Advanced Cell Biology Chapter 2 Oxford Insight

Maintaining proper membrane fluidity is essential for cells to survive. This can be done by changing the length of lipid tails and the amount of cholesterol. The longer the lipid tail, the more interaction between the hydrophobic tails, and the less they will be able to move laterally in the membrane. (Think of Crisco, which has long lipid tails. It is solid at room temperate but becomes liquid as we raise its temperate.) Cholesterol interferes with the interaction of the lipid tails with each other and so increases fluidity. If a bacterium were suddenly knocked off a spot on a warm rock in the sun into the surrounding snow, how could it maintain the proper membrane fluidity? -Produce lipids with longer tails and add more cholesterol -Produce lipids with shorter tails and add less cholesterol -Produce lipids with shorter tails and add more cholesterol -Produce lipids with longer tails and add less cholesterol

-Produce lipids with shorter tails and add more cholesterol

Proteins need to make up about _______ percent of our diet in order for us to maintain good health. 2 50 25 10

10

How many amino acids are commonly incorporated into proteins? -10 -5 -25 -20

20

Consider the DNA sequence: 5'-CGT AGT ATC TCC GAT ATC GAT CTA-3'. What would be the complementary RNA sequence? 5'-TAG ATC GAT ATC GGA GAT ACT ACG-3' 5'-UAG AUC GAU AUC GGA GAU ACU ACG-3' 5'-GCA TCA TAG AGG CTA TAG CTA GAT-3' 5'-GCA UCA UAG AGG CUA UAG CUA GAU-3'

5'-UAG AUC GAU AUC GGA GAU ACU ACG-3'

Which is not true of coenzymes? -They serve as carriers of chemical groups. -They are branched amino acids. -They transfer specific chemical groups among a wide range of substrates. -They work together with enzymes to enhance chemical reactions without being irreversibly altered.

They are branched amino acids.

What is fluorescence microscopy? -A form of microscopy in which speciimens are stained with heavy metal salts and the visualized using a beam of electrons. -A form of light microscopy in which a specimen stained with fluorophores is illuminated with the fluorophore excitation wavelength and its emission wavelength is visualized. -A form of light microscopy in which specimens are visualized using phase-contrast and differential interference of light simultaneously. -A form of microscopy in which cells are lysed and subjected to repeated rounds of centrifugation at increasing speeds to separate subcellular structures

A form of light microscopy in which a specimen stained with fluorophores is illuminated with the fluorophore excitation wavelength and its emission wavelength is visualized.

What is a fluorophore? -A cell that can be grown in culture if provided with a nutrient-rich medium. -A molecule that accelerates the rates of chemical reactions. -A molecule that catalyzes chemical reactions that in turn cause light of a particular wavelength to be emitted, which can be visualized as a specific color. -A molecule that can absorb energy from light of a particular wavelength, which in turn causes it to emit light of another, longer wavelength that can be visualized as a specific color.

A molecule that can absorb energy from light of a particular wavelength, which in turn causes it to emit light of another, longer wavelength that can be visualized as a specific color.

Enzymes affect the transition state of a chemical reaction by -binding to substrate(s). -providing a surface on which reactions converting substrate to product can occur more rapidly. -altering the conformation of substrate(s) to approach that of the transition state. -All of the above

All of the above

The coenzymes NAD+ and NADP+ are structurally related to the vitamin -riboflavin (B2). -pantothenate. -pyridoxal (B6). -niacin.

niacin

Which chemical reaction is correctly associated with its characteristics? -Endergonic reactions: negative ΔG and energetically favorable -Endergonic reactions: negative ΔG and energetically unfavorable -Exergonic reactions: negative ΔG and energetically favorable -Exergonic reactions: positive ΔG and energetically unfavorable

Exergonic reactions: negative ΔG and energetically favorable

The output of an enzyme catalyzed reaction is known as -products. -substrates. -transition state. -catalyst.

products.

