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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Betaines

Betaines are found in plants, animals and microorganisms. Rich sources of betaines in the human diet are seafood, spinach and wheat germ or bran. Research is beginning to indicate that betaines are important nutrients for the prevention of chronic disease. Researchers are also interested in incorporating betaines into polymer brushes used for antifouling and lubrication.

Betaines are compounds with a positively charged functional group linked to a negatively charged functional group with an alkyl chain in between. The alkyl chain is often referred to as an alkyl chain spacer.  The general structure of an N-alkyl betaine is shown below:

The first betaine discovered was found in sugar beets in the nineteenth century. This betaine is (trimethylammonio)acetate, also known as trimethylglycine, and its skeletal structure is shown below:

Another example of a betaine is 2-(trimethylammonio)octadecanoate (also known as hexadecylbetaine) with the skeletal structure shown below:

2-(Trimethylammonio)tetradecanoate, or dodecylbutaine or laurylbutaine, is also a butaine and its skeletal structure is shown below:

Betaines are strongly attracted to water molecules because of these two charged functional groups.
The solubility of betaines in water is dependent on the length of the carbon chain, as well as on temperature and pH. 
In acidic solution, betaines acquire a net positive charge and act like a cationic surfactant. In anionic solutions, betaines acquire a net negative charge and act like an anionic surfactant.

Betaines can also be used in polymer brushes which are polymers bound to a surface. Polymer brushes can be used for antifouling and lubrication because the hydration of the ionic groups reduces the ability of other materials to adhere to the surface. 

Researchers at Kyushu University recently investigated a series of alkly chain spacers of different lengths bound to a silicon surface. They found that the polymer brushes swelled in humid air and water. It is believed that this is due to electrostatic repulsion between charged groups, and not dependent on the length of the alkyl chain.
In deionised water, net positive cations and net negative anions are repelled because of the  electrostatic force which causes the chain dimension to expand, whereas they shrink under high ionic strength by a charge screening effect of the bound ions.

Reference:
https://www.sciencedaily.com/releases/2017/08/170821094302.htm

Further Reading
Introduction to Functional Groups
2-Dimensional Structural Formula
Condensed Structural Formula
Molecular Formula
Amino Acids
Surfactants ( as found in synthetic detergents)
Intermolecular Forces and Solubility

Suggested Study Questions

1. Locate and identify each functional group on the skeletal structural formula of
• general formula N-alkyl betaine 
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
2. Draw a 2-dimensional structural formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
3. Write the condensed structural formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
4. Write the molecular formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
5. Compare the structure of betaines to that of 2-amino acids. Can N-alkyl betaines be classified as alpha amino acids (2-amino acids) ? Justify your answer.
6. Write chemical equations to describe what happens to an N-alkyl betaine in:
• acidic aqueous solution
• basic aqueous solution
7. Compare the structure of N-alkyl betaines to the surfactants found in synthetic detergents. In what ways are surfactant molecules 
• similar to N-alkyl betaines
• different from N-alkyl betaines
8. Explain how N-alkyl betaines act like 
• a cationic surfactant in acidic aqueous solution
• an anionic surfactant in basic aqueous solution
9. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in water? Justify your answer.
10. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in paraffin oil? Justify your answer.

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!

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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.
    

Tasty Chemistry

Taste refers to the ability to detect the flavour of substances. We receive tastes through sensory organs called taste buds which are concentrated on the upper surface of the tongue.
Among the 50 or so cells in each taste bud there are cells responding to each of the five tastes:

• sweetness
• bitterness
• sourness
• saltiness
• umami-ness or savoriness
  

Sweetness is often associated with foods rich in simple carbohydrates such as glucose and sucrose, but many compounds taste sweet. Examples include the amino acids alanine, glycine and serine as well as the glycosides glycyrrhizin (found in licorice root) and stevioside (from the Stevia rebaudiana shrub). Even some inorganic compounds, such as beryllium chloride and lead acetate, taste sweet.

Bitterness is perceived by many people to be unpleasant. It helps prevent us ingesting toxic substances. A bitterant is the chemical that makes a substance taste bitter. Examples of bitterants are sucrose octaacetate which is used as an inert ingredient in pesticides and herbicides, and, brucine which is a bitter alkaloid closely related to strychnine that is found naturally in a number of plant species.

Sourness is the sensation evoked by substances that are acidic such as lemons and pickles. The acids we ingest release protons which enter the cell and cause a direct, detectable, electronic response.

Saltiness is the taste produced by the presence of alkali metal cations such as Na⁺ and K⁺. The less sodium-like the ion is, the less salty the sensation will be, eg, Rb⁺ and Cs⁺ ions are larger than Na⁺ ions so they do not taste as salty.

The umami taste is due to the detection of the carboxylate anion of glutamic acid, a naturally occurring amino acid found in meat, cheese, and other protein-rich foods. Glutamates, the salts of glutamic acid, easily ionize resulting in the same carboxylate anions and therefore producing the same umami taste. As a consequence, glutamates are often used as flavour enhancers, the most common of which is monosodium glutamate (MSG).

Further Reading
Carbohydrates (sugars)
Amino Acids
Properties of Acids and Bases

Study Questions

1. Name the 3 elements common to all carbohydrates.
2. What is the structural difference between molecules classified as monosaccharides and those that are classed as disaccharides or polysaccharides?
   
3. Is glucose an example of a monosaccharide, a disaccharide or a polysaccharide?
4. Is sucrose an example of a monosaccharide, a disaccharide or a polysaccharide?
5. What elements are common to all amino acids?
6. What functional group or groups must a molecule contain in order for it be classified as an amino acid?
7. Draw the structures for glycine, alanine and serine. Identify the functional groups present in each molecule.
8. A number of amino acids are said to taste sweet, but acids generally are said to taste sour. Can you explain these apparently contradictory statements?
   

Growing Glycine Crystals

Chemists from New York University and St. Petersburg State University have been observing the growth of crystals of hippuric acid, a derivative of the amino acid glycine, and have discovered a new crystal growth phenomenon, a crystal that continually changes shape as it grows!

As molecules were added to the end of fine crystalline needles, stresses built up at the tips of the crystals resulting in a helical twist, just like you find in DNA's helix.
The twisiting process was reversed when the crystals thickened from the opposite end of the growing tip, ie, the crystals stiffened, undoing the twisted formations because the elasticity of the crystals decreases as they become thicker and this squeezes out the deformations formed at the growing tip.
The competition between twisting and untwisting creates needles with a rainbow of colours, characteristic of tightly wound helices and untwisted ribbons.

Reference:
New York University (2010, July 17). Chemists grow crystals with a twist -- and untwist. ScienceDaily. Retrieved July 19, 2010, from http://www.sciencedaily.com­ /releases/2010/07/100716125641.htm

Study Questions

1. What is the abbreviation for glycine?
2. Give the formula for glycine.
3. Why is glycine considered to be an amino acid?
4. Explain why glycine would be considered to be amphiprotic.
5. Write an equation to show how glycine could act as an acid.
6. Write an equation to show how glycine could act as a base.
7. Write an equation to show the formation of a cation from glycine in acidic solution.
8. Write an equation to show the formation of an anion from glycine in basic solution.
9. Compare the description of crystal growth as given in the article with what we consider to be the more "traditionally accepted" view of crystal growth.