Cell Death, Stem Cells, Cancer

Question 1

What is necrosis?

Answer 1

Cells killed via mechanical damage, toxic chemicals, lack of blood.

Question 2

What changes occur in a cell undergoing necrosis?

Answer 2

Cell + organelles lose ability to control passage of ions and water, resulting in swelling and leakage of cell contents leading of the inflammation of surrounding tissues.

Question 3

What is apoptosis?

Answer 3

Programmed cell death for proper development and protection from cells that represent at threat to the integrity of the organism

Question 4

What changes occur in a cell undergoing apoptosis?

Answer 4

• cell shrinks
• cytoskeleton collapses
• bubbles appear on surface
• nuclear envelope disassembles
• nuclear DNA breaks up into fragments
• cell breaks into small membrane wrapped fragments

Question 5

What is the role of phospholipid phosphatidylserine on apoptosis?

Answer 5

PT-serine, normally on inner leaflet, is flipped onto the outer leaflet when it is time for the cell to die. PT-serine binds to receptors on phagocytic cells.

Question 6

What role do phagocytic cells play in apoptosis?

Answer 6

Possess receptors that bind to phosphatidylserine which signals the cells to engulf apoptotic cell fragments. They then secrete cytokines that inhibit inflammation.

Question 7

What are examples of apoptosis in development?

Answer 7

1. Resorption of tadpole tail
2. Formation of fingers and toes require removal of tissue between them
3. Menstruation: sloughing off of the inner lining of the uterus
4. Neural innervations in tissues require removal of surplus neurons during development.
5. Liver must be kept at a constant size through regulation of rate of cell death and cell birth.

Question 8

What are examples of apoptosis in organism protection?

Answer 8

1. Cytotoxic T lymphocytes kill virus-infected cells by inducing apoptosis
2. Cytotoxic T lymphocytes induce apoptosis within each other and themselves.
3. In response to DNA damage, cells increase production of p53 protein that induces apoptosis
4. Radiation and chemicals used in cancer therapy induce apoptosis in some types of cancer cells.

Question 9

What are caspases?

Answer 9

Intracellular proteases that trigger apoptosis by cleaving numerous specific intracellular proteins at particular amino acid sequences.

Question 10

What is the difference between initiator and executioner caspases?

Answer 10

Initiator: Begins apoptotic program

Executioner: orchestrate apoptosis program

Question 11

How is the initiator caspase activated?

Answer 11

Apoptotic signal triggers dimerization and cleavage of initiator caspases, activating them.

Question 12

How is the executioner caspase activated?

Answer 12

inactive dimers are activated by the cleavage in their domain by an activated initiator caspase.

Question 13

What is the intrinsic apoptotic pathway?

Answer 13

Activated in response to DNA damage or other intracellular insults and regulated by Bcl2 family of intracellular proteins.

Question 14

What are the members of the Bcl2 family?

Answer 14

Bax + Bak: promote cell death by activating cytochrome c released from the mitochondria into the cytosol

Bcl 2: inhibit apoptosis by preventing Bax and Bak from activating cytochrome c

Question 15

What are the steps of intrinsic apoptosis?

Answer 15

1. In response to apoptotic signal, Bax/Bak molecules on the mitochondria are activated
2. Activated Bax/Bak molecules open allowing release of cytochrome c from intermembrane space
3. Cytochrome C binds to adaptor protein and assembles a seven-armed pinwheel protein complex called apoptosome.
4. Apoptosome recruits and activates a particular initiator procaspase which triggers caspase cascade leading to apoptosis.

Question 16

What are the steps of extrinsic apoptosis (lymphocyte induced)

Answer 16

1. Fas ligand in killer lymphocytes bind to Fas death receptor on cell
2. Fas ligand binding exposes death domain on receptor tails
3. Each exposed death domain on receptor binds to adaptor protein FADD’s death domain
4. Bound FADD protein exposes death effector domain and recruits inactive initiator caspase which gets cleaved and triggers apoptosis

Question 17

Other than with Fas, how do Cytotoxic T cells induce apoptosis?