How do the composition and structure of DNA polynucleotides in cells compare to those of RNA polynucleotides? -Both are polymers of nucleic acids that contain ribose with a 2' hydroxyl group. -Both are polymers of nucleic acids consisting of the two purines adenine and guanine and the two pyrimidines cytosine and thymine. -Both form double stranded helical structures enabling complementary replication within the cell. -Both are polymers of nucleic acids linked by phosphodiester bonds between the 5' phosphate group of one nucleotide and the 3' hydroxyl group of the next nucleotide.

Both are polymers of nucleic acids linked by phosphodiester bonds between the 5' phosphate group of one nucleotide and the 3' hydroxyl group of the next nucleotide.

In enzyme catalyzed reactions, △G -always increases. -always decreases. -does not change. -None of the above—it depends upon the reaction

does not change.

Which statement regarding channel and carrier proteins is correct? -Carrier proteins selectively bind and transport specific small molecules across the membrane. -Both channel and carrier proteins utilize ATP to transport molecules up their concentration gradient. -Channel proteins undergo conformation changes to transport molecules across the membrane. -Carrier proteins allow for the free passage of molecules of the appropriate size across the membrane.

Carrier proteins selectively bind and transport specific small molecules across the membrane.

Note the shape of the nonpolar hydrophobic black and yellow structures at the beginning and end of the video. How do you think that cholesterol makes the membrane thicker? -Cholesterol is longer that the lipid tails and so leads to thickening as it replaces the lipid tails in that region of the membrane. -Cholesterol's highly energetic activity raises the temperature of the membrane and makes it expand. -Cholesterol relaxes the membrane and allows it to expand. -Cholesterol aligns with the lipid tails in that region of the membrane and makes them straighter, which thickens the membrane.

Cholesterol aligns with the lipid tails in that region of the membrane and makes them straighter, which thickens the membrane.

Which lipid is correctly paired with its structural description? -Cholesterol: four ring structure composed of hydrocarbons with a single OH group -Triglycerides: two hydrocarbon chains extending from a glycerol group that is also bonded to a phosphate head group -Phospholipid: two hydrocarbon chains extending from a serine group -Sphingomyelin: two hydrocarbon chains extending from a glycerol group that is also bonded to a phosphate group that is attached to a molecule of choline

Cholesterol: four ring structure composed of hydrocarbons with a single OH group

Which scientist first demonstrated experimental evidence that the information necessary for the folding of proteins is contained in the sequence of their amino acids? Christian Anfinsen Rosalind Franklin Lynn Margulis John Kendrew

Christian Anfinsen

What is the fundamental difference between covalent bonds and noncovalent bonds? -Noncovalent bonds are generally stronger and more stable than covalent bonds. -Covalent bonds entail the equal sharing of electron pairs between two atoms. -Covalent bonds entail the transfer of electrons between atoms. -Noncovalent bonds result from fluctuating electrical charges between two atoms that are close together.

Covalent bonds entail the equal sharing of electron pairs between two atoms.

A disulfide bond is formed between _______ residues. -glycine -cysteine -tyrosine -methionine

Cysteine

What does the term mammalian cell culture refer to? -Growth and maintenance of Drosophila melanogaster(fruit flies) within containers packaged with yeast, sugars, and other nutrients. -The growth and maintenance of E. coli on nutrient—rich agar. -Growth and maintenance of cells derived from tissue of a mammalian organism in nutrient-rich media within culture dishes. -Breeding of mice to produce offspring, which can be further breeded to establish and maintain specific mouse lines.

Growth and maintenance of cells derived from tissue of a mammalian organism in nutrient-rich media within culture dishes.

Which statement relating differences in structure between glycogen and cellular to their function is incorrect? -Despite differences in glycosidic bonding, both glycogen and cellulose are composed of glucose monomers and share the same function as structural components of the cell. -Cellulose is a straight unbranched polymer with β-1,4 glycosidic bonds. -As a result of its structure, cellulose forms the rigid fibers of plant cell walls -Glycogen contains α-1,4 glycosidic bonds with occasional α-1,6 branches.

