BIO203 Exam 1 Quizzes Review

What kind of lipid molecule is represented in this figure?

phospholipid (Phospholipids, glycolipids, and triacylglycerol all consist of a 3-carbon glycerol molecule with fatty acids attached to two of its carbons. The molecule attached to the third carbon differs between the three lipid categories: in triacylglycerol it is another fatty acid, in glycolipids it is a sugar molecule, in phospholipids it is a phosphate.)

All amino acids have which of the following chemical groups in common?

carboxyl group (All amino acids have an amino group (NH2) and a carboxyl group (−COOH) attached to a central carbon. They differ in which side groups are attached to the central carbon, such as a methyl group or aromatic rings, for example.)

How does phosphorylation of a protein affect its activity?

could increase or decrease activity (Phosphorylation of amino acid side chains in a protein changes their charge to a negative charge. It could lead to changes in conformation of the protein, differences in binding to partners, and either increased or decreased activity of an enzyme. Thus, the effects of protein phosphorylation are particular to the protein itself.)

How many bonds are made by a carbon atom?

4 (Carbon has four electrons in its outer shell and it needs eight to fill it. To fill its outer shell, carbon can share electrons with four different atoms, forming four bonds.)

A sodium-potassium antiport maintains the extracellular concentration of sodium at levels that are about 20-30 times higher than inside the cells. What directly supplies the energy for maintaining this gradient?

ATP hydrolysis drives the function of the pump. (The sodium-potassium pump is an antiport that pumps sodium out and potassium into the cell. This pump moves both ions against their concentration gradient, and ATP supplies the energy for this active transport.)

A base is a molecule that will ___________ a proton in water.

Accept (Bases accept protons in water, removing a proton from a water molecule, forming OH?2_ ions. If the hydrogen atoms in water are more attracted to the electronegative atom of a base, they can be stripped off as a proton.)

Which ion is generally maintained at a high concentration inside the cell and a low concentration outside the cell?

K+ (Potassium is maintained at high concentrations inside the cell, contrasted by sodium, which is maintained at high concentrations outside the cell.)

Which of the following is NOT used as a source of energy by a transmembrane pump to actively transport a solute?

K+ (The electrochemical gradient of potassium is not used to drive active transport. Sodium-coupled, proton-coupled, and ATP-coupled active transporters are common mechanisms for moving solutes against their gradients.)

________ are the most abundant molecules in the animal cell membrane, whereas ________ make up 50% of the membrane by mass.

Lipids, proteins (Lipids are the most abundant molecule in the cell membrane. Proteins, however, are much more massive and thus, by mass, make up about 50% of the mass of the plasma membrane.)

A phospholipid is inserted into the cytosolic side of the ER membrane. Which of the following could randomly reposition this phospholipid to the other (lumen) side of the ER membrane?

scramblase (Scramblase is an enzyme that randomly mixes phospholipids from one face of the ER membrane to the other. Flippases selectively move phospholipids from one face to another.)

Ion channels contain a selectivity filter that

selects for ions based on size and charge due to the width of the channel and charge of amino acids lining the channel. (Ion channels allow the influx of ions through a pore that contains a region called the selectivity filter. The selectivity filter's width imparts a size restriction on the ions that can pass through, and the charged amino acid residues in this region repel any ions of the wrong charge.)

Chemical modifications like phosphorylation and acetylation of proteins occur on ___________ of amino acids and can affect interaction of proteins with other cell components or structures.

side chains (The chemical modification of phosphorylation and acetylation occurs on the side chain of the amino acid and can affect how proteins interact with other proteins or components of the cell. This effect can occur through the direct alteration of binding sites if the phosphorylation and acetylation occur on an amino acid in a binding site, or through a conformational change that indirectly alters the binding site.)

Cells, compared with the extracellular fluid are

slightly negatively charged. (Cells, due to the distribution of ions and charges across the membrane, are slightly negatively charged compared to the extracellular fluid. This leads to a slight negative resting membrane potential of cells.)

Which of the following is an inorganic compound?

table salt (e.g., NaCl) (Organic compounds are made up of carbon atoms linked together, frequently along with other atoms and chemical groups. Inorganic compounds do not contain multiple linked carbon atoms.)

If a phospholipid is located in the outer layer of the bilayer in a vesicle, where will it end up when the vesicle fuses with the plasma membrane?

the cytosolic face of the bilayer (When a vesicle fuses with the plasma membrane, the lipids on the outside of the vesicle will end up in the phospholipid layer on the inside (cytosolic face) of the plasma membrane. Lipids on the inside of the vesicle membrane will face the extracellular fluid in the plasma membrane.)

