The Cell and General Physiology

Question 1

The term “glycocalyx” refers to

A) the negatively charged carbohydrate chains that protrude into the cytosol from glycolipids and integral glycoproteins

B)the negatively charged carbohydrate layer on the outer cell surface

C)the layer of anions aligned on the cytosolic surface of the plasma membrane

D)the large glycogen stores found in “fast” muscles

E)a mechanism of cell–cell attachment

Answer 1

B) the negatively charged carbohydrate layer on the outer cell surface

The cell “glycocalyx” is the loose negatively charged carbohydrate coat on the outside of the surface of the cell membrane. The membrane carbohydrates usually occur in combination with proteins or lipids in the form of glycoproteins or glycolipids, and the “glyco” portion of these molecules almost invariably protrudes to the outside of the cell

Question 2

Messenger RNA (mRNA)

A)carries the genetic code to the cytoplasm

B)carries activated amino acids to the ribosomes

C)is single-stranded RNA molecules of 21 to 23 nucleotides that can regulate gene transcription

D)forms ribosomes

Answer 2

A)carries the genetic code to the cytoplasm

mRNA molecules are long, single RNA strands that are suspended in the cytoplasm, and are composed of several hundred to several thousand RNA nucleotides in unpaired strands. The mRNA carries the genetic code to the cytoplasm for controlling the type of protein formed. The transfer RNA (tRNA) transports activated amino acids to the ribosomes. Ribosomal RNA, along with about 75 different proteins, forms ribosomes. MicroRNAs are single-stranded RNA molecules of 21 to 23 nucleotides that regulate gene transcription and translation

Question 3

Which of the following statements is true for both pinocytosis and phagocytosis?

A)Involves the recruitment of actin filaments

B)Occurs spontaneously and non-selectively

C)Endocytotic vesicles fuse with ribosomes that release hydrolases into the vesicles

D)Is only observed in macrophages and neutrophils

E)Does not require ATP

Answer 3

A)Involves the recruitment of actin filaments

Both pinocytosis and phagocytosis involve movement of the plasma membrane. Pinocytosis involves invagination of the cell membrane whereas phagocytosis involves evagination. Both events require the recruitment of actin and other cytoskeleton elements. Phagocytosis is not spontaneous and is selective, being triggered by specific receptor-ligand interactions.

Question 4

In comparing two types of cells from the same person, the variation in the proteins expressed by each cell type reflects

A)differences in the DNA contained in the nucleus of each cell

B)differences in the numbers of specific genes in their genomes

C)cell-specific expression and repression of specific genes

D)differences in the number of chromosomes in each cell

E)the age of the cells

Answer 4

C)cell-specific expression and repression of specific genes

The variation in proteins expressed by each cell reflects cell-specific expression and repression of specific genes. Each cell contains the same DNA in the nucleus and the same number of genes. So differentiation results not from differences in the genes but from selective repression and /or activation of different gene promoters

Question 5

Micro RNAs (miRNAs)

A)are formed in the cytoplasm and repress translation or promote degradation of mRNA before it can be translated

B)are formed in the nucleus and then processed in the cytoplasma by the dicer enzyme

C)are short (21 to 23 nucleotides) double-stranded RNA fragments that regulate gene expression

D)repress gene transcription

Answer 5

A)are formed in the cytoplasm and repress translation or promote degradation of mRNA before it can be translated

MicroRNAs (miRNA) are formed in the cytoplasm from pre-miRNAs and processed by the enzyme dicer that ultimately assembles RNA-induced silencing complex (RISC), which then generates miRNAs. The miRNAs regulate gene expression by binding to the complementary region of the RNA and repressing translation or promoting degradation of mRNA before it can be translated by the ribosome.

Question 6

Studies completed on a 5-year-old boy show an accumulation of cholesteryl esters and triglycerides in his liver, spleen, and intestines and calcification of both adrenal glands. Additional studies indicate the cause to be a deficiency in acid lipase A activity.

Identify the most likely subcellular site listed above for the deficient or mutant protein

Answer 6

Lysosomes

Acid lipases, along with other acid hydrolases, are localized to lysosomes. Fusion of endocytotic and autolytic vesicles with lysosomes initiates the intracellular process that allows cells to digest cellular debris and particles ingested from the extracellular milieu, including bacteria. In the normal acidic environment of the lysosome, acid lipases use hydrogen to convert lipids into fatty acids and glycerol. Other acid lipases include a variety of nucleases, proteases, and polysaccharide-hydrolyzing enzymes

Question 7

The abnormal cleavage of mannose residues during the post-translational processing of glycoproteins results in the development of a lupus-like autoimmune disease in mice. The abnormal cleavage is due to a mutation of the enzyme α-mannosidase II

Identify the most likely subcellular site listed above for the deficient or mutant protein

Answer 7

Golgi apparatus

Membrane proteins are glycosylated during their synthesis in the lumen of the rough endoplasmic reticulum. Most post-translational modification of the oligosaccharide chains, however, occurs during the transport of the protein through the layers of the Golgi apparatus matrix, where enzymes such as α-mannosidase II are localized

Question 8

The observation that abnormal cleavage of mannose residues from glycoproteins causes an autoimmune disease in mice supports the role of this structure in the normal immune response.

Identify the most likely subcellular site listed above for the deficient or mutant protein

Answer 8

Glycocalyx

The oligosaccharide chains that are added to glycoproteins on the luminal side of the rough endoplasmic reticulum, and subsequently modified during their transport through the Golgi apparatus, are attached to the extracellular surface of the cell. This negatively charged layer of carbohydrate moieties is collectively called the glycocalyx. It participates in cell–cell interactions, cell–ligand interactions, and the immune response.

Question 9

Initiation of translation

Match the cellular location for each of the steps involved in the synthesis and packaging of a secreted protein listed below with a term listed above.

