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Chapter 6
DNA Synthesis, Mitosis, and Meiosis
Fourth Edition
Science for Life | with Physiology
Colleen Belk • Virginia Borden Maier
© 2013 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
Passing Genes and Chromosomes to Daughter Cells
 following DNA replication – a cell is ready to divide
 cell division = cell reproduction
 two kinds:
 1. Asexual reproduction:
 Only one parent
 Offspring are genetically identical to parent
 2. Sexual reproduction
 Gametes are combined from two parents
 Offspring are genetically different from one another
and from the parents
© 2013 Pearson Education, Inc.
Eukaryotic Cell Division = Mitosis
eukaryotic cell division consists of two stages:
 Mitosis - the division of the duplicated genetic material in the nucleus
 Cytokinesis - the division of the cytoplasm
mitosis described by the German anatomist Walther Flemming in
 thought the cell was simply growing larger between each period of cell
now known that mitosis is a part of the life cycle of a cell
called the Cell Cycle
 internal “clock” that defines the periods of DNA synthesis and replication
© 2013 Pearson Education, Inc.
Animation: The Cell Cycle
Click “Go to Animation” / Click “Play”
© 2013 Pearson Education, Inc.
The Cell Cycle and Mitosis
 Cell cycle has three steps:
 Interphase: the DNA replicates
 Mitosis: the copied chromosomes
are moved into daughter nuclei
 Mitosis occurs in somatic or body
 Cytokinesis: the cell is split into 2
daughter cells
© 2013 Pearson Education, Inc.
 Interphase has three phases:
 G1: cell grows, organelles duplicate
 time of normal cell functions and cell growth
 portion of cell cycle where the cell commits to division or enters into a
dormancy phase (G0)
 S: DNA replicates
 G2: cell makes proteins needed to complete
 may not be found in all cells
 protein synthesis in preparation for M phase
 duplication of centrioles
 Most of the cell cycle is spent in interphase
© 2013 Pearson Education, Inc.
BioFlix: Mitosis
© 2013 Pearson Education, Inc.
 Mitosis produces genetically-identical daughter
 Mitosis is followed by cytokinesis which splits the
two nuclei into two daughter cells
 Four stages of Mitosis:
 Prophase
 Metaphase
 Anaphase
 Telophase
© 2013 Pearson Education, Inc.
The Duplicated Chromosome
prior to mitosis - the DNA/chromosomes
must condense
they condense so much – they become
visible under a regular light microscope
condensing starts in interphase and
finishes in the early stages of mitosis
unique conformation
duplicated chromosomes are held
together with a structure called a
 two duplicated chromosomes are
called sister chromatids
DNA condensation animation -
© 2013 Pearson Education, Inc.
The Centriole & Mitosis
-mitosis requires the presence of centrioles within the cell
-centriole: short cylinders of a protein known as tubulin
- tubulin is organized into short “straws” – outside the nucleus
-3 straws are joined together
-9 straw triplets are arranged in a circle
-two centrioles are put together as a pair
-one centriole pair is found in cells that can divide
-duplicated in the G2 phase of the cell cycle
-spindle grows in between the two centriole pairs
© 2013 Pearson Education, Inc.
1. Prophase:
1. DNA/chromatin finish condensing to become visible
2. the centriole pairs move apart from each other
3. the spindle forms between the centrioles
-spindle is made up of “strands” of proteins called microtubules
(made up of tubulin)
4. duplicated chromosomes attached to the spindle
5. the nuclear envelope begins to disappear
Spindle with chromosomes attached
© 2013 Pearson Education, Inc.
 Metaphase:
 Chromosomes are aligned across the middle of the spindle
 area of alignment is called the metaphase plate
© 2013 Pearson Education, Inc.
 Anaphase:
 centromeres split & the individual sister chromatids
are pulled apart toward opposite centriole pairs
** At the end of this phase –
each end of the cell has
equivalent numbers
of chromosomes – same
number as the parent cell
© 2013 Pearson Education, Inc.
 Telophase
 basically the reverse of prophase
 Nuclear envelopes reform around chromosomes
 Chromosomes revert to uncondensed form
 telophase is finished upon the division of the cytoplasm/the
cell = cytokinesis
 Cytokinesis:
 division of the cytoplasm and the parent cell into two
identical daughter cells
 part of telophase
 slightly different between animal and plant cells
© 2013 Pearson Education, Inc.
 Cytokinesis – Animal Cells:
(a) Cleavage of an animal cell (SEM)
 formation of a cleavage furrow in the
center of the cell
 cell is divided through a “pursestring” mechanism
100 m
Cleavage furrow
Contractile ring of
© 2013 Pearson Education, Inc.
Daughter cells
 Cytokinesis in Plants:
 Starts with vesicles forming a cell plate.
 contain the materials to build a new cell wall
 fusion of these vesicles produces a new cell wall
between the two daughter plant cells.
