Question 1

The cytosol is a clear, viscous, watery colloid that bathes the cytoskeleton and organelles.

Accepted Answer

It contains enzymes, other proteins, amino acids, ATP, electrolytes, other diverse organic and inorganic ions, oxygen, carbon dioxide, and metabolic wastes. It is the site of glycolysis, anaerobic fermentation, and most protein synthesis.

Question 2

The cytoskeleton is a network of protein filaments and cylinders that structurally support a cell, determine its shape, organize its contents, direct the movement of materials within the cell, and contribute to movements of the cell as a whole.

Accepted Answer

It is connected to transmembrane proteins of the plasma membrane, and they in turn are connected to protein fibers external to the cell, creating a strong structural continuity from extracellular material to the cytoplasm.

Question 3

Cytoskeletal

Accepted Answer

elements even connect to chromosomes in the nucleus, enabling physical tension on a cell to move nuclear contents, mechanically stimulate genetic function, and influence the timing of cell division relative to cell size.

Question 4

The cytoskeleton is composed of microfilaments, intermediate filaments, and microtubules.

Accepted Answer

If you think of intermediate filaments as being like the stiff rods of uncooked spaghetti, you could, by comparison, think of microfilaments as being like fine angel-hair pasta and microtubules like tubular penne pasta.

Question 5

Microfilaments (thin filaments) are about 6 nm thick and are made of the protein actin.

Accepted Answer

They are widespread throughout the cell but especially concentrated in a fibrous mat called the terminal web (membrane skeleton) on the cytoplasmic side of the plasma membrane.

Question 6

The phospholipids of the plasma membrane spread out over the terminal web like butter on a slice of bread.

Accepted Answer

The web, like the bread, provides physical support, whereas the lipids, like butter, provide a permeability barrier.

Question 7

It is thought that without the support of the terminal web, the phospholipids would break up into little droplets and the plasma membrane wouldn't hold together.

Accepted Answer

As described earlier, actin microfilaments also form the supportive cores of the microvilli and play a role in cell movement.

Question 8

Through its role in -----, actin plays a crucial role in embryonic development, muscle contraction, immune function, wound healing, cancer metastasis, and other processes that involve cell migration.

Accepted Answer

cell motility

Question 9

Intermediate filaments (8-10 nm thick) are thicker and stiffer than microfilaments. They give the cell its shape, resist stress, and form junctions that attach cells to their neighbors.

Accepted Answer

In epidermal cells, they are made of the tough protein keratin and occupy most of the cytoplasm. They are responsible for the strength of hair and fingernails.

Question 10

Microtubules (25 nm in diameter) are cylinders made of 13 parallel strands called protofilaments.

Accepted Answer

Each protofilament is a long chain of globular proteins called tubulin

Question 11

Microtubules radiate from an area of the cell called the centrosome.

Accepted Answer

They hold organelles in place, form bundles that maintain cell shape and rigidity, and act like monorail tracks for motor proteins carrying organelles and macromolecules to specific destinations in the cell.

Question 12

Microtubules form the axonemes of cilia and flagella and are responsible for their beating movements, and form the mitotic spindle that guides chromosome movement during cell division. Microtubules aren't permanent structures.

Accepted Answer

They come and go moment by moment as tubulin molecules assemble into a tubule and then break apart again to be used somewhere else in the cell. The microtubules in cilia, flagella, basal bodies, and centrioles, however, are more stable.

Question 13

Organelles (literally, "little organs") are to the cell what

Accepted Answer

organs are to the body-structures that play individual physiological roles in the survival of the whole.

Question 14

There is no universally agreed definition of the word organelle. Some authorities include cilia, microvilli,

Accepted Answer

and even the plasma membrane in this concept, whereas others exclude intracellular structures such as ribosomes and centrioles because they're not enclosed in membranes.

Question 15

This book, however, regards organelles as the intracellular structures, above the molecular level of complexity, that play indispensable roles in cellular metabolism.

Accepted Answer

Some organelles are surrounded by membranes and are therefore referred to as membranous organelles.

Question 16

membranous organelles.

Accepted Answer

These are the nucleus, mitochondria, lysosomes, peroxisomes, endoplasmic reticulum, and Golgi complex.

Question 17

Organelles

Accepted Answer

without membranes include ribosomes, proteasomes, centrosomes, centrioles, and basal bodies.

Question 18

The nucleus (fig. 3.26) is usually the largest organelle and the only one clearly visible with the light microscope.

Accepted Answer

It contains the cell's chromosomes and is therefore the genetic control center of cellular activity.

Question 19

It is typically spheroidal to elliptical in shape and about 5 µm in diameter.

Accepted Answer

Most cells have a single nucleus, but there are exceptions

Question 20

Mature red blood cells have none; they are anuclear.

Accepted Answer

A few cell types are multinuclear.

Question 21

Many cells of the liver, urinary bladder, and heart have two nuclei; bone-dissolving cells called osteoclasts have as many as 50;

Accepted Answer

and a single skeletal muscle cell can have many thousands.

Question 22

The Nucleus as Seen by Electron Microscopy. These photomicrographs were made by different TEM methods to show the internal structure of the nucleus and surface of the nuclear envelope.

Accepted Answer

(a) Interior of the nucleus. (b) Surface of the nucleus, showing clusters of nuclear pores

Question 23

The nucleus is enclosed in a double membrane, the nuclear envelope.

Accepted Answer

The envelope is perforated with nuclear pores formed by a ring of proteins called the nuclear pore complex.

Question 24

Nuclear Pore Complex

Accepted Answer

These proteins regulate molecular traffic through the envelope and act like a rivet to hold the two membrane layers together. Hundreds of molecules pass through the nuclear pores every minute

Question 25

Coming into the nucleus are raw materials for DNA and RNA synthesis, enzymes that are made in the cytoplasm but function in the nucleus, and hormones and other chemical messengers that activate certain genes.

Accepted Answer

Going the other way, RNA is made in the nucleus but leaves to perform its job in the cytoplasm.

Question 26

Why do these nuclear pores have to be larger in diameter than the channels in the cell's plasma membrane?

Accepted Answer

Large molecules such as enzymes and RNA must pass through the nuclear pores, but pores in the plasma membrane must be small enough to prevent such large molecules from escaping the cell.

Question 27

Immediately inside the ------ is a narrow but densely fibrous zone called the nuclear lamina, composed of a web of intermediate filaments.

Accepted Answer

nuclear envelope

Question 28

It supports the nuclear envelope and pores, provides points of attachment and organization for the chromosomes inside the nucleus, and plays a role in regulating DNA replication and the cell life cycle.

Accepted Answer

nuclear lamina

Question 29

Abnormalities of its structure or function are associated with certain

Accepted Answer

nuclear lamina

Question 30

The material in the nucleus is called nucleoplasm. This includes chromatin [3, 4] -fine threadlike matter composed of DNA and protein-

Accepted Answer

and one or more dark-staining masses called nucleoli (singular, nucleolus, where ribosomes are produced.

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