Cell Cycle and DNA replication

Week 9: DNA Replication & The Cell Cycle

Learning Goal: Appreciate how cells replicate their chromosomes to pass genetic information on to the daughter

cells during cell division.

•Outline the stages of the cell cycle.

Two stages of the cell cycle: M phase, interphase

Interphase: 

G1. Kinases are made, preparatory phase for S. Checkpoint for DNA damage

S phase (DNA is replicated). Think synthesis of DNA. Checkpoint for errors in replication

G2 phase: The size and protein content of the cell increases. Checkpoint that all chromosomes are replicated

G0 phase: cells pause in CC, have exited but can still carry out specialized functions. 

MPhase: checkpoint if spindle fibers have been attached to sister chromatids correctly

Mitosis: separation of chromosomes into two nuclei

Cytokinesis: division of the cell into two, two separate cell processes typically go hand in hand

•Explain the mechanisms of action in the replication machinery.

Many enzymes are involved in replication

-Helicase: separates strands of the parent by breaking hydrogen bonds holding bp together

-Single-strand binding proteins: bind to single strands to prevent template strands to prevent template strands

 from coming back together

-Topoisomerase: upstream from replication fork to relax strands, preventing supercoiling. Type one cuts one

strand type two cuts both

-DNA Polymerase: synthesizes new strand, requires a primer

-RNA Primase-synthesizes short pieces of RNA complementary to the DNA parent strand

-DNA ligase-adjacent fragments are joined together

•Describe how the process of DNA replication is initiated in prokaryotes and eukaryotes.

DNA replication begins at a single origin of replication in Prokaryotes while Eukaryotes have multiple origins 

of replication

•Discuss the “end replication problem” and how it is dealt with by cells with linear chromosomes.

The end replication problem is due to the cDNA aka primer that is added to the lagging strand so that

Replication can occur. The last primer is placed and then when it is degraded creates a gap that cannot be 

Filled by nucleotide. To solve this problem, linear chromosomes add telomeres to the end of their

Chromosome which is a repeating sequence. Telomerase contains RNA molecule complementary to telomere

Sequence. 

•Relate events in the process of DNA replication to stages in the cell cycle.

G1: “Is DNA damaged”

Sphase: DNA is replicated

G2:

•Relate the quantity of DNA found in a cell to the cell’s progression through the cell cycle.

•Differentiate between the leading and lagging strands during DNA replication.

The leading strand is synthesized continuously while the lagging strand is synthesized in fragments

•Evaluate how changing components of the replication machinery would alter the replication process.

Replication cannot occur without the proper functioning of critical components like helicase primase, DNA 

polymerase

•Predict how changes in telomerase activity affect cell division.

Less active would mean that the chromosome isn't being capped and would shorten over time

•Describe how “heavy” and “light” nitrogen isotopes can be used to distinguish between different possible

models of DNA replication.

It allows researchers to observe the density of the resulting DNA strands through centrifugation, which will 

reveal whether replication is conservative, semi-conservative, or dispersive,

•Interpret data from a centrifugation experiment to determine whether the data are consistent or

inconsistent with different possible models of DNA replication.

Centrifuge spins and separates DNA fragments by size

•Transcribe and translate a cDNA sequence to determine the resulting amino acid sequence.

•Respectfully debate and discuss the decision in the 2013 Supreme Court ruling that ended Myriad

Genetics’ monopoly on BRCA1 gene testing.