Zoology PDF: Prokaryotic and Eukaryotic Cells

Zoology Prokaryotic Cells ​ Animal cells are eukaryotic. ​ The first type of cell, prokaryotic cells, still exist today, including the majority of bacteria found in the gut and in the environment. ​ Prokaryotic cells are microscopic. Theory from Prokaryotic to Eukaryotic Cells...

Zoology Prokaryotic Cells ​ Animal cells are eukaryotic. ​ The first type of cell, prokaryotic cells, still exist today, including the majority of bacteria found in the gut and in the environment. ​ Prokaryotic cells are microscopic. Theory from Prokaryotic to Eukaryotic Cells ​ The endosymbiotic theory explains the transition from prokaryotic to eukaryotic cells. This theory is accepted and explains the origin of mitochondria and chloroplasts (plastids). ​ Endosymbiosis: ​ Two cells were independent—one anaerobic (doesn’t need oxygen) and one aerobic (requires oxygen). ​ In the past, there was no oxygen, and many cells were not adapted to oxygen, which was toxic to them. ​ According to the theory, the anaerobic cell tried to engulf the aerobic cell, but instead of digesting it, the anaerobic cell kept the aerobic cell inside. Over time, the aerobic cell adapted to live inside the anaerobic cell. ​ This is thought to be the origin of mitochondria and plastids in eukaryotic cells. ​ Proof of Endosymbiosis: ​ The engulfed cell has retained its original membrane, leading to double membranes for certain organelles. ​ Both the engulfed and engulfing cells contain their own genetic material. ​ During cell division, both the larger and smaller cells divide simultaneously. ​ While most animals do not have chlorophyll, certain deep-sea creatures do. From Unicellular to Multicellular Organisms ​ All animals are multicellular, but early organisms were unicellular. ​ The Colonial Flagellate Hypothesis suggests that several cells decided to live together for mutual benefit, leading to specialization. Some cells focused on obtaining nutrients while others focused on reproduction. Eventually, these specialized cells couldn’t function independently. Animal Cell Structure and Function ​ A cell is the basic unit of life. When studying animal life, we look at the relationship between structure and function. ​ Structure is related to function. For example, tissues that are thin often serve functions like diffusion, while thicker tissues are involved in secretion. ​ This relationship between structure and function is essential for understanding biology. Surface Area to Volume Ratio ​ Cells can be thought of as mathematical shapes, where the surface area represents the outer membrane and the volume represents everything inside.  ​ A larger surface area allows for faster exchanges of oxygen and waste, which is essential for cell function. ​ Larger organisms have more cells to maintain efficiency, as larger cells would be inefficient at exchanging materials. ​ Some cell structures have folds to increase surface area without increasing volume. Cell Membrane ​ The cell membrane is the outer boundary that separates the inside of the cell from the outside. It is a phospholipid bilayer. ​ The membrane has hydrophobic and hydrophilic regions, with hydrophobic parts facing inward and hydrophilic parts facing outward. ​ The membrane is fluid, meaning it can move and adjust. ​ Transmembrane proteins help with functions like transport, signal transduction, and cell recognition. ​ Carbohydrates attached to proteins serve as "name tags" for cell recognition. ​ The cell membrane is selectively permeable, meaning it allows some substances to pass while restricting others. Some substances must "pay a toll" to enter or leave. Membrane Transport ​ Diffusion: Small molecules, such as oxygen, pass through the membrane from areas of higher concentration to lower concentration. ​ Facilitated diffusion: Larger molecules, like water, require specific channels to pass through. ​ Active transport: This requires energy (ATP) to move substances against the concentration gradient. ATP molecules attach to enzymes to facilitate the movement of certain substances. Cell Junctions ​ Structures like desmosomes and gap junctions help cells stick together and share materials quickly. ​ Desmosomes: These are structures that allow one cell to stick to another cell. They act as anchors and help provide mechanical stability. ​ Gap Junctions: These allow for fast sharing of materials between cells. They are channels that connect the cytoplasm of adjacent cells, allowing substances to pass directly from one cell to another. Inside the Cell ​ The cytoplasm is shared by both prokaryotic and eukaryotic cells. Hydrophilic regions are exposed to the cytoplasm. ​ The cytoskeleton acts as a scaffold to maintain the cell's shape and allow movement. Centrosome ​ The centrosome is involved in cell division and is unique to animal cells. Nucleus ​ The nucleus is the control center of the cell, containing genetic material (DNA).  ​ DNA dictates the synthesis of proteins and other molecules. During cell division, genetic information is divided. ​ RNA is transcribed from DNA and exits the nucleus through nuclear pores to be translated into proteins. Endoplasmic Reticulum (ER) ​ The rough ER has ribosomes attached and is involved in protein synthesis. ​ The smooth ER does not have ribosomes and is involved in lipid synthesis. Golgi Apparatus ​ The Golgi is a sorting center for proteins. It packages and sends proteins to their destinations, including secretion from the cell. Lysosomes ​ Lysosomes are primarily found in animal cells and are involved in intracellular digestion and recycling of cell components. Lysosomes not only digest food but also recycle unusable components of the cell. Mitochondria ​ Mitochondria are the powerhouse of the cell, generating ATP. They are evidence of endosymbiosis, as they contain their own genetic material and ribosomes. Cell Walls and Membranes ​ Plant cells have cell walls that provide rigidity and protection, while animal cells have flexible membranes that allow for mobility and responsiveness to their environment.