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23.4 Proteins and Amino Acids
The structure allows neighboring molecules to form multiple hydrogen bonds with one another, resulting in the rigid and stable properties we associate with wood and fiber.
Humans don't have the ability to digest cellulose.
When we eat a lot of fiber in our food, it goes through our gut and provides bulk to our stools.
Somebacteria have the enzymes required to metabolize into its component units.
Thesebacteria are found in the guts of cows and other ruminants, which allow them to extract calories.
There are branches in the chains of both of them.
The link between individual glucose units is broken when animals digest starch.
Animals use glycogen in their muscles.
Many end groups can be quickly hydrolyzed to meet energy needs.
Muscle movement and exercise become more difficult when the muscles are not filled with glycogen.
Most marathon runners hit the wall at about mile 20 because they have exhausted most of their muscles.
In living organisms, the workhorse molecule is the proteins, they are involved in virtually every facet of cell structure and function.
Life wouldn't be possible without enzymes.
Structural elements of muscle, skin, and cartilage are also contained in the body's cells.
They transport oxygen in the blood, fight disease, and function as hormones to regulate metabolism.
The working molecule of life is the proteins.
The functions of some of the important classes of proteins are summarized in the table.
They are made from the amino acids.
The presence of an atom--called the a@carbon--bonded to four different groups: an amine group, an R R group, and a carboxylic acid group--indicates a side chain.
Table 23.3 has possible R groups.
The general structure of the Amino acids is different.
Side chains and lysine differ.
serine has a polar R group, whereas phenylalanine has a nonpolar one.
Aspartic acid has an acidic R group, while lysine has a basic one.
The structure and properties of the protein are determined by the chemical properties of the R groups.
There are three-letter abbreviations for the most common amino acids.
There is a chance for an even larger diversity of proteins.
The a@carbon has four different groups attached to it and all of the amino acids are related to it.
The L-enantiomers are called L-amino acids.
There is an interesting question about why life on Earth is based on this enantiomer.
The structure of the amino acids is ionic and depends on the pH.
The equilibrium is far to the right at room temperature.
Since one side of the dipo lar ion is positive and the other is negative, there is a high degree of polarity in the water.
They have high melting points.
Most carboxylic acids and amines are less basic and less acidic because of the acid-base reaction.
An example of a condensation the molecule they form has two distinct ends is an N-terminal end reaction.
One or more polypeptide chains, with each chain consisting of hundreds or even thousands of amino acids joined by peptide bonds, is what functional proteins usually contain.
The reaction by which valine, cysteine, and phenylalanine link is shown.
Designate valine as N-terminal and label the ends of the tripeptide.
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