Transcript Chapter-11

How Cells Reproduce
Chapter 11
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole,
Cengage Learning 2011.
Dividing HeLa Cells – Immortal Cells
Cancer cells
+ poliovirus
Allow researchers to study human
diseases without experimenting on
Cell Division Mechanisms
 Reproduction
• Produces a generation of individuals like parents
 Cell division
• Bridges two generations
 Each daughter cell receives
• A required number of DNA molecules
• Some cytoplasm
Mitosis and Meiosis
 Mitosis = Nuclear division, maintain chromosome #
• Basis of growth, cell replacements, and tissue repair
in multicelled species
• Basis of asexual reproduction in many single-celled
and multicelled species
• Asexual reproduction  offspring arise from a single
 Meiosis
• Basis of sexual reproduction
• Precedes formation of gametes or sexual spores
Cell Division Mechanisms
Chromosome Structure
 Eukaryotic chromosome
• Association of DNA, histones, and other proteins
• Proteins structurally organize the chromosome
and affect access to its genes
 Nucleosome
• Smallest unit of organization
• Double-stranded DNA looped twice around a
spool of histones
Structure of a Condensed Chromosome
Fig. 8.4a, p.127
Fig. 8.4b, p.127
Fig. 8.4c, p.127
Fig. 8.4d, p.127
Sister Chromatids
 A duplicated
chromosome consists
of two sister
chromatids, each with
a kinetochore
• Sister chromatids
remain attached at
their centromere until
late in mitosis (or
Key Concepts:
 Individuals of a species have a characteristic
number of chromosomes in each cell
 Chromosomes differ in length and shape, carry
different portions of cell’s hereditary information
 Mechanisms divide information between
daughter cells, along with enough cytoplasm for
each cell to operate on its own
Introducing the Cell Cycle
 Cell cycle
• A series of events from the time a cell forms until its
cytoplasm divides
• Starts when a new cell forms
• Runs through interphase
• Ends when cell reproduces by nuclear and
cytoplasmic division
 The interval between mitotic divisions when a cell
• grows
• roughly doubles the number of its cytoplasmic
• and replicates its DNA
 Most cellular activities occur in interphase
• G1: Cell grows in mass, doubles number of
cytoplasmic components
• S: DNA replication duplicates chromosomes
• G2: Cell prepares for division
Eukaryotic Cell Cycle
Chromosome Number
 Sum of all chromosomes in cells of a given type
 In human body cells, chromosome number is 46
 Body cells are diploid (have two of each kind of
Human Chromosomes: 23 Pairs
Homologous Chromosomes
Definition: Chromosomes
with the same length,
shape, and set of genes.
Each pair was inherited
from one of two parents
Mitosis and Chromosome Number
 Mitosis maintains parental chromosome number
from one generation to the next
• Bipolar spindle divides sister chromatids
microtubule of
bipolar spindle
One of the
in a parent cell
at interphase
The same two
(duplicated) at
prior to mitosis
After mitosis
and cytoplasmic
division, the two
daughter cells
each have one
Both daughter
cells start life
in interphase.
Fig. 8.6b, p.129
Key Concepts:
 Cell cycle starts when a daughter cell forms and
ends when that cell completes its own division
 A typical cycle goes through interphase, mitosis,
and cytoplasmic division
 In interphase, a cell increases its mass and
number of components, and copies its DNA
8.3 A Closer Look at Mitosis
 Mitosis
• A nuclear division mechanism that maintains the
chromosome number
 Mitosis proceeds in four stages:
 Duplicated chromosomes become threadlike as
they start to condense
 Microtubules extending form both centrosomes
form a spindle
 Nuclear envelope starts to break apart
Transition to Metaphase
 Microtubules from one spindle pole harness one
chromatid of each sister chromatid pair
• Microtubules from the opposite spindle pole
harness its sister chromatid
 Other microtubules extend from both poles and
grow until they overlap at the spindle’s midpoint
 All chromosomes become aligned midway
between the two spindle poles
• Chromosomes in most condensed forms
 Sister chromatids detach from each other
• Spindles move them toward opposite poles
 Microtubules that overlap at spindle’s midpoint
slide past each other, push poles farther apart
 Motor proteins drive movements
 Two identical clusters (one chromosome of each
type) reach opposite spindle poles
 Nuclear envelope forms around each cluster
 Both new nuclei have the parental chromosome
Fig. 8.7a, p.130
Fig. 8.7b, p.130
Fig. 8.7c, p.130
Fig. 8.7d, p.130
e Metaphase
All of the chromosomes have
become lined up midway
between the spindle poles.
