Biology 102 Chapter 6:
This chapter covers cell division, explaining the stages of the cell cycle (interphase and mitosis) and the processes of mitosis and meiosis. Mitosis creates two identical cells, while meiosis forms gametes with half the chromosome number, introducing genetic variation throu...
Biology 102: Learn Before Lecture #7
Q1. What are the 2 main stages of the cell cycle?
Interphase
Cell Division (M phase)
Q2. What critical event occurs during a cell’s S phase? DNA replication
Q3. What best describes a cell that is in the G0 phase? A non-dividing, resting state.
Q4. What are the two main reasons that cell division occurs?
Mitosis – division of the nucleus
Cytokinesis – division of the cytoplasm and plasma membrane
Q5. During mitotic division, what two steps are described below?
Dividing the replicated chromosomes in half - mitosis
Dividing the cytoplasm in half - cytokinesis
Q6. Why do the chromosomes have to be replicated before cell division occurs?
To ensure that each daughter cell receives a complete set of genetic information.
Q7. What are replicated chromosomes called? Sister chromatids
Q8. Describe what is happening at each of the following mitotic phases.
phase events
Prophase Chromosomes condense into distinct units, making them visible under
a microscope. Each chromosome consists of two sister chromatids.
The mitotic spindle begins to form, and the nuclear envelope breaks
down.
Metaphase The nuclear envelope has completely disappeared. Chromosomes line
up at the metaphase plate. Spindle fibers attach to the centromeres of
each chromosome, with each sister chromatid connected to opposite
poles.
Anaphase The sister chromatids are separated and pulled apart by the shortening
of the spindle fibers. They are now considered individual daughter
chromosomes, which are drawn toward opposite poles of the cell.
Telophase Two new nuclear envelopes form around the separated chromosomes at
each pole. Chromosomes begin to decondense, returning to their less
visible chromatin form. The spindle fibers disappear, and cytokinesis
typically begins, leading to the final separation into two distinct cells.
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, Biology 102 Chapter 6 - The Cell Cycle
Cell Cycle
● The continuity of life is based on the reproduction of cells, or cell division.
● In unicellular organisms, division of one cell reproduces the entire organism
● Multicellular organisms depend on cell division for:
1. Development from a fertilized egg (zygote)
2. Growth
3. Injury repair
4. Asexual reproduction (in some)
● Cell cycle - the life of a cell from formation to its own division.
The cell cycle is separated into several stages.
2 major stages:
● Interphase - 90% of the cycle.
○ Cell grows, takes in nutrients, produces biomolecules, performs special functions
Interphase is further divided into 3 phases:
G1 (gap 1):
● first phase of a new cell
● Grows to full size
Normal cell functions
S (synthesis):
● cells begin preparations for division
DNA is copied (synthesized)
G2 (gap 2):
● final preparation for division
Cell division - cells go through the steps necessary to divide in two.
Not all cells complete the cycle
● Some cells may "step out" of the cell cycle during G1
● The cells are said to be in G0 - a non dividing state
● Some cells never leave it
○ Muscle cells
○ Neurons
Cell division and DNA
● Most cell division results in daughter cells with identical DNA.
● DNA is associated with special proteins to form chromatin.
● A eukaryotic cell’s chromatin is divided among several chromosomes.
● Prokaryotes have a single circular chromosome.
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