Biology: Cell Structure and Function

Cell Biology

• The cell is the basic structural, functional, and biological unit of all living organisms.
• Examples of cells: Lactobacillus bacterium (3-5 μm, anaerobic), nerve cell (neuron) (100 μm, aerobic), and egg frog (1 mm, big).
• The cell's genome is the entire collection of genetic information.

Discovery of Cells

• The invention of the light microscope led to the discovery of cells.
• Robert Hooke observed dead plant cells and discovered and called them cells for the first time.
• Van Leeuwenhoek observed live cells (Protozoa).
• Schleiden & Schwann put the Cell Theory.

Cellular Components

• Cytosol: the liquid inside the cell.
• Cytoplasm: the cytosol + organelle and other internal components.
• Nucleolus: a darkly stained structure found inside the nucleus.
• Nuclear Lamina: provides support to the nuclear envelope and defines the shape of the nucleus.
• Nucleosomes: the basic unit of the eukaryotic chromosome structure.
• Ribosomes: make proteins from amino acids.

Cellular Processes

• Dehydration: releases water molecules to form polymers.
• Hydrolysis: adds water molecules to break down polymers into monomers.
• Water acts as an excellent solvent due to hydrogen bonds.

Centrifugation

• Separates cellular components based on size and density:
  • Whole cells, Nuclei, and Cytoskeletons: low speed
  • Mitochondria, Lysosomes, and Peroxisomes: medium speed
  • Microsomes and Small Vesicles: high speed
  • Ribosomes, Viruses, and Large Macromolecules: very high speed

Endoplasmic Reticulum (ER)

• The site where most cell membrane components are made.
• ER is continuous with the membrane of the outer nuclear envelope.
• Smooth ER in muscles is called Sarcoplasmic Reticulum.
• Materials are transported between RER and SER through vesicles.

Golgi Apparatus

• The post office of the cell.
• The site of further protein modification.
• Golgi apparatus pathways: RER -> Cis Golgi -> Median Golgi -> Trans Golgi -> Secretory Vesicles.
• Clathrin: protein molecules form basket-like cages to shape membranes into vesicles.

Mitochondria

• The powerhouse of the cell.
• Cellular Respiration: the process of using oxygen to release energy from digested food.
• Glycolysis: the breakdown of glucose into two smaller molecules of pyruvate.
• Fermentations: produced when organic molecules are broken down.