CELL COMMUNICATION
- animal cells = gap junctions to send signals (must be in direct contact)
- plant cells = plasmodesmata
- local signaling - signaling over a short distance - cell to cell recognition - local regulators
- long-distance signaling - nervous/endocrine system in animals - plants use hormones, transported through vascular system
- three stages of cell signaling - signaling molecule binds to the receptor protein - signal is converted into a form that can produce a cellular response - the transduced signal triggers a cellular response
- G-protein receptors make up 60% of our cells
- quorum sensing - capacity of bacteria to exhibited coordinated behavior in response to a particular population density

CELL DEATH
- apoptosis - controlled cell suicide - components are chopped up and packaged into vesicles = digested by scavenger cells - "blebbing" vs. apoptosis - triggered by death-signaling, DNA damage, protein misfolding - caspases - main proteases that carry out apoptosis - proteases - protein - digesting enzyme
- necrosis - death by cell injury - cell bursts, “stuff” flies out - enzymes are unleashed into the ECF - results in inflammation, redness, pain, etc.

- DNA is organized in chromosomes. -DNA is wrapped around histone proteins = chromatin (long thin fiber) -condenses further during mitosis = chromatin => chromosomes
- mitotic chromosome = 2 sister chromatids -chromatids narrow at the centromere (not necessarily in the center) -homologous = same information
- mitosis - divides the cell’s DNA between 2 daughter nuclei -4 phases = prophase, metaphase, anaphase, telophase
- semi-conservative replication - conserve half of original piece = build two new ones
- original piece is called the template strand

INTERPHASE
- G1 - 1st Gap - cell growth
- S - DNA synthesis - chromosomes are copied -each daughter cell gets identical copy -error rate is about 1/100 million bases
- G2 - 2nd Gap - further cell growth. organelles, proteins, membranes are created.

Nucleus is well-defined, and DNA is loosely packed in long chromatin fibers (aka squiggly in the middle).

PROPHASE
- chromatin condenses => visible chromosomes
- centrioles move to opposite poles of cell - spindle fibers go across cell to form mitotic spindle - microtubules???
- nucleolus disappears/nuclear envelopes burst

TRANSITION TO METAPHASE/PROMETAPHASE
- spindle fibers attach to centromeres - thus creating kinetochores
- microtubules attach at kinetochores - connects centromeres to centrioles
- chromosome begins to move

METAPHASE
- chromosomes align along the middle of the cell (metaphase plate)
- spindle fibers coordinate movement
- ensures that the chromosomes separate properly (1 copy per new nucleus)

ANAPHASE
- sister chromatids are separated at the kinetochores
- move to opposite poles (pulled by centromeres)
- microtubules lengthen as poles move further apart

TELOPHASE
- chromosomes arrive at opposite poles
- nuclei form and chromosomes disperse
- cytokinesis begins

CYTOKINESIS
- animal cells - constriction of actin microfilaments around equator of cell = cleavage furrow - splits cell in two
- plant cells - cell plate forms - vesicles fuse = forms 2 cell membranes - new cell wall laid between membranes - new cell wall fuses with existing cell wall

EVOLUTION OF MITOSIS
- mitosis in eukaryotes likely evolved from binary fission in bacteria characteristics of binary fission: - single circular chromosome - no membrane bound organelles - no mitotic spindle

REGULATION OF CELL DIVISION
- multicellular organisms - must coordinate cell division across tissues/organs -timing,