CELL CYCLE, DNA REPLICATION AND
MITOSIS
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vLzbk8R9i4go1-xj7jLqELF2WhbZ4XlM
CELL CYCLE, DNA REPLICATION AND
MITOSIS
Reasons why cells divide:
 1. Repair
 2. Replace old or damage cells
 3. Reproduction
Cell Size Limitations
Ratio of surface area to volume
•
Smaller cells can transport substances more easily
• Diffusion is inefficient over longer distances
• Cytoskeleton less efficient when cells are larger
•
Cellular communication more efficient in smaller cells
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Cellular Growth
The Cell Cycle
•
Once a cell reaches its size limit it must either stop growing or divide.
•
Cells reproduce by a cycle of growing and dividing called the cell cycle.
•
Each time a cell goes through one complete cycle, it becomes two cells.
•
Three main stages of the cell cycle:
• Interphase: stage during which the cells grows, carries out cellular
functions, and replicates its DNA.
• Mitosis: the cell’s nucleus and nuclear material divide; has four
substages.
• Cytokinesis: cell’s cytoplasm divides, creating two new cells.
Copyright © McGraw-Hill Education
Cellular Growth
CELL CYCLE
IS THE SERIES OF EVENTS THAT TAKE PLACE IN A CELL LEADING TO ITS DIVISION AND
DUPLICATION (REPLICATION) THAT PRODUCES TWO DAUGHTER CELLS.
IN CELLS WITHOUT A NUCLEUS (PROKARYOTIC), THE CELL CYCLE OCCURS VIA A PROCESS
TERMED BINARY FISSION.
G0
Many different Diagrams
CELL CYCLE
The sequence of growth
and division of a cell
An average cycle may be
22 hours
Two general periods:
1. growth phase
2. division phase
INTERPHASE (GROWTH PHASE)
Most of the cell’s life is spent in
interphase
Longest phase –(90% of cell’s
growth)
Centrioles – help to organize cell
division
Chromatin – DNA bound protein
within the nucleus
INTERPHASE (GROWTH PHASE)
New DNA is formed during 4 phases:
G1 – 1st period of growth
1. Increase in size.
2. Makes new proteins and
organelles.
G0 – Resting Phase
1. If cells don’t go into this phase it could
cause cancer (tumor)
S – DNA is synthesized or replicated
1. Chromosomes are replicated.
2. New DNA molecules are
made.
G2 – final cell growth
1. Shortest phase
2. Prepares cell for mitosis
Not a part of Interphase
Mitosis –prophase, metaphase, anaphase and
telophase
Cytokinesis- Division on the cytoplasm (2 new cells)
CELL CYCLE
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AFTER CELL GROWTH (G 1) AND RESTING STAGE (G 0):
THE CELL WILL ENTER INTO THE:
DNA REPLICATION STAGE (S)
Oswald Avery (1944)
 Discovered that the
nucleic acid DNA stores
and transmits the genetic
information from one
generation of an
organism to the next
WHERE
HAVE
SCIENTISTS
BEEN?
A BRIEF HISTORY
ALFRED HERSHEY & MARTHA
CHASE (1952)
 Concluded that the genetic material of the bacteriophage
was DNA, not protein.
 Used radioactive phosphorous and sulfur.
ERWIN CHARGAFF (1950)
Discovered a relationship in
the nitrogenous bases
Adenine (A) = Thymine (T)
Guanine (G) = Cytosine (C)
ROSALIND FRANKLIN (1952)
Took an x-ray of the
DNA structure so the
patterns could be seen.
The x-rays show that
DNA is twisted around
each other like a helix
and has two strands.
Watson and Crick proposed that DNA is made up of
2 chains of nucleotides held together by
nitrogenous bases & that the 2 strands are twisted
together in a shape called a double helix.
DNA REPLICATION: AMOEBA SISTERS
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vLzbk8R9i4go1-xj7jLqELF2WhbZ4XlM
REVISIT PRI0R KNOWLEDGE
1. What is the name of this monomer?
2. What is the name of the polymer or
macromolecule to which this monomer
belongs?
DNA is a polymer
made up of repeating
monomers of
nucleotides.
DNA determines an
organism’s traits by
controlling the
manufacturing of
proteins.
The sequencing of
nucleotides forms
unique genetic
information.
THE
STRUCTURE
OF DNA
OVERVIEW OF DNA
Order from smallest to largest
DNA Double Helix-Nucleosome-Coils-SupercoilsChromosome
The nucleus of
a cell contains
chromosomes
Which
are
made
up of
coiled
DNA
Eukaryotic
chromosomes
contain DNA
wrapped
around proteins
called Histones.
