Download Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle
What molecule stores your genetic information or determines everything about
you?
DNA – a nucleic acid
How are DNA molecules arranged in the nucleus?
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
As you can see DNA is:
1.
Arranged in a double helix conformation
2.
The double helix is wound around histone proteins which serve to compact the
DNA tightly – the resulting structures are called nucleosomes
3.
The nucleosomes are coiled into even tighter packages
4.
The resulting chromatin is a tangled mass of thin threads of DNA
5.
During the process of cell division chromatin condenses into highly compacted
structures called chromosomes which are visible under light microscopy
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
What does a cell have to do to reproduce?
The Cell Cycle
Phases include:
1.
Interphase – Preparation phases for mitosis
2.
Mitosis – Cell division or splitting
How do you think the cell has to prepare for the division or splitting step?
Interphase
1.
G1 (Growth)
2.
S
3.
G2 (Growth)
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Interphase (G1)
Growth & preparation of the cell for division, including an increase in size & the
number of organelles
During G1 an enzyme called S-kinase combines with a protein called S-cyclin.
This interaction activates the S-kinase which will phosphorylate (Do you remember
what this means?) a protein that will initiate the S phase of interphase
Interphase (S)
Synthesis or doubling of the DNA
Each chromosome is duplicated & the resulting sister chromatids are joined at a
pinched region called the centromere
Interphase (G2)
Continued growth & preparation for mitosis
During G2, a second enzyme called M-kinase combines with M-cyclin
This interaction phosphorylates a protein that will initiate mitosis
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
5. Cytokinesis
Prophase
Centrosomes, composed of centrioles & microtubules, migrate toward opposite ends of
the cell
The nuclear envelope & nucleolus begin to & will disappear by the end of prophase
The chromosomes condense & are visible
Spindle fibers (microtubules) will form & specialized ones called kinetochore fibers
will attach to the centromeres of the duplicated chromosomes
Chromosomes are not arranged in any specific orientation
Chapter 8 – The Cell Cycle
Metaphase
The kinetochore fibers push & arranged the duplicated chromosomes along the equator
of the cell (metaphase plate)
Anaphase
The sister chromatids are separated from one another forming two daughter
chromosomes that move toward the opposite poles of the spindle
The chromatids ride the fibers toward the poles like a train on a railroad track
Telophase
Reverse prophase
Spindle fibers disappear
Nuclear envelope & nucleolus reappear
Chromosomes de-condense back into chromatin
Chapter 8 – The Cell Cycle
Cytokinesis – cytoplasmic cleavage to separate the cell into 2 distinct daughter cells
Animal cells
Begins in late anaphase with the initiation of a cleavage furrow, which is an
indentation of the cell membrane
It develops due to the constricting action of a band of actin filaments called the
contractile ring
The ring continues to “pinch off” the cell until it is separated into 2 daughter cells
Plant cells
The cell wall prevents this “pinching” effect as seen in animal cells
Instead the Golgi apparatus produces vesicles which move along the microtubules to
the mid-point of the cell
These vesicles will fuse forming the cell plate, which will eventually form the new cell
membrane of the 2 new daughter cells
Cell wall will be formed following cell membrane formation
Chapter 8 – The Cell Cycle
Chapter 8 – The Cell Cycle
Why is the diploid # of chromosomes in all stages of mitosis the same rather than
being doubled due to the S phase of interphase? Or
How do you count chromosomes?
You count chromosomes by their centromeres
Since the duplicated chromosomes are called sister chromatids connected by their
centromeres, the total is 4 based on the # of centromeres, even though you see a total of
8 sister chromatids in the previous figure
Chapter 8 – The Cell Cycle
Cell division in prokaryotic cells
What do you think a prokaryotic cell has to due to reproduce?
Does it have as many “moving parts” as a eukaryotic cell?
Binary fission
Since the prokaryotic cell does not have to worry about a nuclear envelope or
membrane bound organelles, reproduction in these cells are simpler.
Basically, the single loop of DNA is replicated & each copy is attached to the cell
membrane at the membrane fold where binary fission begins
As the cell pinches in two, the DNA molecules are pulled apart by the moving cell
membrane
Chapter 8 – The Cell Cycle
PRACTICE QUESTIONS
1.
What is a nucleosome?
2.
How does chromatin differ from chromosomes?
3.
What is a karyotype?
4.
What are the phases of the cell cycle?
5.
What are the phases of interphase? What happens during each phase?
6.
What are the phases of mitosis? What happens during each phase?
7.
What does a kinase do?
8.
How do animal & plant cell telophase differ from one another?
9.
What is binary fission?