The cell and cell theory

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Cells are the basic unit of life

they must have a large surface area : volume ratio for optimal function, resulting in their maximum size being limited

prokaryotic and eukaryotic cells

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Cytoplasm:

common to both prokaryotes and eukaryotes

liquid in which cell structures are suspended; the site of chemical reactions; contains water, ions, nutrients, wastes, and in eukaryotes, organelles

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Ribosomes:

site of protein synthesis

subunits synthesized from rRNA (made in the nucleolus) and proteins

common to prokaryotes and eukaryotes, but in eukarya, also found on RER in addition to cytoplasm

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Cytoskeleton:

initially thought to only be in eukarya, but now known to also been in prokaryotes; bacteria have proteins homogenous to tubulin and other cytoskeletal elements

network of fibers within the cytoplasm that provide structural support, maintain cell shape, and support cell division

3 types of fibers in eukaryotes:

microtubules

hollow fibers made of tubulin dimers (α-tubulin and β-tubulin)

provide structural support and provide tracks for organelle movement within the cell; also have a role in cell division by pulling apart chromosomes; make up cilia and flagella

centrioles are a specialized grouping

largest and widest diameter

originate in from microtubule organizing centers, like the centrosome

form and dissemble quickly

intermediate filaments

unique to animal cells

made up of a family of related proteins, particularly keratin

provide structural support, like holding together tissues

medium sized

do not form or dissemble quickly, therefore do not have a role in movement or transport, only structure

microfilaments (aka actin filaments)

made of actin, assist in maintenance of cellular shape by absorbing tension

assembly powered by ATP, provides a track for myosin movement

aside from muscle cells, the interplay between these 2 proteins can be seen during cytokinesis and the formation of the cleavage furrow

cytoplasmic streaming (circular movement of cytoplasm) in plant cells

the thinnest fibers

form and dissemble quickly, allowing for the cell's shape to rapidly change and allow it to move

ex: ameboid movement utilized by WBCs

also form extracellular movement structures like cilia and flagella

cilia

only in eukaryotes

hair-like structures on cell surface that exhibit synchronized movement

involved in movement of entire cells as well as material outside cell surface

ex: cells lining respiratory tract have cilia that move constantly to catch and remove bacteria and particles that should not enter the tract

flagella

in both prokaryotes and eukaryotes, but made of different proteins/have different structure

similar to tails

involved in movement of entire cells

both have a 9 + 2 arrangement of microtubules

9 pairs of microtubules surrounding 2 central microtubules

dyneins (motor protein) are attached to each of the 9 pairs

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Cell wall:

not in animal cells, but present in plant, fungal, and prokaryotic cells

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Cell Theory:

term "cell" coined by Robert Hooke in the 1600s

theory proposed in 1800s by Theodor Schwann and Matthias Schleiden, and elaborated on by Rudolf Virchow

principles:

all organisms are made of cells

cells are the basic unit of life

all cells arise from pre-existing cells

the cell contains hereditary information passed on from cell to cell

prompted the development of the fields of cell biology and microbiology

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Senescence:

cells fail to divide due to shortening of telomeres leading to aging

some cells that express telomerase can prevent senescence by lengthening telomeres, but telomerase may also play a role in the immortality of cancer cells

aging is also the result of the accumulation of chemical and environmental insults over time