The Life and death of the Cell

Eukaryotic cell cycle includes four phases

• G1

• S

• G2

• M phase

G1

• the cell grows so it can split

• grow a lot of proteins so when they split their daughter cells can have a good amount of proteins

• are told to split —> response to extracellular cues whether or not they should divide

• cell repair

• high metabolic activity

Metabolic activity

the sum of all chemical reactions in an organism that sustain life, converting food into energy for processes like breathing, cell repair, and growth

S phase

• DNA synthesis —> dna is being replicated

• 92 total chromosomes —> double the 46 chromosome

G2

• prevents division if the DNA is incorrectly or improperly repaired 

• checks if there is the right number of chromosomes

M phase

• the actually cellular division

• cells divide at different rates

G0

• An arrested state for non-divdiing, mature cells. Cells will carry normal cellular function

• most cells stay in this stage of the cycle ex: heart cells

How are the cell cycle control system regulated?

They have checkpoints

what are the three check points at certain critical steps 

• G1 to S phase 

• G2 to M phase

• M phase 

what is the first check point G1 to S phase do?

confirms whether environment is favorable before it enters the s phase

what is the second check point G2 to M phase do?

confirms that the DNA is undamaged and fully replicated before entering mitosis

Asks:

Is all the DNA replicated? Is all the DNA damaged repaired?

What is the third check point M phase do?

confirm chromosomes are attached to mitotic spindle before pulling the duplicated chromosomes apart

Asks:

Are all the chromosomes properly attached to mitotic spindle?

cell cycle control system

network of regulatory proteins ensures that cells replicate their DNA and organelles, and divide in an orderly fashion

What does the cell cycle depend on?

• cyclin-dependent kinase (Cdks)

cyclin-dependent protein kinase ( cdk) 

• protein kinases that are present in proliferating cells throughout the cell cycle

kinase 

• a protein enzyme that takes a phosphate from atp and sticks it to another molecule 

Cyclins

• switching kinases on/off is 

• concentraction vary over course of cell cycle 

• activated complexes help trigger various cell cycle events 

flow cytometry:

1) Which peak corresponds to each phase of cell cycle?

2) Which phase of cell cycle is the longest

• G1 is always the first peak

• G2 and M are the second, but s phase is never on the chart

Why is the fluorescence doubled in g2 and m phase?

• there is double the DNA, and in this experiment there are labeled with flourescence light. Thus, they have more light

Why is there no peak for s phase? 

There is no distinct peak for S phase in flow cytometry histograms because cells in this phase are actively synthesizing DNA, meaning their DNA content is continuously changing from the

2N2 cap N

2𝑁

(G1) to

4N4 cap N

4𝑁

(G2) levels

The Rb protein

• hibits e2f and when it does it cant make the proteins to grow

• happens in G1 phase

• when phosphate is attached to it changes shape and can no longer attach to the e2f and floats away

mitogen

extracellular signal encourages mitosis

what is the signal that attaches to the RAS and what does it do? 

• signal transduction 

• goes to nucleus to make cyclin

explain the process of the RB protein and to enter mitosios

what happens if there is no RP

• the cell keeps growing and the cell cycle is on a loop and cant stop

What would the effect be from overexpressing Rb in every human cell? Potential cancer therapy or more harm than good? 

• harder for them to grow and overwork the cell