The molecules of life
All living things require four types of large molecules to survive. These are the macromolecules of life. Macromolecules are molecules that contain a very large number of atoms. We'll take a look at each of these types of molecules, and determine what each does for the cell, and where they are found.
Macromolecules are large molecules within your body that serve essential physiological functions. Encompassing carbohydrates, proteins, lipids and nucleic acids, macromolecules exhibit a number of similarities. For example, all except lipids are long chains made up of smaller building blocks, and digestion reduces the size of macromolecules so your body can absorb their component parts. However, they also demonstrate distinct differences.
Let's take a look at what a Macromolecule is :
Biological macromolecules are defined as large molecules made up of smaller organic molecules. There are four classes of macromolecules: carbohydrates, lipids, proteins and nucleic acids. Nucleic Acids will be covered in more detail in a later section (DNA Structure). The base elements of carbohydrates and lipids are Carbon (C), Hydrogen (H) and Oxygen (O). Molecules that contain Crbon are Organic, while those that do not contain carbon are Inorganic.
Types of Biological Macromolecules
Protein molecules are made up of the base elements Carbon (C), Hydrogen (H) and Oxygen (O), and also contain the element Nitrogen (N). The presence of Nitrogen distingushes Protin from two of the other Macromolecules Carbohydrates and Lipids.
Each protein is made up of smaller organic molecules. These smaller molecules are known as monomers. These small molecules are similar to each other, and are repeated in a chain. Monomers are covalently bonded together to create a large polymer molecule. The monomer unit for Proteins are monomers called Amino Acids. There are twenty amino acids and they can be strung together in unique combinations known as polypeptide chains (Polypeptide chains are what we call the polymer unit for proteins). A protein is only complete and functional when the polypeptide chain is folded into a unique 3-D shape, a concept e will discuss further in our Genetic and Heredity section. Proteins are not a good source of energy.
What are Protein sub-units?
The building blocks that make up proteins are called amino acids. Proteins consist of 20 different amino acids, mixed and matched to create a vast array of larger molecules that support every process in your body. Digestion of protein results in a pool of single amino acids that your cells incorporate into new proteins as the need arises in your body. These molecules make up muscles and organs, transmit signals between cells, constitute immune molecules, help create the new proteins your tissues require and can serve as a fuel source in a pinch.
So, what do Proteins do?
Proteins do most of the work in cells and are required for the structure, function, and regulation of the body's tissues and organs.
Examples of protein functions
Function Description Example
Antibody Antibodies bind to specific foreign particles, such as viruses and bacteria, . Immunoglobulin G (IgG)
to help protect the body
Enzyme Enzymes carry out almost all of the thousands of chemical reactions that Protease
take place in cells. They also assist with the formation of new molecules by
reading the genetic information stored in DNA.
Messenger Messenger proteins, such as some types of hormones, transmit signals to Growth hormone
coordinate biological processes between different cells, tissues, and organs.
Structural Actin & Myosin
These proteins bind and carry atoms and small molecules within cells Ferritin
protein molecule - note the Nitrogen atom contained in the molecule
SIRT3 protein molecule- note that the shape and twists determine its functional parts
A carbohydrate is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen:oxygen atom ratio of 2:1 (as in water); in other words, with the empirical formula Cm(H2O)n (where m could be different from n).
What are Carbohydrate sub-units?
Carbohydrates consist of single-sugar units called monosaccharides, double-monosaccharide units known as disaccharides and multiple-monosaccharide molecules that make up starches. The predominant purpose of the carbohydrates you eat is to provide fuel to your cells. Disaccharides and starches undergo digestion to reduce them to their individual sugars, and, once absorbed, they travel to the cells and tissues throughout your body to power your physical activities. A special type of carbohydrate, known as fiber, passes through your gut undigested. While fiber doesn’t provide you with cellular energy, it improves your digestive health by regulating your bowel function.
So, what do Carbohydrates do?
Carbohydrates as a group includes sugars and starches. Carbohydrates perform numerous roles in living organisms. Starches serve for the storage of energy and as structural components (e.g., cellulose in plants and chitin in arthropods). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g., ATP) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA.
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Carbohydrates are commonly found in many foods, especially breads, pastas, dairy products, fruits and vegetables. Carbohydrates provide our bodies with its primary source of energy, although we can also produce energy from fat if we are on a low-carb diet. If our diet provides more carbohydrates than you need the excess will be converted to fat.
