Cytoplasm & Organelles: The Cellular Level of Organization

Cytoplasm & Organelles

The Cellular Level of Organization

Part 2 HTHS 2110 Integrated Human Anatomy & Physiology I Unit 5

Objective 1: Cytoplasm, Cytosol, & Organelles

• Cytoplasm = Cytosol + Organelles

  • Cytosol

  • Definition: The aqueous component of the cytoplasm in which organelles, proteins, and other cell structures are suspended.

    • Composed of:

    • Solvent: Water

    • Solutes:

      • Salts (e.g., Na, K, Cl)

      • Mono- & di-glycerides

      • Proteins (all dissolved in the matrix)

  • Organelles:

  • Definition: Specialized structures within a cell that perform specific functions, often referred to as "little organs."

  • Metaphor: Considered as the fruit pieces in a fruitcake, contributing to the overall function of the cell.

Objective 1: Organelles and Their Functions

Organelles Have a Job to Do

Objective 2: Mitochondria

• Mitochondria:

  • Definition: The energy-producing organelles in cells referred to as "ATP factories."

  • ATP (Adenosine triphosphate):

  • Definition: The energy currency of the cell, analogous to a rechargeable battery used for cellular processes.

  • Observations: Cells with higher energy needs possess a greater number of mitochondria, including:

  • Comparison: Muscle cells vs. skin cells

  • Comparison: Bone cells vs. nerve cells

  • Comparison: Red blood cells vs. white blood cells

  • Structure:

  • Composed of two phospholipid bilayers:

    • Outer membrane

    • Inner membrane: Extensively folded to increase surface area for energy generation.

  • Intermembrane space: Located between the outer and inner membranes.

  • Matrix: Area inside the inner membrane.

  • Genetic Material: Mitochondria contain their own DNA (mtDNA), which is maternally inherited (passed from mother to daughter or son).

Objective 3: Energy Chemical Reactions

• Energy in Chemical Reactions

  • Activation energy is required to initiate chemical reactions.

  • Endergonic Reactions:

    • Type: Energy-absorbing (anabolic) reactions.

    • Requires energy input.

    • Direction: Absorbs energy into chemical bonds.

  • Exergonic Reactions:

    • Type: Energy-releasing (catabolic) reactions.

    • Performs work by releasing energy from chemical bonds.

    • Direction: Energy is released.

• Significance of ATP:

  • Links anabolic (building) and catabolic (breaking down) processes.

    • Anabolic example: Formation of glycogen and proteins.

    • Catabolic example: Breakdown of glucose into simpler forms.

• Burning vs. Metabolism:

  • Burning: Energy is released in one step (inefficient).

  • Metabolism: Energy is released in small, controlled steps, maximizing ATP capture as opposed to heat loss.

Objective 4: Cellular Respiration

• Definition: The oxidation of glucose to produce ATP.

• Overall Reaction:
  C6H{12}O6 + 6 O2
  ightarrow 6 CO2 + 6 H2O + 26-38 ATP

• Four Main Steps:

  1. Glycolysis:

  • Location: Cytoplasm

  • Outcome: Splits glucose into two pyruvates, requiring 2 ATP and yielding 4 ATP (net gain of 2 ATP).

  1. Acetyl-CoA Formation:

  • Location: Mitochondrial matrix

  • Outcome: Converts pyruvic acid to acetyl-CoA, yielding 1 NADH + H+ and releasing 1 CO2 per pyruvate.

  1. Citric Acid Cycle:

  • Location: Mitochondrial matrix

  • Outcome: Each turn produces 2 CO2, 3 NADH + H+, 1 FADH2, and 1 ATP (per acetyl-CoA).

  1. Electron Transport Chain:

  • Location: Inner mitochondrial membrane

  • Function: NADH and FADH2 deliver protons and electrons, producing up to 30-34 ATP.

Objective 5: Glycolysis

• Step 1 – Glycolysis:

  • In the cytosol, glucose is split during the energy investment phase, requiring 2 ATP.

  • Energy payoff phase produces 4 ATP (net gain of 2 ATP) and 2 pyruvic acids.

  • Products of Glycolysis:

    • Inputs: 1 glucose, 2 ATP, 2 NAD+, 2 inorganic phosphates.

    • Outputs: 4 ATP, 2 NADH, 2 pyruvate.

