Genetics Test 1-

Name three post-transcriptional modifications often seen in the maturation of mRNA in eukaryotes.

1.) 5' capping 2.) 3' poly-A tail addition 3.) Splicing

Name two classical experiments that demonstrated that DNA is the genetic material.

1.) Griffith through Avery 2.) Hershey Chase

List two major differences between RNA and DNA at the level of the nucleotide.

1.) ribose in RNA, deoxyribose in DNA 2.) uracil in RNA replaces thymine in DNA

When and in which journal did Watson and Crick publish their now-famous paper entitled "Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" ?

1953, Nature

DNA polymerase III adds nucleotides to the ____ end of the ____

3', RNA primer

If 15 percent of the nitrogenous bases in a sample of DNA from a particular organism is thymine, what percentage should be cytosine?

35 percent A+C=G+T=100% 2x+2(15)=100%

New DNA is always synthesized in the _____ direction.

5'-3'

Given that the origin of replication is fixed in *E* *coli*, what signals the location of the origin?

A region called *oriC*, which consists of about 250 base pairs characterized by repeating sequences of 9 and 13 bases (9mers and 13mers).

In an analysis of the nucleotide composition of double-stranded DNA to see which bases are equivalent in concentration, which of the following would be true: A=C A=G and C=T A+C=G+T A+T=G+C

A+C=G+T

What is the initiator triplet in both prokaryotes and eukaryotes? What amino acid is recruited by this triplet?

AUG, methionine

_____ is a section of RNA that is removed during RNA processing.

An Intron

A ____ is an infecting virus.

Bacteriophage

_____ means that from the point of initiation, replication occurs in both directions along the DNA.

Bidirectional

During the polymerization of nucleic acids, covalent bonds are formed between neighboring nucleotides. Which carbons are involved in such bonds?

C-3' and C-5'

What is the name given to the three bases in mRNA that bind to the anticodon of tRNA to specify an amino acid placement in a protein?

Codon

List at least 4 enzymes known to be involved in the replication of DNA in bacteria:

DNA polymerase I, DNA polymerase III, ligase, RNA primase, helicase, gyrase

*Reverse* *transcriptase* is an enzyme found in association with retroviral activity. It has the property of synthesis of ____ from an ____ template.

DNA, RNA

P32 tracks _____ and S35 tracks _____.

DNA, protein

Central Dogma of molecular biology....

DNA---> RNA---> Protein

Experiments conducted in the 1920's by Griffith involving the bacterium *Diplococcus* *pneumoniae* demonstrated that a substance from one bacterial strain could genetically transform other bacterial strains. What was the name of the substance capable of such transformation?

Deoxyribonucleic acid; Avery et al (1944)

What protein is responsible for the initial step in unwinding the DNA helix during replication of the bacterial chromosome?

DnaA

DNA is best described as (double/single) stranded, (parallel,antiparallel), and having the nucleotide composition of (A+T)/(C+G)=____ and (A+G)/(C+T)=____

Double-stranded, antiparallel, (A+T)/(C+G)= variable (A+G)/(C+T)= 1.0

A 3' poly-A tail and a 5' cap are common components of prokaryotic RNA's. T/F

False

An exonuclease is involved in removing bases sequentially from one end of DNA or the other. T/F

False

Avery et al. (1944) determined that DNA is the genetic material in bacteriophage? T/F

False

Bacteria are dependent on telomerase to complete synthesis of their chromosome ends. T/F

False

DNA replicates conservatively, which means that one of the two daughter double helices is "old" and the other is "new." T/F

False

Deoxyribonuclease is an enzyme that adds 3'-hydroxyl groups to RNA? T/F

False

During replication, primase adds a DNA primer to RNA. T/F

False

Hershey and Chase used labeled DNA and protein to determine that DNA is the genetic material in bacteria? T/F

False

In ligase-deficient strains of *E* *coli*, DNA and chromosomal replication is unaltered because ligase is not involved in DNA replication. T/F

False

Messenger RNA is usually polycistronic in eukaryotes. T/F

False

RNA processing occurs when amino acids are removed from nascent proteins. T/F

False

The transforming principle discovered by Griffith is RNA? T/F

False

Transcription factors function to help move ribosomes along the mRNA. T/F

False

When one speaks of a 5' cap, one is describing the addition of a base, usually thymine, to the 5' end of a completed peptide. T/F

False

If the G-C content of a DNA molecule is 60 percent, what are the molar percentages of the four bases (G,C,T,A)?

