Chapter 14- PowerPoint Flashcards
What is the distance between the 2 strands? diameter of DNA?
2 nm
What is the distance for one turn in DNA
3.4 nm
How many base pairs are need to make 1 turn in the DNA helical structure?
10 base paris
In the beginning what did scientist believe about DNA?
that proteins were the most likely hereditary molecules
What is Hammerling’s experiment?
Cells of green alga (Acetabularia) were cut into pieces and observed to see which were able to express hereditary information.
What did Hammerling’s experiment find?
discovered hereditary information is stored in the cell’s
nucleus
—base of plant (has the nucleus) and determines the head of the plant
What did Frederick Griffith do?
found a substance
that could genetically transform bacteria
(transformation)
What does pathogenic mean?
causes the disease
What were the 2 strains of Streptococcus pneumonia did Frederick Griffith use?
smooth and rough strain
What was the smooth strain (S) of streptococcus pneumoniae?
highly infective (virulent), quickly causing pneumonia and killing mice
What was the rough strain (R) of streptococcus pneumoniae?
nonvirulent and does not kill mice
What is the difference between S and R strain?
presence of a capsule in the S strain
Mice die. Live S cells in their blood;
shows that living R cells can be converted to
virulent S cells with some factor present in and
derived from dead S cells.
via transformation
What happened when Mice injected with live S cells?
mice died, S cells are virulent
What happened when Mice injected with live R cells?
mice lived, R cells are nonvirulent
What happened when Mice injected with heat-killed S cells?
mice live, S cells need to be live to be virulent
What happened when Mice injected with heat-killed R cells?
mice die, living R cells can be converted to virulent S cells with some factor present in and
derived from dead S cells.
What happened in Avery’s experiments?
• Avery broke down heat-killed S bacteria and destroyed one class of molecules: Protein, DNA, or RNA
• When proteins or RNA were destroyed, the extract still
transformed R bacteria into virulent S bacteria
Whose experiments did Avery build off of?
Griffith’s (mice)
What was Avery trying to find out?
transforming principle of Griffith’s mice experiments
What was the transforming principle in Avery’s experiments?
DNA
When did Griffith do his experiment?
1928
When did Avery do his experiment?
1940s
How did Avery conduct his experiment? and what occurred?
- removed almost all lipid and protein from bacteria, and found no reduction in transforming activity
- DNase destroyed all transforming activity
What did Hershey-Chase do in their experiment?
labeled DNA and protein with radioactive isotope tracer
Used radioactive S and P to label protein and DNA
What did Hershey-Chase find in their experiment?
determined hereditary information was DNA, not protein
—reconfirmed it was DNA was the transforming protein
In Hershey-Chase experiment what did the viruses infect?
bacterium E. coli
What is a bacteriophage?
viruses that can infect bacteria
What is the structure of a virus?
protein “head” and DNA core
When does infection occur with viruses?
when virus injects DNA into a bacterial cell.
When did the Hershey-Chase experiments occur?
1953
Can more than one bacteriophage infect a cell?
yes
What was Hershey-Chase’s goal in using bacteriophages?
Wanted to determine which of these molecules is the
genetic material that is injected into the bacteria
What can a bacteriophage also be called?
phage
What is a virus?
Infectious agent made of DNA or RNA,
surrounded by a protein coat.
How do viruses reproduce?
in a host cell, using host cell materials
What are they 2 lifecycles that bacteriophages go through?
lytic and lysogenic
What is the lifecycle of a bacteriophage?
injection, replication, expression, packaging, lysis
How did the Hershey-Chase experiment work?
- They showed that labeled DNA, not labeled protein, entered the cell and appeared in progeny phages
- Bacteriophage DNA was labeled with radioactive phosphorus (32P) — in DNA
- Bacteriophage protein was labeled with radioactive sulfur (35S) — in Protein capsule
- Radioactive molecules were tracked
- Only the bacteriophage DNA (as indicated by the 32P) entered the bacteria and was used to produce more bacteriophage
- Conclusion: DNA is the genetic material
What was the phage studied by Hershey and Chase?
T2 phage
What is the structure of T2 phage?
core of DNA surrounded by proteins
What is in the pellet?
bacteria
What was the blending done for?
to remove empty phage coats
What was Rosalind Franklin missing?
didn’t know if the phosphate groups were on the inside or outside
What did the X-shaped distribution of sports in the diffraction pattern indicate?
DNA’s helical structure
What is X-ray diffraction?
- An X-ray beam is directed at a molecule in the form of a regular solid (ideally a crystal)
- Positions of atoms in the molecule are deduced from diffraction patterns produced on photographic film
Who discovered DNA fibers?
Maurice Wilkins
What did the molecular revolution lead to?
made it possible to relate genetic traits of living organisms to a universal molecular code present in the DNA of every cell
When did Watson and Crick find DNA structure?
1953
Whose work did Watson and Crick use to find the structure of DNA?
Franklin, Chargaff, and others
Did Watson and Crick perform any experiments?
nope
What did Watson and Crick get for discovering the structure of DNA? when?
Nobel Prize in 1962
When did Franklin die of cancer?
1958, she was 38
Where is the phosphate group attached to?
5’ carbon of sugar
Where is the hydroxyl group attached to?
3’ carbon of sugar
How do you differentiate deoxyribose vs ribose?
2’ carbon will have no oxygen, only a hydrogen
What is a nucleotide composed of?
base, deoxyribose, and phosphate
How are nucleotides joined together?
Phosphodiester bond
Which bases need to recognize the structures of?
A, G, C, U
How is a Phosphodiester bond formed?
Formed between the phosphate group of one nucleotide and the 3′ —OH of the next nucleotide
Why can’t C pair with A, and G pair with T?
because of the hydrogen bonding requirements
How many hydrogen bonds between A-T?
