Download Cells

BIOSC 041
v  Today’s
lecture
§  Review questions
§  Chapters 12-13, Mitosis & Meiosis
§  Quiz, beginning of class Monday (covers material thru
today)
v  Today’s
lab
§  Check out plates to finish Scientific Method lab from
last week
§  Lab manual exercises 3-4 (Microscopes)
Review: Cells
Which of the following organelles belong to the
endomembrane system?
a. 
Rough ER, smooth ER, mitochondria
b. 
Rough ER, smooth ER, Golgi, lysosomes
c. 
Nuclueus, DNA, RNA
d. 
Ribosomes, mitochondria, Golgi
Review: Cells
Which of the following organelles belong to the
endomembrane system?
a. 
Rough ER, smooth ER, mitochondria
b. 
Rough ER, smooth ER, Golgi, lysosomes
c. 
Nuclueus, DNA, RNA
d. 
Ribosomes, mitochondria, Golgi
Review: Cells
Mitochondria meet the cell’s energy needs by
producing
a. 
Glucose
b. 
Oxygen
c. 
ADP
d. 
ATP
Review: Cells
Mitochondria meet the cell’s energy needs by
producing
a. 
Glucose
b. 
Oxygen
c. 
ADP
d. 
ATP
Review: Cells
Which of the following is true of cilia vs. flagella?
a. 
Cilia are typically smaller and more numerous than
flagella
b. 
Flagella occur only in pairs
c. 
Cilia occur only in pairs
d. 
Sperm use cilia for locomotion
Review: Cells
Which of the following is true of cilia vs. flagella?
a. 
Cilia are typically smaller and more numerous than
flagella
b. 
Flagella occur only in pairs
c. 
Cilia occur only in pairs
d. 
Sperm use cilia for locomotion
Review: Cells
Which of the following is true of prokaryotes vs.
Eukaryotes?
a. 
Prokaryotes may be multi-celled
b. 
Eukaryote cells are typically larger and more complex
than prokaryotic cells
c. 
Prokaryotic cells contain a nucleus, while Eukaryotic cells
do not
d. 
Bacteria are Eukaryotic
Review: Cells
Which of the following is true of prokaryotes vs.
Eukaryotes?
a. 
Prokaryotes may be multi-celled
b. 
Eukaryote cells are typically larger and more complex
than prokaryotic cells
c. 
Prokaryotic cells contain a nucleus, while Eukaryotic cells
do not
d. 
Bacteria are Eukaryotic
BIOSC 041
The Cell Cycle & Meiosis
Reference: Chapters 12 & 13, a little
bit of Ch. 46
Outline
v 
The Eukaryotic Cell Cycle
§  Phases, or Periods, of the Cell Cycle
§  Mitosis
§  Control of the Cell Cycle
v 
Sexual Reproduction and the Process of Meiosis
§  Sexual vs. Asexual Reproduction
§  Chromosome Numbers
§  Meiosis and the production of gametes
§  Gametogenesis: Spermatogenesis and Oogenesis
The Cell Cycle
v 
You began life as a single cell, but there are now more
cells in your body than stars in the Milky Way
§  The body is a community of about 100 trillion cells
§  Of these, only about 10 trillion are human, give or take a million
or two
§  The rest are all the microorganisms with which we coexist
(primarily bacteria, but other small organisms too)
§  You are a walking ecosystem!
