Download Cell Growth and Division

Notes –Cell Growth and Division: Mitosis
Name
Per
Directions On another sheet of paper copy down the vocabulary. Highlight the main topic of each paragraph. Next
underline the supporting facts of the main topic. Circle examples of the supporting facts. Provide an appropriate title for
each section. Once the first reading is complete go back and provide questions and examples along the left side. Along
the right side, place a + to indicate understanding and a – to indicate needing clarification.
Notes Title of Paragraph
Cell Growth and Efficiency
When a living organism grows, what happens to its cells? Nearly all cells can grow by increasing in size.
However, as cells increase in size they become less efficient. The larger the cell becomes, the more demands
the cell places on its DNA. In addition, larger cells are less efficient in moving nutrients and wastes materials
across the semipermeable cell membrane.
Title of Paragraph
The reasons for the inefficiency when a cell gets too large is that the surface area to volume ratio gets smaller as
the cell gets larger. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the
membrane fast enough to accommodate the increased cellular volume.
Remember a ratio is a comparison. In this case, it compares the amount of surface area a cell hast to its volume.
A ratio can be expressed as a proportion, such as 2:1 or as a fraction, such as 2/1. As the cell grows the volume
increases faster than the surface area. Thus, the smaller surface area has to serve a larger volume.
Title
Before a cell becomes too large, a growing cell divides making two daughter cells. Daughter cells are genetically
identical to the parent cell because they contain the same number and type of chromosomes. The process in
which a cell divides into two new, identical daughter cells is called cell division.
Title
As learned in chapter 7, there are many organelles with specialized function in cells. What would happen if cells
simply split to these organelles? The result might be disastrous. Importantly, if some of the genetic material
was missing in the new daughter cell, they would not be able to carry out cellular functions. Thus, a cell first
must make a complete copy of their genetic material before dividing.
Title
Even a small molecule like the bacterium E. coli has a tremendous amount of deoxyribonucleic acid (DNA). The
DNA in human cells is about 2 meters long, but coiled so tightly it fits into the nucleus. The DNA fits into
eukaryotic cell nuclei because it is tightly bundled into packages of DNA known as chromosomes.
Title
Eukaryotic cells generally have much more DNA than prokaryotic cells (bacterial), thus have multiple
chromosomes. Fruit flies, for example have 8 chromosomes per cell, carrots 18 per cell, chimpanzees 48 per cell
and humans 46 per cell. The chromosomes in eukaryotic cells form close association with histones, a type of
protein. The complex histone protein and chromosome is referred to as chromatin. Chromosomes when
condensed make it possible to separate DNA precisely during cell division.
Title
Eukaryotic cell division is divided into interphase, (G1 phase, G2 phase S phase), and the M phase (mitosis and
cytokinesis). Cells do most of their growing in the G1 Phase: Cell growth. Cells also synthesize (make) new
proteins and organelles. During the S Phase new DNA is synthesized (copied) when the chromosomes are
replicated. If humans have 46 chromosomes, how many are present after replication in the S phase?
During G2 Phase more molecules and organelles necessary for active cell division are made. The final phase is
the M phase, which includes mitosis and cytokinesis. Mitosis is a type of asexual cell division that results in two
identical daughter cells. The final division is when the cytoplasm divides in cytokinesis, resulting in two
separate, identical daughter cells each with
chromosomes, if you are a human.
Label S, G2, M, mitosis, and
cytokinesis
Events
Summary of Event
G1
S
G2
M Phase: Mitosis
M Phase: Cytokinesis
Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and telophase. In the
following reading, also use pages 282- 284 of Miller and Levine.
Title
The first phase is prophase, and is usually the longest. During prophase
the genetic material inside the nucleus condenses and the duplicated chromosomes become visible. Outside
the nucleus, a spindle starts to form. The duplicated strands of chromosomes are connected along an area
called a centromere. Each DNA strand in the duplicated chromosome is referred to as a
chromatid, or sister chromatid. Also during prophase, the cell starts to build a spindle, a
fanlike system of microtubules (stringy-like) that will connect the centromeres and help
pull the duplicated chromosomes apart. Spindle fibers attach to centrioles at the opposite
ends of each cell. The centrioles act like anchors to hold the spindle fibers in place. Draw
and label the picture in prophase – centromeres, nuclear envelope, chromatid or
chromosomes, spindle fibers, and centriole
Phase
Title
The second phase is metaphase, and is generally the
shortest. During metaphase, the centromeres of the duplicated chromosomes line up
across the center of the cell. Spindle fibers connect to the centromeres of each
chromosome and to the centrioles. Draw and label centromeres, chromatid or
chromosomes, spindle fibers, and centriole. What structure is not present in metaphase
that was labeled in prophase?
.
Phase
Title
The phase where the chromosomes separate is celled anaphase. As the spindle
fibers shorten the chromosomes are pulled apart at the centromere to opposite ends of the cell. Draw and label
the following in anaphase – centromeres, spindle fibers, centriole, chromosomes.
Title
Following anaphase is telophase.
During telophase, the chromosomes, which were distinct and
condensed, began to spread out into a tangle of chromatin. The nuclear
envelope begins to reform. The spindle and centrioles begin to break
apart. Draw and label, the nuclear envelop, chromatin, spindle fibers,
and centrioles.
Phase
Phase
Title
As a result of mitosis, two nuclei, each with a complete set of chromosomes- are
formed, which is the goal of mitosis. The last phase of cell division is cytokinesis. Cyto means cell and kinesis
means to move. The cytoplasm in eukaryotic cells pinches together to form two new cells.
Think and Review: Why do cells need to divide via mitosis?
a.
b.
c.