Chapter 17

Question 1

Faulty gene

Answer 1

Gene that contains incorrect information.

Question 2

The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins and of RNA molecules involved in protein synthesis. In other words, proteins are the link between genotype and phenotype.

Answer 2

True

Question 3

One gene-one enzyme hypothesis

Answer 3

Initially proposed by Archibald Garrod and dubbed by Beadly and Tatum, states that the function of a gene is to dictate the production of a specific enzyme.

Question 4

One gene-one polypeptide hypothesis

Answer 4

States that each gene dictates the production of a single polypeptide chain.

Question 5

Getting from DNA to protein requires two major stages:

Answer 5

Transcription and translation

Question 6

Transcription

Answer 6

Is the synthesis of RNA using information in the DNA.

Question 7

Messenger RNA (mRNA)

Answer 7

A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.

Question 8

Translation

Answer 8

The synthesis of a polypeptide using the information in the mRNA.

Question 9

The sites of translation:

Answer 9

Ribosomes

Question 10

In eukaryotic cells, transcription occurs in the…

Answer 10

Nucleus

Question 11

The transcription of a protein-coding eukaryotic gene results in pre-mRNA, and further processing yields the finished mRNA.

Answer 11

True

Question 12

Primary transcript

Answer 12

An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.

Question 13

Cells are governed by a molecular chain of command with a directional flow of genetic information, called the central dogma; shown here:

Answer 13

DNA —> RNA —> Protein

Question 14

Triplets of nucleotide bases are the smallest units of uniform length that can code for all the amino acids.

Answer 14

True

Question 15

Triplet code

Answer 15

The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three nucleotide words.

Question 16

For each gene, only one of the two DNA strands is transcribed; this strand is called the…

Answer 16

Template strand because it provides the pattern, or template, for the sequence of nucleotides in an RNA transcript.

Question 17

Like a new strand of DNA, the RNA molecule is synthesized in an antiparallel direction to the template strand of DNA.

Answer 17

True

Question 18

Codons

Answer 18

mRNA nucleotide triplets. Customarily written in the 5’ —> 3’ direction.

Question 19

The term codon is also used for the DNA nucleotide triplets along the non template strand.

Answer 19

True

Question 20

Coding strand

Answer 20

The non template DNA strand.

Question 21

Because codons are nucleotide triplets, the number of nucleotides making up a genetic message must be three times the number of amino acids in the protein product.

Answer 21

True

Question 22

61 of the 64 triplets code for amino acids. The three codons that do not designate amino acids are “stop” signals, or termination codons, marking the end of translation.

Answer 22

True

Question 23

Codon AUG

Answer 23

Has a dual function: it codes for the amino acid methionine (Met) and also functions as a “start” signal, or initiation codon.

Question 24

Reading frame

Answer 24

On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.

Question 25

RNA polymerase

Answer 25

An enzyme that pries the two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, thus elongating the RNA polynucleotide.

Question 26

RNA polymerases can assemble a polynucleotide only in its 5’ —> 3’ direction.

Answer 26

True

Question 27

RNA polymerases are able to start a chain from scratch; they don’t need a primer.

Answer 27

True

Question 28

Promoter

Answer 28

The DNA sequence where RNA polymerase attaches and initiates transcription.

Question 29

In bacteria, the sequence that signals the end of transcription is called the ____

Answer 29

Terminator

Question 30

Molecular biologists refer to the direction of transcription as “downstream” and the other direction as “upstream”.

Answer 30

True

Question 31

Transcription unit

Answer 31

The stretch of DNA downstream from the promoter that is transcribed into an RNA molecule.

Question 32

RNA polymerase II

Answer 32

The RNA polymerase used for pre-mRNA synthesis.

Question 33

Three stages of transcription

Answer 33

Initiation, elongation, and termination of the RNA chain.

Question 34

Start point

Answer 34

The nucleotide where RNA synthesis actually begins.
-Is part of the promoter.

