Hydrolysis of Proteins

Lots of foods contain protein. When you eat them the proteins undergo hydrolysis reactions to break them down into their constituent amino acids.
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AUS-e-TUTE Members should log-in to use these new resources (listed under Biochemical Reactions).
Non-members can currently access a "free-to-view" tutorial at
https://www.ausetute.com.au/hydrolysisprot.html

Cheesy Chemistry

Now here's the title of an article that sounds like it would make a great teaching and learning tool ..
"Food hacks: The science behind making perfect cheese melts and crispy cookies"
(Sydney Morning Herald, Monday 23rd November 2015)

"Science is great isn't it? ", writes the article's author.
Yes indeed, I couldn't agree more ... looks promising .....

"Even for those of us who find the periodic table of elements a foreign language, we can still reap the benefits of science's life-changing revelations."
Well, that's going a bit far (especially if you happen to teach/learn chemistry), but even so,  it still looks OK ......

"According to science, there's only one type of cheese for your toastie."
...mmm... possibly ...... "science" is rarely capable of making that kind of judgement ..... but we'll continue reading ....

until ........

" That cheese is the one with the right PH to balance the calcium, and release the casein (dairy protein) to create one big soft melty​ mess."
PH? Is that some kind of special food science thing? Could it be phosphorus monohydride?
No, it appears to simply be a mistake, which was, unfortunately repeated on the following line.
The author was referring to pH.

Nevertheless, did you know that different cheeses have different pH values?
I didn't!
So off I went to find the pH of some of my favourite cheeses:

cheese	pH
camembert	7.44
cheddar	5.90
cottage	4.75-5.02
cream	4.10-4.79
edem	5.40
gruyere	5.68-6.62
parmesan	5.20-5.30
stilton	5.70

Apparently, pH and temperature are both critical factors in the production of cheese:

• Addition of starter culture: temperature less than 20°C, pH = 5.1-5.3 (using rennet which contains enzymes for breaking down proteins)
•  Coagulation: temperature = 30°C, pH = 5.35 - 5.45
• Pressing: temperature 16-18°C (mild cheeses) or 25°C (hard cheeses), pH = 5.0-5.3
• Brining in salt solution: temperature 15°C, pH = 5.2
• Ripening: pH increases to optimum value as given in the table above.

A crumbly cheese, like a Cheshire cheese, has a low pH and low calcium content. At low pH the colloidal calcium phosphate between casein micelles becomes soluble and the size of these protein aggregates decreases, which, makes the cheese crumbly.

A low-acid cheese (high pH cheese) like Swiss cheese, has intact casein micelles which provide an extensive string of protein aggregates giving the cheese more elastic properties.

Further Reading:
http://www.ausetute.com.au/phscale.html
http://www.ausetute.com.au/phcalcs.html
http://www.ausetute.com.au/phhcalcs.html 
http://www.ausetute.com.au/enzymes.html 
http://www.ausetute.com.au/proteins.html
http://www.ausetute.com.au/aminoacid.html
http://www.ausetute.com.au/scientificm.html
http://www.ausetute.com.au/labreport.html


Suggested Study Questions:

1. What is meant by the term pH ?
2. Calculate the hydrogen ion concentration for each of the cheeses listed in the table above.
3. Arrange the cheeses in the table from lowest to highest pH.
4. Arrange the cheeses in the table from lowest hydrogen ion concentration to highest hydrogen ion concentration.
5. What is an enzyme?
6. What is a protein made up of?
7. Why do you think the temperature of the mixture during the addition of rennet and the coagulation stages is higher than at other stages during the production of cheese?
8. "According to science, there's only one type of cheese for your toastie."
    Do you think science can really tell you the best cheese to use for your toastie? Why or why not?
9. Who do you think the intended audience of this article is? Explain your answer.
10. Imagine you have just tested the pH the of various cheeses and that it is your results shown in the table above. Rewrite this article as if it were your lab report.
    

Aspartame

In September 2014, NutraSweet Company, producer of the artificial sweetener NutraSweet containing aspartame, announced plans to close its aspartame manufacturing business and focus on more profitable lines of sugar substitutes.

Controversy has surrounded the use of aspartame in food since its introduction in the 1980s.

It has been alleged that aspartame is responsible for causing headaches, Alzheimer's disease, multiple sclerosis, even cancers.

So, what is aspartame and why is it used?

Go to the December 2014 issue of AUS-e-NEWS to find out!

Not a subscriber? Go to http://ausetute.com.au/contact.html to subscribe to our newsletter.

