Cell Structure (Nucleus)

What is the shape of a nucleus?

Spherical or ovoid

What is the structure of the nuclear envelope?

• Double membrane, each being a phospholipid bilayer

• Perforated by numerous nuclear pores to regulate the passage of substances in and out the nucleus

• Outer membrane is continuous with the endoplasmic reticulum

What substances are exchanged between the nucleus and cytoplasm?

Into: Free nucleotides, ribosomal proteins, enzymes

Out: RNA, ribosomal units

What is chromatin?

• The hereditary material of a cell existing as thin, elongated threads outside of cell division i.e. interphase

• Appear as a diffused mass under the microscope

What happens to chromatin prior cell division?

Chromatin condenses to form thicker, shorter structures called chromosomes

What is euchromatin?

• Most of the chromatin

• Chromatin in a loosely coiled, extended and diffused state

• Actively synthesising RNA

What is heterochromatin?

• Some chromatin

• Tightly coiled chromatin, stained intensely

• Not actively synthesising RNA

What is the function of the nucleus?

• Contain the hereditary material of the organism made of DNA

• Control the activities of the cell by regulating protein synthesis

What is the appearance and structure of the nucleolus?

• Densely stained granules under the electron microscope

• One or more nucleoli may be present within a nucleus

• Contains a large concentration of DNA, ribosomal RNA and proteins

What is the function of the nucleolus?

• Site of synthesis of rRNA

• Site of assembly of ribosomal subunits from rRNA and ribosomal proteins