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Protein, Carbohydrates, Lipids & Nucleic Acid - Elements of Biological Molecules

Divya M K, Angela Hartsock, Brenda Grewe
  • Author
    Divya M K

    Divya is passionate about creating engaging teaching, learning, and assessment resources for K-12 Science. She has a Bachelor's Degree in Engineering and a Post Graduate Diploma in Instructional Design. She has 12 years of experience as a Science SME and has written several science lessons aligned to different curriculums as a Consultant with schools and K-12 Education companies.

  • Instructor
    Angela Hartsock

    Angela has taught college microbiology and anatomy & physiology, has a doctoral degree in microbiology, and has worked as a post-doctoral research scholar for Pittsburgh’s National Energy Technology Laboratory.

  • Expert Contributor
    Brenda Grewe

    Brenda has 25 years of experience teaching college level introductory biology and genetics. She earned her PhD in Genetics from Indiana University.

What are Proteins, Carbohydrates, Lipids, and Nucleic Acids? Learn to define the molecular structure and functions of Proteins, Carbohydrates, Lipids and Nucleic Acids. Updated: 07/28/2021

From television programs to newspapers and magazines, we get diet advice on how to prepare and eat balanced meals. A balanced meal is a snapshot of a diet that covers the three core food groups - Proteins, Carbohydrates, and Lipids. Along with nucleic acids, they also comprise a group called biological macromolecules. Biological macromolecules are important cellular components and perform a wide array of functions necessary for the survival and growth of living organisms. The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.

Protein Elements

Proteins are organic molecules composed of Carbon, Hydrogen, Oxygen, and Nitrogen (CHON). Proteins are created by linking together amino acids into protein links called polypeptide chains. Amino acids consist of the following elements: carbon, hydrogen, oxygen, nitrogen, and, sometimes, sulfur and selenium. The general structure of amino acids consists of a carbon center and its four substituents, which consists of an amino group (NH2), an organic acid (carboxyl) group (COOH), a hydrogen atom (H), and a fourth group, referred to as the R-group, that determines the structural identity and chemical properties of the amino acid. The first three groups are common to all amino acids. The basic amino acid structure is R-CH(NH2)-COOH. The arrangement of amino acids along the chain determines the structure and chemical properties of the protein.

The primary structure of a protein is a chain of amino acids

The primary structure of a protein is a chain of amino acids

Functions of Protein

Proteins play an essential role in the cellular maintenance, growth, and functioning of the human body. Serving as the basic structural molecule of all the tissues in the body, protein is present in every single cell.

Types of Protein

Of the twenty-one amino acids, eleven are considered nonessential, meaning that the body is able to adequately synthesize them, and nine are essential, meaning that the body is unable to adequately synthesize them to meet the needs of the cell. They must therefore be supplied through the diet. The quality of protein depends on the level at which it provides the nutritional amounts of essential amino acids needed for overall body health, maintenance, and growth. Animal proteins, such as eggs, cheese, milk, meat, and fish are considered complete, or high-quality, proteins because they provide sufficient amounts of the essential amino acids. Plant proteins, such as grain, corn, nuts, vegetables, and fruits, are lower-quality, or incomplete, proteins because many plant proteins lack one or more of the essential amino acids, or because they lack a proper balance of amino acids.

The Major Macromolecules

Today we are going to do a dissection, but you don't need your scalpel because we won't be doing the classic frog dissection. Instead, we will be dissecting a bacterial cell. Let's take a look down our microscope to find a bacterial cell. Here you can see a rod-shaped cell. Now imagine that we could pick up this cell and slice it open to see the inside. If you look closely, you will start to make out some major cell structures - maybe a flagella, a cell wall, a cell membrane, some DNA, and even some ribosomes. Zoom in a little bit more and you start to see individual proteins floating around inside the cell catalyzing chemical reactions.

Many of these components of the cell are made up of macromolecules, which simply means large molecules formed by linking together small molecules. The major macromolecules within the cell include proteins, nucleic acids like DNA and RNA, carbohydrates, and lipids. In this lesson, we will discuss the structure of these macromolecules and break them down into their individual units, all the way down to individual atoms. To keep track of the elemental building blocks for our macromolecules, we will use this handy table and fill it in as we go.

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  • 0:05 The Major Macromolecules
  • 1:30 Proteins
  • 2:49 Nucleic Acids
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  • 5:09 Lipids
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Carbohydrate Elements

Carbohydrates represent a broad group of substances that include sugars, starches, gums, and celluloses. Carbohydrates contain the elements carbon, hydrogen, and oxygen. The ratio of carbon to hydrogen to oxygen in carbohydrate molecules is 1:2:1. For example, glucose, a simple sugar, contains 6 molecules of carbon, 12 molecules of hydrogen, and 6 molecules of oxygen. Since the ratio of hydrogen to oxygen atoms is 2:1 like in water, it explains the origin of the term ''carbohydrate'': the components are carbon (''carbo'') and the components of water (hence, ''hydrate'').

