BIOCHEMISTRY

Lysosomes

• Lysosomes in animal cells are bounded by a single membrane.
• They have an acidic internal pH (pH 4–5), maintained by proteins in the membrane that pump in Hions.
• Within the lysosomes are acid hydrolases; enzymes involved in the degradation of macromolecules, including those internalized by endocytosis.

Peroxisomes

• Peroxisomes contain enzymes involved in the breakdown of amino acids and fatty acids, a byproduct of which is hydrogen peroxide.
• This toxic compound is rapidly degraded by the enzyme catalase, also found within the peroxisomes.

Cytosol

• The cytosol is the soluble part of the cytoplasm where a large number of metabolic reactions take place.
• Within the cytosol is the cytoskeleton, a network of fibers (microtubules, intermediate filaments and microfilaments) that maintain the shape of the cell.

Plant cell wall

• The cell wall surrounding a plant cell is made up of the polysaccharide cellulose. In wood, the phenolic polymer called lignin gives the cell wall additional strength and rigidity.