Chemistry Reference
In-Depth Information
Figure 1.
Basic architecture of an eukaryotic cell. Basic organelles are indicated on the diagram, as are the
processes of endo- and exocytosis. Note that, with the exception of the nucleus, all organelles are bound
by a lipid bilayer membrane; in the case of the nucleus, a double bilayer surrounds the nuclear
compartment. For simplicity, the ER is arbitrarily represented as having “smooth” (i.e., ribosome-free) and
“rough” (i.e., ribosome-studded ER membranes) regions. Please refer to the text for more description.
bilayer—the area within the cell is called the cytoplasm or cytosol. The endoplasmic
reticulum, Golgi apparatus, vesicles, and mitochondria are also bound by a membrane
bilayer. However, the nucleus is actually bound by a double membrane bilayer.
Membrane bilayers compartmentalize each organelle such that important functions are
isolated and regulated.
Within the nucleus are the chromosomes, i.e., protein-bound deoxyribonucleic acid
(DNA) complexes which contain genetic information (genes). The chromosomal DNA
gives rise to heterogeneous nuclear ribonucleic acid RNA (hnRNA) via a process called
transcription. The hnRNA, in turn, is processed into messenger RNA (mRNA), which is
exported out to the cytoplasm for translation of the genetic code into proteins (i.e.,
protein synthesis). The nucleolus is a large diffuse structure within the nucleus; it is the
site of ribosome-specific RNA synthesis (denoted as rRNA) and the assembly of
ribosomes. DNA, RNA, and ribosome components will be discussed later in this chapter.
Within the cytoplasm, the cell generates energy via metabolic conversion of
molecules. Part of the metabolic cycle concerned with oxygen reduction to water (aerobic
metabolism) takes place within membrane bound organelles called mitochondria.
Mitochondria also possess their own DNA and RNA. Other organelles, such as the
endoplasmic reticulum and Golgi apparatus, are sites for protein synthesis for export,
oligosaccharide and lipid synthesis, membrane growth and post-translational
modification of proteins. Note that the cytoplasm membrane itself is highly dynamic, and