G=30% C=30% A=20% T=20%

What enzyme is responsible for dealing with the supercoils in the DNA during replication?

Gyrase

What enzyme functions to unwind the DNA double helix?

Helicase

In the structure of double-stranded DNA, what kinds of bonds hold one complementary strand to the other?

Hydrogen

Describe the rate of DNA replication in prokaryotes and eukaryotes.

In *E* *coli*, approximately 100 kb are added per minute, while in eukaryotes only 0.5 to 5 kb are added per minute.

Describe a difference between the RNA polymerases of eukaryotes and that of prokaryotes.

In eukaryotes, three polymerases (I, II, III) have been identified while only one has been described in prokaryotes.

Introns are known to contain termination codons (UAA, UGA, or UAG), yet these codons do not interrupt the coding of a particular protein. Why?

Introns are removed from mRNA before translation

The ____ is the side of the replication fork where synthesis is discontinuous.

Lagging strand

What enzyme joins the nick (gap between Okazaki fragments) found on the lagging strand?

Ligase

Meselson and Stahl determined that DNA replication in *E* *coli* is semiconservative. What additive did they initially supply to the medium in order to distinguish the "new" from "old" DNA?

Nitrogen 15 (N with 15 superscript on left-hand side)

____ are short, single-stranded stretches of DNA on the lagging strand.

Okazaki fragments

What is polycistronic mRNA?

Policystronic mRNA is seen primarily among prokaryotes where one mRNA carries coding information and internal punctuation for the translation of more than one protein.

During DNA replication, what is the function of primase?

RNA primase provides a free 3'-OH upon which DNA polymerization depends.

Referring to the genetic code, what is meant by "wobble"?

Relaxed pairing specificities in the third-base position of a codon.

As unwinding of the helix occurs during DNA replication, tension is created ahead of the replication fork. Describe the nature of this tension and state the manner in which this tension is resolved (what enzyme)?

Supercoiling, DNA gyrase

When considering the initiation of transcription, one often finds consensus sequences located in the region of DNA where RNA polymerase(s) bind. Two common consensus sequences are ____ and ____.

TATA and CAAT

Regarding the efficient initiation of transcription by RNA polymerase II in eukaryotes, what specific "upstream" signals appear to be involved?

TATA and CAAT base sequences and enhancers

What does is mean to say that double-stranded nucleic acids are anti-parallel?

The C-5' to C-3' orientations run in opposite directions.

In the classic experiment conducted by Hershey and Chase, why was the pellet radioactive in the centrifuge tube that contained bacteria with viruses, which had been grown on medium containing Phosphorus 32?

The bacteria were in the pellet, and many contained the radioactive viral DNA.

Describe a somewhat extraordinary finding related to the *Tetrahymena* *telomerase* enzyme.

The enzyme contains a short piece of RNA that is essential for its catalytic activity.

DNA replication *in* *vivo* requires a primer with a free 3' end. What molecular species provides this 3' end, and how is it provided?

The free 3' end is provided by an RNA primer, which is provided by the enzymatic activity of RNA primase.

It has been recently determined that the gene for Duchenne muscular dystrophy (DMD) is over 2000 kb (kilobases) in length; however, the mRNA produced by this gene is only about 17 kb long. What is the likely cause of this discrepancy?

The introns have been spliced out during mRNA processing

Describe how the sigma subunit (factor ?) of *E* *coli* RNA polymerase participates in translation.

The sigma subunit (factor ?) may give specificity to the RNA polymerase and play a regulatory function. It may be involved in the recognition of initiation sites or promoters.

What is meant by the term "antiparallel?"

The two chains in a double-stranded nucleic acid are connected in opposite directions in terms of the 5'-3' orientations.

The genetic code is said to be triplet, meaning that....

There are 3 bases in mRNA that code for an amino acid.

The altering of a phenotype is a result of _____.

Transformation

Briefly define transformation and describe the relationship between the phenomenon of transformation and the discovery that DNA is the genetic material in bacteria.

Transformation is the process whereby one organism is genetically altered by exposure to DNA from another organism. Since DNA can carry heritable traits from one organism to another, it must be the genetic material.

When scientists were attempting to determine the structure of the genetic code, Crick and co-workers found that when three base additions or three base deletions occurred in a single gene, the wild-type phenotype was sometimes restored. These data supported the hypothesis that the code is _____.

