Microbial Biochemistry Quiz

Learning Objectives

• List and describe the four basic functions of proteins in living organisms.
• Differentiate between the four levels of complexity of protein structure.
• Explain the importance of proteases in microbial metabolism.
• Explain the biochemistry involved in the utilization of casein by casein protease.
• Investigate the utilization of casein by the environmental isolate.
• Interpret the results found on the casein agar plates.

Introduction

• Studying an organism's structure, growth characteristics, and susceptibility to chemotherapeutics is followed by studying its biochemical or metabolic characteristics.
• Organisms adapt to their specific niches, with adaptations including physical structures and metabolic adaptations to utilize available nutrients in their niche.
• This exercise examines biochemical adaptations of microorganisms and how they contribute to their identification.
• Organisms are classified based on their carbon source (heterotrophs or autotrophs) and energy source (organic chemicals, inorganic chemicals, or sunlight).

Proteins

• Proteins are composed of amino acids (twenty naturally occurring).
• Amino acids are joined together by peptide bonds.
• Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.
• Primary structure: sequence of amino acids.
• Secondary structure: alpha-helices and beta-sheets.
• Tertiary structure: three-dimensional shape resulting from folding of secondary structure.
• Quaternary structure: combination of multiple polypeptide chains held together by weak bonds.

Casein Proteases

• Casein is a milk protein, giving milk its cloudy white color.
• It exists as casein micelles.
• Casein is a common milk product in various foods.
• Microbial fermentation of lactose leads to lactic acid production, which causes casein to coagulate (form curds).
• Casein degradation is detected by checking for a clear zone of proteolysis in a casein agar plate.

Casein Agar Plates

• Cloudy, opaque plates result from milk being added to the agar preparation.
• Microbial growth producing casein-degrading enzymes will result in a clear zone surrounding the growth.
• If the casein protein is not broken down by the microbe, the medium surrounding the growth remains cloudy.