Ribosomes and Cytoskeleton - MCAT Biological and Biochemical Foundations of Living Systems
Card 1 of 176
Primary ciliary dyskinesia (PCD) is a rare genetic lung disorder, also known as immotile cilia syndrome, and is associated with Kartegener's Syndrome. For people with PCD, the tiny hair-like structures (cilia) in the respiratory tract become non-motile.
What is the most likely clinical manifestation of this disease?
Primary ciliary dyskinesia (PCD) is a rare genetic lung disorder, also known as immotile cilia syndrome, and is associated with Kartegener's Syndrome. For people with PCD, the tiny hair-like structures (cilia) in the respiratory tract become non-motile.
What is the most likely clinical manifestation of this disease?
Tap to reveal answer
Mucus begins to accumulate in the lungs because the cilia no longer move. Cilia function in pushing mucus up the respiratory tract so that it doesn't build up in the lungs. When they become non-motile, they lose this capability.
Mucus begins to accumulate in the lungs because the cilia no longer move. Cilia function in pushing mucus up the respiratory tract so that it doesn't build up in the lungs. When they become non-motile, they lose this capability.
← Didn't Know|Knew It →
What happens at the minus-end of actin filaments when the concentration of G-actin is above its critical concentration?
What happens at the minus-end of actin filaments when the concentration of G-actin is above its critical concentration?
Tap to reveal answer
Monomers are lost when concentration of G-actin is below its critical concentration. Monomers are gained when concentration of G-actin is above its critical concentration. If it is in between the critical concentrations, the actin filaments will undergo treadmilling, which is the addition of monomers on the (+) end and loss of monomers on the (–) end.
Monomers are lost when concentration of G-actin is below its critical concentration. Monomers are gained when concentration of G-actin is above its critical concentration. If it is in between the critical concentrations, the actin filaments will undergo treadmilling, which is the addition of monomers on the (+) end and loss of monomers on the (–) end.
← Didn't Know|Knew It →
Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
During mitosis and meiosis chromosomes are separated from homologous pairs at the metaphase plate. A disorder in which of the following proteins could be expected to produce an aberration in cell division?
Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
During mitosis and meiosis chromosomes are separated from homologous pairs at the metaphase plate. A disorder in which of the following proteins could be expected to produce an aberration in cell division?
Tap to reveal answer
Cell division and the corresponding separation of chromosomes occurs via the spindle apparatus, made of microtubules. Therefore, tubulin abnormalities can lead to abnormalities of division. Myosin is a tempting choice because myosin is involved in movement, but only in muscle tissue. Chromosomes do move during cell division, but without myosin involvement, and instead over tubulin pathways.
Cell division and the corresponding separation of chromosomes occurs via the spindle apparatus, made of microtubules. Therefore, tubulin abnormalities can lead to abnormalities of division. Myosin is a tempting choice because myosin is involved in movement, but only in muscle tissue. Chromosomes do move during cell division, but without myosin involvement, and instead over tubulin pathways.
← Didn't Know|Knew It →
Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.
The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.
Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.
A scientist discovers that Neisseria uses flagella to move between host cells. Which of the following is true of the flagella?
Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.
The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.
Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.
A scientist discovers that Neisseria uses flagella to move between host cells. Which of the following is true of the flagella?
Tap to reveal answer
Flagella and cilia share a 9+2 ultrastructure, where there is a ring of 9 doublets of microtubules surrounding a central doublet, and connects via dynein arms.
Flagella and cilia share a 9+2 ultrastructure, where there is a ring of 9 doublets of microtubules surrounding a central doublet, and connects via dynein arms.
← Didn't Know|Knew It →
Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.
In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.
Phagocytosis of the sort that was involved in endosymbiosis makes use of microtubules to orient the cell appropriately. Which of the following processes also directly uses microtubules?
Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.
In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.
Phagocytosis of the sort that was involved in endosymbiosis makes use of microtubules to orient the cell appropriately. Which of the following processes also directly uses microtubules?
