Page 54 - Medicinal Plants_PharmD general

Nucleus

The nucleus (Figure 7a) is a highly specialized organelle that serves
as the information and administrative centre of the cell. It has two major
functions. It stores the cell's hereditary material, or DNA, and it coordinates
the cell's activities, such as metabolism, growth, protein synthesis, and
reproduction (cell division). It consists of a nucleolus, chromatin and
chromosomes surrounded by the nuclear envelope that contains holes
called nuclear pores. While cells may live and even differentiate for a short
time without a nucleus, a nucleus is required for the continued life of a cell
and for cell division. The DNA of the nucleus is located within the
chromosomes together with a small family of histone proteins.

Endoplasmic Reticulum (ER) and Ribosomes

The endoplasmic reticulum (Figure 7b) consists of an array of
extensive flattened vesicles. The membranes of the ER are continuous with
the outer nuclear membrane. There are two types of ER: rough
endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
The surface of the rough endoplasmic reticulum is studded with protein-
manufacturing ribosomes giving it a "rough" appearance. In most cells the
smooth endoplasmic reticulum is scarce. SER lacks ribosomes so it is not
involved in protein synthesis.

Ribosomes (Figure 7c) comprise a complex macromolecular
machine that serves as the site of biological protein synthesis (translation).
Ribosomes link amino acids together in the order specified by messenger
RNA (mRNA) molecules. Plant ribosomes are termed 80S ribosomes,
composed of a 40S small subunit and a 60S large subunit.

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