The Cell Cycle
v 
Just in the past second, millions of your cells have
divided in two
v 
The process of cell division shown below is very similar to
what is occurring inside your tissues at this very moment
The Eukaryotic Cell Cycle
v 
v 
v 
The Cell Cycle: the “life cycle” of a cell
Genes control every step of the cell cycle
The cell cycle consists of 3 Major Periods, or Phases
1.  Interphase
§  The period during which the cell carries out its function in the body
2.  Cell
Division
§  Mitosis: the replication of nuclear DNA and division of the nucleus
§  Cytokinesis: the division of the cytoplasm into two daughter cells
§  Following cell division, the cell returns to Interphase
3.  Death
§  All cells eventually die; in fact, the inability to die is a hallmark of
cancer
The Eukaryotic Cell Cycle: Interphase
v 
Most of the cell’s “life” cycle is spent in
Interphase
§  Interphase consists of G1àSàG2
§  G1: Normal cell function
G1
S
Interphase
G2
Mitosis &
Cytokinesis
§  Duration varies from seconds to
years, depending on cell type
§  Mature cells arrest at G1, enter
“G0”, and never divide again
§  S: Synthesis phase; DNA & Centrosomes (centrioles) replicate
§  Centrosomes are organelles that control the movement of the
cytoskeleton
§  G2: Preparation for Mitosis
§  Synthesis of necessary enzymes and molecular structures to control
mitosis
More about the S phase of Interphase
v 
During the S phase,
each chromosome
replicates, but stays
together as a single,
replicated chromosome
v 
Each half of the
replicated chromosome
is called a chromatid
v 
After mitosis, each sister chromatid becomes a single,
independent chromosome in the new (daughter) cell
Cell Division: Overview
v 
Four Critical Events
1.  Interphase, G1: Cell receives a signal to divide
2.  Interphase, S: chromosomes replicate
3.  Mitosis: Nuclear Division
4.  Cytokinesis: separation of the cell into 2 daughter cells
G1
S
Interphase
Mitosis &
Cytokinesis
G2
Mitosis has 4 stages, followed by Cytokinesis
v 
Mitosis is a continuous process, divided into 4 stages
1.  Prophase
§  Chromosomes become visible; mitotic spindle forms; nuclear
envelope breaks down
2.  Metaphase
§  Chromosomes connect to mitotic spindle and align at center
of cell
3.  Anaphase
§  Chromatids separate at the centrosome and move to opposite
poles of the cell
4.  Telophase
§  Mitotic spindle disassembles; nuclear envelope reforms
v 
Cytokinesis
§  Separate from mitosis; the two daughter cells physically
separate & complete the process of cell division
v 
Mnemonic: Please Make A Telephone Call
Early Prophase: DNA condenses into a mitotic chromosome
DNA is usually bound up with proteins
called histones to form nucleosomes
nucleosome
Centromere
proteins
Nucleosomes wrap
around each other to
form coils
Coils pack into a mitotic
chromosome
Replicated
Mitosis (Part 1)
INTERPHASE (G2)
Centrosomes
Nucleolus
Start Mitosis: PROPHASE
Early mitotic
spindle
Chromatin
(duplicated)
Nuclear
envelope
LATE PROPHASE
Kinetochore
Centromere
Chromosome, with two
sister chromatids
Mitotic spindle
Mitosis (Part 2)
METAPHASE
Spindle
ANAPHASE
Metaphase
plate
Daughter
chromosomes
TELOPHASE
Cleavage
furrow
Nuclear
envelope
Nucleolus
Cytokinesis
v 
Organelles are distributed
between the two daughter
cells
v 
The cell membrane pinches
in like a drawstring
v 
Separates the two daughter
cells
Cleavage
furrow
Cleavage furrow
Contracting ring of
microfilaments
(a) Animal cell cytokinesis
Daughter cells
Figure 8.8a
Following Cell Division: Return to Interphase
v 
The two daughter cells go on to perform their daily function
in the body, usually side by side in the tissue of which they
are a part
v 
Frequency of Cell Division
§  Frequency and total number vary with the type of cell and age
of the organism
§  Examples
§  Cells in the bone marrow continually divide to produce about
2 million red blood cells every second
§  Nerve cells and many muscle cells stop dividing at a certain
point (G0) and never divide again
Cells have a finite number of cell divisions
v 
The number of cell divisions is under genetic control and is
known as the Hayflick limit
§  Limit depends on cell type but ranges from 10-60 in an adult,
can be much greater in an embryo or juvenile
§  The cell keeps an internal count of the number of cell divisions
§  Once the limit is reached the cell stops dividing
v 
The timing of cell division and the total number of times a
cell will divide result from regulation of the cell cycle
Regulation of the Cell Cycle
v 
The cell cycle is regulated by
a control system with a series
of check points through which
the cell must pass before
proceeding to the next step
v 
At each checkpoint the cell
cycle pauses until the cell
receives a go-ahead signal
v 
Similar to a clock (or washing machine dial)
§  Only goes in one direction – forward
§  Directs the sequential events of the cell cycle
The Major Checkpoints of the Cell Cycle
v 
The G1 Checkpoint: to divide or not?