How is an electrical signal converted to a chemical signal at a nerve terminal?

Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters. (An electrical signal is converted to a chemical signal at a nerve terminal by the action of voltage-gated Ca2+ channels, which allow the influx of Ca2+. Ca2+ triggers the fusion of neurotransmitter-containing vesicles with the plasma membrane to release the neurotransmitter into the synaptic cleft.)

How are voltage-gated ion channels opened by voltage sensors?

When membrane potential changes sufficiently, the electrical force causes voltage sensor domains to change conformation. (A voltage-gated ion channel can be opened by the electrical forces of a membrane potential moving the voltage sensor domains into a new conformation that opens the pore of the channel.)

Which of the following is UNLIKELY to be hydrophilic?

a molecule with primarily nonpolar covalent bonds (Hydrophilic molecules carry positive or negative charges, allowing them to interact with the partial charges on water molecules. Polar covalent bonds form partial charges, whereas nonpolar covalent bonds do not.)

Which of the following would be able to cross a protein-free lipid bilayer most rapidly?

a steroid hormone (nonpolar, large) (The lipid bilayer allows nonpolar molecules to pass because they interact favorably with the hydrophobic tails, and it excludes ions and charged molecules from passing through because of their interaction with water. Polar molecules without charge can pass through at a low rate, but are further limited by size constraints.)

What is a protein family?

a structurally related group of proteins. (A protein family is a set of proteins that have similar primary structures (amino acid sequences) and thus have related three-dimensional structures. If the structure of one member of a protein family is determined, it can be used to make predictions about the structure of other members of the protein family.)

Disulfide bonds stabilize protein shape outside the cell by

covalent bonds between cysteines. (Using mechanisms such as noncovalent bonds between charged side chains, proteins fold into their final conformation based on their amino acid sequence inside the cell. However, in the harsh environment outside the cell, this structure needs to be stabilized to keep its final form and function. Disulfide bonds are covalent cross-linkages between cysteine groups juxtaposed in the three-dimensional structure, and they act to hold the shape of the protein.)

Shown is a diagram of a nerve cell. Which line indicates the location of the dendrites?

2 (The dendrites are the extensions of the neuron where the signal is received from the previous neuron. Dendrites are attached to the cell body.)

How does an action potential spread along the cell membrane?

A change in membrane potential triggers the opening of nearby voltage-gated sodium channels in a one-way direction. (An action potential spreads along the cell membrane because the change in membrane potential triggers the opening of nearby Na+ channels, which then change the membrane potential in their local vicinity. This continues down the cell membrane in the direction away from the location of the originally stimulated channels.)

Which of the following represents a symport transporter protein?

A(A symport moves a solute and an ion in the same direction. The first complex on the left represents a symport.)

The figure below shows a depiction of an antibody. Which label correctly identifies the region(s) of the antibody that contains variable amino acids for binding of a specific antigen?

A. (Unique antigen-binding sites in antibodies are formed by varying the terminal amino acid sequences in the heavy chain and the light chain, which come together into a unique three-dimensional conformation for specific side-chain interactions with the antigen. Since each antibody is made up of two heavy chains and two light chains, there are two antigen-binding sites per antibody.)

Which of the following ions has a low cytosolic concentration so that a flood of this ion into the cell can be used as a signal for cell processes like neurotransmitter release and fertilization?

Ca2+ (Calcium ions are a common intracellular signaling molecule. The concentrations in the cell are kept extremely low so that Ca2+ channels can rapidly change the concentration and activate cellular processes.)

If protein folding is determined by the sequence of amino acids in the polypeptide chain, why are chaperone proteins needed to assist folding in the cell?

Certain proteins easily aggregate with other proteins. (All proteins can fold on their own without assistance due to the energetically favorable interactions between amino acid side chains and/or the polypeptide backbone. However, the cytoplasm is crowded and some proteins can form favorable interactions with other proteins before they have a chance to fold. These aggregates could impede proper folding.)

Which of the following levels of protein structure involves the interaction of more than one polypeptide chain into a three-dimensional structure?

Quaternary (Primary structure is the linear order of amino acids in a polypeptide chain. The secondary structure is the formation of organized arrangements to form segments like α helices and β sheets. The tertiary structure is the overall three-dimensional shape of a protein. The quaternary structure is the assembly of multiple folded polypeptide chains into a larger complex.)

