Mastering Biology for Exam 2

Which of the following descriptions best fits the class of molecules known as nucleotides?

a nitrogenous base, a phosphate group, and a sugar

If a DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases, how many guanine bases does it contain?

75 (100 nucleotide pairs are a total of 200 nucleotides. Because of base pairing, if there are 25 adenine there must also be 25 thymine. This leaves 200-50 = 150 nucleotides to be divided evenly between guanine and cytosine.)

In a nucleosome, the DNA is wrapped around

histones

you can recognize the process of pinocytosis when _____.

the cell is engulfing extracellular fluid

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.

1' ... 5'

If one strand of a DNA molecule has the sequence of bases 5-ATTGCA-3, the mRNA synthesized following the template will be ________.

3-UAACGU-5

Nucleic acids are assembled in the _____ direction.

5' to 3'

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?

5´-ATGC-3´ with 5´-GCAT-3´

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

8% (In this example cytosine makes up 42%, which means that guanine also makes up 42%. So 84% of the DNA is a G-C base pair. This leaves 16% for the A-T base pair: 8% adenine and 8% thymine.)

In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?

A + G = C + T

Which molecule is a nucleotide?

ATP

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

DNA in both daughter cells would be radioactive.

The central rule of molecular biology states that ________.

DNA is transcribed into RNA, which is translated into protein

Which of these is a difference between a DNA and an RNA molecule?

DNA is usually double-stranded, whereas RNA is usually single-stranded.

Which of the following investigators was (were) responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?

Erwin Chargaff

Who conducted the X-ray diffraction studies that were key to the discovery of the structure of DNA?

Franklin

Which of the following molecular characteristics cause histones to bind tightly to DNA?

Histones are positively charged, and DNA is negatively charged.

Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine, and cytosine forms hydrogen bonds with guanine. What is the significance of the structural arrangement?

It permits complementary base pairing.

which of the following would likely diffuse through the lipid bilayer of a plasma membrane most rapidly?

O2

If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?

RNA

Which of the following statements about the 5 end of a polynucleotide strand of RNA is correct?

The 5 end has a phosphate group attached to the number 5 carbon of ribose.

What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?

The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand

If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?

The cell's DNA could not be packed into its nucleus.

DNA is a self-replicating molecule. What accounts for this important property of DNA?

The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C.

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes?

The phosphodiester linkages of the polynucleotide backbone would be broken.

Does the distribution of bases in sea urchin DNA and salmon DNA follow Chargaff's rules?

Yes, because the %A approximately equals the %T and the %G approximately equals the %C in both species.

Calculate the average percentage for each base in your completed table. Do Chargaff's equivalence rules still hold true when you consider those six species together?

Yes, the average for A approximately equals the average for T, and the average for G approximately equals the average for C

the force driving simple diffusion is ________, while the energy source for active transport is ________.

a concentration gradient; ATP hydrolysis

When nucleotides polymerize to form a nucleic acid _____.

a covalent bond forms between the sugar of one nucleotide and the phosphate of a second

in which of the following environments would there be the greatest need for osmoregulation?

a salmon moving from a river into an ocean

what kinds of molecules pass through a cell membrane most easily?

small and hydrophobic

if the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?

active transport

active and passive transport of solutes across a membrane typically differ in which of the following ways?

active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.

which of the following molecules dramatically increases the rate of diffusion of water across cell membranes?

aquaporins

which of the following statements is TRUE with regard to this animation?

both sodium and potassium ions are transported against their concentration gradients.

according to the fluid mosaic model of cell membranes, phospholipids _____.

can move laterally along the plane of the membrane

Identify three possible components of a DNA nucleotide.

deoxyribose, phosphate group, thymine

One of the primary functions of RNA molecules is to _____.

function in the synthesis of proteins

The two strands of a DNA double helix are held together by _____ that form between pairs of nitrogenous bases.

hydrogen bonds

which of the following statements correctly describes osmosis?

in osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.

How does DNA (deoxyribonucleic acid) encode information?

in the sequence of nucleotides.

the membranes of winter wheat are able to remain fluid when it is extremely cold by ________.

increasing the proportion of unsaturated phospholipids in the membrane

endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles

according to the fluid mosaic model, a membrane ________

is composed of a fluid bilayer of phospholipids with embedded amphipathic proteins

celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.

is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

which of the following statements describes a characteristic feature of a carrier protein in a plasma membrane?

it exhibits specificity for a particular type of molecule.

The building blocks or monomers of nucleic acid molecules are called _____.

nucleotides

what name is given to the process by which water crosses a selectively permeable membrane?

osmosis

select the correct statement about osmosis.

osmosis is the diffusion of water molecules across a selectively permeable membrane.

which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.

oxygen, carbon dioxide, lipids, and water NOT ions, proteins, sucrose

a white blood cell engulfing a bacterium is an example of _____.

phagocytosis

an organism with a cell wall would most likely be unable to take in materials through _____.

phagocytosis

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?

sequence of bases

which of the following are least likely to diffuse through the phospholipid bilayer of a cell membrane?

small ions

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?

the 3' OH

what will happen to a red blood cell (RBC), which has an internal ion content of about 0.9%, if it is placed into a beaker of pure water?

the cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

Which of the following statements defines a genome?

the complete set of an organism's genes and other DNA sequences

in the U-tube experiment illustrated above, which of the following statements correctly describes side B at equilibrium?

the concentration of NaCl will increase, the concentration of glucose will decrease, and the water level will increase.

which statement is correct?

the contents of a red blood cell are hyperosmotic to distilled water.

which of the following statements is a reasonable explanation for why unsaturated fatty acids help keep a membrane more fluid at lower temperatures?

the double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.

In an RNA sample, ________.

the number of purine may or may not equal the number of and pyrimidine

which of the following statements about osmosis is correct?

the presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis

which factors affect the rate of osmotic movement of water?

the rate of osmosis increases with increasing differences in solute concentrations between two solutions separated by a selectively permeable membrane.

why are lipids and proteins free to move laterally in membranes?

there are only weak hydrophobic interactions in the interior of the membrane.

the permeability of a biological membrane to a specific polar solute depends primarily on which of the following?

the types of transport proteins in the membrane

when a cell is in equilibrium with its environment, which of the following processes occurs for substances that can diffuse through the plasma membrane?

there is random movement of substances into and out of the cell.

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine... cytosine

in facilitated diffusion, what is the role of the transport protein?

transport proteins provide a hydrophilic route for the solute to cross the membrane.

Which of the following is a major difference between RNA and DNA?

type of sugar