The body uses carbohydrates as “fast fuel.” It is the first macromolecule used to obtain energy for the body because very little energy is required to break down carbohydrates. Carbohydrates are sugar molecules. They are made up of the base elements C, H and O in a 1:2:1 ratio. The simplest carbohydrate is a monosaccharide (a simple sugar). An example of a simple sugar is glucose, which is the molecule plants use to store energy, and is created during photosynthesis. Monosaccharides are covalently bonded together to create more complex sugars. A disaccharide is two covalently bonded simple sugars or monosaccharides. A polysaccharide is the carbohydrate polymer and consists of several monosaccharides bonded together. A common polysaccharide is starch. Starch is a storage polysaccharide found in plants. Another plant polysaccharide is cellulose, a major component of a plant’s cell wall.
3. Nucleic Acids
Cells contain two types of nucleic acids, ribonucleic acid and deoxyribonucleic acid, or RNA and DNA, respectively. They differ from the other macronutrients in that they are not a source of calories in your diet, and their role is strictly to direct the synthesis of new protein molecules. Made up of units called nucleotides, the nucleic acid DNA contains the genetic blueprint that influences your personal characteristics, while the nucleic acid RNA pulls together amino acids to form new proteins as your cells need them.
What are Nucleic Acid sub-units?
Nucleic Acids are Macromolecules (Large molecules made up of many atoms), and they are Polymers (molecules that are made up of many small sub-inits called Monomers). The sub-units that make up Nucleic Acid molecule are nucleotides.
So, what do I need to know about Nucleic Acids?
DNA (deoxyribose nucleic acid) and RNA (ribose nucleic acid) are both nucleotide polymers. These molecules are very similar but there are some distinct differences between them. Both molecules are helical structures but DNA is a double helix whereas RNA is a single helix. The Monomer units of Nucleic Acids are Nucleotides. DNA is made up of the nucleotide monomers Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). RNA is also made up of A, G and C but T is replaced with Uracil (U). Another distinct nucleotide difference between them is that DNA has one less oxygen on the 5 carbon sugar than RNA; this accounts for the difference in their names. Deoxyribose simply refers to a ribose sugar lacking an oxygen molecule.
DNA is the main molecule that contains instructions for all of the proceses a cell needs to live. The DNA molecule codes this information in the order of nucleotides it contains. The information coded in this sequence contain the sequence of Amino Acids needed to make specific proteins. The proteins perform the activities needed by the cell.
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DNA (deoxyribose nucleic acid) and RNA (ribose nucleic acid) are both nucleotide polymers. These molecules are very similar but there are some distinct differences between them. Both molecules are helical structures but DNA is a double helix whereas RNA is a single helix. The Monomer units of Nucleic Acids are Nucleotides. DNA is made up of the nucleotides Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). RNA is also made up of A, G and C but T is replaced with Uracil (U). Another distinct nucleotide difference between them is that DNA has one less oxygen on the 5 carbon sugar than RNA; this accounts for the difference in their names and structures. Deoxyribose simply refers to a ribose sugar lacking an oxygen molecule. Nucleic Acids are not a source of energy for the cell.
So what do Nucleic Acids do?
Do you remember that Prokaryotes do not have organelles? Well, this means that Prokaryotes do not have a nucleus, so their DNA is floating in their cytoplasm; but that's not the case for Eukaryotic cells. Cells need to protec their DNA, because DNA is the instruction set for everything the cell does. IT is really important that the cell not have any problems with its DNA, because then it wouldn't be able to work properly, and would die.
So, DNA is protected inside the nucleus of eukaryptoc cells. You may wonder "how do the instructions get used wheren they are needed if the DNA stays in the nucleus?". That's a good question, and that's where RNA comes into play. RNA is a copy of a section of DNA that can move between the nucleus and cytoplasm. RNA isn't restricted to stay inside the nucleus, because RNA is just a copy of t he DNA, and it is disposable. RNA copied from the DNA is used to build strings of Amino Acids (a string of amino acids is called a protein), and once it is done, it is broken down and recycled. The cell can't break down the DNA, because then we would loose the instructions forever, but we don't have that limitation with RNA.
Lipids are molecules that are not polymers; lipids are not made up of smaller units. This is a differenec between lipids and the other macromolecules we have been studying. Lipids are fats, oils, waxes and steroids - and are used by all cells.
