Cell cycle
Starting on page 13 in lab manual
For next weeks lab
 Homework:
1. Be able to identify all parts of the cell
and their functions (pages 13-16 in
manual and Ch. 4 in textbook)
2. Know the cell cycle (3 parts) and be
able to identify them if given a
diagram
What is the cell cycle?
 Includes all events in the life of a cell
from the time the cell forms to the time it
divides
 The original cell is the PARENT CELL
 Why?
 After division, we say there are two
identical DAUGHTER CELLS
 Why?
What is the cell cycle?
 The cell cycle includes three major
stages:
1. Interphase
2. Mitosis
3. Cytokinesis
Interphase
 The stage of the cell cycle BETWEEN cell
divisions
 “inter” means between
 Divided into three phases
1. G1 – first gap phase
2. S – synthesis
3. G2 – second gap phase
Interphase: G1
 G1 – first gap phase
 Longest stage of the cell cycle
 No preparation to divide
What does this mean for what the cell
looks like?
Interphase: S
 S – synthesis
 Linear DNA, or chromosome, is copied
into sister chromatids, held together by a
centromere (“centro” means center;
“mere” means part)
 Where would circular DNA be found?
Mitochondria! mtDNA
Chromatid vs Chromosomes
Duplication
Centromere
Chromosome
Unduplicated
chromosome
Sister
chromatids
Duplicated
chromosome
Interphase: G2
 G2 – second gap phase
 Cell makes final preparations to divide
 Chromosomes condense, becoming
shorter and thicker, and begin to wrap
around histones
 Centrioles replicate and move to
opposite ends of the cell
Histones
Mitosis
 The process of nuclear division (not
cellular division)
 What does this mean?
 Four phases (PMAT):
1. Prophase (and prometaphase)
2. Metaphase (“meta” means between)
3. Anaphase (“ana” means apart)
4. Telophase (“telo” means end)
Mitosis: Prophase
 Linear DNA molecules are fully
condensed
 Nuclear membrane disappears
 Spindle fibers radiate from centrioles and
attach to kinetochores (located on
each chromatid or unduplicated
chromosome)
 Replicated chromosomes are randomly
distributed within cell
Mitosis: Metaphase
 Replicated chromosomes align along
the middle of the cell
Mitosis: Anaphase
 Sister chromatids separate from one
another and move to opposite ends of
the cell
 The spindle fibers are pulling the sister
chromatids apart to opposite ends of the
cell
 Sister chromatids are now called sister
chromosomes
Mitosis: Telophase
 Chromosomes reach opposite poles and
begin to uncoil
 Nuclear membranes begin to reform
Cytokinesis
 When the parent cell divides into two
daughter cells
 Begins when a contraction ring tightens
around periphery of cell causing the
formation of a cleavage furrow
 Squeezing of contraction ring continues
until parent cell is split
 Mitosis in Action
Lab Two Exercise
 Some key things to keep clear:
Haploid versus Diploid
Haploid: 1N
Diploid: 2N
Humans have __________ cells
Lab Two Exercise
 Haploid (1N)
 Number of DIFFERENT types of linear
chromosomes- identified by length,
centromere location, and/or banding
patterns
 What is the haploid number for humans?
23
Lab Two Exercise
 Diploid (2N)
 Two sources of each type of linear
chromosome
 In humans we get one set of DNA from
Mom and one set from Dad
 We say they are a HOMOLOGOUS pair“the same”
 What is the diploid number for humans?
46
*This is to show banding patterns and what homologous chromosomes look
like. Keep in mind these chromosomes are NOT duplicated*
Autosomes (22 pairs)
Sex chromosomes (1 pair)
Female
Male
or
Lab Two Exercise
 Chromosome versus chromatid
 Chromatid- One of two identical linear
DNA molecules held together by
centromere
 Chromosome- can be used two ways:
1. A single, double helix DNA molecule
during G1 of interphase and during
anaphase and telophase of mitosis
2. Two identical DNA molecules (sister
chromatids) during G2 of interphase and
prophase and metaphase of mitosis
Lab Two Exercise – p.17
 TAKE PICTURES!
 Table work as a group
 Kinetochore- gray
area on each
chromosome modelwhere centromere
attaches
 Paper clipcentromere region