PCB 4023 Smartbook

Determine whether the following statement is true or false: A symport protein would function as an antiport protein if its orientation in the membrane were reversed. This statement is ______

F

Determine whether the following statement is true or false: In the chromatin of interphase chromosomes, regions of the chromosome that contain genes being expressed are generally more compact, while those that contain non-expressed genes are generally more extended.This statement is ____

F

Determine whether the following statement is true or false: The nuclear lamina disassembles and re-forms at each cell division.This statement is _____

T

In a typical human secretory cell, which of the following membranes has the largest surface area? a. rough ER b. lysosome c. plasma membrane d. nuclear inner membrane d. smooth ER

a

In the living cell, histone proteins pack DNA into a repeating array of DNA-protein particles called what? a. nucleosomes b. beads on a string c. octamers d. heterochromatin e. euchromatin

a

Many proteins are regulated by the binding of GTP or GDP. Which form is the active state of the protein? a. the GTP-bound form b. the form to which no nucleotide is bound c. different forms for different proteins d. the form that is highest in concentration e. the GDP-bound form

a

Oligosaccharide chains added in the ER can undergo further modification in which organelle(s)? a. both the cis and trans Golgi networks b. only the trans Golgi network c. lysosomes d. only the cis Golgi network e. endosomes

a

Regarding acids, bases, and pH, which of these statements is true? a. Substances that release protons when they dissolve in water are termed acids and result in a pH lower than 7. b. Substances that release protons when they dissolve in water are termed bases and result in a pH lower than 7. c. Substances that release protons when they dissolve in water are termed acids and result in a pH higher than 7. d. Substances that release protons when they dissolve in water are termed bases and result in a pH higher than 7.

a

What does the primary structure of a protein refer to? a. the linear amino acid sequence of the protein b. the locations of the peptide bonds that form the protein's backbone c. the structure that forms first as the protein folds into its most stable form d. the overall three-dimensional shape of the protein e. the locations of the protein's α helices and β sheets

a

What kind of enzyme removes a phosphate group from a protein? a. phosphatase b. kinase c. phosphorylase d. GTPase e. ATPase

a

When grown at higher temperatures, bacteria and yeast maintain an optimal membrane fluidity by doing which of the following? a. producing membrane lipids with tails that are longer and contain fewer double bonds b. producing membrane lipids with tails that are shorter and contain fewer double bonds c. adding cholesterol to their membranes d. producing membrane lipids with tails that are longer and contain more double bonds e. producing membrane lipids with tails that are shorter and contain more double bonds

a

Which four elements make up 96% of the weight of living organisms? a. carbon, hydrogen, nitrogen, and oxygen b. carbon, phosphorus, sodium, and hydrogen c. carbon, sodium, chloride, and oxygen d. carbon, calcium, oxygen, and nitrogen e. carbon, oxygen, sodium, and hydrogen

a

Which is true of ribosomes? a. A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER. b. A special class of ribosomes attached to the ER membrane translates the proteins destined for that organelle. c. All ribosomes are attached to the ER when they begin synthesizing a protein. d. Polyribosomes translate only those proteins that have an ER signal sequence. e. Polyribosomes translate only cytosolic proteins.

a

Which of the following atoms is most likely to participate in an ionic bond? a. chlorine, with an outer electron shell filled with seven of a possible eight electrons b. phosphorus, with an outer electron shell filled with five of a possible eight electrons c. carbon, with an outer electron shell filled with four of a possible eight electrons

a

Which of the following form tiny hydrophilic pores in the membrane through which solutes can pass by diffusion? a. channels b. anions c. transporters d. liposomes e. pumps

a

Which organelle is essentially a small sac of digestive enzymes that functions in degrading worn-out organelles, as well as macromolecules and particles taken into the cell by endocytosis? a. lysosome b. peroxisome c. nucleus d. Golgi apparatus e. endosome

a

Which type of membrane transport protein can perform either passive or active transport? a. transporters b. both channels and transporters c. Neither type of membrane transport protein can perform both passive and active transport. d. channels

a

Which type of movement is the least common for lipids in a bilayer? a. flip-flop b. lateral diffusion c. rotation d. flexion

a

Many viruses enter cells through receptor-mediated endocytosis. Which of the following strategies could be affective in blocking entry of this class of viruses into cells and could be used to treat viral infections? a. Block the receptor with an antibody. b. Block the function of adaptin. c. Block the actin filaments. d. Increase the activity of clathrin.

