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Biology 100 Vandan Desai
Chapter 11: The Cell Cycle
(Lecture Outline)
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• Cell Theory—all organisms are made of cells and all cells rise from preexisting cells
• Rudolf Virchow proposed that new cells arise through division of preexisting cells (cell division)
• Microscopic observation of newly developing individuals (embryos) confirmed Virchow’s
hypothesis
• Researchers focused on the nuclei of dividing cells and the fate of the chromosomes
o Chromosomes—carriers of hereditary material—instructions for building/operating cell
• In animals, two fundamentally different ways nuclei divide prior to cell division
o Meiosis—leads to production of sperm and eggs—male/female reproductive cells
(gametes)
o Mitosis—leads to production of all other cell types—somatic (“body-belonging”) cells
• In both kinds of cell division, parent cell is said to give rise to daughter cells
• Meiosis:
o Type of nuclear division that leads to production of sperm and eggs
o Amount of hereditary material found in the parent cell nucleus is reduced by half
o Daughter cell that becomes sperm/eggs do not contain same genetic material as parent
o Basis of sexual reproduction and genetic inheritance
• Mitosis:
o uclei divide prior to formation of new somatic cells
o Amount of hereditary material in the original cell and the daughter cell remains constant
o Daughter cells contain identical genetic material to their parent cell
o Usually accompanied by cytokinesis—division of cytoplasm into the two daughter cells
o Supplies the cells required for several key activities in eukaryotes—wound repair,
asexual reproduction, and growth
I. Mitosis and the Cell Cycle
A. Wilhelm Waldeyer coined the term chromosome—refer to the threadlike structures
observed in dividing cells
i. Made up in part of deoxyribonucleic acid (D A)
ii. Consists of a single, long D A double helix wrapped around proteins
B. Prior to mitosis, each chromosome is copied and during mitosis, each copy is
distributed to each of the two daughter cells
C. The Cell Cycle
i. Growing cells cycle b/w…
a. Dividing phase—mitotic (M) phase
• Chromosomes condensed into compact structures
• Allow them to be stained and observed w/ light microscope
b. ondividing phase—interphase
• o dramatic changes observed in nucleus
• Chromosomes uncoiled into extremely long, thin structures
ii. Cell cycle—orderly sequence of events that occurs from the formation of a
eukaryotic cell, through the duplication of its chromosomes, to the time it
undergoes division itself
iii. Two key events take place…
a. The replication (copying) of hereditary material in chromosomes
b. Partitioning of copied chromosomes to two daughter cells
Biology 100 Vandan Desai
D. When Does Chromosome Replication Occur?
i. Radioactive labels not found in M-phase nuclei—only in interphase nuclei
ii. Thus, chromosome replication occurs during interphase
iii. New stage in cell cycle identified called synthesis (or S) phase, for D A
synthesis
iv. Duplication of genetic material occurs independently of mitosis
E. Discovery of Gap Phases
i. There were “lags” in the cell cycle besides
mitotic phase and S-phase, which came to
be known gap phases (G1 and G2)
ii. Dividing cells must replicate organelles and
manufacture additional cytoplasm
iii. Before mitosis can take place, parent cell
must grow larger enough & synthesis
enough organelles that its daughter cells
will be normal in size/function
iv. The two gap phases provide enough time
required to accomplish these tasks
v. The long G1 phase is when cells perform
normal function
II. How Does Mitosis Take Place?
A. Mitosis results in division of chromosomes/formation of two daughter nuclei
B. Humans have a total of 46 chromosomes in each cell
C. Eukaryotic chromosomes normally exist as extremely long, threadlike strands
consisting of DNA associated w/ globular proteins called histones
D. In eukaryotes the DNA-protein complex is called chromatin
E. Prior to mitosis, each chromosome is replicated and condensed
F. Important Vocabulary:
i. Each of the DNA copies in a replicated chromosome is called a chromatid
ii. The two strands are joined together along their entire length as well as a
specialized region of the chromosome called the centromere
iii. Chromatids from the same chromosome are referred to as sister chromatids
a. Once replication is complete, each chromosome = 2 sister chromatids
b. Represent exact copies of the same genetic information
c. Each chromatid contains one long D A double helix
iv. During mitosis, two sister chromatids separate to form independent
chromosomes & 1 copy of each chromosome goes to each of 2 daughter cells
G. ***Refer to the Phases of Mitosis Document for description of each phases***
