Eukaryotic Cell Structure and Function

• Eukaryotic cells are compartmentalized by internal membranes.
• Eukaryotic cells have four basic functions, including:
  • Genetic control
  • Manufacture, distribution, and breakdown of molecules
  • Energy processing
  • Structural support, movement, and communication
• Many organelles are not visible under a light microscope, and can only be seen under an electron microscope.

Membrane-Bound Organelles

• Nucleus:
  • Controls cell activities, like growth and repair.
  • Essential for cell division
• Endoplasmic Reticulum:
  • Rough ER (RER): Ribosomes attached synthesize proteins, transport proteins out of the cell
  • Smooth ER (SER): Synthesizes fats and steroids (including sex hormones in mammals) and detoxifies substances
• Ribosomes
  • Free and bound ribosomes synthesize proteins
• Golgi Body:
  • Chemically modifies substances from the ER.
  • Stores and packages substances into vesicles for secretion
• Mitochondria:
  • Site of aerobic respiration.
  • Releases energy in the form of ATP (adenosine triphosphate)
• Chloroplasts:
  • Contain chlorophyll.
  • Essential for photosynthesis (only in plant cells)
• Vacuole:
  • Large and mostly central in plant cells, stores dissolved substances, such as sugars, mineral salts, and amino acids
  • Small and numerous in animal cells, functions as a temporary storage for water and food substances

Non-Organelle Structures

• Not located within cytoplasm, but within the cell
• Cell Surface Membrane: Selectively permeable, controls movement in/out of cell
• Cellulose Cell Wall

Comparing Structural Features

• Must state a similarity and a difference.
• Cannot state that both are membrane-bound organelles as a similarity

Process of Protein Secretion

• Proteins synthesized by ribosomes attached to the outer surface of rough ER.
• Newly synthesized proteins are drawn into the lumen of the rough ER.
• Vesicles containing proteins pinch off the rough ER.
• Vesicles fuse with the Golgi apparatus, releasing the proteins made by the rough ER (modified).
• Secretory vesicles with modified proteins pinch off from the Golgi apparatus and move to the cell surface membrane.
• Secretory vesicles fuse with the cell surface membrane, and proteins exit the cell.

Cell Differentiation

• Differentiation is the process where a cell becomes specialized for a specific function
• Red Blood Cells (RBC):
  • Absence of a nucleus allows more space for hemoglobin.
  • Bi-concave shape increases surface area to volume ratio for efficient oxygen absorption.
  • Flexible, allows for squeezing through capillaries
• Nerve Cells:
  • Long, thin axon transmits electrical impulses over distances.
  • Dendrites receive signals from other neurons.
  • Myelin sheath insulates the axon and speeds up impulse transmission.
• Intestinal Epithelial Cells:
  • Microvilli increases surface area for absorption of digested food into the bloodstream.
  • Tightly packed cells form protective barriers.
  • Can be thin or thick for absorption or protection, respectively.
• Goblet Cells:
  • Found in respiratory, digestive tracts, conjunctiva and reproductive tract
  • Mucus secretion protects underlying cells from damage and irritation
• Respiratory Epithelial Cells:
  • Cilia move mucus and trapped particles out of airways
• Root Hair Cells:
  • Long, thin projection increases surface area for efficient water and nutrient absorption.
  • Large vacuole → stores water and minerals
  • Lacks chloroplasts and does not perform photosynthesis
• Muscle Cells:
  • Elongated and cylindrical for shape
  • Many nuclei and mitochondria provide more energy for contraction