CHAPTER 7 - DNA replication + Cell cycle and mitosis Flashcards
What is the purpose of DNA replication?
To turn 1 DNA double helix into 2 identical DNA double-helices
How does DNA replication work?
Separates the 2 strands of the parent DNA and uses each as a template to synthesize new complementary strands until we have 2 complete double-helices.
What is step 1 of DNA replications?
The parent DNA molecule consists of two complementary strands of DNA, with multiple origins of replication along its length (we’ll focus on just one)
What is step 2 of DNA replication?
-Helicase enzymes separate the parent strands in both directions to widen the replication bubble as the parent DNA ‘unzips’ at two replication forks.
-Meanwhile, primase deposits the RNA primers that will provide the 3’ end that DNA polymerase III will need (to add DNA, to start building leading strands).
What is step 3 of DNA replication?
-DNA pol III builds the leading strands towards each replication fork as helicase separates the parent strands.
-Once the bubble is big enough, primase adds primers to the lagging strand so that DNA Pol III can add DNA from 5’ to 3’ (away from the replication fork) in smaller Okazaki fragments.
What is step 4 of DNA replication?
The RNA primers do not belong in the final DNA molecule, so once each Okazaki fragment reaches the primer of the previous Okazaki fragment, DNA Pol I uses its exonuclease activity to remove the primer’s RNA nucleotides, to replace them with DNA nucleotides instead.
What is step 5 of DNA replication?
Once the RNA primer has been wholly replaced with DNA, DNA Ligase seals the two Okazaki fragments together with a covalent bond.
How does the loss of DNA happen?
When the 5’ end of both new strands, and with every cycle of DNA replication, … and this results in chromosomes getting shorter and shorter.
What prevents the loss of DNA, though?
Thankfully, both ends of each of our chromosomes have telomeres (= long repeating sequences of DNA that don’t contain any genes), so we can ‘afford’ to keep losing pieces of these telomeres for many cycles of DNA replication before we lose any genes.
But wouldn’t we (and our offspring, if they inherit our shorter telomeres) eventually run out of telomeres and start losing important genes? (This may be a factor in aging!)
Our germ-line cells have telomerase: an enzyme that uses a built-in RNA template to add more length to telomeres!
What is the Cell Cycle
It’s the life cycle of a cell. It includes cell division (via mitosis and cytokinesis), as well as everything else that happens between one round of cell division and the next.
Analogous example = a plant life cycle, which describes everything that happens from when a seed is made to when that seed is grown up & begins to make its own seeds.
What happens during Interphase?
During interphase, the DNA is in the less-coiled chromatin form, allowing gene expression as the cell performs its normal function.
- However, some cells like mature cardiac muscle cells stop dividing entirely by entering a stable G0 phase.
What is the G1 phase?
When cells grow larger, by making more proteins, organelles and membranes
What is the S phase?
This is when DNA replication occurs. End result being each chromosome goes from having one DNA double-helix to having 2 identical DNA helices. still joined together at the centromere.
When 2 sister chromatids are stuck together, do they count as 2 chromosomes?
No, they count as just one chromosome.
What is the G2 phase?
Cells grow larger by making more protiens, organelles and membranes.