Despite differences in glycosidic bonding, both glycogen and cellulose are composed of glucose monomers and share the same function as structural components of the cell.

Which types of chemical reactions is energetically unfavorable and therefore requires coupling of free energy to drive them forward? -Neither type of reactions -Both types of reactions -Endergonic reactions -Exergonic reactions

Endergonic reactions

What effect do enzymes have on the equilibrium of chemical reactions? -Enzymes have no effect on the equilibrium of chemical reactions. -Enzymes physically alter the substrate component of chemical reactions. -Enzymes alter both the substrate and the product of chemical reactions. -Enzymes drive reactions towards product.

Enzymes have no effect on the equilibrium of chemical reactions.

Lysine, arginine, and glutamic acid are commonly found in membrane spanning helices. TRUE FALSE

FALSE

Nicotinamide adenine dinucleotide (NADH) is an enzyme that catalyzes oxidation-reduction reactions. TRUE FALSE

FALSE

Phospholipids are amphipathic and hydrophobic and hydrophilic interactions drive the formation of the bilayer where the fatty acid chains interact with the aqueous environment and the polar head groups form the interior. TRUE FALSE

FALSE

The activation energy of a chemical reaction refers to the amount of energy needed for the reactant to produce a product. TRUE FALSE

FALSE

The driving force behind hydrophobic interactions is the ability of water to form hydrogen bonds with other polar organic molecules. TRUE FALSE

FALSE

How would you expect nucleosides to cross the plasma membrane? -Facilitated diffusion via channel proteins -Active transport -Facilitated diffusion via carrier proteins -Simple diffusion

Facilitated diffusion via carrier proteins

Question: Based on these data, compose a statement that describes the effect of 10 nM paclitaxel treatment on the subcellar localization of FOXO3a in MCF-7 breast cancer cells.

Feedback: 10 nM paclitaxel treatment causes the translocation of FOXO3a from the cytoplasm to the nucleus. The effect 10 nM paclitaxel treatment has on the localization of FOXO3a is that it keeps the FOXO3a localized within the nucleus rather than the cytoplasm. In the untreated cells, the data indicates that FOXO3a is localized primarily in the cytoplasm (this is indicated by the actin and FOXO3a reads appearing in the same location). In the treated cells, FOXO3a is located in the nucleus, which is the same as the DAPI reads (which we previously learned about, binds to double stranded DNA - which is located in the nucleus)

Question: What do the data indicate about the localization of actin? Is it consistent with the role that actin is known to play in cells.

Feedback: Actin is localized mostly in the cytoplasm and especially concentrated at the plasma membrane, which is consistent with the known role of actin in cells. The data indicates that actin is located primarily within cytoplasm (which is consistent with the role that actin plays in cells) Role: Has a major role in cell movement, cell structure, etc. Therefore, the actin reads can be helpful in determining the localization of the FOXO3a - if actin and FOXO3a is localized in the same area, FOXO3a is in the cytoplasm!

Question: Why was it important to study an enzyme with a readily detectable activity in this experiment?

Feedback: Because enzyme activity could be readily used to follow refolding to the active conformation. It was important to study an enzyme with a readily detectable activity in this experiment because a baseline is necessary for determining effect on function. By developing a baseline activity (ie: the protein is folded correctly), the researchers were able to compare the function of the enzyme when disrupting the noncovalent bonds and reducing disulfide bonds to sulfhydryl groups. Ribonuclease activity could already be determined by its ability to degrade RNA to nucleotides, which provided a practical and effective way to track the function as the protein refolds/undergoes renaturation.

Question: If you were conducting this study, what new question(s) would you want to investigate based on these data?

Feedback: Examples of questions rasied by the data: How do cells localize FOXO3a to the cytoplasm in the absence of paclitaxel, but to the nucleus in the presence of paclitaxel? How does paclitaxel cause FOXO3a to translocate from the cytoplasm to the nucles? Does the translocation of FOXO3a from the cytoplasm to nucleus play a role in the mechanism by which paclitaxel induces apoptosis? Is so, how? What is the function of FOXO3a in the cytoplasm and/or nucleus? I think that the logical progression of this study is to investigate what specific characteristic about this drug causes the FOXO3a to change its subcellular localization from the cytoplasm to the nucleus. Since there are less cells present in the treated culture (7 cells to 3 cells), I would like to investigate the function of the treatment, and how it specifically targets the MCF-7 breast cancer cells. It seems like the drug inhibits cell division, but the experiment does not go into detail about the specific function of the treatment.

