THE CHEMISTRY OF LIFE 49 



Proteins. These compounds are an integral part of all protoplasm. 

 They have the largest and most complex molecules of all compounds. 

 Carbon, hydrogen, and oxygen again make up the bulk of the protein 

 molecule, but there will also be atoms of nitrogen and usually some 

 other elements such as sulfur, potassium, iron, etc. The chemical for- 

 mula for hemoglobin (the substance which is found in the red blood 

 cells) is : C3032H4 816 8 72N 78 oS 8 Fe4. (S is the symbol for sulfur and Fe 

 for iron.) The important place of carbon in the protein molecule is 

 shown by the formula. About one half the weight of the protein mole- 

 cule is carbon. There are more hydrogen atoms, but hydrogen atoms 

 are much lighter than carbon atoms. The proteins can be split into 

 simpler compounds known as amino acids. About thirty different 

 amino acids have been identified from the breakdown of proteins. Pro- 

 teins cannot go into solution, but amino acids can. We shall learn the 

 significance of this in the next chapter. 



Proteins vary from organ to organ within an animal — those from 

 cells of the kidney of a man will be somewhat different from those of 

 the heart of a man. They may also vary in the same body part of dif- 

 ferent individuals of the same species — the blood of one person often 

 cannot be mixed with the blood of another because of protein incom- 

 patibility. Finally, they vary from species to species — bone can some- 

 times be grafted from one person to another person, but bone from a 

 dog cannot be grafted onto a human bone because of the protein dif- 

 ferences in the bone cells. 



REVIEW QUESTIONS 



1. Chemical reactions take place more rapidly at high temperatures than at 

 low temperatures. In view of what you have learned about the movements of 

 molecules, why do you think this is true? 



2. How may the movement of molecules be demonstrated even though the 

 molecules themselves cannot be seen? 



3. Tell how mixtures differ from compounds. 



4. Why is the number of known atoms the same as the number of known 

 elements ? 



5. Hydrogen has one proton and one electron, helium has two protons and two 

 electrons, yet helium is four times as heavy as hydrogen. How can you explain this ? 



6. Oxygen has eight protons, eight neutrons, and eight electrons. An isotope 

 of oxygen weighs one eighth more than ordinary oxygen. How many protons, neu- 

 trons, and electrons would this isotope have? 



7. An ancient mummy is found with dating which indicates that it is 9,400 

 years old. What proportion of carbon fourteen would you expect to find in this 

 mummy in comparison with the bodies of persons who have died recently? 



8. How do ions differ from atoms ? 



