CH. 2 - Cell Physiology

Question 1

1. State the principles of the cell theory.

Answer 1

■ The cell is the smallest structural and functional unit capable of carrying out life processes.
■The functional activities of each cell depend on the specific structural properties of the cell.
■Cells are the living building blocks of all multicellular organisms.
■An organism’s structure and function ultimately depend on the collective structural characteristics and functional capabilities of its cells.
■All new cells and new life arise only from preexisting cells.
■Because of this continuity of life, the cells of all organisms are fundamentally similar in structure and function.

Question 2

2. Compare the average size of cells in your body with those in a mouse and in an elephant.

Answer 2

They are about the same size

Question 3

1. State the functions of DNA and the different types of RNA.

Answer 3

1. DNA provides the genetic code for protein synthesis and serves as a genetic blueprint during cell replication. The DNA code is transcribed into messenger RNA (mRNA), which is translated into the specified protein by ribosomes that contain ribonucleic RNA (rRNA). Transfer RNA (tRNA) delivers the appropriate amino acids to their designated site in the protein under construction.

Question 4

2. Define genome, proteome, and epigenetics.

Answer 4

2. The genome is all of the genetic information coded in a complete single set of DNA in a typical body cell. The proteome is the complete set of proteins coded for by the genome. Epigenetics refers to the environmentally induced modifications that influence gene activity without altering the gene’s DNA code.

Question 5

3. Distinguish among cytoplasm, organelles, cytosol, and cytoskeleton.

Answer 5

3. • Cytoplasm is the portion of the cell interior not occupied by the nucleus. It consists of organelles, cytosol, and cytoskeleton. Organelles are distinct, highly organized structures that perform specialized functions within the cell.
     - The cytosol is the gel-like portion of cytoplasm that surrounds the organelles.
     - The cytoskeleton is a scaffolding of proteins within the cytoplasm that serves as the cell’s “bone” and “muscle”

Question 6

Compare the contents of a transport vesicle and a secretory vesicle.

Answer 6

A transport vesicle contains a mixture of proteins that have been newly synthesized by the rough ER. A secretory vesicle contains a specific finished protein product that has been modified and sorted by the Golgi complex.

Question 7

1. Distinguish between the rough ER and smooth ER structurally and functionally.

Answer 7

1. The endoplasmic reticulum (ER) is one continuous, extensive organelle. The rough ER consists of stacks of relatively flattened interconnected sacs studded with ribosomes that synthesize proteins. The smooth ER is a meshwork of tiny interconnected tubules that in most cells serves as a central packaging and discharge site for products synthesized by the ER.

Question 8

2. Discuss the structure and function of a ribosome.

Answer 8

2. A ribosome is a nonmembranous organelle consisting of a large and a small subunit that are brought together to serve as the “workbench” for protein synthesis. When messenger RNA moves through a groove formed between the two subunits, the ribosome translates the mRNA into chains of amino acids in the ordered sequence dictated by the DNA code.

Question 9

3. State the destination of proteins synthesized by the rough ER.

Answer 9

3. secreted out of the cell or used for construction of new membrane

Question 10

4. Describe the function of the ubiquitin–proteasome pathway.

Answer 10

4. Misfolded, damaged, or unneeded intracellular proteins are tagged with ubiquitin. Proteasomes break down ubiquinated proteins into recyclable building blocks.

Question 11

What happens to the surface area of the plasma membrane as a result of exocytosis and of endocytosis?

Answer 11

The surface membrane increases during exocytosis and decreases during endocytosis.

Question 12

1. Describe the structure and functions of a Golgi complex.

Answer 12

1. The Golgi complex consists of a stack of flattened, slightly curved, membrane-enclosed sacs. It
   (1) processes raw materials synthesized by the ER into their final form and
   (2) sorts and directs the finished products to their final destinations.

Question 13

2. Define secretion.

Answer 13

2. Secretion is release to the cell’s exterior by exocytosis of a specific product synthesized by the cell for a particular function.

Question 14

3. Explain how secretory vesicles can dock only with the plasma membrane to release their contents to the cell’s exterior.

Answer 14

3. The v-SNARE docking marker of a secretory vesicle can bind lock-and-key fashion only with the t-SNARE docking-marker acceptor on the targeted plasma membrane, thus ensuring that secretory vesicles can dock only with the plasma membrane to release their contents to the cell’s exterior.

Question 15

1. State the function of hydrolytic enzymes.

Answer 15

1. Hydrolytic enzymes catalyze hydrolysis, the breakdown of organic molecules by the addition of water at a bond site.

Question 16

2. Illustrate the three types of endocytosis.

Answer 16

2. See Figure 2-9, p. 32. Forms of endocytosis:
   (a) pinocytosis. The surface membrane dips inward to form a pouch, then seals the surface, forming an intracellular endocytic vesicle that nonselectively internalizes a bit of ECF.
   (b) receptor-mediated endocytosis. When a large molecule such as a protein attaches to a specific surface receptor, the membrane pockets inward with the aid of a coat protein, forming a coated pit, then pinches off to selectively internalize the molecule in an endocytic vesicle.
   (c) phagocytosis. White blood cells internalize multimolecular particles such as bacteria or old red blood cells by extending pseudopods that wrap around and seal in the targeted material. A lysosome fuses with and degrades the vesicle contents.

