Cytoskeletal Element Quiz Questions

Complementary refers to the fact that the sequence of one DNA strand specifies the sequence of the other strand in the double helix. This means that the two strands are paired together in a way that the bases on one strand can only form hydrogen bonds with their complementary bases on the other strand. This complementary base pairing allows for the accurate replication of DNA during cell division and is essential for maintaining the genetic code.

Proteins are targeted to specific destinations through a combination of sorting signals located on the proteins themselves and receptors in transport vesicle walls that recognize these signals. The sorting signals on the proteins act as a molecular address, guiding the protein to its intended location within the cell. The receptors in transport vesicle walls recognize these sorting signals and facilitate the transport of the protein to the appropriate cellular compartment. Therefore, the correct answer is b and c.

The sequence of sugar addition to glycoproteins traveling through the Golgi complex is determined by the spatial arrangement of specific glycosyltransferases that come into contact with the proteins as they pass through the Golgi complex. These glycosyltransferases are responsible for adding specific sugars to the proteins in a specific order, resulting in the formation of complex sugar structures on the glycoproteins. The spatial arrangement of these enzymes ensures that the correct sugars are added in the correct sequence, leading to the proper glycosylation of the proteins.

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) is a potentially lethal situation because it disrupts normal cellular function. In response to this, the unfolded protein response (UPR) is triggered. The UPR is a cellular stress response pathway that aims to restore ER homeostasis by increasing the production of chaperone proteins, enhancing protein folding capacity, and reducing protein synthesis. It also promotes the degradation of misfolded proteins and can induce cell death if the stress cannot be resolved. Therefore, the UPR is the correct answer as it is the specific process that is triggered in response to the accumulation of misfolded proteins in the ER.

Microtubules are characterized as a hollow, rigid cylindrical tube with walls composed of tubulin subunits. They are a type of cytoskeletal element involved in various cellular processes such as cell division, intracellular transport, and maintenance of cell shape. Microfilaments, on the other hand, are made up of actin subunits and are involved in cell movement and contraction. Intermediate filaments provide structural support to the cell and are composed of various proteins. Therefore, the correct answer is microtubules.

The correct answer is a, b and c. Vesicle trafficking through the cytoplasm has been discovered to occur through the biosynthetic pathway, secretory pathway, and endocytic pathway. The biosynthetic pathway involves the transport of newly synthesized proteins and lipids from the endoplasmic reticulum to the Golgi apparatus and then to the plasma membrane. The secretory pathway involves the release of proteins and other molecules from the cell through exocytosis. The endocytic pathway involves the internalization of substances from the extracellular environment into the cell through endocytosis. The hydrolytic pathway is not a recognized pathway of vesicle trafficking.

The similarity of the heads of kinesin like proteins can be explained by their similar roles in interacting with microtubules. This suggests that the heads have evolved to perform a specific function in the cell, which requires a conserved amino acid sequence. On the other hand, the diversity in the tails reflects the variation of cargoes to which they bind. This implies that the tails have evolved to interact with different types of cargoes, leading to a greater diversity in their amino acid sequences. Overall, this explains the seeming contradiction between the similarity of the heads and the diversity of the tails in kinesin like proteins.

The correct answer suggests that the protein added to the liposome mixture is involved in the initiation of vesicle formation. This means that the protein plays a role in the process of vesicles budding from the liposomes.

Proteins that are to remain in the cytosol, peripheral proteins of the inner cell membrane surface, and proteins to be transported to the nucleus are all made on free ribosomes. Free ribosomes are ribosomes that are not attached to the endoplasmic reticulum and are responsible for synthesizing proteins that function within the cytosol or are destined for other organelles such as the nucleus. Therefore, options a, b, and d are all correct answers.

COPI-coated vesicles are responsible for moving materials in a retrograde direction from the ERGIC and Golgi stack back to the ER. This is achieved through the binding of COPI proteins to cargo molecules and the subsequent formation of COPI-coated vesicles. These vesicles then bud off from the Golgi stack and transport the cargo molecules back to the ER.

