Topics

Structure and Function of Amino Acids

Introduction

Amino acids are the building blocks of proteins. There are 20 standard amino acids, each containing an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R-group attached to a central carbon atom.

Structure of Amino Acids:

1.     General Formula: NH2-CHR-COOH (where R represents the side chain, which varies for each amino acid).

2.   Classification:

o    Non-polar (Hydrophobic): Glycine, Alanine, Valine, Leucine, Isoleucine, etc.

o    Polar (Hydrophilic): Serine, Threonine, Cysteine, Tyrosine, etc.

o    Acidic: Aspartic acid, Glutamic acid.

o    Basic: Lysine, Arginine, Histidine.

Function of Amino Acids:

1.     Protein Synthesis: Amino acids polymerize to form polypeptide chains, which fold into functional proteins.

2.   Metabolic Roles: Amino acids act as precursors for important molecules such as hormones (e.g., thyroxine) and neurotransmitters (e.g., dopamine).

3.   Buffering Capacity: Due to their amino and carboxyl groups, amino acids can act as buffers, helping maintain the pH of body fluids.

NEET Focus: Questions on amino acid classification (essential vs. non-essential, polar vs. non-polar) and their role in protein synthesis are common in NEET.

Structure and Function of Proteins

Introduction

Proteins are complex biomolecules made up of one or more polypeptide chains. They play a wide range of roles in biological processes, including structural support, catalysis, transport, and defense.

Structure of Proteins:

1.     Primary Structure: The sequence of amino acids in a polypeptide chain.

2.   Secondary Structure: Folding of the polypeptide chain into α-helices or β-sheets, stabilized by hydrogen bonds.

3.   Tertiary Structure: The three-dimensional folding of a polypeptide chain due to interactions between side chains (R-groups). This gives the protein its functional shape.

4.   Quaternary Structure: The association of two or more polypeptide chains to form a functional protein (e.g., hemoglobin).

Function of Proteins:

1.     Enzymatic Catalysis: Proteins function as enzymes to speed up biochemical reactions (e.g., DNA polymerase).

2.   Transport: Hemoglobin transports oxygen in the blood.

3.   Structural Support: Collagen provides strength to connective tissues.

4.   Defense: Antibodies (immunoglobulins) help in immune defense.

5.    Hormonal Regulation: Some proteins act as hormones (e.g., insulin).

NEET Focus: Focus on understanding the different levels of protein structure, protein folding, and the diverse functions of proteins in the body.

Biomolecules with Molecular Weight >1000 Da

Introduction

Biomolecules with molecular weights greater than 1000 Daltons (Da) are generally considered macromolecules. These include proteins, nucleic acids, and polysaccharides.

Examples of Biomolecules >1000 Da:

1.     Proteins: Most proteins have molecular weights ranging from a few thousand to several million Daltons.

o    Collagen: Molecular weight ~300 kDa.

o    Hemoglobin: Molecular weight ~64.5 kDa.

2.   Nucleic Acids:

o    DNA: The molecular weight of DNA can reach millions of Daltons due to its long polymer chain.

3.   Polysaccharides:

o    Starch: A polysaccharide with a molecular weight of several hundred thousand Daltons.

o    Glycogen: The storage form of glucose in animals, with molecular weights exceeding 1000 kDa.

NEET Focus: Emphasize the structural complexity and functional roles of macromolecules such as proteins and nucleic acids, and their importance in biological processes.

Structure and Function of Lipids

Introduction

Lipids are hydrophobic biomolecules that include fats, oils, phospholipids, and steroids. They play key roles in energy storage, membrane structure, and signaling.

Structure of Lipids:

1.     Triglycerides: Composed of one glycerol molecule linked to three fatty acid chains via ester bonds.

2.   Phospholipids: Consist of two fatty acids, a glycerol backbone, and a phosphate group. They are key components of cell membranes.

3.   Steroids: Lipids with a characteristic four-ring structure. Cholesterol is an important steroid that maintains membrane fluidity.

Function of Lipids:

1.     Energy Storage: Triglycerides are stored in adipose tissue and provide a dense form of energy.

2.   Cell Membrane Structure: Phospholipids form the bilayer of cell membranes, providing structural integrity and fluidity.

3.   Insulation and Protection: Lipids provide insulation (thermal and electrical) and cushioning for vital organs.

4.   Signaling Molecules: Steroid hormones (e.g., testosterone, estrogen) act as signaling molecules that regulate various physiological processes.

NEET Focus: Understanding the structure of triglycerides, phospholipids, and steroids, as well as their biological functions, is essential for NEET.

Structure and Function of Nucleic Acids

Introduction

Nucleic acids are biomolecules responsible for storing and transmitting genetic information. They are polymers made up of nucleotide monomers. The two main types of nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Structure of Nucleic Acids:

1.     Nucleotide Composition: Each nucleotide consists of a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, thymine for DNA, uracil for RNA).