Question: What do the data indicate about the localization of FOXO3a in untreated cells? -It is localized in the cytoplasm. -It is not expressed. -The data do not indicate anything about FOXO3a localization. -It is localized in the nucleus.

Feedback: Notice that the green fluorescence emitted from the antibody that binds FOXO3a is distributed throughout each cell except in the nucleus, which can be determined by comparing the green fluorescence and the blue fluorescence from DAPI. This indicates that FOXO3a is localized in the cytoplasm and excluded from the nucleus. It is localized in the cytoplasm.

Question: What do the data indicate about the localization of FOXO3a in paclitaxel-treated cells? -It is localized in the cytoplasm. -The data do not indicate anything about FOXO3a localization. -It is localized in the nucleus. -It is not expressed.

Feedback: Notice that the green fluorescence emitted from the antibody that binds FOXO3a now overlaps almost perfectly with the blue fluorescence from DAPI, indicating that FOXO3a is localized in the nucleus. It is localized in the nucleus.

Question: Based on what you know about DAPI (discussed in Chapter 1; see Figure 1.30), what structure within cells is shown by the blue fluorescence? -Golgi apparatus -Endoplasmic reticulum -Nuclei -Plasma membrane

Feedback: Recall from Chapter 1 that DAPI is a molecule that binds DNA and emits a blue fluorescence, thus it is commonly used to visualize nuclei in cells by fluorescence microscopy. Nuclei

Question: Based on the DAPI fluorescence, how many cells are shown in the micrographs for the untreated sample and the sample treated with paclitaxel? -It is not possible to predict the number of cells in the images. -7 in untreated and 3 in paclitaxel-treated. -2 in untreated and 1 in paclitaxel-treated. -1 in both the untreated and paclitaxel-treated.

Feedback: Since each cell contains one nucleus, you can discern the number of cells by counting the number is nuclei. 7 in untreated and 3 in paclitaxel-treated

Question: How does the identification of transmembrane proteins support the fluid mosaic model versus the earlier alternative of a lipid bilayer sandwiched between proteins?

Feedback: The earlier model would have proteins only on the surfaces of the membrane, not spanning the membrane. The fluid mosaic model predicted that proteins were to be found randomly distributed in the plane of the membrane. (The previous sandwich membrane theory proposed that there would be three layers of the membrane, two protein layers sandwiching a lipid bilayer.) The experiments that led to evidence of transmembrane proteins: Electron microscopy of membranes provided evidence that proteins were embedded in the lipid bilayer. Through staining the surface of the cells, it was evident that the proteins were found randomly distributed in the plane of the membrane. Also, Larry Frye and Michael Edidin showed that proteins could move laterally through the membrane (a key feature of the fluid mosaic model). Most importantly, the fluid mosaic model was continually supported extensively after its proposal. - The model made sense in the consideration of the laws of thermodynamics - The model made sense when considering all of the diverse processes that occur throughout the cell, with the transmembrane

Individual amino acids are linked together through a dehydration reaction that forms a _______ bond. -peptide -glycosidic -ionic -phosphodiester

peptide

Which of the following is not a type of bond through which atoms and molecules can interact? -Hydrophobic interactions -Polar bonds -Gibbs interactions -Van der Waals interactions

Gibbs interactions

What characteristics of histidine allows it to play a role in enzymatic reactions? -Histidine is a hydrophobic amino acid that interacts with hydrophobic side chains of preferred substrates. -Histidine is polar allowing it to interact with the N-terminal portion of the peptide following enzymatic cleavage. -Histidine is a negatively charged amino acid that forms ionic bonds with preferred substrates. -Histidine can be either uncharged or positively charged at physiological pH, allowing it to be used for exchange of hydrogen ions.