Question 35

Transcription factors

Answer 35

Mediate the binding of RNA polymerase and the initiation of transcription.
-Present only in eukaryotes.

Question 36

Only after transcription factors are attached to the promoter does RNA polymerase II bind to it.

Answer 36

True

Question 37

Transcription initiation complex

Answer 37

The whole complex of transcription factors and RNA polymerase II bound to the promoter.

Question 38

TATA box

Answer 38

A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.

Question 39

Transcription progresses at a rate of about ________ nucleotides per second in eukaryotes.

Answer 39

40

Question 40

Which sequence marks the end of mRNA transcription in eukaryotes?

Answer 40

The polyadenylation sequence (AAUAAA)

Question 41

RNA processing produces…

Answer 41

An mRNA molecule ready for translation.

Question 42

5’ cap

Answer 42

A modified form of guanine (G) nucleotide added onto the 5’ end after transcription of the first 20-40 nucleotides.

Question 43

The 3’ end of the pre-mRNA molecule is also modified before the mRNA exits the nucleus.

Answer 43

True

Question 44

poly-A tail

Answer 44

An additional 50-250 adenine nucleotides added to the 3’ end of the mRNA in RNA processing.

Question 45

The 5’ cap and the poly-A tail share several important functions. First, they seem to facilitate the export of the mature mRNA from the nucleus. Second, they help protect the mRNA from degradation by hydrolytic enzymes. And third, they help ribosomes attach to the 5’ end of the mRNA once the mRNA reaches the cytoplasm.

Answer 45

True

Question 46

UTR

Answer 46

Untranslated region
-Function in ribosome binding

Question 47

RNA splicing

Answer 47

After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remains portions (exons).

Question 48

Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides, regions that are not translated.

Answer 48

True

Question 49

Intervening sequences or introns

Answer 49

The noncoding segments of nucleic acid that lie between coding regions.

Question 50

Exons are so named because…

Answer 50

They are eventually expressed, usually by being translated into amino acid sequences.
-Or because they exit the nucleus

Question 51

The terms intron and exon are used for both RNA sequences and the DNA sequences that encode them.

Answer 51

True

Question 52

Spliceosome

Answer 52

A large complex made of proteins and small RNAs that accomplishes the removal of introns.

Question 53

Ribozymes

Answer 53

RNA molecules that function as enzymes.

Question 54

Self-splicing

Answer 54

When the intron RNA functions as a ribozyme and catalyzes it’s own excision.

Question 55

Three properties of RNA enable some RNA molecules to function as enzymes. First, because RNA is single-stranded, a region of an RNA molecule may base-pair, in an antiparallel arrangement, with a complementary region elsewhere in the same molecule; this gives the molecule a particular three-dimensional structure. Second, like certain amino acids in an enzymatic protein, some of the bases in RNA contain functional groups that can participate in catalysis. Third, the ability of RNA to hydrogen-bond with other nucleic acid molecules (either RNA or DNA) adds a specificity to its catalytic activity.

Question 56

Alternative RNA splicing

Answer 56

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

Question 57

Because of alternative splicing, the number of different protein products an organism produces can be much greater than its number of genes.

Answer 57

True

Question 58

Proteins often have a modular architecture consisting of discrete structural and functional regions called ________

Answer 58

Domains

Question 59

In quite a few cases, different exons code for the different domains of a protein.

Answer 59

True

Question 60

Exon shuffling

Answer 60

Introns crossing over with exons potentially creating new proteins.

Question 61

Transfer RNA (tRNA)

Answer 61

-The translator
Functions to transfer amino acids to a growing polypeptide in a ribosome.

Question 62

A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long (whereas most mRNA molecules have hundreds of nucleotides).

Answer 62

True

Question 63

Anticodon

Answer 63

The particular nucleotide triplets that base-pairs to a specific mRNA codon.

Question 64

The loop extending from one end of the L-shaped tRNA includes the anticodon. From the other end of the L protrudes its 3’ end, which is the attachment site for an amino acid.

