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Biophysics in Space

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INTRO TO BIOPHYSICS

Biophysics: Physics of biological systems

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Self-Assembly and folding

Microbial behavior and biofilm formation

Protein Crystallization

Biophysics is the field that uses physics to study the behavior of small-scale biological phenomena. For a long time, biology and physical sciences were treated as two different fields, and it was thought that biology was too complex to be explained by simple physical laws. Recently, however, more and more physcists and engineers have been applying physical science to biological systems. Physics such as thermodynamics, fluid mechanics, heat and mass transport, surface science, and more can be applied to explain biological behavior.

For example, proteins are able to self-assemble and fold into specific shapes. Without protein folding correctly, life wouldn’t exist. Thermodynamics has now explained that proteins fold into their shapes due to hydrophobic and hydrophilic interactions, where the hydrophobic portions of the protein try to fold towards the interior and hydropiliic areas fold towards the outside.

Another application of physics into biological system is the crystallization of proteins to determine their structure. Scientists have used crystallization (for example, of salt), as a purification process for a long time, but more recently they have found that the simple laws of crystallization can also apply to large, complex molecules such as proteins.

Even microbes follow the same physical laws despite being on a small scale. Fluid mechanics can explain microbial behavior and biofilm formation.

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PROTEIN

Proteins are responsible for many biological functions:

DNA replication
Transporting molecules
Metabolism
Cell structure

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Protein: Macromolecules composed of amino acid chains.

Primary structure: molecular chain
Secondary structure: folding into helixes and beta sheets
Tertiary structure: folding of helixes into a monomer

Proteins are macromolecules, meaning they are very large in comparision to other types of molecules. Water is a molecule composed to two hydrogen atoms and one oxygen atom. Protein molecules contain thousands or tens of thousands of individial atoms, which is why they are called “macro”. Proteins have 4 different structures. The first is a long chain of amino acids. There are only 20 different amino acids in total; but different combinations make up hundreds and thousands of different proteins. These amino acid chains fold into secondary structures of either alpha-helixes or beta sheets. The alpha helix structure is similar to the structure of DNA, with these long twisty spirals that look like old-fashioned phone cords (point to image where ~8 different helices are visible). The other type of secondary structure is called beta-sheets. These are flat segments where proteins are bound close together (point to the light blue and dark blue arrows on the picture. Next, the protein folds again into the tertiary (or third) structure. This is the structure formed when the alpha-helices and beta sheets fold into each other (ie, the overall structure shown on the image). Finally, these individual proteins, called monomers, will sometimes bind to other proteins to create a multimer (multiple monomers). This combination of multiple proteins is called the quartenerary (or 4^th) structure.

A proteins structure dictates it’s function in the body. Proteins do almost everything within the body. They build structural elements of your cells, they transport molecules, they are responsible for your metabolism, they build muscle cells, and more.

Even though protein folding is very complicated, your body almost always gets it correct. This is very very important for people, because when proteins stop folding correctly you get sick. Some illnesses associated with protein misfolding include alzheimers, parkinsons, and diabetes.

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CRYSTALLIZATION - WHY

Proteins are very large molecules with a complicated structure.
Determining the structure important for curing disease
To find structure, crystallize the molecules

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Crystal: Repeating units in an organized structure

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CRYSTALLIZATION IN SPACE

Why might this be the case?

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Video: Protein crystallization on the space station

Crystals that are grown in microgravity are larger and more pure than crystals grown on the ground.

https://youtu.be/9p0czSsawVw

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ACTIVITY – SALT CRYSTALS

Materials

Water
Salt (sodium chloride)
Plastic cups (2 each)
Plastic spoons
Paper towels or napkins
Aluminum foil to cover cup
Position to leave cups over the course of a week

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Procedure

Fill cup 3/4^th the way with water
Add salt, a spoon at a time, and mix

How many spoons do you need before the salt stops dissolving?

Once salt will no longer dissolve, use the paper towel to make a filter on a second cup
Carefully and slowly pour the salt water through the filter to remove excess salt

You have just created a saturated solution of sodium chloride

If you want, you can add dust, a single hair, or piece of dirt to your salt mixture.

This creates nucleation zones for the salt to grow

Cover solution and put aside
Check crystals in a week�

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MICROBES AND BIOFILMS

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Micro-organisms: Bacteria, viruses, and other microscale, single-cell organisms

Biofilms: Bacteria survive on surfaces by creating a viscous layer to protect themselves. Video: https://www.youtube.com/watch?v=1XNM4bLgt_U

Micro-organisms are all around us, and many that we encoutner are harmless or even beneficial. For example, there are microbes that live inside your stomach that help you digest different types of foods. Microbes can also make people sick. Microbes are a group of single-cell organims that are too small to see with the eye. Instead, we need to look through a microscope to see them. Some types of viruses and bacteria can make you sick. These types of microbes are called pathogens. Bacteria are responsible for many types of infections and for making food go bad. Can anyone tell me why it’s important to wash your hands after going to the bathroom or touching a surface? … Because microbes live on surfaces and can get on your hands. If you touch your hand to your face without washing off the pathogenic bacteria you can get infected with them. Most viruses can’t survive outside of the body for very long, but some types of bacteria can. They do this by forming biofilms.

First, bacteria attach to the surface. This might happen when someone coughs or sneezes and a drop reaches the surface. The bacteria then start laying down a film that they can grow on. The biofilm grows as more and more bacteria join the new colony. They excrete a layer of goop to help protect them, which allows them to survivce disinfection. When the colony grows large enough, some bacteria will be excreted and spread from the original point. The silmy layer you feel on your teeth in the morning is due to biofilm formation, and that is why its important to brush your teeth.

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BIOFILMS IN SPACE

Despite the small size of bacteria, biofilms are made differently in space.

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Why do you think this is?

Bacteria are very small, and usually we assume that they do not feel the influence of gravity. However, experimental evidence suggests that biofilms are constructed differently in space. This is important because (1) It gives us clues as to how biofilms are created, (2) biofilms in space can damage electronics, clog life support systems, and cause astronauts to become sick.

Can anyone guess why biofilms are different in space? Give some time for students to think, maybe even have them discuss amongst each other and write a hypothesis A: We actually don’t know. New experiments are trying to find out. Some reasonable hypotheseses might be: (1) Airflow in microgravity is different because of lack of convection, which influences how microbes receive oxygen. (2) Microbes that want to eject from surface may not know which direction to grow, so grow outward instead. (3) Surface tension in microgravity allows for different shapes (4) spaceflight causes alteration in genes or stress responses that cause them to behave differently.

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REFERENCES AND RESOURCES

Alternative crystallization hands-on demo from NASA: https://www.nasa.gov/pdf/315960main_Microgravity_Rapid_Crystallization.pdf
Space Life Sciences from NASA: https://www.nasa.gov/audience/foreducators/spacelife/home/index.html
NASA’s researcher guide to macromolecular crystal growth: https://www.nasa.gov/connect/ebooks/researchers_guide_macromolecular_crystal_growth_detail.html
NASA’s researcher guide to microbial research: https://www.nasa.gov/connect/ebooks/researchers_guide_microbial_research_detail.html
References for biofilms in space: Kim, W.S., Tengra, F.K., Young, Z., Shong, J., Marchand, N., Chan, H.K., Pangule, R.C., Parra, M., Dordick, J.S., Plawsky, J.L., and Collins, C.H. “Spaceflight promotes biofilm formation by Pseudomonas aeruginosa.” PLoS One 8, e62437 (2013)
https://www.sciencedirect.com/science/article/pii/S0094576517317083

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