in many cells, microtubules grow out of a centrosome near the nucleus. The centrosome is a "microtubule-organizing center." In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring
true or false, microtubules control the beating of cilia and flagella in some cells
what common ultrastructure do cilia and flagella share?
1. a core of microtubules sheathed by the plasma membrane
2. A basal body that anchors the cilium or flagellum
3. A motor protein called dynein, which drives the bending movements of a cilium or flagellum
how does dynein "walking" move flagella and cilia?
1. the dynein arms alternately grab, move, and release the outer microtubules
2. Protein cross-links limit sliding
3. Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum
what is the structurral role of microfilaments?
the structural role of microfilaments is to bear tension, resisting pulling forces within the cell. They form a 3-D network called the cortex just inside the plasma membrane to help support the cell's shape. Also, bundles of microfilaments make up the core of microvilli of intestinal cells
what are microfilaments made of?
they are built as a twisted double chain of actin subunits
explain microfilaments' role in cell motility
Microfilaments that function in cellular motility contain the protein myosin in addition to actin.
In muscle cells, thousands of actin filaments are arranged parallel to one another. Thicker filaments composed of myosin interdigitate the thinner actin fibers
Localized contraction brought about by actin and myosin also drives amoeboid movement. Pseudopodia extend and contract through the reversible assembly and contraction of actin subunits into microfilaments.
what is cytoplasmic streaming and how is it brought about?
cytoplasmic streaming is a circular flow of cytoplams within cells. This streaming speeds distributon of materials within the cell. In plants actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming
describe the structure and function of intermediate filaments
intermediate filaments range in diameter from 8-12 nanometers, larger than microfilaments but smaller than microtubules. They support cell shape and fix organelles in place. Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes
what are the common extracellular structures that are secreted onto the outer part of the plasma membrane
-cell walls of plants
-the extracellular matrix of animal cells
briefly describe plant cell walls
the cell wall protects the plant cell, maintains it shape, and prevents excessive uptake of water
Plant cell walls are made of cellulose fibers embedded in other polysaccharides and proteins
what are the three layers of the plant cell wall and describe them
primary cell wall: relatively thin and flexible
middle lamella: thin layer between primary walls of adjacent cells
secondary cell wall: added between the plasma membrane and the primary cell wall
what are plasmodesmata?
plasmodesmata are channels between adjacent plant cells. Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell
Describe the ECM and its functions
The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin.
ECM proteins bind to receptor proteins in the plasma membrane called integrins
Functions of the ECM:
what are the types of intercellular junctions?
- gap junctions
what are tight junction?
tight junction, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid.
what are desmosomes
fasten cells together into strong sheets
what are gap junctions?
provide cytoplasmic channels between adjacent cells