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CHAPTER 8
THE CELL CYCLE
P.213-229
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CELL DIVISION

PROKARYOTES
 ASEXUAL
REPRODUCTION/BINARY
FISSION (VOLUME DOUBLES
AND THE CELL SPLITS)SUCH
AS BACTERIA

EUKARYOTES
 UNICELLULARASEXUAL
REPRODUCTION/BINARY
FISSION TO GET 2 NEW
ORGANISMS SUCH AS
PROTISTS
 MULTICELLULARASEXUAL
/BINARY FISSION FOR NEW
TISSUES (GROWTH, REPAIR,
MAINTENANCE)
+

THE CELL CYCLE
REGULATED BY CHEMICALS CALLED CYCLINS
+
INTERPHASE
(THE PERIOD BETWEEN DIVISIONS )

G1GROWTH


G0


A POINT DURING G1 WHERE CELLS
STOP DIVIDING AS THEY HAVE
REACHED A MATURE STATE (SUCH
AS BRAIN AND NERVE CELLS)
SDNA SYNTHESIS


CELL GROWTH AND SYNTHESIS
(RNA, PROTEINS,
MACROMOLECULES)
DNA OF CHROMOSOMES
REPLICATES FORMING A NEW
IDENTICAL SET
G2GROWTH

CELL GROWTH AND SYNTHESIS
(ORGANELLES)
+ MITOSIS (M)

4 PHASES OF NUCLEAR DIVISION, WITH SORTING AND
DISTRIBUTION OF CHROMOSOMES

MADE UP OF 2 CHROMATIDS AND A CENTROMERE
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4 STAGES OF MITOSIS
1.PROPHASE

BREAKDOWN OF NUCLEAR
MEMBRANE, THE SPINDLE FORMS
FROM MICROTUBULES (COMPOSED OF
SPINDLE FIBERS)
2.METAPHASE

CHROMOSOMES BECOME ARRANGED
AT THE EQUATOR (MIDDLE) OF THE
CELL
3.ANAPHASE

CHROMATIDS ARE SEPARATED AND
PULLED APART BY THE SPINDLE
FIBERS TO OPPOSITE ENDS OF THE
CELL (NOW THEY ARE INDIVIDUAL
CHROMOSOMES)
4.TELOPHASE

TWO NEW NUCLEI WITH THE SAME
NUMBER OF CHROMOSOMES FORM
 AFTER TELOPHASECYTOKINESIS
OCCURS
+ WHERE 2 NEW DAUGHTER CELLS ARE FORMED
 IN ANIMAL CELLSFORMS FROM A CLEAVAGE
FURROW
 IN PLANT CELLSFORMS FROM VESICLES
ALONG THE CELL PLATE
+ S PHASE (DNA REPLICATION)
HOW THE PROCESS WORKS

4 MAJOR STEPS
1. ENZYMES AND PROTEINS CALLED HISTONES BIND AT ORIGINS OF
REPLICATION (ALSO KNOWN AS REPLICATION FORKS OR BUBBLES )
2. ENZYMES (CALLED HELICASES) USE ENERGY FROM ATP TO UNWIND THE DNA
DOUBLE HELIX (AT HYDROGEN BONDS BETWEEN THE NITROGEN BASES).
3. ENZYME DNA POLYMERASE CATALYZES FORMATION OF NEW STRANDS BY
ADDING NUCLEOTIDES (SUGAR, PHOSPHATE, NITROGEN BASE).
4. NEW BASES ADDED IN OPPOSITE DIRECTIONS AS DNA POLYMERASE CAN
ONLY WORK IN ONE DIRECTION.
DNA
REPAIR
IN
THE
S
PHASE
+

4 MAJOR STEPS IN THE
PROCESS
1. ENZYME DNA POLYMERASE
PROOFREADS BASE-PAIR MATCHING
AND REPLACES WRONG
NUCLEOTIDE WITH CORRECT ONE.
2. ENZYME (CALLED NUCLEASE)
RECOGNIZES MISMATCH AND BINDS
TO DNA TO BREAK APART DNA PIECE
THAT IS DAMAGED AND REMOVES IT.
3. DNA POLYMERASE FILLS IN
CORRECT SEQUENCE.
4. ANOTHER ENZYME, DNA LIGASE,
RESEALS DNA WITH SUGARPHOSPHATE BACKBONE.