U3 AOS1 Topic 2: Protein Structure and Function

Proteins (aka Polypeptides) are a sequence/chain of amino acids which are bound together by a peptide bond.

The proteome: is the entire set of proteins expressed by a particular organism at a given time.

The proteome is composed of various types of proteins:

  • Enzymes: biological catalysts which expedite (speed up) chemical reactions (e.g. DNA polymerase, which helps replicate DNA strands during DNA replication)
  • Receptors: Receive signals from the environment (e.g. Hormone receptors on certain cells)
  • Defense: Contribute to the identification and elimination of pathogens in the immune system. (e.g. Complement proteins and antibodies)
  • Structural: Maintain cell and tissue shape (Elastin, found in Elastic tissue such as skin)

Amino Acids

In Polypeptides, the individual amino acids are monomers - building blocks.

Amino Acids: Properties, Structure, Sources and Function

- The only variable (changing) region in Amino acids is the R-group

- There are 20 different types of amino acids, each with a distinct R-group.

- When Amino acids are joined together, they form long chains called polypeptides (as mentioned previously).

- The reaction by which Amino Acids are bound together is CONDENSATION POLYMERISATION, whereby, Energy is an input, and a peptide bond + water are the outputs (hence, the name condensation.

Water was both essential and a barrier to early life on Earth – microdroplets are one potential solution to this paradox

Note: Reactions that require energy can generally also be referred to as Anabolic/Endergonic, whilst those which produce energy are typically described as catabolic/exergonic. Reactions that require the construction of new molecules tend to be endergonic.

Protein structure:

Primary: refers simply to the polypeptide sequence of amino acids - the way the amino acids are ordered

Secondary: structures caused by chemical interaction (Hydrogen bonding) between amino acids in different sections of polypeptide - E.g. Alpha Helixes and Beta Pleated sheets or Random Coils

          

Tertiary: overall 3-dimensional structure of protein, which is essential in determining protein functionality - alterations/changes in the tertiary structure could render a protein dysfunctional.

Quaternary structure: Only applicable to SOME proteins which are a combination of multiple, different polypeptides joined together (e.g. Haemoglobin).

All functional proteins have a tertiary structure, but only SOME have a quaternary structure.

Protein Structure | BioNinja