The Nucleus and The Nucleus and RibosomesRibosomes

By M. WickenheiserBy M. Wickenheiser

NucleusNucleus

• Is surrounded by the nuclear envelope Is surrounded by the nuclear envelope • A double membrane perforated by pores that A double membrane perforated by pores that

regulate the movement of large macromolecules regulate the movement of large macromolecules between the nucleus and the cytoplasm.between the nucleus and the cytoplasm.

• Is the largest organelle in the cellIs the largest organelle in the cell• Directs protein synthesis Directs protein synthesis

Nuclear Lamina• Lines inner membrane • Is a layer of protein filaments that

helps to maintain the shape of the nucleus

Chromatin

• Is where cell’s DNA along with associated proteins diffuse into a mass • Located in the nucleus

ChromosomesChromosomes

• Thin chromatin fibers that coil up to Thin chromatin fibers that coil up to become thick enough to be a separate become thick enough to be a separate structure. Only coil when cell is about structure. Only coil when cell is about to divide.to divide.

• Inside the nucleusInside the nucleus• Provides DNA for the mother and Provides DNA for the mother and

daughter cell.daughter cell.

Nucleolus

• Prominent structure within the nondividing nucleus

• Location– Center of nucleus

• Appears through the electron microscope as a mass of densely strained granules and fibers adjoining part of the chromatin

• A special type of RNA called ribosomal RNA is synthesized and assembled with proteins imported from the cytoplasm into the main components

RibosomesRibosomes• Particles made of ribosomal RNA and proteinParticles made of ribosomal RNA and protein• Organelles enclosed in membraneOrganelles enclosed in membrane• FunctionFunction– Protein synthesisProtein synthesis

• LocationsLocations– Free Ribosomes are suspended in the cytoplasmic Free Ribosomes are suspended in the cytoplasmic

localeslocales– Bound Ribosomes are attached to the outside of the Bound Ribosomes are attached to the outside of the

endoplasmic reticulum or nuclear envelope.endoplasmic reticulum or nuclear envelope.• Both are structurally identical and can alternate Both are structurally identical and can alternate

between the two rolesbetween the two roles