Cell bio quiz 3

Question 1

Where is N-linked glycosylation initiated?

Answer 1

N-linked glycosylation is initiated in the endoplasmic reticulum (ER).

Question 2

What is the role of GPI anchors?

Answer 2

GPI anchors are used to attach some proteins to the plasma membrane, as opposed to having membrane-spanning regions.

Question 3

Why are many proteins synthesized in the ER rapidly degraded?

Answer 3

Many proteins synthesized in the ER are rapidly degraded because they fail to fold correctly.

Question 4

What triggers the unfolded protein response?

Answer 4

The unfolded protein response is triggered by an excess of unfolded proteins in the endoplasmic reticulum.

Question 5

Where are membrane lipids primarily synthesized?

Answer 5

Membrane lipids are primarily synthesized in the ER

Question 6

What are the three main types of lipids in eukaryotic cell membranes?

Answer 6

The three main types are phospholipids, glycolipids, and cholesterol.

Question 7

How are proteins and lipids transported along the secretory pathway?

Answer 7

They are transported in transport vesicles, which bud from the membrane of one organelle and fuse with another.

Question 8

What is the role of the Golgi apparatus?

Answer 8

The Golgi apparatus functions as a factory where proteins received from the ER are further processed and sorted for transport to their eventual destinations.

Question 9

How are lysosomal proteins targeted?

Answer 9

Lysosomal proteins are targeted by the addition of a phosphate group to mannose residues, which is recognized by the mannose-6-phosphate receptor in the trans Golgi network.

Question 10

What is the significance of the COP II coat in vesicular transport?

Answer 10

COP II-coated vesicles carry proteins from the ER to the ER-Golgi intermediate compartment and then on to the Golgi.

Question 11

How is the specificity of vesicular transport established?

Answer 11

The specificity is established by the localization of Rab proteins on the correct membrane, which facilitates the formation of v-SNARE/t-SNARE complexes.

Question 12

What is autophagy?

Answer 12

Autophagy is the process by which the cell digests its own parts, including cytoplasm or internal organelles, through the formation of autophagosomes that fuse with lysosomes.

Question 13

How do both proteins and phospholipids travel along the secretory pathway?

Answer 13

Both proteins and phospholipids travel along the secretory pathway in transport vesicles which bud from the membrane of one organelle and then fuse with the membrane of another.

Question 14

What are ERES and ERGIC?

Answer 14

ERES=ER exit side. From there they go to the ERGIC=ER Golgi intermediate compartment and then on to the Golgi.

Question 15

How are resident ER proteins destined to remain in the lumen of the ER marked?

Answer 15

Resident ER proteins destined to remain in the lumen of the ER are marked by KDEL or KKXX retrieval sequences at their carboxy terminus.

Question 16

What functions as a factory in which proteins received from the ER are processed and sorted?

Answer 16

The Golgi apparatus or Golgi complex functions as a factory in which proteins received from the ER are further processed and sorted for transport to their eventual destinations—endosomes, lysosomes, the plasma membrane, or secretion from the cell.

Question 17

Where are the complex polysaccharides of the cell wall synthesized in plant cells?

Answer 17

In plant cells, the Golgi apparatus further serves as the site at which the complex polysaccharides of the cell wall are synthesized.

Question 18

What distinguishes the processing of the N-linked oligosaccharide of lysosomal proteins from that of secreted and plasma membrane proteins?

Answer 18

The processing of the N-linked oligosaccharide of lysosomal proteins differs from that of secreted and plasma membrane proteins. Lysosomal proteins are specifically recognized and modified by the addition of a phosphate group to the number 6 position of mannose residues.

Question 19

What role does the Golgi apparatus play in lipid metabolism?

Answer 19

In addition to its activities in processing and sorting glycoproteins, the Golgi apparatus functions in lipid metabolism— in particular in the synthesis of glycolipids and sphingomyelin from ceramide (which is synthesized in the ER).

Question 20

How are proteins, as well as lipids and polysaccharides, transported from the Golgi apparatus?

Answer 20

Proteins, as well as lipids and polysaccharides, are transported from the Golgi apparatus to their final destinations through the secretory pathway.

