Chapter 14
What might happen if DNA helicase was not functional?
replication could not occur, if the DNA does not open there is no template available for DNA polymerase to use
What might happen if the RNA primers were not all removed from the new DNA strand?
result in a DNA molecule that is embedded with stretched of RNA sequence
Which method of DNA replication was suggested by Watson and Crick and was then further confirmed by Meselson and Stahl?
semiconservative method
How do errors in DNA replication relate to evolution?
sequence changes (mutations) are the source of the genetic variation upon which natural selection operates
Prokaryotic Replication
single origin, one circular DNA molecule, occurs in cytoplasm, DNA pol 3, one replication, replication is quick, okazaki fragments are long
What are SSBP's and what do they do in the context of DNA replication?
single strand binding proteins, bind to and stabilize single stranded DNA
What might happen if DNA polymerase incorporated the wrong nucleotide in the new DNA strand?
the bond would be unstable
What happens to the length of the chromosomes every time a cell divides?
the chromosomes are shortened
What are Chargaff's rules?
the proportion of A always equals that of T and the proportion of G always equals that of C, and the ratio of G-C and A-T varies with different species
What might happen if SSBPs were not functional?
the two strands of DNA that were broken apart by helicase would bind back together
Why might cell division be detrimental to our children?
they would lose some DNA sequences that make up their genes and it would lead to premature aging
5' ATGGGACTCACT 3'
3' TACCCTGAGTGA 5'
Which direction is the new strand built?
5' to 3'
Within the structure which nitrogenous bases "pair" together?
A-T and G-C
How did this correlate with Chargaff's rules?
The amount of adenine present in DNA always equals the amount of thymine and the amount of guanine always equals the amount of cytosine
What is topoisomerase (DNA gyrase) and what does it do in the context of DNA replication?
enzymes that can alter the topological state of DNA, act to relieve the torsional strain cause by unwinding and to prevent supercoiling from happening
What is DNA polymerase and what does it do in the context of DNA replication?
an enzyme that matches the existing DNA bases with complementary nucleotides and then links the nucleotides together to make a new strand
What is DNA helicase and what does it do in the context of DNA replication?
an enzyme that uses energy from ATP to unwind the DNA template
What is the difference between the leading strand and the lagging strand?
leading strand- the strand that is continuously replicated lagging strand- replicated discontinuously in short sections
What is the basic structure of DNA that was published by Watson and Crick?
double helix
What is primase and what does it do in the context of DNA replication?
enzyme that can start an RNA chain from scratch, adds nucleotides at a time using parental DNA as a template, it can only build off an existing 3'OH group
Which organisms were first tested in the experiments aiming to identify the molecule of inheritance?
mice, bacteria, and viruses
Eukaryotic Replication
multiple origins, 46 linear chromosomes, occurs in the nucleus, DNA pol epsilon, DNA pol delta, large number of replicons, replication is slow, okazaki fragments are short
Is DNA polymerase a "perfect" enzyme?
no, uses 3' to 5' exonuclease activity to correct incorrect nucleotides
How many RNA primers are needed for the lagging strand?
one for each fragment
semiconservative method
one strand of the parental duplex remains intact in daughter strands; a new complementary strand is built for each parental strand consisting of new molecules
What is the name for the regions of DNA where replication begins?
origin of replication
How are thymine dimers repaired?
photorepair, an enzyme called photolyase absorbs light in the visible range and uses the energy to cleave the thymine dimers
How many RNA primers are needed for the leading strand?
1
After the RNA primers are all removed, which enzyme is responsible for joining the fragments of DNA together into one long continuous strand?
DNA ligase
Why do we need primase at all? Why can't DNA polymerase just build the new DNA strand on its own?
DNA polymerase require a primer to begin synthesis, they cannot begin without a strand or RNA or DNA base paired to the template
What might happen if DNA polymerase was not functional?
DNA replication would stop, no other function would be carried out, complementary nucleotides would not be added and a new strand would not be made
What are the DNA segments on the lagging strand called?
Okazaki fragments
What does antiparallel mean?
Subunits 5' and 3' run in opposite directions
What are thymine dimers?
formed by a photochemical reaction of UV light and adjacent thymine bases in DNA, UV radiation causes the thymine's to react covalently linking them together
What might happen if primase was not functional?
if inactivated DNA polymerase 3 would not be able to build a complementary strand
Why might cell division be detrimental to us?
if our DNA keeps getting shortened we could lose some of our DNA or a portion of important genes
What might happen if topoisomerase was not functional?
supercoiling that could cause damage to the DNA from overwinding
What is the name of the enzyme that is critical in DNA replication in gamete formation?
telomerase
How do we replicate the ends of our chromosomes?
telomerase uses internal RNA as a template and not the DNA itself, this allows short stretches of DNA to be synthesized composed of repeated nucleotide sequences complementary to the RNA of the enzyme