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Membrane Transport

Membrane transport is essential to the functioning of a cell because it allows for substances, such as ions and chemicals, to pass membrane barriers. Remember that membranes are selectively permeable, meaning that some substances are able to pass freely while others cannot.

Biological membranes are both hydrophobic and hydrophilic in nature. Thus they are amphiphilic molecules. Cell membranes are organized in bilayers, with their hydrophobic tails facing inwards and their hydrophilic heads facing outwards. This specific arrangement means that small, nonpolar molecules can freely cross the membrane. Conversely, large polar molecules such as sugars and charged ions cannot freely pass.

There are two basic types of membrane transport: 

  1. Passive Diffusion: This is a type of transport which follows a concentration gradient. The flow of particles is from a high concentration area to a low concentration area and requires no energy input. In addition, this process depends on the characteristics of the substance requiring transport such as its size, charge and hydrophobicity. For example, nonpolar molecules and small polar molecules can move freely with a concentration gradient. Furthermore, passive diffusion includes osmosis, which describes the movement of water across a membrane and facilitated diffusion, which uses channel proteins or carrier proteins to transport particles.
  2. Active Transport: This is a type of transport which requires energy because molecules are pumped against a concentration gradient. There is both primary active transport, which directly uses ATP from a pump, and secondary active transport which does not directly utilize ATP, but rather an electrochemical gradient. Carrier proteins, such as antiporters and symporters are used in secondary active transport. Endocytosis and exocytosis are two types of transport requiring energy. Endocytosis brings particles into a cell, while exocytosis takes particles out of a cell.  

Different Factors Influencing the Diffusion Rate

All cells are surrounded by a phospholipid bilayer membrane. The function of the phospholipid bilayer is to act as a barrier between the living cell and the environment. The phospholipid bilayer also regulate the passage of solutes into and out of the cell. The phospholipid bilayer membrane can differentiate which solutes to mov

Discussion of Diffusion, Osmosis and Cell Membrane Potential

Begin by distinguishing between osmosis and diffusion; how are they similar? In what ways are they different? What properties of the cell membrane do they utilize to transport substances across the cell membrane? Let's end with definitions and explanations of membrane potentials.

Movement of Water Across Semi-Permeable Membranes

1. As a person becomes very dehydrated, the concentration of water in her blood decreases. In which direction will water move across the plasma membranes of her blood cells? What will happen to the volume of the cells as a consequence? Why is proper hydration important for multicellular organisms? 2. Oops! You were cleaning

EPSPs and IPSPs

1. Several ions are responsible for the resting membrane potential. Describe the forces that determine resting membrane potential. 2. How are graded potentials created, and how are they different from action potentials? 3. Discuss the ion channels that are involved in the generation of an action potential. 4. Descri

Compartments in the secretory pathway

Please provide some information about the relationships between the intra -cellular compartments involved in the secretory and endocytic pathways, also please distinguish between co-translational and post translational protein targeting.

Nerve action potentials

Describe an action potential and its representation on an EGG, labeling all activity. Compare the divisions of the autonomic nervous system's effect on heart rate and stroke volume.

A chemiosmosis hypothesis is presented.

Certain chemicals block ATP synthesis by allowing protons and other ions to "leak across membranes," disrupting the charge and protein gradients established by electron flow through an electron transport chain. Does this observation support the chemiosmosis hypothesis? Please Explain your reasoning.

Surcose solution used to describe osmosis briefly.

If you put a 2% sucrose solution on one side of a selectively permeable membrane and a 7% surcose solution on the other side, the side with the 2% solution is _____ to the side with the 7% solution: a. hypotonic b. hypertoinc c. isotonic

Membrane Permeability and passive movement

1) Would the passive movements of substances occur if the interstitial solute concentration was the same as the filtrate solute concentration? 2) Matching: 1.) Causes production of dilute urine 2.) results in increased sodium loss. 3.) Causes the body to retain more Potassium. 4.) Will cause water retention due to sodiu

Nigericin and Valinomycin's Effect On Electron Transport Chain

Nigericin is an ionophore that exchanges K+ for H+ across membranes. Explain how the treatment of functioning mitochondria with nigericin uncouples electron transport form oxidative phosphorylation. Does valinomycin, an ionophore that transports K+ but not H+, do the same? Explain.

Effect of Inhibitors on Electron Transport and ATP

What is the effect of each of the following inhibitors on electron transport and ATP formation by the respiratory chain? a) Rotenone b) DNP (dinitrophenol) c) Carbon Monoxide d) Antimycin (details are needed)

Oligomycin Inhibition: Mechanism And Effect On Metabolism

The addition of oligomycin to mitochrondria markedly drecreased both the rate of electron transfer from NADH to oxygen and the rate of ATP formation. The susbequent addition of DNP leads to an increase in the rate of electron transfer without changing the rate of ATP formation. What does oligomycin inhibit and what is the mech

Give a functional definition of a eukaryotic gene.

2. Give a functional definition of a eukaryotic gene. Please include all parts of a eukaryotic gene and what the function of each element is. Which parts of a newly synthesized eukaryotic mRNA molecule do not transmit information for the synthesis of protein? Why? 3. What is the difference between a lytic and a lysogenic

Membrane Potential Measurements of Axon of Giant Squid

During an experiment a neuropsychologist measures the membrane potential of a squid giant axon in the presence of a bathing solution of known composition. He then removes the cytoplasm and replaces it with a synthetic solution. At the same time he alters the external medium from that used before and again measures the membrane

Free Energy for Transport of Chloride Ion Using Membrane Potential

Blood contains 0.1 M Cl-. Brain tissue contains about 0.02 M Cl-. Calculate: (1) the G for the transport of Cl- from blood into brain cells (2) the energy expended by brain cells in transporting Cl- outward against the concentration gradient. Assume a membrane potential of -75mV (inside).

Cell Biology..

1. Explain why the coupling of the import of amino acids or sugars into cells is typically linked to Na+ ion import. 2. What happens to the post-synaptic cells' membrane potential at an inhibitory synapse? 3. Explain what pumps and/or transporters are involved in moving neurotransmitters into synaptic vesicles.

Active transport

Active transport is the A) diffusion of molecules within a cell B) movement of molecules into or out of a cell against a concentration gradient C) movement of molecules into or out of a cell down a concentration gradient D) movement of molecules into or out of a cell using special proteins and not requiring an

Mitochondrial Membrane and Free Release Energy

The difference in pH between the internal and external surfaces of the inner mitochondrial membrane is 1.4 pH units (external side acidic). If the membrane potential is assumed to be 0.06 V (inside negative) what is the free energy released upon transporting 1 mol of protons back across the membrane? How many protons must be tr

Study Guide Question

Synaptic Vesicles are (Choose all that Apply) Are contained within the postsynaptic cell cytoplasm Fuse with the presynaptic membrane in response to increased intracellular calcium concentration House the neurtransmitters that will ultimately be released into the synaptic cleft in response to an action potential arr

Discussin of Membrane Transport

Question: Discuss various aspects of membrane transport: passive, facilitated types and active transport. This needs to be very detailed so I can get a full understanding of it. Thank you