Chapter 16 Flashcards
Nucleic acids are unique in their ability to direct their own replication from monomers.
True
Who provided evidence that DNA can transform bacteria?
Frederick Griffith
Bacterium that Griffith was studying
Streptococcus pneumoniae
Streptococcus pneumoniae
Bacteria that causes pneumonia in mammals.
Pathogenic
Disease-causing
Nonpathogenic
Harmless
Transformation
A change in genotype and phenotype due to the assimilation of external DNA by a cell.
Bacteriophages (phages)
Viruses that infect bacteria.
Virus structure
DNA enclosed by a protective coat, often protein.
Which scientists performed experiments that showed that DNA is the genetic material of a phage?
Alfred Hershey
Martha Chase
They used a phage known as T2
Antiparallel
Subunits run in opposite directions
With the bases stacked just ________ apart, there are _________ in each full turn of the helix.
0.34 nm, ten layers of base pairs
Purines (A and G) are about twice as wide as pyrimidines (C and T).
True
Diameter of double helix
2 nm
Conservative model
The two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix.
Semiconservative model
The two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand.
Dispersive model
Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA.
Which scientists experiment supported the semiconservative model of DNA replication?
Mathew Meselson and Franklin Stahl
The replication of a chromosome begins at particular sites called origins of replication.
True
Replication fork
A Y-shaped region where the parental strands are being unwound.
Helicases
Are enzymes that untwist the double helix at the replication forks.
Single-strand binding proteins
Bind to the unpaired DNA strands, keeping them from re-pairing.
Topoisomerase
Relieves the strain at the replication fork caused by the untwisting of the double helix by breaking, swiveling, and rejoining the DNA strands.
Primer
The initial nucleotide chain that is produced during DNA synthesis.
Is an RNA chain and is synthesized by the enzyme primase.
The completed primer is generally ________ long
5-10 nucleotides long
The new DNA strand will start from the 3’ end of the RNA primer.
True
DNA polymerases
Catalyze the synthesis of new DNA by adding nucleotides to a preexisting chain.
In E. Coli, there are several different DNA polymerases, but two appear to play the major roles in DNA replication:
DNA polymerase III and DNA polymerase I
DNA polymerase III
Adds a DNA nucleotide to the RNA primer and then continues adding DNA nucleotides complementary to the parental DNA template strand to the growing end of the new DNA strand.
As each monomer joins the growing end of a DNA strand, two phosphate groups are lost as a molecule of pyrophosphate.
True
Because of their structure, DNA polymerases can add nucleotides only to the free 3’ end of a primer or growing DNA strand, never to the 5’ end.
True
Only one primer is required for DNA pol III to synthesize the entire leading strand.
True
DNA polymerase III works in the direction away from the replication fork when synthesizing the lagging strand.
True
Okazaki fragments
Segments of the lagging strand.
DNA polymerase I
Replaces the RNA nucleotides of the primer.
DNA ligase
Joins all the sugar-phosphate backbones of the Okazaki fragments into a continuous DNA strand.
DNA polymerase II
Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand
Mismatch repair
Other enzymes (not DNA polymerase) remove and replace incorrectly paired nucleotides that have resulted from replication errors.
Mutations
Permanent changes in DNA
Nuclease
DNA cutting enzyme
Nucleotide excision repair
A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.
A DNA polymerase can add nucleotides only to the 3’ end of a preexisting polynucleotide.
True
Two protective functions of telomeres
First, specific proteins associated with telomeric DNA prevent the staggered ends of the daughter molecules from activating the cell’s symptoms for monitoring DNA damage.
Second, telomeric DNA acts as a kind of buffer zone that provides some protection against the organism’s genes shortening. Telomeres postpone the erosion of genes near the ends of chromosomes.
Telomeres become shorter during every round of replication.
True
Telomerase
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells, thus restoring their original length and compensating for the shortening that occurs during DNA replication.
More than a fifth of a histone’s amino acids are positively charged (lysine or arginine) and therefore bind tightly to the negatively charged DNA.
True
Nucleosome
The basic unit of DNA packing; the strings between beads is called linker DNA.
Consists of DNA wound twice around a protein core of eight histones, two of each main histone types.
Types of histones
H2A, H2B, H3, and H4
-H1, also.
30-nm fiber
Results from interactions between the histone tails of one nucleosome and the linker DNA and nucleosomes on either side.
Looped domains (300-nm fiber)
Results from loops formed by the 30-nm fiber.
Progressive levels of DNA coiling and folding
-DNA, the double helix
-Histones
-Nucleosomes, or “beads on a string (10-nm fiber)
-30-nm fiber
-Looped domains (300-nm fiber)
-Metaphase chromosome
Heterochromatin
The type of interphase chromatin that is visible as irregular clumps with a light microscope.
Euchromatin
Less compacted, more dispersed chromatin.
The only difference between the ATP of energy metabolism and dATP, the adenine nucleotide used to make DNA, is the sugar component, which is deoxyribose in the building block of DNA but ribose in ATP.
True
