Cell Structure and Function

Cytoskeleton

The cytoskeleton is a network of protein filaments that provides structural support and shape to cells. In microbes, it plays a crucial role in maintaining cell integrity and facilitating cellular processes.

• Mycobacterium: Has an armored structure outside the cell, giving the cell its shape.

• Intermediate Filament: Found between the nucleus and the middle of the cell; provides structural support and anchors organelles.

• Microtubules: Constantly changing structures that help with chromosome movement during cell division.

Flagella and Cilia

Flagella and cilia are appendages that aid in cell movement. They differ in structure and function between prokaryotes and eukaryotes.

• Flagella: In eukaryotes, flagella are very different from those in prokaryotes. They are covered by the plasma membrane and contain microtubules arranged in a 9+2 pattern. Eukaryotic flagella move in a whip-like fashion and can go backward and forward.

• Cilia: Similar to flagella but smaller and more numerous. They move in coordinated waves.

Types of Eukaryotes

• Animal: Lacks a cell wall; has a glycocalyx (a glycoprotein and glycolipid covering).

• Plant: Has a cell wall composed mainly of cellulose.

• Fungi: Has a cell wall made of chitin.

Microbial Metabolism

Metabolism Overview

Metabolism encompasses all chemical reactions within a cell, divided into two main categories:

• Catabolism: Breakdown of molecules to release energy. Examples: cellular respiration, fermentation.

• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy. Examples: protein synthesis, DNA synthesis.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required. They are typically proteins and function under specific conditions.

• Active Site: The region on the enzyme where the substrate binds.

• Specificity: Each enzyme is specific to a particular substrate.

• Factors Affecting Enzyme Activity:

  • Substrate concentration: Increased substrate increases reaction rate until saturation.

  • Temperature: Each enzyme has an optimal temperature; too high can denature the enzyme.

  • pH: Each enzyme has an optimal pH range.

Microbial Nutrition and Energy Sources

Classification by Energy and Carbon Source

• Phototrophs: Obtain energy from light.

• Chemotrophs: Obtain energy from chemical compounds.

• Autotrophs: Use CO2 as their carbon source.

• Heterotrophs: Use organic carbon sources (e.g., glucose).

Example: Animals and most bacteria are chemoheterotrophs, using organic compounds for both energy and carbon.

Glucose Metabolism

Glycolysis

Glycolysis is the process of breaking down glucose (a 6-carbon sugar) into two molecules of pyruvate (3 carbons each), generating ATP and NADH.

• Net products: 2 ATP, 2 NADH, 2 pyruvate per glucose molecule.

Krebs Cycle (Citric Acid Cycle, TCA Cycle)

The Krebs cycle further oxidizes acetyl-CoA (derived from pyruvate) to CO2, producing NADH, FADH2, and ATP.

• Main steps: Acetyl-CoA (2C) combines with oxaloacetate (4C) to form citrate (6C), which is then metabolized through a series of steps back to oxaloacetate.

• Products per glucose: 6 NADH, 2 FADH2, 2 ATP, 4 CO2

Electron Transport Chain (ETC) and ATP Synthesis

The ETC uses electrons from NADH and FADH2 to create a proton gradient across the membrane, driving ATP synthesis via ATP synthase.

• Oxygen: Serves as the terminal electron acceptor in aerobic respiration.

• ATP Yield: Approximately 36 ATP per glucose in eukaryotes.

Fermentation

Fermentation is an anaerobic process that allows glycolysis to continue by regenerating NAD+. It produces only 2 ATP per glucose and is less efficient than cellular respiration.

• Products: Lactic acid, ethanol, or other organic molecules, depending on the organism.

• Speed: Fermentation is faster but yields less ATP compared to cellular respiration.

Comparison of Cellular Respiration and Fermentation

Summary Table: Types of Microbial Nutrition

Key Equations

• Glycolysis (overall):

• Krebs Cycle (per glucose):

• Cellular Respiration (aerobic, per glucose):

Additional info:

• Some details about the cytoskeleton and eukaryotic cell structures were inferred based on standard microbiology knowledge.

• Tables and equations were expanded for clarity and completeness.