2
How many hydrogen bonds between G-C?
3
Does DNA have a consistant diameter?
yes
What is Chargaff’s rule?
A = T and G = C
Does a polynucleotide chain of DNA have polarity?
yes
Are DNA strands always antiparallel?
yes
What does a purine always bind to?
pyridine
Does A+T = G+C?
NOPE
What type of replication does E coli follow?
prokaryotic replication
What is a replicon?
DNA controlled by an origin
What does the bidirectionally of prokaryotic replication allow?
shortens replication time
What is a replisome?
Enzymes involved in DNA replication form a macromolecular assembly
What do the replication forks in prokaryotic replication move to?
termination origin
How many origin of replication do eukaryotes have?
multiple
What is the shape of eukaryotic chromosomes?
linear
Is eukaryotic chromosomes replication bidirectionally?
yes
What is eukaryotic replication complicated by?
larger amount of DNA and linear structure
Is the basic enzymology identical between eukaryotic and prokaryotic replication?
No, it is similar
What are the 2 main components of a replisome?
1) primosomes (primase, helicase, SSB topoisomerase)
2) complex of 2 DNA pol III (one for each strand)
What does primase do?
initiates all new strands in DNA replication
What does DNA polymerase III do?
main polymerase
What does DNA polymerase I do?
removes RNA primers and replaces them with deoxyribonucleotides
Acts on lagging strand to remove primers and
replace them with DNA
What does DNA polymerase I do?
removes RNA primers and replaces them with deoxyribonucleotides
Acts on lagging strand to remove primers and
replace them with DNA
What does DNA polymerase II do?
involved in DNA repair processes
Which polymerase have 3′-to-5′ exonuclease activity – proofreading?
all 3
What is a exonuclease?
chews polynucleotides from the ends
What is a endonuclease?
chews polynucleotides from the middle
Which polymerase has 5′-to-3′ exonuclase activity
DNA polymerase I
What is a ribonuclease?
catalyzes the degradation of RNA into smaller components
Where do nicks occur?
lagging strand
What seals up the nicks?
DNA ligase
What seals up the nicks?
DNA ligase
Does the lagging stand loop around? if so what does this cause?
yes, causes the DNA polymerases to move in the same direction
What are telomeres?
Protect ends of chromosomes from nucleases and maintain the integrity of linear in eukaryotic
chromosomes
What is the result of Gradual shortening of chromosomes with each round of cell division?
Unable to replicate last section of lagging strand
What happens when the RNA primer is removed?
eaves a gap at the 5′ end of the new DNA strand that
DNA polymerase can’t fill, – causing the chromosome to shorten with each replication.
What is the structure of a telomere?
noncoding short repeating sequences (telomere repeat).
When does Buffering fails occur?
when the entire telomere is lost
What happens to the telomere after each replication?
some telomere repeats are lost, but the genes are unaffected
What does telomerase do?
stops the shortening of telomeres by adding telomere repeats to chromosome ends.
How does telomerase work?
An RNA section binds to DNA and is the template for addition of telomere repeats
When is telomerase active?
rapidly dividing embryonic cells, in germ cells, and in cancerous somatic cells.
What type of template does telomerase use?
RNA
How is telomerase regulated?
developmentally
There is a relationship between telomere length and?
senescence
Cancer cells generally show what in telomerase?
activation of telomerase
Which strand does telomerase act upon?
lagging strand
What is the importance of complementary base pairing to DNA replication?
DNA sequence will be preserved
Why is a primer needed for DNA replication? How is the
primer made?
DNA needs a free hydroxyl end to replicate, made by primase
DNA polymerase III and DNA polymerase I are used in DNA replication in E. coli. What are their roles?
pol III = main replication enzyme, has 3’ to 5’ exonuclease activity
pol I = removes the primer on both strand, has 3’ to 5’ and 5’ to 3’ exonuclease activity
Why are telomeres important?
prevent chromosomes from shortening during replication
What is DNA pol 1 5’ to 3’ exonuclease activity?
idk
What is a mutagen?
any agent that increases the number of mutations above background level
What are some examples of mutagens?
Radiation and chemicals
What has the importance of DNA repair is indicated by?
the multiplicity of repair systems that have
been discovered
What corrects the errors made during replication (base-pair mismatches)? how does it work?
—proofreading mechanism by DNA polymerases
—The proofreading mechanism allows DNA polymerases to back up and remove mispaired nucleotides
What type of activity does the proofreading mechanism use when correcting of errors in DNA?
3′→5′ exonuclease activity to remove the newly added incorrect nucleotide
What happens after the proofreading mechanism allow correction of errors in DNA?
DNA polymerase then resumes forward synthesis and inserts the correct nucleotide
How can mismatch repair enzymes find recognition sites?
Distortions in DNA structure
How do the repair enzymes cut DNA?
cut the new DNA strand on each side of the mismatch, and remove a portion of the chain
What happens after the repair enzymes cut out a section of DNA?
DNA polymerase fills the gap with new DNA, and DNA ligase seals the nucleotide chain
How often does DNA damage occur in cells?
constantly
What are the 2 type of excision repair?
base-excision repair and nucleotide-excision repair
What happens in Base-excision repair?
repair nonbulky damage by removing the erroneous
base and replacing it with the correct one based on complementary pairing rules.
What happens in Nucleotide-excision repair?
repairs bulky distortions in DNA (such as in thymine
dimers) by removing an entire segment of DNA.
What happens to Errors that remain in DNA after proofreading and DNA repair?
leads to mutations
What is the ultimate source of variability acted on by natural selection.
mutations
What are thymine dimers?
2 thymines next to each other that form a bulky distorted structure (can be due to damage via radiation)
