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THE CELL CYCLE
Chapters 6
Do organisms grow?
How do organisms grow?
Generally, do –
(1) individual cells keep getting larger and larger?
or(2) cells divide to form new cells?
Why don’t individual cells keep growing larger and larger?
Cells are limited in size because they get their nutrients by diffusion. If cells become too large, nutrients such as oxygen and glucose (which are necessary for aerobic cell respiration) will not be able to diffuse quickly enough into the cell in order for it to survive.
Another way to look at it …
Surface Area = x2 (the area of the surface of the cell)
Volume = x3 (the volume of cytoplasm)
So, if a cell gets larger, what happens to the surface area/volume ratio?
•If x = 1, SA/V =•If x = 2, SA/V =•If x = 3, SA/V =
The math way, continued
If x = 1, then the surface area/volume ratio (SA/V) is x2/x3 = ______________
If x = 2, then the SA/V ratio is _____________If x = 3, then the SA/V ratio is _____________
As the cell increases in size, the SA/V ratio __________________________. Cells need a large SA/V ratio in order to insure that all parts of the cell can get their nutrients by ____________.
Can a cell simply split in two to form two new cells?
No.
Why not?
Remember the 4 parts of every cell?
What part is the “brain”? Each cell in an organism needs exactly the same DNA in every cell.
Let’s start with some definitions….
Chromatin and Chromosome
Remember: Chromatin is long and thin. It is uncoiled DNA. (DNA still keeps it’s double helix shape, however.
A chromosome is coiled DNA. The DNA coils around proteins.
Chromatin and Chromosome
GeneA section of DNA that contains the code to make a protein.
Somatic Cells versus Gametes
Somatic cell = body cell. Each somatic cell contains 46 chromosomes
It contains the diploid number of chromosomes (having 2 sets of chromosomes in the cell) Often written as 2n
Gamete = reproductive (sex) cell. Each gamete contains 23 chromosomes.
It is haploid (having 1 set of chromosome in the cell). Often written as n
Karyotype ( a chart of chromosomes) showing homologous chromosomes -
female
Homologous chromosomes are similar in size, shape and genetic content.
Autosomes are pairs 1-22. The chromosomes of pair 23 are sex chromosomes and determine a person’s gender.
Diploid and Haploid Cells
Two haploid cells merge to form one diploid cell. This process is called fertilization.Male gametes are called sperm; female gametes are called eggsTwo sex cells (sperm and egg) merge to form a zygote.
Zygotes and Specialization
Once a zygote is formed, it undergoes cell division many, many times to form a multicellular organism.
The cells specialize to perform specific functions for the organism.
Mitosis
Mitosis: the process in cell division in which the nucleus of a cell is divided into two nuclei. Each nucleus has the same number of chromosomes as the original cell.
Prokaryotic Cell Division
Prokaryotes (bacteria) have only one chromosome. It is circular in shape and is attached to the cell membrane. When a prokaryote divides, the cell makes a copy of its DNA, then the cell divides. Each cell has one copy of the chromosome. Prokaryotic cell division is called binary fission. Prokaryotes do not go through mitosis, nor do they have gametes or zygotes.
The Cell Cycle
Cell Cycle: a repeating sequence of growth and division during the life of a cell. The cell cycle has three parts:1. Interphase: the part of the cell cycle in which an organism grows and carries out its metabolism Before it is about to divide, the cell will copy its DNA.
The Cell Cycle, Parts 2 and 3
2. Mitosis: Division of the nucleus. There are 4 phases of mitosis3. Cytokinesis: the splitting of
the cytoplasm of the cell.
DNA copies itself at the end of interphase (before mitosis begins)
Early Prophase
Early Prophase
Chromatin coils or condenses into visible chromosomes
Nuclear membrane begins to break down
Centrioles move toward opposite poles of the cell and form the spindle
Late Prophase
Late Prophase
Spindle has formedNuclear membrane has broken down
Chromosomes attach to the spindle
Metaphase
Metaphase
Spindle fibers move the chromosomes to the “equator” of the cell so the chromosomes are lined up along the middle of the spindle.
Anaphase
Anaphase
Centromeres split
Spindle fibers shorten and pull the chromatids apart toward opposite poles of the cell.
Anaphase
Telophase
Telophase in an animal
cell
Telophase
Chromatids reach the poles and uncoilNuclear membranes reformSpindle fibers break downFurrow forms in animal cells while cell plate
forms in plant cells.
Cytokinesis comes after mitosis
Cytokinesis means cell splitting
Final separation of the two daughter cells
Cell Cycle in Animal Cells
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
INTERPHASE
EARLY PROPHASE
LATE PROPHASE
METAPHASE
EARLY ANAPHASE
LATE ANAPHASE
TELOPHASE
CYTOKINESIS
Cell Cycle - Normal vs. Cancerous Cells
Normal Chicken Stomach Cells:
Interphase – 120 min
Prophase – 60 min
Metaphase – 10 min
Anaphase – 3 min
Telophase – 12 min
Cancerous Chicken Stomach Cells:
Interphase – 16 min
Prophase – 15 min
Metaphase – 2 min
Anaphase – 1 min
Telophase – 3 min
Cancer – the enemy!
Cancer – the uncontrolled dividing of cells
Video animation: Cancer
Types of Tumors
Benign tumor – slow-growing or has stopped growing and does not spread to other tissues
Malignant tumor– is actively growing and tends to spread to other tissues
Metastasis – the spreading of cancer cells to other parts of the body
Types of Tumors
