Cell Biology: Organelles and Functions

Nucleus Appearance

• Large organelle located in the center of the cell
• Stains darkly with DNA stains

Nucleus Function

• Contains chromosomes which are made up of genes
• Genes contain instructions to make proteins

Nucleolus Appearance

• Dark spots within the nucleus

Nucleolus Function

• Site of ribosome production

Nuclear Membrane/Envelope Appearance

• Membrane that surrounds the nucleus

### Nuclear Membrane/Envelope Function

• Separates the nucleus from the cytoplasm
• Protects DNA
• Contains pores that allow molecules to pass in and out of the nucleus

Rough Endoplasmic Reticulum Appearance

• Interconnected network of flattened sacs
• Ribosomes attached to the surface of the membrane

### Rough Endoplasmic Reticulum Function

• Protein synthesis

Smooth Endoplasmic Reticulum Appearance

• Interconnected network of membranes, not flattened sacs
• No ribosomes attached

Smooth Endoplasmic Reticulum Function

• Lipid and carbohydrate synthesis

Ribosomes Appearance

• Contains ribosomal (rRNA) and protein
• Hamburger-like structure

Ribosomes Function

• Protein synthesis using mRNA as an instruction
• Forms a complete ribosome from a small and large subunit

Transport Vehicles/Vesicles Appearance

• Membrane components

### Transport Vehicles/Vesicles Function

• Transport molecules from one organelle to another or to the cell membrane
• Types:
  • Transport vehicles
  • Secretory vesicles

Golgi Apparatus/Body Appearance

• Flattened sacs, not interconnected

Golgi Apparatus/Body Function

• Modifies and packages proteins received from the rough ER
• Packaged into a secretory vesicle for export to another organelle or to the cell membrane

Cytoskeleton

• Network of fibers that provides structure and support to the cell

Microtubules Appearance

• Long, rigid fibers made of tubulin protein

Microtubules Function

• Form various structures:
  • Cilia
  • Flagella
  • Centrioles
  • Network for intracellular transport

Cilia Function

• Motile cilia move fluid over the surface of the cell (e.g., respiratory system)
• Sensory cilia detect vibrations (e.g., in the inner ear)

Flagella Function

• Move the cell (e.g., sperm cells)

Centrioles Function

• Form spindle fibers during cell division (mitosis and meiosis)

Microtubule Network Function

• Transport organelles within the cell

### Microfilaments Appearance

• Very thin fibers

### Microfilaments Function

• Change the shape of the cell
  • Cell movement (e.g., white blood cell movement)
  • Cytokinesis (division of the cytoplasm)

Intermediate Filaments Appearance

• Intermediate size fibers, between microtubules and microfilaments

Intermediate Filaments Function

• Provide structural integrity and support to the cell

Cell Wall Appearance (Plants, Fungi, Prokaryotes)

• Structure surrounding the cell membrane

Cell Wall Function

• Provide strength and support

Cell Wall Composition

• Cellulose in plants
• Chitin in fungi
• Peptidoglycan in prokaryotes (bacteria)

Cell Membrane/Plasma Membrane Appearance

• Phospholipid bilayer with embedded proteins

Cell Membrane/Plasma Membrane Function

• Separate the cell interior from the exterior

Mitochondria Appearance

• Large organelle with an outer membrane and an inner membrane with folds called cristae

Mitochondria Function

• Aerobic respiration
• ATP production

Chloroplasts Appearance

• Large organelle with an outer membrane and an inner membrane enclosing a fluid called stroma
• Thylakoids (folded membrane structures) within the stroma

Chloroplasts Function

• Photosynthesis

Eukaryotes vs Prokaryotes

• DNA Structure:
  • Eukaryotes: Linear DNA in a nucleus, associated with histones
  • Prokaryotes: Circular DNA located in cytoplasm, considered naked
• Organelles:
  • Eukaryotes: Membrane-bound organelles (e.g., Golgi apparatus, ER)
  • Prokaryotes: No membrane-bound organelles
• Ribosome Size:
  • Eukaryotes: 80s ribosomes
  • Prokaryotes: 70s ribosomes
• Cell Wall:
  • Eukaryotes: Present in plants, fungi
  • Prokaryotes: Peptidoglycan cell wall
• Cell Membrane:
  • Eukaryotes: Outermost layer in animal cells, with different lipids than prokaryotes
  • Prokaryotes: Cell membrane is not the outermost structure, cell wall surrounds the membrane

Essential Retrieval Questions

• How do organelles work together in protein synthesis?
• What are the structures and functions of organelles in protein synthesis?
• What are the similarities and differences between prokaryotic and eukaryotic cells?