§  If the cell receives a signal to divide, it moves through the
checkpoint and enters the S phase
§  If the cell doesn’t receive the signal it either stays in G1 or
moves to G0, where it will be “mature” and never divide again
The Major Checkpoints of the Cell Cycle
v 
The G2 Checkpoint: the gateway to mitosis
§  The cell only carries out mitosis if
1.  Chromosomes and centrosomes have been fully replicated
2.  All mitosis components have been synthesized and are
good to go
The Major Checkpoints of the Cell Cycle
v 
The M Checkpoint: During Mitosis
§  Right before Anaphase the cell pauses until it receives a
signal that Metaphase is complete:
§  All chromosomes are connected to the mitotic spindle
and aligned in the middle of the cell
Chemical signals regulate the Checkpoints
v 
The signals the cell receives are chemicals
§  Usually small protein molecules
§  The signals bind to specific protein receptors on the cell surface
v 
Signals come from both inside and outside the cell
§  Signals can come from neighboring cells or even from glands far away
in another part of the body
§  The cell produces internal signals as a go-ahead when key events, such
as chromosome replication, have been completed
Image Credit: Nicolle Rager, National Science Foundation
Example: Protein Growth Factors
v 
Small proteins secreted by cells stimulate other, neighboring
cells to divide
§  Important in building and maintaining tissues and organs
v 
Cells capable of division have special protein receptors on
their surfaces that bind only to these growth factors
§  When mature, a cell loses the receptors and can no longer
respond to the growth factor
Loss of Cell Cycle Controls in Cancer Cells
v 
Cancer cells get it all wrong
§  Do not respond normally to the body’s cell-cycle control
signals that limit cell division
§  The affected cell has lost the ability to respond and keeps
dividing even when sent a signal not to divide
Or
§  It will respond in an inappropriate manner
§  Some cancer cells “help” each other along by secreting
growth factors at the wrong time (or place)
§  Affected cells will divide uncontrollably, forming a tumor
Cell Cycle Summary
v  The
Cell Cycle
§  Periods of the cell cycle
§  Process of cell division
§  Phases of Mitosis
§  Cytokinesis
v  Regulation
of the Cell Cycle
§  Checkpoints
§  Cancer – a genetic disorder of the cell cycle
Reproduction
v 
Asexual = vegetative
§  Mitotic division produces clones
§  The goal is genetic constancy
§  Any variation is due to mutation
v 
Sexual
§  Involves meiosis
§  Each parent contributes one cell (gamete)
§  Results in genetic diversity
§  Offspring are different from parents and each other
Chromosome Numbers
v 
v 
Somatic Cells and Germ Line Cells
§  Contain two sets of chromosomes, one from each
parent = homologous pair (2 homologs)
§  Cells with two sets are diploid (2n)
§  Most common ploidy in animals and many plants
§  Humans: 23 homologous pairs = 46 chromosomes
Gametes
§  Germ Cells derived from Germ Line Cells
§  Haploid (1n)
§  Contain only one set of chromosomes
§  This one set is a mix of parental chromosomes
Describing Chromosomes
2n = 6
Maternal set of chromosomes (n = 3)
Paternal set of chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
S phase
Two non-sister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each parent)
Meiosis: production of gametes
v 
v 
v 
Interphase
§  Chromosomes replicate
Meiotic Division I halves the chromosome number
§  Homologous chromosomes pair up and form bivalents (4 chromatids)
§  Crossing Over (aka Recombination) occurs
§  Homologous pairs then separate but each chromosome remains intact
Meiotic Division II
§  Sister chromatids separate
Meiosis: Crossing Over yields genetic diversity
v  Chiasmata
form in Prophase I
§  These are regions on the
chromosome where the
homologs physically join to
exchange genetic material
chiasmata
Meiosis I
Meiosis I
Meiosis I
Meiosis II
Meiosis II
The Purpose of Meiosis
v 
Products:
§  4 haploid (1n) gametes
§  Genetically distinct from one
another and from either parent
v 
Recombinant chromatids contain
DNA from each parent
v 
Independent assortment
§  Which homolog winds up in which
gamete is a matter of chance
§  Homologs assort in a random
manner and independent of one
another
Mitosis vs.
