examen 1 🧪

Which elements account for more than 97% of the weight of most organisms?

C, H, N, O, P, S

Proteins in biological membranes may be

a. porous

b. attached to the membrane surface

c. span the membrane

Which statement about cellulose is false?

it is a branched polymer of glucose

When Keq of a reaction = 1, then

more products are formed than reactants.

Which statement is true about a reaction with an equilibrium constant, Keq, equal to 1000?

The forward rate constant is 1000 times greater than the reverse rate constant.

The study of the energy changes during metabolic reactions is called ___________.

bioenergetics

A spontaneous chemical reaction always has a __________ change.

negative Gibb’s free energy

Prokaryotes are valuable tools for biochemists because

many of their chromosomes are sequenced.

Which cellular component carries out oxidation reactions, some of which produce hydrogen peroxide?

peroxisomes

Why is it important that the enzymes in lysosomes are more active at acidic pH than at neutral pH?

It prevents them from accidentally degrading the macromolecules in the cytosol.

Molecules from living cells cannot be synthesized outside of living cells.

False

Fermentation in the absence of cells demonstrated that metabolic processes were chemical in nature.

True

Enzymes are protein catalysts that form an intermediate with a substrate that fits into it.

True

The modified lock-and-key theory of enzyme action proposed by Emil Fischer has been completely replaced by more modern ideas of catalysis.

False

Enzymes are not as efficient as most catalysts used in organic chemistry, since they must function at body temperature.

False

Bioinformatics has permitted rapid advances in our understanding of structural macromolecules from living cells.

True

The role of DNA as the genetic material was confirmed by transforming Streptococci in experiments performed several years after the famous Watson and Crick description of DNA structure.

False

Crick referred to the flow of information from nucleic acid to protein as the Central Dogma.

True

Functional groups describe one or more portions of organic compounds found in living cells

True

A phosphate ester contains a phosphate functional group.

True

Under most biological conditions, acid groups and amino groups are fully protonated.

False

Removal of water from residues of a macromolecule results in the formation of that macromolecule.

True

Mr is the mass of a molecule relative to 1/12 the mass of an atom of the most common isotope of carbon.

True

Biochemists describing the molecular weight of a protein really mean the atomic weight in grams.

False

The absolute molecular mass of macromolecules is given in daltons, where 1 dalton = 1 atomic mass unit.

True

A peptide bond is formed by the condensation of different functional groups from two amino acids.

True

The conformation of a protein enzyme determines whether it is functional or not.

True

Lysozyme is an enzyme with a cleft or depression at its active site.

True

The Haworth projection of the ring form of a monosaccharide always shows a flat plane with one edge projecting out of the page (using thicker lines).

True

Sugars with six carbons are the only ones capable of forming a ring structure as shown in a Haworth projection.

False

ATP contains both phosphoester and phosphoanhydride linkages.

True

A phosphodiester linkage in DNA contains two phosphorus atoms.

False

Lipids aggregate to form bilayers because some lipid molecules are hydrophobic and other lipid molecules are hydrophilic.

False

Thermodynamics and its laws are obeyed by living cells.

True

The tendency of a metabolic reaction to proceed is due to the free energy of both the reactants and products as well as the change in randomness of that reaction.

True

Biochemical reactions are more likely to proceed if the reaction has an increase in enthalpy (🔺H) and a decrease in entropy (🔺S).

False

All prokaryotic cells are about 1/10 the size of an average eukaryotic cell or smaller.

False

All cells have kept the same general patterns of metabolism, a very similar genetic code and the same monomers or residues.

True

Eukaryotes include plants, animals and bacteria.

False

The only reason phages are not considered to be cells is because they do not contain a plasma membrane.

False

Diffusion is an adequate means of distributing nutrients in prokaryotic cytoplasm because they have more surface area than volume compared to most eukaryotes.

True

Eukaryotic cells are distinguished from prokaryotes by their usually larger size, a complex cytoskeleton and membrane-bounded organelles.

True

Chloroplasts are organelles found in plants, algae and some protists and are the site of photosynthesis.

True

The endoplasmic reticulum is the major site of RNA synthesis and the site of assembly of ribosomes.

False

The nuclear envelope is a membrane that surrounds the nucleus and is continuous with the endoplasmic reticulum.

True

Ribosomes on the surface of rough endoplasmic reticulum are the site of ATP synthesis.

False

The Golgi apparatus consists of flattened, fluid-filled, membranous sacs and is responsible for chemical modification and sorting of some biomolecules.

True

Mitochondria are the main sites of energy transduction in aerobic eukaryotic cells.

True

The mitochondria and Golgi apparatus are two organelles which originated from bacteria and were incorporated into eukaryotic cells via symbiosis.

False

In an animal cell, DNA can be found only in the nucleus.

False

Actin has been shown to be one of the most evolutionarily conserved proteins. It is present in all eukaryotic cells and frequently is the most abundant protein in the cell.

True

The mitotic spindles are formed from microtubule proteins.

True

The filament fibers in the cytoskeleton are composed primarily of carbohydrate molecules.

False

The diffusion of large molecules such as enzymes is significantly showed by the presence of the cytoskeleton.

