Re: how does heat kill living things?

Hello Marissa,

Heat kills living organisms primarily by denaturing proteins.  Proteins 
typically function in a very narrow range of temperatures; for humans, this 
temperature is 37 degrees C.  Once the temperature rises more than a few 
degrees above 37, proteins start to denature (literally, fall apart).  And 
since so many of your body's structures and functions are protein-based, 
once denaturation starts, all heck breaks loose.

As an example, consider the structure of cell membranes.  You probably know 
that a cell membrane consists of a phospholipid bilayer.  Well, there are 
also many kinds of proteins embedded in the phospholipid bilayer, doing a 
variety of jobs - regulating what enters and leaves the cell, maintaining 
the chemical composition of the cell, identifying the type of cell to other 
cells, maintaining the integrity of the cell membrane itself, and providing 
sites for many biochemical processes.  You can imagine that if all these 
proteins were to crumble and fall to pieces, due to heat or some other 
mechanism of denaturation, the cell wouldn't function very long.  

Nucleic acids (DNA and RNA) are also susceptible to denaturation by heat.  
When DNA is denatured, the strands of the double helix unzip and fall apart.  
As you can imagine, once the nucleic acids are denatured, the organism is 
toast, so to speak.

I hope this helps!

Allison J. Gong
Mad Scientist