Tap to reveal answer
Mitosis makes use of microtubules to organize and move DNA into appropriate daughter cells. These specific structures are known as mitotic spindles.
The other processes are closely linked to protein, enzyme, or ribosome function and do not involve microtubules.
Mitosis makes use of microtubules to organize and move DNA into appropriate daughter cells. These specific structures are known as mitotic spindles.
The other processes are closely linked to protein, enzyme, or ribosome function and do not involve microtubules.
← Didn't Know|Knew It →
Which of the following is true of microtubules?
Which of the following is true of microtubules?
Tap to reveal answer
Microtubules are a component of the cell cytoskeleton formed by polymers of tubulin protein. They are larger than microfilaments and make up the internal structures of cilia and flagella. Microtubules have a positive and negative end. The negative end of a microtubule attaches to a microtubule-organizing center (MTOC) within the cell, which then allows the microtubule to grow away from the MTOC at its positive end.
Microtubules are a component of the cell cytoskeleton formed by polymers of tubulin protein. They are larger than microfilaments and make up the internal structures of cilia and flagella. Microtubules have a positive and negative end. The negative end of a microtubule attaches to a microtubule-organizing center (MTOC) within the cell, which then allows the microtubule to grow away from the MTOC at its positive end.
← Didn't Know|Knew It →
Actin is the major protein that composes which part of the cytoskeleton?
Actin is the major protein that composes which part of the cytoskeleton?
Tap to reveal answer
The cytoskeleton is important for cell support and movement. It is composed of microfilaments made of actin, microtubules made of tubulin, intermediate filaments that bear tension, and cilia/flagella which are made of microtubules (tubulin).
The cytoskeleton is important for cell support and movement. It is composed of microfilaments made of actin, microtubules made of tubulin, intermediate filaments that bear tension, and cilia/flagella which are made of microtubules (tubulin).
← Didn't Know|Knew It →
The cytoskeleton acts as a scaffold for the cell and maintains cellular integrity. Which of the following is a component of the cytoskeleton?
The cytoskeleton acts as a scaffold for the cell and maintains cellular integrity. Which of the following is a component of the cytoskeleton?
Tap to reveal answer
The cytoskeleton is comprised of actin filaments, intermediate filaments, and microtubules.
Spindle complexes are found within cells undergoing mitosis; they are made of microtubules, but are not a fundamental part of the cytoskeleton. Cilia and flagella are also largely composed of microtubules; however, these structures are also not fundamental components of the cytoskeleton. Myosin filaments work in coordination with actin filaments during muscle contraction, but are not involved in the cytoskeleton.
The cytoskeleton is comprised of actin filaments, intermediate filaments, and microtubules.
Spindle complexes are found within cells undergoing mitosis; they are made of microtubules, but are not a fundamental part of the cytoskeleton. Cilia and flagella are also largely composed of microtubules; however, these structures are also not fundamental components of the cytoskeleton. Myosin filaments work in coordination with actin filaments during muscle contraction, but are not involved in the cytoskeleton.
← Didn't Know|Knew It →
Which of the following is not a function of microtubules?
Which of the following is not a function of microtubules?
Tap to reveal answer
Microtubules are made of the tubulin protein and play integral roles in cell structure. They are prominent in the cytoskeleton and form the fundamental structures for cilia and flagella. The mitotic spindles are also comprised of microtubules, and are used to draw apart the sister chromatids of each chromosome during cell division.
Microtubules do not play a significant role in the structure or function of sarcomeres. Actin and myosin compose the main functional basis of the sarcomere, while titin and the Z disc proteins provide the sarcomere structure.
Microtubules are made of the tubulin protein and play integral roles in cell structure. They are prominent in the cytoskeleton and form the fundamental structures for cilia and flagella. The mitotic spindles are also comprised of microtubules, and are used to draw apart the sister chromatids of each chromosome during cell division.
Microtubules do not play a significant role in the structure or function of sarcomeres. Actin and myosin compose the main functional basis of the sarcomere, while titin and the Z disc proteins provide the sarcomere structure.
