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Organic Molecules

Organic Molecules

What comes to mind when you hear the word organic? Do you think about produce that is not genetically modified or grown without synthetic chemicals? In biology, you will frequently encounter the terms "organic compounds" or "organic molecules," but "organic" here takes on an entirely different meaning! So, let's talk about what organic molecules are.

  • First, we will define organic molecules and distinguish them from inorganic molecules.
  • Then, we will discuss organic molecules' components, structure, and formula.
  • Finally, we will cite the four major groups of organic molecules found in all living organisms.

Organic Molecules Biology

Living matter is made up largely of organic molecules.

Organic molecules contain carbon and hydrogen and have at least one covalent bond between carbon and hydrogen or between two carbon atoms.

Recall that a covalent bond is a linkage formed between two atoms sharing a pair of valence electrons (or four electrons in its outermost shell).

A mnemonic you can use to remember elements found in organic molecules is CHNOPS: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

Organic Molecules Structure

The structure of the carbon skeleton of organic molecules can be ring-shaped, branched, or straight. Organic molecules consist of chains of carbon atoms of various lengths, with many being relatively long, allowing for a large number and variety of compounds.

Organic molecules contain

Organic molecules are made up of carbon and hydrogen atoms, and they might sometimes contain nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S) atoms.

Let's take ethane for example. Ethane is an organic molecule containing carbon and hydrogen.

Notice that the carbon atoms in ethane each has four covalent bonds. Carbon has four valence electrons, so it can form up to four covalent bonds with up to four atoms all at once. Because of its size and bonding properties, carbon atoms can bind together in large numbers, which allows it to produce a chain or carbon skeleton.

However, keep in mind that while all organic molecules contain carbon, not all molecules containing carbon are organic. For a carbon-containing molecule to be considered organic, its carbon atom must be reduced and not fully oxidized.

  • An atom such as carbon or oxygen is said to be reduced if they form covalent bonds with another atom with lower electronegativity.

  • An atom is said to be oxidized when it forms a covalent bond with an atom with higher electronegativity.

Recall that electronegativity refers to the tendency of an atom to attract electrons toward itself!

When an atom is reduced, it gains a majority of the electrons that form the covalent bond, while the oxidized atom gains only a small portion of the electrons.

For example, carbon dioxide (CO2) is considered an inorganic molecule because its carbon atom is bonded only to oxygen atoms and is therefore oxidized rather than reduced.

Functional Groups

In addition to carbon, organic molecules may also contain functional groups. Let's look at its definition.

Functional groups are groups of atoms in a molecule that are named according to their chemical composition and the chemical reactions they participate in.

So, when present in a molecule, a functional group will exhibit its unique chemical behavior! Functional groups have specific names typically incorporated into the names of the compounds that include them.

For example, formaldehyde (a strong-smelling gas used in many building materials and household products) contains the functional group aldehyde.

Figure 2 below shows some common functional groups. You should try to remember these functional groups because they typically determine how organic molecules will react!

In the figure above, notice how formulas contain the symbol R. R stands for "residue," and it represents the other parts of the molecule. In other words, R can represent a single hydrogen atom or many atoms!

Also, notice that some functional groups are made up of just one or two atoms, while others are made up of these simpler functional groups.

For example, carbonyl is a simple functional group consisting of a carbon atom double bonded to an oxygen atom (C=O). Carbonyl can be found in many larger functional groups, such as carboxylic acids, aldehydes, and ketones.

When we are interested in something that is happening in a specific spot on a huge biological molecule, denoting the 'R' group is a convenient way to call attention to that part of the molecule and abbreviate the rest of the structure.

Organic Molecules Formula

Organic molecules can be represented through a molecular formula, which indicates what elements and how many atoms of each element are present in a compound. The number of atoms is represented by a subscript after the element's symbol unless there is only one atom of the element present.

For example, methane can be represented through the molecular formula CH4, which tells us that it contains one carbon (C) atom and four hydrogen (H) atoms.

Molecules can also be represented by their structural formula, which is a graphic illustration of the arrangement of the atoms within the molecule.

