18.1: Introduction
- Page ID
- 89019
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)To early microscopists the cell looked like a sack of liquid containing a nucleus. Recall Nikolai Koltsov, the Russian biologist who nearly 35 years before Watson and Crick had already predicted that the genetic material would be a” large genetic molecule” composed of “two mirror-image strands” that would replicate semi-conservatively? Well, in 1903 Nikolai also predicted the existence of a network of tubes in cells to account for cell shape ( The Remarkable Nikolai Koltsov). He called this network a cytoskeleton! His prediction predates the mid-twentieth century electron microscope observations of the cytoskeleton composed of rods, tubes, and filaments which are responsible for maintaining cell shape and for cell motility. We will see that intracellular structures and organelles are enmeshed in these microfilaments, intermediate filaments and microtubules. To start this chapter, we revisit these structures and more closely examine how they work to support cell shape, motility, and overall organization. Remember that cell motility includes the movement of cells and organisms, as well as the movements of organelles (e.g., vesicles) and other structures inside the cell. Of course, these movements are not random, and they require chemical energy. After a close look at movements in and of cells, we’ll look at the interaction of actin and myosin in skeletal muscle contraction. We’ll look at a famous paradox arising from early studies that showed that ATP was required for muscle contraction but also for relaxation. Then we’ll look at experiments that resolve the paradox. Animals control skeletal muscle contraction, but some muscles contract rhythmically or with little or no control on the part of the animal—think cardiac muscles of the heart or smooth muscles like those in the digestive and circulatory systems. We focus here on the regulation of skeletal muscle contraction by calcium ions and regulatory proteins and at responses of voluntary (i.e., skeletal) muscle to neural commands. Finally, we’ll look at skeletal muscle elasticity and its contribution to skeletal muscle function.
When you have mastered the information in this chapter, you should be able to:
1. Compare and contrast roles of cytoskeletal structures in different kinds of cell motility.
2. Distinguish the roles of microfilaments, microtubules and intermediate filaments in the maintenance and alteration of cell shape and structure.
3. Suggest how ciliary and spindle fiber microtubules can maintain their length.
4. Explain how spindle fiber microtubules can change their length.
5. Propose an experiment to show which part of a motor protein has ATPase activity.
6. Define the actin-myosin contraction paradox.
7. Outline the steps of the contraction cycle involving myosin and actin.
8. Compare and contrast mucle and flagellar structure and function.
9. Explain why smooth muscles do not show striations in the light microscope.
10. Outline the structure of a skeletal muscle, from a whole muscle down to a sarcomere.
11. Propose alternate hypothesis to explain hereditary muscle weakness involving specific proteins/genes, and suggest how you might test one of them.