To gain knowledge of the cell cycle and the stages involved in mitotic division.
The cell cycle will be separated into Interphase and Mitosis. These two stages will further be broken down into their individual components: Interphase into G1, S, G2 and Mitosis into P, M. A. T.
Video explaining the cell cycle
Source: Bozeman Science
THE CELL CYCLE AND MITOSIS
Newborn baby: hard to believe 9 months ago a single cell
Small acorn grow into an Oak tree
How fast grass grows (mow)
Billions and trillions of cells in an organism
Always making new cells
Adult produces 25 million new cells every second
Every time an organism grows in size or repairs worn out/damaged tissue = new cells are made.
Method that organisms use is very similar
CELL GROWTH AND REPRODUCTION
Cells of a mother lion are on avg the same size as her cub.
CELL SIZE LIMITATION
Wide variety of sizes
Red blood cell = 8 micrometers in diameter
Micrometer = 100,000th of a meter 10–6
Nerve cells in large animal can reach up to 1meter
Yolk of an ostrich egg is largest = 8 cm in diameter
Most living cells are between 2 and 200 micrometers in diameter
Why not just one big cell?
Diffusion Limits Size
Cells require constant supply of glucose and oxygen and produce large amounts of ATP
Waste moves out
All by the process of diffusion
Into by PM and through the cytoplasm
- Cells can metabolize only as quickly as they receive raw materials by diffusion.
Molecule of oxygen takes only a small fraction of a second to diffuse through the cytoplasm from the PM to the center of a cell.
Innermost mitochondria of a cell 20 micrometers in diameter will receive supplies of oxygen and food a fraction of a second after they pass PM.
- If the cell is bigger?
Diffusion is fast and efficient over a short distance
Becomes slow and inefficient as distance increases
Hypothetical: If mitochondria at center of a cell that is 20 cm in diameter would have to wait a month before receiving nutrients.
Die if one giant cell.
Cell DNA Limits Size
Most cells contain only one nucleus
If a cell doesn’t have enough DNA to program its metabolism, it cannot live.
Giant amoeba (Pelomyxa) more than one nucleus has evolved
Large amounts of DNA in many nuclei ensure that cell activities are being carried out.
Surface Area-To-Volume Ratio
As cell size increases, its volume increases much faster than its surface area
Smallest has 1 mm sides:
Surface Area = 6mm squared
Volume - 1 mm cubed
-. If the side of cell is doubled to 2mm
Surface area increases 4 fold (6x2x2) = 24 mm squared
Volume increases 8 fold = 8 mm cubed
If cell size is doubled, cell would require 8 times more nutrients and would have to expel 8 times more waste.
The surface area however would increase by a factor of only 4
PM would not have enough surface area through which oxygen, nutrients, and water could diffuse.
Cell starve to death or build up poisonous waste.
Cells divide before they reach that point.
WHY DO CELLS DIVIDE?
Many cells are growing, dividing, and dying as you read this.
Old cells on feet and hands shed and replace
Cuts and bruises are healing
Intestines producing millions of cells each second
No net growth of Intestines
Tadpoles become frogs
Tomato plant grows and wraps around a stake
All organisms grow and change
Worn out tissues are repaired or replaced by new cells.
CELL REPRODUCTION- THE ROLE OF CHROMOSOMES
Middle of 19th Century scientists knew that cells divide
Microscopes improved = see more detail
Most interesting discovery was just before cell division, several short, stringy structures suddenly appeared in the nucleus.
Even stranger, these structures vanished as mysteriously as the appeared after division was over.
Chromosomes = contain DNA
Become darkly colored when stained
Chromosomes are the carriers of the genetic material DNA
Copied and passed from generation to generation of cells
Chromosomes always present, but too short to be seen until division
During most of cells life cycle = chromosomes exist as chromatin
Chromatin = strands of DNA wrapped around protein molecules.
Tangled up spaghetti
Before division the threads of chromatin begin to coil
The coils shorten and thicken, forming distinct chromosomes that are tightly packed with chromatin.
When DNA is uncoiled it can be actively involved in carrying out metabolic functions.