Meiosis
Spermatogenesis
Spermatogenesis
v 
Fun facts:
§  A normal human male produces about 45-200
million sperm per day, or about 2000 per second
§  Only about 25% survive for more than a few hours
." § 
The only part of the sperm that makes its way
into the egg is the haploid nucleus
§  The male contributes nothing else; no
mitochondria or other organelles
For males, quantity overrules quality
Oogenesis
(Human)
Oogenesis
v  Fun
facts
§  The number of oocytes declines from about 7 million
during prenatal development to fewer than 400,000 at
birth
§  Over her lifetime, a woman can expect to produce only
about 450 ova
For females, it pays to be choosy!
Meiosis Summary
v 
Chromosome Counting
§  Diploid and haploid chromosome numbers
§  Gametes
v 
Meiosis
§  Homologous pairs of chromosomes
§  Crossing over and independent assortment
§  Phases of Meiosis I and Meiosis II
v 
Meiosis vs. Mitosis
v 
Production of Gametes
§  Spermatogenesis in males
§  Oogenesis in females
Review: Mitosis
Which of the following best describes mitosis:
a. 
Chromosome duplicates once, divides twice, and produces
four haploid (1n) cells
b. 
Chromosome duplicates twice, divides twice, and
produces four diploid (2n) cells
c. 
Chromosome duplicates once, divides once, and produces
two haploid (1n) cells
d. 
Chromosome duplicates once, divides once, and produces
two diploid (2n) cells
Review: Mitosis
Which of the following best describes mitosis:
a. 
Chromosome duplicates once, divides twice, and produces
four haploid (1n) cells
b. 
Chromosome duplicates twice, divides twice, and
produces four diploid (2n) cells
c. 
Chromosome duplicates once, divides once, and produces
two haploid (1n) cells
d. 
Chromosome duplicates once, divides once, and
produces two diploid (2n) cells
Review: Meiosis
Which of the following best describes meiosis:
a. 
Chromosome duplicates once, divides twice, and produces
four haploid (1n) cells
b. 
Chromosome duplicates twice, divides twice, and
produces four diploid (2n) cells
c. 
Chromosome duplicates once, divides once, and produces
two haploid (1n) cells
d. 
Chromosome duplicates once, divides once, and produces
four diploid (2n) cells
Review: Meiosis
Which of the following best describes meiosis:
a. 
Chromosome duplicates once, divides twice, and
produces four haploid (1n) cells
b. 
Chromosome duplicates twice, divides twice, and
produces four diploid (2n) cells
c. 
Chromosome duplicates once, divides once, and produces
two haploid (1n) cells
d. 
Chromosome duplicates once, divides once, and produces
four diploid (2n) cells
Review: Mitosis & Meiosis
Which of the following is true of mitosis and meiosis:
a. 
Mitosis is used for asexual reproduction, while meiosis is
used for sexual reproduction
b. 
Meiosis is used for asexual reproduction, while mitosis is
used for sexual reproduction
c. 
Meiosis is used to repair tissue
d. 
Mitosis is a form of sexual reproduction
Review: Mitosis & Meiosis
Which of the following is true of mitosis and meiosis:
a. 
Mitosis is used for asexual reproduction, while meiosis
is used for sexual reproduction
b. 
Meiosis is used for asexual reproduction, while mitosis is
used for sexual reproduction
c. 
Meiosis is used to repair tissue
d. 
Mitosis is a form of sexual reproduction