Which of the following is true about amyloid protein structures?

They consist of stacked β sheets.(Amyloid protein structures are β sheets that interlock with each other through their side chains and form stacks. Since they are made from many β sheets, they form strong structures that have many roles in the cell, including formation of important cellular compartments. However, some amyloid structures, but not all, are abnormal and cause disease.)

What is the role of K+-gated ion channels in an action potential?

They help reverse the action potential by repolarizing the cell (K+-gated ion channels open after membrane depolarization to allow K+ movement across the membrane to reestablish resting potential.)

Plasma membrane proteins that move ions in and out of cells using active transport are called

Transporters (Transporters move ions using active transport. Channels allow cells to move in and out of cells down their concentration gradient.)

Which of the following is a difference between transporters and channels?

Transporters can facilitate both active or passive transport of solutes; channels facilitate only passive transport. (Channels are multipass transmembrane proteins that form a pore that discriminates loosely between ions when open, allowing their passive flow across the membrane and down the concentration gradient. Transporters are highly selective and active transporters can move solutes against the concentration gradient with the input of energy.)

Amino acids with side chains that contain −COOH groups, like those shown below, would be ___________ in the aqueous environment of a cell.

acidic (Amino acids like glutamic acid and aspartic acid have side chains that terminate in carboxylic acid groups (−COOH). This group loses a proton in water and is acidic in nature.)

How does binding of GTP to a GTP-binding protein affect its activity?

always activates the protein (Proteins in the GTP-binding protein family are always in their active conformation when GTP is bound, in contrast to phosphorylation of a protein, which can activate or inactivate a protein. The hydrolysis of GTP to GDP returns the protein to the inactive state.)

Detergent molecules are ___________ in nature and bind with membrane proteins and membrane lipids to disrupt their interactions and release the proteins from the membrane.

amphipathic (Detergents have a hydrophobic portion that disrupts the hydrophobic interaction of lipids with membrane proteins. They also have a hydrophilic region that stabilizes the protein in solution by interacting with the aqueous environment.)

When a ligand binds to an allosteric enzyme's regulatory site, it changes the activity of that enzyme by

inducing a conformational change. (Once a regulatory molecule or ligand binds to a regulatory site, an allosteric protein undergoes a conformational change that is transmitted to the active site. Inducing the conformational change can change the activity of the enzyme, but it does NOT directly block the active site.)

A molecule with a lot of polar covalent bonds is likely to

be highly soluble in water.(Polar covalent bonds are formed when two atoms unequally share an electron, forming partial positive and partial negative charges at either end of the bond. Water also has partial positive and negative charges, and thus will easily interact with other molecules' partial charges, thus making it soluble.)

If the backbone of a polypeptide is hydrophilic, how can a transmembrane alpha helix span the hydrophobic portion of the lipid bilayer?

because amino acid side chains in a transmembrane helix are hydrophobic and interact with the hydrophobic interior of the bilayer (Although the backbone is hydrophilic, the amino acid side chains of an alpha helix stick out from the helix. If those amino acid side chains are hydrophobic, they will interact with the hydrophobic tails in the bilayer and shield the hydrophilic backbone from unfavorable interactions.)

Which of the following is a common transmembrane protein structure that can traverse the membrane to form a pore or channel by alternating hydrophobic and hydrophilic amino acids? An example of this is a porin protein.

beta barrel (A beta barrel is a beta sheet structure that is rolled into a cylinder. In beta sheets, the amino acid side chains protrude out from the sheet in an alternating fashion from one side of the sheet to another. For a beta barrel to form a transmembrane pore, the side chains facing the lipid bilayer must be hydrophobic, while the adjacent side chains, which face the aqueous pore, must be hydrophilic.)

A readily available source of energy that cells use to drive reactions is stored in the ___________ bond.

phosphoanhydride (Nucleotide triphosphates, notably ATP, have three phosphoanhydride which can be hydrolyzed easily to release energy.)

A stretch of amino acids in a polypeptide chain that is capable of independently folding into a defined structure is called a

domain (A domain is a sequence of amino acids in a polypeptide chain that adopts a defined folding pattern based on the interactions of the side chains, as well as contributions from the polypeptide backbone molecules. This is distinct from a subunit, which is a term used for a single, complete polypeptide chain that can interact with other subunits to form a larger complex.)