Histidine can be either uncharged or positively charged at physiological pH, allowing it to be used for exchange of hydrogen ions.

Why are the bonds between phosphates in ATP referred to as "high energy"? -The bonds are relatively weak and easy to break. -Hydrolysis of the bonds is accompanied by a large decrease in free energy. -Hydrolysis of the bonds is accompanied by a large increase in free energy. -The bonds are strong and difficult to break.

Hydrolysis of the bonds is accompanied by a large decrease in free energy.

Which correctly matches the amino acid and its contribution to tertiary structure through bonding or interactions? -Ionic bonds: lysine and glumatic acid -Hydrophobic interactions: histidine and tryptophan -Hydrogen bonds: proline and leucine -Salt bridges: cysteine and asparagine

Ionic bonds: lysine and glumatic acid

What is the effect of a β barrel on the permeability of a membrane? -It increases permeability. -It decreases permeability. -β barrels are peripheral membrane proteins. -It has no effect.

It increases permeability.

Which correctly identifies the classification of amino acids based on their structure? -Serine andlysine are classified as modified as they can undergo post-translational modifications that affect function. -Serine and glutamine are classified as nonpolar because their sidechains are composed of hydrocarbons with nonpolar bonds -Lysine amd aspartic acid are classified as charged because their sidechains carry a full positive or negative charge, respectively. -Alanine and valine are classified as polar due to side chains containing nitrogen and/or oxygen that can form polar bonds.

Lysine amd aspartic acid are classified as charged because their sidechains carry a full positive or negative charge, respectively.

Which class of amino acids is buried within the folded structure of the protein? Nonpolar Basic Acidic Polar

Nonpolar

Proteins are made up of chains of amino acids that linked by -hydrogen bonds. -R-groups. -acidic bonds. -peptide bonds.

peptide bonds.

Dipalmitoylphosphatidylcholine (DPPC) is a lipid that can form membranes. When it is added to water, it spontaneously forms a lipid bilayer. Where would you expect to find the polar head group? -On the membrane's surface -Scattered throughout the membrane. -In the interior of the membrane. -Alternating between the inner and outer membrane surface.

On the membrane's surface

Why do phospholipids form bilayers in aqueous environments? -Phospholipids are nonpolar and therefore form bilayers to avoid interacting with the aqueous environment. -Phospholipids are polar and therefore form bilayers to optimize interactions with the aqueous environment. -Phospholipids are amphipathic and therefore form bilayers oriented such that the polar groups interact with the aqueous environment. -All of the above

Phospholipids are amphipathic and therefore form bilayers oriented such that the polar groups interact with the aqueous environment.

Which class of molecule accelerates transport across biological membranes? -Proteins -Carbohydrates -Nucleic acids -Lipids

Proteins

The α helix is an example of which level of protein structure? -Quaternary -Primary -Secondary -Tertiary

Secondary

Proteins must have more than one _______ to have a quaternary structure. -transmembrane segment -βsheet -α helix -polypeptide chain

polypeptide chain

What is the major carbohydrate-storage molecule in plants? -Cellulose -Glycogen -Deoxyribonucleic acid -Starch

Starch

The binding pocket of trypsin contains an aspartate residue. How would changing this amino acid to lysine affect the enzyme's substrate specificity? -Substitution of aspartate with lysine would interfere with substrate binding and catalysis, decreasing the rate of reaction. -Substitution of aspartate with lysine would modify substrate binding and catalysis, increasing the rate of reaction. -Substitution of aspartate with lysine would have no impact on substrate binding and catalysis. -Both a and c

Substitution of aspartate with lysine would interfere with substrate binding and catalysis, decreasing the rate of reaction.