Functions of carbohydrate

Carbohydrates are the primary source of energy to all cells in the body. Apart from being the main source of energy, they are essential for energy storage, building macromolecules, sparing protein, and assisting in lipid metabolism.

Types of Carbohydrate

There are two major types of carbohydrates: simple and complex.

Simple carbohydrates: These are simple sugars and are also called monosaccharides and disaccharides. For example, the sugar in fruits, honey, and table sugar.

Complex carbohydrates: These are complex sugars such as starches found in grain products, such as bread, crackers, pasta, and rice. They are polysaccharides and are composed of repetitive units of monosaccharides.

Lipids Elements

Lipids are a group of structurally and functionally diverse organic compounds that are insoluble in water. Lipids are mainly composed of hydrocarbons and contain the same elements as carbohydrates: carbon, hydrogen, and oxygen (C, H, and O). However, lipids contain fewer polar hydroxyl groups (-OH). Lipids include fats and oils (triglycerides), phospholipids, waxes, and steroids.

A triglyceride molecule

A triglyceride molecule

Functions of Lipids

  • They are structural components of cellular membranes, energy reservoirs, and signaling molecules.
  • They help in regulating body temperature.
  • They are essential for absorbing fat-soluble nutrients.
  • As visceral fat, they surround and protect vital organs such as the heart, kidneys, and liver.

Types of Lipids

Lipids include fats and oils (triglycerides), phospholipids, steroids, and waxes.

Proteins

Proteins play important roles within a cell. Some make up the structure of cell components, like a flagella or a pilus, and many play the role of enzymes to catalyze the reactions necessary for life.

Let's take a look at a protein. As you can see, they are complicated structures that can be made up of hundreds to thousands of individual units, called amino acids, all linked up in a chain and then folded up like origami into complicated shapes.

The structure may seem complex, but all proteins are actually made up of around 21 different amino acids, just in many different combinations. Every amino acid has the basic structure shown here consisting of carbon, hydrogen, oxygen, and nitrogen. This could be called the backbone of the amino acid. Let's add this information to our table. For the protein row, we will add carbon, hydrogen, oxygen, and nitrogen.

But each of these amino acids has a different molecular group that hangs off one side. Most of the special side groups contain the already mentioned carbon, hydrogen, oxygen, and nitrogen. To help you out, I will just point out the oddballs: these three amino acids have sulfur and selenium. So let's add those to our table.

Nucleic Acids

I am sure you are already familiar with nucleic acids, those incredibly important compounds that include both DNA and RNA. But let's take a closer look and break down these macromolecules to their basic elemental composition.

Let's start with the classic image of a double helix of DNA. If we analyze that macromolecule, we see that there are four basic building blocks that make up the structure: adenine, guanine, cytosine, and thymine. These are part of the DNA nucleotides.

Like DNA, RNA is also made up of nucleotides. It has the same A, G, and C, but instead of thymine, RNA contains uracil. So let's add the structure of uracil to our discussion. Don't forget, these DNA and RNA nucleotides also include a ribose sugar, either deoxyribose for DNA or ribose for RNA, as well as a phosphate molecule.

Let's analyze these structures and add the elements we find to our table. As we can see, the nucleic acid building blocks of DNA and RNA are made up of carbon, hydrogen, oxygen, nitrogen, and phosphorous.

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Video Transcript

The Major Macromolecules

Today we are going to do a dissection, but you don't need your scalpel because we won't be doing the classic frog dissection. Instead, we will be dissecting a bacterial cell. Let's take a look down our microscope to find a bacterial cell. Here you can see a rod-shaped cell. Now imagine that we could pick up this cell and slice it open to see the inside. If you look closely, you will start to make out some major cell structures - maybe a flagella, a cell wall, a cell membrane, some DNA, and even some ribosomes. Zoom in a little bit more and you start to see individual proteins floating around inside the cell catalyzing chemical reactions.

Many of these components of the cell are made up of macromolecules, which simply means large molecules formed by linking together small molecules. The major macromolecules within the cell include proteins, nucleic acids like DNA and RNA, carbohydrates, and lipids. In this lesson, we will discuss the structure of these macromolecules and break them down into their individual units, all the way down to individual atoms. To keep track of the elemental building blocks for our macromolecules, we will use this handy table and fill it in as we go.

Proteins

Proteins play important roles within a cell. Some make up the structure of cell components, like a flagella or a pilus, and many play the role of enzymes to catalyze the reactions necessary for life.

