Biochemistry : Transport Proteins

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #23 : Protein Structure And Functions

How does an increase in carbon dioxide affect oxygen transport in hemoglobin?

Possible Answers:

Hemoglobin will have a greater oxygen affinity, which allows for a greater release of oxygen into tissue

Hemoglobin will have a lower oxygen affinity, which means that subunit cooperation will be lost

Hemoglobin will have greater oxygen affinity, which allows more oxygen to be carried

Hemoglobin will have a lower oxygen affinity, which allows for a greater release of oxygen into tissue

Correct answer:

Hemoglobin will have a lower oxygen affinity, which allows for a greater release of oxygen into tissue

Explanation:

A high carbon dioxide concentration will decrease the pH and produce the Bohr effect. These conditions will cause a slight conformational change in hemoglobin that results in a lower oxygen binding affinity. However, since the partial pressure of oxygen in the lungs in so high, most of the available oxygen will be loaded on to the hemoglobin anyway. Since the oxygen affinity is lowered, the hemoglobin will release the oxygen more freely, resulting in a greater oxygen to load in tissue. Functioning hemoglobin always has four cooperative subunits.

Example Question #24 : Protein Structure And Functions

Which of the following steps list in chronological order, the creation of a transport vesicle from a membrane via clathrin coating?

Possible Answers:

The clathrin coat is assembled, the membrane buds out, the vesicle forms, the clathrin coat is disassembled, dynamin pinches the vesicle

The clathrin coat is assembled, the membrane buds out, the vesicle forms, dynamin pinches the vesicle, the clathrin coat is disassembled

The vesicle forms, dynamin pinches the vesicle, the clathrin coat is assembled, the clathrin coat is disassembled, the membrane buds out

The membrane buds out, the vesicle forms, dynamin pinches the vesicle, the clathrin coat is assembled, the clathrin coat is disassembled

The membrane buds out, the clathrin coat is assembled, the vesicle forms, dynamin pinches the vesicle, the clathrin coat is disassembled

Correct answer:

The clathrin coat is assembled, the membrane buds out, the vesicle forms, dynamin pinches the vesicle, the clathrin coat is disassembled

Explanation:

The process of creating transport vesicles via clathrin coats proceeds in distinct steps. Before any budding occurs of the membrane, clathrin attaches to it, bound to adaptin which is attached to a transmembranal cargo receptor. (Cargo molecules are what trigger the creation of the vesicle in the first place.) The clathrin coating is believed to cause the membrane to bud. After the vesicle forms, dynamin uses GTP to pinch the vesicle off, and it is only then that the clathrin coat disassembles and we have a transport vesicle.

Example Question #1 : Transport Proteins

Which of the following lists these molecules in order of increasing permeability to a lipid bilayer?

Possible Answers:

Glucose, carbon dioxide, sodium ion, water

Sodium ion, glucose, water, carbon dioxide

Glucose, carbon dioxide, water, sodium ion

Carbon dioxide, water, glucose, sodium ion

Sodium ion, glucose, carbon dioxide, water

Correct answer:

Sodium ion, glucose, water, carbon dioxide

Explanation:

Charged molecules do not permeate the lipid bilayer easily at all. So despite its small size, among our choices, a sodium ion passes least easily through. Polar molecules also have a hard (but less difficult) time passing through, and the larger the molecule, the harder that becomes, so after the sodium ion comes glucose, followed by water, which is polar but much smaller. Small, hydrophobic molecules -- such as carbon dioxide -- diffuse through most easily, because they can pass through the longest (hydrophobic) part of the membrane.

Example Question #26 : Protein Structure And Functions

Which type of transport does not require a protein?

Possible Answers:

Passive transport

Active transport

Facilitated diffusion

Osmosis

Correct answer:

Osmosis

Explanation:

There are two types of transport: passive transport and active transport. Active transport requires an expenditure of energy and a protein pump. Passive transport includes simple diffusion and facilitated diffusion. Diffusion is the movement of a substance from an area of high concentration to one of low concentration. Simple diffusion is the name for the diffusion process which does not require a protein; facilitated diffusion is the name for the diffusion process which requires a carrier protein for transport. Osmosis is the simple diffusion of water and thus does not require protein.

Example Question #16 : Protein Functions

Which of the following amino acids coordinates the heme ring in hemoglobin?

Possible Answers:

Phenylalanine

Glycine

Lysine

Arginine

Histidine

Correct answer:

Histidine

Explanation:

In hemoglobin, the nitrogen group on the amino acid Histidine coordinates the heme ring in hemoglobin by binding to an iron atom located in the middle of the heme ring.

Example Question #41 : Biochemistry

A nonspecific hexagonal structure that functions to allow movement of molecules between adjacent cells is termed a(n) __________.

Possible Answers:

desmosome

gap junction

transport protein

tight junction

integrin

Correct answer:

gap junction

Explanation:

A gap junction is a hexagonal protein that openly connects two adjacent cells. It is nonspecific, meaning it allows various different molecules and ions to travel through it. This type of transport is important for rapid communication between adjacent cells. For instance, gap junctions serve an important function in the heart - allowing the many cells present there to act as a functional syncytium. Integrins and tight junctions do not allow the passage of molecules between adjacent cells.

Example Question #42 : Biochemistry

GLUT (glucose transporters) proteins transport glucose from the blood to cells. Which of the following statements about them are true?

I. GLUT proteins are integral membrane proteins.

II . GLUT proteins have their amino and carboxyl termini on the extracellular side of the plasma membrane.

III. Binding of glucose to the transporter protein leads to a conformation change and the transport of glucose to the inner side of the membrane. 

IV. GLUT-1, GLUT-3, and GLUT-4 proteins are ubiquitous; GLUT-2 is found in the liver, pancreas and kidney.

Possible Answers:

I, III, and IV

I and II

II, III, and IV

II and III

I, II, and III

Correct answer:

I, III, and IV

Explanation:

GLUT are integral membrane proteins.The proteins cross the membrane having the amino and carboxyl termini on the cytoplasmic side of the plasma membrane. Binding of glucose to the transporter leads to a conformational change, transport of glucose to the other side of the membrane. GLUT-1, GLUT -3 and GLUT-4 are present in most tissues; GLUT-2 is found in the liver, pancreas and kidney.

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