Biochemistry 2 - Lesson 12: Cell Differentiation

Biochemistry 2 Lesson 12

Lesson 12: Cell Differentiation

Lesson 12: Cell Differentiation

If cells did not have Contact Inhibition, what would likely result?

Without Contact Inhibition, Cancer would likely result. Contact Inhibition is a mechanism by which cells know to stop dividing due to their contact with many surrounding cells.

Compare Neoplasm to Tumor.

A Neoplasm is an abnormal growth of tissue, which when it forms into a mass, it will then be referred to as a Tumor.

What is the difference between a Benign and a Malignant Tumor?

A Benign Tumor is harmless whereas a Malignant Tumor is a tumor that is dangerous due to high speed growth, invasiveness, and nonfunctional daughter cells.

Your doctor tells you that your recently discovered tumor has "Metastasized." What does he mean?

He means that part of your tumor has split off and traveled to another area of your body.

Your mom tells you that she believes that all cells are stem cells. How might you respond?

You should tell your mom you love her but that she is misguided. ;) Stem cells are cells that can specialize into several other types of cells. Our body is mainly composed of mature cells, which have a specialized function. The primary purpose of stem cells is to divide and differentiate instead of perform daily functions.

Compare Embryonic and Somatic Stem Cells.

Embryonic Stem cells are cells within a Zygote or other cell during early development. These cells are very potent and can differentiate into hundreds of different cell types. Their purpose is to differentiate into the various cells that will form a fully functional organism.

Somatic Stem Cells are found within babies as well as adults. They are less potent than Embryonic Stem Cells with a primary purpose of repairing/replacing surrounding cells that may get damaged.

Compare the roles of the following stem cells:

(1) Epidermal Stem Cells
(2) Hematopoietic Stem Cells
(3) Neural Stem Cells
(4) Mesenchymal Stem Cells

(1) Epidermal Stem Cells divide into skin cells.
(2) Hematopoietic Stem Cells divide into various blood cells.
(3) Neural Stem Cells divide into various types of neurons.
(4) Mesenchymal Stem Cells divide into cells that make up bone, cartilage, adipose, and other connective tissues.

Compare the two processes of cell division that occur in Stem Cells:

(1) Obligate Asymmetric Replication
(2) Stochastic Differentiation

Obligate Asymmetric Replication is when a cell divides into a mother cell and a daughter cell. The Mother cell can then go on to divide again.

Stochastic Differentiation is when one cell divides into two daughter cells and then a nearby cell notices this and divides into two mother cells.

Put the following in order of decreasing potential for differentiation:

I. Multipotent
II. Totipotent
III. Pluripotent
IV. Unipotent

(A) II > I > III > IV
(B) II > III > I > IV
(C) IV > I > III > II
(D) IV > III > I > II

(B) II > III > I > IV

In order of decreasing potential for differentiation: Totipotent > Pluripotent > Multipotent > Unipotent.

Compare and contrast each of the following:

(1) Multipotent
(2) Totipotent
(3) Pluripotent
(4) Unipotent

(1) Totipotent Stem Cells can divide into any type of cell.
(2) Pluripotent Stem Cells can divide into any type of cell except those in the placenta. Pluripotent Stem Cells can be called Embryonic Stem Cells.
(3) Multipotent can divide into several different cell types with a certain category (i.e. Mesenchymal Stem Cells, Neural Stem Cells, etc).
(4) Unipotent Stem Cells can only divide into one type of cell.

Are each of the following developing cell types Totipotent, Pluripotent, Multipotent, or Unipotent?

(1) Zygote cells
(2) Trophoblast cells
(3) Inner Cell Mass (ICM)

(1) Zygote cells are Totipotent.
(2) Trophoblast cells are Multipotent, only being able to form the cells found in the placenta.
(3) Inner Cell Mass (ICM) are Pluripotent, being able to form all cell types but those found in the placenta.

Jimmy has a failing liver. Describe how Induced Pluripotent Stem Cells (iPS) might be used to help Jimmy.

You would take healthy stem cells from Jimmy and then induce them to become Pluripotent. You would then program them using transcription factors, etc. to become a new liver for Jimmy! Yay! You should then tell Jimmy not to drink alcohol ever again!!!

