Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 6.3 The Eukaryotic Cell’s Genetic Instructions Are Housed in the Nucleus and Carried Out by the Ribosomes
In eukaryotic cells, the nucleus serves as the command center, housing genetic material, while ribosomes act as the machinery that translates this genetic information into functional proteins.
1. The Nucleus: Information Central
Structure: The nucleus is a membrane-bound organelle, typically the most prominent feature in a eukaryotic cell, averaging about 5 micrometers in diameter.
Nuclear Envelope: This double membrane encloses the nucleus, separating its contents from the cytoplasm. It is perforated by nuclear pores, which regulate the entry and exit of molecules.
Chromosomes: Within the nucleus, DNA is organized into discrete units called chromosomes. Each chromosome contains one long DNA molecule associated with proteins, forming chromatin.
Nucleolus: A prominent structure within the nucleus, the nucleolus is the site of ribosomal RNA (rRNA) synthesis and ribosome subunit assembly.
2. Ribosomes: Protein Factories
Composition: Ribosomes are complexes made of rRNA and proteins. They are not membrane-bound and thus are not considered organelles.
Subunits: Each ribosome consists of two subunits—a large subunit and a small subunit—that join to carry out protein synthesis.
Location and Function:
Free Ribosomes: Suspended in the cytosol; synthesize proteins that function within the cytosol.
Bound Ribosomes: Attached to the endoplasmic reticulum or nuclear envelope; make proteins for membranes, organelles, or secretion.
3. The Process of Protein Synthesis
Transcription: Within the nucleus, genes are transcribed into messenger RNA (mRNA).
Translation: The mRNA is then transported to the cytoplasm, where ribosomes translate the genetic message into the primary structure of a specific polypeptide.
In a Nutshell
The nucleus houses DNA and directs protein synthesis through mRNA.
Ribosomes, whether free or bound, translate genetic instructions into proteins.
Together, they represent the cell’s central system for controlling and executing genetic information.