CELL CYCLE AND DIVISION BEGINS The Cell Cycle

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CELL CYCLE AND DIVISION BEGINS

CELL CYCLE AND DIVISION BEGINS

The Cell Cycle • In eukaryotes, there is a very orderly progression of events

The Cell Cycle • In eukaryotes, there is a very orderly progression of events that takes place between the formation of a new cell and the division of that “parent” cell into 2 new “daughter” cells. • Result of cell cycle: more cells! – 1 cell becomes 2, becomes 4, becomes 8, etc.

The Cell Cycle • What is the purpose of making more cells? • Growth

The Cell Cycle • What is the purpose of making more cells? • Growth – Larger bones, bigger heart, more brain tissue • Repair of damaged tissues – Muscle tears, dead skin cells, broken blood vessels

The Cell Cycle 2 Main Stages 1. Interphase: normal cell functions and preparation for

The Cell Cycle 2 Main Stages 1. Interphase: normal cell functions and preparation for mitosis 2. Mitosis: nuclear division

The Cell Cycle Stage 1: Interphase • Most of a cell’s life is spent

The Cell Cycle Stage 1: Interphase • Most of a cell’s life is spent in interphase. – Normal cell functions are carried out in interphase. – Some cells never leave interphase. (translation: they never divide) – Interphase has 3 steps…

The Cell Cycle Stage 1: Interphase 3 stages of Interphase: 1. • 1. G

The Cell Cycle Stage 1: Interphase 3 stages of Interphase: 1. • 1. G 1 • 2. S • 3. G 2 2. 3.

The Cell Cycle • It is also correct to say that the cell cycle

The Cell Cycle • It is also correct to say that the cell cycle has 4 stages: • The first 3 stages are collectively called Interphase. – 1. G 1 – 2. S – 3. G 2 – 4. M (mitosis) More about mitosis in a few…

 • Those are the 3 stages of interphase. • The 4 th stage

• Those are the 3 stages of interphase. • The 4 th stage of the cell cycle is mitosis. • The chromosome– the chromosomal info is made up of DNA Remember me. I told you I would be back. te phospha gar se ba n ge Ni tro D e su s o b i r y eox

You can see from the diagrams that a chromosome is made up of DNA

You can see from the diagrams that a chromosome is made up of DNA plus proteins. The proteins serve the function of helping to organize the DNA ( histone proteins are like the spools for the thread of DNA) ntic e d i e s ar m r p” A NA “ o D Tw al

Chromosomes duplicate themselves during the S phase but they are not visible as sister

Chromosomes duplicate themselves during the S phase but they are not visible as sister chromatids until prophase. Note the centromere attaching the chromosomes together. ere dh e t a c ate lo res l p n i rote pindle fib p a s to s ore i t h n c e o t Kine achm t t a r fo Centromere is constricted area of chromosome

Chromosome numbers • Each type of eukaryote has a characteristic number of chromosomes in

Chromosome numbers • Each type of eukaryote has a characteristic number of chromosomes in the nucleus of each cell. • Examples: – – – Humans- 46 Dog- 78 Housefly- 12 Potato plant- 48 Cat- 38 Aspergillus (fungus)- 8

The cell cycle connection to mitosis • The cell cycle starts with Interphase •

The cell cycle connection to mitosis • The cell cycle starts with Interphase • Mitosis occurs next and is a nuclear division – The nucleus and its contents are divided. • There are 4 phases of mitosis: – Prophase – Metaphase – Anaphase – Telophase You can remember the cell cycle in order with the little saying: I Pee on the M A T IPMAT = cell cycle + mitosis PMAT = mitosis only

Chromosomes condense and become visible with light microscope Poles formed by asters and spindle

Chromosomes condense and become visible with light microscope Poles formed by asters and spindle fibres Cells at equatorial plate Chromosomes pulled to each pole Nuclear membrane reforms and cell forms into two

 • Mitosis stage descriptions – Prophase • Chromatin condenses into chromosomes visible under

• Mitosis stage descriptions – Prophase • Chromatin condenses into chromosomes visible under the microscope. • Nuclear envelope fragments. • Spindle fibers begin to form. – Metaphase • Chromosomes (2 chromatids) line up along the metaphase plate. • Spindle is fully formed and attached to chromosomes. – Anaphase • Chromatids separate and begin moving toward the poles. – Telophase • Daughter cells are forming as nuclear envelope begins to reform. Chromosomes unwind into chromatin.