We have many different types of lipids in our bodies including fats, oils, waxes and steroids. Organisms body uses fats as a supply and store of energy: a gram of fat contains more than double the amount of energy present in a gram of carbohydrate. The steroids in your body include some hormones. Other lipids make up the outer layer of all your cells, and the fatty sheaths that insulate nerve fibres. Cells use yet another type
of lipid to communicate with each other.
What are Lipid sub-units?
Lipids are not made uf sub-units - there are no monomers, because lipids are not polymers.
So, what do Lipids do?
You have many different types of lipids in your body including fats, oils, waxes and steroids. Your body uses fats as a supply and store of energy: a gram of fat contains more than double the amount of energy present in a gram of carbohydrate. The steroids in your body include some hormones. Other lipids make up the outer layer Membranes) of all your cells, and the fatty sheaths that insulate nerve fibres. Cells use yet another type of lipid to communicate with each other.
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Unlike the other macromolecules, lipids are not soluble in water, and they don’t form long sequences made up of similar or repeating smaller units. The fats you consume are molecules called triglycerides, consisting of three fatty acids attached to a glycerol. The chemical nature of the fatty acids contained within the lipid determines its physical characteristics. For instance, a fatty acid that is saturated with as many hydrogen atoms as it can hold is solid at room temperature, while unsaturated fatty acids are liquid. These macromolecules store energy within fat tissue, and they cushion your internal organs against trauma. They also form the structure of cell membranes and contribute to the synthesis of hormones.
But what about energy storage?
Can I see some examples?
Cell membranes are made up of a phospholipid bi-layer (Bi-layer = 2 layers; Phospho-lipid = a lipid with a phosphate group attached). These molecules have long tails, with a Hydrophillic end and a Hydrophobic end. Since the cell is made primarily of water, the hydrophillic ends will stick out, andthe Hydrophobic ends will point towards each other, making a membrane that is sandwich-like.
Phospholpids, Tri-Glycerides and Steroids:
a protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms. In humans, it acts as a buffer against iron deficiency and iron overload.
filaments that are responsible for many types of cell movements. Myosin is the prototype of a molecular motor—a protein that converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement.
IgG is the main type of antibody found in blood and extracellular fluid allowing it to control infection of body tissues. By binding many kinds of pathogens such as viruses, bacteria, and fungi, IgG protects the body from infection.
any enzyme that performs proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in a polypeptide chain.
stimulates growth, cell reproduction and regeneration in humans and other animals.
These proteins provide structure and support for cells.
On a larger scale, they also allow the body to move.
Glucose (form of sugar we get our energy from) can be represented chemically meany ways.
Its checmical formula is C6H12O6
The base sugar (Deoxyribose) that forms DNA is very similar to the base sugar that forms RNA (RIbose.
Look ath the names:
Ribose is a sugar (all sugars end in -ose)
So then, Deoxyribose is a compound word that can be broken down as follows:
Deoxy means without Oxygen
ribose is the sugar name.
So Deoxyribose means ribose with one less Oxygen molecule than Ribose.
The most important similarity between the two molecules is that they are both essential in protein synthesis.
The most important difference between the two molecules is that DNA is a double-stranded molecule, while RNA is a single stranded molecule.
So what's so special about the shape of these molecules?
DNA and RNA (the two types of Nucleic Acids) are similar in composition, but they have very diffferent shapes. DNA has the shape of a double helix (a helix is a spiral, like the threads on a screw). These two helixes spiral around a centerpoint, and are held together by Nucleotides. The legs of the spirals are a repeating pattern of sugar (deoxyribose in DNA, ribose in RNA) and phosphate. The rungs of this twisted ladder are made up of nucleotides - special molecules that code information by their sequence. This all may seem too complicated to understad right now, but we'll go over this a couple of times throughout the school year, as this is a really important concept for us to understand.
The nitrogen bases that make up the nucleotide monomers are two different types of chemicals: Purines and Pyimidines. Purines can't bond to otgehr purines; Pyrimidines cannot bond to other pyrimidines. This causes these nitrogen bases to pair up in a speific way: Guanine (a purine) can only bond with Cytosine (a pyriidine), and Adenine (a purine) can only bond to Thymine (a DNA specific Pyrimidine). RNA does not contain Thymine; all Adenines in RNA bond to a Uracil (an RNA specific Pyrimidine).
A listing of lipids, grouped into categores based on structure.
The Phospholipid bi-layer is labeled in the diagram to the left. Remeber that membranes are envelopes that have contents, so they are really better displayed as a three dimensional structure, as shown below.