Facilitated diffusion transports molecules in the energetically favorable direction, whereas active transport couples the energetically unfavorable transport of molecules to another source of energy, such as ATP hydrolysis. TRUE FALSE

TRUE

Hydrogen bonds and ionic bonds are both noncovalent bonds formed by attraction between positive and negative charges. TRUE FALSE

TRUE

Many biochemical reactions are energetically unfavorable under physiological conditions. The cell completes these types of reactions by coupling them to an energetically favorable reaction, such as the hydrolysis of ATP. TRUE FALSE

TRUE

For many enzymes that are activated by phosphorylation of a serine residue, substitution of the serine that is phosphorylated with aspartic acid causes the enzyme to be constitutively (always) active. Why might such a substitution have this effect? -The aspartic acid is similar in structure to serine but is negatively charged allowing tighter binding in the active site of the phosphorylating enzyme. -The negative charge inhibits interaction with the phosphorylating enzyme therefore maintaining the protein in a non-phosphorylated state. -The negative charge on the aspartic acid mimics phosphoserine leading to activation of enzymes that are normally activated by serine phosphorylation. -The negative charge decreases the activation energy of the phosphorylation reaction.

The negative charge on the aspartic acid mimics phosphoserine leading to activation of enzymes that are normally activated by serine phosphorylation.

Which feature of carbohydrates affect their solubility in water? -The glycosidic bonds -The C5 side chains -The six-carbon ring structure -The polar OH groups

The polar OH groups

Why are the membrane-spanning regions of most transmembrane proteins α-helical? -The α-helical structure allows CO and NH groups to interact with the polar head groups of the phospholipids, anchoring the proteins in place. -The α-helical structure allows CO and NH groups to interact with the hydrophobic tails of the phospholipids, anchoring the proteins in place. -The α-helical structure allows CO and NH groups to form hydrogen bonds with each other, neutralizing their polar character. -The α-helical structure allows the hydrophobic side chains to form channels facilitating the passage of ions through the membrane.

The α-helical structure allows CO and NH groups to form hydrogen bonds with each other, neutralizing their polar character.

Which base is not found in DNA? -Uracil -Adenine -Thymine -Cytosine

Uracil

Which of the following is not one of the four major classes of organic molecules in the cell? -Proteins -Water -Carbohydrates -Lipids

Water

What characteristic of water contributes to its function as the most abundant molecule in cells? -Water is an amphipathic molecule that can interact with both polar and nonpolar molecules, which leads to the formation of important structures like cell membranes. -Water is a polar molecule that can form hydrogen bonds with nonpolar molecules or parts of molecules. -The properties of water force polar molecules to associate with each other guiding the folding of proteins and the formation of cell and organelle membranes. -Water is a polar molecule that can form hydrogen bonds with other polar organic molecules and inorganic ions.

Water is a polar molecule that can form hydrogen bonds with other polar organic molecules and inorganic ions.

The three-dimensional structure of a protein is analyzed most definitively by subcellular fractionation. X-ray crystallography. electron microscopy. light microscopy.

X-ray crystallography.

Channel proteins and carrier proteins allow for passive transport of substances across the phospholipid bilayer. This means that they allow substances to move _______ their concentration gradients and _______ an additional input of energy. -down; require -down; do not require -up; do not require -up; require

down; do not require

Substrates bind to the _______ site of an enzyme. -activation energy -active site -products -allosteric

active site

Molecules that are partly water-soluble and partly water-insoluble are called -hydrophobic. -amphipathic. -allosteric. -hydrophilic.

amphipathic.

All of the following are ways in which enzyme activity can be regulated except -through feedback inhibition. -by modulation of intracellular sucrose concentrations. -by binding to an allosteric site. -through phosphorylation.

by modulation of intracellular sucrose concentrations.

While small, uncharged molecules can diffuse through the hydrophobic core of a phospholipid bilayer, larger polar molecules such as glucose must enter cells by binding to -the carbohydrate portion of glycolipids. -a nonphospholipid such as cholesterol. -carrier proteins that facilitate the passage of specific molecules across membranes. -peripheral membrane proteins located on the inner side of the membrane.

carrier proteins that facilitate the passage of specific molecules across membranes.