Why is there now interest in keeping Cord Blood.

Cord Blood is the blood from a baby's umbilical cord, and it has been found to contain multipotent or even pluripotent stem cells.

CRB We often talk about Stem Cell Therapies as being Regenerative. Compare Complete and Incomplete Regeneration.

In Complete Regeneration, the stem cells that migrate to the site of injury will become exact replacements. It will look like there was never any damage!
Incomplete Regeneration will still have stem cells migrate to the injured site, but the newly formed tissue will not be identical in structure/function to the original tissue.

MHC II presentation to a T Cell receptor is an example of which type of cell-cell communication?

(A) Paracrine Signaling
(B) Autocrine Signaling
(C) Juxtacrine Signaling
(D) Endocrine Signaling

(C) Juxtacrine Signaling

MHC II presentation to a T Cell receptor is an example of Juxtacrine Signaling (aka Direct Cell-cell Communication) in which a signal is transmitted from one cell to another cell via direct contact.

Pre-synaptic neurons communicating with Post-synaptic Neurons across the Synapse is an example of which type of cell-cell communication?

(A) Paracrine Signaling
(B) Autocrine Signaling
(C) Juxtacrine Signaling
(D) Endocrine Signaling

(A) Paracrine Signaling

Pre-synaptic neurons communicating with Post-synaptic Neurons across the Synapse is an example of Paracrine Signaling in which a cell sends out a signal to nearby cells.

Growth Hormone being released into the blood and carrying signals to various organs and tissues is an example of which type of cell-cell communication?

(A) Paracrine Signaling
(B) Autocrine Signaling
(C) Juxtacrine Signaling
(D) Endocrine Signaling

(D) Endocrine Signaling

Growth Hormone being released into the blood and carrying signals to various organs and tissues is an example of Endocrine Signaling in which signals are transmitted over long distances.

Monocytes produce a chemical called Cytokine Interleukin-1 which then binds to a receptor on Monocytes. This is an example of which type of cell-cell communication?

(A) Paracrine Signaling
(B) Autocrine Signaling
(C) Juxtacrine Signaling
(D) Endocrine Signaling

(B) Autocrine Signaling

Monocytes produce a chemical called Cytokine Interleukin-1 which then binds to a receptor on Monocytes. This is an example of Autocrine Signaling in which signals are transmitted from one cell to the very same cell.

CRB Match each of the following cell-cell communication terms to their descriptions:

I. Competent
II. Responder
III. Inducer

(A) The cell that responds to a signal
(B) The cell is able to respond
(C) The cell that secretes the signal.

I. Competent - (B) The cell is able to respond

II. Responder - (A) The cell that responds to a signal

III. Inducer - (C) The cell that secretes the signal.

CRB When transforming cells in my research with plasmids, I often use cells that have lots of CaCl2 and heat-shock them. Could these cells be considered Competent Cells?

Because these cells are prepared so that they can receive (and later respond to) the signal (my plasmids), these cells can be called Competent Cells.

Your best friend, and also your roommate, comes home from Biology class and is extremely excited. He proceeds to tell you that the cell in your butt and the cell in your brain are exactly the same! Clarify what your friend is actually saying...

Every cell in our body contains basically the same exact DNA. The difference between these cells is the expression of that DNA. The expression of the DNA in your butt is vastly different from the expression of the DNA in your brain.

CRB Recall that applying different transcription factors was able to change a differentiated cell into an undifferentiated cell. What does this tell you about their role in forming different cell types?

The different transcription factors that a cell contains must be able to affect which DNA is expressed in certain cells, and that transcription factors are Differentially Expressed in different cell types.

It can be said that differentiation (the process by which stem cells change and divide into different cell types) can take place via "asymmetric segregation of cellular determinants." Describe what this process might look like.

When a cell divides, certain transcription factors ("cellular determinants") will become unevenly distributed between the two daughter cells. This results in two daughter cells that will have different genetic expression.

CRB In cell specification, which would come first: Specification or Determination? Compare these two steps.

