Ch.13 Biochem Book Questions

acetylcholine

Neurotransmitter that diffuses across a synapse and produces an impulse in the cell membrane of a muscle cell(synaptic cleft)

connexin

gap junction protein; six of these in a connexon, have hydrophillic R groups that allow molecules between cells, use calcium control system

aquaporin

A membrane protein, specifically a transport protein, that facilitates the passage of water through channel proteins.

ABC transporter

ATP Binding Cassettes. Has a transmembrane part and a nucleotide binding domain. Transports AA, peptides, metal ions, lipids, drugs.

patch-clamp technique

Allows the investgation of a small set or even single ion channels. A glass pipette with an electrolyte solution is tightly sealed on to the cell membrane

Carbonyl cyanide 4-(trifluoromethoxy phenyhydrazone (FCCP) is a proton ionophore: it enables protons to pass freely through membranes. Treatment of E. coli with FCCP prevents the accumulation of lactose in these cells explain

E. coli's lactose transporter is a secondary acrive transporter that uses a gradient of protons to drive the transport of lactose against its gradient. The addition of carbonyl cynide 4-(trifluoromethoxy) phenylhydrazone (FCCP) to E. coli prevents lactose from accumulating inside the cell and FCCP is a proton ionophore that allows protons to diffuse freely across the membrane. We can conclude that eliminating the proton gradient by adding FCCP prevents the lactose transporter from importing lactose into the cell.

long QT syndrome

Genetic disorder affecting Na+ and K+ channels. If you have less K+ channels, you will have longer repolarization. So you look at the QT interval. If it is greater than the normal range (<450 for men and <470 for women) it is called Long QT Syndrome.

The K+ channel and the Na+ channel have similar structures and are arranged in the same orientation in the cell membrane. Yet the Na+ channel allows sodium ions to flow into the cell and the K+ channel allows potassium ions to flow out. Explain

Ion channels only allow the passage of specific ion at the same rate only in one direction bc the concentration of the Na+ ion is higher outside of the cell, the sodium channel allows Na+ ions to flow into the cell. Conversely because the potassium ion is higher inside the cell, the potassium channel allows potassium ions to move out of the cell.

Differentiate between ligand gated and voltage gated channels.

Ligand gated channels open only when appropriate molecule, or ligand binds to its receport. Votage gated channels, on the other hand, will open depending on the membrane potential or charge. For example, there may be a chase when voltage gated channel opens only when the extracellular matrix is pore positive than the intracellular matrix. Alternatively, a neurotransmitter binding to a specific ligand gated channel will trigger a conformational change in the channel, allowing it to open

Differentiate between simple diffusion and facilated diffusion.

Simples diffusion is when small, non-polar molecules can pass through the membrane with out requiring energy. It travels down its concentration gradient (from higher concentration (extracellular matrix) to lower concentration (cytoplasm) During facilitated diffusion also energy is not reqired during the process bc the molecules travel down their concentration gradient. However its passage through the cell membrane requires proteins channels or carrier proteins bc the molecules may be polar, charged, and or too large to pass through the phospholipid bilayer directly

What two forms of energy can power active transport

The first and most common is the hydrolysis of ATP to ADP, the rxn generates enough energy to power active transport. The second form is to couple a passive transport with an active transport. The passive movement of a molecule down its concentration gradient harnesses the energy that can propel a molecule against its concentration gradient.

Acetylcholine is rapidly destroyed by the enzyme acetylcholinesterase. This enzyme, which has turnover number of 25,000 per second, has attained catalytic perfection with a kcat/KM pf 2 x 108 M-1 s-1. Why is the efficiency of this enzyme physiologically crucial?

The given graph shows thr transport of glucose and indole. The curve exhibited is a transport curve which indicated that it requires a carrier for its transportation. This is observed because initially the rate is high but levels off at higher conventrations, consistant with saturation of the carrier. This is reminiscent of Michaelis-Menton enzymes. Indole does not show any such saturation phenomenon. This indicates that it does not require any carrier molecule for its transportation and its lipophilic (with affinity for lipids). Due to this rxn the molecule can simply diffuse across the membrane. Ouabain is a specific inhibitor of Na+-K+ pump. If Ouabain inhibits the transport of glucose, then a Na+-glucose co-transporter would be assisting in transport.

Name three types of carrier proteins. Which of these can mediate secondary transport?

The three types of carrier proteins are the symporter, antiporter, and uniporter. A symporter uses the transport of one species to assist in the transporting a second species in the same direction as the first across the membrane. An antiporter uses the transport of one species to assist in transporting a second species in the opposite direction of the first across the membrane. Finally, a uniporter can transport a particular species across the membrane in either direction depending on the concentration gradiet. Secondary active transporters of cotransporters are capable of moving molecules against the concentration gradient. Uniporters can only transport molecules from high concentration to low concentration through passive transport while symporters and antiporters can move molecules against the concentration gradient from low to high concentration. Symporters and antiporters are both secondary active transporters.

Distinguish the mechanisms by which uniporters and channels transport ions or molecules across the membrane.

Uniporters conform to their target molecule and transition through various conformational changes as they carry that molecule across the membrane. In contrast, cannels do not change in conformation and are open for a variety of ions to travel through them. As a result, molecules diffuse through the channels at a faster rate than they diffuse through uniporters.

Cone snails are carnivors that inject a powerful set of toxins into their prey, leading to rapid paralysis. Many of these toxins are found to bind to specific ion channel proteins. What are such molecules so toxic? How much such toxins be useful for biochemical studies?

When these toxins bind to ion channel proteins , they may block the transport of ion channels, leafing to the loss of action potentials. Action potentials are crucial for the operation of the nervous system, and hence these molecules are so toxic. This may be useful for biochemical studies, because these toxins are highly specific. They can be used to study the physiological effects of blocking specific ion channels.

Nernst equation

equation in determining electrical potential created by one ion