Chromosomes & Cell Cycle
What the heck is a Chromosome anyway? Chromosomes Chromosomes are tightly coiled rod like structures
They consists of DNA & proteins. DNA itself is wound up into a thin fiber which is wrapped around proteins called Histones
The Histone & DNA structure forms a beadlike structure known as a Nucleosome The Nucleosomes pack together to form a thick fiber which starts to coil.
These coils wind up even more and become Supercoils The super coils are wound up to form a larger structure that is called a Chomosome
Only during cell division are these chromosomes ever visible. What part of the chromosomes should I know?
Centromere holds together the two chromatids Sister Chromatids genetic material from each parent This is a duplicated copy
This is 1 chromosome At one period of time scientists thought that cells were constantly dividing and replacing old and dead cells. During the time they were not duplicating and just growing, scientists gave this term a name called: Interphase which means resting phase Eventually scientists found that a lot happens between the resting phases. This is now what we call the Cell Cycle CELL CYCLE M phase We start along this line and cover this section.
This section is known as the G1 phase M phase - This is where cells do most of their growing G1 phase - Cells synthesize new proteins and organelles. After all the thngs in G1 are done, the cell then moves to the next phase in its life called the S phase M phase - Chromosomes are duplicated G1 phase - Key proteins used in replication are being made S phase After all the chromosomes have duplicated in the S phase, the cell then moves to the next phase in its life called the G2 phase M phase - Cell organelles and molecules required for cell division are being made. G1 phase S phase G2 phase Next comes the M phase which stands for Mitosis.
Mitosis is the actual cell division of one cell into two daughter cells M phase Mitosis has 4 parts in which we will cover each separately. G1 phase S phase G2 phase Mitosis has 4 steps to it:
Prophase Metaphase Anaphase Telophase Ill show you how to draw a simple illustration for each step for your notes. But first, lets review 3 critical events during interphase just before the cell prepares to go into Mitosis. Early Prophase The cell has divided all its DNA
The Nucleolus disappears The Centrioles appear It is now ready to divide. PROPHASE Chromosomes form and then duplicate into sister chromatids.
The Nuclear envelope slowly disappears The centrioles head to the poles Spindle fibers start to appear METAPHASE In the military you form a line
The sister chromatids line up in a straight line along the Metaphase Plate 2. Spindle fibers attach to the chromosomes near the middle called a Kinetochore ANAPHASE 1. The spindle fibers pull apart the sister chromatids and pulls each chromosometoward its pole. Ana is a cheerleader Cheerleaders do the splits TELOPHASE The Centrioles fade away.
The nuclear envelope starts to form The chromosomes start to unwind to long strands The cell starts to pinch in the center ready to split. OK, were almost done, but the cell still has one more thing to go through before it gets out of the m phase Cytokinesis M phase Cytokinesis Animal Cell
The Cell now has two separate nuclei The Cell then pinches in the middle and splits in two The 2 cells have the exact same DNA in each cells The two cells are now called Daughter Cells Movie Mitosis Cytokinesis Plant Cell
Vesicles containing cell wall material forms a plate line 2. The vesicles connect to form a cell plate 3. The cell plate divides the daughter cells and becomes a cell wall. Now could you identify the phase in a real cell?
ANAPHASE METAPHASE PROPHASE CYTOKINESIS (PLANT) TELOPHASE PROPHASE METAPHASE PROPHASE ANAPHASE Late ANAPHASE or EARLY TELOPHASE 46 46 + 46 46 46 Mitosis Daughter Cells
The important thing to remember is that your two daughter cells (the final product of Mitosis) Will have the same number of chromosomes as the original cell did. 46 Mitosis 46 46 Daughter Cells VOCABULARY ! Chromosome Histome Nucleosome Super coils Centromere
Chromatids Interphase Cell cycle G1 phase S phase G2 phase Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis Cell plate