a,b

In a cytosolic folded protein, what orientation and/or interaction do the hydrophobic amino acids tend to have? a. They are interacting with other nonpolar amino acids. b. They are clustered near the N-terminus of the protein. c. They are tucked away inside the protein. d. They are exposed on the outside of the protein.

a,c

Intracellular Ca2+ levels are important in cardiac muscle. Increasing intracellular Ca2+ levels in heart muscle cells leads to an increase in muscle contraction. Lowering the intracellular Ca2+ levels decreases the strength of cardiac muscle contraction. Congestive heart failure can occur when the heart's pumping of blood is weaker than normal, which leads to fluid collecting around organs, including the heart. One treatment method is to give the patient drugs that increase the strength of the heart muscle contraction. Which of the following might function as an effective treatment of congestive heart failure by increasing the strength of heart muscle contraction? a. a drug that decreases the activity of the Na+/Ca2+ transporter b. a drug that blocks the calcium channel in heart muscle cells c. a drug that inhibits the Na+-K+ pump from establishing a strong Na+ gradient d. a diuretic drug that triggers removal of excess Na+ from the body

a,c,d

Endocrine cells that synthesize lipid hormones, such as steroids, contain extensive amounts of which of the following? a. cytosol b. smooth ER c. rough ER d. nucleus e. Golgi apparatus

b

In a classic experiment designed to study nuclear transport, investigators added a dye molecule to the subunits of a protein called nucleoplasmin, which is involved in chromatin assembly. They then injected the intact protein or combinations of its subunits into the cytosol of a frog oocyte or into its nucleus. The results of the experiment are shown in the diagram, where red indicates the location of the labeled protein. Based on these results, which part of the nucleoplasmin protein bears a nuclear localization signal? a. both the head and the tail b. the tail only c. neither the head nor the tail d. the head only e. No conclusion about the nuclear localization signal can be drawn from the data.

b

In which process do Rab proteins function? a. vesicle docking b. vesicle tethering c. vesicle fusion d. cargo protein delivery

b

The movement of an ion down its concentration gradient is called what? a. pumping b. passive transport c. active transport d. osmosis

b

What is the general name given to the most highly condensed form of chromatin? a. euchromatin b. heterochromatin c. 30-nm chromatin fiber d. X chromatin e. nucleosome

b

What kind of enzyme adds a phosphate group to another protein? a. phosphorylase b. kinase c. ATPase d. GTPase e. phosphatase

b

What reaction involving ATP releases a large amount of energy? a. the release of the hydroxyl group b. the release of the terminal phosphate group c. the release of adenine d. the release of the sugar group e. the release of the base

b

What type of bond is formed when two atoms share electrons? a. hydrogen bond b. covalent bond c. electronic bond d. electrostatic bond e. ionic bond

b

Where in a cell are most damaged proteins broken down? a. Golgi apparatus b. cytosol c. endoplasmic reticulum d. peroxisomes

b

Which of the following correctly describes phosphorylation of a protein? a. It is catalyzed by a protein phosphatase. b. It can increase or decrease the protein's activity. c. It is an irreversible protein modification. d. It always increases the protein's activity. e. It always decreases the protein's activity.

b

Which portion of a membrane phospholipid faces the outside of the membrane? a. none, because phospholipids are confined to the interior of the membrane b. head c. fatty acids d. amphipathic portion e. tail

b

Chaperone proteins can aid in protein folding by doing which of the following? a. providing the binding energy for possible protein conformations before achieving the one that is most stable b. steering partially folded polypeptide chains along the most energetically favorable folding pathway c. isolating a polypeptide chain within the crowded cytoplasm to prevent aggregation of proteins

b,c

Given the type of transporter as determined in Part 1, choose all of the correct statements below that relate to the function of the Na+/Ca2+ transporter. a. The transporter directly uses ATP as an energy source for transporting ions. b. Ca2+ is transported against its electrochemical gradient. c. The transporter uses the Na+ electrochemical gradient as an energy source for transporting ions. d. Na+ is transported against its electrochemical gradient.

