Module 4 Flashcards
Lipids
Form the phospholipid bilayer. Hydrophilic head (phosphate group and 2 hydrophobic fatty acid tails)
Fluid mosaic model
Membrane is constantly changing. When insulin is present glucose enters the cell.
Selectively permeable
The hydrophobic core creates a barrier preventing movement of hydrophilic substances, ions & large molecules. Hydrophobic (lipid soluble) move readily.
Cholesterol
Hydrophobic molecule resides among fatty acid tails. Cholesterol limits lateral movement of phospholipids. It maintains proper fluidity over many temps.
Peripheral/extrinsic Proteins
proteins found only on the surface of the membrane. Attach the membrane to the cytoskeletal proteins inside the cell or to proteins of the extracellular matrix
Integral/Intrinsic Proteins
Segments that associate with the hydrophobic region of the membrane.
Channels
Allow hydrophilic materials, ions, to cross the membrane
Carrier Proteins
Have sites that bind to specific solutes and then changes shape allowing the solute to move across the membrane one way.
Receptor Proteins
Integral proteins act as receptors and allow the cell to respond to chemical messengers which regulate the activities of the cell. hormones
Enzymes
Catalyzing important chemical reactions. Lactase digests lactose
G protein coupled receptors
Molecular switches. Bind to a specific ligand from outside the cell and then convert that binding to an intracellular signal. GTP=on GDP=off
Attachment Proteins
Attaching cells to each other as well as to the extracellular matrix and to intracellular structural proteins. Give strength and shape
Marker Proteins
Allow cells to identify one another. Find foreign cells, invaders
Carbohydrates
short chained polysaccharides that attach to the proteins and lipids on the extracellular layer of the membrane. Attached to a protein= glycoprotein. Attached to a lipid= glycolipid.
Form markers like blood type
Passive transport
No energy input required
Active transport
Cellular energy in the form of ATP is required
Simple Diffusion
Movement from high to low concentration. Concentration gradient without the aid of a membrane protein.
Diffusion Equilibrium
Molecules evenly distributed with no net change in concentration.
Factors that affect rate of diffusion
Concentration gradient: greater diff. between 2 sides of membrane= faster diffusion
Temp. Higher temp= faster molecules=faster diffusion
Size. Smaller diffuse faster
Membrane permeability: ions/ charged molecules are hydrophilic do not cross. Non-polar diffuse
Surface Area: Greater surface area= faster
Distance: thin membranes=fast
Facilitated Diffusion: voltage gated, ligand gated, mechanically gated channels
ion specific channels
Facilitated Diffusion:
- Large/ electrical charge (ion) do not pass through membrane
- Integral proteins assist in diffusion of solutes, sugars & amino acids
- carrier protein
- solute specific & NO energy req’d
Facilitated Diffusion: Channel Proteins
-Down concentration gradients, resembles a fluid filled tube
-Assist ions; Na+, K+, Ca2+, Cl-
-Ion specific
-Open to both sides
Voltage gated= voltage difference traveling across the membrane
Ligand gated= specific signal molecules
Mechanically gated= stretching or compressing the membrane
Facilitated Diffusion: Carrier Proteins
- Change shape, 1 side open Not an = sign but rather <
- Solute binds and changes shape
- Specific solute receptor
- Because has a max rate it can become SATURATED
- GLUT 1-12. GLUT 2: liver & pancreatic islets. GLUT 4: skeletal muscle & fat tissue & only one needs insulin for MAX activity
Active Transport
Movement of solutes against concentration gradient & requires energy input ATP
Primary active transport
Movement of solutes such as ions against conc. gradient. Requires carrier protein for binding ATP. Can move 1 or multiple ions.
3 Na+ out, 2 K+ in ATPase
One of the most important active transport systems
K is the primary intracellular cation
Na+ is the primary extracellular cation
Secondary active transport
Against conc. gradient. NO ATP. uses instead energy stored in conc. gradients to move solute. Solute binds to carrier protien then symport into or anti port out. Na+ moves down conc. grad. into cell
ATP in primary is required to create the Na conc. gradient but not directly involved in moving aross the membrane
-Glucose amino acids are organic molec. transported by this process
Endocytosis
Bulk transport of material into the cell
Requires ATP, Active transport
Phagocytosis
Cell eating. Immune sys. pseudopodia surround and create a vesicle containing the particle. This phagosome can then unite with a lysosome inside the cell and the engulfed material can be digested for use within the cell
Requires ATP, Active transport
LIMITED cells: immune sys
Pinocytosis
Cell drinking. No pseudopodia. It forms a pocket and engulfs anything in the fluid. Found in intestines and kidneys
Requires ATP, Active transport.
Occurs in MOST cells of body
Non-efficient because it is Non-specific
Moves large amounts of material in Intestines & Kidneys
Receptor mediated endocytosis
Employs specific receptors that bind to material (ligand) of be brought into the cell. Advantage is that it can engulf large amounts of a specific solute.
Migrates to specific area of membrane, a clathrin-coated pit then pinocytosis takes over.
Exocytosis
Opposite of endocytosis. Bulk transport out
-Secretory vesicles filled with the material to be released migrate to the plasma membrane where the membrane of the vesicle fuses with and actually become part of the plasma membrane.
Material is released into extracellular fluid.
Calcium is an extracellular ion & and diffusion into cell initiate the exocytosis process
Electrophysiology
- Study of electrical properties of biological cells involving measurements of electrical current & activity of neurons & other cells.
- External stimuli (light, smell, sound, taste) using various sensory organs of the body & convert these stimuli into unique perceptions in the brain.
Which ion drives the Resting Membrane Potential?
K+ moves down its concentration gradient
Na/K pump found in most cells of body is more 50-100x’s more permeable to K+ because the Na closed are shut during resting conditions
Electrochemical Gradient
When electrical & chemical gradients equal each other & net movement is 0
Resting membrane potential
When the membrane reaches a state of equilibrium we can measure the negative charge inside the cell.
Leak Channels
Protein channels that are open all the time
Small number of Na+ leak channels
More K+ channels
Gated channels
Closed most of the time and opened by stimuli
Large # of gated channels for Na+
Voltage gated ion channels
opened in response to electrical changes
Mechanical gated ion channels
open in response to mechanical stimulation
Chemically gated or ligand gated ion channels
response to a chem stimulant
Polarized
At rest the membrane is in a polarized state because of charge separation caused by diff. ions
Depolarization
Change in the membrane towards 0 or more positive
Occurs with minimal changes in overall conc. of Na+ or K+
Repolarization
Change in membrane back towards membrane potential away from 0 more negative
Hyperpolarization
Movement away resting potential in a more negative direction away from 0
Graded potential
The magnitude of the response is proportional to the strength of the stimulus & result from opening of mechanical or ligand gated channels. If summed or added to pass threshold = action potential
Action potential
Represents a rapid change in membrane potential followed by a rapid return to the resting membrane potential.
The basis of transmitting signals in nerve cells inducing contraction or perception of our senses
Caused by activation of voltage-gated ion channels (Na+ voltage gated ion ch)
Which ions cause depolarization?
Na+ & Ca++ cause depolarization
K+ & Cl- cause Repolarization
Refractory period
Time during which a cell is incapable of repeating an action potential after the excitable membrane is ready to respond to a 2nd stimulus
once returning to a resting state
Caused by inactivation gate of Na+ ch. Once inactivated the Na+ ch cannot respond to another stimulus until gates are reset.
-Absolute refractory period- corresponds to depolarization & repolarization
-Relative Refractory Period- corresponds to Hyperpolarization.
