Biochemistry: Proteins, Enzymes, and Nucleotides

Introduction

  • The video patch is a recording for the final 15-20 minutes of Lecture Video 3 where the original audio failed during playback.

  • This patch serves to provide the missing content from the lecture focused on proteins and enzymes.

Proteins and Enzymes

  • Definition and Function of Enzymes

    • Enzymes are biological catalysts that speed up chemical reactions.

    • They are vital for various biochemical processes in living organisms.

Characteristics of Enzymes

  • Composition:

    • Typically composed of proteins, with some exceptions being RNA.

  • Optimal Conditions:

    • Enzymes work best at specific temperatures and pH levels, referred to as their optimal conditions.

    • Example: Enzymes in the stomach function optimally at body temperature and a low pH of approximately 1-2.

  • Specificity:

    • Enzymes exhibit specificity towards their substrates, which are the molecules upon which they act.

  • Reusability:

    • Enzymes can be reused after catalyzing a chemical reaction.

Enzyme Structure

  • Enzymes possess a unique three-dimensional structure, often likened to a "Pac Man" shape.

  • Active Site:

    • The active site (also called the catalytic site) is where the enzyme binds to the substrate.

    • The substrate has a complementary shape to the active site.

    • Example: For the enzyme lactase, the substrate lactose binds at the active site to undergo a chemical reaction.

Substrate Interaction and Hydrolysis

  • When the enzyme and substrate bind, a chemical reaction occurs that typically results in the splitting of the substrate into products.

  • Example Output: Binding lactase with lactose yields glucose and galactose as products.

Control of Enzyme Activity

  • Enzyme activity can be regulated through various mechanisms:

1. Competitive Inhibition

  • A molecule other than the substrate competes for binding at the active site.

  • Impact of Competitive Inhibition:

    • Increased levels of the competitive inhibitor result in decreased enzyme activity, as it blocks substrate access to the active site.

  • Real-World Example:

    • ACE Inhibitors: These drugs inhibit angiotensin-converting enzyme (ACE), reducing blood pressure by preventing sodium and water reabsorption and vasoconstriction.

2. Noncompetitive Inhibition

  • A molecule binds to a different site (regulatory site) on the enzyme, affecting its activity without blocking the active site.

  • Effect on Enzyme Function:

    • This alters the enzyme's shape, preventing it from effectively binding to the substrate, ultimately leading to a decrease in enzyme activity.

  • Example:

    • Regulation of biochemical pathways often involves feedback inhibition, where the end product, if abundant, binds to the first enzyme in the pathway to halt its activity, thus preventing overproduction.

Nucleic Acids

  • Nucleic acids are diverse with varying functions.

Structure of Nucleic Acids

  • Nucleotides:

    • The basic units of nucleic acids, consisting of a nitrogen base, a phosphate group, and a five-carbon sugar (pentose).

  • Main Types of Nucleic Acids:

    • DNA (Deoxyribonucleic Acid):

    • Contains the genetic code, structured as a double helix comprised of two strands of nucleotides.

    • The sugar-phosphate backbone consists of alternating phosphate and sugar units. The rungs of the ladder represent the nitrogenous bases bound together by hydrogen bonds. Bases are adenine (A), thymine (T), cytosine (C), and guanine (G).

    • Approximately 40,000 genes coding for proteins exist in the human genome.

    • DNA serves as a master template for protein synthesis.

    • RNA (Ribonucleic Acid):

    • Generally single-stranded and plays critical roles in protein synthesis.

    • Types of RNA include:

      • Messenger RNA (mRNA):

      • A copy of the DNA that exits the nucleus to guide protein synthesis into polypeptides.

      • Transfer RNA (tRNA):

      • Transports specific amino acids to ribosomes for protein assembly.

      • Ribosomal RNA (rRNA):

      • Forms part of ribosomes, crucial for protein assembly.

Protein Coding and Genetic Diseases

  • The sequence of nucleotides in DNA codes for amino acids and ultimately the formation of proteins.

  • Example of mutations impacting protein function, such as sickle cell anemia, where a single nucleotide change leads to glutamic acid being replaced by valine in hemoglobin, causing red blood cell deformation.

ATP (Adenosine Triphosphate)

  • ATP is the primary energy carrier in cells.

  • Structure:

    • Comprises adenosine bonded to three phosphate groups.

  • Function:

    • ATP can undergo hydrolysis to release energy when one of the phosphate groups is cleaved, converting ATP into ADP (Adenosine Diphosphate) and a free phosphate.

  • Energy Use in Cells:

    • Released energy can power muscle contractions and other cellular activities.

  • Energy Regeneration:

    • ATP can be recirculated through energy provided by diverse macromolecules (carbohydrates, fats, and proteins) when they are metabolically processed.

Conclusion

  • This concluding section aims to finalize and summarize the key points from Lecture 3, ensuring a comprehensive understanding of proteins, enzymes, nucleic acids, and ATP for the forthcoming lessons and discussions in class.