The given correct answer is incorrect. COPI-coated vesicles do indeed move materials from the Golgi to the ER, not from the Golgi to the secretory vesicle. The other statements are true: tethering proteins mediate docking between target and vesicle, COPII-coated vesicles move materials from the ER to the Golgi, and movement may be mediated by microtubules.

Microfilaments, also known as actin filaments, are described as solid, thinner structures composed of actin subunits. They form a branching network within the cell and play a crucial role in cell shape, movement, and contraction. Microtubules, on the other hand, are larger, hollow structures composed of tubulin subunits and are involved in cell division and intracellular transport. Intermediate filaments provide structural support to the cell and are made up of various proteins. Therefore, the correct answer is microfilaments.

The cisternal maturation model suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC. Each cisterna then travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses. This model proposes that the Golgi cisternae mature and transform into the next cisterna in the stack, rather than vesicles transporting cargo between the cisternae.

Protein coats select the contents of vesicles they help to form by having a specific affinity for the cytosolic tails of integral membrane receptors for cargo proteins that reside in the donor membrane. This means that the protein coats are able to recognize and bind to specific receptors on the membrane, ensuring that the correct cargo proteins are packaged into the vesicles.

Sar1 is a GTP-binding protein that plays a regulatory role in the formation and disassembly of the COPII coat. The COPII coat is responsible for vesicle formation and transport of proteins from the endoplasmic reticulum to the Golgi apparatus. Sar1 is involved in the initial step of COPII coat assembly by recruiting other proteins to the ER membrane. It functions by binding to GTP, which induces a conformational change and allows Sar1 to associate with the ER membrane. This interaction leads to the recruitment of other COPII coat proteins and the subsequent formation of transport vesicles.

In a pulse-chase procedure, radioactively labeled proteins are initially synthesized at a specific site in the cell. The pulse involves adding a labeled precursor to the cell, allowing it to be incorporated into newly synthesized proteins. The chase involves removing the labeled precursor and replacing it with an unlabeled precursor. The chase period allows for the labeled proteins to be further distributed within the cell. Therefore, if the chase is longer, the labeled proteins will have more time to move away from the synthesis site, resulting in them being farther from the synthesis site.

The ER is well-suited and ideally constructed for its role as a port of entry for secretory proteins because it has a large surface area allowing the attachment of many ribosomes, which are responsible for protein synthesis. Additionally, the ER cisternae lumen provides an environment that favors the folding and disassembly of proteins. Furthermore, the RER segregates secretory, lysosomal, and plant-cell vacuolar proteins from other newly made proteins, allowing their modification, and sends them to their destination. Therefore, all of these factors make the ER highly efficient in processing and transporting secretory proteins.

Pinocytosis refers to the process of the uptake of fluid, dissolved solutes, and suspended macromolecules by cells. It involves the formation of small vesicles at the cell membrane, which then engulf and internalize the extracellular material. This process is non-specific, meaning it can take up a variety of substances from the surrounding environment. Unlike phagocytosis, which involves the engulfment of solid particles, pinocytosis primarily focuses on the uptake of fluids and dissolved substances. Autophagy refers to the degradation of a cell's own components, while exocytosis involves the release of substances from the cell.

The signal recognition particle (SRP) and its components, RNA and protein, recognize the signal sequence as it exits the ribosomes. The SRP is a ribonucleoprotein complex composed of both RNA and protein subunits. Together, they form a complex that binds to the signal sequence of newly synthesized proteins. This binding helps to target the protein to the endoplasmic reticulum, where it can be properly folded and processed. Therefore, the correct answer is SRP and its components, RNA and protein.

When the rate of loss of actin subunits from the pointed end of an actin filament is balanced by the rate of their addition to the barbed end, the filaments are said to be in a steady state. In this state, the length of the filaments remains the same, and treadmilling occurs. Treadmilling refers to the simultaneous addition of subunits at one end of the filament and the loss of subunits at the other end, resulting in no net change in filament length. Therefore, all options a, b, and c are correct.