Answer 9

Cytosol

Initiation of translation, whether of a cytosolic protein, a membrane-bound protein, or a secreted protein, occurs in the cytosol and involves a common pool of ribosomes. Only after the appearance of the N-terminus of the polypeptide is it identified as a protein destined for secretion. At this point, the ribosome attaches to the cytosolic surface of the rough endoplasmic reticulum. Translation continues, and the new polypeptide is extruded into the matrix of the endoplasmic reticulum.

Question 10

Protein condensation and packaging

Match the cellular location for each of the steps involved in the synthesis and packaging of a secreted protein listed below with a term listed above.

Answer 10

Golgi apparatus

Secreted proteins are condensed, sorted, and packaged into secretory vesicles in the terminal portions of the Golgi apparatus, also known as the trans-Golgi network. It is here that proteins destined for secretion are separated from those destined for intracellular compartments or cellular membranes

Question 11

Gene transcription

Match the cellular location for each of the steps involved in the synthesis and packaging of a secreted protein listed below with a term listed above.

Answer 11

Nucleus

All transcription events occur in the nucleus, regardless of the final destination of the protein product. The resulting messenger RNA molecule is transported through the nuclear pores in the nuclear membrane and translated into either the cytosol or the lumen of the rough endoplasmic reticulum.

Question 12

“Redundancy” or “degeneration” of the genetic code occurs during which of the following steps of protein synthesis?

A)DNA replication

B)Transcription

C)Post-transcriptional modification

D)Translation

E)Protein glycosylation

Answer 12

D)Translation

During both replication and transcription, the new nucleic acid molecule is an exact complement of the parent DNA molecule. This is a result of predictable, specific, one-to-one base pairing. During the process of translation, however, each amino acid in the new polypeptide is encoded by a codon, a series of three consecutive nucleotides. Whereas each codon encodes a specific amino acid, most amino acids can be encoded for by multiple codons. Redundancy results because 60 codons encode a mere 20 amino

acids

Question 13

Which of the following does not play a direct role in the process of transcription?

A)Helicase

B)RNA polymerase

C)Chain-terminating sequence

D)“Activated” RNA molecules

E)Promoter sequence

Answer 13

A)Helicase

Helicase is one of the many proteins involved in the process of DNA replication. It does not play a role in transcription. RNA polymerase binds to the promoter sequence and facilitates the addition of “activated” RNA molecules to the growing RNA molecule until the polymerase reaches the chain-terminating sequence on the template DNA molecule.

Question 14

Which of the following proteins is most likely to be the product of a proto-oncogene?

A)Growth factor receptor

B)Cytoskeletal protein

C)Na+channel

D)Ca++-ATPase

E)Myosin light chain

Answer 14

A)Growth factor receptor

An oncogene is a gene that is either abnormally activated or mutated in such a way that its product causes uncontrolled cell growth. A proto-oncogene is simply the “normal” version of an oncogene. By definition, proto-oncogenes are divided into several families of proteins, all of which participate in the control of cell growth. These families include, but are not limited to, growth factors and their receptors, protein kinases, transcription factors, and proteins that regulate cell proliferation

Question 15

Which of the following events does not occur during the process of mitosis?

A)Condensation of the chromosomes

B)Replication of the genome

C)Fragmentation of the nuclear envelope

D)Alignment of the chromatids along the equatorial plate

Answer 15

B)Replication of the genome

DNA replication occurs during the S phase of the cell cycle and precedes mitosis. Condensation of the chromosomes occurs during the prophase of mitosis. Fragmentation of the nuclear envelope occurs during the prometaphase of mitosis. The chromatids align at the equatorial plate during metaphase and separate into two complete sets of daughter chromosomes during anaphase

Question 16

Which of the following characteristics of a biological membrane is most influenced by its cholesterol content?

A)Thickness

B)Ion permeability

C)Fluidity

D)Glycosylation

E)Hydrophobicity

Answer 16

C)Fluidity

The cholesterol content of a membrane determines the packing density of phospholipids. The higher the cholesterol content, the more fluid the membrane and the greater the lateral mobility of membrane components, including proteins and phospholipid molecules themselves. To a lesser extent, cholesterol content also affects the “leakiness” of a membrane to water-soluble molecules

Question 17

The appearance of which of the following distinguishes eukaryotic cells from lower units of life?

A)DNA

B)RNA

C)Membranes

D)Protein

E)Nucleus

Answer 17

E)Nucleus

Nucleic acids and proteins, together, constitute the fundamental replicable unit of life,exemplified by viruses. Membranes and even organelles appear in prokaryotic cells, but only eukaryotic cells possess a nucleus

Question 18

Assume that excess blood is transfused into a patient whose arterial baroreceptors are nonfunctional and blood pressure increases from 100 to 150 mm Hg. Then, assume that the same volume is blood is infused into the same patient under conditions where his arterial baroreceptors are functioning normally and blood pressure increases from 100 to 125 mm Hg. What is the approximate feedback “gain” of the arterial baroreceptors in this patient when they are functioning normally?

A)−1.0

B)−2.0

C)0.0

D)+1.0

E)+2.0

Answer 18

A)−1.0

The feedback gain of the control system is calculated as the amount of correction divided by the remaining error of the system. In this example, blood pressure increased from 100 to 150 mm Hg when the baroreceptors were not functioning. When the baroreceptors were functioning, the pressure increased only 25 mm Hg. Therefore, the feedback system caused a “correction” of −25 mm Hg, from 150 to 125 mm Hg.The remaining increase in pressure of +25 mm is called the “error.” In this example the correction is therefore −25 mm Hg and the remaining error is +25 mm Hg. Thus, the feedback gain of the baroreceptors in this person is −1, indicating a negative feedback control system.