There are different types of formulas that chemists can use to show the structure of an organic molecule. Here, we will look at four of them:

  • The Lewis structure formula

  • The condensed formula

  • The bond-line formula

  • The dashed-wedged formula

The Lewis structure is a diagram showing how a molecule's atoms are bonded together. In a Lewis structure, valence electrons are represented as dots, while bonds are represented by two dots between bonded atoms or a line. Double bonds are represented by two lines, while triple bonds are represented by three.

A condensed formula consists of elemental symbols, with the order of each element suggesting how they are connected. On the other hand, bond-line formulas consist of bonds and lines, with carbon atoms no longer drawn in and are instead indicated using the ends and bends of the lines.

The Dashed-Wedged line structure is similar to the Bond-Line formula, except that the structure of the atoms is also illustrated: dashed lines show atoms and bonds facing away from the viewer, while wedged lines represent bonds and atoms facing the viewer.

Figure 3 below shows how ethanol (C2H6O) is represented using these various structural formulas.

Concept of Isomerism in Organic Molecules

It is important for the structure of organic molecules to be adequately represented because different compounds can have the same molecular formula.

For example, the monosaccharides fructose, galactose, and glucose all have the same molecular formula, C6H12O6, but the atoms are bound to one another differently, as seen in figure 3 below.

Substances with identical molecular formulas but different atom bonding arrangements are called isomers. Chemistry places a great deal of emphasis on the concept of isomerism because the structure of organic molecules structures are often closely linked to their functions. So, a small change in the structural arrangement of atoms in a molecule can result in very different properties!

Large Organic Molecules Examples

Lastly, let's look at some examples of large organic molecules. The four major types of organic molecules that make up cells and cell structures are:

  1. Carbohydrates

  2. Proteins

  3. Nucleic acids

  4. Lipids

Carbohydrates, proteins, and nucleic acids are polymers, or large complex molecules made up of smaller, identical repeating units called monomers. These monomers are typically linked together through dehydration synthesis, a chemical reaction in which monomers bind end to end, resulting in the formation of water molecules as a byproduct.

On the other hand, polymers can be broken down into monomers through hydrolysis, where water is split into -OH and H.

To makes things simpler, let's go through each of these organic molecules more in-depth!

Carbohydrates

You've probably encountered the term carbohydrates in the context of food. In biology, the term carbohydrates is used a bit differently.

Carbohydrates are organic molecules made up of monomers called monosaccharides.

Monosaccharides are molecules with the composition [CH2O]n, where n is usually 3-6. For example, glucose is a 6-carbon sugar whose chemical formula is C6H12O6. Monosaccharides are linked together via glycosidic bonds to form polysaccharides.

Carbohydrates play an important role in energy storage and structural support in cells.

Starch, which you might be familiar with, is a common carbohydrate. Starch is found in pasta, bread, rice, and many other foods. Green plants produce it for energy storage. Other examples of carbohydrates are cellulose (which makes up the cell walls of plants) and chitin (which makes up the exoskeleton of insects and marine invertebrates).

Proteins

You've probably also encountered the term protein before, but in biology, it's much more than the stuff bodybuilders use to increase muscle mass!

Proteins are organic molecules composed of amino acid monomers joined together by peptide bonds.

An amino acid contains an amino group (-NH2), a carboxyl group (-COOH), and a side chain (called the R group). The amino and carboxyl groups are joined to the central carbon atom of each amino acid molecule. There are 20 different amino acids, each containing a different R group.

Proteins play an essential role in enzymatic activities, cell signaling, and providing structural components that help bind cells into tissues.

Examples of proteins include:

Nucleic acids

Next, we have nucleic acids.

Nucleic acids are organic molecules that are made up of nucleotide monomers linked together by a phosphodiester linkage.

Nucleotide monomers are made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.

Both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), which carry genetic information on living organisms, are nucleic acids. RNAs also play a major role in protein synthesis.

Lipids

Lastly, let's look at the definition of lipids.

Lipids are large organic molecules made up of glycerol and fatty acids.

Phospholipids, which make up the cell membrane, are an example of lipids. The phospholipid bilayer creates a hydrophobic environment that separates the cytosol's internal aqueous environment from the exterior of the cell. Fats and oils which serve as energy storage are also examples of lipids.

