Molecular Biology: DNA And RNA

Question 0

______ are derivatives of purines and pyrimidinesthat have a sugar linked to a ring nitrogen

Answer 0

Nucleosides

Question 1

_______—the monomer units or building blocks ofnucleic acids—serve multiple additional functions.

Answer 1

Nucleotides

Question 2

The sugar inribonucleosides is D-ribose, and in deoxyribonucleo-sides it is 2-deoxy-D-ribose. The link the base is called ____.

Answer 2

beta-N-glycosidic bond

Question 3

Conversion of purines, their ribonucleosides, and theirdeoxyribonucleosides to mononucleotides involves so-called “______” that require far less energythan de novo synthesis.

Answer 3

salvage reactions

Question 4

Reduction of the 2′-hydroxyl of purine and pyrimidineribonucleotides, catalyzed by the ______ forms deoxyribonu-cleoside diphosphates (dNDPs).

Answer 4

ribonucleotide re-ductase complex

Question 5

The catalyst for the initial reaction of the ____ syntheis is cytosolic carbamoylphosphate synthase II, a different enzyme from the mi-
tochondrial carbamoyl phosphate synthase I of urea syn-thesis

Answer 5

Pyrimidine

Question 6

__________, an overproduction hyper-uricemia characterized by frequent episodes of uric acidlithiasis and a bizarre syndrome of self-mutilation, re-flects a defect in hypoxanthine-guanine phosphoribo-syl transferase, an enzyme of purine salvage

Answer 6

Lesch-Nyhan syndrome

Question 7

The two strands of the double-helicalmolecule, each of which possesses a polarity, are _______; ie, one strand runs in the 5′ to 3′ directionand the other in the 3′ to 5′ direction

Answer 7

an-tiparallel

Question 8

The strands of a given molecule of DNA separateover a temperature range. The midpoint is called the _____. It is influenced bythe base composition of the DNA and by the salt con-centration of the solution. DNA rich in G–C pairs,which have three hydrogen bonds, melts at a higher tem-perature than that rich in A–T pairs, which have two hy-drogen bonds.

Answer 8

melting temperature, or Tm

Question 9

______ is a polymer of purine andpyrimidine ribonucleotides linked together by 3′,5′-phosphodiester bridges analogous to those in DNA

Answer 9

Ribonucleic acid (RNA)

Question 10

cytoplasmic RNA molecules that serve as tem-plates for protein synthesis (ie, that transfer genetic in-formation from DNA to the protein-synthesizing ma-chinery) are designated _____

Answer 10

messenger RNAs, or mRNAs

Question 11

have structural roles wherein they contribute to the formation and function of ribosomes (theorganellar machinery for protein synthesis)

Answer 11

rRNA

Question 12

In all eukaryotic cells there are _____ species that are not directly involved in pro-tein synthesis but play pivotal roles in RNA processing.These relatively small molecules vary in size from 90 toabout 300 nucleotides

Answer 12

small nuclear RNA(snRNA)

Question 13

Although some RNAviruses never have their information transcribed into aDNA molecule, many animal RNA viruses—specifi-cally, the retroviruses (the HIV virus, for example)—aretranscribed by an RNA-dependent DNA polymerase,the so-called ________, to produce a dou-ble-stranded DNA copy of their RNA genome.

Answer 13

reverse transcriptase

Inmany cases, the resulting double-stranded DNA tran-script is integrated into the host genome and subse-quently serves as a template for gene expression andfrom which new viral RNA genomes can be tran-scribed.

Question 14

In mammalian cells, including cells of humans, themRNA molecules present in the cytoplasm are not theRNA products immediately synthesized from the DNAtemplate but must be formed by processing from a pre-cursor molecule before entering the cytoplasm. Thus,in mammalian nuclei, the immediate products of genetranscription constitute a fourth class of RNA mole-cules. These nuclear RNA molecules are very heteroge-neous in size and are quite large. The ________ may have a molecu-lar weight in excess of 10 raised to 7th power, whereas the molecularweight of mRNA molecules is generally less than 2 ×10 raised to the 6th

Answer 14

heterogeneousnuclear RNA (hnRNA) molecules

Question 15

In active protein synthesis, many ribosomesare associated with an mRNA molecule in an assemblycalled the____

Answer 15

polysome

Question 16

Some nucleases are capable of hydrolyzing a nu-cleotide only when it is present at a terminal of a mole-cule; these are referred to as ____

Answer 16

exonucleases.

