Lecture 3 & 4 Outline Flashcards
What are the 4 functions of the cell membrane?
- Physical barrier
- separates intracellular fluid from ECF - Gateway for exchange
- controls movement of solutes: allows some to cross, prevents others from crossing (semipermeable…) - Communication
- home to receptors that detect physical & chemical stimuli & starts cascade of response to stimuli - Cell structure
- some membrane proteins hold cytoskeleton proteins to give cell structure
- may also form specialized junctions
What is the structure of cell membranes?
made of mostly protein & lipid
- ratio of protein & lipid is different for different cell types
early model was a “Butter sandwich”
- a clear layer of lipids sandwiched b/t 2 dark layers of protein
- implies that it is homogenous that is NOT accurate
present day model is “Fluid mosaic”
- proteins are afloat on a sea of lipid
What are the 4 types of lipids?
- Glycolipids
- Phospholipids
- Cholesterol
- Sphingolipids
Glycolipids (a lipid, & its role in cell membrane structure)
a carbohydrate that is covalently linked to a lipid. Glycolipids are biomolecular structures in the phospholipid bilayer of the cell membrane whose carbohydrate component extends to the outside of the cell. Glycolipids are essential in providing stability of the plasma membrane.
Phospholipids (a lipid, & its role in cell membrane structure)
- mostly phospholipids
- several different varieties: (R-group, saturation)
- polar head groups toward aqueous sides, non-polar fatty acid tails inside
Cholesterol (a lipid, & its role in cell membrane structure)
- flat molecule, slips b/t fatty acid tails
what it does:
- cholesterol regulates membrane fluidity
- slows diffusion of molecules across membrane
Sphingolipids (a lipid, & its role in cell membrane structure)
have longer tails than phospholipids
tend to aggregate together = lipids raft
- rafts also have a high density of cholesterol
- some proteins associated ONLY with lipid rafts, leading to areas of SPECIALIZATION on cell membranes
- for ex: some G-protein couples receptors!
What are the 5 components of proteins for the cell membrane structure?
- Integral
- Peripheral
- Lipid-anchored
- Cytoskeletal
- Extracellular matrix
Integral proteins (role in cell membrane structure)
- polytopic (=transmembrane, more than one MSR)
- bitopic (=transmembrane, one MSR)
- monotropic (=permanently associated from one side)
Integral proteins (transmembrane)
permanently attached to cell membrane
- integral polytopic/bitopic = transmembrane proteins (span the lipid bilayer once or several times & approximately 20-25 hydrophobic AA’s to span the cell membrane)
Integral proteins (monotopic)
permanently attached to cell membrane
- integral monotopic proteins - permanently attached to the membrane from one side
A. may have strong hydrophobic sections that allow it to tightly associate with lipid portion of bilayer
B. may be modified by the addition of a fatty acid
C. may be electrostatic or ionic interactions b/t protein & phospholipid (tightly bound)
Peripheral proteins (role in cell membrane structure)
associate non-covalently with integral proteins, or polar heads of phospholipids
Cytoskeletal/cytoskeleton (role in cell membrane structure)
- not a membrane protein, but often interact with membrane proteins
- flexible skeleton of fibrous proteins throughout the cytoplasm (give physical strength)
Extracellular matrix (role in cell membrane structure)
- membrane proteins & secreted protein found on the extracellular side of cell membranes
- forms a “husk” around cells
- highly variable GLYCOSYLATION
- contribute to physical strength of cells
Definition of diffusion
- process of moving solute molecules away from an area of high concentration towards area of low concentration (“down the concentration gradient”)
- passive (no external energy, just kinetic energy of molecules)
- process continues until equilibrium is reached
What are the 5 factors that influence diffusion?
- Fast over short distances
- Slow over long distances
- Rate of diffusion is faster at high temp
- Rate of diffusion is faster for small molecules
- Rate of diffusion is slower across a membrane
What are the rules for diffusion across cell membranes?