Objective 6: Formation of Acetyl Coenzyme A

• Step 2 – Acetyl CoA Formation:

  • Occurs in mitochondrial matrix.

  • Reactants: Starts with pyruvic acid, requiring CoA and O2.

  • Products (per pyruvate):

  • 1 acetyl CoA

  • 1 CO2

  • 1 NADH + H+

  • Overall yield (per glucose):

  • 2 acetyl CoA

  • 2 CO2

  • 2 NADH + H+

Objective 7: The Citric Acid Cycle

• Step 3 – Citric Acid Cycle:

  • Takes place in mitochondrial matrix.

  • Initiates with acetyl CoA and CoA is released.

  • Produces (per cycle):

  • 2 CO2

  • 3 NADH + H+

  • 1 FADH2

  • 1 ATP

  • Biological yield (per glucose):

  • 4 CO2

  • 6 NADH + H+

  • 2 FADH2

  • 2 ATP

Objective 8: The Electron Transport Chain

• Occurs in inner mitochondrial membrane.

• Mechanism:

  • NADH + H+ delivers protons and electrons which are separated in the electron transport chain.

  • Protons are pumped into the intermembrane space, creating a gradient that drives ATP production through ATP synthase.

• Output: 22–34 ATP produced depending on efficiency.

Cellular Respiration Summary

• Basic Process:

  • Glucose in cytosol → Glycolysis → Pyruvic acid → If O2 is present → Acetyl-CoA Formation → Citric Acid Cycle → Electron Transport Chain → Production of ATP.

• Inefficiencies: Actual ATP yield is approximately 30-32 ATP per glucose.

Objective 9: Glycogen, Lipids, & Proteins as Energy Sources

• Glycogen:

  • Long, branching chains of glucose, primarily stored in liver (70-100 g) and muscles (200-400 g).

  • Used for quick energy availability.

• Lipids:

  • Excess glucose and fats can be stored as triglycerides.

  • Breakdown of triglycerides generates ketones and acids, which can lead to ketoacidosis.

• Gluconeogenesis:

  • The process of creating new glucose from non-carbohydrate sources (fat or protein).

Objectives 10-13: Organelles

Meet the Organelles

Objective 10: Structural Organelles

• Function: Provide cell structure and shape.

  • Examples: Cytoskeleton

Objective 11: Motility Organelles

• Function: Move substances or the cell itself.

  • Examples: Cilia and Flagella

Objective 12: Synthesis Organelles

• Function: Synthesize cell components.

  • Examples: Ribosomes, Rough ER

Objective 13: Storage & Digestion Organelles

• Function: Store or break down materials.

  • Examples: Lysosomes, Peroxisomes, Proteasomes

Cytoskeleton Objective 10

• Cytoskeleton: Provides structural stability and movement within cells.

• Made up of different types of structural proteins:

  • Microfilaments (actin) - smallest (7 nm).

  • Intermediate filaments (keratin, vimentin) - medium size (8-12 nm).

  • Microtubules (tubulin) - largest (25 nm) involved in cell division and transport.

Cilia and Flagella

• Cilia: Hair-like extensions on the cell surface that move fluids across the cell.

• Flagella: Whip-like structures that move cells through fluid.

• Structure: Both have a 9+2 arrangement of microtubules.

• Function: Cilia use a rowing motion; flagella use a wave-like motion.

Ribosomes

• Site of protein synthesis, made of large (60S) and small subunits (40S).

• Function: Translate mRNA into proteins either attached to rough ER or as free ribosomes in the cytoplasm.

Endoplasmic Reticulum

• Types:

  • Rough ER: Studded with ribosomes; synthesizes proteins for export.

  • Smooth ER: Functions in lipid synthesis, detoxification, and calcium storage.

Golgi Complex

• Modifies, sorts, and packages proteins produced in rough ER.

• Structure includes cis (entry face) and trans (exit face) regions.

Storage & Digestion Organelles

• Lysosomes: Contain enzymes to break down waste and cellular debris, work best at an acid pH (5).

• Peroxisomes: Contain enzymes to break down fatty acids and produce hydrogen peroxide which is further degraded.

• Proteasomes: Responsible for degrading damaged or unneeded proteins with the help of ubiquitin.

Conclusion

• The organelles and their functions are crucial for cellular homeostasis, energy production, and metabolism. Understanding these processes is fundamental for the study of human anatomy and physiology.