Question 17

Most coding sequences for a singlemRNA are interrupted in the genome (and thus in theprimary transcript) by at least one—and in some casesas many as 50—noncoding intervening sequences (in-trons). In most cases, the introns are much longer thanthe continuous coding regions ____

Answer 17

(exons).

Question 18

Human mitochondria contain two to ten copies of asmall circular double-stranded DNA molecule thatmakes up approximately ___ of total cellular DNA.

Answer 18

1 percent

Question 19

An alteration in the sequence of purine and pyrimidinebases in a gene due to a change—a removal or an inser-tion—of one or more bases may result in an alteredgene product. Such alteration in the genetic material re-sults in a_____

Answer 19

mutation

Question 20

Deoxynucleotide polymerization

Answer 20

DNA polymerases

Question 21

Processive unwinding of DNA

Answer 21

Helicases

Question 22

Relieve torsional strain that results from helicase-induced unwinding

Answer 22

Topoisomerases

Question 23

Initiates synthesis of RNA primers

Answer 23

DNA primase

Question 24

Prevent premature reannealing of dsDNA

Answer 24

Single-strand binding proteins

Question 25

Seals the single strand nick between the nascent chain and Okazaki frag-
ments on lagging strand

Answer 25

DNA ligase

Question 26

On the leading (for-ward) strand, the DNA is synthesized continuously.On the lagging (retrograde) strand, the DNA is syn-thesized in short (1–5 kb;) fragments,the so-called ______

Answer 26

Okazaki fragments

Question 27

Themobile complex between helicase and primase has beencalled a______

Answer 27

primosome

Question 28

________ molecules en-gage in DNA replication. These share three importantproperties: (1) chain elongation, (2) processivity, and(3) proofreading.

Answer 28

DNA polymerase

Question 29

In mammals, aftermany Okazaki fragments are generated, the replicationcomplex begins to remove the RNA primers, to fill inthe gaps left by their removal with the proper base-paired deoxynucleotide, and then to seal the fragments of newly synthesized DNA by enzymes referred to as ____

Answer 29

DNA ligases.

Question 30

The nicking-resealing enzymes are called ______

Answer 30

DNAtopoisomerases.

Question 31

The _____ function is provided by specificenzymes that introduce “nicks” in one strand of theunwinding double helix

Answer 31

swivel

Question 32

In animal cells, including human cells, the replicationof the DNA genome occurs only at a specified timeduring the life span of the cell. This period is referred toas the _______.

Answer 32

synthetic or S phase

Question 33

Termination of the synthesis of the RNA moleculein bacteria is signaled by a sequence in the templatestrand of the DNA molecule—a signal that is recog-nized by a termination protein, the ______

Answer 33

rho (ρ) factor

Question 34

_____ are RNA molecules with catalytic activity.

Answer 34

Ribozymes

Question 35

There may be no detectable effect because of thedegeneracy of the code. This would be more likely ifthe changed base in the mRNA molecule were to be atthe third nucleotide of a codon; such mutations areoften referred to as ________

Answer 35

silent mutations

Question 36

A _________ will occur when a differentamino acid is incorporated at the corresponding site inthe protein molecule. This mistaken amino acid—ormissense, depending upon its location in the specificprotein—might be acceptable, partially acceptable, orunacceptable to the function of that protein molecule.

Answer 36

missense effect

Question 37

A partially acceptable missense mutation (Figure 38–4,center) is best exemplified by _____

Answer 37

hemoglobin S

Question 38

An unacceptable missense mutation (Figure 38–4, bot-tom) in a hemoglobin gene generates a nonfunctioninghemoglobin molecule. For example, the ______ mutations generate molecules that allow the Fe2+ of theheme moiety to be oxidized to Fe3+, producing methe-moglobin. Methemoglobin cannot transport oxygen.

Answer 38

hemoglobin M