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Proteins and Amino Acids - The Basics
What Are Amino Acids?
- Amino acids are simple organic compounds and are the monomers of all proteins.
- They all have the same basic structure.
- The 20 different naturally occurring amino acids that are involved in protein synthesis only differ because of the R-Group that is bonded to the central carbon.
- The R-group in different amino acid molecules differ in charge (positive or negative), size (some are larger than others) and polarity.
- All amino acids have an amino group at one end of the molecule, an carboxyl group at the other end and a carbon in between.
- Amino acids join end-to-end to create a 'repeating backbone'.
What Are Proteins?
- Proteins make up about 50% of the organic matter of a cell.
- Proteins are large molecules that are made out of carbon, nitrogen, hydrogen and oxygen.
- Their functions include:
- They provide structure - for muscles and bone.
- They can be protein carriers and channels in cell membranes.
- Many hormones are proteins.
- All enzymes are proteins.
- Antibodies are proteins.
Amino Acids - Animals vs Plants
- Plants are able to make their own amino acids that they need to live - providing they can obtain a sufficient amount of nitrate from the soil.
- They convert the nitrate into amino groups which then bond to organic groups which are the product of photosynthesis.
- Animals however cannot manufacture 8-10 of the amino acids that they need (essential amino acids) and therefore must eat protein (in the form of meat) which is then digested into amino acids.
- Animals cannot store excess amino acids, the amino group makes them toxic if too much is present.
- The amino group is removed in a process called deamination - this takes place in the liver in animals.
- The removed amino groups form urea and is removed in the urine.
Joining Amino Acids
- All amino acids join together in the same way no matter what kind of R-Group they may contain!
- A condensation reaction (where a water molecule is removed) between the acid group of one amino acid and the carboxyl group of the other forms a covalent bond between the two amino acids.
- The bond formed is called a peptide bond and the molecule produced is called a dipeptide.
- The peptide bond can be broken by adding water, this is called a hydrolysis reaction and is basically the opposite of a condensation reaction.
- Making and breaking peptide bonds is essential for building proteins in organisms, for example the breaking down of proteins into amino acids during digestion.
- Lots of dipeptide molecules can join (in a hydrolysis reaction) to form polypeptide molecules.