b,c

Botulism is a potentially fatal foodborne disease caused by the bacterium Clostridium botulinum. C. botulinum produces different toxins, several of which are proteases that cleave neuronal SNARE proteins. What normal process is blocked by cleavage and inhibition of SNARE proteins? a. entry of proteins with ER signal sequences into the ER lumen b. docking of vesicles to target membranes c. fusion of vesicles with target membranes d. budding of vesicles from the endoplasmic reticulum

c

How do protein, nucleic acid, and polysaccharide molecules polymerize (grow in length)? a. by hydrolysis reactions b. by oxidation reactions c. by condensation reactions d. none of these

c

In muscle cells, which organelle sequesters Ca2+ from the cytosol? a. rough ER b. endosome c. smooth ER d. lysosome e. mitochondrion

c

Organisms that live in cold climates adapt to low temperatures by doing which of the following? a. increasing the amounts of unsaturated fatty acids in their membranes to help decrease the fluidity of their membranes b. increasing the amounts of saturated fatty acids in their membranes to help decrease the fluidity of their membranes c. increasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid d. increasing the amounts of saturated fatty acids in their membranes to help keep their membranes fluid e. decreasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid

c

Protein molecules that have a quaternary structure must have two or more of which of the following? a. disulfide bonds b. α helices and β sheets c. polypeptide chains d. protein domains e. binding sites

c

The movement of an ion against its concentration gradient is called what? a. facilitated diffusion b. passive transport c. active transport d. osmosis

c

The outer membrane of the nucleus is continuous with the membrane of which other organelle? a. mitochondrion b. Golgi apparatus c. endoplasmic reticulum d. endosome e. peroxisome

c

What type of reaction is the reverse of a condensation reaction? a. oxidation b. reduction c. hydrolysis d. decondensation

c

What would happen to a protein that is engineered to contain both a nuclear localization signal and a nuclear export signal? a. It would spend most of its time in the nucleus. b. It would spend most of its time in the cytosol. c. It would shuttle in and out of the nucleus. d. It would be unable to fold properly and would be targeted for destruction. e. It would bind to nuclear import receptors and nuclear export receptors, forming a nonfunctional complex.

c

Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell? a. mitochondrion b. endosome c. Golgi apparatus d. peroxisome e. nucleus

c

Which statement is true of hydrophilic molecules? a. They form few or no hydrogen bonds b. They are typically hydrocarbons c. They mix well with water d. They are generally uncharged.

c

The FRAP technique occurs in a series of steps. Select every statement that correctly describes a step in the FRAP procedure. Choose one or more: a. The speed of repair of the fluorescent marker is measured. b. All fluorescent molecules in the cell are irreversibly bleached. c. The relative mobility of the fluorescently labeled molecule is measured. d. The molecule of interest is fluorescently labeled.

c,d

As a polypeptide is being translocated across the membrane of the endoplasmic reticulum, a stop-transfer sequence can halt the process. What eventually becomes of this stop-transfer sequence? a. It stops protein synthesis and causes the ribosome to be released back to the cytosol. b. It remains in the cytosol. c. It is cleaved from the protein. d. It forms an α-helical membrane-spanning segment of the protein. e. It is translocated into the lumen of the endoplasmic reticulum.

d

Carbon, which has four electrons in its outer shell (with a capacity of eight electrons), can form a maximum of how many covalent bonds with other atoms? a. 2 b. 8 c. 0 d. 4

d

Cardiac muscle cells contain a Na+/Ca2+ transporter responsible for maintaining a low cytosolic Ca2+ concentration, which helps regulate cardiac muscle contraction. Ca2+ is transported out of the cell as Na+ is brought into the cell. What type of transporter is this protein? a. symport b. channel c. uniport d. antiport

d

If a signal sequence is removed from an ER protein, what happens to the altered protein? a. It is escorted to the ER by chaperone proteins. b. It is immediately degraded. c. It is unable to exit the ER. d. It remains in the cytosol. e. It can enter any organelle other than the ER.

d

In their search for the molecular basis of cystic fibrosis, researchers identified a chlorine ion channel in which a variety of inherited mutations can precipitate the disease. These studies also showed that people who do not have cystic fibrosis can harbor amino acid substitutions in this protein—even in a critical stretch of amino acids that forms a membrane-spanning α helix. How is it possible for such amino acid substitutions to exist within the population without disrupting the α helical structure of that region of the channel? a. The formation of an α helix is not dependent upon the amino acid sequence in that region, so all substitutions are permitted. b. Formation of a membrane-spanning α helix is dictated by the phospholipid bilayer, and thus it is independent of the amino acid residues in that region of the protein. c. The structure of a membrane-spanning α helix is always maintained by disulfide bonds between certain amino acids. d. The formation of an α helix is governed by hydrogen bonding between atoms that are not in the side chains (R groups) of the amino acids in this region. e. Covalent bonding between amino acids forming an α helical region is responsible for maintaining this conformation, irrespective of the side chains present.

