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Example Questions
Example Question #2 : Other Lipid Classifications
Glycolipids are characterized by which non-lipid component?
Sphingosine
Polypeptide
Phosphate
Sugar
Sugar
The prefix "glyco-" means "sugar." Glycolipids are thus lipids that have a sugar component. Glycolipids containing sphingoid bases are called sphingolipids. Glycolipids containing phosphate are called phospholipids. Lipoproteins are molecules that contain both lipid and peptide components.
Example Question #32 : Lipid Structures And Functions
Lipids built from the five-carbon unit isoprene are called __________.
glycerophospholipids
lipoproteins
sphingomyelins
terpenoids
sphingolipids
terpenoids
Terpenoids (also called isoprenoids) are produced mostly by plants. Many vitamins such as A, E, and K are terpenoids, and steroids/sterols also belong to this group.
Example Question #1 : Other Lipid Classifications
There are many different lipoproteins used by the body to transport lipids and cholesterol. Which of the following is a true statement about lipoproteins?
HDL carries lipids that are synthesized in the liver.
VLDL is the largest of the lipoproteins.
LDL is a dense lipoprotein that carries dietary fats around the body.
Chylomicrons are very dense lipoproteins that carry dietary fats.
HDL is a dense lipoprotein that carries cholesterol from the body to the liver.
HDL is a dense lipoprotein that carries cholesterol from the body to the liver.
Only "HDL is a dense lipoprotein that carries cholesterol from the body to the liver" is a true statement. Chylomicrons are the largest and least dense lipoprotein, and they carry dietary lipids. VLDL carries lipids synthesized in the liver to the body. they are more dense the chylomicrons. LDL carries cholesterol around the body, and HDL is the most dense and carries cholesterol to the liver for breakdown.
Example Question #1 : Glycosidic Linkages
Glucose polysaccharides are linked together at branch points in glycogen by what type of bond?
Beta-1,4 linkages
Peptide linkages
Beta-1,6 linkages
Alpha-1,6 linkages
Alpha-1,4 linkages
Alpha-1,6 linkages
In glycogen, glucose molecules are attached one after the other by alpha-1,4 linkages. However, in order to make glycogen more compact for storage, branch points are created to created links between many shorter glucose polysaccharides. These branch points connect glucose molecules by alpha-1,6 linkages.
Example Question #1 : Glycosidic Linkages
Why does glycogen have more branches than starch?
There are more alpha-1,4 linkages
There are less alpha-1,6 linkages
None of these answers; glycogen is not more branched than starch
There are less alpha-1,4 linkages
There are more alpha-1,6 linkages
There are more alpha-1,6 linkages
Lots of alpha-1,4 linkages allow for longer chain lengths in carbohydrates like starch and glycogen. However, it is the amount of alpha-1,6 linkages that determine the number of branches - since glycogen has many more alpha-1,6 linkages than starch does, it has more branches. This allows for easy breakdown of glycogen into glucose in the liver should there not be enough glucose in the body to supply the body's demand for energy production. Recall that glycogen phosphorylase can only break terminal alpha-1,4 glycosidic bonds; hence, with more branches there are more terminal glucose molecules that are substrates for this catabolic enzyme.
Example Question #1 : Carbohydrate Structures And Functions
During times of glucose deprivation in the human body, the liver is able to supply glucose to the bloodstream by breaking down a large, branched polysaccharide that it holds in reserve until it is needed. Which of the following lists the correct type of glycosidic bonds found in this polysaccharide.
for branch points and for straight chain
for branch points and for straight chain
for branch points and for straight chain
for branch points and for straight chain
for branch points and for straight chain
for branch points and for straight chain
For this question, we're told some background information about the liver's role in providing glucose homeostasis. We're told that when blood glucose levels are lowered, the liver is able to help restore glucose levels by keeping a large polysaccharide of glucose in store. In times of need, the liver can break this compound down to provide glucose to the bloodstream.
