Biology: Kingdoms of Life and Evolution

Kingdoms of Life

• Bacteria and blue-green algae are prokaryotic cells.
• Other kingdoms contain eukaryotic cells.
• Archaea are often found in extreme environments.
• Eukarya includes fungi, algae, protozoa, plants, and animals.

Tracing Biological Evolution

• Ribosomes are crucial for tracing evolution.
• Ribosomes are sites of protein synthesis and found in all organisms.
• Ribosomes consist of RNA and proteins.
• Ribosomal RNA (rRNA) changes slowly during evolution.
• rRNA is used to study relatedness among organisms, especially 16S and 18S.

Golgi Apparatus

• Further processes and sorts proteins and lipids from the ER.
• Adds carbohydrates, phosphate groups, and alters membrane phospholipids to act as sorting signals.
• Manufactures molecules such as polysaccharides, like pectins and non-cellulose polysaccharides in plant cells.

Lysosomes

• Membranous sacs filled with hydrolytic enzymes for macromolecule digestion.
• Hydrolytic enzymes function best in acidic environments.
• Leakage from multiple lysosomes can destroy a cell.
• Enzymes and lysosomal membranes are manufactured in the RER and processed in the Golgi.
• Bud off from the trans face of the Golgi apparatus.
• The inner surface of the lysosomal membrane and digestive enzymes are protected from destruction.

Lysosome Functions

• Performs intracellular digestion in various circumstances: - Unicellular protists engulf food through phagocytosis and the food vacuole fuses with lysosomes for digestion. - Macrophages engulf bacteria and pathogens and use hydrolytic enzymes for digestion. - Autophagy, where lysosomes recycle cell material by engulfing damaged organelles or cytosol.
• Genetic disorders, like Tay-Sachs disease, result from missing or inactive lipid-digesting enzymes causing lipid accumulation in the brain.

Vacuoles

• Vesicles derived from the endoplasmic reticulum.
• Vacuolar membrane selectively transports solutes, leading to a different internal solution from the cytosol.
• Functions vary depending on the cell type.
• Some plant vacuoles contain pigments like red and blue pigments in petals for attracting pollinators.
• Mature plant cells have a large central vacuole formed by the coalescence of smaller vacuoles.

Mitochondria

• Typically 1–10 μm long.
• Outer membrane is smooth, while the inner membrane is convoluted with infoldings called cristae that increase surface area for respiration.
• Inner membrane divides the mitochondrion into two compartments:
  • Intermembrane space between the inner and outer membranes.
  • Mitochondrial matrix enclosed by the inner membrane.
• Human mitochondrial DNA is 16569 bp and codes for 37 genes.
• Autonomous organelles, growing and reproducing within the cell.

Microtubules

• Provide shape and support to cells.
• Serve as tracks for organelle movement using motor proteins.
• Guide vesicles from the ER to Golgi and from Golgi to the plasma membrane.
• Involved in chromosome separation during cell division.

Cilia and Flagella

• Cilia are shorter than flagella and have an alternating power and recovery stroke pattern.
• Flagella are longer and have an undulating motion.
• A cilium can also act as a signal-receiving antenna.
• Both share a common structure:
  • A group of microtubules sheathed in an extension of the plasma membrane.
  • Nine doublets of microtubules arranged in a ring with two single microtubules in the center ("9 + 2" pattern).