All Biochemistry Resources
Example Questions
Example Question #155 : Macromolecule Structures And Functions
Which of the following is true of eicosanoids produced from alpha-linolenic acid?
Their production is increased by adding vegetable oil in the diet
A decreased amount is recommended for those with high risk of heart disease
They are considered pro-inflammatory
They produce a weak platelet aggregation response
They produce a strong platelet aggregation response
They produce a weak platelet aggregation response
Alpha-linolenic acid (ALA) is an omega-3 fatty acid that is utilized to produce series 3 eicosanoids. Series 3 eicosanoids lead to a weak platelet aggregation response, and are considered anti or less-inflammatory. Thus, a diet rich in omega-3 fatty acids is recommended for those with heart disease risk. Omega-3 fatty acids are primarily found in fish or flax and chia seeds, not vegetable oil, which is rich in omega-6 fatty acids.
Example Question #2 : Lipid Structures And Functions
Micelle formation is a result of which of these?
Hydrophobic interactions with the carbon chain end of free fatty acids
Hydrogen bonding between water and the polar head of free fatty acids
Hydrogen bonding between water and the carbon chain end of free fatty acids
Hydrophobic interactions with the polar head of free fatty acids
Covalent bonding between fatty acids and water
Hydrophobic interactions with the carbon chain end of free fatty acids
The hydrocarbon tail of free fatty acids is nonpolar, and so it interacts unfavorably with water molecules. So, when free fatty acids are placed in a polar environment, the nonpolar tails are driven together and inward in order to avoid water molecules. A micelle is formed from the circular formation of free fatty acids.
Example Question #11 : Lipid Structures And Functions
Increased unsaturation in a fatty acid results in __________.
no change in membrane fluidity
an increase or decrease in fluidity dependent of the temperature
decreased membrane fluidity
no change with respect to membrane fluidity
increased membrane fluidity
increased membrane fluidity
A greater degree of unsaturation results in a disruption of van der Waals forces between fatty acid chains. This is due to the "kinks" that occur within an unsaturated fatty acid. It is easy to visualize a fatty acid membrane with kinks being less tightly packed, and therefore more fluid. This increase in fluidity is independent of temperature.
Example Question #12 : Lipid Structures And Functions
Which of the following is true of an omega-6 fatty acid?
It has six double bonds located throughout the fatty acid
It has a single bond at the sixth position, counting from the carboxyl end of the fatty acid
It has a single bond at the sixth position, counting from the methyl end of the fatty acid
It has a double bond at the sixth position, counting from the methyl end of the fatty acid
It has a double bond at the sixth position, counting from the carboxyl end of the fatty acid
It has a double bond at the sixth position, counting from the methyl end of the fatty acid
The rules for fatty acid nomenclature state that Omega 6 means that a double bond is located at the sixth position of the fatty acid - counting from the methyl end.
Example Question #11 : Fatty Acids
Which of the following statements about lipids is incorrect?
Myristic acid is saturated with 14 carbons and 0 double bonds
Linolenic acid's nomenclature is C18:29,12
Lipid double bonds are almost always cis
None of these
Biological waxes are nonpolar esters of fatty acids and long chain alcohols
Linolenic acid's nomenclature is C18:29,12
Linoleic acid's nomenclature is C18:29,12. Linolenic acid's nomenclature is C18:39,12,15. They both have 18 carbons but differ by one extra double bond in linolenic acid.
Example Question #1 : Glycerolipids And Triglycerides
In fat, which glycolysis metabolite is a reactant in single-step synthesis of glycerol 3-phosphate?