Which factors determine the force driving the passive transport of charged solutes across the membrane?

electrochemical gradient (Passive transport of charged solutes depends not only on concentration gradient, but also on the charge distribution across the membrane. The combined contributions of concentration gradient and membrane potential are referred to as "electrochemical gradient.")

Where are new phospholipids made?

endoplasmic reticulum (Enzymes that are bound to the cytosolic face of the ER membrane make new phospholipids and insert them into the ER membrane.Made in smooth ER)

Which type of movement is the least common for lipids in a bilayer?

flip-flop (Lipids rarely flip-flop between the different faces of the bilayer because the polar heads would have to contact the hydrophobic interior of the membrane. This only happens when catalyzed by transporter proteins.)

What is responsible for moving glucose from the gut lumen into intestinal epithelial cells?

glucose-sodium symport (Glucose is found at higher concentrations inside the cell, so it must be actively transported into the cell. The sodium gradient outside the cell powers the symport that co-transports glucose, along with sodium, into the cell.)

Which type of noncovalent interaction can involve either the polypeptide backbone or amino acid side chains?

hydrogen bonds (The backbone of the polypeptide consists of uncharged polar covalent bonds. Because the bonds in the backbone are neither charger nor hydrophobic (i.e. nonpolar), hydrophobic forces and electrostatic interactions do not involve the backbone. Hydrogen bonds, however, are formed between atoms in the polar covalent bonds found in both amino acid side chains and in the carboxyl group and amino groups of the polypeptide backbone.)

What is the conformation of the voltage-gated Na+ channel that keeps the action potential from traveling backward along the axonal membrane?

inactivated (During an action potential, Na+ channels change conformations from closed to open to inactivated, then back to closed. Channels are in the inactivated state directly after opening, which keeps them from being reactivated immediately, and leads to the movement of the action potential away from the site of activation.)

An extracellular molecule binds to a channel and triggers it to move more often to the open conformation than the closed conformation, as shown in the figure. This is referred to as a ___________ channel.

ligand-gated (Molecules that bind to channels to alter their conformation to open more frequently are called ligands; a channel that is regulated in this way is a ligand-gated channel. The opening of other channels can be triggered by a membrane potential (voltage-gated) or by mechanical forces (mechanically gated).)

A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)?

long, saturated fatty acid tails (The longer the fatty acid tail, the more tendency for interaction between the tails, which reduces the fluidity of the membrane. In addition, the more closely packed the fatty acid tails, the less fluid the membrane; saturated fatty acid tails have no double bonds and can pack more closely together.)

A binding site on the surface of a protein interacts specifically with another protein through

many weak noncovalent interactions. (Covalent interactions are rarely used between protein molecules because they are difficult to break, often requiring an enzyme. Interactions between proteins and their partners need to be reversible but very specific. A specific interaction, but one that is able to be altered, can be achieved through formation of many weak noncovalent interactions between proteins and their binding partners.)

Which of the following is a cell type in humans that uses voltage-gated ion channels?

muscle cells (Many cell types use voltage-gated ion channels—in humans, these are mainly part of the nervous system and the cells that respond to nerve stimulation, like muscle cells.)

Which of these macromolecules is NOT commonly found in the plasma membrane?

nucleic acids (The plasma membrane is primarily made up of a lipid bilayer with the fatty acid tails facing each other, and membrane proteins are also found throughout the membrane. Both membrane lipids and proteins are frequently modified with carbohydrate groups to form glycolipids and glycoproteins.)

What is the molecular target of the antidepressant Prozac?

the symport that drives reuptake of serotonin (Prozac binds to and inhibits the Na+-driven symport that brings serotonin back into the cell. This leads to sustained levels of serotonin signaling in the synaptic cleft.)

The following image shows two triacylglycerol molecules with different fatty acid chains. If these fatty acids were in a phospholipid molecule, which of the two would form the most fluid membrane?

unsaturated(Unsaturated fatty acids have double bonds in their hydrocarbon chains, and so have kinks in them; these keep them further apart. Thus, membranes made from unsaturated fatty acids are more fluid because they cannot pack as closely together as saturated fatty acids, which have no double bonds and are straighter.)

Ionic bonds are ___________ than covalent bonds and are ___________ common in cells.

weaker; less (Ionic bonds are weak bonds commonly found in salts that form ions in aqueous solution. Because the cell environment is primarily aqueous, ionic bonds are dissociated by interaction with water.)