DNA Replication
Third line and beyond
-130 different repair mechanisms in human
In bacteria there are
-5 different DNA polymerases; in human there are >/5
30 - nm Fiber
-A level of DNA folding in which nucleosomes are wrapped together due to the binding of the histone H1
Nucleosome core partical
-A partical that consists of eight histone proteins: 2 copies of H2A, 2 copies of H2B, 2 copies of H3, and 2 copies of H4
Nucleosome
-A structure in which the DNA double helix is wrapped two times around a nucleosome core particle
Semi-conservative
-A term that describes how DNA is replicated. Specifically, this described describes how each new DNA molecule consists of one old, parental strand of DNA and one newly synthesized strand
Bidirectional, arrows will meet
-DNA molecules is fully replicated
In E coli, which enzyme adds new nucleotides to a growing DNA strand in a 5' to 3' direction?
-DNA polymerase III
RNA primase
-DNA polymerase cannot build RNA fragments -this is the job of this enzyme -RNA primer
Front line
-DNA polymerases proofread newly made DNA
True or false? The process of DNA replication is extremely accurate. Few errors in the process occur.
-False
The formation of phosphodiester bonds between nucleotides requires energy. Where do DNA polymerases get the energy needed to catalyze the formation of phosphodiester bonds?
-From the hydrolysis of nucleoside triphosphates (dATP, dGTP, dCTP, and dTTP)
There are 5 different kinds of histone proteins
-H2A, H2B, H3, and H4 = form nucleosomes core particle -H1 important in allowing DNA that is the nucleosome un-condensed form to start condensing into tighter and tighter packages
Which statements accurately describe what happens when DNA replication reaches the end of a linear chromosome? Choose all statements that are correct.
-No unusal events occur on the leading strand; the end of the strand is replicated -Unusual events occur on the lagging stand; a small segment on the end is not replicated -The RNA primer of the last Okazaki Fragment on the lagging strand cannot be replaced with DNA -Because a segment of DNA at the end of the lagging strand is not copied, repeated rounds of replication result in chromosomes that become shorter
In E. coli, Which enzyme creates the RNA primers that are necessary for synthesis of new DNA strands?
-Primase
What determines the nucleotide sequence of the newly synthesized strand during DNA replication?
-The nucleotide sequence of the template strand
Which statement accurately describes the observation that DNA replication is bidirectional?
-The replication of DNA proceeds in both directions away from the origin of replication
True or false? A telomere is region of DNA that consists of a single sequence that repeated over and over again. Telomeres mitigate the shortening of chromosomes that occurs with repeated rounds of replication.
-True
True or false? At any given time, most of the DNA in the nucleus of a human cell is condensed beyond the level of nucleosomes into 30 nm fibers. Consequently, this DNA cannot be replicated or transcribed.
-True
True or false? During DNA replication, the leading strand is synthesized continuously in the direction of the replication fork while the lagging strand is synthesized discontinuously in direction away from the replication fork.
-True
True or false? While DNA polymerase I can replace the RNA nucleotides of the RNA primer with DNA nucleotides, it cannot connect fragments of DNA together. Thus, another enzyme is required to connect the fragments of the lagging strand.
-True
Bacterial chromosomes have
-a single origin of replication
DNA polymerase (list)
-add new nucleotides only to the 3' end of an existing nucleotide -cannot initiate synthesis of a new DNA strand -cannot link (ligate) pre-existing nucleotides that are not connected by a phosphodiester bond
Leading strand
-always gets bigger in a nice continuous fashion going from 5' to 3' -synthesize continuously in the direction of the replication fork
Strands are
-antiparallel -hydrogen bonds hold together strands
DNA helicase
-are going to latch onto DNA and split the 2 strands apart -> unzipping double helix
DNA polymerase III
-attaches at the 3' end of an RNA primer and begins adding DNA nucleotides -builds a new strand -is not completely accurate, errors slip through sometimes
Histone proteins (definition)
-basic (+ charged) proteins that help chromosomes condense. H2A, H2B, H3 & H4 help form nucleosomes, H1 allows adjacent nucleosomes to bind
New strands begin with an RNA primer that is
-built by a special enzyme (primase)
Any nucleotide if you attach 3 extra phosphate groups ...