THE CELL CYCLE
Fall follows Summer
Night follows Day
Low tide follows High Tide
Cyclical patterns in nature
Cell Cycle = sequence of growth and division of a cell.
Two general periods = period of growth and period of division
Interphase = period of growth
most of cells life
grows in size and carries out metabolism
chromosomes duplicated in prep for division
chromosomes contain DNA
Important that new cells have copies of DNA
Mitosis = period of division
nucleus then cytoplasm forms 2 daughter cells
each complete set of chromosomes
Busiest part of the Cell Cycle
Cell making ATP, repairing themselves, excreting waste
Making protein, new organelles, copying chromosomes
Carrying out Photosynthesis and Respiration
Divided into 3 parts:
cell grows in size and protein production is high
cell copies its chromosomes
mitochondria and other organelles made and parts needed for division are made
Cell division is a continuous process: organized into 4 phases
Each phase merges into the next
first and longest phase
long stringy chromatic coils up into visible chromosomes
each duplicated chromosome made up of two halves
Sister chromatids = DNA exact copies
Centromeres hold the sisters together
- Nucleus begins to disappear
Nucleolus and Nuclear Envelope disintegrate (completely disappear)
- Centrioles begin to migrate toward opposite ends (poles)
Centriole = small, dark cylindrical structure made of microtubules and located just outside of nucleus
Only in Animal Cells
- Spindles begin to form between centrioles
Spindles = football shaped, cagelike structure, microtubules
Double chromosomes become attached to spindle fibers by centromeres
Chromosomes line up at the midline (equator)
One sister chromatid spindle extends to one pole and the other sister’s extends to the opposite pole.
Ensures each new cell gets an identical set of chromosomes
Separation of sister chromatids marks beginning
Centromeres split apart and chromatid sisters separate from each other
Start migration toward poles
Believed to move by the spindle fiber shortening and pulling the chromosomes.
Chromosomes reach opposite poles
Prophase changes are reversed
Chromosomes unwind to direct metabolic activities
Spindle fibers break down
Nucleolus and nuclear envelope reappear
Form around the new set of chromosomes
PM begins to separate the 2 new nuclei
Division of cytoplasm
Animal = PM pinches along the equator
2 new cells formed = identical
Plant = Cell plate forms at the equator and splits the cell wall.
RESULTS OF MITOSIS
2 new identical cells (identical to parent cell)
Daughter cells carry out the same cellular processes and functions of the parent cell
Grow until divide
CONTROL OF THE CELL CYCLE
Intestines complete a cell cycle in 24-48 hours
Frog embryo less than an hour
Liver cells only once a year
Nerve cells never after they mature
NORMAL CONTROL OF CELL CYCLE
Past 25 years intensive research into what causes a cell to divide
Still not fully known
Series of Enzymes
most biologist agree that it is the production of a series of enzymes that monitors cells progress from phase to phase
Some enzymes trigger progression of cell cycle (start cells)
Some enzymes inhibit progression (stop cells)
Cancer = cell death or uncontrolled cell division
Result from a failure to produce certain enzymes or from over production or production of the wrong enzymes.
Enzyme production is directed by genes located on chromosomes (genetic given)
Gene = segments of DNA that controls the production of a protein
A portion of Interphase just before DNA replication as being a key control period in the cell cycle.
Produce and secrete chemical signals
Normal cells allowed to grow in cultures will stop dividing when they come in contact with one another (fill up bottom).
Mistake in the cell cycle
Caused by changes in one or more of the genes controlling production of enzymes involved in the cell cycle.
Cancer cells affect normal cells
Form masses of tissue called Tumors
Tumors deprive normal cells of nutrients
In the final stage, cancer cells enter the blood stream and spread, forming new tumors in other organs.
Cancer is 2nd leading cause of death in US
Heart diseases is #1
Cancer can affect any tissue in the body
US main killers: lung, colon, breast, and prostate
All on the rise
Environmental factors are involved
Different countries have different dominating cancers
US = breast cancer is high but low in Japan
China = stomach cancer but low in US
When move to another country, more susceptible to that cancer
Cigarette smoke, air/water pollution, UV exposure
Source: Eric Atkins