Chapter 2

Question 1

Cytosol

Answer 1

The cytosol of the cell is a concentrated, dense fluid. This fluid matrix contains the following important components:
* Much of the machinery involved in protein synthe- sis, protein degradation and carbohydrate metabo- lism (it is therefore rich in enzyme systems)
* Filamentous proteins that form the cytoskeleton (see p. 26)
* Some products of metabolism, such as glycogen and free lipid, for which it acts as a storage compartment
* Numerous ribosomes, both free in the cytosol and associated with cytosolic surface of rough ER.

Question 2

RNA

Answer 2

Ribosomes synchronize the alignment of both messen- ger RNA and transport RNA in the production of peptide chains during protein synthesis. Ribosomes are
small electron-dense particles which impart a blue colour (basophilic) to the cytoplasm of protein-producing cells on light microscopy (Fig. 2.7). Each ribosome is com- posed of a small subunit which binds RNA, and a large subunit which catalyses the formation of peptide bonds. They are made up of specific ribosomal RNA, as well as specific proteins. Ribosomal RNA is manufactured in the nucleolus

Question 3

Nucleus

Answer 3

The nucleus is the largest single membrane-bound compartment in the cell and contains the cellular DNA (Fig. 2.8).
In light microscopic preparations, nuclei are spheri- cal or ovoid in shape, generally measuring 5–10μm in diameter; they stain with basic dyes, such as haema- toxylin (i.e. basophilic) and contain a smaller spherical structure, the nucleolus, which synthesizes ribosomal subunits.
Nuclei are bound by two concentric membranes with different functional roles. The inner nuclear membrane contains specific membrane proteins that act as attach- ment points for filamentous proteins, termed lamins, which form a scaffolding to maintain the spherical shape. The outer nuclear membrane binds the perinuclear space, which is continuous with the lumen of the ER; it may be associated with ribosomes in a similar manner to rough ER.
The nuclear membrane is perforated by numerous pores which establish continuity between the cytosol and the nuclear lumen containing the chromatin