L8: Cell Biology VII Flashcards
Nucleolus. What is it? What are the components of it? Function?
- Organelle within the nucleus that is not membrane bound, serves as location for ribosome synthesis and assembly
- Rich in rRNA and protein, size proportional to state of protein synthesis
- Three components:
a. ) Nucleolar-organizer DNA: contains sequence of bases that code for the transcription of rRNA
b. ) Pars fibrosa: Newly transcribed rRNA just beginning to become complexed with proteins
c. ) Pars granulose: maturing subunits or ribosomes
What is nucleostemin?
- p53 binding protein found in undifferentiated cells. It decreases as cells become differentiated. Presence in CA cells may play a role in unchecked proliferation.
List steps of cell cycle
- Interphase
a. ) G1-gap 1
b. ) S-synthesis
c. ) G2-gap 2
d. ) G0-gap not - M-phase
Describe details of interphase
a. ) G1
- most variable in length, replication of centrioles begins here, has checkpoints: G1 DNA-damage checkpoint, restriction
b. ) S
- DNA synthesis with or without division of nucleus (tetraploid, octaploid cardiomyocytes), centriole replication continues, S DNA-damage checkpoint
c. ) G2
- accumulation of ATP for mitosis, synthesis of tubulin to form microtubules, centriole replication complete, checkpoints: unreplicated DNA, G2 DNA-damage
d. ) G0
- Seen in non-dividing cells such as striated muscle and most neurons
* * Cell cycle is driven by cyclin-cdk complexes
List steps of mitosis/M-phase
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
List detailed steps of mitosis
- ) Prophase
- chromatids condense, tetrads/bivalents seen, kinetochore forms on centromere, cytoplasmic microtubules disassemble, centriolar pairs migrate to opposite ends of cell - ) Prometaphase
- nuclear envelope starts to disappear, mitotic apparatus is becoming organized and microtubules are beginning to attach to kinetochores, chromatids start to become organized at equator of cell, nucleoli disappeared by early prometaphase - ) Metaphase
- chromatids located at equator of cell - ) Anaphase
- chromatids separate from one another and are referred to as chromosomes, chromatids have their cohesion complex enzymatically degraded by the APC (anaphase promoting complex) - ) Telophase
- nuclear membrane reporms, nucleoli reappear, chromosomes unwind into chromatin - ) Cytokinesis
- division of cytoplasm
Effect of colchicine on mitosis
- Arrests dividing cells at metaphase
Discuss segregation of organelles in mitosis
- Cell undergoing division must enlarge its existing organelles, which divide and are distributed in the daughter cells
Function of telomerase
- In somatic cells, telomere length decreases with every cell division. When too short, cell loses its capacity to divide
- Germinal / stem cells contain telomerase that maintains length of telomere thus sustaining the capacity of cells to divide
- Most tumor cells express telomerase
Two processes of cell death
- ) Apoptosis – programmed cell death
2. ) Necrosis – premature cell death
What occurs at lipid bilayer to indicate cell death? Why?
- Phosphatidylserine is normally located in the cytosolic lipid monolayer
- When translocated to the extracellular lipid monolayer, it marks cell as dead
- This signals neighbouring cells to phagocytose and digest the dead cell
Two pathways involved in apoptosis
- ) Extrinsic pathway
- Fas ligand binds to Fas receptor (known as death receptor)
- Adaptor proteins activated intracellularly
- Inactive procaspase-8 is cleaved to form activated caspase-8 (executioner caspase) - ) Intrinsic pathway
- Cell injury causes release of cytochrome c
- Cytochrome c-adaptor protein (Apaf-1) oligomerizes
- Inactive procaspase-9 is cleaved to form activated caspase-9 (executioner caspase)
What apoptotic strategies are seen with cancer cells?
- Some types of tumor cells evade an immune attack by expressing Fas ligand (FasL) referred to as FasL counterattack. This causes destruction of immune cells by triggering their elimination via apoptosis
- Increase anti-apoptotic factors
How does estrogen have an anti-apoptotic effect? Clinical relevance.
- Estrogen has anti-apoptotic effect on osteoblasts
- Estrogen causes inactivation of Bad (pro-apoptotic molecule) through phosphorylation
- Aging causes decrease in estrogen, no shutting off of Bad and osteoblasts don’t survive as much, therefore bone cell loss, bone matrix loss and osteoporosis
A newborn male was born with complete syndactyly of digits three and four. To correct the problem, surgery was performed at 6 months of age. How was apoptosis implicated?
- Apoptosis is crucial in many developmental process. They need to occur between digits, otherwise polydactyly can occur.