An Itchy Polypeptide

Scientists have a discovered that a small molecule, natriuretic polypeptide b (Nppb), is responsible for that itchy feeling in mice. When natriuretic polypeptide b is removed, and mice are exposed to itch-inducing substances, nothing happens! No itching! The nervous systems of mice and humans are similar, so the scientists believe that the same molecule is probably responsible for making you feel itchy.

Natriuretic polypeptide b  is a polypeptide made up of 32 amino acid residues as shown below:

 The amino acid residues in order of appearance are:

amino acid name	structure
serine
proline
lysine
methionine
valine
glutamine
glycine
cysteine
phenylalanine
arginine
aspartic acid
isoleucine
leucine
histidine

This research could be of enormous benefit to people who suffer from chronic itch conditions like eczema and psoriasis. Unfortunately, natriuretic polypeptide b is also used in other body processes in the heart and kidneys, so its removal in humans could cause major problems.

Reference:
S. K. Mishra, M. A. Hoon. The Cells and Circuitry for Itch Responses in Mice. Science, 2013; 340 (6135): 968 DOI: 10.1126/science.1233765

Further Reading:
Amino Acids 
Proteins 

Suggested Study Questions:

1.  What is meant by the term polypeptide?
2. Refer the structure of natriuretic polypeptide b. Draw up a table giving the name and the number of each amino acid present in each molecule of natriuretic polypeptide b.
3. What two functional groups are common to all amino acids?
4. On the structure of alanine shown below, label each of the functional groups:
   
   
5. What type of bond holds the amino acids together in the chain of natriuretic polypeptide b ?
6.  Using two molecules of serine, show how they are joined together to form a dipeptide.
7. What is the name given to the type of chemical reaction in which two serine molecules combine to form a dipeptide?
8. Name the type of bond shown between two cysteines on the structure of natriuretic polypeptide b shown above.
9. What is the primary structure of natriuretic polypeptide b ?
10. How would you describe the secondary structure of natriuretic polypeptide b ?   

Mammoth Collagen

University of York and Manchester scientists have extracted protein from the bones of a 600,000 year old mammoth. The scientists used an ultra-high resolution mass spectrometer to produce an almost complete sequence of amino acids for the collagen protein.

About 30% of all the protein found in mammals is collagen, making it the most abundant protein found in mammals. It is the main component of connective tissue and is found in muscles, tendons, ligaments and skin as well as in the cornea, cartilage, bone, blood vessels, the gut and intervertebral discs.

A collagen molecule can be about 300nm long and 1.5nm wide and is made up of 3 polypeptide chains in the structure of a left-handed helix. These helices twist together into a right-handed coil forming a triple helix which is stabilized by hydrogen bonds.
In each of the three polypeptide chains there is a regular arrangement of amino acids, often following the sequence Gly-Pro-X or Gly-X-Hyp where X is another amino acid.

Bio-archaeologists are excited about this because it is believed that protein can last in a useful form ten times longer than DNA. So, while DNA is useful in discoveries up to 100,000 years old, collagen could be used in identifying extinct animals up to 1,000,000 years old.

Reference
M. Buckley, N. Larkin, M. Collins. Mammoth and Mastodon collagen sequences; survival and utility. Geochimica et Cosmochimica Acta, 2011; 75 (7): 2007 DOI: 10.1016/j.gca.2011.01.022

Further Reading
http://www.ausetute.com.au/aminoacid.html
http://www.ausetute.com.au/proteins.html
http://www.ausetute.com.au/dna.html

Study Questions

1. What is the general name given to the smaller units that make up a protein?
2. Name the four elements found in all proteins.
   
3. What is meant by the term polypeptide?
4. Explain why proteins are considered to be biological polymers.
   
5. What is a peptide bond?
6. Amino acids are often represented by a three letter code. Give the name for each of the following amino acids:
   
   • gly
   • ala
     
   • hyp
   • pro
7. Draw a structure for each of the following tripeptides:
   
   • gly-ala-hyp
   • gly-pro-ala
8. Identify the peptide bond(s) in each of the tripeptides above.
9. What is meant by each of the following terms with respect to proteins:
   
   • primary structure
   • secondary structure
   • tertiary structure
10. Describe the primary, secondary and tertiary structures for collagen.
    

Spinach Protein Could Help Make Biofuel

Plants use photosynthesis to convert the energy of sunlight into chemical energy. Scientists would love to be able to mimic this process in order to harness the sun's energy for the production of electricity and fuel.

Scientists at the Oak Ridge National Laboratory have been studying the LHC-II protein extracted from spinach. The primary role of the LHC-II protein is as a solar collector, absorbing sunlight and transferring it to the photosynthetic reaction centres, but it can also carry out electron transfer reactions.