Specification is when a cell is Reversibly designated to be a certain cell type, and must occur first.
Determination is when that previously specificed cell is now locked into being that particular cell type

CRB True or false? A cell could undergo Specification, but then instead of going to Determination, could go back to being an Unspecified Cell.

True. A cell could undergo Specification, but then instead of going to Determination, could go back to being an Unspecified Cell.
This is because Specification is Reversible!

CRB Which of the following terms best describes the cell actually making the changes to become the cell type it has been assigned to in Determination?

(A) Specialization
(B) Differentiation
(C) Completion
(D) Fulfillment

(B) Differentiation

Differentiation is when the cell actually makes the changes to become the cell type it has been assigned to in Determination.

CRB In which of the steps of Cell Specialization would Morphogens, molecules secreted from nearby cells to follow a particular developmental pathway, be found?

(A) Specification
(B) Determination
(C) Differentiation
(D) Undifferentiation

(B) Determination

In Determination, Morphogens would be found to push entire groups of nearby cells to follow a particular developmental pathway.

As the eye cup comes into contact with any neighbouring epidermis, it transforms that particular region into a lens. This is how the lens of your eye develops. It is an example of:

(A) Dissipation
(B) Transfusion
(C) Induction
(D) Transplantation

(C) Induction

Induction is the process by which cells influence other cells to follow a particular differentiation pathway.

Post-Mitotic Cells, as compared to Mitotic Cells, are likely in which stage of the cell cycle?

Post-Mitotic Cells are cells which can no longer undergo mitosis and divide into new cells. For this reason, these cells would be in G₀ of Interphase.

The ends of our DNA are capped with Telomeres. Each time your DNA is copied what happens to these Telomeres?

Each time your DNA is copied, your Telomeres shorten.

Compare Replicative Senescence and Hayflick Limit.

The Hayflick limit is the number of times a cell can divide (approx. 60) before it can no longer divide, becoming senescent. Because this senescence is caused by telomere shortening, we call it Replicative Senescence.

What does it mean to say that a cell is Senescent?

It is basically a mitotic cell that no longer divides. It is a mitotic cell that has entered G₀ of Interphase.

In what way is cells becoming senescent a good thing? Bad thing?

Cells becoming senescent is a good thing because it means that these cells will not become cancerous.

It is a bad thing because it leaves the tissue with a decreased ability to repair itself. Senescent cells are closely related to age-related diseases.

CRB Becoming Senescent is a great alternative to dividing too often and needing to undergo Apoptosis. Which of the following is least likely to trigger Apoptosis?

(A) Oxidative Stress
(B) Excessive DNA Damage
(C) Extracellular Death Signals
(D) Intracellular Peroxisome Formation

(D) Intracellular Peroxisome Formation

Each of the following are likely to trigger Apoptosis:
I. Oxidative Stress
II. Excessive DNA Damage
III. Extracellular Death Signals
IV. Intracellular Death Signals

CRB Which of the following statements about Reactive Oxygen Species (which cause Oxidative Stress) are true?

I. Activated Phagocytes actually use Superoxide (O2 -) to cause oxidative stress in pathogens to kill them off.
II. Reactive Oxygen Species can damage DNA, proteins and even the lipid bilayer.
III. Oxidative Stress is linked to cancer, because it can turn proto-oncogenes into oncogenes.

(A) II only
(B) I and II only
(C) I and III only
(D) I, II and III

(D) I, II and III

Each of the following about Reactive Oxygen Species are true:

I. Activated Phagocytes actually use Superoxide (O2 -) to cause oxidative stress in pathogens to kill them off.
II. Reactive Oxygen Species can damage DNA, proteins and even the lipid bilayer.
III. Oxidative Stress is linked to cancer, because it can turn proto-oncogenes into oncogenes.

CRB True or false? When trying to reprogram aerobic glial cells to anaerobic neurons, reducing Oxidative Stress greatly increases the reprogramming efficiency.

False. When trying to reprogram Anaerobic glial cells to Aerobic neurons, reducing Oxidative Stress greatly increases the reprogramming efficiency.

What allows Stem Cells to avoid Replicative Senescence?

Stem cells have a special protein called Telomerase, which will extend the telomeres after each round of DNA replication.