Table of contents
- 1. Introduction to Biology2h 42m
- 2. Chemistry3h 37m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 44m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses19m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 6m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport1h 2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System1h 10m
- 40. Circulatory System1h 49m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System1h 4m
- 44. Animal Reproduction1h 2m
- 45. Nervous System1h 55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
47. Muscle Systems
Musculoskeletal System
Problem 5
Textbook Question
How did data on sarcomere structure inspire the sliding-filament model of muscle contraction?
Explain why the observation that muscle cells contain many mitochondria and extensive smooth endoplasmic reticulum turned out to be logical once the molecular mechanism of muscular contraction was understood.

1
Begin by understanding the structure of a sarcomere, which is the basic unit of a muscle fiber. A sarcomere is composed of thick filaments (myosin) and thin filaments (actin) that are arranged in a repeating pattern. This structure is crucial for muscle contraction.
The sliding-filament model was inspired by observations of sarcomere structure during muscle contraction. Researchers noticed that the length of the sarcomere changes as the muscle contracts, but the lengths of the individual filaments remain constant. This led to the hypothesis that the filaments slide past each other, rather than shortening, to produce contraction.
Consider the role of ATP in muscle contraction. ATP is required for the myosin heads to bind to actin filaments and then detach after the power stroke. This cycle of binding and detachment is essential for the sliding-filament mechanism, which explains why muscle cells contain many mitochondria. Mitochondria are the powerhouses of the cell, providing the necessary ATP for sustained muscle contraction.
The presence of extensive smooth endoplasmic reticulum (SER) in muscle cells is logical because the SER is involved in calcium storage and release. Calcium ions are crucial for muscle contraction as they bind to troponin, causing a conformational change that allows myosin to bind to actin. This process is integral to the sliding-filament model.
Summarize how the sliding-filament model and the cellular components of muscle cells (mitochondria and SER) work together to facilitate muscle contraction. The model explains the mechanical aspect of contraction, while the cellular components provide the necessary energy and regulatory ions to support this process.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sarcomere Structure
The sarcomere is the fundamental unit of a muscle fiber, composed of actin and myosin filaments. Its structure, characterized by the arrangement of these filaments, is crucial for muscle contraction. Observations of sarcomere shortening during contraction led to the development of the sliding-filament model, which explains how muscles contract by the sliding of actin over myosin.
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Sliding-Filament Model
The sliding-filament model describes the process of muscle contraction where actin filaments slide past myosin filaments, shortening the sarcomere and thus the muscle. This model was inspired by the observation of sarcomere structure and dynamics, providing a molecular explanation for how muscles generate force and movement.
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Role of Mitochondria and Smooth Endoplasmic Reticulum
Muscle cells are rich in mitochondria and smooth endoplasmic reticulum, which are essential for energy production and calcium storage, respectively. Mitochondria supply ATP needed for muscle contraction, while the smooth endoplasmic reticulum regulates calcium ions, crucial for initiating contraction. Understanding these roles clarified why these organelles are abundant in muscle cells.
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