True

In eukaryotic cells lysosomes are specialized digestive vesicles with a highly acidic interior.

True

The process of cell division that occurs in the tissues is called mitosis.

True

Photosynthesis involves capturing energy from light that is then used to drive the formation of carbohydrates from carbon dioxide and water.

True

The chemical name for ATP is alanine triphosphate.

False

Absolute zero is equal to 0ºC.

False

One Angstrom is equal to 1 × 10^-10 meters.

True

Which is not a proper way to form a hydrogen bond? (The symbol ʺRʺ represents a general organic group. The hydrogen bonding is represented by dashed lines.)

Which statement does not explain the polarity of water?

The oxygen in water has sp2 hybrid orbitals.

Which substance do you expect to be most soluble in water?

ammonia, NH3

What is the maximum number of hydrogen bonds that one water molecule can have with neighboring water molecules?

4

The abundance of water in the cells and tissues helps to minimize temperature fluctuations. This is due to what property of water?

specific heat

Compounds that ionize when dissolved in water are called __________.

electrolytes

Electrolytes dissolve readily in water because

water molecules can cluster about cations and anions.

A molecule or ion is said to be hydrated when it __________

is surrounded by water molecules

Which would you expect to be more soluble in water?

I

Solutes diffuse more slowly in cytoplasm than in water because of

the presence of many crowded molecules in the cytoplasm.

The __________ pressure is the pressure required to prevent the flow of solvent through a solvent-permeable membrane that separates two solutions of different solute concentration.

osmotic

Which is true about the solubility of electrolytes in water?

They often form super-saturated aqueous solutions.

What is the difference between a particle being hydrated versus being solvated?

A hydrated particle is surrounded by a shell of water. A solvated molecule is surrounded by a shell of solvent molecules, not necessarily water.

The osmotic pressure of an aqueous solution depends on

the molar concentration of solute.

The osmotic pressure of a 0.010M sucrose (C12H22O11) solution at 25ºC is 0.24 atm. How does the osmotic pressure of a 0.010M glucose (C6H12O6) solution at 25ºC compare to this? Note that neither solute is volatile or ionizable.

The osmotic pressures are equal because the solutions have the same molar concentration.

Oil and water do not form a solution due to __________

the hydrophobic effect, the inability of oil to hydrogen bond with water, and the nonpolarity of oil

Molecules that are both hydrophobic and hydrophilic are _________

amphipathic

Which molecule or ion below is amphipathic?

CH3(CH2)14COO-

Which statement explains the cleaning action of soap on greasy dishes?

The grease is trapped inside the hydrophobic interior of micelles made of soap molecules.

Some ions such as thiocyanate that are poorly solvated in water and can enhance the solubility of nonpolar compounds in water by disordering the water molecules are called __________.

chaotropes

Which of the following is NOT a ʺweakʺ interaction?

disulfide bonds

Which of the following weak interactions is not an electrostatic interaction?

hydrophobic interactions

Which of these noncovalent forces in biological systems is usually the strongest?

hydrogen bonds

Hydrogen bonds can occur when hydrogen is covalently bonded to atoms like nitrogen and oxygen. What property of nitrogen and oxygen is important for this?

electronegativity

Attractions of oppositely charged functional groups of proteins are sometimes called __________.

salt bridges or ion pairing

Which is true about hydrogen bonding for biological molecules?

(1) Hydrogen bonds are strong enough to confer structural stability, for example in DNA. (2) Hydrogen bonds are weak enough to be easily broken (weaker than covalent bonds). (3) They contribute to the water solubility of many macromolecules.

London dispersion forces are attractive forces that arise due to

infinitesimal dipoles generated by the constant random motion of electrons.

The aggregation of nonpolar molecules or groups in water is thermodynamically due to the

increased entropy of the water molecules.

Water clustered about nonpolar molecules contribute to hydrophobic interactions because

Their number is minimized to increase the total entropy of water.

The three dimensional structure of most proteins is largely determined by

weak noncovalent interactions.

The oxygen atom of water is nucleophilic because

it has two unshared pair of electrons.

Water is a nucleophile, yet it does not usually hydrolyze macromolecules in cells because

(1) covalent bonds linking macromolecule subunits are stable at cell pH. (2) covalent bonds linking macromolecule subunits are stable at cell temperatures.

Enzymes which condense subunits of macromolecules during their synthesis usually

exclude water from the active site.

The ion-product constant for water, Kw, is

1 × 10^-14 M²

In pure water hydronium ions are formed by __________ attack of oxygen on a proton in an adjacent water molecule.

nucleophilic

Pure water has a concentration of

55M.

Which statement best characterizes the distribution of charge in the hydronium ion, H3O+?

The positive charge is distributed over all of the atoms in the ion.

Which statement below is true about the relative lifetime of a hydrogen bond, compared to the rate of waterʹs ionization to hydroxide ions and hydronium ions?

The lifetime of a water molecule before it is ionized is about 109 greater than the lifetime of a hydrogen bond.

The self-ionization of water is __________.

a biomolecular reaction between two water molecules to yield H3O+ and OH-

How does the ion-product of water, Kw, relate to the equilibrium constant, Keq, for the dissociation reaction of water?

Kw is found by multiplying Keq by the concentration of water.