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Protein Function



Ensign = enzyme
Cat = catalyst


Sugar-messenger = Insulin

Fats, Lipids

Fat-lipped-leopard = fats, lipids


Floater, boater = Motor

Motor Protein

Floater-marine = Motor protein


Moccasin, minuteman = collagen


Carrot, pelican = keratin


Hobgoblin = hemoglobin


Ant-bot = antibody

Human Growth Hormone

Huge-drill-instructor = human growth hormone


Egyptian = transcription


Proteins can cut other proteins

Protein Function


There are many different kinds of proteins are present in any given cell. Proteins are necessary for every activity in an organism, from metabolism and growth to development and reproduction. Different types of proteins serve different purposes.

Proteins and their structure

Proteins are chains of twenty different amino-acids. The sequence in which the amino-acids are arranged is decided by the genetic code in the DNA, which is transcribed and passed on through the RNA, which then synthesize proteins at ribosomes. The sequence of the of amino acids in a polypeptide chain is also called its primary structure. Secondary and tertiary structuring produce a three-dimensional form, resulting in a finished protein. If there are more than one polypeptide chains, a quaternary structuring holds them together to give a macromolecule. The sequence of amino-acids and the three-dimensional form of the proteins determine its function.


Each cell has many proteins that determine its structure and function. Each protein can have more than one role, or just one single role.

  • Structural
  • Transport
  • Storage of material
  • DNA regulation
  • Responding to stimuli
  • Enzymes
  • Hormones
  • Antibodies
  • Contractile
  1. Structural

Structural proteins work at various levels, from cell to tissue to the whole body. In the cell, there are different kinds of structural proteins, which are responsible for maintaining its form. Eukaryotic cells are bigger than prokaryotic cells, and need more of them.protein

Structural proteins are present and very important to any tissue that is hard, such as bones, horns, hair, skin, etc. The structural proteins collagen and elastin are found in tendons and ligaments, and provide support to the whole body. Another structural protein, collagen, connects different tissues and organs in the vertebrate body like bones, muscles, blood vessels and skin, and accounts for 25% of the proteins in a body. 

  1. Transport of material

These proteins bind to electrons or atoms and transport them throughout a cell or body. Within the cell, cytochrome help in electron transport during cell mechanisms.

Transport proteins also provide for metabolic respiration by transporting nutrients to all parts of the body. Waste produced by cells is also transported away by proteins. For example, hemoglobin is a protein with a quaternary structure that is found in red blood cells.. It carries oxygen from the lungs to every cell in the body.

  1. Storage proteins

Storage proteins store atoms or molecules at the cellular or tissue level. For example, ferritin binds to iron and stores it. Most the iron in the body is bond to ferritin. This protein is found in the liver, spleen, bone marrow, and the blood. Some proteins also store amino-acids, like the ovalbumin in egg whites and the casein in milk.

  1. DNA regulation

Some proteins, like histone and cohesin, regulate the structure of chromosomes, and therefore gene expression. Various complexes of proteins are necessary for the repair of DNA. For example (MutSα) and (MutSβ) in eukaryotes have functions like recognition of strand mismatch, which is the first step in DNA repair.

  1. Responding to stimuli

Proteins are capable of picking up signals from outside the cell. They then help the cell to react to these stimuli. As part of this job, some proteins also regulate movement of certain molecules in and out of a cell by acting as channel proteins.

  1. Enzymes

One of the major roles of proteins is to act as catalysts as enzymes. They lower the activation energy needed for biochemical reactions to levels found in the cells, and thereby catalyze these reactions. Enzymes act by providing active receptor sites for substrate/substrates to bind to, and help in cleaving molecules or synthesizing bigger molecules. Anabolic enzymes build more complex molecules from smaller ones, and catabolic enzymes breakdown large molecules to smaller ones. Without enzymes, cells would not be able to function at all.

At the level of organs, enzymes are needed for the digestion of food and are found in the saliva and digestive tract. Catabolic enzymes, like pepsin and lipase, breakdown proteins and lipids respectively.

  1. Hormones

As hormones, proteins act as messengers between different tissues or organs of a body to co-ordinate body functions. They act as receptors and detect concentrations of chemicals, then they send signals to attract chemicals if concentrations are low. Hormones are secreted by endocrine cells, and are involved in all functions of the organism like metabolism, growth, and development.

Examples of hormones are insulin, oxytocin, and somatotropin. Insulin co-ordinates the amount of glucose cells absorb. This action by insulin regulates the level of sugar in blood.

8. Antibodies

antibodiesAntibodies are proteins that protect the body against foreign substances and prevent infections. They are produced by the immune system to immobilize pathogens like bacteria, viruses, and fungi by binding to them. These pathogens are then destroyed by the immune system. Sometimes, they are involved against harmful cells of the same organism, like cancer cells. Antibodies, for example immunoglobulins, are specific to each foreign particle.

  1. Contractile proteins

These proteins allow the body to move, and are found in muscles. For example, actin and myosin help in muscle contraction.


Proteins are chains of amino acids, and are built at ribosomes by mRNA from the genetic information decoded from DNA. There are many different types of proteins present all throughout the body, and each type serves one or more unique function.

Structural proteins provide structure and aid in cell division. Transport and storage proteins transport and store materials, and contractile proteins allow for movement in the body. Hormones are messenger proteins. Antibodies are specialized proteins that fight off certain infections, and enzymes lower the required activation energy, enabling chemical reactions to occur. Some proteins regulate and repair DNA, while others yet recognize and initiate cellular responses to stimuli surrounding the cell. Proteins are a vital component of cellular and body functions, and without them, life would not exist.

