Question

Indicate whether each statement is true or false: (a) Fat molecules contain amide bonds. (b) Phosphoplipids can be zwitterions. (c) Phespholipids form bilayers in water in order to have their long hydrophobic tails interact favorably with each other, leaving their polar heads to the aqueous environment.

Short answer

(a) False: Fat molecules contain ester bonds, not amide bonds. (b) True: Phospholipids can be zwitterions due to their polar head groups containing both positive and negative charges. (c) True: Phospholipids form bilayers in water, allowing their hydrophobic tails to interact favorably with each other while their polar heads face the aqueous environment.

Step-by-step solution

Statement (a) Analysis

Fat molecules, which are primarily triglycerides, consist of three fatty acids and one glycerol molecule esterified together through ester bonds. Amide bonds, on the other hand, are characteristic of protein molecules where amino acid residues are linked together. In this case, we can conclude that fat molecules do not contain amide bonds.

Statement (a) Answer

False

Statement (b) Analysis

Zwitterions are molecules that contain both positive and negative charges but overall have a net charge of zero. Phospholipids are composed of a hydrophilic (polar) head and hydrophobic (nonpolar) tail. The polar head group can be a phosphate and choline group, leading to a positive and negative charge, respectively, which can form a zwitterion.

Statement (b) Answer

True

Statement (c) Analysis

The statement describes the formation of bilayers by phospholipids in water. When interacting with water, phospholipids spontaneously arrange themselves into bilayers because their polar heads are hydrophilic (attract water) and their tails are hydrophobic (repel water). This arrangement allows them to form a membrane or vesicle in which their hydrophobic tails interact favorably with one another and their polar heads face the aqueous environment.

Statement (c) Answer

True

Key concepts

Zwitterions

Zwitterions are unique molecules that carry both a positive and a negative charge, yet maintain an overall net charge of zero. This might sound confusing at first, but it becomes clearer when we break it down. Imagine a molecule that's part positive and part negative. These opposing charges balance each other out, leading to an electrically neutral molecule.

In the context of phospholipids, which are a big part of cell membranes, we often see this concept in action. The head of a phospholipid contains a phosphate group that can be negatively charged and a choline group that might bring in a positive charge. Even though these parts of the molecule have their own charges, they balance out, allowing the phospholipid to act as a zwitterion.

This balancing act is vital for cell membranes, providing stability and flexibility. Zwitterions also have a key role in the functioning of proteins and biomolecule interactions in the body.

Hydrophobic interactions

Hydrophobic interactions are fundamental to the behavior of phospholipids in water. But what does 'hydrophobic' mean? Simply put, hydrophobic substances don't get along with water. They're like oil, which doesn't mix with water. These interactions drive the formation of many structures in the body, like cell membranes.

In phospholipids, we find two distinct parts: A hydrophilic (water-loving) head and hydrophobic (water-fearing) tails. When placed in water, phospholipids spontaneously form bilayers with their heads facing the water and tails tucked away from it.

This occurs because the hydrophobic tails naturally want to avoid water and prefer to interact with each other. Thus, forming a barrier that's crucial for cell integrity.

• Provides a stable barrier between the inside and outside of cells.
• Helps maintain the structure of cellular membranes.
• Influences the transport of substances across membranes.

Hydrophobic interactions are incredibly important in biological systems, guiding processes like protein folding and the creation of lipid bilayers.

Ester bonds

Ester bonds play a critical role in the formation of fats and lipids, different from amide bonds which you find in proteins. Let's look at how ester bonds form and function. An ester bond is formed when an acid (usually a carboxylic acid) reacts with an alcohol, releasing water in a process called condensation. This bond is prominent in the building of triglycerides and phospholipids.

In the case of fats, typically made of triglycerides, ester bonds link three fatty acid molecules to a glycerol backbone. This linkage stores energy efficiently, which is why fats are an important energy source for the body.

Ester bonds are also found in phospholipids—key components of cell membranes. Here, they connect fatty acid tails to glycerol, forming the backbone of the cell membrane structure.

• Essential for storing and delivering energy.
• Crucial in the formation of cell membranes.
• Created through a reaction involving dehydration synthesis.

Understanding ester bonds helps in appreciating how energy is stored and how cellular structures are maintained.