Chromosome
Solenoid
Histone Proteins
DNA Double Helix
Each strand of
DNA is made
up
of subunits
called
Each nucleotide is
constructed of 3
parts:
a PHOSPHATE group,
a SUGAR molecule
&
1 of 4 nitrogen bases
Purines
Pyrimidines
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
DNA
REPLICATION
Copying process by which a
cell duplicates its DNA
DNA molecule separates
into two strands, then
produces two new
complementary strands
following the rules of base
pairing
Each strand of the double
helix of DNA serves as a
template for the new strand
Enzyme (Helicase) unzips
DNA by breaking the
hydrogen bonds
between the base pairs,
which produces two
replication forks
DNA polymerase
 Joins individual nucleotides
to make a new strand.
 Proofreads each new strand.
 Joins the hydrogen bonds
Ligase: Enzyme creating the
covalent bond that connect
the sugar phosphate
backbone.
DNA REPLICATION
Because of the
hydrogen bonds,
Adenine can only
bond with Thymine
& Guanine can only
bond with Cytosine
Adenine
Thymine
Guanine
*A purine is always paired with a
pyrimidine.
Cytosine
This is known as
COMPLEMENTARY base pairing
For example:
 GCA ATC TA
 CGT TAG AT
Now you try:
CCA GAT TGA
GGT CTA ACT
All classes
PAP Homework
In class assignment for all classes
G2 PHASE
G2 – final cell growth
1. Shortest
phase
2. Prepares
cell for mitosis
3. Check for no
mistakes in the
chromosomes
4. Repairs any
Mistakes
OCCURRENCES DURING
THE CELL CYCLE
MITOSIS:
The Making of
Body Cells
(Somatic Cells)
TERMS TO KNOW
Chromosome – contains
genetic information (DNA)
passed from one
generation to the next
Spindle – microtubule that
helps separate
chromosomes
A – Centromere:
center of chromosome
B – Chromatids: two
identical “sister” parts
of the chromosome
MITOSIS
(DIVISION PHASE OF BODY CELLS)
4 Phases:
(PMAT)
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
Mitosis Mnemonic &
Hand Motions
Handout papers
MITOSIS ACRONYM
Mitosis only
All cell cycle
Passed (prophase)
I (interphase)
My (metaphase)
Passed (prophase)
Algebra (anaphase)
My (metaphase)
Test (telophase)
Algebra (anaphase)
Test (telophase)
Corrections (cytokinesis)
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
4 phases that blend from one to another.
PROPHASE
1st and longest phase of
mitosis
Chromatin condenses into
chromosomes (chromosomes
become visible)
Nuclear envelope
disappears
Centrioles migrate to poles
Spindles are formed
METAPHASE
2nd phase of mitosis
Chromosomes meet in the
middle of cell
Pulled by spindles
Each chromosome is
attached to top of spindle
ANAPHASE
3rd phase of mitosis
Centromeres are split
apart
Chromatids are pulled
apart and begin to drift to
opposite poles
TELOPHASE
Final phase of mitosis
Begins when chromatids reach
poles
New nucleus starts to form
Chromosomes start to unwind
Spindles disappear
Cytoplasm begins to divide;
cell plate forms
CYTOKINESIS
Cytoplasm pinches completely in half
Cell plate becomes cell wall (if
present)
Each daughter cell has an identical set of
chromosomes
CYTOKINESIS
Animal cells
 The cell membrane is drawn inward forming a cleavage
furrow until the cytoplasm is pinched into 2 nearly equal
parts
Plant cells
 A cell plate gradually develops into a separating
membrane.
All classes
PAP Homework
CELL CYCLE AND CANCER
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CANCER
Cancer is a disorder where the cell has uncontrolled growth. (Does not
go into the G0 phase
Cancer cells do NOT respond to regulators that control timing of cell
cycle (cyclins).
This causes the cells to form masses called tumors, which can damage
surrounding tissues.
Growing out of control, cancer cells produce malignant tumors
Cancer cells do not respond normally to the cell cycle control system
 Divide excessively
 Can invade other tissues
 May kill the organism
If an abnormal cell avoids destruction by the immune system, it may
form a tumor
 Benign: abnormal cells remain at original site
 Malignant: abnormal cells can spread to other tissues and parts of
the body
 Metastasis: spread of cancer cells through the circulatory system
Cancers are named according to location of origin
 Carcinoma: external or internal body coverings
 Sarcoma: tissues that support the body
 Leukemia and lymphoma: blood-forming tissues
Radiation and chemotherapy are effective as cancer treatments
because they interfere with cell division
Aka: Mutagenic Agents
BREAST CANCER CELLS
METASTASIZING CANCER CELL
LUNG CANCER CELLS