Triplet

*DNA* *polymerase* *III* is an enzyme that adds nucleotides to the 3' end of each growing DNA strand. T/F

True

A characteristic of aging cells is that their telomeres become shorter. T/F

True

An intron is a section of RNA that gets spliced out. T/F

True

DNA has no sulfur, and proteins have no phosphorus? T/F

True

DNA replication occurs in the 5' to 3' direction; that is, new nucleoside triphosphates are added to the 3' end. T/F

True

DNA strand replication begins with an RNA primer. T/F

True

G and C are present in both DNA and RNA? T/F

True

In 1953, Watson and Crick published a paper that described the structure of DNA? T/F

True

In RNA, uracil is present instead of thymine (in DNA)? T/F

True

In general, DNA replicates semiconservatively and bidirectionally. T/F

True

In ribose, the 2'C has an OH attached to it? T/F

True

Telomerase is an RNA-containing enzyme that adds telomeric DNA sequences onto the ends of linear chromosomes. T/F

True

The code is non-overlapping, meaning that, assuming "standard translation," a given base participates in the specification of one an only one amino acid. T/F

True

The triplet AUG is commonly used as a start codon during translation. T/F

True

When considering the structure of DNA, we would say that complementary strands are antiparallel? T/F

True

The genetic code is fairly consistent among all organisms. The term often used to describe such consistency in the code is____.

Universal

The term ____ means to "cause disease."

Virulent

The Avery et al. (1944) contribution to an understanding of molecular biology was ________.

a demonstration that DNA is the genetic material in *Diplococci*

Name the purines in DNA

adenine and guanine

The basic structure of a nucleotide includes the following components:____, ____, and ____

base, sugar, and phosphate

Replication in the chromosome of *E* *coli* is best described as _____ and ____

bidirectional and fixed point of initiation

DNA replication in prokaryotes is said to be _____, _____, and have a _____ point of initiation

bidirectional, semiconservative, fixed

When examining the genetic code, it is apparent that there can be more than one ____ for a particular _____.

codon, amino acid

Name the pyramidines in DNA

cytosine and thymine

What primary ingredients, coupled with DNA polymerase I, are needed for the *in* *vitro* synthesis of DNA?

dNTP, DNA template, primer DNA or RNA, Mg(2+). Appropriate buffering, temperature, and salt concentrations might be considered "secondary" ingredients.

When comparing the base sequences of related genes from different species, it is likely to find that corresponding _____ are usually conserved, but the sequences of _____ are much less well conserved.

exons, introns

A class of mutations that results in multiple contiguous (side-by-side) amino acid changes in proteins is probably caused by this type of mutation: ______

frameshift

The relationship between codon and anticodon can be characterized as involving _____ bonding and ______ base pairing in typical antiparallel fashion.

hydrogen, complementary

DNA polymerase I is thought to add nucleotides _____

in place of the primer RNA after it is removed.

The relationship between a gene and a mRNA is that _____ are made from ______.

mRNA's, genes

The finding that virtually all organisms use the same genetic code provides the basis for declaring that the code is universal. Name exceptions to such universality.

mitochondrial DNA, *Mycoplasma* *capricolum*, some protozoans.

Three post-transcriptional modifications often seen in the maturation of mRNA in eukaryotes occur in which cellular organelle?

nucleus

The classic Hershey and Chase (1952) experiment that offered evidence in support of DNA being the genetic material in bacteriophages made use of the following labeled components: ____, and ____.

phosphorus and sulfur

In eukaryotes, what factors or elements (cis and trans) encourage the specific association of RNA polymerase(s) to a specific region of DNA?

promoters, enhancers, and transcription factors.

DNA replication *in* *vivo* is best described as _____

semidiscontinuous

How is DNA used in the central dogma of molecular biology?

storage and expression of information, variation through mutation.

Of the following three types of nucleic acids: --DNA, mRNA, and tRNA-- which is most likely to contain modified bases?

tRNA

Structures located at the ends of eukaryotic chromosomes are called _____

telomeres

The discontinuous aspect of replication of DNA *in* *vivo* is caused by:

the 5'-3' polarity restriction.

A base at the first position of an anticodon on the tRNA would pair with the base at the ____ position of the tRNA.

third

What is the name of the precursor molecule (subunit) used in nucleic acid synthesis?

triphosphonucleoside