repel each other and prevent simple diffusion
- Permeability of membrane for each ion (potassium moves more easily than any other ion we talk about)
- Concentration difference of each ion across membrane
- Modified Nernst for multiple ions: Goldman-Hodgkin-Katz equation
