2/19-2/24 Flashcards
List and explain the seven general functions of cell membrane (Book Ch 4.1)
- Enclosing compartments (Cell itself and organelles- allows cell activities to proceed in specialized areas and to be regulated independently of each other)
- Act as a scaffold for substances to bump into and react with
- Selectively permeable barrier
- Solute transfer (low to high usually) to store things. Critical for nerve and muscle cells
- Contain receptors that, with molecules (ligands) respond to stimuli
- Mediates cell-cell interactions (letting them recognize/interact with each other, adhere, exchange info/materials. Proteins in PM also can facilitate interactions between extracellular materials and intracellular cytoskeleton
- Energy transduction- EG photosynthesis and transferring energy from carbs and fats to ATP
- Recall the primary components of the cell membrane (Last unit, also refresh with 4.2
“Membrane Lipids” and “Membrane Carbohydrates”)
o Special Note: There are two special linkages (Fig 4.11):
▪ N-glycosidic linkage
▪ O-glycosidic linkage
▪
Phosphoglycerides, sphingolipids, cholestrol
Three main types of membrane proteins (Book Ch 4.3)
o Special Note: The first K+ channel protein (KcsA) (Fig 4.39) and X-ray crystallography
Integral, peripheral, intermembrane
- Describe the requirements and structure of transmembrane domains
~20 mostly NP AA that span the core of the lipid bilayer as an α helix. 17 are hydrophobic (the others are serine, threonine, which are nonpolar). Each alpha helix has a pair of charged residues with side chains that can interact with innermost polar regions, even if they need to alter their structure
- Read and explain a hydropathy plot – What differences, if any, would you see in alpha helices vs
beta-pleated sheets?*****
Positive- Hydrophobic segments/nonpolar side chains
- Explain how researchers can identify conformation changes in proteins
EPR spectroscopy- Determines the distance between regions of a protein by analyzing the strength of a signal when a nitroxide is added to part of a protein and conformational changes happen
- Explain the four ways in which molecules can move across a cell membrane, including which are
active or passive, and how concentrations and energy play roles in the movement of these
molecules
simple diffusion through the lipid bilayer (always high to low, no pump)
simple diffusion through an aqueous, protein-lined channel (through channel, no energy used, high to low)
diffusion that is facilitated by a protein transporter;
active transpor-, requires energy-driven protein “pump” that can move substances against concentration gradient (Figure 4.33).
ONE MORE??
Primary active transport
Transport of one type of molecule against concentration gradient by use of ATP
Explain how ion concentration gradients and membrane permeability contribute to the resting
membrane potential.*****
Movement of ions across the membrane determines ,magnitude and direction of voltage- concentration of ions in a certain space determines charge.
- Describe the role of the sodium-potassium (Na⁺/K⁺) ATPase pump in maintaining membrane
potential.
Moves 3 Na+ out, 2 K+ in. The movement of ions out affects charge, creates the membrane potential
- Explain how threshold potential is reached and how it triggers an all-or-none response. Fig 4.53
helps to illustrate this process.**
=
Depolarization beyond threshold value leads to influx of Na+ Ions through opening of voltage gated channels, making membrane voltage temporarily positive. REVERSAL OF MEMBRANE POTENTIAL CONSTITUTES ACTION POTENTIAL
- Describe the process of synaptic transmission at chemical synapses, including neurotransmitter
release and receptor activation. Figure 4.57 helps illustrate this process.
- Nerve impulse travels down neuron
- Calcium channels open
- Acetylcholine is released from vesicles of first neuron
- Binding of ACh by receptor
- Na+ gates open/Cl- gates open
- Nerve impulse travels down neuron
Graded potentials
vary in strength and are transmitted over short distances,
▪ N-glycosidic linkage in the cell membrane uses
asparagine
▪ O-glycosidic linkage in the cell membran uses
serine or threonine
Explain the similarities and differences in symport
versus antiport
Both transmembrane proteins
Symport- two transported species (Na+ and glucose or H+ and sucrose) move in the same direction
Antiport- two transported species move in the opposite direction
Secondary active transport
Transporting 2 types of molecules across membrane, driven by concentration gradient
Integral Membrane protein
Integral- Penetrate lipid bilayer, domains protrude from it on both sides. Can have one or more membrane spanning segment
Peripheral membrane protein
Peripheral- Entirely outside lipid bilayer- can be on cytoplasmic or extracellular side. Bound with noncovalent bonds
Intermembrane membrane protein
Intermembrane- On cytoplasmic or extracellular side, but covalently linked to a lipid within the bilayer.
Phosphoglycerides-
2 hydroxyl groups bound to fatty acids, 3rd bound to hydrophilic phosphate group. Phosphate also bound to group (Commonly choline, ethanolamine, serine, or inositol). Phosphate+group=head.
Sphingolipids
-Derivatives of sphingosine, linked to fatty acid. Total molecule aka ceramide. Groups added to ends. +phosphorocholine, sphingomyelin, + carb, glycolipid. VERY important in nervous system
Cholesterol-
up to 50 percent of the lipid molecules in plasma membrane. Small hydrophilic hydroxyl group towards membrane surface, rest of molecule in lipid bilayer. Interfere with fatty acid tail of phospholipid’s movement
simple diffusion
through the lipid bilayer (always high to low, no pump)
Leak channel-
Always stay open, allow ions to pass through whenever
Voltage gated channel-
Conformational state depends on the difference in ionic charge on the two sides of the membrane.
Ligand channel-
Conformational state depends on the binding of the ligand, which is usually not the solute that passes through the channel. ligand-gated channels can opened (or closed) following the binding of a molecule to the outer or inner surface of the channel.
simple diffusion through an aqueous, protein-lined channel
(through channel, no energy used, high to low)
diffusion that is facilitated by a protein transporter;
active transpor-, requires energy-driven protein “pump” that can move substances against concentration gradient (Figure 4.33)
