First-Year MBBS Biochemistry Notes: Key Concepts and Topics

Biochemistry helps you understand the chemical processes that keep the human body functioning. In the first year of MBBS, topics such as cellular organisation, proteins and enzymes introduce concepts that connect basic science with physiology, pathology and clinical medicine. Learning these fundamentals can make it easier to understand how changes at the molecular level affect normal body functions and contribute to disease.

For university examinations, revising key concepts regularly can help you retain important definitions and mechanisms. These First-Year MBBS Biochemistry Notes cover selected topics in cell biology, protein structure and enzymology. PW MedEd offers medical lectures, revision resources, question banks and assessments to support your MBBS studies and postgraduate entrance exam preparation.

First-Year MBBS Biochemistry Notes: Important Topics

The following topics introduce some of the foundational concepts you may encounter while studying Biochemistry in the first year. Use them for revision alongside your prescribed textbooks, lecture notes and university syllabus.

Cell Organelles and Their Functions

Cell organelles perform specialised functions that help maintain cellular activity. Understanding their roles provides a foundation for studying metabolism, energy production and other biochemical processes.

Mitochondria are often called the powerhouse of the cell because of their role in ATP production. They also contain their own DNA and ribosomes and are therefore described as semi-autonomous organelles.

An important point to remember is that mature human erythrocytes do not contain mitochondria. This affects how they obtain energy and use metabolic pathways.

Cell Membrane and Membrane Transport

The plasma membrane separates the cell's internal environment from its surroundings. Its lipid bilayer and associated proteins help regulate the movement of substances into and out of the cell.

Membrane transport can be divided into passive and active processes.

The sodium-potassium ATPase pump is an important example of primary active transport. It uses ATP to move three sodium ions out of the cell and two potassium ions into the cell during each transport cycle. This helps maintain the ionic gradients required for normal cellular function.

Understanding the difference between passive and active transport is useful because it explains how cells maintain their internal environment despite changes outside the cell.

Protein Structure and Protein Misfolding

Proteins perform many functions in the human body, including catalysing biochemical reactions, transporting substances, providing structural support and participating in immune responses.

Protein structure is commonly described at four levels.

A protein's shape is closely related to its function. Changes in folding can affect how a protein interacts with other molecules and performs its biological role.

Protein misfolding occurs when a protein fails to adopt or maintain its normal functional conformation. Misfolded proteins may accumulate or aggregate and are associated with certain disorders, including amyloid diseases and prion diseases.

When revising this topic, focus on distinguishing the four levels of protein structure and understanding why the correct three-dimensional conformation matters.

Denaturation of Proteins

Protein denaturation refers to the disruption of a protein's normal conformation, which can affect its biological activity. It may occur due to heat, extreme pH values, certain chemicals or other conditions that disrupt the interactions stabilising the protein.

During denaturation, secondary, tertiary and, where present, quaternary structure may be disrupted. The primary amino acid sequence generally remains intact because denaturation does not ordinarily involve the hydrolysis of peptide bonds.

Denaturation may be reversible under some conditions, while in other cases the protein undergoes irreversible changes.

For example, heating egg white causes its proteins to unfold and aggregate, producing a visible change in texture and appearance.

NOTE: Do not confuse denaturation with the breakdown of a protein into individual amino acids. Denaturation primarily changes the protein's conformation rather than its primary sequence.

Enzymes: Classification and Activity

Enzymes are biological catalysts that increase the rate of biochemical reactions without being consumed in the overall reaction. Most enzymes are proteins, although some RNA molecules can also act as catalysts.

Enzymes are classified according to the reactions they catalyse. The traditional classification commonly taught in introductory Biochemistry includes six major classes.

Enzyme activity depends on several factors, including temperature, pH, substrate concentration and the presence of inhibitors or activators.

• Temperature: Activity often increases with temperature up to an optimum range, but excessive heat can disrupt enzyme structure.

• pH: Each enzyme has a characteristic pH range for optimal activity. Significant deviations may alter ionisation and protein conformation.

• Substrate concentration: Increasing substrate concentration can increase reaction rate until the enzyme approaches saturation.

• Cofactors and activators: Some enzymes require metal ions or other non-protein components for catalytic activity.

• Inhibitors: Certain substances reduce enzyme activity by interfering with substrate binding or catalytic function.

These factors help explain why enzyme activity changes under different physiological and experimental conditions.

Explore the PW MedEd YouTube channel for medical lectures, concept explanations and revision videos to support your MBBS preparation.

 Isoenzymes and Their Clinical Significance

Isoenzymes, also called isozymes, are different molecular forms of an enzyme that catalyse the same overall reaction but may differ in structure, tissue distribution or biochemical properties.

Their distribution can make them useful in understanding tissue-specific metabolism and certain clinical conditions.

For example, lactate dehydrogenase (LDH) has different isoenzyme forms found in varying proportions across tissues. Creatine kinase also has distinct isoenzymes associated with different tissues.

Cardiac troponins, particularly cardiac troponin I and T, are important biomarkers used in assessing myocardial injury. Although they are not isoenzymes, they illustrate how tissue-associated proteins can contribute to clinical investigation.

When studying this area, distinguish the general definition of isoenzymes from the clinical use of specific enzymes and biomarkers. Their interpretation depends on the clinical context and other investigation findings.

 Allosteric Regulation and Enzyme Inhibition

Enzyme activity can be regulated by molecules that bind to an enzyme and change its catalytic behaviour. Allosteric regulation is one such mechanism.

Allosteric enzymes have a regulatory binding site distinct from the catalytic site. A molecule binding to the regulatory site can increase or decrease enzyme activity by influencing the enzyme's conformation.

• Allosteric activation: A regulator increases enzyme activity.

• Allosteric inhibition: A regulator decreases enzyme activity.

• Feedback inhibition: A product formed later in a biochemical pathway inhibits an enzyme involved earlier in that pathway, helping regulate the pathway's activity.

Enzyme inhibition is another important topic because inhibitors can interfere with enzyme function in different ways.

These categories help explain how biochemical reactions are controlled and how certain drugs or toxic substances affect enzyme activity.

For revision, focus on the binding mechanism of each inhibitor and how it differs from allosteric regulation. Some forms of inhibition can be distinguished further through their effects on enzyme kinetics.

Learn from experienced medical educators and explore PW MedEd faculty for dedicated guidance and concept-focused teaching to support your MBBS preparation.

First-Year MBBS Biochemistry Notes PDF

The First-Year MBBS Biochemistry Notes PDF gives you a convenient revision resource to revisit important concepts without having to search through multiple chapters. Use it to review key explanations, definitions, question-and-answer material, diagrams and other topic-wise notes included in the PDF.