Question 1

Dan is confused about the reason you advise him that in fact a healthy diet includes fats. He tells you that all fats are bad fats. You correct him, telling him that lipids are essential for cells. Which of the following is NOT true of lipids?

Accepted Answer

Lipids are not composed of identical subunits, unlike proteins and nucleic acids. Instead, they are a diverse group of molecules that include triglycerides, phospholipids, steroids, and waxes.

Question 2

Unsaturated fats have lower melting points than saturated fats.

Accepted Answer

Unsaturated fats have double bonds which create kinks in their chains, preventing the molecules from packing tightly together. This results in a lower melting point as compared to saturated fats which have straight chains and pack tightly together, leading to a higher melting point.

Question 3

Dan tells you that he knows proteins are needed to build muscle mass but that he doesn't quite understand the role of proteins in a cell. He tells you five things he believes proteins are needed for in cell function, but he is mistaken on one of these. Which of the following statements regarding the role of proteins in cells is INCORRECT?

Accepted Answer

Proteins are not a major component of starch. Starch is a carbohydrate composed of glucose molecules. Proteins are composed of amino acids and are not involved in the formation of glucose molecules.

Question 4

Which of the following statements about enzymes is FALSE?

Accepted Answer

Enzymes do not increase the temperature of a reaction; they simply speed up the rate of a reaction by lowering the activation energy required for the reaction to occur.

Question 5

Which of the following pairs is mismatched?

Accepted Answer

Carboxyl group contains both a carbonyl group (-C=O) and a hydroxyl group (-OH), but does not have a CH3 group.

Question 6

Microorganisms use hydrogen bonds to attach themselves to the surfaces that they live on. Many of them lose hold of the surface because of the weak nature of these bonds and end up dying or being washed away. Why don't microbes just use covalent bonds instead?

Accepted Answer

Covalent bonds require more energy and enzyme involvement, which is not feasible for many microbes. Hydrogen bonds provide a weaker but efficient alternative for attachment. The other answer choices are not entirely accurate or relevant to the question.

Question 7

You tell Dan that while many of his cell components do indeed contain amino acids, carbohydrates and lipids are also essential for cells. Which of the following components contain both amino acids AND lipids?

Accepted Answer

The cytoplasmic membrane is composed of phospholipids, which contain both a polar (hydrophilic) head made of a glycerol molecule and a phosphate group, and nonpolar (hydrophobic) tails made of fatty acid chains. Some of these fatty acid chains contain amino acids, which makes the cytoplasmic membrane a component that contains both amino acids and lipids. The other choices listed contain either amino acids or lipids, but not both.

Question 8

A biologist determined the amounts of several amino acids in two separate samples of pure protein. His data showed that Protein A contained 7% leucine, 12% alanine, 4% histidine, 2% cysteine, and 5% glycine. Interestingly, Protein B had the same percentages of the same amino acids. He concluded from this data that Proteins A and B are the same protein. Based on this information and his conclusion, determine which of the following is the correct statement regarding his findings:

Accepted Answer

The biologist's conclusion that Proteins A and B are the same protein based solely on their amino acid composition is incorrect. A protein's overall structure is determined by its amino acid sequence, not just the percentages of each amino acid present. Therefore, Proteins A and B could be very different in shape even though they have the same percentages of the same amino acids.

Question 9

Enzymes are required to break which of the following bonds?

Accepted Answer

The answer of Enzymes are required to break which of...

Question 10

You are working in a laboratory, making media for growing bacteria. The recipe you are following calls for the addition of TRIS buffer. You can't find any TRIS in the lab, so you decide to leave it out of the medium. Select the FALSE statement regarding your decision.

Accepted Answer

Bacteria actually live within a narrow pH range, close to pH 7, not pH 14. However, maintaining the correct pH is essential for cells (B), buffers are added to solutions to stabilize the hydrogen ion concentration of that solution (C), and the acidity of the medium without buffer may change dramatically as the bacteria grow (D). Leaving out the TRIS buffer is likely to make the medium too acidic as bacteria produce acids as they grow.

Question 11

Please identify the correct definition.

Accepted Answer

An electrolyte is a compound that conducts electricity when dissolved in water because it dissociates into positive and negative ions, allowing an electric current to flow. Salts are a type of electrolyte. A is incorrect because molecules containing carbon and hydrogen are organic compounds. C is incorrect as compounds are made up of two or more different elements. D is incorrect as in a polar covalent bond, electrons are not shared equally. E is incorrect as the starting components of a chemical reaction are called reactants, not products.

Question 12

You are a biochemist working on a molecule found in a recently discovered bacterium. You determine that the molecule is composed of a chain of similar subunits and can thus conclude that the molecule is unlikely to be a

Accepted Answer

The answer of You are a biochemist working on a...

Question 13

Phospholipids are polar molecules.

Accepted Answer

Phospholipids have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail, which makes them polar molecules.

Question 14

Dan tells you that he believes that proteins are the primary source of energy for his cells because proteins are easily digested. You tell him that this is

Accepted Answer

While it is true that proteins can be used for energy, they are not the primary source of energy for cells. Carbohydrates are the most easily accessible and efficient source of energy for cells. Proteins are primarily used for building and repairing tissues.

Question 15

Lipids are polar, hydrophilic molecules.

Accepted Answer

Lipids are non-polar and hydrophobic molecules.

Question 16

Simple lipids contain carbon, hydrogen, and oxygen in a 1:2:1 ratio.

Accepted Answer

This statement is false. Simple lipids, such as triglycerides, contain carbon, hydrogen, and oxygen, but not in a 1:2:1 ratio. The ratio varies depending on the specific compound.

Question 17

Dan asks you how his cells are able to use complex molecules such as proteins. You explain to him that proteins are macromolecules composed of ________ and that proteins can be broken down by ________, a type of reaction in which the addition of ________ breaks covalent bonds between subunits.

Accepted Answer

Proteins are macromolecules composed of amino acids, and they can be broken down by hydrolysis, a type of reaction in which the addition of water breaks covalent bonds between subunits.

Question 18

Which of the following is the correct order from most acidic to least acidic?

Accepted Answer

Stomach acid is highly acidic with a pH around 1.5-3.5. Vinegar, which is acetic acid, has a pH around 2.5-3.5. Unpolluted rainwater is slightly acidic due to dissolved CO2, with a pH around 5.6. Blood is slightly alkaline with a pH around 7.35-7.45. Drain cleaner is highly alkaline, often with a pH of 12 or more. Therefore, the correct order from most acidic to least acidic is stomach acid, vinegar, unpolluted rainwater, blood, and then drain cleaner.

Quiz 2: The Molecules of Life