The asymmetry of the phospholipid bilayers is initially established in the ER during lipid and protein synthesis. During this process, specific enzymes and proteins are involved in the selective incorporation of different phospholipids into the inner and outer leaflets of the bilayer. This results in the establishment of an asymmetric distribution of phospholipids, with different compositions and functions on each side of the bilayer.

not-available-via-ai

Dynamin is a GTP-binding protein that plays a crucial role in the release of clathrin-coated vesicles from the membrane. It functions by constricting and pinching off the vesicle from the membrane, allowing it to be transported to its destination within the cell. The other options, AP2, GGA, Clathrin, and Opscrin, are not directly involved in the release of clathrin-coated vesicles and do not possess GTP-binding activity.

The proposed role of the Rabs in recruiting cytosolic tethering proteins to specific membrane surfaces is supported by several pieces of circumstantial evidence. Firstly, the fact that there are over 60 Rab genes identified in humans suggests that Rabs play a significant role in membrane trafficking, making them potential candidates for recruiting tethering proteins. Additionally, Rabs have the ability to give each cell compartment a unique surface identity, indicating their involvement in recruiting specific proteins. Moreover, different Rabs have been associated with different membrane compartments, further supporting their role in recruiting tethering proteins to specific surfaces. Lastly, the preferential localization of Rabs would enable them to recruit the various proteins involved in targeting specificity.

Microtubules grow out of a centrosome in a polarized manner, with one end known as the plus end and the other end known as the minus end. The plus end is associated with the centrosome and contains beta-tubulin at the tip, while the minus end does not. Therefore, both option a (the plus end) and option d (the end with alpha-tubulin at the tip) are correct.

Rabs are GTP-binding proteins that play a crucial role in targeting vesicles to the appropriate compartments within the cell. They act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state. By interacting with specific effector proteins, Rabs help to tether and fuse vesicles to the correct target membrane, ensuring accurate delivery of cargo. Thus, the presence of Rabs facilitates the targeting of vesicles to their appropriate compartments, making them the correct answer in this context.

Chargaff's rules of bases state that the amount of G (guanine) is equal to the amount of C (cytosine), the amount of purines (G and A) is equal to the amount of pyrimidines (C and T), the sum of the percentages of C and T is equal to the sum of the percentages of A and G, and the amount of A (adenine) is equal to the amount of T (thymine). Therefore, all of the given statements are components of Chargaff's rules of bases.

Proteins that normally reside in the ER lumen or membrane have short amino acid sequences at their C-terminus that serve as retrieval sequences. These retrieval sequences help in retrieving the escaped proteins and directing them back to the ER.

Receptor down-regulation refers to the process in which receptors for hormones or growth factors are destroyed during endocytosis, resulting in a decrease in the cell's sensitivity to further stimulation by that specific hormone or growth factor. This mechanism allows cells to regulate their ability to respond to extracellular messengers.

Keratin is often a component of intermediate filaments. Intermediate filaments are a type of cytoskeletal protein that provide structural support to cells. Keratin is a fibrous protein that is found in the skin, hair, and nails of animals, including humans. It forms intermediate filaments in epithelial cells, which help to maintain the integrity and strength of these tissues. Therefore, keratin is the correct answer as it is commonly associated with intermediate filaments.

The correct answer is "a and c" because the slow growing end of a microtubule is the minus end, which is also the end with alpha-tubulin at the tip. This is because microtubules are polar structures with distinct plus and minus ends, and the minus end is known to grow at a slower rate compared to the plus end. Additionally, alpha-tubulin is found at the minus end of the microtubule, while beta-tubulin is found at the plus end. Therefore, both options "a" and "c" correctly identify the slow growing end of a microtubule.

The answer is c and d because both the 3'-carbon and the 5'-carbon of the sugar in a nucleotide participate in the formation of the phosphodiester bond. The 3'-carbon forms a bond with the phosphate group of the next nucleotide, while the 5'-carbon forms a bond with the phosphate group of the previous nucleotide, creating a chain of nucleotides in DNA or RNA.

Early endosomes serve as a sorting station that directs different types of receptors and ligands along different pathways. They receive cargo from the plasma membrane through the process of endocytosis and then sort and direct this cargo to different destinations within the cell. This sorting process helps regulate the cellular trafficking of receptors and ligands, ensuring that they are transported to the appropriate locations for further processing or degradation. Late endosomes and lysosomes are involved in later stages of the endocytic pathway, while medial endosomes and medial lysosomes are not commonly recognized components of the endocytic pathway.