d

Margarine is produced from vegetable oil by a process that does which of the following? a. removes carbons, which decreases the length of their phospholipid tails b. freezes the phospholipids, which removes their double bonds c. adds carbons, which increases the length of their phospholipid tails d. adds hydrogen, which removes the double bonds from their phospholipid tails e. removes hydrogen, which increases the number of double bonds in their phospholipid tails

d

Nuclear import is driven by the hydrolysis of GTP, which is triggered by an accessory protein called Ran-GAP (GTPase-activating protein). Which is true of this process? a. Ran-GDP displaces proteins from nuclear import receptors inside the nucleus. b. Ran-GTP is present in high concentrations in the cytosol. c. Nuclear receptors carry Ran-GTP from the nucleus to the cytosol. d. Nuclear import receptors have the ability to catalyze hydrolysis of GTP. e. Ran-GAP is present exclusively in the nucleus.

d

Proteasomes act primarily on proteins that have been marked for destruction by the attachment of which small protein? a. termination factor b. protease c. histone d. ubiquitin e. prion

d

The DNA in eukaryotic chromosomes is folded into a compact form by interactions with which of the following? a. centrioles b. RNA c. microtubules d. histones

d

The tails of the core histone proteins can be chemically modified by the covalent addition of what type of chemical group? a. acetyl b. methyl c. phosphate d. all of these e. none of these

d

What do the segments of a transmembrane protein that cross the lipid bilayer usually consist of? a. an α helix with mostly polar side chains b. a β sheet with alternating polar and nonpolar side chains c. a β sheet with mostly polar side chains d. an α helix with mostly nonpolar side chains

d

What protein can assemble into a basketlike network that gives budding vesicles their shape? a. Rab protein b. SNARE c. adaptin d. clathrin e. dynamin

d

When glucose moves across a phospholipid bilayer by passive transport, which factor determines the direction of its transport? a. whether the cell is metabolically active or not b. the amount of energy available to fuel the transport process c. the charge difference across the membrane d. the concentrations of glucose on either side of the membrane

d

Which bond term describes a covalent bond in which electrons are shared unequally? a. hydrogen b. ionic c. nonpolar d. polar

d

Which of the following components of receptor-mediated endocytosis of LDL is incorrectly matched with its function? a. clathrin: forms the coated vesicle b. LDL receptors: form bridges between the LDL particle and adaptin c. adaptin: binds to the specific receptors and recruits clathrin d. lysosome: releases LDL from the receptor

d

Why do phospholipids aggregate to form cell membranes? a. They are water-fearing b. They are attached to sugars c. They are water-loving d. They are amphipathic e. They are acids.

d

A protein can be unfolded by a process called

denaturation

How does the GTP-bound form of a GTP-binding protein switch to a GDP-bound form? a. It releases GTP and takes up GDP from the cytosol. b. It interacts with a phosphatase, which removes a phosphate from GTP. c. In the presence of high concentrations of GDP, it trades GTP for GDP. d. It releases GTP and takes up GDP from the mitochondrion. e. It hydrolyzes GTP, releasing a phosphate.

e

In a lipid bilayer, where do lipids rapidly diffuse? a. in and out of the bilayer b. back and forth from one monolayer to the other in the bilayer c. within the plane of one monolayer and back and forth between the monolayers d. not at all, because they remain in place e. within the bilayerwithin the plane of their own monolayer

e

Porin proteins—which form large, water-filled pores in mitochondrial and bacterial outer membranes—fold into β-barrel structures. The amino acids that face the outside of the barrel have what kind of side chains? a. hydrophilic b. polar c. charged d. amphipathic e. hydrophobic

e

What type of bond links two polynucleotide chains to each other in a double helix of DNA? a. phosphoanhydride bonds b. phosphodiester bonds c. glycosidic bonds d. disulfide bonds e. hydrogen bonds

e

Which characteristic describes the tails of phospholipids? a. amphipathic b. stiff c. coated with sugars d. hydrophilic e. hydrophobic

e

Which part of an amino acid gives it its unique properties? a. amino group b. peptide bond c. carboxyl group d. α-carbon e. side chain

e