Question 21

What distinguishes the constitutive secretory pathway?

Answer 21

The constitutive secretory pathway, which operates in all cells, leads to continual unregulated protein secretion. In the absence of specific targeting signals, proteins carried to the plasma membrane by constitutive secretion.

Question 22

What mediates the fusion of a transport vesicle with a target membrane?

Answer 22

The SNARE hypothesis states that vesicle fusion is mediated by pairs of transmembrane proteins (v-SNARE and t-SNARE on the vesicle and target membranes respectively).

Question 23

What are some clinical symptoms of laminopathies and other nuclear envelopathies?

Answer 23

Laminopathies and other nuclear envelopathies have a large variety of clinical symptoms including skeletal and/or cardiac muscular dystrophy, lipodystrophy (degenerative conditions of the body’s adipose tissue), diabetes, dysplasia (epithelial anomaly), dermo- or neuropathy, leukodystrophy (degeneration of the white matter), and progeria (premature aging).

Question 24

What are B-type lamins and where are they expressed?

Answer 24

B-type lamins are present in every cell. B-type lamins B1 and B2 are expressed from the LMNB1 and LMNB2 genes.

Question 25

When are A-type lamins expressed, and what are the most common A-type lamins?

Answer 25

A-type lamins are only expressed following gastrulation. Lamin A and C are the most common A-type lamins and are splice variants of the LMNA gene.

Question 26

What gene is mutated in patients with classical laminopathy?

Answer 26

Patients with classical laminopathy have mutations in the gene coding for lamin A (LMNA gene).

Question 27

What are some mutations implicated in nuclear envelopathies?

Answer 27

Mutations implicated in other nuclear envelopathies were found in genes coding for lamin-binding proteins such as lamin B receptor (LBR gene), emerin (EMD gene), LEM domain-containing protein 3 (LEMD3 gene), and prelamin-processing enzymes.

Question 28

What are the earliest features of Emery-Dreifuss muscular dystrophy, and what genes cause it?

Answer 28

Among the earliest features of Emery-Dreifuss muscular dystrophy are joint deformities called contractures, which become noticeable in early childhood and most often involve the elbows, ankles, and neck. Mutations in the EMD (Emerin, a lamin-binding protein) and LMNA genes cause Emery-Dreifuss muscular dystrophy.

Question 29

What is progeria, and how many known cases are there currently in the world?

Answer 29

Progeria, narrowly referring to Hutchinson-Gilford Progeria Syndrome, is an extremely rare genetic condition that causes physical changes resembling greatly accelerated aging in sufferers. Currently, there are 51 known cases in the world.

Question 30

What causes Gaucher's disease, and how common is it?

Answer 30

Gaucher's disease is caused by a deficiency of the enzyme glucocerebrosidase, leading to an accumulation of glucocerebroside. It is the most common of the lysosomal storage diseases and occurs in approximately 1 in 50000 live births, most often among persons of Ashkenazi Jewish heritage.

Question 31

What enzyme activity is insufficient in Tay-Sachs disease, and what does it lead to?

Answer 31

Tay-Sachs disease is caused by insufficient activity of an enzyme called hexosaminidase A, which catalyzes the biodegradation of gangliosides. Insufficient activity of this enzyme leads to the accumulation of lipids in the brain, causing problems.

Question 32

What does the structure of a cell membrane function to do?

Answer 32

The structure of a cell membrane functions to separate the interior of the cell from its environment and to define the internal compartments of eukaryotic cells including the nucleus and cytoplasmic organelles.

Question 33

How do lipid bilayers behave?

Answer 33

Lipid bilayers behave as two-dimensional fluids in which individual molecules are free to rotate and move in lateral directions.

Question 34

Who gave the cell membrane its "fluid mosaic" description, and why?

Answer 34

“Fluid mosaic” was the description Jonathan Singer and Garth Nicolson gave the cell membrane when they observed that proteins are inserted into a lipid bilayer.

Question 35

What is formed by oligosaccharides of glycolipids and transmembrane glycoproteins?

Answer 35

The glycocalyx is formed by oligosaccharides of glycolipids and transmembrane glycoproteins.

Question 36

What are lipid rafts, and who suggested their existence?

