Ch 16 The Molecular Basis of Inheritance Flashcards
Origin of Replication (ORI)
- site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides
- proteins open up the strand forming a replication fork
Replication Fork (bubble)
- a Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized
Helicase
- an enzyme that untwists the double helix of DNA at the replication forks, separating the two strands and making them available as template strands
- unwinds parental double helix at replication forks
Single-strand binding proteins
- a protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA
- binds to and stabilizes singled-stranded DNA until it is used as a template
Topoisomerase
- an enzyme that breaks, swivels, and rejoins DNA strands
- during DNA replications, helps to relieve strain in the double helix ahead of the replication fork
Primer
- a short polynucleotide with a free 3’ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication
- synthesized by primase
Primase
- an enzyme that joins RNA nucleotides to make a primer during DNA replication using the parental DNA strand as a template
- synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand
DNA Polymerase
- an enzyme that catalyzes the elongation of new DNA by the addition of nucleotides to the 3’ end of an existing chain
- proofread newly made DNA
Leading Strand
- the new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5’ –> 3’ direction
Lagging Strand
- a discontinuously synthesized DNA strand the elongates by means of Okazaki fragments each synthesized in a 5’–> 3’ direction away from he replication fork
DNA Ligase
- a linking enzyme essential for DNA replication
- catalyzes the covalent bonding of the 3’ end of one DNA fragment (such as an Okazaki fragment) to the 5’ end of another DNA fragment (such as a growing DNA chain)
- joins Okazaki fragments of lagging strand
- on leading strand, joins 3’ end of DNA that replaces primer to rest of leading strand DNA
Mismatch Repair
- the cellular process that uses specific enzymes to remove and replace paired nucleotides
-repair enzymes correct errors in base pairing
Nucleotide Excision Repair
- a repair system that removes and then correctly replaces a damage segment of DNA using the undamaged strand as a guide
Nuclease
- an enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides
- cut out damaged pieces of DNA
- recruits DNA polymerase to correct DNA
Telomeres
- repeating noncoding nucleotides so end replication doesn’t cut out important nucleotides
- tandemly repetitive DNA at the end of a eukaryotic chromosome’s DNA molecule
- protect the organism’s genes from being eroded during successive rounds o f replication
- postpone the erosion of genes
Telomerase
- lengthens telomeres
Chromatin
- the complex of DNA and proteins that make up eukaryotic chromosomes when the cell is not dividing
- exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope
Euchromatin
- the less condensed form of eukaryotic chromatin that is available for transcription
- able to be transcribed
Heterochromatin
- eukaryotic chromatin that remains highly compacted during interphase and is generally NOT transcribed
- inaccessible for transcription
In a comparison between asexually reproducing bacteria and sexually reproducing multicellular eukaryotes, uncorrected errors in replication are more likely to be transmitted to subsequent generations in bacteria than in multicellular eukaryotes. Which of the following provides the best evidence-based explanation for this difference?
Because they are asexual and single-celled, all uncorrected errors of replication in bacteria are transmitted to subsequent generations. Multicellular eukaryotes typically reproduce sexually, so uncorrected errors are transmitted only if they occur in germ cells that meiotically divide to produce gametes.
A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?
DNA Ligase
DNA polymerase adds nucleotides to the (BLANK) of the leading strand, and to the (BLANK) of the lagging strands (Okazaki fragments)
3’ end; 3’ end
The role of DNA polymerase in DNA replication is to…
attach free nucleotides to the new DNA strand
The unwinding of DNA at the replication fork causes twisting and strain ahead of the fork, which is relieved by an enzyme called…
topoisomerase
DNA replication begins at a site called the origin of replication, forming a bubble which is followed by a (BLANK) where parental stands are unwound by (BLANK).
replication fork; helicases
Proteins that are involved in packaging the eukaryotic chromosomes called (BLANK) are (BLANK).
nucleosomes; histones
Of the three alternative models of DNA replication, which are the (BLANK) models, the one that explains how DNA replicates is the (BLANK) model.
conservative, semiconservative, and dispersive; semiconservative
Telomeres are (BLANK).
repeating noncoding sequences at the ends of linear eukaryotic chromosomes
In DNA, the two purines are (BLANK), and the two pyrimidines are (BLANK).
adenine and guanine; cytosine and thymine
Which description of DNA replication is correct?