To keep learning about lipids, nucleic acids, proteins, and carbohydrates, check out "Macromolecules"!

Organic Molecules - Key takeaways

  • Organic molecules are those that contain carbon and hydrogen and have at least one covalent bond between carbon and hydrogen or between two carbon atoms.
  • While all organic molecules contain carbon, not all molecules containing carbon are organic.
    • The carbon atom in an organic molecule must be reduced.
  • Organic molecules can also contain functional groups.
  • The four major types of organic molecules that make up cells and cell structures are carbohydrates, proteins, nucleic acids, and lipids.

References

  1. OpenStax. “7.1: Organic Molecules - Biology LibreTexts.” Biology LibreTexts, 10 July 2016.
  2. “Illustrated Glossary of Organic Chemistry - Molecular Formula (Chemical Formula).” Illustrated Glossary of Organic Chemistry - Molecular Formula (Chemical Formula). Accessed 28 Oct. 2022.
  3. “Organic Molecules - General College Chemistry.” Organic Molecules - General College Chemistry. Accessed 28 Oct. 2022.
  4. Biological Molecules | Biological Principles.” Biological Molecules | Biological Principles. Accessed 28 Oct. 2022.
  5. Choo, Ezen. “Structure of Organic Molecules - Chemistry LibreTexts.” Chemistry LibreTexts, 2 Oct. 2013.

Frequently Asked Questions about Organic Molecules

The 4 major organic molecules are carbohydrates, proteins, nucleic acids, and lipids.

The types of molecules that are organic are those that 

contain carbon and hydrogen and have at least one covalent bond between carbon and hydrogen or between two carbon atoms. 

Examples of organic molecules are starch (a molecule which stores energy), formaldehyde (a compound commonly used in household products), and methane (an atmospheric gas).

Organic molecules are made up of carbon and hydrogen and may have nitrogen, oxygen, phosphorus, and/or sulfur. 

Organic molecules make up all living matter. For example, carbohydrates function as energy storage and structural support, while proteins play an important role in enzymatic activities, cell signaling, and providing structural components that bind cells into tissues.

Final Organic Molecules Quiz

Question

What are carbohydrates?

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Answer

Simple carbohydrates are carbohydrates made of one or two molecules of sugar. 

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What are macromolecules?

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Answer

Macromolecules are large molecules vital to biological processes such as proteins, nucleic acids, and carbohydrates. 

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What are monosaccharides?

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Monosaccharides are simple sugars, like glucose and fructose, and are considered monomers or building blocks of carbohydrates.

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What are examples of monosaccharides?

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Answer

glycogen

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What are disaccharides?

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Answer

In photosynthesis, plants produce sucrose or table sugar, which consists of fructose and glucose. 

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What are examples of disaccharides?

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Answer

Maltose or malt sugar is produced through the breakdown of starch and is usually used to make beer. 

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What are polysaccharides? 

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Polysaccharides consist of multiple monosaccharides or more complicated structures, making them complex carbohydrates.

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What are examples of polysaccharides?

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Polysaccharides consist of multiple monosaccharides or more complicated structures, making them complex carbohydrates.

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What is starch?

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Answer

Starch is a polysaccharide.

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Question

What's the most abundant biopolymer in the world? 

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Answer

cellulose

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What's the glycemic index? 

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The glycemic index sorts carbohydrates based on how fast and how much it raises blood sugar levels on a scale of 0 to 100.

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What can affect a carbohydrate's glycemic index?

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processing

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Why are simple carbohydrates, in general, less healthy than complex carbohydrates?

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Simple carbohydrates are used for energy faster by the body than complex carbohydrates because they are shorter and less complex. This means that simple carbohydrates usually lead to a quicker rise in blood sugar and pancreatic insulin secretion, sometimes resulting in harmful health effects.


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What's the difference between amylose and amylopectin?

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amylose is a starch and it's branched 

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What's the difference between polysaccharides and oligosaccharides?

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Oligosaccharides are carbohydrates usually consisting of three to ten monosaccharides, while polysaccharides are, on average, longer.