2.   DNA Structure: DNA is a double helix with two complementary strands running in opposite directions. The strands are held together by hydrogen bonds between nitrogenous bases (A-T, G-C).

3.   RNA Structure: RNA is typically single-stranded and plays roles in protein synthesis (mRNA, tRNA, rRNA).

Function of Nucleic Acids:

1.     Storage of Genetic Information: DNA stores genetic information that is used to direct the synthesis of proteins.

2.   Transmission of Genetic Information: RNA is involved in the transcription and translation of genetic information from DNA to proteins.

3.   Regulation: Some RNA molecules (e.g., microRNA) play regulatory roles in gene expression.

NEET Focus: Emphasize the structure of DNA and RNA, nucleotide composition, and the processes of transcription and translation.

Structure and Function of Carbohydrates

Introduction

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen, usually in the ratio 1:2:1. They serve as a primary energy source and play structural roles in living organisms.

Structure of Carbohydrates:

1.     Monosaccharides: The simplest form of carbohydrates, consisting of single sugar units (e.g., glucose, fructose, galactose).

2.   Disaccharides: Formed by the combination of two monosaccharides via a glycosidic bond (e.g., sucrose = glucose + fructose, lactose = glucose + galactose).

3.   Polysaccharides: Long chains of monosaccharide units. Examples include:

o    Starch: The storage form of glucose in plants. Composed of two components: amylose (unbranched) and amylopectin (branched).

o    Glycogen: The storage form of glucose in animals. It is highly branched, allowing for rapid release of glucose when needed.

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o    Cellulose: A structural polysaccharide found in the cell walls of plants. It consists of long chains of β-glucose units linked by β(1→4) glycosidic bonds, making it indigestible by humans.

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o    Chitin: A structural polysaccharide found in the exoskeletons of arthropods and in fungal cell walls.

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Function of Carbohydrates:

1.     Energy Source: Carbohydrates, especially glucose, are the primary source of energy for cells. Glycolysis and oxidative phosphorylation break down glucose to generate ATP.

2.   Energy Storage: Starch in plants and glycogen in animals serve as energy storage molecules.

3.   Structural Role: Cellulose provides rigidity to plant cell walls, while chitin offers structural support in fungi and arthropods.

4.   Component of Nucleic Acids: Ribose and deoxyribose sugars are part of the backbone of RNA and DNA, respectively.

NEET Focus: Be familiar with the different types of carbohydrates, their functions, and their importance in metabolism and structure.

Structure and Function of Enzymes

Introduction

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process. They are highly specific and work by lowering the activation energy required for reactions.

Structure of Enzymes:

1.     Protein Nature: Most enzymes are globular proteins, composed of long chains of amino acids folded into a specific three-dimensional structure.

2.   Active Site: The region of the enzyme where the substrate binds and undergoes a chemical reaction. The shape of the active site is complementary to the substrate.

3.   Cofactors: Some enzymes require non-protein molecules called cofactors to be functional. These can be metal ions (e.g., Mg²⁺, Zn²⁺) or organic molecules (coenzymes, such as vitamins).

4.   Enzyme-Substrate Complex: Enzymes bind to their substrates, forming an enzyme-substrate complex, which helps facilitate the conversion of substrates into products.

Function of Enzymes:

1.     Catalysis: Enzymes increase the rate of biochemical reactions by lowering the activation energy.

o    Lock and Key Model: Suggests that the active site of an enzyme is a perfect fit for the substrate.

o    Induced Fit Model: Suggests that the enzyme undergoes a conformational change to fit the substrate more snugly.

2.   Specificity: Each enzyme is specific to a particular substrate or type of reaction. For example, amylase breaks down starch, and lipase breaks down lipids.

3.   Regulation of Metabolic Pathways: Enzymes are regulated by factors such as temperature, pH, substrate concentration, and the presence of inhibitors or activators.

Enzyme Kinetics:

1.     Michaelis-Menten Kinetics: Describes how the rate of enzyme-catalyzed reactions depends on substrate concentration.

o    Vmax: The maximum rate of the reaction.

o    Km: The substrate concentration at which the reaction rate is half of Vmax.

Factors Affecting Enzyme Activity:

1.     Temperature: Enzyme activity increases with temperature up to an optimum point, after which activity declines due to denaturation.

2.   pH: Each enzyme has an optimal pH at which it functions best.

3.   Inhibitors:

o    Competitive Inhibitors: Bind to the active site, competing with the substrate.

o    Non-Competitive Inhibitors: Bind to a different part of the enzyme, altering its shape and reducing its activity.

NEET Focus: Focus on enzyme structure, mechanisms of action, and factors affecting enzyme activity. Questions about enzyme inhibition and reaction rates are common.