Helicases separate the two stands of the double helix, and DNA polymerases then construct two new strands using each of the original stands as templates
The information in DNA is contained in…
the sequence of nucleotides along the length of the two new strands of the DNA molecule
In DNA replication, the next nucleotide is incorporated into the growing polymer at the (BLANK) of the molecule by an enzyme called (BLANK)
3’ (hydroxyl) end; DNA polymerase
The 5’ end of a DNA strand always has a free (BLANK) group while the 3’ end always has a free (BLANK) group.
phosphate; hydroxyl
The two sugar-phosphate strands that form the rungs of a DNA double helix are joined to each other through…
hydrogen bonds between nucleotide bases
Chargaff analyzed DNA and found that the numbers of adenine molecules is approximately equal to the numbers of (BLANK) molecules and the numbers of (BLANK) molecules is approximately equal to the numbers of (BLANK) molecules.
thymine; guanine; cytosine
In analyzing the number of different bases in a DNA sample which result would be consistent with the base-pairing rules?
A+G=C+T
Which of the following components is required for DNA replication?
RNA primer
Replication of the lagging strand of DNA is accomplished by repeatedly making (BLANK) followed by 1,000-2,000 nucleotide segments called (BLANK)
short RNA primers; Okazaki fragments
Monomers for the synthesis of DNA are called…
nucleotides
Chargaff found that for DNA…
the ration of A to T is close to 1:1 and the ration of C to G is close to 1:1
Which of the following statements is correct?
Adenine forms two hydrogen bonds with thymine; guanine forms three hydrogen bonds with cytosine
The two antiparallel strands of nucleotides that form the DNA double helix are held together by…
hydrogen bonds between nucleotide bases
The information in DNA is contained in…
the sequence of nucleotides along the length of the two stands of the DNA molecule
Which of the following attributes of DNA is most crucial to its accurate duplication?
its specific base pairing through hydrogen bonds
During the replication of DNA…
both strands of a molecule acts as templates
`Which of the following statements about replication origins is/are correct?
All of the listed responses are correct
-Replication proceeds in both directions from each origin
-The DNA sequence at the origin of replication is recognized by specific proteins that bind to the origin’
-Bacterial chromosomes have a single origin of replication, but eukaryotic chromosomes have any origins
-The two strands of DNA at the origin of replication are separated creating a replication bubble
At the end of a DNA replication bubble is…
a replication fork
In prokaryotes the rate of elongation during DNA replication is (BLANK) the rate in eukaryotes.
much faster than
After the formation of a replication bubble, which of the following is the correct sequence of enzymes used for synthesis of the lagging DNA strand?
Helicase 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 (BLANK).
DNA polymerase I
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
the incorporation of an incorrect base into the DNA during replication…
can be repaired by the mismatch repair system
Which set of enzymes is involved in nucleotide excision repair?
nuclease, DNA polymerase, and ligase
Unlike prokaryotic DNA replication, replication of eukaryotic chromosomes…
cannot be completed by DNA polymerase
Telomeres…
get shorter with each round of DNA replication
Telomerase…
is an enzyme that lengthens telomeres
What is the major difference between bacterial chromosomes and eukaryotic chromosomes?
Bacteria usually have a singular circular chromosome, whereas eukaryotes have several linear chromosomes
In the “beads on a string” structure of unfolded chromatin, the “beads” are…
nucleosomes
What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
DNA polymerase can join new nucleotides only to the 3’ end of a growing strand
In a nucleosome the DNA is wrapped around…
histones
The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?
nuclease, DNA polymerase, DNA ligase
What is the function of helicase in DNA replication?
It unzips the double helix and separates two DNA strands
The DNA template strand is “read” by DNA polymerase in the (BLANK) direction
3’ to 5’
Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?
8
After DNA replication is complete..
each new DNA double helix consists of one old (parental) strand and one new (daughter) strand
What is the difference between the leading stand and the lagging strand in DNA replication?
The leading strand is synthesized continuously in the 5’ to 3’ direction, while the lagging strand is synthesized discontinuously in the 5’ to 3’ direction
In the polymerization of DNA a phosphodiester bone is formed between the phosphate group of the nucleotide being added and (BLANK) of the last nucleotide in the polymer?
the 3’ OH