When LHC-II is introduced into a liquid environment containing polymers, it interacts with the polymers to form sheets similar to those found in natural photosynthetic membranes. The ability of LHC-II to force the assembly of structural polymers into an ordered, layered state, could make the development of biohybrid photoconversion systems possible. These systems would consist of high surface area, light-collecting panes that use the proteins combined with a catalyst such as platinum to convert the sunlight into hydrogen, which could be used for fuel.

Reference
Mateus B. Cardoso, Dmitriy Smolensky, William T. Heller, Kunlun Hong, Hugh O'Neill. Supramolecular assembly of biohybrid photoconversion systems. Energy & Environmental Science, 2011; 4 (1): 181 DOI: 10.1039/C0EE00369G

Further Reading
Carbon Cycle
Proteins
Oxidation and Reduction
Polymers
Fuel

Study Questions:

1. Describe the process of photosynthesis.
2. Write a chemical equation to demonstrate this process of photosynthesis.
3. What is meant by the term 'electron transfer reaction' used in the article above?
4. Is photosynthesis an example of an electron transfer reaction?
5. Many electron transfer reactions in nature. Describe one example.
6. Describe what Chemists mean when they call something a protein.
7. Explain what is meant by the term 'polymer' as used by Chemists.
8. When Chemists refer to a protein forming sheets, what type of protein structure are they referring to? Explain how this type of structure can form.
9. What is meant by the term 'catalyst'?
10. Why is a catalyst necessary for man-made systems designed to convert sunlight into hydrogen to be used as a fuel?
    

Growing Egg Shells

For a long time scientists have believed that a chicken egg shell protein called ovocledidin-17 (OC-17) played a part in the formation of egg shells. This protein is only found in the mineral region of the egg which is the hard part of the shell, and, it appears to influence the transformation of amorphous calcium carbonate into calcite crystals by acting as a catalyst for crystal growth.

Scientists have now created simulations to show how the protein binds to the amorphous calcium carbonate surface using two clusters of arginine residues located on two loops of the OC-17 protein and creating a chemical clamp to nano sized particles of calcium carbonate. While clamped in this way, the OC-17 protein encourages the nanoparticles of calcium carbonate to transform into calcite crystallites that form the tiny nucleus of crystals that can continue to grow on their own. When the crystal nucleus is sufficiently large to grow on its own, the OC-17 protein desorbs, or, falls off. This frees up the OC-17 protein to promote yet more crystallization.

Reference:
Colin L. Freeman, John H. Harding, David Quigley, P. Mark Rodger. Structural Control of Crystal Nuclei by an Eggshell Protein. Angewandte Chemie International Edition, 2010; 49 (30): 5135 DOI: 10.1002/anie.201000679

Study Questions

1. What are the elements common to all proteins?
2. Proteins are actually polymers. What is the name given to the monomers that make up a protein?
3. What kind of bond binds these monomers together within the protein?
4. What is the formula for arginine?
5. Would the "loops" referred to in reference to the structure of OC-17 be part of its primary, secondary or tertiary structure? Explain your answer.
6. What does the term amorphous mean?
7. How does amorphous calcium carbonate differ from calcite crystals?
8. What is the definition of a catalyst?
9. Do you think OC-17 could be accurately described as a catalyst? Explain your answer.
   

Life on Mars?

Was there life on Mars?
Scientists continue to look for organic compounds such as proteins in Martian soil, but to date none have been found, even though organic molecules are found in many other places in the Solar System.

Astrobiologists are beginning to wonder if the iron oxides that make up the soil on Mars, giving the planet its distinctive red colour, are photocatalysts which use energy from ultraviolet light to oxidize carbon-containing molecules trapped in soil particles converting them to carbon dioxide and gases such as methane. This suggests that the absence of proteins or other organic molecules on Mars does not necessarily mean it has never supported life forms.

Reference:
Ilya A. Shkrob, Sergey D. Chemerisov, Timothy W. Marin. Photocatalytic Decomposition of Carboxylated Molecules on Light-Exposed Martian Regolith and Its Relation to Methane Production on Mars. Astrobiology, 2010; 10 (4): 425 DOI:
10.1089/ast.2009.0433

Study Questions:

1. Define an organic compound.
2. What elements are proteins made up of?
3. Proteins are produced when what smaller compounds react?
4. What is the name given to the bond between these smaller compounds making up a protein?
5. Why do you think Astrobiologists look for proteins in order to determine if life existed on Mars in the past?

Further Reading:

1. http://www.ausetute.com.au/proteins.html
2. http://www.ausetute.com.au/aminoacid.html