LO12 Flashcards
Describe Griffith’s experiment.
Showed that some material could be transferred from disease-causing bacterial strains (S cells) to non infected strains (R cells) which transformed the R cells into S cells
What was the contribution of Avery and his colleagues to Griffith’s experiment?
Showed that the transforming material was DNA
Griffith’s and Avery’s work showed that DNA was the genetic material in which group of organisms?
prokaryotes (bacteria)
What did Hershey and Chase’s experiment show?
That DNA was the genetic materials in bacteriophages
definition: viruses that infect bacteria
bacteriophages
How did Hershey and Chase demonstrate that DNA was the genetic material and not proteins?
They radioactively labelled both the proteins and DNA to which entered the bacteria cells
Watson and Crick proposed what model of DNA?
Double helix model of DNA
What was Watson and Cricks model based on?
Rosalind Franklin’s X-ray diffraction images of DNA
What is X-ray diffraction used for?
to determine the distance between atoms in a molecule
Watson, Crick, and Maurice Wilkins won what?
The nobel prize for discovering the structure of DNA
What was initially wrong with Watson and Crick’s first model of DNA?
They placed the bases on the outside and the sugar-phosphate backbone on the inside
Meselson and Stahl confirmed what?
The semiconservative mode of replication
What was Meselson and Stahl’s experiment?
They used different N isotopes to show that the double helix produced had one parent strand and a new daughter strand
What monomers make up a single strand of DNA?
adenine, thymine, cytosine, guanine
What are the three parts of a monomer?
pentose sugar, phosphate group, nitrogenous base
What are the two purine bases?
adenine and guanine
What are the two pyrimidine bases?
cytosine and thymine
What is the 1’ Carbon connected to?
nitrogenous base
What is the 2’ Carbon connected to?
hydroxyl group
What is the 3’ Carbon connected to?
-OH group
What is the 5’ Carbon connected to?
Phosphate group
What is found at the 5’ end of a DNA molecule?
exposed phosphate group
What is found at the 3’ end of a DNA molecule?
exposed -OH group
What is the name of the bond joins nucleotides together in a single strand?
phosphodiester bond
What type of bond is a phosphodiester bond?
covalent bond
Where does the phosphodiester bond form?
3’ Carbon of one sugar molecule and 5’ Carbon of another
What bond forms the double helix?
hydrogen bonds
DNA strands are what?
antiparallel and complementary
What does antiparallel mean?
One strand is 5–>3 and the other is 3–>5
Cargaff determined what?
base pair rules
Adenine and Thymine are joined by how many hydrogen bonds?
2
Cytosine and Guanine are joined by how many hydrogen bonds?
3 bonds
definition: breaks down hydrogen bonds at one or more origins of replication
DNA helicase
definition: stabilizes unwound DNA and prevents reforming of hydrogen bonds and DNA from being degraded
Single-strand binding proteins (SSB)
definition: relieves tension as DNA is unwound
Topoisomerase
Which enzyme forms replication forks?
DNA helicase
What does it mean for DNA replication to be bidirectional?
The process of replication happens at the same time in opp directions
How many replication forks are formed at each origin of replication?
two
definition: break and rejoin DNA strand to prevent supercoiling
topoisomerases
What enzyme begins replication?
DNA helicase
definition: enzyme that uses parent strand as a template and adds nucleotides to form daughter strand
DNA polymerase
What are DNA ploymerases limitations?
- Can only add nucleotides to 3’ end
- Can’t add first nucleotide of a new daughter
definition: makes a complementary RNA primer at each origin of replication
DNA primase
DNA polymerase replicates in what direction?
5–>3
definition: daughter strand that is synthesized continously
leading strand
In what direction is the leading strand synthesized?
Towards the replication fork
Where is a single RNA primer synthesized?
At the origin of each leading strand
What is the RNA primer synthesized by?
DNA primase
How many RNA primers will by synthesized by DNA primase for the leading strand?
one
definition: short pieces of the lagging strand
okazaki fragments
definition: the daughter strand synthesized away from the replication fork
lagging strand
What bond does DNA ligase use to link okazaki fragments?
phosphodiester bonds
Lagging strand is synthesized in what direction?
5–>3
What are the roles of DNA polymerases during lagging strand?
- adds nucleotides to 3’ end
- degrades RNA primer and replaces with nucleotides
definition: links adjacent okazaki fragments
DNA ligase
definition: enzyme that proofreads as it synthesizes each new daughter strand
DNA polymerase
How many points of origin does prokaryotic chromosomes have?
only one
How many points of origin does eukaryotic chromosomes have?
multiple origins of replication
When would a cell use mismatch repaired?
When DNA. has been incorrectly paired
When would a cell use nucleotide excision repair?
When DNA has been damaged by UV radiation or carcinogens
What do nucleases do in the DNA proofreading and repair process?
cuts out DNA
What does DNA polymerase do in the DNA proofreading and repair process?
it adds the correct nucleotides
What does DNA Ligase do in the DNA proofreading and repair process?
It links the new pieces of DNA with phosphodiester bonds
definition: repair that cuts out DNA that has been incorrectly paired
mismatch repair
definition: cuts out DNA that has been damaged by UV radiation or carcinogens
Nucleotide excision repair
A small portion at the end of each linear chromosomes cannot be what?
replicated
Why can a small part at the end of a chromosome not be replicated?
limitation of DNA polymerase
- cant replace RNA primer at 5’ end
What happens to the RNA primer at the end of replication?
it is eventually degraded
What happens to chromosomes at the end of each cell cycle?
they shorten sligtly
definition: short, noncoding, repetitive DNA sequences at the end of chromosomes
telomeres
What does telomerase do?
extends length of chromosomes by adding telomere sequences
Telomerase is active in what kind of cells?
Ones that have unlimited cell division
definition: cells that have unlimited cell division
epithelial stem cells
What relates to telomere shortening?
cell aging and apoptosis
Why do cells lose their ability to divide?
Because telomeres get too short
Henry and Chase radioactively labelled the DNA with what?
phosphorus
Henry and Chase radioactively labelled the proteins with what?
sulfur
What is the sugar phosphate backbone of DNA formed by
phosphate groups, phosphodiester linkages, deoxyribose sugars, covalent bonds