Mitosis: the beginning Here you can watch the chromosomes appear Note: prophase and prometa

Mitosis: the beginning Here you can watch the chromosomes appear Note: prophase and prometa phase are only condiser ed as prophase in the precious note

Mitosis – finishing the chromosomal break up Note – spindle fibres are actually contracting

Mitosis – finishing the chromosomal break up Note – spindle fibres are actually contracting at the kinetochore of each sister chrmotid to pull them to each pole.

Cytokinesis- division of the cytoplasm Note: mitochondria in these animal cells must be split

Cytokinesis- division of the cytoplasm Note: mitochondria in these animal cells must be split into each new cell with the equal division of the cytoplasm

Cytokinesis- division of the cytoplasm Note: Cleavage furrow develops due to microfilaments

Cytokinesis- division of the cytoplasm Note: Cleavage furrow develops due to microfilaments

Mitosis in PLANT CELLS • Similar to mitosis in animal cells • One difference:

Mitosis in PLANT CELLS • Similar to mitosis in animal cells • One difference: Centrioles are not present (groups of tubulin ) Interesting fact- animal cells have been chemically altered so they have no centrioles, yet they form asters and spindle fibres to move chromosomes to the poles just like plant cells. • Second difference: plants must build a new cell wall between the two daughter cells. It starts off as a cell plate. Cell plate New cell wall

Checkpoints • The cell cycle is very tightly controlled. • At specific times, proteins

Checkpoints • The cell cycle is very tightly controlled. • At specific times, proteins called “cyclins” STOP the cell cycle to make an assessment. This is a CHECKPOINT. • If cell checks out , the cycle continues to the next stage. • Checkpoint G 1 –RESTRICTION POINT If cell receives “go ahead” it passes and continues on in the cell cycle. If cell get “no go ahead”, it enters G 0 - no more division t os ng - m ini t in rm o p ete n n io in d isio t ic nt iv r t s rta ll d e R o ce p im

CELLS STOP DIVIDING NORMALLY There a lot of normal cells in the G 0

CELLS STOP DIVIDING NORMALLY There a lot of normal cells in the G 0 state in the body EX Nerve cells in the brain Normal cells undergo about 20 divisions before they stop division. These are fully differentiated cells = cells mature and capable of only specific functions. In most animals this means that the cells are very capable of performing a function but cannot change to complete the tasks nor take on the morphology of other cells. Its like a great baseball player who has only trained for this all life long. It would make the player unable to become the best nuclear physicist. Undifferentiated cells retain the capability to change into many different forms. These cells are capable of cell division and are responsible for the tremendous growth of the animal form from a fertilized egg to the developed tissues of the adult.

Is there something wrong? Checkpoints & Apoptosis • If something is wrong, the cycle

Is there something wrong? Checkpoints & Apoptosis • If something is wrong, the cycle does not continue until the error is fixed. • If the error cannot be fixed, the cell will undergo apoptosis (programmed cell death). Apoptosis is cell suicide!

Checkpoints

Checkpoints

Checkpoints • What is the purpose? • No good reason to make a copy

Checkpoints • What is the purpose? • No good reason to make a copy of a damaged cell. • Cancer prevention – A “cancerous” cell is one that multiplies out of control. The checkpoints are ignored.

My God Doc. You’re telling me that I have cancer! What does that mean?

My God Doc. You’re telling me that I have cancer! What does that mean? • Cell division OUT OF CONTROL. • ways cancer can begin – Mutations of proteins used in cell cycle checkpoints. – Stimulatory pathway- cell is stimulated to divide uncontrollably. (growth factors/proto-oncogenes) – Inhibitory pathway- the normal cell machinery that prevents cancer is inactivated. Cell division is left uncontrolled. (growth-inhibitory factors/tumor-supressor genes) – Increased telomerase

as p 53

as p 53

A telomere is the section of DNA at the tip of a chromosome. No

A telomere is the section of DNA at the tip of a chromosome. No useful genes are found in a telomere. It is just a “buffer” at the tip of a chromosome to protect the useful genes. Telomeres shorten each time a chromosome divides. Eventually, telomeres are short enough to signal the cell to undergo apoptosis. Telomerase is an enzyme that prevents telomeres from shortening. The cell keeps dividing, because the telomeres don’t get short enough to signal apoptosis. Telomeres

Prokaryotes No nucleus. Binary fission = dividing in half.

Prokaryotes No nucleus. Binary fission = dividing in half.

Cell division: unicellular vs. multicellular organisms

Cell division: unicellular vs. multicellular organisms

Cell cycle and Division End

Cell cycle and Division End