The Cellular Basis of Life
Cells and Tissues- carry out all chemical reactions needed to sustain life
- cells are the building blocks of all living things
- tissues are groups of cells that are similar in structure and function
- cells are made up of carbon, hydrogen, oxygen, nitrogen and trace elements like iron,
sodium, potassium and calcium
- cells are about 60% water
- cells of the body are bathed in a dilute solution of salt water called interstitial fluid
which is derived from blood. All exchanges between cells and blood are made in this
fluid
- cells structure dictates its function
- cells have different roles
Anatomy of a cell- cells are not the same size, but they all share general structures
- they are organized into 3 main regions- the nucleus, cytoplasm and plasma
membrane
NUCLEUS- the cell control center, contains DNA and the instruction for protein
synthesis
Nuclear membrane- double membrane (phospholipids) selectively permeable, fluid
inside is called nucleoplasm
Nucleoli- nucleus contains from 1-4, sites where the ribosomes (organelles) are
assembled
Chromatin- DNA called chromatin when cells are not dividing, loose network of
bumpy threads scattered throughout the nucleus, when cell is dividing, the chromatin
threads coil and condense to form rod like bodies called chromosomes.
PLASMA MEMBRANE- transparent barrier that is fragile, flexible and composed
primarily of phosphlipids (hydrophilic heads and hydrophobic tails) protein, cholesterol
(for flexability) and glycoproteins. Is selectively permeable.
PLASMA MEMBRANE SPECIALIZATIONSMicrovilli- fingerlike projections that increase surface area for absorption and secretion.
Looks like shag carpet, found mostly in the digestive tract.
Membrane JunctionsTight Junctions- impermeable junction; binds cells together to prevent leakage of
fluids between cells. Adjacent plasma membranes fuse together like a zipper (in small
intestine to prevent digestive enzymes from seeping into the bloodstream)
Desmosomes- anchoring junctions that prevent cells subjected to mechanical stress.
Holds cells tightly together, these junctions are formed by the connections between fine
protein filaments in adjacent membranes.
Gap Junctions- commonly seen in heart and embryonic cells, their function is to allow
communication between adjacent cells to move nutrients and ions between cells of heart
and embryo connexons.
CYTOPLASM- cellular material outside the nucleus and inside the plasma membrane
- site of cellular activities (contain organelles)
Cytosol- clear fluid portion of cytoplasm; a semitransparent fluid that suspends the
organelles and inclusions.
Organelles- metabolic machinery of a cell
Inclusions- non-functioning units of cytoplasm; may or may not be present in
cytoplasm. Most store nutrients or cell products like fat droplets, glycogen granules,
melanin pigments or mucus.
ORGANELLESRibosomes- made of protein and RNA. They are tiny, round bodies that are the sites of
protein synthesis; found either as free floating in the cytoplasm or attached to the rough
ER
Endoplasmic Reticulum (ER)- fluid filled tubules for carrying substances
Two Types:
Rough Endoplasmic Reticulum- filled with Ribosomes, site where building materials of
cellular membrane are formed and synthesize secretory proteins to be secreted from the
cell
Smooth Endoplasmic Reticulum- a combination of rough ER except it has no
ribosomes attached; functions in cholesterol synthesis and breakdown, fat metabolism
and detoxification of drugs (liver has abundance of smooth ER)
Golgi Apparatus- appears as a stack of flattened membraneous sacs found close to the
nucleus. Function is to modify and package secretory proteins. The different types of
packages are secretory vesicles, cell membrane components and lysosomes.
Lysosomes- organelle that contains powerful enzymes that rid cell of nonusable materials
in the cell and cell invaders; found in abundance in WBC’s.
Peroxisomes- organelle that helps detoxify the harmful substances like alcohol and
formaldehyde from the body. Most important function is to disarm the body of dangerous
free radicals. Peroxisomes convert free radicals in hydrogen peroxide (H2O2 and then the
H2)2 is converted to H2O by the enzyme catalase. Many peroxisomes are found in the
liver and kidneys.
Mitochondria- “power houses of the cell,” consoists of a double membrane. The outer
membrane is smooth and the inner membrane has shelf like protrusions called cristae.
Carries out reactions where oxygen is used to break down food providing ATP to carry
out cellular activity. Muscle and livercellshave many mitochondria.
Cytoskeleton- a network of protein structures that extend throughout the cytoplasm that
provides the cell with an internal framework.
Three types of proteins are:
Microfilaments- examples are actin and myosin that are active in cell motility and also
changes the cell’s shape (found in muscle cells)
Intermediate filaments- help to form desmosomes and resist pulling forces on the cell
(stresses) Found in cells of skin and heart
Microtubules- determines cell’s shape and distribution of cell’s organelles and are
important during cellular division
Centrioles- rod-shaped bodies made of microtubules that lie close o the nucleus. During
cell division, they direct the movement of chromosomes by forming the mitotic spindle.
Cellular Projections- not in all cells. Used for movement
Cilia- moves material across the cell surface; yakes ATP to operate. Found in the
trachea, respiratory system.
Flagellum- propels the cell
Cell Transport & PermeabilityTERMS TO KNOWKinetic energy- the energy of motion; energy that is doing work
Brownian motion- the term used to refer to the visible movement of large particles being
hit by invisibly small molecules.
Concentration gradient- when the concentration of a substance differs from one point to
another.
Diffusion- the movement of particles from a place of high concentration to an area of low
concentration
Molecular weight- heavy molecules move more sluggishly and diffuse more slowly.
Diffusion rate- determines how quickly a cell can acquire nutrients or rid itself of wastes
Selective permeability- allows some things to pass through but prevents others from
entering or leaving
Osmosis- the diffusion of water through a selectively permeable membrane
Hypertonic solution- has a higher concentration of non-permeating solutes than the ICF
Creanate- means to shrink or shrivel
Hypotonic solution- has a lower concentration of non-permeable solutes than the ICF
Filtration- particles are driven through a selectively permeable membrane by hydrostatic
pressure
Passive transport- diffusion through a membrane down its concentration gradient- doesn’t
use energy
Active transport- diffusion through a membrane up its concentration gradient using ATP