Wow slide 6 Flashcards
1 micrometer (micron)
1/1000 of a mm
1 nanometer
1/1000 of a micron
Light microscopes
can magnify effectively to
about 1,000 times the size of the actual specimen
Most subcellular structures are too small to be
resolved by a light microscope.
Various techniques in light microscopy can
increase visibility of structures
Scanning electron microscopes (SEMs)
focus a beam
of electrons onto the surface of a specimen and collect
emitted electrons to provide images that look 3-D
Transmission electron microscopes (TEMs)
focus a
beam of electrons on a specimen and collect electrons
that pass through the specimen.
TEMs are used mainly to study
the internal structure of
cells and can magnify up to 1 million times the size of the
actual specimen.
Cell Theory
All living things are composed of cells.
Basic features of all cells*
– Semiautonomous, reproduce
– Carry a genetic program in the form of DNA
– Enclosed by a plasma membrane
– Semifluid internal substance called cytoplasm
– Contain ribosomes (make proteins)
Prokaryotic Cells
Simple, prokaryotic bacteria
cells have existed for at
least 3.5 billion years.
Cellular processes occur
diffusely within the
prokaryotic cell.
Genetic material is in the
form of a single large,
naked DNA molecule.
Eukaryotic cells appear
in the fossil record 1.5 billion years
after the first bacteria and are the cells that comprise all
living organisms besides bacteria.
Eukaryotic cells have a distinct, membrane bound nucleus
containing the cell’s genetic material.
Eukaryotic cells have separate organelles
specialized
structures that perform specific functions.
Robert Hooke (1653 - 1703) was the first to
observe and describe cells in
plant tissues
He published the bestseller
“Micrographia” of images he
observed with his microscope
A high surface-to-volume ratio
facilitates exchange of materials with
the surrounding environment.
Dividing a volume into smaller cells
increases the total surface area
The plasma membrane is
a selective barrier comprised primarily of a
phospholipid bilayer that encloses the interior of the cell, the cytoplasm
plasma membrane
It maintains the differences between internal and external environments
Plant and bacteria
cells also have a
cell wall
in addition to their cell membrane that protects and supports the cell
The nucleus of a cell
contains the cell’s genetic
material. Every cell has a
copy of the organism’s
“blueprint”
Pores in the membrane of the
nucleus
allow molecules to
move between the nucleus
and the cytoplasm
Within the nucleus the
nucleolus is the site where
ribosomal RNA (rRNA) is
synthesized.
The rRNA exits the nucleus
and assembles into
ribosomes in cytoplasm
The endoplasmic reticulum (ER)
is an extensive folded surface continuous with the plasma membrane within which proteins, lipids (fats, steroids), and phospholipids are produced
Ribosomes
are the structures that read the instructions in the genetic “blueprint” and assemble proteins.
Ribosomes can occur
freely within the cytoplasm
or attached to the
endoplasmic reticulum
The Golgi apparatus is a
complex of membrane vesicles that function in storage, processing, and packaging of proteins produced by the rough endoplasmic reticulum
Lysosomes
are vesicles that
contain hydrolytic enzymes
used to break down various
macromolecules in the cell
The endomembrane
system*
is comprised of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, vesicles and the plasma membrane.
Phagocytosis
is the formation of a food vacuole
which is merged with a lysosome for digestion.
Autophagy
is the destruction of cellular components by
collecting them in a vacuole that merges with a lysosome.
Chloroplasts
Possess a membrane system dividing the chloroplast into three
compartments (intermembrane space, stroma, thylakoid)
Contain the green pigment chlorophyll that absorbs solar
energy for use in synthesizing sugars
Are self-replicating and contain their own genetic material
independent of the cell as a whole
Mitochondria
are the “powerhouses” of the cell. Chemical
reactions occurring on the surface of an inner membrane
produce energy carrying molecules (ATP).
Mitochondria are self-replicating
and have their own
genetic material independent of that of the cell as a whole
Endosymbiosis
is one organism living inside another.
The endosymbiotic theory
of the origin of eukaryotes
states that some organelles such as mitochondria are
derived from once free-living bacteria that colonized the
cytoplasm of other single-celled organisms either through
ingestion or parasitism
Mitochondria (and chloroplasts in plant cells) have their
own
genomes with DNA sequences closer to those of
bacteria than to those in the nuclear DNA of the cells in
which they occur
Mitochondria (and chloroplasts in plant cells) have their
own
genomes with DNA sequences closer to those of
bacteria than to those in the nuclear DNA of the cells in
which they occur
cytosol
The jellylike substance in which the organelles of the
cytoplasm are suspended is called
A fibrous network called the cytoskeleton
spans the cytosol
to support the membranes and organelles of the cell.
Cytoskeleton includes
actin, intermediate filaments, and
microtubules.
Actin
is arranged to bear pulling forces (tension).
In muscle cells, actin is pulled upon by filaments
comprised of the motor protein myosin
Amoeboid movement
of the cell is achieved by
the action of actin microfilaments that extend a
pseudopodium outward from the surface of the cell.
Cytoplasmic streaming
moves the mass of the cell
in the direction of the pseudopodium.
The motor protein dynein
moves organelles and other
materials within the cell by
“walking” along microtubules.
Arrangements of
microtubules are
responsible
for the beating of flagella and cilia, external appendages used for locomotion
Flagella and cilia
contain dynein that acts against the
microtubule structure to produce movement.
Microvilli
are fingerlike
projections of the plasma
membrane supported by
bundles of actin.
Microvilli increase
the area
of absorptive and digestive
surfaces.
Tight junctions
proteins across membranes bind cells closely together preventing molecules from passing between (e.g. intestinal cells)
Desmosomes
“spot welds” between cells formed from proteins and bundles of intermediate filaments that increase the strength of tissues (e.g. skin cells)
Gap junctions
– tiny canals between cells through which cytoplasm and small molecules can pass (e.g. in nerve and muscle cells)
cell junctions
tight junctions, desmosomes, gap junctions
Animal cells are surrounded by a complex extracellular matrix
comprised of glycoproteins (proteins bonded to carbohydrates)
including collagen.
Functions in:
- Support
- Adhesion
- Movement
- Regulation
The cell wall of plants
is an extracellular structure that protects and supports the cell and helps maintain water balance.
plasmodesmata
The nonliving cell walls of plants are perforated with channels
called plasmodesmata that connect the cytoplasm of cells
