Chapter 4.11

How Do Cells Move?

AP BiologyFall 2010

Objectives

• Describe the differences between psudopods, cilia, and flagella

• Understand the mechanism which moves cilia and flagella

Moving Along with Motor Proteins

• Kinesines, dyneins, myosins, and other motor proteins function as the freight engines

• Energy from ATP fuels the movement • Some motor proteins move chromosomes • Others slide one microtubule over another

and others inch along tracks inside nerve cells

Cilia, Flagella, and False Feet

• Both flagella and cilia are motile structures that extend from the surface of many cells and is completely sheathed by an extension of the plasma membrane

Cilia

• Cilia: short, numerous, and provide locomotion for free-living cells or may move surrounding water and particles if the ciliated cell is anchored

Cilia

• Ciliated protists swim by beating their many cilia in synchrony

• Cilia in certain areas of the lungs beat nonstop

Flagella

• Flagella: quite long, not usually numerous, and are found on one-celled protistans and animal sperm cells

9 + 2 Array

• Microtubular extensions of the plasma membrane have a 9 + 2 cross-sectional array that arises from a centriole extending below the array as a basal body

• 9 pairs of microtubules form a ring around a central pair, all stabilized by protein spokes and links

9 + 2 Array

• Centrosome gives rise to a centriole • Barrel shaped structure produces and

organizes microtubules into the 9 + 2 array, then it remains below the finished array as a basal body

Cilia and Flagella Movement

• Move by sliding mechanism• Dynein arms project from each pair in the outer ring • When ATP energizes them, arms grab microtubule pair

in front of them, tilt in short, downward stroke, then let go

• Bound pair slides down, its arms bind the pair in front of it, forcing it to slide down– and so on around the ring

• Microtubules cannot slide too far, but bends a bit • Sliding motion converted to bending motion

Psudopods

• Pseudopods (flase feet): temporary lobes that project from the cell, used in locomotion and food capture – Macrophages and amoebas – Advance in steady direction as microfilaments

inside them are elongated– Motor proteins attached to microfilaments are

dragging the plasma membrane along with them in direction of interest

Review

1. What is the difference between cilia, flagella, and false feet?

Answers

1. Flagella are quite long, not usually numerous, and are found on one-celled protistans and animal sperm cells. Cilia short, numerous, and provide locomotion for free-living cells or may move surrounding water and particles if the ciliated cell is anchored. Pseudopods are temporary lobes that project from the cell, used in locomotion and food capture.