All Biochemistry Resources
Example Questions
Example Question #11 : Identification By Function
Which of these amino acids is unlike the others?
S, A, T, Q, N
T
N
S
A
Q
A
Alanine (A) is the only hydrophobic amino acid in the group.
Serine (S), threonine (T), glutamine (Q), and asparagine (N) have polar, uncharged R groups.
Example Question #4 : Identifying Specific Protein Functions
Which of the following statements best describes low-density lipoproteins as compared to other lipoproteins?
They have the highest content of cholesterol and cholesterol esters
They have a higher content of triglycerides than very low-density lipoproteins
They have the highest protein content
They have the most triglycerides and least protein
They have the highest content of cholesterol and cholesterol esters
Low-density lipoproteins have the highest content of cholesterol and cholesterol esters. There are essentially five classes of blood lipoproteins: chylomicrons, very-low-density lipoproteins, intermediate-density lipoproteins, low-density lipoproteins, and high-density lipoproteins. Chylomicrons have the lowest density of the five classes of lipoproteins. This is because the have the highest proportion of triglycerides and the least lowest proportion of protein. Very-low-density lipoproteins are a bit more dense than chylomicrons; however, the relative amount of triglycerides is still high. Intermediate-density lipoproteins which are formed from the very-low-density lipoproteins have a higher density than very-low-density lipoproteins due to the fact that they have less than half of the amount of triglycerides as very-low-density lipoproteins. Low-density lipoproteins have the highest amount of cholesterol and an even lesser amount of triglycerides than intermediate-density lipoproteins. Lastly, high-density lipoproteins are the densest of the lipoproteins due to the fact that they have the highest amount of protein in relation to the amount of triglycerides they contain.
Example Question #2 : Identifying Specific Protein Functions
A an excess intake of __________ leads to its conversion to triglycerides.
water
carbohydrates
nucleic acids
vitamins
carbohydrates
The dietary intake of carbohydrate, in excess of the fuel requirement of the liver, leads to their conversion into triacylglycerols. These triacylglycerols are packaged into very-low-density lipoproteins (VLDL's) and released into the circulation for delivery to the various tissues (primarily muscle and adipose tissue) for storage or production of energy through oxidation. VLDL's are, therefore, the molecules formed to transport endogenously derived triacylglycerols to extra-hepatic tissues. The fatty acid portion of VLDL's is released to adipose tissue and muscle in the same way as for chylomicrons, through the action of lipoprotein lipase.
Example Question #2 : Identifying Specific Protein Functions
The cell requirement for cholesterol as a membrane component is satisfied by which of the following?
Low-density lipoproteins
Glycoproteins
High-density lipoproteins
Intermediate-density lipoproteins
Low-density lipoproteins
A cell's necessity for cholesterol as a part of the cell membrane is accomplished by two ways: either it is synthesized from within the cell by the cell, or it is supplied by low-density lipoproteins and chylomicrons. The dietary cholesterol that goes into chylomicrons is supplied to the liver by the interaction of chylomicron remnants with the remnant receptor. In addition, cholesterol synthesized by the liver can be transported to extra-hepatic tissues if packaged in very-low-density lipoproteins (VLDL's). In the circulation VLDLs are converted to low-density liporoteins through the action of lipoprotein lipase.
Example Question #4 : Identifying Specific Protein Functions
Very-low-density lipoproteins are degraded by which of the following?
Lipoprotein dehydrogenase
Lipoprotein lyase
Lipoprotein hydrolase
Lipoprotein lipase
Lipoprotein lipase
Very-low-density lipoprotein (LDL) triglycerides are broken down by lipoprotein lipase forming intermediate density lipoproteins. Intermediate density lipoproteins can either be brought into the liver through a receptor-mediated event or it may be further digested to form low density lipoproteins. LDL may be brought into the liver also by a receptor-mediated even in the liver.
Example Question #1 : Identifying Specific Protein Functions
__________ can be converted into variant forms of high density lipoproteins.
Nascent high-density lipoproteins
Nascent intermediate-density lipoproteins
Nascent chylomicrons
Nascent low-density lipoproteins
Nascent high-density lipoproteins
High density lipoproteins (HDL's) are converted into spherical lipoprotein particles through the accumulation of cholesterol esters. This accumulation converts nascent HDL to HDL2 and HDL3. Any free cholesterol present in chylomicron remnants and intermediate-density lipoproteins can be esterified through the action of the HDL-associated enzyme, lecithin-cholesterol acyltransferase (LCAT). LCAT is synthesized in the liver and so named because it transfers a fatty acid from the second carbon position of lecithin to the hydroxyl group on the third carbon of cholesterol, generating a cholesterol ester and lysolecithin. The activity of LCAT requires interaction with apoA-I, which is found on the surface of HDLs.
Example Question #2 : Identifying Specific Protein Functions
Which is not a function of apoprotein-100?
Activates lipoprotein lipase
Uptake of remnant intermediate-density lipoproteins by liver
Assembly and secretion of chylomicrons
Assembly and secretion of very-low-density lipoproteins
Assembly and secretion of chylomicrons
Apoprotein-100 is not responsible for the secretion and assembly of chylomicrons. That is the responsibility of apoprotein-48. Apoprotein-48 is a shortened version of apoprotein-100. The exclusive apolipoprotein of low density lipoproteins (LDL's) is apoB-100. LDL's are taken up by cells via intermediate-density lipoprotein receptor-mediated endocytosis. The uptake of LDL's occurs predominantly in liver (75%), adrenal glands, and adipose tissue. As with intermediate-density lipoproteins, the interaction of LDL's with LDL receptors requires the presence of apoB-100. Apoprotein-48 is also responsible for activation of lipoprotein lipase and uptake of chylomicron remnants by liver. Chylomicrons function in the transport of dietary triglycerides and cholesterol from intestine to peripheral tissues
Example Question #7 : Identifying Specific Protein Functions
How are gap junctions regulated?
concentration
concentration
concentration
concentration
concentration
Gap junctions are are closed at high concentrations and open at low concentrations.
Example Question #12 : Identification By Function
Kinase reactions involve enzymes that __________.
transfer groups from one part of a molecule to another part
add phosphate groups to another molecule
reduce aldehydes to alcohols
use as an oxidizing agent
add phosphate groups to another molecule
Kinases are enzymes that add phosphate groups to molecules. Phosphatases remove phosphate groups from molecules. Common reducing agents in biological systems are , , and antioxidant molecules such as vitamins C and E. Transferases catalyze reactions in which one part of a molecule is transferred elsewhere on that same molecule or onto another molecule.
Example Question #13 : Identification By Function
What is the action of a phosphatase?
Breaks a chemical bond
Forms a chemical bond
Rearranges bonds in a molecule
Removes of a phosphate group
Adds of a phosphate group
Removes of a phosphate group
The action of a phosphatase is to remove a phosphate group from a molecule. A kinase adds phosphate groups, an isomerase rearranges bonds, a ligase forms a chemical bond, and a lyase breaks a chemical bond.