Functions of Proteins Script

1. Zoom: whole image

Hot Spot: advanced-training = side chains; Marines = proteins

Learning: As discussed in the previous lesson, proteins are chains of amino acids bonded together in peptide bonds. The arrangement of amino acids in the chain and their side chain reactions determine what sort of protein is built and what function it will serve. In this CoursePic, we'll look at twelve important roles that proteins play in the body.

Story: After months of intense advanced-training, the new recruits emerge as true Marines. The Marines are each trained for one specific task, but they often work together to make more complex missions go smoothly.

2. Zoom: ensign cat with tool shelf

Hot Spot: ensign = enzyme; cat = catalyst

Learning:  Enzymes are proteins that act as catalysts, or specialized agents that reduce the energy required to activate a reaction. Here we have an ensign cat to represent an enzyme catalyst. He has chosen a hammer from the nearby tool shelf to show that he is ready to   smash the activation barrier to the reaction he was produced to help.

Story: Ensign cats always choose the correct tool for the job. This grinning fellow wisely chooses the large hammer to smash the activation barrier that stands between him and his assigned reaction.

3. Zoom: mail carrier

Hot Spot: sugar-messenger = insulin

Learning: Insulin is a messenger protein, represented here by the sugar toting messenger, that lets cells know to take in glucose from the bloodstream.

Story: The sugar-messenger runs his route from cell to cell and diligently carries the order to take in sugar.

4. Zoom: fat leopard

Hot Spot:  fat-lipped-leopard = fats, lipids

Learning: Lipids are proteins that carry fat through the bloodstream. In this scene, the lipid is represented by the fat-lipped-leopard carrying a fat cell.

Story: The fat-lipped-leopard transports fat cells through the bloodstream.

5. Zoom: whole boat, with both proteins

Hot Spot:  floater, boater = motor

Learning:  Motor proteins are essential to cell mobility. This particular motor protein, shown by a duck float wearing marine on a boat, is helping the lipid carry fat cells.

Story: This floater-marine is a boater. His expert navigation of the bloodstream is a big help to the fat-lipped-leopard riding in his boat.

6. Zoom: floater marine and robotic arm

Hot Spot:  floater-marine = motor protein

Learning:  Motor proteins in muscle cells are also responsible for contracting muscles. This motor protein, represented by the floater-marine, controls a robotic arm with muscles. 

Story: This floater-marine is  trained to operate the muscled robotic arm, which would stand motionless without him.

7. Zoom: minuteman and wall

Hot Spot: moccasin, minuteman =  collagen

Learning: Collagen is an important structural protein. To show this, we have collagen, or the moccasin wearing minuteman, building a wall to keep the bloodstream from overflowing its banks.

Story: Don't let the casual footwear fool you. This minuteman in moccasins is an expert craftsman. He can build a sturdy wall without breaking a sweat.

8. Zoom: pelicans

Hot Spot:  carrot, pelican = keratin

Learning:  Keratin is another important structural protein. Keratin is hydrophobic. This means it is not attracted to water and may appear to repel water, though there is no actual repulsive force at play. These two carrot beaked pelicans interlock their wings and create a dry spot in the bloodstream to show that water can't get through.

Story: The carrot beaked pelicans can keep anything dry between their wings. Their feathers interlock so tightly that no water can get through.

9. Zoom: hobgoblin

Hot Spot:  hobgoblin = hemoglobin

Learning: Hemoglobin carries oxygen through the bloodstream. To show this, we have a hobgoblin wearing an oxygen tank swimming in the bloodstream.

Story: The hobgoblin is an expert swimmer, and carries out the vital mission of making sure everyone has enough oxygen.

10. Zoom: ant-bot

Hot Spot: ant-bot = antibody

Learning: Antibodies are proteins keyed to specific bacteria and viruses that seek out and fight off infection. This antibody, shown as an ant-bot, is working out and eating to stay in fighting shape for the next infection.

Story: The ant-bot is an efficient killing machine, the bane to all invaders. To stay in fighting shape, he eats right and trains constantly.

11. Zoom: huge drill instructor and antbot

Hot Spot:  huge-drill-instructor = human growth hormone

Learning: Human growth hormone is a protein that promotes growth. In this scene, human growth hormone, represented by the huge-drill-instructor, is promoting growth by drilling the ant-bot.

Story:  To keep everyone in fighting shape and make sure they continue to grow as Marines, this huge-drill-instructor never lets them stop training. Right now, he's making sure this ant-bot maintains a healthy diet and work out routine.

12. Zoom: Egyptian and puzzle table

Hot Spot:  Egyptian  = transcription

Learning:  Transcription proteins transcribe DNA into mRNA for further protein synthesis. To show this, we have an Egyptian working on a puzzle.

Story: The Egyptian is the master trainer. Without his skills at putting the puzzle together, there would be no way to train future Marines.

13. Zoom: Egyptian and guy with sword

Hot Spot:  proteins can cut other proteins

Learning: When proteins get too old or damaged to function properly or simply aren't needed anymore, other proteins can cut them so that they can be recycled. The Marine drawing his sword is ready to cut the Egyptian, who has become too old and feeble minded to accurately finish the puzzle.

Story: This Egyptian has fulfilled his duties faithfully, but now he's getting too old to keep up. The pieces just don't seem to fit together like they used to, and he gets confused often. To make room for a new Egyptian, this Marine draws his sword and prepares to cut down the old Egyptian. For the Marines, retirement is a real killer!

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