← Didn't Know|Knew It →
Which of the following structures is not composed of microtubules?
Which of the following structures is not composed of microtubules?
Tap to reveal answer
While eukaryotic flagella are composed of microtubules, prokaryotic flagella are composed of a long protein called flagellin. Microtubules are composed of the tubulin protein, and play keys roles in mitosis and cell motility. Cilia and spindle fibers are both composed of microtubules. Prokaryotes do not contain developed microtubules.
While eukaryotic flagella are composed of microtubules, prokaryotic flagella are composed of a long protein called flagellin. Microtubules are composed of the tubulin protein, and play keys roles in mitosis and cell motility. Cilia and spindle fibers are both composed of microtubules. Prokaryotes do not contain developed microtubules.
← Didn't Know|Knew It →
Which of the following is true about microtubules?
Which of the following is true about microtubules?
Tap to reveal answer
Microtubules are found in various structures that promote cell motility. The axoneme is the name given to the cytoskeletal core that makes up whip-like appendages in eukaryotic cells. Axonemes display a "9+2" organization of microtubules.
Microtubules are also important in vesicle trafficking and utilize motor proteins like dynein and kinesin to accomplish this. Actin filaments use the motor protein myosin. The GDP/GTP gradient helps control microtubule treadmilling, while the ADP/ATP gradient helps control actin treadmilling. The contractile ring formed during cytokinesis consists of actin and myosin rather than microtubules.
Microtubules are found in various structures that promote cell motility. The axoneme is the name given to the cytoskeletal core that makes up whip-like appendages in eukaryotic cells. Axonemes display a "9+2" organization of microtubules.
Microtubules are also important in vesicle trafficking and utilize motor proteins like dynein and kinesin to accomplish this. Actin filaments use the motor protein myosin. The GDP/GTP gradient helps control microtubule treadmilling, while the ADP/ATP gradient helps control actin treadmilling. The contractile ring formed during cytokinesis consists of actin and myosin rather than microtubules.
← Didn't Know|Knew It →
Desmosomes are specialized cell junctions that anchor cells to one another by connecting the of the cytoskeleton to transmembrane proteins known as .
Desmosomes are specialized cell junctions that anchor cells to one another by connecting the of the cytoskeleton to transmembrane proteins known as .
Tap to reveal answer
Desmosomes are specialized cell junctions that are important in anchoring certain cell types to one another. Intermediate filaments are used to stabilize these connections by interacting with cadherins. Cadherins are transmembrane proteins that interact with cadherins of adjacent cells on the exoplasmic face of the plasma membrane. Adherens junctions have similar function,s but make use of actin and integrins/cadherins.
Desmosomes are specialized cell junctions that are important in anchoring certain cell types to one another. Intermediate filaments are used to stabilize these connections by interacting with cadherins. Cadherins are transmembrane proteins that interact with cadherins of adjacent cells on the exoplasmic face of the plasma membrane. Adherens junctions have similar function,s but make use of actin and integrins/cadherins.
← Didn't Know|Knew It →
Which of the following choices describes a function of the eukaryotic centriole?
Which of the following choices describes a function of the eukaryotic centriole?
Tap to reveal answer
Centrioles have diverse functions. Particularly, they are important portions of centrosomes and help develop the mitotic spindle that aids in the separation of chromosomes during cell division.
Peroxisomes are responsible for the catabolism of very long chain fatty acids. Lysosomes are responsible for handling pathogens in the cytosol in a process called phagocytosis. The pathogens are then digested by hydrolytic enzymes in the lysosome interior. Chromosome condensation is accomplished by various proteins.
Centrioles have diverse functions. Particularly, they are important portions of centrosomes and help develop the mitotic spindle that aids in the separation of chromosomes during cell division.
Peroxisomes are responsible for the catabolism of very long chain fatty acids. Lysosomes are responsible for handling pathogens in the cytosol in a process called phagocytosis. The pathogens are then digested by hydrolytic enzymes in the lysosome interior. Chromosome condensation is accomplished by various proteins.