Phosphoenolpyruvate
3-phosphoglycerate
Dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate
Pyruvate
Dihydroxyacetone phosphate
Glycerol phosphate can be created by the glycerol phosphate shuttle. Insects use this process in their muscles for flying, because they require quick ATP synthesis. To generate that ATP, the NADH synthesized during glycolysis ends up being regenerated into , and is shuttled over to the mitochondria to participate immediately in oxidative phosphorylation. Via the glycerol phosphate shuttle, NADH reduces dihydroxyacetone phosphate directly into glycerol phosphate, in a reaction that is catalyzed by glycerol 3-phosphate dehydrogenase. The metabolite here that can be recognized from glycolysis is the dihydroxyacetone phosphate. Phosphoenolpyruvate, pyruvate, and 3-phosphoglycerate are all indeed glycolysis metabolites, but none could be easily reduced to glycerol 3-phosphate. If you guessed glyceraldehyde 3-phosphate, you’d be close, because structurally, it appears that it could also be directly reduced to glycerol phosphate. Indeed, during glycolysis, it is interconverted to dihydroxyacetone phosphate. But the glycerol phosphate shuttle uses dihydroxyacetone phosphate; hence, the answer is dihydroxyacetone phosphate.
Example Question #175 : Biochemistry
Which component of a phospholipid imparts a charge upon the macromolecule and therefore makes the head hydrophilic?
Glycerol backbone
Unsaturated fatty acid
Ketone group
Phosphate group
Saturated fatty acid
Phosphate group
Phospholipids are amphipathic, meaning they have an end that is hydrophobic (the fatty acid tail) and an end that is hydrophilic (the head). Phosphate groups have a negative charge, thus attracting them to water, and the presence of a phosphate group at the head of a phospholipid makes that head hydrophilic. Glycerol itself polarizes a fatty acid, but the glycerol is located in the head, not the backbone, and is not charged like phosphate.
Example Question #176 : Biochemistry
In sufficient concentrations, one-tailed phospholipids will form a __________ in solution.
micelle
vesicle
liposome
bilayer
micelle
The polar head groups and the hydrocarbon tails will separate themselves in such a way that one-tailed phospholipids will form micelles, whereas two-tailed phospholipids will form a bilayer (liposome).
Example Question #1 : Phospholipids
Which of the following is false about phospholipids?
The fluidity of membranes composed of phospholipids is affected by the length and degree of saturation of fatty acid tails.
Their hydrophilic tails are exposed to the interior of membranes, and their hydrophobic heads to the exterior.
When, in water, they form a sphere, it is called a micelle.
Typically, at least one tail is saturated and another tail is unsaturated.
If a phospholipid bilayer slightly breaks apart, the lipids rearrange on their own to refill the layer.
Their hydrophilic tails are exposed to the interior of membranes, and their hydrophobic heads to the exterior.
Phospholipids have two hydrocarbon tails, and one is indeed usually relatively saturated (has no double bonds) and the other relatively saturated (has double bonds). The degree of saturation, as well as the length, influences membrane fluidity; more cis-double bonds pack together less tightly, and decrease fluidity. In order to minimize free energy, the hydrophobic parts of phospholipids rearrange to refill a bilayer if it happens to break. In water, phospholipids can form a membrane, or a sphere called a micelle in which the hydrophobic tails pack together. Note that the tails are hydrophobic, and the heads are hydrophilic; tails are oriented toward the interior of a bilayered membrane.
Example Question #2 : Phospholipids
Why do phospholipids and glycolipids form bilayers rather than micelles when placed in an aqueous media?
Phospholipids and glycolipids are far less unsaturated than free fatty acids
Hydrophobic interactions do not drive the fatty acid hydrocarbons inwards in phospholipids and glycolipids as they do for free fatty acids
Phospholipids and glycolipids do not have hydrocarbon tails, and so there is nothing to drive them towards micelle formation
None of these
The two fatty acid chains present in glycolipids/phospholipids are too bulky to form micelles
The two fatty acid chains present in glycolipids/phospholipids are too bulky to form micelles
Phospholipids and glycolipids have two hydrocarbon chains, whereas free fatty acids only have one. The extra carbon tail, in combination with the unsaturation of these types of lipids (double bonds present) makes them far bulkier than free fatty acids. The extra bulk disallows micelle formation, and bilayers (liposomes) form instead.
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