A scientist assembles a bacteriophage with the protein coat of phage T2 and the DNA of phage T4. If this composite phage were allowed to infect a bacterium, the phages produced in the host cell would have _____.
the protein and DNA of T4
Which one of the following is not true about double-stranded DNA?
Adenine and uracil are present in equal amounts
In DNA, the two purines are _____, and the two pyrimidines are _____.
adenine and guanine ... cytosine and thymine
How many hydrogen bonds does adenine form with thymine. How many bonds does guanine form with cytosine?
Adenine forms two hydrogen bonds with thymine; guanine forms three hydrogen bonds with cytosine
The two sugar-phosphate strands of a DNA molecule are joined to each other through _____.
hydrogen bonds between nucleotide bases
The information in DNA is contained in _____.
the sequence of nucleotides along the length of the two strands of the DNA molecule
The DNA structures of prokaryotes and eukaryotes are different in several ways, but one way in which they are the same is that _____.
both have sugar-phosphate backbone
The role of DNA polymerases in DNA replication is to _____.
attach free nucleotides to the new strand
The two strands of a DNA double helix are antiparallel. This means that _____.
one strand runs in the 5' to 3' direction, and the other runs in the 3' to 5' direction
DNA polymerase adds nucleotides to the _____ of the leading strands, and to the _____ of the lagging strands (Okazaki fragments).
3' and 3' end
After the formation of a replication bubble, which of the following is the correct sequence of enzymes used for the synthesis of the lagging DNA strand?
helicases, primase, DNA polymerase, ligase
The removal of the RNA primer and addition of DNA nucleotides to the 3' end of Okazaki fragments in its place is carried out by _____.
dna polymerase I
The unwinding of DNA at the replication fork causes twisting and strain in the DNA ahead of the fork, which is relieved by an enzyme called _____.
Once the DNA at the replication fork is unwound by helicases, what prevents the two strands from coming back together to reform a double helix?
Single-strand binding proteins bind the unwound DNA and prevent the double helix from reforming
Which description of DNA replication is correct?
Helicases separate the two strands of the double helix, and DNA polymerases then construct two new strands using each of the original strands as templates.
The incorporation of an incorrect base into the DNA during replication _____.
can be repaired by the mismatch repair system
Unlike prokaryotic DNA replication, replication of eukaryotic chromosomes _____.
cannot be completed by DNA polymerase
What is the difference in the DNA nucleotide and RNA nucleotide?
there is a sugar with two, and not three, oxygen atoms
Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
DNA polymerase can assemble DNA only in the 5' to 3' direction
The synthesis of a new strand begins with the synthesis of a(n) _____.
RNA primer complementary to a preexisting DNA strand
responsible for catalyzing the formation of an RNA primer?
Helicase is responsible for unwinding the DNA double helix
Discuess the origins of replication in eukaryotes.
replication begins at certain sites where two parental strands seperate to from replication bubbles. bubbles expand laterally, as DNA replication proceeds in both directions. the repilication bubbles eventually fuse and the synthesis of hte daughter strands is complete.
Discuss the synthesis of leading and lagging strands during DNA replication.
dna ploymerase elongates DNA strands only in 5' to 3' direction. one new strand, leading strand, elongates continulously as rep fork progreses. other new starnd, lagging starand grows in 3' to 5' direction by addition of okazaki fragments that grow 5' to 3'. ligase connects the okzaki fragments.
Discuss priming DNA synthesis with RNA.
primase joins RNA nucleotides into primer. DNA polymerase adds DNA nucletodies to primer. A different DNA polymerase replaces RNA with DNA. daugther strand is now complete.
What occurs in nucleotide excision repair of dna damage?
thymine dimer distorts dna molecule. nuclease enzyme cuts damaged dna strand at two points. repair synthesis by a dna polymerase fills the gap. dna ligase seals the remaining nick.
Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of _____.
The number of nucleotide bases "read" together on the mRNA to designate each amino acid is _____; this unit is called a(n) _____.
3 and its a codon.
In many cases, more than one codon codes for the same amino acid. Because of this, we say that the code is _____.
At one point as a cell carried out its day-to-day activities, the nucleotides GAT were paired with the nucleotides CUA. This pairing occurred _____.
Which one of the following catalyzes the linkage between ribonucleotides to form RNA during gene expression?
In eukaryotic cells, a terminator in mRNA synthesis is _____.
specific nucleotide sequence in DNA that signals the RNA polymerase to stop
One strand of a DNA molecule has the following sequence: 3'-AGTACAAACTATCCACCGTC-5'. In order for transcription to occur in that strand, there would have to be a specific recognition sequence, called a(n) _____, to the left of the DNA sequence indicated
During the transcription of a given portion of a DNA molecule _____.
mRNA is synthesized on only one of the chains
In eukaryotes, which of the following mechanisms of gene regulation operates after transcription, but before translation of mRNA into protein?
rna splicing and editing
Usually, in eukaryotic genes _____.
exons are transcribed, but the RNA transcribed from introns does not leave the nucleus.
