Cell Division & Replication
Cell Cycle and Cell Division
Cells go through a series of events and it starts from a very small cell that increases to a stable size. From that point there is a decision to make: become a stable mature cell and stop growing, or follow a path that will result in two identical daughter cells. The cell has two major cycles to interphase, where it grows and performs its normal anabolic activities.
Cell division – the cycle where the cell reproduces itself. Interface is the longest phase of the cell cycle, where it is very metabolically active.
Preparations for DNA Replication
The cell’s goal is to make an identical copy of the genetic code and distribute enough organelles for the cell to survive and thrive. DNA replication always occurs first, where the code is duplicated exactly. This occurs near the end of the interphase period.
In replication the strands of the double helix are separated, and each strand is a template for the new complementary strand. The two strands will produce two identical double helix. Nucleotides join in a complementary fashion where adenine bonds to thymine, and guanine binds to cytosine (A – T, G – C).
The cell cycle is highly regulated. Most cells spend their time maintaining normal functions and are not in the active replication process. Cells do have a limited number of times that they can replicate, limited by their “built in clocks.” On the tips of the chromosome are telomeres, which limits the number of replications.
Interphase – greatest metabolic activity. Cell grows, replicates DNA, and synthesizes new molecules and organelles.
Mitosis is described as a series of four stages but the process is continuous.
I. Prophase
A. Chromatin condenses so chromosomes appear visible.
B. Nuclear envelope disappears.
C. Centrioles begin to migrate.
D. Spindle fibers begin to form.
II. Metaphase – chromosomes and organelles line up in the middle.
III. Anaphase
A. Chromatids split and begin to move apart.
B. Spindle fibers are shortening and pulling the chromatids toward the opposite pole, anaphase ends when the chromosomes stop moving.
IV. Telophase – (prophase in reverse)
A. Chromosomes uncoil to loosely coiled chromatin.
B. Nuclear envelope begins to reappear.
C. Spindle fibers disappear.
D. Cytokinesis ends.
Cytokinesis – division of cytoplasm, begins during late anaphase and ends during telophase. Microfilaments form and produce a contractile ring around the cell that creates a cleavage furrow.
At the end of mitosis each daughter cell is smaller and has less cytoplasm than the mother cell, but is genetically identical. Each cell will now grow and carry out its normal cell activities until its turn to carry out cell division.
Questions:
What would happen if one of the daughter cells was not given any mitochondria? _________________
What are the function of centrioles? ____________________________________________________________________________
Where do the spindle fibers attach on the sister chromatids? What is the definition of sister chromatids?
______________________________________________________________________________
Why do we usually keep a nuclear envelope around the DNA? _____________________________________________________________________________
What would happen if prophase started before the genetic code was completely copied? ________________________________________________
Why is it easier to have all the cellular products lined up in the middle before anaphase? _________________________________________________
Meiosis
Meiosis is the process of genetic division for creation of a sperm or an egg. Each daughter cell will have half the genetic code instead of two copies. This allows for the sperm to bring one copy of the father’s genetic code to the egg where fertilization will then create a complete genetic code.
Question:
What would happen if the sperm carried two copies of the father’s genetic code? _________________________________________
Cell Differentiation
Cells develop into different types of cells with very specialized functions. The end result of cell differentiation is that a nerve cell looks completely different than a red blood cell. Each cell becomes very specialized for its function in the body. Cell differentiation is a result of specific genes being turned on, which processes inside the cell to develop in a very specific and particular fashion. A stem cell is a very early undifferentiated cells that can become many different types of cells with the correct signals.
Questions:
Why is medicine interested in developing and controlling stem cells? ______________________________________________________________
Can a skeletal muscle cell become a cardiac muscle cell? ______________________________________________________________________________
Why is a red blood cell unable to replicate on its own? _____________________________________________________________________________
Cell Death
Apoptosis is a form of cell death that is controlled in part of normal development. The body very specifically destroys cells when it is time to replace or turn them over.
Uncontrolled cell growth is called cancer. The body can no longer tell the cell to destroy itself.
Proteins
Proteins are one of the key substances for cell life. Proteins can be structural, such as a building block. They can also be functional and do things. Enzymes are specific proteins that do things in the body. They are catalysts; they can help a reaction occur or make it occur faster. The blueprint for all proteins in the body is contained in the genetic code.
Proteins are made of a specific sequence of amino acids. Different arrangements of amino acids produce variations in structure and design.
RNA
RNA is a copy of DNA that leaves the nucleus and travels to ribosomes. RNA is slightly different than DNA in that it contains uracil (U) instead of thymine (T) that is in DNA. The creation of RNA replaces thymine with uracil at every location.
This copy can safely leave the protection of the nuclear envelope and travel to the ribosomes, where its specific sequence is used to produce a specific protein.
Transcription is the process of copying DNA to RNA.
Translation is the process of taking the RNA copy and creating a protein at the ribosomes.
Questions:
What would happen if the nuclear envelope allowed proteins to get near the DNA? ______________________
What would happen if proteins interacting with the DNA changed the genetic code? ______________________
Why is using mRNA as a translator in between the DNA and the ribosomes a safe and effective process?
______________________________________________________________________________
Thought question:
Is the process of DNA transcribing RNA and then creating proteins with that copy at the ribosomes similar to taking an English book and translating it into Spanish, then finally to French? If done properly, will the correct information be produced as a final product?