2: Amino Acids and Polypeptides Flashcards
Describe an amino acid.
central carbon atom with four different atoms or groups linked to it:
- hydrogen atom
- amine group (-NH2)
- carboxyl group (-COOH)
- R group or radical (R)
Draw the molecular structure of an amino acid. (p24)
-
What does the “R” indicate in the molecular structure of an amino acid?
a radical group - this part varies between amino acids
Where are amino acids synthesized in living organisms? How many different amino acids do most living organisms synthesize? How many different types of amino acids can be synthesized in a lab?
- ribosomes
- 20
- hundreds
Almost all living organisms only synthesize about 20 different amino acids to use in polypeptides. Why is this significant? Are there any discrepancies to this trend? Does this change the significance?
this is one of the pieces of evidence supporting the theory that all organisms share common ancestry.
yes - two other amino acids are included in a few polypeptides:
- selenocysteine
- pyrrolysine
but only a minority of polypeptides in a minority of organisms contain either of these amino acids
not really:
- in both cases special mechanisms are needed to incorporate these amino acids into polypeptides
- it is therefore more likely that these mechanisms evolved after the basic method of making polypeptides from the 20 amino acids
- two extra amino acids = extra variations NOT a falsification of the theory that there are 20 basic amino acids in all organisms
What is the name of the bond formed between two amino acids in a condensation reaction? Where is the bond formed?
- a peptide bond
- between the amine group of one amino acid and the carboxyl group of the next amino acid
What do polypeptides consist of?
many amino acids linked together by peptide bonds
What is a polypeptide?
an unbranched chain of amino acids
How many amino acids in a polypeptide?
variable:
- most have: 50 - 2,000
- largest have: 10,000+
Why are some polypeptides called peptides?
- chains of fewer than 40 amino acids are usually called peptides
How are amino acids linked? Comment on the significance of this.
- can be linked in any order
consider a polypeptide with 100 amino acids, the number of possible sequences is 20^100 = MASSIVE NUMBER
How many possible sequences of amino acids are made by living organisms over their lifetime?
- only a small portion of possible sequences
- particular sequences are made in very large quantities because they have useful properties
How many different polypeptides have been discovered so far in living organisms
2mil+
How is the amino acid sequence of a polypeptide coded for?
- by a gene
- the sequence of bases in the DNA of the gene determines the sequence of amino acids in the polypeptide
What does a protein consist of?
either a single polypeptide or more than one polypeptide linked together