Which one of the following statements correctly describes mRNA processing?
Introns are cut out of the primary transcript, and the resulting exons are spliced together
The function of tRNA during protein synthesis is to _____.
deliver amino acids to their proper site during protein synthesis
Discuss protein synthesis
Messenger RNA is made on a DNA template, and then amino-acid-bearing transfer RNAs bind to it through codon-anticodon pairing.
During translation in a eukaryotic cell _____.
polypeptides are synthesized at ribosomes, according to instructions carried by mRNA
The first amino acid inserted into a new polypeptide chain in eukaryotic cells is always _____.
During translation, amino acid chain elongation occurs until _____.
the ribosome encounters a "stop" codon
Cells are able to distinguish proteins destined for secretion or for segregation to specific intracellular compartments from those that will remain in the cytoplasm because _____.
some proteins, as they begin to be synthesized, contain a signal region that causes the ribosome with its growing polypeptide to attach to the ER and translocate the polypeptide into the lumen (space) of the ER
What is the proper order of the following events in the expression of a eukaryotic gene?
transcription, RNA processing, translation, and modification of protein
What is a key difference in gene expression between eukaryotic and prokaryotic cells?
In prokaryotic cells, the mRNA transcript is immediately available as mRNA without processing
geneticist found that a particular mutation had no effect on the polypeptide encoded by the gene. This mutation probably involved _____.
Which one of the following types of mutation is least likely to affect the function of the protein corresponding to the gene in which the mutation occurs?
base pair substitution
A base-pair substitution mutation in a germ cell line is likely to have no effect on phenotype if the substitution _____.
ocurrs in intron
virus infects a cell and randomly inserts many short segments of DNA containing a stop codon throughout the organism's chromosomes. This will probably cause _____.
manufactured proteins to be short and defective
A point mutation in which a single base pair is inserted or deleted from DNA is called a(n) _____.
frame shift mutation
occurs in nucleus in eukaryotic cells and cytoplasm in prokaryotic cells. is the syntehsis of RNA under direction of DNA. infromation is simply copied from one molecule to another. provides template for assmebling a sequence of RNA nucleotides.
ocurrs in cytoplasm. actual synthesis of a polypeptide which occurs under direction of mRNA. cell translates base sequence of an mRNA moelcule into the amino acid sequence of a polypepetide. the sites of translation are the ribosomes.
Discuss the stages of transcription.
iniation...after rna polyermase binds to promoter, dna strands unwind and enzyme initiates RNA synthesis at start point on template strand.elongation....polyemerase moves downsteram, unwinding the DNA and elongating RNA trancscript from 5' to 3'. the dna stands reform ad ouble helix. termination..eventually polymerase transcribes a terminator sequence, signals end of transcrtiption unit. polymerase detaches from the DNA.
During RNA processing a(n) _____ is added to the 3' end of the RNA
long string of adenine nucleotides
Discuss transcription and tranlsation.
Used DNA to make RNA, RNA is used in trraslation to make amino acids.
Discuss the intiation of translation.
small ribosomal subnite binds to mRNA. mRNA biding site recognizes specific nucleotide sequence on mRNA upstream of start codon. an initiator tRNA basepairs with start codon. arrival of a large ribosomal subunit completes intiation complex. protians are required to bring all the translation components together. gtp provides energy.
What are the three sites of the ribosome?
e-exit site, p-peptidyl-tRNA binding site, a- aminoacyl-tRNA binding site.
Discuss elongation of translation.
codon recongition-incoming anoacyl tRNA binds to the codon in a site. peptide bond formation-ribosome catalyzes formation of a peptide bond b/w new aminio acid and carboxyl end of growing polypeptide. translocation-tRNA in a site is translocated to p site, taking mRNA along with it. tRNA in the p site moves ot the e site and is relased from the ribosome. it ***** the mRNA by one codon.
Discuss the termination of translocation.
when ribosome reaches a termination codon on mRNA, a site of ribosome accepts a realse factor instead of tRNA. realse factor hydrolyzes bond b/w the tRNA in p sire and last amino acid of polypeptide chain. chain free from ribosome. ribosomal subunites and other components dissociate.
What are base-pair substitutions?
replament of one nucelotide and its partner in the complementary DNA strand w/ another pair of nucelotides.
