MCAT Biology › Proteins
Which of the following is not an example of positive feedback?
As blood calcium levels increase, parathyroid hormone (PTH) is reduced.
As more buffalo begin to run in a herd, the overall level of panic increases. This results in even more buffalo running.
A forest fire slowly expands outward, which provides it with even more fuel to burn.
During childbirth, oxytocin creates a stimulus which causes the hypothalamus to release more oxytocin.
Negative feedback provides the body with a method for shutting down a reaction once sufficient product has been created. Parathyroid hormone (PTH) is responsible for increasing blood calcium levels, but once the level is sufficient, the parathyroid glands detect the sufficient calcium level and no longer produce PTH. PTH works in coordination with calcitonin to maintain this balance via its negative feedback loop.
Positive feedback, in contrast, involves the exponential increase of a reaction upon detection. Very few examples of positive feedback exist in the body, though oxytocin follows this model during childbirth.
A peptide bond is formed between __________.
a carboxyl group and an amino group
two amino groups
two carboxyl groups
two aromatic groups
an ester group and an amine group
Each amino acid has an N and a C terminus. The N terminus contains an amino group and the C terminus contains a carboxylic acid group. In order to make a peptide linkage (and eventually create a polypeptide), a bond must form between the amino and carboxylic groups, with water as a byproduct.
A peptide bond is formed between __________.
a carboxyl group and an amino group
two amino groups
two carboxyl groups
two aromatic groups
an ester group and an amine group
Each amino acid has an N and a C terminus. The N terminus contains an amino group and the C terminus contains a carboxylic acid group. In order to make a peptide linkage (and eventually create a polypeptide), a bond must form between the amino and carboxylic groups, with water as a byproduct.
Which of the following statements is NOT true regarding the comparison of the alpha-helix structure to the beta-sheet structure in proteins?
Each is stabilized by inter-chain hydrogen bonds
All possible hydrogen bonds between the peptide carbonyl oxygen (C=O) and the amide hydrogen (N-H) are formed in each
The peptide bond in each is planar and trans
Each may occur in typical globular proteins
Each is an example of secondary structure
Alpha-helices and beta-sheets are secondary structure motifs that occur when sequences of amino acids are linked by hydrogen bonds. These secondary structures are an integral part of globular proteins, such as hemoglobin. Alpha-helices resemble a coiled spring, with hydrogen bonding occurring in an intra-chain arrangement between carbonyl oxygens and amide hydrogens that is parallel to the central axis. Beta sheets, on the other hand, may have either inter- or intra-chain hydrogen bonding between carbonyl oxygens and amide hydrogens. Thus, the correct answer (and false statement) is that each is stabilized by interchain hydrogen bonds.
Which of the following is not an example of positive feedback?
As blood calcium levels increase, parathyroid hormone (PTH) is reduced.
As more buffalo begin to run in a herd, the overall level of panic increases. This results in even more buffalo running.
A forest fire slowly expands outward, which provides it with even more fuel to burn.
During childbirth, oxytocin creates a stimulus which causes the hypothalamus to release more oxytocin.
Negative feedback provides the body with a method for shutting down a reaction once sufficient product has been created. Parathyroid hormone (PTH) is responsible for increasing blood calcium levels, but once the level is sufficient, the parathyroid glands detect the sufficient calcium level and no longer produce PTH. PTH works in coordination with calcitonin to maintain this balance via its negative feedback loop.
Positive feedback, in contrast, involves the exponential increase of a reaction upon detection. Very few examples of positive feedback exist in the body, though oxytocin follows this model during childbirth.
Which of the following statements is NOT true regarding the comparison of the alpha-helix structure to the beta-sheet structure in proteins?
Each is stabilized by inter-chain hydrogen bonds
All possible hydrogen bonds between the peptide carbonyl oxygen (C=O) and the amide hydrogen (N-H) are formed in each
The peptide bond in each is planar and trans
Each may occur in typical globular proteins
Each is an example of secondary structure
Alpha-helices and beta-sheets are secondary structure motifs that occur when sequences of amino acids are linked by hydrogen bonds. These secondary structures are an integral part of globular proteins, such as hemoglobin. Alpha-helices resemble a coiled spring, with hydrogen bonding occurring in an intra-chain arrangement between carbonyl oxygens and amide hydrogens that is parallel to the central axis. Beta sheets, on the other hand, may have either inter- or intra-chain hydrogen bonding between carbonyl oxygens and amide hydrogens. Thus, the correct answer (and false statement) is that each is stabilized by interchain hydrogen bonds.
