1 Structure and Function of the Human Genome
15
for synthesis of a complementary strand. The daughter strand is elongated by sequential addition of dNTPs that are complementary to the
parent strand. Phosphodiester bonds are found between the 5' phosphate
of the dNTP and a free 3' hydroxyl of the nascent daughter strand. A
polymerase always requires the presence of an oligonucleotide primer
to supply the free 3' -hydroxyl group and start polymerization. Polymerases can work only in one direction synthesizing first the 5' end
and then proceeding towards the 3' end of the newly formed strand.
Since the 2 template strands are in anti-parallel orientation, replication
Ieads to a "leading strand" on ohe template strand and a "lagging
strand" on the other template strand (Figure SC). Since replication proceeds in the same direction on both strands, but polymerization of a
daughter strand for the lagging strand proceeds from 5' to 3' as in
the leading strand, the lagging strand has tobe "stitched backwards".
Short RNA primers serve as primers for the polymerase that binds to
the lagging strand (Figure SC). Starting from these primers so-called
Okazaki fragments are polymerized. To finally connect the individual
Okazaki fragments, the RNA primers are replaced with DNA by DNA
polymerases exhibiting an exonuclease activity. Finally, a ligase joins
the Okazaki fragments.
• Replication Ieads to a moving replication fork (Figure SC) as dernonstrahle in electron microscopy (Figure SD).
• The error rate of replication is about one in 10 8 - 10 12 nucleotides. This is
a relatively low error rate, owing to the semi-conservative mechanism
and the presence of DNA repair enzymes.
• The cell cycle is shown in Figure 9A for a yeast as a representative eukaryotic cell. Progression through the cell cycle is regulated by so called
"cell division cycle genes". For example, Figure 9B shows how cyclin
concentrations increase until the cdc2 kinase component of maturation
promoting factor (MPF) is activated at metaphase, the midpoint of mitosis. The cyclin is then degraded and MPF activity drops as the cell divides. Then the cycle repeats.
Transcription and translation
Replication ofDNA is a prerequisite for cell division and permits growth to
occur in an organism. Transcription of genomic DNA into messenger RNA
(mRNA), with the consecutive translation of mRNA into protein, represents
15
for synthesis of a complementary strand. The daughter strand is elongated by sequential addition of dNTPs that are complementary to the
parent strand. Phosphodiester bonds are found between the 5' phosphate
of the dNTP and a free 3' hydroxyl of the nascent daughter strand. A
polymerase always requires the presence of an oligonucleotide primer
to supply the free 3' -hydroxyl group and start polymerization. Polymerases can work only in one direction synthesizing first the 5' end
and then proceeding towards the 3' end of the newly formed strand.
Since the 2 template strands are in anti-parallel orientation, replication
Ieads to a "leading strand" on ohe template strand and a "lagging
strand" on the other template strand (Figure SC). Since replication proceeds in the same direction on both strands, but polymerization of a
daughter strand for the lagging strand proceeds from 5' to 3' as in
the leading strand, the lagging strand has tobe "stitched backwards".
Short RNA primers serve as primers for the polymerase that binds to
the lagging strand (Figure SC). Starting from these primers so-called
Okazaki fragments are polymerized. To finally connect the individual
Okazaki fragments, the RNA primers are replaced with DNA by DNA
polymerases exhibiting an exonuclease activity. Finally, a ligase joins
the Okazaki fragments.
• Replication Ieads to a moving replication fork (Figure SC) as dernonstrahle in electron microscopy (Figure SD).
• The error rate of replication is about one in 10 8 - 10 12 nucleotides. This is
a relatively low error rate, owing to the semi-conservative mechanism
and the presence of DNA repair enzymes.
• The cell cycle is shown in Figure 9A for a yeast as a representative eukaryotic cell. Progression through the cell cycle is regulated by so called
"cell division cycle genes". For example, Figure 9B shows how cyclin
concentrations increase until the cdc2 kinase component of maturation
promoting factor (MPF) is activated at metaphase, the midpoint of mitosis. The cyclin is then degraded and MPF activity drops as the cell divides. Then the cycle repeats.
Transcription and translation
Replication ofDNA is a prerequisite for cell division and permits growth to
occur in an organism. Transcription of genomic DNA into messenger RNA
(mRNA), with the consecutive translation of mRNA into protein, represents