Answer 64

True

Question 65

The tRNA molecule is a translator in the sense that it can read a nucleic acid word (the mRNA codon) and interpret it as a protein word (the amino acid).

Answer 65

True

Question 66

Aminoacyl-tRNA synthetase

Answer 66

An enzyme that joins each amino acid to the appropriate tRNA.

Question 67

Linkage if a tRNA to its amino acid is an endergonic process that occurs at the expense of ATP, which loses two phosphate groups, becoming Amp (adenosine monophophate).

Answer 67

True

Question 68

Aminoacyl tRNA or charged tRNA

Answer 68

tRNA with its corresponding amino acid covalently bonded to it.

Question 69

Wobble

Answer 69

The flexible base pairing at the third codon position that allows for some tRNAs to bind to more than one codon.

Question 70

In ribosomes, a large and a small subunit join to from a functional ribosome only when attached to an mRNA molecule.

Answer 70

True

Question 71

P site

Answer 71

Peptidyl-tRNA binding site holds the tRNA carrying the growing polypeptide chain.

Question 72

A site

Answer 72

Aminoacyl-tRNA binding site) holds the tRNA carrying the next amino acid to be added to the chain.

Question 73

E site

Answer 73

Discharged tRNAs leave the ribosome from the exit site.

Question 74

As the polypeptide becomes longer, it passes through an exit tunnel in the ribosome’s large subunit.

Answer 74

True

Question 75

Translation initiation complex

Answer 75

The union of mRNA , initiator tRNA, and a small ribosomal subunit followed by the attachment of a large ribosomal subunit.

Question 76

Initiation factors

Answer 76

Are required to form the translation initiation complex.

Question 77

In the elongation stage of translation, amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain.

Answer 77

True

Question 78

Elongation factors

Answer 78

Are required in the elongation stage of translation.

Question 79

The mRNA is moved through the ribosome in one direction only, 5’ end first.

Answer 79

True

Question 80

Release factor

Answer 80

Causes the addition of a water molecule instead of an amino acid to the polypeptide chain.
-Shaped like a tRNA, instead of an aminoacyl tRNA

Question 81

Breakdown of the translation assembly requires the hydrolysis of two more GTP molecules.

Answer 81

True

Question 82

Polypeptide synthesis always begins in the cytosol as a free ribosome starts to translate an mRNA molecule. There the process continues to completion— unless the growing polypeptide itself cues the ribosome to attach to the ER.

Answer 82

True

Question 83

Signal peptide

Answer 83

Targets the protein to the ER

Question 84

Signal recognition particle (SRP)

Answer 84

A protein-RNA complex that recognizes signal peptides and functions as an escort that brings the ribosome to a receptor protein built into the ER membrane.

Question 85

Polyribosomes (polysomes)

Answer 85

Enable a cell to make many copies of a polypeptide very quickly.

Question 86

Point mutations

Answer 86

Changes in a single nucleotide pair of a gene.

Question 87

Point mutations within a gene can be divided into two general categories:

Answer 87

-Single nucleotide-pair substitutions
- nucleotide-pair insertions or deletions

Question 88

Nucleotide-pair substitution

Answer 88

The replacement of one nucleotide and its partner with another pair of nucleotides.

Question 89

Silent mutation

Answer 89

Has no observable effect on the phenotype.

Question 90

Missense mutations

Answer 90

Substitutions that change one amino acid to another.

Question 91

Nonsense mutation

Answer 91

A point mutation that changes a codon for an amino acid into a stop codon.

Question 92

Insertions and deletions

Answer 92

Are additions or losses of nucleotide pairs in a gene.

Question 93

Frameshift mutation

Answer 93

Occurs whenever the number of nucleotides inserted or deleted is not a multiple of three.

Question 94

Mutagens

Answer 94

Physical and chemical agents that interact with DNA in ways that cause mutations.