At this stage of mitosis, the
chromosomes are in their
most tightly condensed form.
Fig. 8.7e, p.130
Fig. 8.7f, p.130
Fig. 8.7g, p.130
Fig. 8.7h, p.130
Key Concepts:
 Mitosis divides the nucleus, not the cytoplasm
• Mitosis has four sequential stages: prophase,
metaphase, anaphase, and telophase
 A microtubular spindle forms
• Moves cell’s duplicated chromosomes into two
parcels, end up in two genetically identical nuclei
Cytoplasmic Division Mechanisms
 Cytokinesis
• Cytoplasmic division
 Mechanisms of cytoplasmic division differ in
plant and animal cells
 In animal cells
• A contractile ring of microfilaments (part of cell
cortex) contracts and pulls the cell surface inward
until the cytoplasm is divided
• Energized by ATP
Cytoplasmic Division in Animal Cells
Fig. 8.8a1, p.132
Fig. 8.8a2, p.132
Cleavage Furrow
indentation where
division will occur
Fig. 8.8a3, p.132
Fig. 8.8a4, p.132
Cytoplasmic Division in Plant Cells
 In plant cells
• have cell wall  prevents the cell from pinching
into two
• A band of microtubules and microfilaments forms
around the nucleus before mitosis starts
• Marks site where cell plate will form
 Cell plate becomes a cross-wall that partitions
the cytoplasm
Cytoplasmic Division in Plant Cells
Fig. 8.8b1, p.132
Fig. 8.8b2, p.132
Fig. 8.8b3, p.132
Fig. 8.8b4, p.132
Results of Cell Division:
A Human Embryo
Key Concepts:
 After nuclear division, the cytoplasm divides and
typically puts a nucleus in each daughter cell
 The cytoplasm of an animal cell is simply
pinched in two
 In plant cells, a cross-wall forms in the
cytoplasm and divides it
Controls Over Cell Division
 Neoplasm
• An accumulation of abnormally dividing cells
• Cause
• Sister chromatid do not separate as they should
during mitosis
• OR DNA gets damaged when a chromosome is
being duplicated
• OR cell’s DNA can also be damaged by free
radicals, or environmental assaults such as
chemicals or ultraviolet radiation
Controls Over Cell Division
 Products of checkpoint genes control cell cycle
• Growth factors  stimulate mitosis
• Epidermal growth factor causes receptors to become
enzymatic and phosophorylate itself
• Receptor is the product of a checkpoint gene
• Cells of most neoplasms carry mutations resulting in its
overactivity or overabundance
When Control is Lost
 Mutant checkpoint genes can cause tumors by
disrupting normal controls
 Occurs when a neoplasm physically and
metabolically disrupts body tissues
 Altered cells grow and divide abnormally
• Malignant cells may metastasize (break loose
and colonize distant tissues)
 Proto-oncogene
• Gene that can become an oncogene
 Oncogene  mutated gene
• Gene that has the potential to transform a normal
cell into a tumor cell
• Some mutation can be passed to offspring
 Tumor
• A neoplasm that forms a lump
 Metastasis
• The process in which cancer cells spread from one
part of the body to another
Benign and Malignant
benign tumor
Fig. 8.12a, p.135
malignant tumor
Fig. 8.12b, p.135
a Cancer cells
break away from
their home tissue.
2 The metastasizing
cells become attached
to the wall of a blood
vessel or lymph vessel.
They release digestive
enzymes onto it. Then
they cross the wall at
the breach.
3 Cancer cells creep or
tumble along inside blood
vessels, then leave the
bloodstream the same way
they got in. They start new
tumors in new tissues.
Fig. 8.12c, p.135
Key Concepts:
 Built-in mechanisms monitor and control the
timing and rate of cell division
 On rare occasions, surveillance mechanisms
fail, and cell division becomes uncontrollable
 Tumor formation and cancer are the outcome
Animation: Cancer and metastasis
Animation: Chromosome structural
Animation: Cytoplasmic division
Animation: Mitosis step-by-step
Animation: The cell cycle