Enzymes, Vitamins, Nucleic Acids, and Metabolic Pathways: GOB Chemistry Study Notes

Chapter 20: Enzymes and Vitamins

Definition and Function of Enzymes

Enzymes are biological catalysts that accelerate chemical reactions in living organisms by lowering the activation energy required. They do not change the overall reaction process or the free energy change ($\Delta G$).

• Enzyme: Protein that speeds up chemical reactions without being consumed.

• Activation Energy: The minimum energy required for a reaction to occur; enzymes lower this barrier.

• Example: Amylase catalyzes the breakdown of starch into sugars.

Blood Sugar and Buffering Systems

Blood sugar regulation and buffering systems are essential for maintaining homeostasis in the body.

• Blood Sugar: Glucose levels are regulated by hormones and enzymes.

• Buffering Systems: Maintain pH balance in blood, often involving bicarbonate and phosphate buffers.

Enzyme Substrate and Active Site

Enzymes have specific regions called active sites where substrates bind and reactions occur.

• Substrate: The molecule upon which an enzyme acts.

• Active Site: The region of the enzyme where substrate binding and catalysis take place.

• Example: Lactase acts on lactose at its active site.

Enzyme-Catalyzed Reaction Steps

Enzyme-catalyzed reactions typically follow three steps: formation of the enzyme-substrate complex (ES), conversion to the enzyme-product complex (EP), and release of the product (P).

• General Reaction: $\text{E} + \text{S} \rightarrow \text{ES} \rightarrow \text{EP} \rightarrow \text{E} + \text{P}$

Enzyme Classification and Types

Enzymes are classified into six major types based on the reactions they catalyze. With a given reaction, it is possible to identify which type the enzyme belongs to.

• Types: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.

• Example: Hydrolases catalyze hydrolysis reactions, such as proteases breaking down proteins.

Enzyme Inhibition and Regulation

Enzymes can be inhibited or regulated by various factors, including competitive and noncompetitive inhibitors, feedback mechanisms, and covalent modification.

• Competitive Inhibition: Inhibitor competes with substrate for the active site.

• Noncompetitive Inhibition: Inhibitor binds elsewhere, altering enzyme function.

• Feedback Regulation: End product of a pathway inhibits an earlier step.

Vitamins as Coenzymes

Many vitamins act as coenzymes, assisting enzymes in catalyzing reactions. Deficiency in vitamins can impair enzyme function.

• Coenzyme: Non-protein molecule required for enzyme activity, often derived from vitamins.

• Example: NAD+ (from niacin) is a coenzyme in redox reactions.

Chapter 21: Nucleic Acids

Structure and Function of Nucleotides

Nucleotides are the building blocks of nucleic acids (DNA and RNA). They consist of a nitrogenous base, a pentose sugar, and a phosphate group.

• DNA: Deoxyribonucleic acid, stores genetic information.

• RNA: Ribonucleic acid, involved in protein synthesis.

• Base Pairing: DNA: A-T, G-C; RNA: A-U, G-C.

• Hydrogen Bonds: Hold complementary bases together in double-stranded DNA.

DNA Replication and Transcription

DNA replication is the process by which DNA makes a copy of itself. Transcription is the synthesis of RNA from a DNA template.

• Replication: DNA polymerase synthesizes new DNA strands.

• Transcription: RNA polymerase synthesizes mRNA from DNA.

• Directionality: DNA and RNA are synthesized in the 5' to 3' direction.

Translation and Protein Synthesis

Translation is the process by which mRNA is decoded to produce a specific polypeptide (protein).

• mRNA: Messenger RNA, carries genetic code from DNA to ribosome.

• tRNA: Transfer RNA, brings amino acids to the ribosome.

• rRNA: Ribosomal RNA, forms the core of ribosome structure.

• Codon: Sequence of three nucleotides in mRNA that specifies an amino acid.

Gene Regulation and Expression

Gene expression is regulated at multiple levels, including transcription, mRNA processing, and translation.

• Regulation: Promoters, enhancers, and repressors control gene transcription.

• mRNA Processing: Addition of 5' cap, poly-A tail, and splicing of introns.

Chapter 22-24: Metabolism

Overview of Metabolism

Metabolism encompasses all chemical reactions in the body, including catabolism (breakdown of molecules) and anabolism (synthesis of molecules). It is divided into three main stages: digestion, conversion to acetyl-CoA, and energy production in the citric acid cycle and electron transport chain.

• Catabolism: Breakdown of complex molecules to release energy.

• Anabolism: Synthesis of complex molecules from simpler ones.

• Stages: Digestion, Acetyl-CoA production, ATP generation.

Cell Structure and Function

Cells contain organelles that perform specific functions in metabolism.

• Mitochondria: Site of TCA cycle and electron transport chain.

• Lysosome: Digestion of cellular waste.

• Ribosome: Protein synthesis.

• Nucleus: Contains genetic material.

ATP and Energy Production

ATP (adenosine triphosphate) is the primary energy currency of the cell. Hydrolysis of ATP releases energy for cellular processes.

• ATP Hydrolysis: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

• Energy-Rich Molecules: NADH, FADH2, and CoA are involved in energy transfer.

Glycolysis and Citric Acid Cycle

Glycolysis is the breakdown of glucose to pyruvate, producing ATP and NADH. The citric acid cycle (TCA cycle) further oxidizes acetyl-CoA to CO2 and generates additional ATP, NADH, and FADH2.

• Glycolysis: Occurs in cytosol; converts glucose to pyruvate.

• Citric Acid Cycle: Occurs in mitochondria; oxidizes acetyl-CoA.

• Overall Reaction: $\text{Glucose} + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy}$

Metabolic Pathways for Carbohydrates, Lipids, and Proteins

Carbohydrates, lipids, and proteins are metabolized through distinct pathways to produce energy and building blocks for the cell.

• Glycogenesis: Formation of glycogen from glucose.

• Glycogenolysis: Breakdown of glycogen to glucose.

• Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources.

• Lipid Metabolism: Fatty acid oxidation produces acetyl-CoA.

• Protein Metabolism: Amino acids are deaminated and used for energy or biosynthesis.

Energy Yield and Storage

The body stores energy in the form of glycogen and fat. ATP is generated from the oxidation of glucose, fatty acids, and amino acids.

• Energy Storage: Glycogen (liver, muscle), triglycerides (adipose tissue).

• Energy Yield: Complete oxidation of glucose yields approximately 30-32 ATP molecules.

Key Metabolic Intermediates

Important intermediates include acetyl-CoA, pyruvate, and intermediates of the TCA cycle.

• Acetyl-CoA: Central molecule in metabolism, links carbohydrate, lipid, and protein metabolism.

• Pyruvate: End product of glycolysis, can be converted to acetyl-CoA or lactate.

Summary Table: Major Metabolic Pathways

Pathway	Main Substrate	Location	Main Products
Glycolysis	Glucose	Cytosol	Pyruvate, ATP, NADH
Citric Acid Cycle	Acetyl-CoA	Mitochondria	CO2, ATP, NADH, FADH2
Electron Transport Chain	NADH, FADH2	Mitochondria	ATP, H2O
Glycogenesis	Glucose	Liver, Muscle	Glycogen
Glycogenolysis	Glycogen	Liver, Muscle	Glucose
Lipid Oxidation	Fatty Acids	Mitochondria	Acetyl-CoA, ATP

Additional info: Some details, such as specific enzyme names and regulatory mechanisms, were inferred for completeness and academic clarity.