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Microbiology - Prokaryotes and Eukaryotes

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    Study Guide Microbiology – Prokaryotes and Eukaryotes 1. Eukaryotic Cells Eukaryotic cells are generally larger and more complex than prokaryotic cells. A key feature that sets them apart is the presence of membrane - bound organelles — specialized structures that carry out specific jobs inside the cell. These organelles act like compartments, keeping different metabolic activities organized and efficient. Many microorganisms, including protozoa, unicellular algae, and fungi , have eukaryotic cells. 1.1 The Nucleus: The Control Center Every eukaryotic cell has a well - defined nucleus . It is made mainly of protein and DNA (deoxyribonucleic acid) . • DNA is arranged into linear structures called chromosomes . • When chromosomes are not clearly visible, they are referred to as chromatin . • Specific working sections of chromosomes are called genes , which carry instructions for cell functions. Nuclear Proteins and Division DNA is supported by special proteins known as histones , which help package and organize it. DNA replication in eukaryotic cells occurs during mitosis . Nuclear Envelope and Pores The nucleus is surrounded by a nuclear envelope , a double membrane similar to the cell membrane. This envelope has pores , allowing communication between the nucleus and the cytoplasm. Nucleolus Inside the nucleus are one or more dense regions called nucleoli (singular: nucleolus). The nucleolus is rich in RNA and is the site where ribosomes are assembled before moving into the cytoplasm.

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    Study Guide 1.2 Cellular Organelles: Specialized Cell Structures The fluid inside the cell is called the cytoplasm (or cytosol ). Floating within it are many organelles, each with a specific role. Endoplasmic Reticulum (ER) The endoplasmic reticulum is a network of membranes spread throughout the cytoplasm. • Rough ER has ribosomes attached and is involved in protein synthesis . • Smooth ER lacks ribosomes and is involved in other metabolic activities. Eukaryotic ribosomes are 80S ribosomes , where amino acids are linked together to form proteins. The spaces inside the ER membranes are called cisternae . Golgi Apparatus The Golgi body (Golgi apparatus) consists of flattened, stacked sacs. • It modifies, processes, and packages proteins and lipids . • The edges of Golgi sacs often form secretory vesicles , which carry materials to their final destination in or outside the cell. Lysosomes and Peroxisomes • Lysosomes are enzyme - filled sacs derived from the Golgi apparatus. o They digest food particles and recycle worn - out cell components. • Peroxisomes also contain enzymes and help break down harmful substances inside the cell. Mitochondria: The Powerhouses Mitochondria are the sites where most cellular energy is released. • Energy is stored as adenosine triphosphate (ATP) . • Because of this role, mitochondria are often called the “powerhouses of the cell.”

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    Study Guide Vacuoles Some protozoa contain a large contractile vacuole . • It may occupy more than 75% of the cell interior . • Its main function is to remove excess water and prevent the cell from bursting. Cytoskeleton The cytoskeleton is a network of protein fibers that gives the cell its shape and internal organization. It includes: • Microtubules • Microfilaments • Intermediate filaments All are made of protein subunits and help with movement, transport, and structural support. Flagella and Cilia Many eukaryotic cells have flagella or cilia for movement. • Flagella are long, whip - like structures that propel the cell. • Cilia are shorter, more numerous, and move in coordinated waves. Both structures have a characteristic 9 + 2 arrangement of microfilaments . A well - known example of a ciliated protozoan is Paramecium . The Cell Wall Some eukaryotes, especially fungi and algae , have a cell wall outside the cell membrane. • Fungal cell walls contain chitin and some cellulose. • Algal cell walls contain cellulose only . Cell walls: • Provide support and protection • Help cells resist mechanical pressure • Are not selective , unlike cell membranes

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    Study Guide The Cell Membrane The eukaryotic cell membrane follows the fluid mosaic model , similar to prokaryotic membranes. Functions include: • Regulating movement of substances into and out of the cell • Maintaining the internal environment of the cytoplasm However, unlike prokaryotic membranes, it: • Does not contain metabolic enzymes • Does not participate in DNA replication 1.3 Transport Across the Cell Membrane For cells to survive, materials must move across the membrane. This happens in several ways: Diffusion • Movement of molecules from high concentration to low concentration • Occurs randomly along a concentration gradient Osmosis • Diffusion of water only • Occurs across a semipermeable membrane Facilitated Diffusion • Uses membrane proteins • Moves substances down the concentration gradient • Requires no energy Active Transport • Moves substances from low concentration to high concentration • Goes against the concentration gradient • Requires energy , usually from ATP

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