Charged ions can move across the plasma membrane down their concentration gradient through the use of -both channel proteins and carrier proteins. -ATP-using pumps. -carrier proteins. -channel proteins.

channel proteins.

Amino acids are joined via _______ reactions, in which water molecules are released as the peptide bond is formed. -peptide -condensation -secondary -hydrolysis

condensation

Enzymes act by decreasing the distance that reactants must diffuse to find one another. lowering the overall change in free energy of a reaction. decreasing activation energy. increasing activation energy.

decreasing activation energy.

Enzymes speed up chemical reactions by -decreasing the energy of the products. -increasing the transition state energy needed to carry out the reaction. -decreasing the transition state energy needed to carry out the reaction. i-ncreasing the energy of the products.

decreasing the transition state energy needed to carry out the reaction.

In the fluid mosaic model of biological membrane structure, transmembrane proteins are -segregated into large protein clusters or rafts. -embedded nearly randomly in the lipid bilayer. -almost completely surrounded by membrane lipid. -weakly held in place on the surface of the lipid bilayer.

embedded nearly randomly in the lipid bilayer.

When enzymes bind substrates, they form the _______, which lowers the transition state energy of the reaction allowing catalysis to occur. -activation energy -products -transition state -enzyme-substrate complex

enzyme-substrate complex

Cholesterol, a membrane lipid in animals, has a chemical structure similar to -triacylglycerol. -phosphatidylinositol. -thymine. -estradiol.

estradiol.

Phospholipids consist of a 3-carbon core to which two fatty acids and a phosphate group are linked. The most common 3-carbon core is -serine. -glycerol. -glyceraldehyde. -dihydroxyacetone.

glycerol.

In polysaccharides, individual sugar molecules are held together by -phosphodiester bonds. -glycosidic bonds. -peptide bonds. -ionic bonds.

glycosidic bonds.

Lipids with unsaturated fatty acids -increase fluidity of membranes. -decrease fluidity of membranes. -are present only on the inner side of the plasma membrane. -increase the charge associated with the inner face of a membrane.

increase fluidity of membranes.

Introducing a double bond into a fatty acid puts a(n) _______ into the conformation of the molecule. -kink -branch -reverse spiral -amino acid bulge

kink

The activation energy of a chemical reaction is the difference in energy between the -substrates and transition state. -None of the answer choices are correct. -transition state and products. -substrates and products.

substrates and transition state.

In the formation of a phosphodiester bond between two nucleotides a hydroxyl oxygen from the _______ of one nucleotide reacts with the _______ of a second nucleotide. -sugar; sugar -sugar; nitrogenous base -sugar; phosphate group -nitrogenous base; sugar

sugar; phosphate group

About 50% of the mass of most biological membranes consists of lipids and about 50% consists of proteins. Therefore, -the membranes contain equal numbers of lipid and protein molecules. -the membranes contain more molecules of lipid than of protein. -the membranes contain fewer molecules of lipid than of protein. -only a few membrane proteins are exposed at the cell surface.

the membranes contain more molecules of lipid than of protein.

Passive transport across a membrane refers to -transport in the energetically favorable direction. -simple diffusion across membranes, without the help of proteins such as channels or carriers. -transport into the interior of a cell. -transport out of a cell.

transport in the energetically favorable direction.

The phospholipid bilayer is permeable to molecules that are small and _______ but impermeable to molecules that are large or _______. -charged; polar -uncharged; polar -nonpolar; uncharged -polar; uncharged

uncharged; polar

Chymotrypsin, trypsin, elastase, and thrombin are all members of the serine protease family because each -has similar charge and shape properties in its substrate insertion pockets. -uses the same catalytic mechanism involving the same key amino acids. -can be modified by the cell-wall degrading enzyme chitinase. -can form a heptahedral complex with its substrate.

uses the same catalytic mechanism involving the same key amino acids.

Coenzymes are chemically related to -inorganic phosphate. -glucose. -amino acids. -vitamins.

vitamins.

The most abundant molecule in cells is -water. -sucrose. -aspartic acid. -DNA.

water.