Mechanisms of Disease I: Cell growth and cell differentiation Flashcards
Define hyperplasia
increase in cell numbers (hyperplasia (most common) – cell division
Define hypertrophy
increase in cell size (hypertrophy – more proteins, more membranes, elevated levels of protein synthesis. Such as the heart)
What do hyperplasia and hypertrophy depend on?
Depends on the integration of intra- and extracellular signals (checks on cellular physiology, growth and inhibitory factors, cell adhesion etc.)
What is differentiation?
Differentiation: exit from the cell cycle, known as post-mitotic cells. It involves a program of cell type-specific gene expression. The cell morphology and function changes.
What are the cell cycle phases?
• G1 is growth phase 1, S is synthesis (where DNA is replicated), M is for mitosis
o Progression controlled at three key checkpoints (restriction points)
What is programmed cell death called?
• Loss of cells by programmed cell death (apoptosis)
o A coordinated program of cell dismantling ending in phagocytosis. Distinct from necrosis
o Occurs during normal development (e.g. separation of the digits, involution, immune and nervous system development)
o And in response to DNA damage and viral infection
Is there anything in common between cell growth and differentiation?
- Yes – the mechanisms governing them
- Cell growth and differentiation are both governed by the integration of multiple signals:
- Depends on integration of intra- and extracellular signals (checks on cellular physiology, growth and inhibitory factors, cell adhesion etc.)
- These signals converge on the promoters of key genes – these promoters act as “co-incidence detectors.” These then determine if the gene is expressed and how much expression.
What are Growth factors, cytokines and interleukins?
Proteins that:
• Stimulate proliferation (called mitogens) and maintain survival
o Usually named after originally identified target e.g. EGF, FGF, Interleukins (IL2 & IL4), NGF
o But see also PDGF (platelet-derived GF) and IGF1 (Insulin-like GF – the main effector of pituitary growth hormone)
• Stimulate differentiation and inhibit proliferation e.g. TGF Beta (transforming growth factor)
• Induce apoptosis e.g. TNFα and other members of the TNF family (tumour necrosis factor)
briefly explain how extracellular signals work
What are the three broad classes of extracellular
Ligand – receptor – intracellular cascade
Three broad classes:
1. Paracrine: produced locally to stimulate proliferation of a different cell type that has the appropriate cell surface receptor
2. Autocrine: produced by a cell that also expresses the appropriate cell surface receptor
3. Endocrine: like conventional hormones, released systemically for distant effects
Describe cell population growth
• When you add growth factor, the cells will respond and enter the cell cycle and start to divide
• If the PDGF is no longer available, there is a plateau until they receive more PDGF
o If the cells receive TGF Beta, they will stop dividing
• TNF Alpha will lead to the cells committing suicide and the number of cells going down
• So, we can influence cell number according to what factors we add
What are the phases of the cell cycle?
• M is mitosis. This is the separation of the chromosomes and the physical separation of the cell into 2 daughter cells
o After the M phase, one of the daughter cells undergoes interphase. The cell grows using nutrients to create more cytoskeleton etc.
• Synthesis is when DNA replication takes place two copies of the genomic DNA
• In the growth phases the cells get ready, so they have everything that is required for mitosis
• Quiescent Cells are cells that are arrested in the G0 phase
o These cells can re-enter the cell cycle if we add mitogens and will start proliferating
o Some quiescent cells may start to differentiate. E.g. they could become gut cells. This is called terminal differentiation. Some cells undergo apoptosis and die
• After cell division, the cells have two copies of each chromosome so that is 2N
o After the S phase, there is more duplication, so it is 4N
What does Fluorescence activated cell sorter (FACS) analysis. show us?
• In G1 phase 2N- diploid state, in M phase 4N state as chromosome has been duplicated.
• Take cells and label the DNA with dye.
• The dye is read by a laser and the laser tells us how intense the cells are in each phase.
o We can see in what stage cells are in.
• This graph shows the difference between a slow and fast rate of proliferation.
o In the high rate of proliferation, there are a lot more cells that are in the S phase
Describe the principles of DNA replication
- DNA is replicated semiconservatively (daughter cells inherit one parental and one new strand)
- New DNA is synthesised in the 5’ to 3’ direction from deoxynucleotide triphosphate precursors at a replication fork by a multienzyme complex (a replication machine)
- Fidelity is determined by base pairing (A=T, G≡C) and presence of a proof-reading enzyme in DNA polymerase
- Synthesis of the new DNA strand uses an RNA primer and occurs continuously on the leading strand and discontinuously on the trailing strand (giving rise to Okazaki fragments, which are ligated together after removal of the RNA primer)
What do the different stains show?
- Stain in blue is for DNA
- Stain in red is for gamma tubulin which is required to form the microtubules that will bind to the centrioles and chromosomes
- Stain in green is for CHEK2 which is a cell cycle checkpoint protein
What are the phases of mitosis?
• Prophase (1)
• Nucleus becomes less definite
• Microtubular spindle apparatus assembles
• Centrioles (yellow) migrate to poles
• This is due to the overlap in the green and the red
• Prometaphase
o Nuclear membrane breaks down
o Kinetochores attach to spindle in nuclear region
• Metaphase (2)
o Chromosomes (blue) align in equatorial plane
• Anaphase (3)
o Chromatids separate and migrate to opposite poles
• Telophase (4)
o Daughter nuclei form
• Cytokinesis
o Division of cytoplasm
o Chromosomes decondense
