Cell Biology: Endoplasmic Reticulum and Lysosomes

Cell Structure

• Endoplasmic reticulum: present in both plant and animal cells, involved in molecule degradation of waste cellular products.
• Lysosomes: present in animal cells, contain digestive enzymes to break down cellular macromolecules; rarely present in plant cells.
• Vacuoles: present in both plant and animal cells, membrane-bound organelles that can contain water, inorganic and organic molecules, and enzymes in solution.
• Nucleus: present in both plant and animal cells, located at the center of the cell in plant cells and on the side of the cell in animal cells, contains genetic information.
• Centrioles: present in animal cells, involved in the cell division process; absent in plant cells.
• Microfilaments and microtubules: present in both plant and animal cells, involved in movement and cell division.
• Cilia and flagella: present in animal cells, involved in movement; absent in plant cells.
• Plastides: present in plant cells, involved in pigmentation and photosynthesis; absent in animal cells.
• Cell walls: present in plant cells, algae, fungi, and some bacteria, composed of various polysaccharides and polymers; absent in animal cells.

Cytoplasm

• Present in all types of cells, semi-fluid medium containing water and various molecules.
• Contains proteins, which account for its semi-fluid nature.
• Eukaryotic cells have organelles, which are internal compartments with specialized functions.

The Nucleus

• Stores genetic information in the form of DNA.
• Every cell in the body contains the same genes.
• Genes are segments of DNA that contain information for the production of specific proteins.
• DNA, with RNA acting as an intermediary, specifies the proteins in a cell.

Movement and Cell Junctions

• The cytoskeleton helps maintain a cell's shape and anchors or assists in the movement of organelles.
• Microtubules are larger than actin filaments, help maintain cell shape, and act as tracks for organelle movement.
• Actin filaments are long, thin fibers involved in movement, and are present in microvilli.

Vacuole

• A membrane-bound organelle present in all plant and fungal cells, and some protist, animal, and bacterial cells.
• Functions vary depending on the type of cell, including:
  • Isolating materials that might be harmful or a threat to the cell.
  • Containing waste products.
  • Containing water in plant cells.
  • Maintaining internal hydrostatic pressure.
  • Maintaining an acidic internal pH.
  • In protists, storing food and assisting in the digestive and waste management process.

The Chemistry of Life

• Elements: basic building blocks of matter, 92 naturally occurring elements.
• Over 90% of the human body is composed of four elements: C, N, O, and H.
• Biomolecules can be classified into micromolecules and macromolecules.
• Micromolecules: small, low molecular weight molecules (<1000 Daltons), including water, minerals, amino acids, sugars, and nucleotides.
• Micromolecules act as substrates for various reactions and are also the products of metabolism.
• Examples of protein functions:
  • Digestive enzymes: digest food into monomeric units.
  • Transport proteins: carry oxygen in the blood.
  • Structural proteins: construct different structures, like the cytoskeleton, hair, and nails.
  • Hormones: coordinate the activity of different body systems.
  • Defense proteins: protect the body from foreign pathogens.
  • Contractile proteins: effect muscle contraction.
  • Storage proteins: provide nourishment in early development of the embryo.

Nucleic Acids

• Polymers of nucleotides, store and process genetic information.
• Nucleotides are composed of phosphate, a pentose sugar, and a nitrogen-containing base.
• DNA contains the sugar deoxyribose, while RNA contains the sugar ribose.
• Nitrogen bases are grouped into two categories: purine (adenine and guanine) and pyrimidine (cytosine, thymine, and uracil).
• The nucleotides link to form a polynucleotide called a strand, with a backbone made up of phosphate-sugar-phosphate-sugar.