Answer 36

Lipid rafts are clusters of sphingolipids and cholesterol. Kai Simons and Gerrit van Meer suggested the existence of microdomains present in cell membranes, which are enriched with cholesterol and sphingolipids, called "lipid rafts."

Question 37

What can diffuse through phospholipid bilayers?

Answer 37

Gases, hydrophobic molecules, and small polar uncharged molecules can diffuse through phospholipid bilayers.

Question 38

What are the two types of endocytosis?

Answer 38

Two types of endocytosis are phagocytosis or cell eating, which is the ingestion of large particles such as bacteria, and pinocytosis or cell drinking, which is the uptake of fluids or macromolecules in small vesicles.

Question 39

What provides a mechanism for the selective uptake of specific macromolecules?

Answer 39

Receptor-mediated endocytosis, a form of pinocytosis, provides a mechanism for the selective uptake of specific macromolecules.

Question 40

What role does dynamin play in clathrin-coated vesicle formation?

Answer 40

Dynamin, a membrane-associated GTP-binding protein, assists in the budding off of pits from the plasma membrane during clathrin-coated vesicle formation.

Question 41

What happens to the LDL receptor in patients with Familiar hypercholesterolemia?

Answer 41

In patients with Familiar hypercholesterolemia, mutations prevent the LDL receptor from concentrating in coated pits, which can be as subtle as the change of a single tyrosine to cysteine.

Question 42

What role do mitochondria play in eukaryotic cells?

Answer 42

Mitochondria play a critical role in the generation of metabolic energy in eukaryotic cells.

Question 43

Where does oxidative phosphorylation take place?

Answer 43

Oxidative phosphorylation takes place within mitochondria.

Question 44

How are proteins destined for the mitochondria generally made and transported?

Answer 44

Proteins destined for the mitochondria are generally made on free ribosomes and transported as completed polypeptides.

Question 45

What does the mitochondrial genome encode?

Answer 45

Mitochondrial genomes encode tRNAs, rRNAs, and only a small number of proteins that are essential components of the oxidative phosphorylation.

Question 46

How is the structure of a mitochondrion organized?

Answer 46

Mitochondria are surrounded by a double-membrane system consisting of inner and outer mitochondrial membranes separated by an intermembrane space.

Question 47

What is the role of the mitochondrial matrix?

Answer 47

The matrix contains the mitochondrial genetic system as well as enzymes required for oxidative phosphorylation.

Question 48

How are mitochondrial proteins with presequences imported?

Answer 48

Import of proteins into mitochondria is posttranslational, with proteins targeted to the outer membrane by presequences - amino-terminal sequences of 20 to 35 (positively charged) amino acids.

Question 49

What are mitochondrial diseases?

Answer 49

Mitochondrial diseases are a group of disorders relating to the mitochondria and comprise disorders that affect the function of the mitochondria and/or are due to mitochondrial DNA.

Question 50

What is one example of a mitochondrial disease and its effects?

Answer 50

One example of a mitochondrial disease is Leber's hereditary optic neuropathy (LHON) which results in blindness due to degeneration of the optic nerve.

Question 51

What is the main difference between chloroplasts and mitochondria?

Answer 51

The major difference between chloroplasts and mitochondria in terms of both structure and function is that chloroplasts contain a thylakoid membrane.

Question 52

How do chloroplasts and mitochondria generate ATP?

Answer 52

Chloroplast electron transport occurs in the thylakoid membrane, and the hydrogens are pumped across the thylakoid membrane from the stroma to the thylakoid lumen, where protons travel back into the stroma via ATP synthase to generate ATP.

Question 53

What is the genetic system of chloroplasts like?

Answer 53

The chloroplast genome encodes approximately 30 proteins that are involved in photosynthesis, and like mitochondria, this reflects their evolutionary origins from photosynthetic bacteria.

Question 54

How are proteins imported into the chloroplast stroma?

Answer 54

Protein translocation across the chloroplast envelope membranes is directed by transit peptides, N-terminal sequences of 30 to 100 amino acids.

Question 55

What are peroxisomes, and what functions do they serve?