Even though the question doesn't explicitly tell us what the polysaccharide is, we should be able to infer that the compound in question is glycogen. Therefore, to answer the question, we need to know which kind of glycosidic bonds are found in glycogen.
First, let's recall that an individual glucose molecule is composed of six carbon atoms. In its ring form, glucose can exist as one of two epimers, depending on how its ring closes when transitioning from its straight chain form to its closed ring form. The anomeric carbon of the glucose molecule can be arranged in one of two ways when its ring closes. The anomeric carbon is the one that goes from being achiral to chiral as the ring closes. In the alpha configuration, the hydroxyl group attached to the anomeric carbon faces down, while in the beta configuration it faces up.
In addition to existing as either an alpha or a beta epimer, glucose also participates in glycosidic linkages using its first, fourth, and sixth carbon atom.
In glycogen, each individual glucose molecule is in the alpha configuration. Thus, we can rule out both answer choices that include beta. Moreover, the fourth carbon atom of each glucose molecule is attached to the first carbon atom (the anomeric carbon) in the next glucose molecule in the straight chain. To make branch points at various points along the straight chain, some of the glucose molecules have their sixth carbon atom attached to the anomeric carbon of other glucose molecules.
In conclusion, glycosidic bonds are responsible for branch points and glycosidic bonds are responsible for the straight chain.
Example Question #1 : Glycosidic Linkages
Glycogen is not a single chain of glucose units, but many chains branching off of one another. Why is the branching of glycogen important?
All of these are reasons why glycogen branching is important
Branching makes glycogen more compact
Branching increases the rate of glycogen synthesis
Branching increases the rate of glycogen degradation
Branching increases glycogen solubility
All of these are reasons why glycogen branching is important
Because glycogen is so heavily branched, it is able to pack more glucose units together in a small space, thus it is more compact and has a greater solubility. Moreover, the branching allows for glycogen enzymes to act more efficiently on the chains of glucose, and so both degradation and synthesis have increased rates.
Example Question #1 : Glycosidic Linkages
You discover that your patient is lactose intolerant, having a mutation that does not allow them to produce an enzyme that cleaves the disaccharide lactose. If they had the lactase enzyme, which glycosidic bond would it cleave?
Glucose-alpha 1,2-fructose
Galactose-alpha-1,4-glucose
Glucose-beta 1,4-glucose
Glucose-alpha-1,4-glucose
Galactose-beta-1,4-glucose
Galactose-beta-1,4-glucose
lactose is made up of galactose and glucose and is bound via a beta 1,4 glycosidic bond.
the enzyme lactase cleaves this bond to break down the sugar lactose. Maltose is glucose- alpha 1,4- glucose, and sucrose is glucose- alpha, 1,2- fructose.
Example Question #2 : Carbohydrate Structures And Functions
What is an aldotriose?
A monosaccharide that contains three aldehydes and one carbon
A disaccharide that contains three aldehydes and one carbon
A monosaccharide that contains both an aldehyde and three carbons
A disaccharide that contains an aldehyde and three carbons
A monosaccharide that contains both an aldehyde and three carbons
Aldotrioses are monosaccharides that contain both an aldehyde (an aldose) and three carbons (a triose). Knowing the definition of the word, and the breakdown of parts of the word, can help you recognize the molecule. The simplest aldotriose is glyceraldehyde.
A related concept involves ketotrioses, which are monosaccharides that contain both a ketone (a ketose) and three carbonds (a triose). Dihydroxyacetone is an example of a ketotriose.
Example Question #1 : Epimers, Chirality, And The Anomeric Carbon
Mirror-image stereoisomers are called __________.
enantiomers
epimers
anomers
diastereomers
enantiomers
Enantiomers are chiral molecules that are non-superimposable mirror images of each other. Diastereomers result when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent stereocenters and are not mirror images of each other. An epimer is one of two stereoisomers that differ in configuration at only one stereocenter. An anomer is a type of epimer; it is one of two stereoisomers of a cyclic sugar that differs only in its configuration at the hemiacetal or acetal carbon (the anomeric carbon).
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