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Midterm

NSCI 1404 Study Guide - Midterm Guide: Cell Membrane, Nucleolus, Nuclear Membrane


Department
Natural Science
Course Code
NSCI 1404
Professor
Mark Botton
Study Guide
Midterm

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Cell Cycle and Cell Division:
1. a) Events of the eukaryotic cell cycle!
i) Reproductive signal: initiates cell division and may originate from either inside or
outside the cell!
ii) Replication of DNA/genetic material; each of the 2 new cells will have identical sets of
genes!
iii) Mitosis/division of the nucleus/splitting of genetic material!
iv) Cytokinesis: division of the cytoplasm !
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-G1 phase. Metabolic changes prepare the cell for division. At a certain point - the restriction
point - the cell is committed to division and moves into the S phase. !
-S phase. DNA synthesis replicates the genetic material. Each chromosome now consists of
two sister chromatids. !
-G2 phase. Metabolic changes assemble the cytoplasmic materials necessary for mitosis
and cytokinesis. !
-M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis). The period
between mitotic divisions - that is, G1, S and G2 - is known as interphase.!
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b) regulation of the cell cycle!
-Control of the cell cycle is necessary for a couple of reasons. First, if the cell cycle were not
regulated, cells could constantly undergo cell division. While this may be beneficial to certain
cells, on the whole constant reproduction without cause would be biologically wasteful.
Second, internal regulation of the cell cycle is necessary to signal passage from one phase
to the next at appropriate times. This regulation is not achieved through strict time
constraints, but rather with feedback from the cell.!
-Cyclin-Dependent Protein Kinase (Cdks)- A Cdks is an enzyme that adds negatively
charged phosphate groups to other molecules in a process called phosphorylation. Through
phosphorylation, Cdks signal the cell that it is ready to pass into the next stage of the cell
cycle. As their name suggests, Cyclin-Dependent Protein Kinases are dependent on cyclins,
another class of regulatory proteins. Cyclins bind to Cdks, activating the Cdks to
phosphorylate other molecules.!
-Cyclins- Cyclins are named such because they undergo a constant cycle of synthesis and
degradation during cell division. When cyclins are synthesized, they act as an activating
protein and bind to Cdks forming a cyclin-Cdk complex. This complex then acts as a signal
to the cell to pass to the next cell cycle phase. Eventually, the cyclin degrades, deactivating
the Cdk, thus signaling exit from a particular phase. There are two classes of cyclins: mitotic
cyclins and G1 cyclins.!
-G1 cyclins- G1 cyclins bind to Cdk proteins during G1. Once bound and activated, the Cdk
signals the cell's exit from G1 and entry into S phase. When the cell reaches an appropriate
size and the cellular environment is correct for DNA replication, the cyclins begin to degrade.
G1 cyclin degradation deactivates the Cdk and leads to entry into S phase.!
-Mitotic Cyclins- Mitotic cyclins accumulate gradually during G2. Once they reach a high
enough concentration, they can bind to Cdks. When mitotic cyclins bind to Cdks in G2, the
resulting complex is known as Mitosis-promoting factor (MPF). This complex acts as the
signal for the G2 cell to enter mitosis. Once the mitotic cyclin degrades, MPF is inactivated
and the cell exits mitosis by dividing and re- entering G1. The cellular signals that we
described earlier (cell size, completion of DNA replication, and cellular environment) provide
the signals that regulate the synthesis and degradation of cyclins.
2. a) Organization of the eukaryotic chromosome (chromosome; chromatids; centromere);
Chromosome: a structure composed of DNA and proteins that bears part of the genetic
information of the cell
Chromatid: one copy of a newly copied chromosome which is still joined to the other copy by a
single centromere. Before replication, one chromosome is composed of one DNA molecule.
Centromere: The region where sister chromatids join.
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