Answer 55

Peroxisomes are small single membrane-enclosed organelles that contain enzymes involved in a variety of metabolic reactions, including the breakdown of very long-chain fatty acids.

Question 56

What is the genetic code used by the mitochondrial genetic system?

Answer 56

The mitochondrial genetic system uses a slightly different genetic code which is distinct from the “universal” genetic code used by both prokaryotic and eukaryotic cells.

Question 57

What genetic mutations are associated with classical laminopathies?

Answer 57

Classical laminopathies are associated with mutations in the LMNA gene coding for lamin A.

Question 58

What is the significance of mutations in lamin B (LMNB2 gene) or genetic defects leading to changes in lamin B abundance?

Answer 58

Mutations in lamin B (LMNB2 gene) or genetic defects leading to changes in lamin B abundance have been identified as a cause for laminopathies.

Question 59

Describe the fluid mosaic model of membrane structure.

Answer 59

The fluid mosaic model describes the cell membrane as a two-dimensional fluid where proteins are inserted into a lipid bilayer, allowing for lateral movement.

Question 60

How are lipid rafts characterized within the cell membrane?

Answer 60

Lipid rafts are characterized as microdomains enriched with cholesterol and sphingolipids, playing a role in cellular signaling processes.

Question 61

What are the two main types of endocytosis and their functions?

Answer 61

The two main types of endocytosis are phagocytosis (cell eating) for the ingestion of large particles, and pinocytosis (cell drinking) for the uptake of fluids or macromolecules.

Question 62

How do mitochondria contribute to cellular respiration?

Answer 62

Mitochondria are critical for cellular respiration, converting glucose and oxygen to CO2, H2O, and ATP through processes including glycolysis, the Krebs cycle, and oxidative phosphorylation.

Question 63

What is the role of the mitochondrial matrix?

Answer 63

The mitochondrial matrix contains the organelle's genetic system and enzymes required for oxidative phosphorylation.

Question 64

How are proteins imported into mitochondria and chloroplasts?

Answer 64

Proteins are imported into mitochondria and chloroplasts posttranslationally, with mitochondrial proteins having presequences and chloroplast proteins directed by transit peptides.

Question 65

What are the differences between the electron transport and ATP synthesis in chloroplasts and mitochondria?

Answer 65

In chloroplasts, electron transport occurs in the thylakoid membrane with protons pumped across from the stroma to the lumen, whereas in mitochondria, it occurs in the inner mitochondrial membrane, both generating ATP.

Question 66

What role do peroxisomes play in the cell?

Answer 66

Peroxisomes contain enzymes for metabolic reactions, including the breakdown of very long-chain fatty acids and detoxification of hydrogen peroxide.

Question 67

What are the key steps and locations within the cell for converting glucose to ATP?

Answer 67

The key steps for converting glucose to ATP include glycolysis in the cytoplasm (converting glucose to pyruvate), conversion of pyruvate to acetyl-CoA in the mitochondrial matrix, the Krebs cycle in the mitochondrial matrix, and oxidative phosphorylation in the inner mitochondrial membrane.

Question 68

What is the structure and function of the cristae within mitochondria?

Answer 68

The cristae are the numerous folds that form the inner membrane of mitochondria, increasing the surface area for oxidative phosphorylation to occur, thereby enhancing ATP production.

Question 69

How do mitochondrial genomes differ from the nuclear genome in terms of genetic code and encoded components?

Answer 69

Mitochondrial genomes use a slightly different genetic code from the “universal” genetic code and primarily encode tRNAs, rRNAs, and a small number of proteins essential for oxidative phosphorylation, with most mitochondrial proteins being encoded by the nuclear genome.

Question 70

Describe the role of the TOM and TIM complexes in mitochondrial protein import.

Answer 70

The TOM (translocase of the outer membrane) and TIM (translocase of the inner membrane) complexes facilitate the import of proteins into mitochondria, with proteins passing directly from TOM to TIM and requiring partial unfolding for translocation.

Question 71

What triggers the onset of mitochondrial diseases, and how are these diseases inherited?

Answer 71

Mitochondrial diseases often manifest when the number of affected mitochondria reaches a critical level and are uniquely inherited due to mitochondrial DNA being passed solely from the mother. The random division and duplication of mitochondrial DNA can lead to varying disease expression.