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What are carbohydrates?

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Carbohydrates are the most common organic compounds that consist of carbon, hydrogen, and oxygen that serve as a source of energy for living organisms. 

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What are structural carbohydrates?

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Structural carbohydrates are carbohydrates that mainly aid in the structural integrity of cells.

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What are monosaccharides?

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Monosaccharides are the monomers or building blocks of carbohydrates. 

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What's the difference between polysaccharides and oligosaccharides?

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Only polysaccharides are considered complex carbohydrates. 

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What are complex carbohydrates?

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Polysaccharides consist of multiple monosaccharides or more complicated structures, making them complex carbohydrates. 

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What are examples of structural carbohydrates?

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hemicellulose

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What are examples of non-structural carbohydrates?

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starch

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What are some oligosaccharides? 

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fructooligosaccharides (FOS)

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What are fructans?

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Fructans are polysaccharides made up of fructose monomers. 

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What are gums?

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Natural gums are polysaccharides usually found in woody parts of plants. 

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What is cellulose?

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Cellulose is a polysaccharide or complex carbohydrate made of glucose linkages. 

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Which of the following structural carbohydrates work together to form a matrix for plants?

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hemicellulose

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How does chitin compare to cellulose?

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The structure of chitin is similar to that of cellulose, and it's behind cellulose as the second most abundant biopolymer in the world.

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What are the structural carbohydrates that can be altered by proteins? 

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Fructooligosaccharides (FOS)

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Why are monosaccharides or simple sugars not considered structural carbohydrates?

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Although structural carbohydrates can be built from monosaccharides such as glucose and fructose and disaccharides such as sucrose, most simple sugars aren't structural, as their primary function is to store sugars. Structural carbohydrates can essentially be compounds that living organisms use to maintain their shape or structural integrity.

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What are proteins?

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Proteins are another type of organic compound, like carbohydrates, but their main functions include acting as antibodies to protect our immune system, enzymes to speed up chemical reactions, etc. 

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How are proteins generally classified?

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globular

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What type of protein is the majority of structural proteins?

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fibrous

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What structures do all proteins have?

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primary

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How does collagen's shape help with its function?

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Collagen proteins are naturally fibrous. This sheet-like elongated shape helps collagen serve its structural and protective role in the cell. This is because collagen's rigidity and ability to resist being pulled or stretched make it the perfect support for our bodies.

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What are some common types of proteins?

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enzymes such as amylase 

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What is the most common structural protein found in mammals?

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collagen

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What structural protein helps with blood clotting?

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fibrinogen 

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What is currently the largest protein?

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titin

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What proteins work directly together in muscle contraction and relaxation?

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titin, elastin, and collagen

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What is elastin's function?

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Elastin is also part of the extracellular matrix and works with other structural proteins, such as collagen, in connective tissues.

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What are some facts regarding collagen?

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Collagen is an elongated fibrous protein made of amino acids that bind together to form triple helix-shaped long rod structures that are usually referred to as fibrils. 

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Why are structural proteins naturally found in the body?

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Structural proteins are proteins that are naturally found in the body, and this is because they have functions that are integral to living organisms. Structural proteins maintain cell shape and form and comprise bones and even tissues! We can essentially compare structural proteins to the skeletons of our cells. 

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What are tubulin's main functions?

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cell division such as mitosis

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Why is a protein's primary structure so important?

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A protein's primary structure is its amino acid sequences linked into a polypeptide chain. This sequence determines a protein's shape. This is very important as a protein's shape determines its function. 

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What are carrier proteins?

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Carrier proteins transport molecules from one side of the cell membrane to another. 

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How does the cell membrane relate to carrier proteins?

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The cell membrane's selective permeability is why carrier proteins are necessary. 

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What are the different phospholipid arrangements?

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liposome

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What are amphipathic molecules?

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The hydrophobic tails and hydrophilic head make the phospholipids an amphipathic molecule. An amphipathic molecule is a molecule that has both hydrophobic and hydrophilic parts.

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How do carrier proteins function?

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Carrier proteins function by changing shape. This change in form allows molecules and substances to pass through the cell membrane. 

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