Eukaryotic and Prokaryotic Cell Structures and Organelles

Eukaryotes

Cells that have a membrane-enclosed nucleus encapsulating the DNA, including higher organisms like plants, animals, fungi, protozoa, and most algae.

Prokaryotes

Cells that lack a discrete nucleus and nuclear membrane, including bacteria and cyanobacteria.

Plasma Membrane

Holds the cell together, serves as a selective barrier permitting entrance of essential nutrients, preventing loss of needed substances, secreting waste products, and binding certain regulatory substances.

Nucleus

Repository of genetic information; information is encoded in the base sequence of DNA molecules of the chromosomes.

Nucleolus

Site of ribosomal assembly that contains copies of genes for rRNA.

Endoplasmic Reticulum

A complicated array of vesicular spaces separated from cytoplasmic fluids or cytosol by a system of membranes.

Rough Endoplasmic Reticulum

Lined on the cytoplasmic surface with ribosomes and is the site of protein synthesis.

Smooth Endoplasmic Reticulum

Absence of ribosomes; enzymes present differ according to the function of the system.

Citric Acid Cycle

A metabolic pathway that contains enzymes involved in energy production.

B-oxidation of Fatty Acids

A metabolic process that breaks down fatty acids to generate acetyl-CoA.

Electron Transport Chain

A series of complexes that transfer electrons from electron donors to electron acceptors via redox reactions.

Oxidative Phosphorylation

The process of ATP production that occurs in the mitochondria, utilizing the electron transport chain.

Cytochrome P450

A family of enzymes involved in the metabolism of steroids, drugs, and other substances.

in intestinal cell

process occurring for the synthesis of triglycerides.

in adrenal cortex

process occurring cells for the synthesis of steroid hormones.

LYSOSOMES

Vesicles surrounded by membrane

GOLGI APPARATUS

Flattened sacs or vesicles continuous with ER to which the newly synthesized proteins are transported and temporarily stored; functions to digest material ingested by endocytosis and recycle cellular components.

PEROXISOMES

Also microbodies; contain oxidative enzymes (oxidases) and catalase which synthesize and degrade hydrogen peroxide; function to protect sensitive cell components from oxidative attacks.

CYTOSKELETON

Array of filaments; give the cell its shape and ability to move; responsible for the arrangement and internal motion of its organelles.

MITOCHONDRIA

Site of cellular respiration and production of ATP; number and size may reflect the need for energy and particular nature of metabolic activity occurring in the tissue.

MICROTUBULES

Composed of the protein tubulin; form the supportive framework that guides the movement of organelles within a cell, e.g., mitotic spindle; constituent of cilia.

MICROFILAMENTS

Consist of actin; form contractile assemblies that are responsible for intracellular movements.

INTERMEDIATE FILAMENTS

Prominent in parts of the cell subject to mechanical stress.

PLANT CELLS

Cells that have a cell wall, major component is cellulose, which accounts for structural strength of plants.

CHLOROPLAST

Resembles mitochondria; stroma encloses interconnected stacks of sacs called thylakoids which contain chlorophyll; generate ATP to drive photosynthetic reaction forming carbohydrate and other products.

CYTOSOL

Aqueous matrix that remains after the insoluble components of the cytoplasm are removed; metabolic processes that occur in the cytosol include glycolysis, gluconeogenesis, pentose phosphate pathway, activation of amino acids, biosynthesis of fatty acids.

VACUOLE

Typically occupy 90% of volume of mature cells; storage depots for nutrients, waste and specialized materials such as pigments.

SUBCELLULAR FRACTIONATION

Process of isolating specific organelles in relatively pure form, free of contamination by other organelles.

EXTRACTION

Avoids extreme pH and osmotic pressure and high temperature; employs aqueous solution; T = 0 - 4oC; to avoid loss of biologic activity.

HOMOGENIZATION

Disrupts the cell to liberate its constituents, resulting suspension contains intact organelles known as homogenate.

CENTRIFUGATION

Repeated ______ at progressively higher speeds will fractionate cell homogenates into their components.

ISOLATION OF BIOMOLECULES AND ORGANELLES

Methods include salt fractionation, chromatography (paper, ion exchange, thin layer), gel filtration, electrophoresis (paper, high voltage, agarose), and ultracentrifugation.

Nuclear fraction

One of the three pellets obtained from centrifugation.

Mitochondrial fraction

One of the three pellets obtained from centrifugation.

Microsomal fraction

One of the three pellets obtained from centrifugation.

Final supernatant

Content corresponds to the cytosol; fractions are not absolutely pure organelles; measured with suitable marker enzymes or chemical components.

Isolation of biomolecules

Methods include salt fractionation, chromatography, gel filtration, and electrophoresis.

Determination of structure of biomolecules

Methods include elemental analysis, spectroscopy, acid/alkaline hydrolysis, use of enzymes, mass spectrometry, sequencing methods, and X-ray crystallography.

Analysis of function and metabolism of biomolecules

Studies may be done on different levels such as whole animal, isolated perfused organ, tissue slice, or isolated cell organelle.