← Didn't Know|Knew It →
Which of the following accurately represents the compositions of eukaryotic cilia and flagella?
Which of the following accurately represents the compositions of eukaryotic cilia and flagella?
Tap to reveal answer
Eukaryotic cilia and flagella are incredibly similar in protein composition. Their primary functions include helping cells move and maintaining fluid flow within the body. They accomplish this by maintaining a structure of 9 microtubule doublets surrounding 2 microtubule singlets (9+2). The motor protein dynein is then responsible for allowing the sliding of filaments that is necessary for movement.
Eukaryotic cilia and flagella are incredibly similar in protein composition. Their primary functions include helping cells move and maintaining fluid flow within the body. They accomplish this by maintaining a structure of 9 microtubule doublets surrounding 2 microtubule singlets (9+2). The motor protein dynein is then responsible for allowing the sliding of filaments that is necessary for movement.
← Didn't Know|Knew It →
In which of the following structures do actin microfilaments play a crucial role?
I. Contractile ring formed during cytokinesis
II. Sarcomeres
III. Adherens junctions
IV. Eukaryotic flagella
In which of the following structures do actin microfilaments play a crucial role?
I. Contractile ring formed during cytokinesis
II. Sarcomeres
III. Adherens junctions
IV. Eukaryotic flagella
Tap to reveal answer
Eukaryotic flagella are primarily made up of microtubule doublets and singlets organized in a "9+2" manner (two singlets surrounded by nine doublets). Actin microfilaments are not present in flagella.
The contractile ring formed during cytokinesis consists of actin and myosin, and helps separate the two daughter cells to conclude mitosis. Sarcomeres consist of actin and myosin overlaps that are crucial to muscle contraction. Adherens junctions are specialized cell junctions that use the actin cytoskeleton to anchor adjacent cells.
Eukaryotic flagella are primarily made up of microtubule doublets and singlets organized in a "9+2" manner (two singlets surrounded by nine doublets). Actin microfilaments are not present in flagella.
The contractile ring formed during cytokinesis consists of actin and myosin, and helps separate the two daughter cells to conclude mitosis. Sarcomeres consist of actin and myosin overlaps that are crucial to muscle contraction. Adherens junctions are specialized cell junctions that use the actin cytoskeleton to anchor adjacent cells.
← Didn't Know|Knew It →
Which of the following statements is true about intermediate filaments?
I. Intermediate filaments display treadmilling
II. Intermediate filaments maintain a tightly regulated gradient of ADP/ATP bound monomers
III. Intermediate filaments play a crucial role in the function of desmosomes
IV. Intermediate filaments are a major component of the mitotic spindle
Which of the following statements is true about intermediate filaments?
I. Intermediate filaments display treadmilling
II. Intermediate filaments maintain a tightly regulated gradient of ADP/ATP bound monomers
III. Intermediate filaments play a crucial role in the function of desmosomes
IV. Intermediate filaments are a major component of the mitotic spindle
Tap to reveal answer
Intermediate filaments are a component of the cytoskeleton that do not display treadmilling. Both actin microfilaments and microtubules undergo treadmilling, during which the structure is built on one end and deconstructed at the other. The result is an apparently "moving" structure with a forward and reverse end. Intermediate filaments are nor polarized and have no distinct ends, making them incapable of this action.
Actin microfilaments and microtubules also maintain gradients of ADP/ATP or GDP/GTP bound monomers respectively, used to indicate their polarity, while intermediate filaments do not. The mitotic spindle is made of microtubules.
Desmosomes, however, are specialized cell junctions that use the intermediate filament cytoskeleton to anchor adjacent cells. Membrane proteins called cadherins bind to the filaments on the intracellular surface of the membrane and bind to the extracellular regions of membrane proteins on the adjacent cell. The result is two intermediate filaments, linked by the bound proteins, to form a junction.
