BIOL 314 Final

Maintaining pH and salt concentrations is critical to keeping proteins functional. What is the molecular mechanism by which pH affects protein function? -Only the primary structure is altered, which changes the folding and function of the protein. -A few of the polar R-groups can change charge, and the new attraction or repulsion can alter the shape of the protein. -The hydrogen bonds within the polypeptide backbone that form the secondary structures are completely disrupted. -The N- and C-terminus amino acids with their amino and carboxyl ends can change the shape of the entire protein.

Which of the following is NOT a feature commonly observed in α helices? -cylindrical shape -left-handedness -1 helical turn every 3.6 amino acids -amino acid side chains that point outward

Two or three α helices can sometimes wrap around each other to form coiled-coils. The stable wrapping of one helix around another is typically driven by __________ interactions. hydrophilic hydrophobic ionic van der Waals

The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein’s structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein’s secondary structures (α helices and β sheets)? space-filling ribbon backbone wire

Cyclic AMP (cAMP) is a small molecule that associates with its binding site with a high degree of specificity. Which types of noncovalent interactions are the most important for providing the “hand in a glove” binding of cAMP? hydrophobic interactions electrostatic interactions hydrogen bonds van der Waals interactions

Some proteins have α helices, some have β sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements? specific amino acid sequences side-chain interactions the hydrophobic-core interactions hydrogen bonds along or between strands of the protein backbone

The variations in the physical characteristics between different proteins are influenced by the overall amino acid compositions, but even more important is the unique amino acid sequence. bond. number. orientation.

Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein’s ligand-binding site. Where is the binding site typically located in the protein structure? buried in the interior of the protein on the surface of the protein inside a cavity on the protein surface on the surface of the protein in the presence of ligand

In the polypeptide sequence shown below, which letter represents the peptide bond? bond between c=o and n-h bonds, removes the h from nh2 and oh from cooh to form bond Figure 4-2 C A B D

Complete the sentence with the best option provided below. The primary structure of a protein is the lowest energy conformation. amino acid sequence. amino acid composition. average size of amino acid side chains.

A lab has sequenced a novel cancer-causing gene in humans. What can we learn from the protein sequence by inputting the predicted protein sequence into a computer and conducting bioinformatic analysis? the rate at which the protein will be degraded how many protein-binding partners it will have, including its quaternary structure the complete tertiary structure of this protein how to predict the domains by matching the amino acids with another similar sequence

Polypeptides are synthesized from amino acid building blocks. The condensation reaction between the growing polypeptide chain and the next amino acid to be added involves the loss of a(n) carbon atom. carboxylic acid group. water molecule. amino group.

Cells utilize several mechanisms for restricting the movement of membrane proteins within the plasma membrane. One of these mechanisms allows cells to form specialized attachment structures called focal adhesions to promote cell motility. Which of the following mechanisms describes how motile cells form focal adhesions on the plasma membrane? Proteins are tethered to the cell cortex. Proteins are tethered to the proteins on the surface of another cell. Proteins are tethered to the extracellular matrix. Protein movement is limited by the presence of a diffusion barrier.

Which of the following types of lipids is the most abundant in the plasma membrane? phospholipids sterols triacylglycerides glycolipids

Porin proteins form large, barrel-like channels in the membrane. Which of the following statements about these channels is FALSE? They are made primarily of β sheets. They cannot form narrow channels. They have alternating hydrophobic and hydrophilic amino acids. They are made primarily of α helices.

New membrane phospholipids are synthesized by enzymes bound to the __________ side of the __________ membrane. luminal; Golgi cytosolic; mitochondrial cytosolic; endoplasmic reticulum extracellular; plasma

Consider a transport vesicle containing a membrane glycoprotein. The glycoprotein and the vesicle’s phospholipids are delivered to the plasma membrane, as shown in the figure below. Which of the following is an accurate description of the outcome of this process? Figure 11-4 -The portion of the glycoprotein that was inside of the vesicle ends up in the cytosol after it is delivered to the plasma membrane. -Some of the individual phospholipid molecules are released into the cytosol to prevent the plasma membrane, and thus the cell, from becoming too large. -The phospholipids that are delivered to the noncytosolic face of the plasma membrane used to be in the interior (luminal) face of the vesicle. -The fusion event between the vesicle and the plasma membrane randomizes the phospholipids between the cytosolic and noncytosolic faces of the bilayer.

Which of the following is most likely to occur after the lipid bilayer is pierced? The membrane expands. The membrane reseals. A tear forms. The membrane collapses.

Which of the following substances is most commonly used to help purify a membrane protein? sucrose ethanol high salt solution detergent

Cholesterol serves several essential functions in mammalian cells. Which of the following is NOT influenced by cholesterol? membrane permeability membrane fluidity membrane thickness membrane rigidity

Cells utilize several mechanisms for restricting the movement of membrane proteins within the plasma membrane. One of these mechanisms allows cells to present antigens to other cells to trigger the adaptive immune response. Which of the following mechanisms describes how antigen-presenting cells perform this function? Proteins are tethered to the cell cortex. Proteins interact with the proteins on the surface of another cell. Protein movement is limited by the presence of a diffusion barrier. Proteins are tethered to the extracellular matrix.

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of fluidity in its cell (plasma) membrane? decrease the amount of cholesterol in the membrane add lipids with hydrocarbon tails that are shorter and have more double bonds add lipids with hydrocarbon tails that are longer and have fewer double bonds decrease the number of glycolipids in the membrane

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold? All channels open completely. A few channels remain closed and most open completely. All channels open partly, each to a different degree. All channels open partly, to the same degree.

Which of the following occur without coupling transport of the solute to the movement of a second solute? the export of Na+ from cells to maintain resting membrane potential export of Ca2+ from the cytosol export of H+ from animal cells for pH regulation export of glucose out of gut epithelial cells