What are missense and nonsense mutations?
missense-alotered codon still codes for an amino acid. makes sene, although it isn't the right sense.
nonsense-alterations that change an amino acid codon to a stop signal
What is a viral outer covering over the protein capsid that is obtained from host cell membranes?
What are transposons?
piece of DNA that can move from one location to another in a cell's genome. in bacteria, can move within chromosome. a "cut and paste" type of transposable element.
What are two human dieaseas that are thought to be caused by prions?
kuru and cruetzfeld-jacob disease
Recombinant DNa can be introduced into a bacterial cell by combinig it with teh DNA of a plasmid or DNa of a .....
What is the lysogenic cycle?
Integration of viral DNA into host DNA is an early stage of the lysogenic cycle.
What is the function of reverse transcriptase?
It catalyzes the formation of DNA from an RNA template.
What does lactose do in the lac operon?
Lactose inactivates the repressor protein so that the lactose-utilization genes can be transcribed
Discuss simplified viral reproductive cycle.
vriuse enters into cell and uncoting of DNA. after entering the cell, teh viral DNA uses host nucleotides nad enzymes to replicate itself. the viral DNA uses other host resources to rpoduce its capside proteins by transcription and translation. the new viral DNA adn capsdie proteins assemble into new virus particles, which leave the clel.
Discuss the lytic cycle.
phage uses its tail fibers to stick to specific receptor sites on out surface of cell. sheath of the tail cotnracts through wall and membrane of cell. phage injects DNA into the cell. empty capsid of phage is left outside of cell and DNA is hyrdolyzed. phage dna ciruclarizes. three seperate sets of phage heads, tails and tail fibers. new phage DNA and proteins are syntehsized and assembled into phages. the phage then direcdts production of lysozyme, enzyme that digest the bacterial cell wall. osmosis causes cell to lyse, releasing phages.
What occurss in the lysogenic cycle?
page attaches to host cell and injects dna. phage dna circularizes. phage dna integrates into bacterial chromosome becmoing a prophage. bacterium reproduces nomrally, copying the prohpaage and transmitting it to the daughter cells. porphage exits the bacterial chromoes sometimes and then goes to the lytic cycle.
What is retorvirus?
RNA viruses with the most complicated reproductive cycles. equipped with reverse transcriptase which transcribes DNA from an RNA template providing an RNA to DNA information flow.
What is provirus?
newliy made DNA integrates into a chromosome within nucleues of animal cell. it remains permanent resident of the host cell's genome.
Discuss the sturcture of HIV.
vuris fuses with cells plasma membrane. capside proteins are removed realsign viral genome. reverse transcriiptase catalyzes the synthesis of a DNA strand complementary to the viral RNA. rever. trasncrip. ctalyzes the synthesis of a scond DNa strant complementary to first. the double stranded DNA is incporporate as a provirs into the cell's DNa. proviral geens are transcirbed into RNA molecules. RNa transcribed form provirs serves as mRNa for trnaslation into HIV proteins and as genomes for the next viral generation. capsids are assembled aroudn viral genomes adn rev. trans. molecules.
Discuss genralized transduction.
phage infects bacterial cell. host DNA is hydrolyzed into pieces adn phage DNA and proteins are made. a bacterial DNA gragments is packaged in a phage capsid. transducing phages infect new host cells where crossing over can ocurr. recombinanats have genotypes differen than either the donor or recipient.
Discuss speciliazed transduction.
bacteral cell has prophage between genes A and B. prophage DNa exits incorrectly taking adjoing bacterial DNA with it. phage particles carry bacterial DNA along with phage DNA. transducing phages infect new host cells where crossing over can ocurr. recombinanats have genotypes differen than either the donor or recipient.
What is conjugation?
the direct ransfer of genetic material between two bacterial cells that are temporarily joined.
Disucss the trp operon.
if tryptophan is absnet, the repressor is incative can't join to operator, so rna polymerase is free to move,and the operon is on. the RNA polymerase attaches to the DNA at the promoter and trasncribes the operon's genes.
if tryp is present, the repressor is active, and the operon is off. repressor binds to operator causing the polymerase to not be able to continue and the operon is off.
Discuss the lac operon.
if lactose is absent, repressor is active, operon is off. the active repressor can fit and gets in teh way of the rna polymerase therefore it cannot go on and transcribe and operon is off.
if lactose is presnet, repressor is inactive, and the operon is on. The anactive repressor cannot bind to the operator due to the inducer and therefore the rna polymerase can trasncribe and the operon is on.
How can a single RNA transcript lead to the translation of different proteins?
The same RNA transcript may be spliced in several different ways.
The nuclear membrane's role in the regulation of gene expression involves _____.
regulating the transport of mRNA to the cytoplasm
Protein-phosphorylating enzymes' role in the regulation of gene expression involves _____.