BIO-111 Exam 3

How is information stored in DNA?

in the sequence of base pairs

How is DNA transmitted?

through replication to make a new DNA copy and through transcription to make RNA

How do base pairing interactions allow the faithful propagation of the information stored in DNA?

each purine pairs with exactly one pyrimidine, meaning DNA can be easily copied. The sequence of the base pairs (genes) stores information and can encode specific proteins

What are the 3 potential models of DNA replication?

conservative, semiconservative, dispersive

What is semiconservative replication?

each parent strand is a template; new molecules have one old and one new strand

What is conservative replication?

the original molecule serves as a template only; out of the two helixes created, one will be completely old, one will be completely new

What is dispersive replication?

fragments of DNA are templates; old and new parts are assembled into new molecules (each strand has some old and some new)

What was the Messelson-Stahl experiment?

an experiment done to determine which model of DNA replication is used by cells to copy DNA

What happened to the first generation of DNA in the M-S experiment?

all of the DNA in the first generation after moving the original DNA from N15 to N14 was intermediate, meaning half of each new strand was heavy and half was light; this rules out the conservative model of DNA replication

What happened to the second generation of DNA in the M-S experiment?

half of the DNA in the second generation was intermediate and half was light, ruling out the dispersive model; if DNA replication was dispersive, there would have been DNA at various densities and not just intermediate and light

What isotopes were used to label DNA in the M-S experiment?

Nitrogen isotopes: N14 (light) and N15 (heavy)

Why is nitrogen a good choice for labeling DNA?

nucleotides have nitrogenous bases

Which model of replication is supported by the M-S experiment?

semiconservative

How do the results of the M-S experiment support the semiconservative model of DNA?

after two generations, some of the DNA was intermediate, meaning half was heavy and half was light, and some of the DNA was completely light, meaning both strands were light and therefore generated in the light isotope. If the first generation intermediate had one heavy and one light strand, when replication occurs, the heavy strand would get a new light strand, and the light strand would also get a new light strand, keeping one new helix intermediate and making a new completely light helix

What is a genome?

the complete set of DNA in a living organism

What is a gene?

a sequence of DNA that encodes a specific protein

What are the complementary base pairs?

A-T, C-G

True/False: the entire strand of DNA is transcribed into RNA

false

What location does the DNA open at during replication?

the replication fork

What is the replication fork?

the place where DNA is unwound and replication proceeds in both directions

What does primase add to one of the DNA strands?

an RNA primer that is complementary to the template strand

What is the function of DNA polymerase in replication?

the enzyme that adds nucleotides to the new DNA strand

What end are new DNA nucleotides added at?

the 3' end

What is the leading strand in DNA replication?

the strand that grows at its 3' end as the replication fork opens

What is the lagging strand in DNA replication?

the strand that's 3' end gets farther from the replication fork leaving unreplicated gaps

What are the short fragments of the lagging strand called?

Okazaki fragments

What are Okazaki fragments?

small, discontinuous stretches on the lagging strand

Why does the lagging strand have to be synthesized in shorter fragments?

there is no exposed 3' end to have continued synthesis

How are Okazaki fragments joined together?

DNA ligase

True/False: each Okazaki fragment requires its own primer

true

What does the DNA ligase enzyme do?

joins the unjoined fragments of the new DNA strand

What type of bonds are nucleotides linked by?

phosphodiester bonds

What is the origin of replication?

the place where DNA replication begins

True/False: Eukaryotic chromosomes only have one origin of replication

false

True/False: Eukaryotic chromosomes have multiple origins of replication

true

True/False: Prokaryotic chromosomes have multiple origins of replication

false

What direction do nucleic acids grow in?

5' to 3'

What is a primer in DNA replication

a short RNA strand that binds to DNA and begins replication

What is a primer typically made of in DNA replication?

RNA

What are telomeres?

repetitive DNA sequences at the end of eukaryotic chromosomes

What do telomeres do/prevent?

prevent genes from being lost during DNA replication

What is telomerase?

an enzyme that lengthens telomeres

How does telomerase work?

it uses an RNA template to make complementary DNA

What enzyme lengthens telomeres?

telomerase

What are the three DNA repair mechanisms that make sure DNA is copied correctly?

proofreading, mismatch repair, and excision repair

What is DNA proofreading?

