BIOL M02A Ch6

size of most plant and animal cells, most bacteria and nuclei

most cells are between 1 and 100 µm in diameter

fluorescence

locations of specific molecules are revealed by labeling the molecules with fluorescent dyes or antibodies, which absorb ultraviolet radiation and emit visible light. In this fluorescently labeled uterine cell, DNA is blue, organelles called mitochondria are orange, and part of the cell’s “skeleton” (called the cytoskeleton) is green.

Brightfield

lght passes directly through the specimen. Unstained (left), the image has little contrast. Staining with dyes (right) enhances contrast. Most stains require cells to be preserved, which kills them

Phase-contrast.

Variations in density within the specimen are amplified to enhance contrast in unstained cells; this is especially useful for examining living, unstained cells.

Nomarski

As in phase-contrast microscopy, optical modifications are used to exagger-ate differences in density; the image appears almost 3-D

Confocal

(Nerve cells are green, support cells orange, areas of overlap yellow.) In confocal microscopy, a laser is used to create a single plane of fluorescence; out-of-focus light from other planes is eliminated. By capturing sharp images at many different planes, a 3-D reconstruction can be created. A standard fluorescence micrograph is blurry because out-of-focus light is not excluded

Deconvolution

This process digitally removes out-of-focus light and reassigns it to its source, creating a much sharper 3-D image. The bottom is a compilation of standard fluorescent micrographs through the same cell

Super-resolution.

individual fluorescent molecules were excited by UV light and their position recorded. (DNA is blue, mitochondria red, and part of the cytoskeleton green.) Combining information from many molecules in different places ”breaks” the resolution limit, resulting in the sharp image on top. The size of each dot is well below the 200-nm resolution of a standard light microscope, as seen in the confocal image (bottom) of the same cell

Transmission electron microscopy (

transmission electron microscope profiles a thin section of a specimen

Scanning electron microscopy

Micrographs taken with a scanning electron microscope show a 3-D image of the surface of a specimen.

nucleus

found in eukaryotes

bounded by a double membrane

nucleolus

Here a type of RNA called ribosomal RNA (rRNA) is synthesized from genes in the DNA. Also in the nucleo-lus, proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes. These sub-units then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small subunit can assemble into a ribosome.

chromatin

The complex of DNA and proteins making up chromosome

Nuclear lamina

Help organize the genetic material so it functions efficiently

nuclear pore complex

provide access to the nucleus and regulate the transport of proteins and RNA across the nuclear envelope.

Smooth ER

Because its outer surface lacks ribosomes

these processes include synthesis of lipids, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions

Rough ER

studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope.

Many cells secrete proteins that are produced by ribosomes attached to it. For instance, certain pancreatic cells synthesize the protein insulin in the ER and secrete this hormone into the bloodstream.

ribosomes

the cellular machinery responsible for making proteins

Membrane-bound ribosomes, attached to the cytosolic side of the ER membrane, are engaged in the synthesis of proteins that are being concurrently translocated into the ER. Free ribosomes, unattached to any membrane, synthesize all other proteins encoded by the nuclear genome.

golgi applaratus

warehouse for receiving, sorting, shipping, and even some manufactur-ing. Here, products of the ER, such as proteins, are modified and stored and then sent to other destinations

lysosomes

membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules. Lysosomal enzymes work best in the acidic environment found in lysosomes.

vacuoles

large vesicles derived from the endoplasmic reticulum and Golgi apparatus.

the vacuolar membrane is selective in transporting solutes; as a result, the solution inside a vacuole differs in composition from the cytosol

In plants, small vacuoles can hold reserves of important organic compounds, such as the proteins stockpiled in the storage cells in seeds

mitochondria

the sites of cellular respiration, the meta-bolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels.

Chloroplasts

the sites of photosynthesis.

endosymbiont theory

This theory states that an early ancestor of eukaryotic cells (a host cell) engulfed an oxygen-using non-photosynthetic prokaryotic cell.

Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont (a cell living within another cell).

microtubules

largest

hollow rods constructed from globular proteins called tubules.

microtubules grow in length by adding tubulin dimers;

plus and minus end

microfilaments

structure and support in the cell

thin solid rods. They are also called actin filaments because they are built from molecules of actin, a globular protein.

can form structural networks when certain proteins bind along the side of such a filament and allow a new filament to extend as a branch

Intermediate Filaments

Named for their diameter, which is larger than the diameter of microfilaments but smaller than that of microtubules

more permanent fixtures of cells than microfilaments and microtubules

especially sturdy and play an important role in reinforcing the shape of a cell and fixing the position of certain organelles.

Dynein

transporting intracellular cargos in interphase cells and mediating spindle assembly and chromosome positioning during cell division.

kinesin

generate force and displacement along microtubules

myosin motors

moves its head groups along the actin filament in the direction of the plus end

Centrosome

Helps to organize the microtubules

Contrast centrosome and centriole

a centrosome is a complex containing two centrioles, whereas a centriole is a single microtubule-based structure within the centrosome

miotic spindle

a complex structure that separates chromosomes during cell division

primary cilium

acts as a cellular antenna, protruding from the cell surface to receive and transduce extracellular signals from the surrounding environment

basal body

A basal body is a protein structure that's located at the base of a cilium or flagellum

cell wall

the wall protects the plant cell, maintains its shape, and prevents excessive uptake of water. At the level of the whole plant, the strong walls of specialized cells hold the plant up against the force of gravity.

collagen

forms strong fibers outside the cells

accounts for about 40% of the total pro-tein in the human body.

proteoglycans

consists of a small core protein with many carbohydrate chains covalently attached, so that it may be up to 95% carbohydrate.

fibronectin

bind to cell-surface receptor proteins called integrins

integrins

span the membrane and bind on their cytoplasmic side to associated proteins attached to microfilaments of the cytoskeleton.

plasmodesmata

allow the movement of molecules and substances between cells

desmosomes

provide strong adhesion between cells.

gap junctions

allow the exchange of ions, second messengers, and small metabolites between adjacent cells

tight junction

prevent ions and molecules from passing between cells

protein complexes that act as semipermeable barriers between cells in epithelial and endothelial tissues