Cell Components: Structure and Function

Concept 6.3: The Eukaryotic Cell's Genetic Instructions and Ribosomes

Eukaryotic cells contain specialized structures that house genetic material and facilitate protein synthesis. The nucleus and ribosomes are central to these processes.

• Nucleus:

  • Structure: Surrounded by a double nuclear envelope, perforated by nuclear pores; contains chromatin (DNA and proteins); nucleolus present; continuous with endoplasmic reticulum (ER).

  • Function: Houses chromosomes (DNA); site of DNA replication and transcription; nucleolus produces ribosomal subunits; regulates gene expression.

• Ribosome:

  • Structure: Composed of two subunits made of ribosomal RNA and proteins; can be free in cytosol or bound to ER.

  • Function: Site of protein synthesis; translates mRNA into polypeptide chains.

Example: Ribosomes attached to the rough ER synthesize proteins for secretion or membrane insertion.

Concept 6.4: The Endomembrane System

The endomembrane system is a network of organelles that regulates protein traffic and performs metabolic functions within the cell.

• Endoplasmic Reticulum (ER):

  • Structure: Extensive network of membrane-bound tubules and sacs; rough ER has ribosomes attached, smooth ER does not.

  • Function: Rough ER synthesizes proteins for secretion and membrane; Smooth ER synthesizes lipids, metabolizes carbohydrates, detoxifies drugs, and stores calcium ions.

• Golgi Apparatus:

  • Structure: Stacks of flattened membranous sacs (cisternae); has polarity (cis and trans faces).

  • Function: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosome:

  • Structure: Membranous sac of hydrolytic enzymes (in animal cells).

  • Function: Digests macromolecules, recycles cellular components, and breaks down ingested substances.

• Vacuole:

  • Structure: Large membrane-bounded vesicle (prominent in plant cells).

  • Function: Storage, waste disposal, water balance, and protection; central vacuole in plants maintains turgor pressure.

Example: The Golgi apparatus receives proteins from the ER, modifies them, and sends them to their destination.

Concept 6.5: Energy Conversion in Mitochondria and Chloroplasts

Mitochondria and chloroplasts are organelles responsible for energy conversion in eukaryotic cells. They transform energy from one form to another through cellular respiration and photosynthesis.

• Mitochondrion:

  • Structure: Bounded by a double membrane; inner membrane has infoldings called cristae.

  • Function: Site of cellular respiration; converts chemical energy in glucose to ATP.

• Chloroplast:

  • Structure: Two membranes around fluid stroma; contains thylakoid stacks (grana).

  • Function: Site of photosynthesis; converts solar energy to chemical energy stored in glucose.

• Peroxisome:

  • Structure: Specialized metabolic compartment bounded by a single membrane.

  • Function: Contains enzymes that transfer hydrogen from substrates to oxygen, producing hydrogen peroxide (), which is then converted to water.

Example: Chloroplasts in plant cells capture sunlight and produce glucose through photosynthesis.

Comparison Table: Cell Components, Structure, and Function

Additional info: The notes above expand on the brief points in the original table, providing definitions, examples, and context for each organelle's role in eukaryotic cells.