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Cell Biology Flashcards

Plasma Membrane Definition

The plasma membrane surrounds cells, defines their boundaries, and acts as a barrier between the internal environment (cytoplasm) and the external environment (extracellular area).

Function as Selective Barrier

Functions as a selective barrier, controlling what substances cross the membrane. Most substances cannot pass directly through the phospholipid bilayer, requiring specific channels and transporters. Allows for selective passage of nutrients while blocking others. Oxygen and carbon dioxide can pass freely, demonstrating passive transport, but nutrients like sugars require specific transport mechanisms.

Importance of Surface Area to Volume Ratio

A cell's ability to function effectively relies on a high surface area to volume ratio. A large surface area allows sufficient nutrient intake and waste removal to occur, vital for metabolic functions. Larger organisms possess more cells instead of larger cells to maintain this essential surface area to volume ratio.

Cell Types and Size Comparisons

Prokaryotic Cells (e.g., Bacteria and Archaea):

  • Size and Structure: Typically smaller, ranging from 0.1 to 5.0 micrometers. They are simpler in structure and lack membrane-bound organelles.

  • Cell Structure:

    • Nucleoid Region: Contains the genetic material (DNA) in a single, circular chromosome that is not enclosed by a membrane, allowing for rapid replication and expression.

    • Ribosomes: Present for protein synthesis, considered organelles but not membrane-bound; they are smaller than those in eukaryotic cells (70S instead of 80S) and differ in molecular composition, which allows for the development of specific antibiotics targeting bacterial ribosomes.

    • Cell Wall: Provides structural support. Most prokaryotes have a rigid cell wall made of peptidoglycan, a polymer consisting of sugars and amino acids, which plays a crucial role in maintaining cell integrity and shape. Archaea have varying cell wall compositions (e.g., pseudopeptidoglycan or proteins) that do not include peptidoglycan.

    • Plasma Membrane: Similar to eukaryotic membranes but may contain unique lipids such as hopanoids that help maintain membrane stability under extreme conditions.

    • Flagella and Cillia: Many prokaryotes possess flagella made of the protein flagellin that they use for movement, and cillia which are hair-like structures that facilitate adherence to surfaces and genetic exchange through processes like conjugation.

  • Metabolism: Prokaryotic cells can thrive in a variety of environments, using diverse metabolic pathways, including anaerobic vs. aerobic respiration and fermentation. They can be autotrophic (producing their own food via photosynthesis or chemosynthesis) or heterotrophic (requiring organic compounds for nourishment).

  • Reproduction: Typically reproduce asexually through binary fission, a process that allows for rapid population growth under favorable conditions. Some prokaryotes can exchange genetic material through transformation, transduction, or conjugation, promoting genetic diversity.

Eukaryotic Cells: More complex with internal membrane-bound compartments called organelles, each serving specific functions.Key Organelles in Eukaryotic Cells:

  • Chloroplasts: Present in plant cells for photosynthesis, comprised of multiple membranes...

  • Mitochondria: Considered the powerhouse of the cell...

  • Rough and Smooth Endoplasmic Reticulum (ER):...

  • Golgi Apparatus: Functions in modifying, sorting, and packaging...

  • Central Vacuole: Largest compartment in plant cells...

  • Cell Wall: Provides structure...

Eukaryotic cells exhibit more functional compartmentalization, allowing for complex processes such as mitosis and meiosis with precise regulation.

Cytoskeleton Structure and Function

The cytoskeleton is a network of fibers crucial to shape maintenance and cellular organization.

  • Components: Microfilaments, Intermediate Filaments, Microtubules...

  • Functions of Cytoskeleton: Helps maintain cell shape, organizes cellular activities, and quickly reorganizes during processes...

Dynamic Nature of Cytoskeleton

Not static; can rapidly reconfigure for differing cellular functions. Acts like scaffolding for structural integrity, yet can be quickly assembled and disassembled to adapt to activity demands. Quick reorganizations enable cells to respond to their environment and manage complex processes like division.

Conclusion

Understanding the structure and function of the plasma membrane, organelles, and the cytoskeleton is essential for grasping the complexity of cellular processes and interactions within and outside the cell.

  • Rough Endoplasmic Reticulum (RER):

    • Characterized by the presence of ribosomes on its surface, giving it a rough appearance.

    • Involved in protein synthesis; ribosomes translate mRNA into polypeptide chains that enter the RER for folding and modifications.

    • Plays a significant role in the production of secretory proteins, membrane proteins, and those destined for lysosomes.

    • Continuous with the outer membrane of the nuclear envelope.

  • Smooth Endoplasmic Reticulum (SER):

    • Lacks ribosomes, resulting in a smooth appearance.

    • Functions include lipid synthesis (phospholipids and cholesterol), carbohydrate metabolism, and detoxification of drugs and poisons.

    • In muscle cells, the SER regulates calcium ion concentration, essential for muscle contraction.

Both rough and smooth ER are critical components of eukaryotic cells, contributing to the overall function and maintenance of the cell by ensuring proper protein and lipid production, along with metabolic processes.