Intermediate filaments are a component of the cytoskeleton that do not display treadmilling. Both actin microfilaments and microtubules undergo treadmilling, during which the structure is built on one end and deconstructed at the other. The result is an apparently "moving" structure with a forward and reverse end. Intermediate filaments are nor polarized and have no distinct ends, making them incapable of this action.
Actin microfilaments and microtubules also maintain gradients of ADP/ATP or GDP/GTP bound monomers respectively, used to indicate their polarity, while intermediate filaments do not. The mitotic spindle is made of microtubules.
Desmosomes, however, are specialized cell junctions that use the intermediate filament cytoskeleton to anchor adjacent cells. Membrane proteins called cadherins bind to the filaments on the intracellular surface of the membrane and bind to the extracellular regions of membrane proteins on the adjacent cell. The result is two intermediate filaments, linked by the bound proteins, to form a junction.
← Didn't Know|Knew It →
Which of the following structures that promote cell motility generates motion by sliding actin microfilaments?
Which of the following structures that promote cell motility generates motion by sliding actin microfilaments?
Tap to reveal answer
The only choice that consists of actin microfilaments is microvilli. These motile structures are composed of cross-linked actin microfilaments. Cilia and flagella are composed of a "9+2" organization of microtubule doublets and singlets (nine doublets surrounding two singlets).
The only choice that consists of actin microfilaments is microvilli. These motile structures are composed of cross-linked actin microfilaments. Cilia and flagella are composed of a "9+2" organization of microtubule doublets and singlets (nine doublets surrounding two singlets).
← Didn't Know|Knew It →
Arp2/3 is a protein complex that helps nucleate branch points on chains.
Arp2/3 is a protein complex that helps nucleate branch points on chains.
Tap to reveal answer
Arp2/3 is a large protein complex that is specifically responsible for aiding in the organization of the actin microfilament cytoskeleton. In particular, it helps nucleate branch points from already formed actin microfilaments. Arp2/3 is not involved in the branching of microtubules, intermediate filaments, or glycogen.
Arp2/3 is a large protein complex that is specifically responsible for aiding in the organization of the actin microfilament cytoskeleton. In particular, it helps nucleate branch points from already formed actin microfilaments. Arp2/3 is not involved in the branching of microtubules, intermediate filaments, or glycogen.
← Didn't Know|Knew It →
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Which statement is true of microtubules and actin?
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Which statement is true of microtubules and actin?
Tap to reveal answer
Microtubules are composed of the protein tubulin, a GTP-binding protein, which forms a ring around a hollow center. This is in contrast to actin, a protein that forms microfilaments, which are thinner than a tubulin-based microtubule.
Microtubules are composed of the protein tubulin, a GTP-binding protein, which forms a ring around a hollow center. This is in contrast to actin, a protein that forms microfilaments, which are thinner than a tubulin-based microtubule.
← Didn't Know|Knew It →
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Microtubules involved in the vesicular transport model are similar to microtubules that are involved during mitosis. Which of the following phases of mitosis is likely to involve chromosomes moving the greatest distance along microtubules?
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Microtubules involved in the vesicular transport model are similar to microtubules that are involved during mitosis. Which of the following phases of mitosis is likely to involve chromosomes moving the greatest distance along microtubules?
Tap to reveal answer
Microtubules form the basis of the spindle fiber structures responsible for separating sister chromatids during mitosis. These fibers attach to chromosomes at the centromere by binding to the kinetochore during metaphase. During anaphase, the microtubules retract, pulling apart the sister chromatids and sequestering them in opposite ends of the cell. As a result, anaphase is likely to be the phase during which movement along microtubules is greatest.
Microtubules form the basis of the spindle fiber structures responsible for separating sister chromatids during mitosis. These fibers attach to chromosomes at the centromere by binding to the kinetochore during metaphase. During anaphase, the microtubules retract, pulling apart the sister chromatids and sequestering them in opposite ends of the cell. As a result, anaphase is likely to be the phase during which movement along microtubules is greatest.
← Didn't Know|Knew It →