© 2013 Pearson Education, Inc.
Animation: Mitosis
Click “Go to Animation” / Click “Play”
© 2013 Pearson Education, Inc.
Mitosis – A Summary
© 2013 Pearson Education, Inc.
Mitosis – A Summary
© 2013 Pearson Education, Inc.
Cell Cycle Control and Mutation
 the cell cycle is a tightly controlled process
 before the cell moves onto the next stage in its cell cycle – must STOP and CHECK
to see if everything is okay
 these STOP and CHECK points are called checkpoints
 cell must pass certain conditions to proceed onto the next stage
 3 checkpoints: G1,G2, and metaphase
© 2013 Pearson Education, Inc.
Cell Cycle Control and Mutation
 one factor that can change the control of the cell cycle is
a mutation in a gene that functions in the cell cycle
 Mutation: a change in the sequence of DNA
 changes to DNA can change the structure and function of
the protein coded by the DNA
 mutations may be inherited or caused by carcinogens
 problems in the cell cycle arise when two kinds of genes
are mutated
 1. Proto-oncogenes
 2. Tumor suppressor genes
© 2013 Pearson Education, Inc.
Cell Cycle Control and Mutation
 Proto-oncogenes: genes that code for cell cycle control
 play normal roles in the normal cell cycle
 BUT when proto-oncogenes mutate - they can become
 Their proteins no longer properly regulate cell division
 They usually overstimulate cell division
© 2013 Pearson Education, Inc.
Cell Cycle Control and Mutation
 Tumor suppressor genes: genes for proteins that stop
cell division if conditions are not favorable
 When mutated - can allow cells to override checkpoints
© 2013 Pearson Education, Inc.
Cell Cycle Control and Mutation
 uncontrolled cell cycle  uncontrolled cell growth  tumor
 tumor formation depends on the kinds and numbers of mutations
 two kinds of tumors: benign and malignant (cancer)
 Multiple hit model:
process of cancer
development requires
multiple mutations
 Some mutations may be
inherited (familial risk)
 Most are probably
acquired during a
person’s lifetime
© 2013 Pearson Education, Inc.
What Is Cancer?
 Tumor: Unregulated cell division that form a mass of cells with no function
 Benign tumor: doesn’t affect surrounding tissues
 Malignant tumor: invades surrounding tissues; cancerous
 Metastasis: cells break away from a malignant tumor and start a new cancer
at another location
travels through the circulatory and the lymphatic systems - invades other tissues
© 2013 Pearson Education, Inc.
Cancer Development Requires Many Mutations
 Progression from benign tumor to cancer requires many mutations.
 also requires several events to happen:
 1. Angiogenesis: tumor gets its own blood supply
 tumor secretes growth factors  new blood vessel growth
 2. Loss of contact inhibition: cells will now pile up on each other
 not seen in normal cells
 3. Loss of anchorage dependence: enables a cancer cell to move to another
 results in metastatic capacity
 4. Cancer cell becomes Immortalized: cells no longer have a fixed number of
cell divisions
due to an enzyme called telomerase
prevents the ends of a chromosome from shortening with every round of mitosis
© 2013 Pearson Education, Inc.
What Is Cancer?
 Risk factors: increase a person’s risk of developing a
 Tobacco use: tobacco contains many carcinogens
 Alcohol consumption
 High-fat, low-fiber diet
 Lack of exercise
 Obesity
 Increasing age which weakens the immune system
 Cells that divide frequently such as ovarian cells
© 2013 Pearson Education, Inc.
Cancer Detection and Treatment
 Early detection increases odds of survival
 there are different detection methods for different
kinds of cancers
 Some cancers produce increased amount of a
characteristic protein
 e.g. prostate cancer – PSA antigen????
 Biopsy: typical method for analysis of a possible
 surgical removal of cells or fluid for analysis
 Needle biopsy: removal is made using a needle
 Laparascope: surgical instrument with a light, camera, and
small scalpel
© 2013 Pearson Education, Inc.
Cancer Treatment Methods
 Chemotherapy: drugs that selectively kill dividing cells
 Combination of different drugs used (“cocktail”)
 Interrupt cell division in different ways
 new chemotherapies help prevent resistance to the drugs
from arising
 PROBLEM: normal dividing cells are also killed (hair
follicles, bone marrow, stomach lining)
 many come from nature
 e.g. Taxol – pacific Yew tree
© 2013 Pearson Education, Inc.
Cancer Treatment Methods
 Radiation therapy: use of high-energy particles to
destroy cancer cells
 Damages their DNA so they can’t continue to divide or
 Usually used on cancers close to the surface
 Typically performed after surgical removal of tumor
 If a person remains cancer free after treatment for 5
years they are in remission and after 10 years they are
© 2013 Pearson Education, Inc.