Nuclear transport is a very important concept of study in modern cellular biology. Transport of proteins into the nucleus of an organism requires energy in the form of GTP, which is attached to a protein called Ras-related Nuclear protein (RAN).
RAN is a monomeric G protein found in both the cytosol as well as the nucleus and its phosphorylation state plays an important role in the movement of proteins into and out of the nucleus. Specifically, RAN-GTP and RAN-GDP binds to nuclear import and export receptors and carries them into or out of the nucleus. They also play a role in dropping off cargo that import and export receptors hold onto. RAN's functions are controlled by two other proteins: RAN guanine exchange factor (RAN-GEF) and RAN GTPase activating protein (GAP). RAN-GEF binds a GTP onto RAN, while RAN-GAP hydrolyzes GTP into GDP. As a result, there is a RAN-GTP and RAN-GDP concentration gradient that forms between the cytosol and nucleus.
One of the main roles of RAN is to bind to nuclear import and export receptors and carry them into or out of the nucleus. Given that import and export receptors are proteins, what can we say about the cooperativity displayed by RAN when it comes to binding to import and export proteins?
No cooperativity
Positive cooperativity
Negative cooperativity
Both negative and positive cooperativity
There is not enough information to determine what type of cooperativity exists
Binding cooperativity occurs when binding of one substrate increases or decreases the affinity for the other substrates. For cooperativity to work, the protein in question must have multiple subunits, therefore being at least a dimer. RAN is a monomer, and therefore cannot show any cooperativity.
Nuclear transport is a very important concept of study in modern cellular biology. Transport of proteins into the nucleus of an organism requires energy in the form of GTP, which is attached to a protein called Ras-related Nuclear protein (RAN).
RAN is a monomeric G protein found in both the cytosol as well as the nucleus and its phosphorylation state plays an important role in the movement of proteins into and out of the nucleus. Specifically, RAN-GTP and RAN-GDP binds to nuclear import and export receptors and carries them into or out of the nucleus. They also play a role in dropping off cargo that import and export receptors hold onto. RAN's functions are controlled by two other proteins: RAN guanine exchange factor (RAN-GEF) and RAN GTPase activating protein (GAP). RAN-GEF binds a GTP onto RAN, while RAN-GAP hydrolyzes GTP into GDP. As a result, there is a RAN-GTP and RAN-GDP concentration gradient that forms between the cytosol and nucleus.
One of the main roles of RAN is to bind to nuclear import and export receptors and carry them into or out of the nucleus. Given that import and export receptors are proteins, what can we say about the cooperativity displayed by RAN when it comes to binding to import and export proteins?
No cooperativity
Positive cooperativity
Negative cooperativity
Both negative and positive cooperativity
There is not enough information to determine what type of cooperativity exists
Binding cooperativity occurs when binding of one substrate increases or decreases the affinity for the other substrates. For cooperativity to work, the protein in question must have multiple subunits, therefore being at least a dimer. RAN is a monomer, and therefore cannot show any cooperativity.
Collagen, the most abundant protein in the body, is an example of what type of protein?
Structural
Globular
Integral
Peripheral
Collagen is a structural protein that adds significant strength and resilience to the skin, tendons, and ligaments. Structural proteins, including collagen, also fall under the category of fibrous proteins. Globular proteins, in contrast, usually act as enzymes in the body or transport channels in the membrane.
Peripheral proteins are a type of globular protein found adjacent to the membrane, while integral proteins are transmembrane globular proteins.
Collagen, the most abundant protein in the body, is an example of what type of protein?
Structural
Globular
Integral
Peripheral
Collagen is a structural protein that adds significant strength and resilience to the skin, tendons, and ligaments. Structural proteins, including collagen, also fall under the category of fibrous proteins. Globular proteins, in contrast, usually act as enzymes in the body or transport channels in the membrane.
Peripheral proteins are a type of globular protein found adjacent to the membrane, while integral proteins are transmembrane globular proteins.