Let's take a look at a protein. As you can see, they are complicated structures that can be made up of hundreds to thousands of individual units, called amino acids, all linked up in a chain and then folded up like origami into complicated shapes.

The structure may seem complex, but all proteins are actually made up of around 21 different amino acids, just in many different combinations. Every amino acid has the basic structure shown here consisting of carbon, hydrogen, oxygen, and nitrogen. This could be called the backbone of the amino acid. Let's add this information to our table. For the protein row, we will add carbon, hydrogen, oxygen, and nitrogen.

But each of these amino acids has a different molecular group that hangs off one side. Most of the special side groups contain the already mentioned carbon, hydrogen, oxygen, and nitrogen. To help you out, I will just point out the oddballs: these three amino acids have sulfur and selenium. So let's add those to our table.

Nucleic Acids

I am sure you are already familiar with nucleic acids, those incredibly important compounds that include both DNA and RNA. But let's take a closer look and break down these macromolecules to their basic elemental composition.

Let's start with the classic image of a double helix of DNA. If we analyze that macromolecule, we see that there are four basic building blocks that make up the structure: adenine, guanine, cytosine, and thymine. These are part of the DNA nucleotides.

Like DNA, RNA is also made up of nucleotides. It has the same A, G, and C, but instead of thymine, RNA contains uracil. So let's add the structure of uracil to our discussion. Don't forget, these DNA and RNA nucleotides also include a ribose sugar, either deoxyribose for DNA or ribose for RNA, as well as a phosphate molecule.

Let's analyze these structures and add the elements we find to our table. As we can see, the nucleic acid building blocks of DNA and RNA are made up of carbon, hydrogen, oxygen, nitrogen, and phosphorous.

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  • Activities
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Identification of Biological Molecules from Growing Bacterial Cells

In this activity, you will use your knowledge of the four different classes of macromolecules (proteins, nucleic acids, carbohydrates and lipids) to make predictions for the outcomes of an experiment in which bacterial cells are grown in nutrient broth in which the common isotope of carbon, hydrogen, phosphate or sulfur is replaced with the radioactive isotope (radioisotope) of that element.

Experiment

A student set up four cultures of the bacterium E. coli that were switched from their normal growth medium to nutrient broth containing the radioactive isotope of one the major elements of biological molecules:

  1. Radioactive Carbon: C-14 in place of normal C-12
  2. Radioactive Hydrogen: H-3 (tritium) instead of normal H-1
  3. Radioactive Phosphorus: P-32 instead of normal P-31
  4. Radioactive Sulfur: S-35 instead of normal S-32.

After 40 generations of cell growth and division, the student collected the bacterial cells, lysed them open to release the cell contents, and separated the cell contents into water-soluble and water-insoluble fractions. Any new biological molecules that incorporated the radioisotope are detectable in the fractions by the radioactivity they emit, just as electronic devices such as cell phones can be tracked to their locations by the signal they emit.

Predict the Experimental Results

For each of the bacterial cultures (1-4) grown in the presence of a different radioisotope of a major element (C-14, H-3, P-32, and S-35) of biological molecules, predict a) the macromolecules that will have incorporated the radioisotope and b) whether the(se) macromolecule(s) will be in the water soluble or insoluble fraction.

What are the elements of a carbohydrate?

Carbohydrates contain the elements carbon, hydrogen, and oxygen. Carbohydrates represent a broad group of substances that include sugars, starches, gums, and celluloses.

How many elements are in proteins?

Proteins are created by linking together amino acids into protein links called polypeptide chains. Amino acids consist of the following elements: carbon, hydrogen, oxygen, nitrogen, and, sometimes, sulfur and selenium.

Which elements help create a lipid?

Lipids are a group of structurally and functionally diverse organic compounds that are insoluble in water. Lipids are mainly composed of hydrocarbons and contain the same elements as carbohydrates: carbon, hydrogen, and oxygen (C, H, and O). However, lipids contain fewer polar hydroxyl groups (-OH). Lipids include fats and oils (triglycerides), phospholipids, waxes, and steroids.

What are the 4 main types of lipids?

The four main types of lipids are fats and oils (triglycerides), phospholipids, waxes, and steroids.

  • Triglycerides - They make up more than 95 percent of lipids in the diet and are commonly found in fried foods, vegetable oil, butter, whole milk, cheese, cream cheese, and some meats.
  • Phospholipids - They make up only about 2 percent of dietary lipids. They are water-soluble and are found in both plants and animals.
  • Steroids - They are the least common type of lipid. Cholesterol is the most common steroid. It is an important component of the cell membrane and is required for the synthesis of sex hormones, vitamin D, and bile salts.
  • Waxes - Wax covers the feathers of some aquatic birds and the leaf surfaces of some plants. Because of the hydrophobic nature of waxes, they prevent water from sticking on the surface.

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