Answer 17

Directional release of cytosolic granules containing perforin and granzymes. Perforin forms pores in the cell membrane, and granzymes are serine proteases.

Question 18

What are survival factors?

Answer 18

Molecules secreted by cells that promotes survival by increasing the production of Bcl2, a protein that suppresses apoptosis.

Question 19

What is the pathway of survival factor to Bcl2?

Answer 19

1. Survival factor reaches receptor on target cell
2. Activated receptor triggers a cascade that activates a transcription regulator
3. Transcription regulator enters the nucleus and binds to enhancer regions on the Bcl2 gene
4. Bcl2 gene is activated and produces mRNA that translates Bcl2 protein.
5. Bcl2 protein blocks apoptosis.

Question 20

What is the difference between IVF and ICSI?

Answer 20

In vitro fertilization: Sperm and eggs interact in a dish leading to fertilization.

Intra-cytoplasmic Sperm Injection: Sperm and eggs are collected, holding pipette secures one egg in place and micropipette injects a single sperm into the centre of the egg.

Question 21

What happens in the first 5 days of fertilization

Answer 21

Day 1: post 12 hrs, two bundles of genetic material is seen, 18-20hrs bundles fuse and combine genetic material to create one cell (fertilized egg)

Day 2: Cell divides into 2 cells and then 4 cells

Day 3: The four cells divides to create 8 cells

Day 4: Continued dividing

Day 5: Blastocyst forms. Cells outside become placenta, cells inside become getus.

Question 22

What is differentiation?

Answer 22

Process by which stem cells become specialized.

Question 23

What are the 3 criteria to be classified as a stem cell?

Answer 23

1. Undifferentiated or unspecialized
2. Have the ability to self renew
3. Have power to produce many different types of differentiated cells

Question 24

What is population asymmetry / symmetrical differentiation?

Answer 24

When stem cells divide, one daughter cell is a result of self renewal, and the other is a committed cell that will differentiate

Question 25

What is the difference between totipotent, pluripotent, and multipotent stem cell?

Answer 25

Totipotent: capable of producing all the cell type in embryonic and extraembryonic lineages; includes the fertilized egg and first 4-8 cells

Pluripotent: capable of producing all the cell types in embryonic lineages only; reside in inner cell mass of blastocyst

multipotent: adult stem cells with a restricted array of cell types they can create

Question 26

What is the difference between embryonic and extraembryonic stem cell lineages?

Answer 26

1. Embryonic lineages: form body and germ cells
2. Extraembryonic lineages: placenta, amnion, allantois and yolk sac

Question 27

What factors contribute to cell stability in a tissue?

Answer 27

Cell communication, selective cell adhesion, cell memory

Question 28

What is the function of adult stem cells?

Answer 28

Replenishing dying cells and regenerating damaged tissues, since terminally differentiated cells do not divide or make copies of themselves.

Question 29

What are proliferating precursor cells/transit amplifying cells?

Answer 29

Cells that a divide from a precursor cell a limited number of times before they terminally differentiate.

Question 30

What is the pathway of terminal differentiation?

Answer 30

1. Stem cell divides into daughter stem cell and precursor cell
2. Precursor cell divides into proliferating precursor cells
3. Proliferating precursor cell divides and differentiates into terminally differentiated cells

Question 31

How is intestinal tissue renewed?

Answer 31

1. Stem cells at bottom of crypt give rise to precursor cells higher up the crypt
2. Proliferating precursor cells slide upward and terminally differentiate into secretory or absorptive cells
3. Absorptive cells slide upwards and shed from the tip of the villus, paneth cells move to the bottom of the crypt.

Question 32

How is tissue renewed in the skin?

Answer 32

1. Proliferating stem cells and precursor cells are confined to the basal layer, adhering to basal lamina
2. Differentiating cells travel from their site of origin in a direction perpendicular to the plane of the cell sheet
3. Terminally differentiated cells are shed from the skin surface.

Question 33

What is a hemopoietic stem cell?

Answer 33

Stem cells found in the bone marrow that differentiate into mature blood cell types found in circulation.

