Chapter 16 Flashcards
Who showed that genes exist as parts of chromosomes?
T.H. Morgan’s group
DNA replication
The process by which a DNA molecule is copied; also called DNA synthesis
Pathogenic is _____, while nonpathogenic is ____
disease-causing, harmless
Transformation
A change in genotype and phenotype due to the assimilation of external DNA by a cell
When Fredrick Griffith killed pathogenic bacteria with heat and then mixed the cell remains with living bacteria of the nonpathogenic strain what happened to the cells?
some of the living cells became pathogenic
showing transforming principle
Phages
A virus that infects bacteria; also called a bacteriophage.
How do viruses produce more viruses
a virus must infect a cell and take over the cell’s metabolic machinery
Virus
An infectious particle incapable of repli- cating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope.
What did Alfred Hershey and Martha Chase’s experiment show?
That DNA is the genetic material of a phage known as T2. (one of many phages that infect E. coli)
Base composition varies from species to species T or F?
T
Adenine bonds with…
Thymine
Guanine bonds with…
Cytosine
What are Chargaff’s rule?
(1) DNA-base composition varies between species
(2) For each species, the %s of A and T bases are roughly equal, as are G and C bases
Who discovered the structure of DNA?
James Watson and Francis Crick
What is the structure of DNA?
Double Helix
What did Rosalind Franklin do?
(1) Took an X-ray diffraction image of DNA- helped Watson and crick confirm DNA structure
(2) Concluded that the Sugar-Phospahte back- bones were on the outside of the DNA molecule (phosphates have a negative charge)
DNA strands runs parallel to each other T or F?
F. They run Antiparallel- run in opposite directions
How long (length) does it take for the DNA double helix to make one full turn
3.4nm (10 layers of base pairs)
How far are bases stacked apart from each other
.34nm
How many bonds are between A and T?
2 hydrogen bonds
How many bonds are between G and C?
3 hydrogen bonds
Semiconservative model
Two stands of the parental molecule separate
each functions as a template for synthesis of a new complementary strand
Where does the replication of chromosomal DNA begin?
particular sites called origins of replication
A eukaryotic chromosome may have hundreds or even thousands replication origins T or F?
True. Multiple replication bubbles form and eventually fuse, thus speeding up the copying of the very long DNA
Which direction does DNA replication process in from the replication origin?
Both directions
What is at the end of each replication bubble?
Replication fork
Replication fork
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 replication forks, separating the two strands and making them available as template strands
Single-strand binding proteins
A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and hold- ing them apart while they serve as templates for the synthesis of complementary strands of DNA
Topoisomerase
A protein that breaks, swivels, and rejoins DNA strands. During DNA replication, topoisomerase helps to relieve strain in the double helix ahead of the replication fork
How is DNA replication synthesis initiated?
RNA primer (usually 5-10 nucleotides long) synthesized by the enzyme primase
DNA polymerase
n enzyme that catalyzes the elongation of new DNA
(for example, at a replication fork) by the addition of nucleotides to the 3′ end of an existing chain. There are several different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA replica- tion in E. coli
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
Ho
Dehydration reaction
Which side of a DNA strand can DNA polymerases add nucleotides?
Only to the 3’ end of a primer or growing DNA strand. Never the 5’ end.
How is DNA elongated in replication?
DNA elongates only in the 5’—–>3’ direction
DNA pol III
Synthesizes a complementary strand continuously, remaining in the replication fork on the template strand
adds nucleotides to the 3’ end
Leading strand
The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5′ S 3′ direction
Lagging strand
A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5′ S 3′ direction away from the replication fork.
Okazaki Fragments
(ō′-kah-zah′-kē) A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together to make up the lagging strand of newly synthesized DNA
what is the 1st step in the synthesis of the lagging strand?
Primase joins RNA nucleotides into a primer
what is the 2nd step in the synthesis of the lagging strand?
DNA pol III adds DNA nucleotides to the primer, forming Okazaki fragments
what is the 3rd step in the synthesis of the lagging strand?
After reaching the next RNA primer, DNA pol III detaches
what is the 4th step in the synthesis of the lagging strand?
The next fragment is primed, then DNA pol III adds DNA nucleotides, detaching when it reaches the fragment 1 primer
what is the 5sth step in the synthesis of the lagging strand?
DNA pol I replaces the RNA with DNA, adding nucleotides to the 3’ end of the fragment
what is the 6th step in the synthesis of the lagging strand?
DNA ligase forms a bond between the newest DNA and the Okazaki fragments into a continuous strand.
DNA pol I only replaces the nucleotides and doesn’t join the final nucleotide of the primer to the Okazaki fragments
what is the 7th step in the synthesis of the lagging strand?
the lagging strand is now complete
RNA pol I
removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added to the 3’ end of the adjacent fragment
Mismatch repair
The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides
nuclease
enzyme that cuts DNA or RNA, either removing one or a few bases or hydro- lyzing the DNA or RNA completely into its component nucleotides
Nucleotide excision repair
A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide
Telomeres
The tandemly repeti- tive DNA at the end of a eukaryotic chromo- some’s DNA molecule. Telomeres protect the organism’s genes from being eroded during successive rounds of replication
much like the aglet of a shoelace protect the lace from unwinding
Histones
responsible for the first level of DNA packing in chromatin
Heterochromatin
Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.
Euchromatin
The less condensed form of eukaryotic chromatin that is available for transcription
What two properties, one structural and one functional, distinguish heterochromatin from euchromatin?
Euchromatin is chromatin that becomes less compacted during interphase and is accessible to the cellular machinery responsible for gene activity. Heterochromatin, on the other hand, remains quite condensed during interphase and contains genes that are largely inaccessible to this machinery
In a nucleosome, the DNA is wrapped around
histones
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 pre-existing strand, and the strands are
antiparallel-run in opposite directions
Telomerase
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.
Mutagen
A chemical or physical agent that interacts with DNA and causes a mutation
what did Avery, McCarthy, & MacLeod do?
Purified both DNA and protein from the harmful streptococcus pneumonia bacteria and injected both into the non harmful bacteria. Discovered that only the DNA caused the transforming principle and death. DNA must be genetic material
what did Hersey and chase do?
Used the “blender experiment”. Used bacteriophages in mediums that caused either the protein or DNA within them to become radioactively labeled. Then they had the phage infect the bacteria, blended the mixture, and centrifuged the liquid. They then checked the pellet and liquid for radioactivity and found that radioactive DNA stayed in the pellet. Confirmed DNA is genetic material
