Zoology Lecture 2: Cell Structure

Cell Classification

• Cells are classified into two main categories: prokaryotic and eukaryotic
• Prokaryotes are single-celled microorganisms, include Bacteria and Archaea, and have a single membrane
• Eukaryotes have a clearly defined nucleus, nuclear membrane, and organelles such as mitochondria, Golgi apparatus, and lysosomes

Animal Cell Characteristics

• Animal cells are generally smaller than plant cells
• They have an irregular shape due to the absence of a cell wall
• They have only a cell membrane, whereas plant cells have a cell wall and a cell membrane
• Animal cells do not have chloroplasts, which are found in plant cells

Cell Organelles

Cell Membrane

• A thin, semipermeable membrane layer of lipids and proteins surrounding the cell
• Composed of a phospholipid bilayer that forms a stable barrier between two aqueous compartments
• Regulates the transport of materials entering and exiting the cell
• Provides protection and a fixed environment inside the cell
• Has proteins embedded within the phospholipid bilayer that carry out specific functions, including selective transport of molecules

Nucleus

• Contains DNA and other genetic materials
• Has a double-membrane structure called the nuclear envelope
• Has pores that allow for the selective passage of certain molecules into and out of the nucleus
• Contains a nucleolus that produces and assembles ribosomes

Centrosome

• A small organelle found near the nucleus with a thick center and radiating tubules
• Plays an important role in cell division
• Produces microtubules

Lysosome

• A membrane-bound organelle containing digestive enzymes that help in digestion, excretion, and cell renewal

Cytoplasm

• The gelatinous liquid that fills the inside of a cell
• Composed of water, salts, and various organic molecules
• Contains some intracellular organelles, such as the nucleus and mitochondria, which are enclosed by membranes that separate them from the cytoplasm

Golgi Apparatus

• A flat, smooth, layered sac-like organelle near the nucleus
• Involved in manufacturing, storing, packing, and transporting particles throughout the cell
• Processes and sorts proteins received from the ER for transport to their eventual destinations

Mitochondrion

• A spherical or rod-shaped organelle with a double membrane
• The powerhouse of a cell, releasing energy through chemical reactions
• Generates most of the chemical energy needed to power the cell's biochemical reactions
• Produces ATP (adenosine triphosphate) as a source of energy

Ribosome

• An intercellular structure made of RNA and protein
• The site of protein synthesis in the cell
• Translates messenger RNA (mRNA) sequence into a specified string of amino acids that form proteins

Endoplasmic Reticulum (ER)

• A cellular organelle composed of a thin, winding network of membranous sacs originating from the nucleus
• Has two forms: rough ER with ribosomes and smooth ER without ribosomes

Learn about the fundamental unit of life, cell structure, and classification into eukaryotic and prokaryotic cells in this zoology lecture for pre-medicine students.