In the current model for the nucleation of microtubules, a helical array of y-tubulin subunits forms a template in the shape of an open, nng structure. This template allows the first row of alphabeta-tubulin dimers to assemble. The model suggests that only the alpha-tubulin of a heterodimer can bind to the ring of y-subunits, which explains the polarity of microtubules. This means that the alpha-tubulin subunit is oriented towards the minus end of the microtubule, while the beta-tubulin subunit is oriented towards the plus end. Thus, the model accounts for the polarity of microtubules by specifying which tubulin subunit can bind to the y-subunit ring.

After Sar1 binds to GTP, it binds to the cytosolic leaflet of the ER membrane. This is because Sar1 is a small GTPase protein involved in vesicle trafficking between the endoplasmic reticulum (ER) and the Golgi apparatus. It functions as a molecular switch, where it is activated by binding to GTP and then recruits coat proteins to form transport vesicles. The cytosolic leaflet of the ER membrane is the site where Sar1 binds to initiate the formation of these transport vesicles.

The building blocks of a nucleoside are a pentose sugar and a nitrogenous base. Nucleosides are composed of a five-carbon sugar molecule (pentose sugar) and a nitrogen-containing base. These two components are linked together to form the nucleoside structure. The phosphate group is not a part of the nucleoside structure, but it is present in the nucleotide, which is formed when a phosphate group is attached to the nucleoside. An amino acid is not involved in the structure of a nucleoside.

Kinesin movement along a microtubule is said to be processive, meaning that it can move long distances along an individual microtubule without falling off. This indicates that kinesin molecules are able to maintain a stable attachment to the microtubule and continue their movement in a coordinated and efficient manner. This processive movement is crucial for kinesin's role in transporting cargo within cells.

When the neck and stalk of a minus-directed kinesin are joined to the head of a plus-directed kinesin, the resulting hybrid motor protein will have a minus-directed component. This means that the protein will move in the opposite direction of the normal plus-directed kinesin, which is towards the minus end of the microtubule. Therefore, the hybrid motor protein will travel in a retrograde direction along the microtubule.

Inner peripheral membrane proteins are not made on the membrane-bound ribosomes of the RER. The RER is responsible for synthesizing proteins that are either secreted or membrane-bound. Inner peripheral membrane proteins are proteins that are associated with the inner leaflet of the plasma membrane but are not embedded within it. These proteins are typically synthesized by free ribosomes in the cytoplasm and then targeted to the plasma membrane. Therefore, inner peripheral membrane proteins are not made on the membrane-bound ribosomes of the RER.

By mixing a S strain (which does not have the ability to cause disease) with R cells (which do have the ability to cause disease), one can demonstrate transformation in bacteria. This is because the S strain contains the transforming substance, which is DNA, that can be transferred to the R cells, causing them to acquire the ability to cause disease. This experiment would replicate the same principle that Avery, MacLeod, and McCarty demonstrated in their experiment, further supporting the idea that DNA is the molecule of heredity.

Avery, MacLeod, and McCarty concluded that DNA was the transformation principle reported by Griffith and others because when exposed to various enzymes, the transforming principle was only inactivated by DNAse. This suggests that the transforming principle is a substance that shares chemical properties with DNA, as DNAse specifically targets and breaks down DNA. This finding supports the idea that DNA is responsible for the transformation observed in Griffith's experiment.

The small subfamily of kinesins that is incapable of movement is believed to encourage depolymerization. This means that they promote the breakdown of microtubules, which are important structures within cells. By encouraging depolymerization, these kinesins play a role in regulating the dynamics and stability of microtubules.

Non-muscle myosins are a type of motor proteins that are involved in vesicular transport, along with microtubule motor proteins. These proteins are responsible for moving vesicles and other cellular cargo along the actin cytoskeleton. They generate force by interacting with actin filaments, enabling the transport of vesicles to their intended destinations within the cell.

not-available-via-ai