DNA Replication Flashcards
Why is mitotic division essential?
Growth and regeneration of tissues
The original strand of DNA opens and pairs with a new strand. This “parent” strand pairing with “daughter” strand is known as what?
Semi-conservative replication
Describe DNA replication
Gyrase relieves tension from the DNA strand and causes it to unwind from the double helix
Helicase breaks the hydrogen bonds and unzips the complementary parent strands make, resulting in an unzipped helix that terminated at a replication fork.
Single-stranded binding proteins keep the separated strands of DNA apart by blocking hydrogen bonding between complementary strands.
Primase lays down RNA primers (sections of 40-50 nucleotides) that will be used by DNA polymerase III as a starting point to build the new complementary strands.
DNA polymerase III adds the appropriate nucleotide to the 3’ end of the new strands using the template strand as the guide. It does this by removing water (condensation reaction).
DNA poylmerase I cuts the RNA primers and replaces them with the appropriate nucleotides. DNA ligase joins the faps in the Okazaki fragments by the creation of phosphodiester bonds.
DNA polymerase I and DNA polymerase III (exonucleases) proofread the strand by excising incorrectly paired nucleotides immediately at the end of the complementary strand and addicting the correct nucleotides.
What is the section between two ravelled portions of DNA called?
Replication bubble
What is the difference between the leading and lagging strand?
Leading strand is read 3’ to 5’ and starts at the beginning of the DNA strand.
Lagging strand is also read 3’ to 5’ but because DNA runs antiparallel, DNA poylmerase III must start at the beginning of the replication fork, which opens little by little. Therefore DNA polymerase III is constantly reattaching itself which creates Okazaki fragments.
What is the difference between ribose and deoxyribose?
Ribose has an extra oxygen atom at the 2nd carbon
What type of enzymes proofread DNA after replication and remove errors?
Exonucleases
What group of enzymes stabilize DNA as it is being opened and replicated?
Topoisomerases
Describe telomeres
Since no DNA is assembled on the lagging strand of th elast primer, the final DNA is shorter by this amount. Telomeres are repeating sequences of non-coding DNA at the end of the chromosome.
Prevent chromosomes from fusing, prevent DNA degradation by nucleases, determine lifespan of organisms.
Define cell senescence
Decline of cell due to division past the telomere
Define Hayflick limit
Amount of times a cell can divide (in humans, around 50)
Define telomerase
Enzyme that replaces telomeres in the cells that cannot afford to lose them (germ, cancer, stem, white blood cells, etc.)
How are telomeres related to cancer?
It takes many divisions and an accumulation of mutations for a cell to become cancerous, so cells often become senescent before having the capacity for cancer. However, if we were to extend the lifespan of these cells with telomerase, they would more often become cancerous over time.
The aim is to find a way to completely control telomerase so to immortalize healthy cells but kill cancer ones.
What are some applications of manipulating telomeres?
Cell engineering fields such as bone marrow transplants, burn treatment, cosmetic changes to aging skin, therapy for muscular dystrophy, immunity to macular degeneration.
