m5 p5

Module 5 Overview

  • Introduction to Hemoglobin and Allosteric Control

    • Hemoglobin's role in oxygen transport is influenced by allosteric control.

    • Differential oxygen affinity is dictated by effector molecules that bind to hemoglobin.

    • Binding of effector molecules leads to conformational changes that can shift equilibrium towards:

    • R State (relaxed state)

    • T State (tense state)

  • Membrane Transport Proteins

    • Discusses the transport of polar molecules across cell membranes.

    • Membrane proteins shield transported molecules to navigate the hydrophobic membrane interior.

  • Actin-Myosin Motor and Muscle Contraction

    • Mechanism of muscle contraction mediated by actin and myosin in response to calcium release.

    • Discussed at both cellular and molecular levels within a biochemical context.

Module 5 Lecture Topics and Textbook Readings

  • Topic 1: Hemoglobin: Allostery and Evolution

    • Reference: Chapter 6.2

  • Topic 2: Membrane Transport Proteins

    • Reference: Chapter 6.3

  • Topic 3: Passive Transport

    • Reference: Chapter 6.3

  • Topic 4: Active Transport

    • Reference: Chapter 6.3

  • Topic 5: Muscle Contraction

    • Reference: Chapter 6.4

Molecular Mechanism of Muscle Contraction

  • Historical Context

    • Andrew Huxley and Hugh Huxley independently proposed the sliding filament model for muscle contraction.

    • Hugh Huxley's work provided biochemical evidence supporting this model.

Structure of Muscle Cells

  • Components of Muscle Cells

    • Muscle cells contain:

    • Thick filaments: Comprising hundreds of myosin protein molecules arranged tail-to-tail; myosin heads extend outwards.

    • Protein Titin: Anchors thick filaments to Z disk.

    • Thin filaments: Composed of polymerized actin proteins, which bind to myosin head during contraction; includes troponin and tropomyosin.

  • Functionality

    • Muscle contraction is initiated by Ca2+ release due to neuronal signaling.

    • Release of Ca2+ leads to conformational changes in troponin, facilitating myosin binding to actin.

    • ATP is necessary for the complete actin-myosin reaction cycle.

Sliding Filament Model of Muscle Contraction

  • Mechanism of Contraction

    • Thick and thin filaments slide past each other, reducing the distance between adjacent Z disks.

    • Key points:

    • The A band retains constant width during contraction.

    • The I band contracts during contraction.

Myosin Structure and Function

  • Structural Regions of Myosin

    • Three regions: head, neck, and tail.

    • Tails intertwine to form a coiled coil.

    • Myosin head groups:

    • Bind to and hydrolyze ATP.

    • Regulate binding to actin subunits in thin filaments.

Calcium Control in Muscle Contraction

  • Role of Calcium Ions (Ca2+)

    1. In relaxed muscle, tropomyosin blocks myosin binding sites on actin.

    2. Ca2+ binds to TnC, causing conformational changes in troponin and tropomyosin to expose myosin binding sites on actin.

    3. Myosin heads then bind to actin, initiating muscle contraction.

  • Key Components Involved:

    • Calcium (Ca2+)

    • Troponin complex

    • Tropomyosin

    • Actin polymer

    • Myosin heads

Actin-Myosin Reaction Cycle

  • Cycle Overview

    • ATP binding, hydrolysis, and inorganic phosphate (Pi) release lead to:

    • Conformational changes in myosin.

    • Pulling of actin thin filament approximately 70 Angstroms towards the center of the sarcomere.

  • Conformational Dynamics

    • The conformation of the myosin head significantly alters depending on whether ATP or ADP is bound.

Conclusion

  • Summary of Key Concepts

    • The module covers essential aspects of hemoglobin's functionality, membrane transport mechanisms, and the biochemical processes behind muscle contraction, emphasizing molecular interactions and structural components.