Question 72

What is the significance of chloroplasts having a double membrane and a thylakoid membrane?

Answer 72

The double membrane of chloroplasts defines their boundary and internal environment, while the thylakoid membrane, with its high surface area, is crucial for the light reactions of photosynthesis, enabling efficient light absorption and ATP synthesis.

Question 73

How do chloroplasts and mitochondria differ in their roles in ATP synthesis?

Answer 73

Chloroplasts synthesize ATP using light energy during photosynthesis with electron transport and proton pumping occurring in the thylakoid membrane, while mitochondria generate ATP through oxidative phosphorylation, utilizing the electron transport chain in the inner mitochondrial membrane.

Question 74

What are peroxisomes, and how do they contribute to cell metabolism?

Answer 74

Peroxisomes are organelles containing enzymes for metabolic reactions including fatty acid oxidation (beta-oxidation) and the decomposition of hydrogen peroxide, playing key roles in lipid metabolism and cellular detoxification.

Question 75

Describe the significance of protein targeting signals for the import of proteins into peroxisomes.

Answer 75

Proteins are selectively imported into peroxisomes using specific protein signals (PTS or peroxisomal targeting signal), which can be localized to either the C-terminus or N-terminus, guiding proteins to peroxisomes for their proper function.

Question 76

What role does the matrix processing peptidase (MPP) play in the import of mitochondrial proteins?

Answer 76

The matrix processing peptidase (MPP) cleaves presequences from proteins imported into the matrix of the mitochondria, facilitating their proper functioning within the organelle.

Question 77

How does the chloroplast's thylakoid membrane contribute to photosynthesis?

Answer 77

The thylakoid membrane houses the photosystems and electron transport chain components necessary for the light reactions of photosynthesis, enabling the creation of a proton gradient used to synthesize ATP.

Question 78

What is the role of peroxins in peroxisomes?

Answer 78

Peroxins are a group of at least 32 known proteins that participate in importing peroxisomal proteins via ATP hydrolysis and are involved in peroxisome assembly.

Question 79

Describe the significance of the chloroplast envelope.

Answer 79

The chloroplast envelope, consisting of an outer and inner membrane, segregates the chloroplast's internal environment from the cytosol, maintaining the distinct biochemical conditions necessary for photosynthesis and other chloroplast-specific functions.

Question 80

How does the electron flow through Photosystems I and II contribute to the light reactions of photosynthesis?

Answer 80

Electron flow through Photosystems I and II generates a proton gradient across the thylakoid membrane and produces NADPH (and ATP via cyclic electron flow), which are essential for the Calvin cycle in the stroma.

Question 81

Explain the process and significance of cyclic electron flow in chloroplasts.

Answer 81

Cyclic electron flow involves electrons from Photosystem I cycling back to the electron transport chain, generating additional ATP without producing NADPH, thus balancing the ATP/NADPH ratio required for the Calvin cycle.

Question 82

How does the proton gradient drive ATP synthesis in chloroplasts and mitochondria?

Answer 82

In both organelles, the energy stored in the proton gradient across a membrane (thylakoid membrane in chloroplasts, inner mitochondrial membrane in mitochondria) is used by ATP synthase to convert ADP and Pi to ATP.

Question 83

What mechanisms ensure proteins are correctly targeted to specific mitochondrial compartments?

Answer 83

Proteins destined for different mitochondrial compartments are guided by specific signal sequences and chaperone proteins that ensure they reach their correct location, such as the outer membrane, inner membrane, intermembrane space, or matrix.

Question 84

How do environmental signals influence plastid development and interconversion among plastid types?

Answer 84

Plastid development and the ability of mature plastids to switch types are controlled by both intrinsic cellular differentiation programs and external environmental cues, reflecting their adaptability to changing cellular needs and conditions.

Question 85

What metabolic processes occur in peroxisomes, and how are they related to cellular detoxification?

Answer 85

Peroxisomes are involved in beta-oxidation of very long-chain fatty acids and the detoxification of hydrogen peroxide, produced as a byproduct of fatty acid oxidation, through catalase-mediated decomposition into water and oxygen.