-can be an energy containing molecule
DNA polymerase
-can only add new nucleotides to an existing 3' end -the DNA polymerase that is generally involved in synthesizing new DNA cannot replace RNA with DNA, you would have to have another type of DNA polymerase to do that
Repeated rounds of DNA replication =
-chromosomes get shorter, because you can't replace those RNA primer nucleotides on one strand with DNA at the very end of a chromosome -erosion
Telomeres (list)
-consists of one short nucleotide sequence that is continually repeated (TTAGGG) -protects genes from being eroded away by repeated replications -in germ cells an enzyme (telomerase) catalyzes the lengthening of telomeres
Replication is semi-conservative:
-each new DNA molecule consists of one parental strand and one newly synthesized strand
To fit inside your cells
-each of your 46 chromosomes must be tightly packed or condensed
DNA polymerase (definition)
-enzymes that catalyze the addition of nucleotides to a new DNA strand -builds a polymer
Histone proteins only occur in
-eukaryotic cells
Telomeres
-eukaryotic chromosomes have special nucleotide sequence at their ends -is present in cancer cells (when you turn on telomerase when its not suppose to be turned on = cancer)
DNA
-evolved from RNA -is the molecule of hereditary -molecule that gets copied and passed on to the next generation -influence the overall anatomy, physiology, and behavior of organisms
Have DNA polymerases have to be given an
-existing 3' end to attach to -make a short RNA primer once it is in place the DNA polymerase now has a 3' end to attach to
Lagging strand
-gets bigger in a discontinuous fashion, discontinuous fragments, 3' to 5' -synthesized discontinuously in the direction away from the replication fork
Single stranded binding proteins
-gonna keep the 2 strands from reforming double helix
Histone proteins
-help DNA fold and coil, it is important they do this because it wouldn't fit inside the cells -also play an important roll in regulation of gene expression -when histones bind to DNA they are not bound permanently
DNA replication is complicated because
-it had to evolve from a pre-existing process that replicated RNA
DNA Ligase
-joins DNA segments -links fragments together
Inability to replace RNA primers at the end of the lagging strand means
-means that chromosomes get shorter each time they are replicated
Life ultimately depends on
-molecules that act as templates for their own replication -DNA molecules (chromosomes) in extant cells -molecular process by which DNA molecules are replicated -should be as faithful (accurate) as possible
Eukaryotic chromosomes have
-multiple origins of replication -hundred of thousands of origins of replication on one larger chromosomes (makes the process faster)
Energy to power formation of phosphodiester bonds by DNA polymerases comes from
-nucleoside triphosphate
Nucleotides that are going to be linked together are going to become
-our energy source -charge them by adding extra phosphate groups
telomeres are actually important in preventing
-premature aging of certain cells
Replication is bidirectional:
-proceeds in both directions from the origin of replication
DNA polymerase I
-replaces RNA nucleotides with DNA nucleotides -replaces RNA nucleotides of the primers with DNA
Replisome
-replication of DNA depends on > 12 different proteins that form a complex, molecular machine
Okazaki fragments
-segments that contain RNA primers and DNA -consists of an RNA primer with DNA
Second line
-specialized enzymes remove & replace incorrectly paired nucleotides = mismatch repair -defects in one mismatch repair enzyme can result in colon cancer
First thing you do when you replicate DNA:
-split 2 strands apart
DNA Replication
-starts at > 1 origin of replication -bidirectional -semi-conservative -antiparallel -nucleotides are added only to the 3' end of a growing strand, a new strand grows in the 5' -> 3' direction
Another type of DNA polymerase replaces
-the RNA nucleotides of primers with DNA nucleotides
Region
-the center of the origin of replication -want lots of adenine and thymine in an origin of replication
One type of DNA polymerase builds
-the new strand
The older you live
-the shorter and shorter the chromosomes become, the more and more the stem cells become unable to perform their function, less able you are to repair your tissues = die
When DNA is condensed beyond the level of nucleosomes:
1) DNA cannot be replicated 2) Genes cannot be transcribed
