Cell Biology: Endoplasmic Reticulum and Lysosomes

Cellular Structure and Function

• Endoplasmic reticulum is present in both plant and animal cells, whereas lysosomes are rarely found in plant cells
• Vacuoles are present in both plant and animal cells, with the plant cell vacuole handling molecule degradation of waste cellular products
• The nucleus is present in both plant and animal cells, with the animal cell nucleus located at the center of the cell and the plant cell nucleus located on the side of the cell
• Centrioles are present in animal cells, assisting in the cell division process, but are absent in plant cells
• Microfilaments and microtubules are present in both plant and animal cells
• Cilia and filaments are present in animal cells, allowing for cell movement, but are absent in plant cells
• Plastides are present in plant cells, providing pigmentation color and facilitating trapping of light energy used for photosynthesis

Protein Types and Functions

• Digestive proteins: break down food into monomeric units (e.g., mylase, lipase, trypsin)
• Transport proteins: carry molecules throughout the body (e.g., hemoglobin)
• Structural proteins: construct different structures (e.g., actin, tubulin, keratin)
• Hormones: coordinate the activity of different body systems (e.g., insulin, thyroxine)
• Defense proteins: protect the body from foreign pathogens (e.g., immunoglobulins)
• Contractile proteins: effect muscle contraction (e.g., actin, myosin)
• Storage proteins: provide nourishment in early development of the embryo (e.g., egg white/albumin)

Nucleic Acids

• Nucleic acids (DNA & RNA) are polymers of nucleotides, storing and processing genetic information
• Each nucleotide is 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 (A) and guanine (G)) and pyrimidine (cytosine (C), thymine (T), and uracil (U))
• DNA is double-stranded, with the two strands twisted about each other in the form of a double helix
• RNA is single-stranded and has multiple uses, including mRNA, tRNA, and rRNA

Membrane Transport Mechanisms

• The plasma membrane is selectively permeable, allowing certain molecules to enter the cell
• The plasma membrane is composed of a phospholipid bilayer with embedded proteins
• Proteins scattered throughout the plasma membrane play important roles in allowing substances to enter the cell
• Carbohydrates are attached to the outer surface of the cell membrane (glycoproteins & glycolipids)
• Passive transport is a type of membrane transport that does not require energy, moving substances from an area of higher concentration to an area of lower concentration
• Active transport requires energy to move substances across cell membranes

Cell Cycle

• The cell cycle is the sequence of cellular events that occur from one cell division to another
• A typical Eukaryotic cell cycle comprises of the following phases: G0 (resting phase), G1 (growth phase), S (synthesis phase), and more