Week 1 Part 3 Flashcards
- Apoptosis
o Process by which cell die in a systemic manner
- In most cases the two processes are balanced to maintain a fixed number/ density of cells.
o Some excptions
Division is greater than death
• Fetal development
• Cancer
• Tissue repair
Death is greater than division
• Aging
• Illness
Fetal development if cells in between fingers don’t die of apopotptis they stick together
Cell cycle 2
2 components
- Interphase
- Mitosis
o Interphase
Time of growth that prepares cell to divide
• Gap phases (G) , G1 and G2 between these is where’s S phase is.
• S phase (Synthesis) – where dna replication occurs- everything has to be replicated
o Mitosis
Process that physically divide DNA and cells to create 2 new (daughter cells).
3 phases that prepare cell to divide
G1 to S to G2
Interphase - G1
Immediately follows the previous mitosis that created the cell Once cell divides the new cell goes into G1 phase.
16 – 24 hrs in rapidly dividing cells
High amount of synthesis, metabolism, and growth
Interphase - G0
Cell can exit cell cycle
Cell division machinery is removed
When
• Cell division is not needed, slow growing tissues
• Damage is detected
o Gives extra time for cell to repair itself.
After it is in G0 it has 3 options 1 it may remain and just do its duties, 2 it may be signaled to die 3 it may be signaled later to divide again. Not a terminal point.
Interphase S -synthesis
Time period where cells replicates its entire genome
o Usually 8 – 10 hrs
• Each chromosome is replicated to form sister chromatids
o Sister chromatids remain attached to one another at centromere.
Other synthesis continues
• Centrioles duplicate – for structures that pull everything apart
o Coordinates microtubules to form mitotic spindle
Interphase G2
Final preparations for mitosis
Membrane synthesis
Mitosis and Cytokinesis
et of 5 distinct steps that divides replicated chromosome, then splits cell into two identical cells (daughter cells)
o Idea is that will split genetic content then divide the rest of cell and split cytoplasm. -videos
Mitosis
- Mitosis begins when cells transition from interphase to prophase
o Before prophase
Chromosomes are replicated into sister chromatids that are attached by the centromere and uncondensed
Centrioles have replicated
Nuclear envelope is intact
o During prophase
Chromosomes become highly condensed
Centrioles migrate to opposite poles of cell and spindle begins to form
Nuclear envelope
- Mitotic spindle
o A cells microtubules grow from the centrioles ( centrisome)
Pair of short microtubules perpendicular to one another
Sorrounded by matrix of other proteins
o During interphase centrioles replicate
o During prophase replicated centrioles migrate
o Microtubules grow from centrioles to form spindle that will pull chromosomes apart during mitosis.
- Metaphase
o Spindle pushes and pulls sister chromatids until they are lined up in the cell ( metaphase plate)
Mitosis will not proceed further until this occurs
- Anaphase
o Centromere break apart and sister chromatids are pulled to opposite sides of cell.
- Telophase
o Spindle breaks down
o Nuclear envelope reforms
o Microfilament ring forms at plasma membrane, creating a furrow
- Cytokinesis
o Microfilament ring keeps tightening until cell separates into tow separate daughter cells
o Divides cytoplasm between the two cells.
o Videos
CeLL Cycle control
- Cell cycle is highly controlled to ensure correct timing and quality
o Cell cycle must pass specific checkpoints before cycle can continue
Mainly controlled by levels of proteins called cycling and cyclin dependent kinases
G1 checkpoint (also called “start”) is commitment to divide
• Ensures DNA is not damaged and that previous mitosis occurred correctly
o If damage occurred then cell will enter G0
• Ensures that conditions are correct for division to occur
o Correct external signals and enough nutrients, organelles, growth, etc.
S checkpoint ensures that genome was replicated once and only once
M checkpoint ensures that chromosomes are correctly attached to spindle.
- Cells have a limited number of times that they can divide
o Usually 40 – 6o times for cultures cells depending on the type
o Partially controlled by telomere
Special repeating units of DNA at ends of each chromosome
• Chromosomes shorten slightly each time DNA is replicated
• Telomeres protect chromosomes from losing essential DNA sequences during shortening
o Telomeres become shorter with each replication until they can not shorten anymore.
o In constantly dividing cells and many cancers telomere length is maintained allowing cells to keep dividing.
- Cell division in individual cells is also controlled externally
y growth factors and other hormones
o Most cells require external signals to pass start
Bind to signal receptors in plasma membrane activate signal network inside of cell
o Prevents cells from acting autonomously.
Apoptosis
- Cell may be signaled to enter apoptosis for many reasons;
o Remove unneeded cells during development
o Remove cells that entered G0 but could not correct damage
o Remove aged or dying cells
o Remove cells infected with a virus - Cells require constant survival signals to prevent apoptosis. Also specific death signals can induce apoptosis.
Apoptosis
- Ordered set of events that dismantle cells and prepare it for removall by phagocytes
o Initiated by class of enzymes called caspases
o Causes mitochondria to release cytochrome C
Increases caspase activity
Stops energy production
o Destroys enzyme that replicate and repair DNA
o DNA is chopped up into pieces
o Cytoskeleton is degraded
o Stop cell form adhering to other cells
o Attracts phagocytes to remove cell - Allows cell to be removed without relabeling any cell contents into tissue
o Opposite of necrosis.
Stem cells
- All of our cell types were derived from a fertilized egg by differentiation ( specialization )
- Fully differentiated cells lose the ability to divide. Instead tissue growth and replacement of cells is done by stem cells and progenitor cells
o Stem cells are undifferentiated cells that can become most types of differentiated cells
Retain the ability of self-renewal
The fertilized egg is the ultimate stem cell
o Progenitor cells are more specialized than stem cells
Cannot self-renew.
o Two types of stem cells
Totipotent can become any type of differentiated cell
• Fertilized egg
Pluripotent can become any one type of several related cell types but not all possible cell types
• Cells from early developing embryo.
Stem cell therapies
- Most are in early experimental stage
o Replace damaged or diseased tissues
o Treat specific diseases
o Slow aging process - If stem cell could be induced to form specific cells/ tissues then they could be transplanted into recipient to replace specific tissues
o Bone marrow transplant are one currently used application of stem cells. - Sources of stem cells