Question 17

3. Define autophagy.

Answer 17

3. Autophagy is selective self-digestion of dysfunctional organelles

Question 18

How many each of NADH and FADH2 molecules are generated for each “turn” of the citric acid cycle? How many of each are produced for every glucose molecule processed?

Answer 18

3 NADH and 1 FADH2 are generated for each “turn” of the citric acid cycle. Because glycolysis splits glucose into two pyruvate molecules, each of which enters one “turn” of the citric acid cycle, 6 NADH and 2 FADH2 are produced by this cycle for every glucose molecule processed.

Question 19

Where does the O2 that serves as the final electron acceptor at Step 4 come from?

Answer 19

From air breathed in

Question 20

If no O2 is available, pyruvate is converted to lactate instead of an acetyl group. Compare the energy yield of glucose degradation with O2 and without O2.

Answer 20

32 ATPs with O2 , 2 ATPs without O2

Question 21

1. Draw and label a mitochondrion.

Answer 21

1. See Figure 2-10a, p. 34.
   The outer membrane is smooth, whereas the inner membrane forms folds known as cristae that extend into the matrix. An intermembrane space separates the outer and inner membranes. The electron transport proteins embedded in the cristae are ultimately responsible for converting much of the energy of food into a usable form.

Question 22

2. List the stages of cellular respiration, and state where each is accomplished.

Answer 22

2. The stages of cellular respiration:
   (1) glycolysis in the cytosol,
   (2) the citric acid cycle in the mitochondrial matrix, and
   (3) oxidative phosphorylation (consisting of the electron transport system and chemiosmosis) at the mitochondrial inner membrane.

Question 23

3. Compare the amount of ATP produced from one glucose molecule in anaerobic and aerobic conditions.

Answer 23

3. In anaerobic conditions 2 molecules of ATP are produced (by glycolysis) and in aerobic conditions 32 molecules of ATP are produced (2 by glycolysis, 2 by the citric acid cycle, and 28 by oxidative phosphorylation) from one glucose molecule.

Question 24

4. Contrast apoptosis and necrosis.

Answer 24

4. Apoptosis is intentional suicide of a cell that is no longer useful. Necrosis is uncontrolled, accidental death of useful, injured cells.

Question 25

1. Describe the structure of a vault.

Answer 25

1. When closed, vaults are hollow, octagonal-shaped barrels. When open, each half looks like unfolded flowers with eight “petals” attached to a central ring.

Question 26

2. Discuss the speculated functions of vaults.

Answer 26

2. Vaults are thought to serve as cellular “trucks” that carry cargo (either mRNA or the ribosomal subunits) from the nucleus to cytoplasmic sites of protein synthesis.

Question 27

1. List the three general categories of activities associated with the cytosol.

Answer 27

1. (1) intermediary metabolism,
   (2) protein synthesis by free ribosomes, and
   (3) storage of nutrients (as glycogen and fat) and secretory vesicles

Question 28

2. Define intermediary metabolism.

Answer 28

2. Intermediary metabolism encompasses the intracellular chemical reactions involving the degradation, synthesis, and transformation of simple sugars, amino acids, and fatty acids.

Question 29

Microtubules disintegrate during the course of Alzheimer’s disease. How could this breakdown lead to death of involved neurons?

Answer 29

Without its microtubule “highway” intact, the damaged neuron cannot transport secretory products from the cell body to the axon terminal for release to the ECF or debris from the axon terminal to the cell body for degradation by lysosomes. Failure to transport these materials to their sites of elimination from the cell leads to their accumulation within the cell, which can lead to disruption of cellular activities and ultimately death of the neuron.

Question 30

1. List the three types of cytoskeletal elements and state one function of each.

Answer 30

1. (1) microtubules (maintain asymmetric cell shapes, serve as highways for transport of secretory vesicles, provide movement of cilia and flagella, form mitotic spindle);
   (2) microfilaments (play a key role in cellular contractile systems, serve as mechanical stiffeners); and
   (3) intermediate filaments (help resist mechanical stress)

Question 31

2. Explain how motor proteins transport proteins along a cytoskeletal “highway.”

Answer 31

2. A motor protein attaches to a particle to be transported, then walks along a microtubular “highway” by alternately attaching and releasing its “feet” as it cyclically swings the rear foot ahead of the front foot, stepping on one tubulin molecule after another.

Question 32

3. Discuss the role of centrioles in the formation of cilia and flagella.

Answer 32

3. A duplicated centriole moves from the centrosome to a position just under the plasma membrane, where microtubules grow outward from the centriole to form a cilium or flagellum. The centriole remains at the base of this motile appendage as the basal body of the structure.

Question 33

4. Describe how treadmilling forms pseudopods during amoeboid movement.

Answer 33

4. In a process called treadmilling in amoeboid movement, actin filaments extend forward at the leading edge through the addition of actin molecules that have been removed from the rear of the filament and transferred to the front of the filament, an action that pushes a pseudopod (a fingerlike protrusion) forward. In treadmilling, the filament does not get any longer, it just advances forward.

Question 34

1. Discuss the function of the oxidative enzymes in peroxisomes.

Answer 34

1. Peroxisomes detoxify various wastes and foreign compounds within the cell by means of oxidative enzymes that use oxygen to strip hydrogen from these organic molecules.

Question 35

2. Name the major product generated in peroxisomes.

Answer 35

2. hydrogen peroxide (H2 O2 )