DNA polymerase can recognize mismatched pairs and remove the nucleotide

When does DNA proofreading occur?

as DNA polymerase adds nucleotides

What is DNA mismatch repair?

the newly replicated DNA is scanned for mistakes by other proteins and can correct mismatches; removes the mistake and the surrounding nucleotides; DNA polymerase adds new nucleotides and DNA ligase repairs the gaps

When does DNA mismatch repair occur?

after new DNA has been replicated

What is DNA excision repair?

when enzymes constantly scan DNA for damaged bases; removes damaged and surrounding bases and DNA polymerase adds new bases; DNA ligase repairs the gaps

When does DNA excision repair occur?

after new DNA has been replicated

What happens at the ends of the lagging strand?

no new DNA can be synthesized, so the remaining small piece of DNA is removed and the chromosome becomes shorter

True/False: the chromosome becomes shorter with each replication

true

True/False: after so many divisions, genes can be lost and the cell can die

true

True/False: all cells have telomerase

false

Why would mistakes made during DNA replication be a problem for the cell?

mistakes could potentially cause mutations in cells

What is the "central dogma" of molecular biology?

the flow of genetic information from DNA to RNA to proteins

What is transcription?

when a DNA sequence is copied to a complementary RNA sequence

What is translation?

when an RNA sequence is a template for an amino acid sequence

What is replication?

When DNA is a template for a new DNA strand

What are the 3 steps/phases of transcription?

initiation, elongation, termination

What is transcription initiation?

RNA polymerase binds to a DNA promoter sequence that directs the RNA polymerase where to start and which strand of DNA to transcribe

What is transcription elongation?

RNA polymerase unwinds approximately 10 base pairs of DNA and reads the template in a 3' to 5' direction, then synthesizes RNA in a 5' to 3' direction

What is transcription termination?

transcription stops and the RNA is released

Where is the information for initiation and termination contained?

in the DNA sequence

Where do transcription and translation occur in prokaryotes?

in the cytoplasm

True/False: transcription and translation occur at the same place/time in prokaryotes?

true

True/False: in eukaryotes, transcription and translation are separated by the nuclear envelope?

true

What is the order of the relationship between RNA, DNA, and Proteins?

DNA, RNA, protein

Who coined the term "the central dogma of molecular biology"?

Watson and Crick

Where does transcription occur in eukaryotes?

in the nucleus

Where does translation occur in eukaryotes?

in the cytoplasm

What are the three types of RNA produced by transcription?

mRNA, tRNA, rRNA

What is mRNA?

messenger RNA

What is tRNA?

transfer RNA

What is rRNA?

ribosomal RNA

How is mRNA made?

one strand of DNA is copied to make a complementary mRNA strand

What is mRNA used for?

carries the information to make a protein

What is tRNA used for?

can bind a specific amino acid and recognize specific sequences in mRNA; links mRNA codons with specific amino acids

What is rRNA used for?

catalyzes peptide bond formation between amino acids in order to form a polypeptide

What is RNA polymerase?

an enzyme that catalyzes the synthesis of RNA

True/False: RNA polymerase requires a primer

false

What is a promoter sequence?

a sequence of DNA that directs RNA polymerase where to start and which strand of DNA to bind to

What part of the DNA does an RNA polymerase bind to?

promoter sequence

What direction does RNA synthesis occur in?

5' to 3'

True/False: eukaryotic mRNAs are NOT processed before they are exported from the nucleus

false

What are introns?

the non-coding DNA found between exons

What are exons?

the coding regions of DNA sequences that correspond to proteins

What part of mRNAs are removed before the mRNA is exported from the nucleus?

introns

What is a 5'cap?

a modified GTP which facilitates mRNA binding to a ribosome

What is a poly A tail?

100 to 300 Adenines that are added the 3' end of mRNAs

What end is the poly A tail added at?

3' end

What is the importance of a poly A tail?

it assists in the export from the nucleus and is important for stability of mRNA

What is a "mature mRNA"?

mRNA that has been spliced and processed and is ready for translation

How many nucleotides are in a codon?

3

What is the start codon?

AUG

How many stop codons are there?

3

What are the 3 stop codons?

UAA, UAG, UGA

How many amino acids does each codon code for?

one

What is RNA splicing?

the removal of introns and joining of exons