Ch. 16: DNA Replication
Many proteins work together in DNA replication and repair
• The relationship between structure and function
– Is manifest in the _________________________
• Since the two strands of DNA are_____________________
– Each strand acts as a template for building a new strand
in replication
• In DNA replication
– The parent molecule unwinds, and two new daughter
strands are built based on ________________________
• DNA replication is ___________________________
– Each of the two new daughter molecules will have one
old strand, derived from the parent molecule, and one
newly made strand
•
Experiments performed by ___________________________________
– Supported the ___________________________ model of DNA replication
DNA Replication
• The copying of DNA
– Is remarkable in its speed and accuracy
• More than a dozen enzymes and other proteins
– Participate in DNA replication
• The replication of a DNA molecule
– Begins at special sites called _______________, where the two strands are separated
•
A eukaryotic chromosome
– May have hundreds or even
thousands of replication
_______________
• Elongation of new DNA at a
replication fork
– Is catalyzed by enzymes
called _______________,
which add nucleotides to
the____end of a growing
strand
How does the antiparallel structure of the
double helix affect replication?
• DNA polymerases add nucleotides
– Only to the free ____ end of a growing strand
• Along one template strand of DNA, the ________________________________
– _________________________________ can synthesize a complementary strand
_______________________, moving ___________________ the replication fork
• To elongate the other new strand of DNA, the _____________________________
– ____________________________ must work in the direction __________ from the
replication fork
• The lagging strand
– Is synthesized as a series of segments called ___________________________, which are then
joined together by ____________________
• Synthesis of leading and lagging strands during DNA replication
1 DNA pol Ill elongates
DNA strands only in the
5
3 direction. 3
5
Parental DNA
5
3
Okazaki
fragments
2
1
3
5
DNA pol III
2 One new strand, the leading strand,
can elongate continuously 5
3
as the replication fork progresses.
3 The other new strand, the
lagging strand must grow in an overall
3
5 direction by addition of short
segments, Okazaki fragments, that grow
5
3 (numbered here in the order
they were made).
Template
strand
3
Leading strand
Lagging strand
2
Template
strand
Figure
16.14
1
DNA ligase
Overall direction of replication
4 DNA ligase joins Okazaki
fragments by forming a bond between
their free ends. This results in a
continuous strand.
Priming DNA Synthesis
• DNA polymerases cannot initiate the synthesis of a
polynucleotide
– They can only add nucleotides to the 3 end
• The initial nucleotide strand
– Is an __________________________
• Only one primer is needed for synthesis of the leading
strand
– But for synthesis of the lagging strand, each
Okazaki fragment must be primed separately
• ______________________,___________________, and
____________________________
– Are all proteins that assist DNA replication
A summary of DNA replication
•
•
•
•
•
The various proteins that participate in DNA replication
– Form a single large complex, a DNA replication “machine”
The DNA replication machine
– Is probably stationary during the replication process
___________________________ proofreads newly made DNA
– Replacing any incorrect nucleotides
In mismatch repair of DNA
– Repair enzymes correct errors in base pairing
In nucleotide excision repair
– Enzymes cut out and replace damaged stretches of DNA
•
•
•
•
The ends of eukaryotic chromosomal DNA
– Get _______________with each round of replication
Eukaryotic chromosomal DNA molecules
– Have at their ends nucleotide sequences, called ___________________, that postpone the
erosion of genes near the ends of DNA molecules
If the chromosomes of germ cells became shorter in every cell cycle
– Essential genes would eventually be missing from the gametes they produce
An enzyme called _________________________
– Catalyzes the lengthening of telomeres in germ cells