Question 34

What are induced pluripotent stem cells?

Answer 34

Differentiated cells grown in culture and reprogrammed into embryonic-like state by adding appropriate factors.

Question 35

What are two heritable properties of cancer cells and their progeny?

Answer 35

1. Proliferate without adhering to the usual constraints
2. Invade and colonize territories normally reserved for other cells

Question 36

What is the difference between a benign and malignant tumour?

Answer 36

Benign: Proliferate excessively but remain clustered together

Malignant: proliferating cells with the ability to invade surrounding tissue and may form metastases (secondary tumours) at other sites

Question 37

What is epidemiology?

Answer 37

Statistical analysis of human populations to identify factors that correlate with disease incidence

Question 38

What is the cause of cancer?

Answer 38

• spontaneous mutations
• mutagen induced mutations
• mutations due to DNA replication error

Question 39

What is the difference between a passenger mutation and a cancer-critical/driver mutaiton?

Answer 39

Passenger: mutations do not contribute to cancer

Driver: contribute to cancer development

Question 40

What are factors that contribute to genetic instability?

Answer 40

1. Defects in DNA replication
2. Defects in DNA repair
3. Defectis in cell-cycle checkpoint mechanisms
4. Mistakes in mitosis
5. Abnormal chromosome numbers

Question 41

How does cancer evolve?

Answer 41

New mutations are accumulated progressively due to natural selection favouring mutations that enhance cell proliferation and/or survival

Question 42

What characteristics distinguish cancer from normal cells?

Answer 42

1. Reduced dependence on signals from other cells for their survival, growth and division
2. Avoid cel apoptosis
3. Often proliferate indefinitely
4. Genetically unstable
5. Abnormally invasive
6. High consumption of glucoase
7. Survive and proliferate in abnormal locations
8. Secrete signals that influence behaviour of cells in surrounding connective tissue.

Question 43

What are the two main classes of genes critical for cancer?

Answer 43

1. oncogenes: genes that acquire a function contributing to cancer development; dominant mutations (e.g. excessive cell survival)
2. Tumor suppressor genes: genes that lose a function that contributes to cancer development; recessive mutation (e.g. recessive mutations)

Question 44

What are 3 ways a proto oncogene can be converted into its corresponding oncogene?

Answer 44

1. Mutation in coding sequence: results in mutant protein made in normal amounts
2. Gene amplification: normal protein overproduced
3. Chromosome rearrangement: normal protein is overproduced or fusion with actively transcribed gene produces hyperactive fusion protein

Question 45

What are events that can eliminate the activity of a tumour suppressor gene?

Answer 45

1. Whole normal tumor suppressor gene is lost
2. Region containing normal gene is deleted
3. Loss of function mutation in tumor suppressor gene
4. Paternal gene silenced by epigenetic mechanism

Question 46

What pathways cause cancer-critical mutations to cluster?

Answer 46

1. Pathways that govern initiation of cell division cycle
2. Pathways that transmit signals for cell growth and cell division
3. Pathways regulating responses to stress and DNA damage

Question 47

How does the loss of a tumor suppressor gene cause colorectal cancer?

Answer 47

Adenomatous polyposis coli, aka tumor suppressor gene APC may be inactivated which coupled with other driver mutations can progress to cancer.

Question 48

What are types of cancer treatments?

Answer 48

1. Surgery: performed on cancers that have not spread
2. DNA damaging chemotherapy/radiotherapy: cancer cells die from chromosome fragmentation when they divide
3. imunotherapy: Development of immune checkpoint inhibitors on the T cell that prevent tumour cells from inhibiting the activation of T-cells

Question 49

What are chimeric antigen receptor T cells?

Answer 49

Fusion proteins designed to target T cells to antigens expressed on cancer cells

Question 50

What is chronic myeloid leukemia’s treatment with Gleevec?

Answer 50

CML is associated with chromosomal translocation (philadelphia chromosome) fusing Abl and Bcr genes. When fused, they create Bcr-Abl gene that translates to a hyperactive kinase. Gleevec blocks activity of hyperactive mutant kinase.