- Permeability across cell membrane
- size
- lipid solubility: polar or non-polar or VERY non polar - Concentration gradient
- Surface area
- Temp
- Composition of membrane
- simple lipid bilayer vs membrane with many proteins & extracellular matrix
- types of phospholipids & sphingolipids
- presence of cholesterol
What solutes can and cannot diffuse across cell membranes?
can:
- hydrophobic, non-polar (O2, CO2, lipids, steroids, fat soluble molecules)
- small uncharged polar molecules (urea, H20?)
cannot:
- large uncharged polar molecules (glucose, proteins, amino acids)
- charged molecules (ions K+ Cl- Na+, phosphate ions, bicarbonate, etc)
Definition of osmosis
is the diffusion of water
- water can have a concentration gradient
- water will “diffuse down its concentration gradient”
- pure water has the “highest concentration of water”
- solutes lower the concentration of water
- movement of water can cause pressure
Osmolarity describes…
the # of particles in a solution
Hyposmotic
fewer osmoles per unit volume
Hyperosmotic
more particles per unit volume, more concentrated
Isosmotic
if 2 solutions contain the same amount of solute particles per unit volume
Why is osmolarity important?
- changing osmolarity of the extracellular solution causes redistribution of water & some solutes in cells
- this causes cells to shrink or swell (& die)
What is the difference b/t osmolarity & tonicity?
osmolarity:
- describes only the # of solute molecules in a cell (units of Osm)
- can compare any 2 solutions
- DOES NOT ALWAYS TELL IF A CELL SWELLS OR SHRINKS
tonicity:
- a comparative term describes whether a cell changes volume (has no units)
- compares a intracellular solution (for our purposes 290 mOsm)
- SPECIFICALLY TELLS IF A CELL SWELLS OR SHRINKS
How to predict hypotonic vs hypertonic
hyposmotic solutions are always hypotonic but, hyperosmotic solutions are not necessarily hypertonic
How to predict hypotonic vs hypertonic
hyposmotic solutions are always hypotonic but, hyperosmotic solutions are not necessarily hypertonic
Definition of a channel
a channel protein is a water filled pore
- can open to both sides
Examples of channels
- water channels
- ion channels
Carrier proteins definition
never form an open channel b/t the 2 sides of the membrane
In terms of energy requirements, there are 3 categories of carrier proteins
- facilitated diffusion
- primary active transport
- secondary active transport
Facilitated diffusion definition
is defined as moving a molecule across the cell membrane via a carrier protein, & the transport does not require energy other than the concentration gradient
- does not require ATP, or other solutes
- also sometimes called passive transport
this process alone cannot accumulate solute against a concentration gradient
Example of facilitated diffusion
glucose transporter: GLUT protein
Primary active transport definition
- uses ATP
- establishes gradients
- sometimes called pumps
Examples of primary active transport
Na+/K+/ATPase is the most widely known ex, but there are others
- Ca2+ ATPase
- H+ ATPase
- H+/K+ ATPase
Definition of Secondary active transport
does not directly utilize ATP as a source of energy
- instead, uses the concentration gradient of one molecule/ion to move another against its gradient
Example of secondary active transport
Na+-glucose is a good example: SGLT-protein
Complex ex: Transport of glucose across the kidney or gut epithelia
1) Na+ K+ ATPase. Establishes & maintains a Na+ gradient - primary active transport
2) Using the Na+ gradient, glucose is transported into the cell via the Na+ glucose co-transporter - secondary active transport
3) Glucose is transported across the basal membrane by the GLUT transporter - facilitated diffusion
Complex ex: Transport of glucose across the kidney or gut epithelia
1) Na+ K+ ATPase. Establishes & maintains a Na+ gradient - primary active transport
2) Using the Na+ gradient, glucose is transported into the cell via the Na+ glucose co-transporter - secondary active transport
3) Glucose is transported across the basal membrane by the GLUT transporter - facilitated diffusion
What are the 3 types of vesicular transport?
- Phagocytosis
- Endocytosis
- Exocytosis
