Chapter 4 Cellular Metabolism

About this Chapter Energy for synthesis and movement Energy transformation Enzymes and how they speed reactions Metabolic pathways ATP its formation and uses in metabolism Synthesis of biologically important molecules

Energy (E) Transfer Overview Energy does work Kinetic energy Potential energy Energy conversion

Energy (E) Transfer Overview Figure 4-1: Energy transfer in the environment

Chemosynthesis versus Photosynthesis 6CO2 + 6H2S → C6H12O6 + 6S Needs heat added such as from hydrothermal vents in the deep ocean Photosynthesis 2n CO2 + 2n H2O + photons → 2(CH2O)n + 2n O2 Occurs in Two Stages Stage 1: Light energy used to form ATP and NADPH Stage 2: Uses ATP and NADPH to reduce CO2

Energy and Chemical Reactions Figure 4-5: Energy transfer and storage in biological reactions

Formation of ATP from Carbs, Proteins and Fat Enzymes of metabolic pathways are able to capture the energy contained in carbohydrates, proteins and fatty acids in small portions and store it in form of internal high energy compounds such as ATP, drastically reducing the amount of energy lost as heat.

Adenosine Triphosphate (ATP) Source of immediately usable energy for the cell Adenine-containing RNA nucleotide with three phosphate groups

Adenosine Triphosphate (ATP) Figure 2.22

How ATP Drives Cellular Work Figure 2.23

Protein Macromolecules composed of combinations of 20 types of amino acids bound together with peptide bonds Figure 2.16

Structural Levels of Proteins Primary – amino acid sequence Secondary – alpha helices or beta pleated sheets

Structural Levels of Proteins Figure 2.17a-c

Structural Levels of Proteins Tertiary – superimposed folding of secondary structures Quaternary – polypeptide chains linked together in a specific manner

Structural Levels of Proteins Figure 2.17d, e

Fibrous and Globular Proteins Fibrous proteins Extended and strandlike proteins Examples: keratin, elastin, collagen, and certain contractile fibers Globular proteins Compact, spherical proteins with tertiary and quaternary structures Examples: antibodies, hormones, and enzymes

Protein Synthesis Figure 4-34: Summary of transcription and translation

Post – Translational protein modificaiton Figure 4-35: Post-translational modification and the secretory pathway

Post – Translational protein modificaiton Folding, cleavage, additions: glyco- lipo- proteins

Characteristics of Enzymes Most are globular proteins that act as biological catalysts Holoenzymes consist of an apoenzyme (protein) and a cofactor (usually an ion) Enzymes are chemically specific Frequently named for the type of reaction they catalyze Enzyme names usually end in -ase Lower activation energy

Characteristics of Enzymes Figure 2.19

Enzymes speed biochemical reactions Figure 4-8: Two models of enzyme binding sites

Mechanism of Enzyme Action Enzyme binds with substrate Product is formed at a lower activation energy Product is released

Enzymes speed biochemical reactions Lower activation E Specific May require Cofactors or Coenzymes Modulators Acidity Temperature Competitive inhibitors Allosteric Concentrations

Cofactors and Enzyme Activity Cofactors are inorganic substrates. Some cofactors are required to produce a chemical reaction between the enzyme and the substrate, while others merely increase the rate of catalysis. Cofactors are sometimes attach to the enzyme, much like a prosthetic limb. Others are loosely bound to the enzyme.

Coenzymes and Enzyme Activity Unlike the inorganic cofactors, coenzymes are organic molecules. Certain enzymes need coenzymes to bind to the substrate and cause a reaction. Since the coenzymes are changed by the chemical reaction, these are considered to be secondary substrates of the reaction. Though enzymes are specific to the substrate, coenzymes are not specific to the enzymes they assist. Some chemical reactions within the cells of the body do require a cofactor or a coenzyme to work properly, while others do not. The body is unable to manufacture these products, so the way to get the vitamins necessary to produce cofactors and coenzymes is to eat a healthy, balanced diet full of all the vitamins necessary for bodily functions.

Protein Denaturation Reversible unfolding of proteins due to drops in pH and/or increased temperature Figure 2.18a

Protein Denaturation Irreversibly denatured proteins cannot refold and are formed by extreme pH or temperature changes Figure 2.18b

Law of Mass Action Defined: Equlibrium Reversible Figure 4-17: Law of mass action

Types of Enzymatic Reactions Oxidation–reduction Hydrolysis–dehydration Addition–subtraction exchange Ligation

Figure 4-18b: A group of metabolic pathways resembles a road map Cell Metabolism Pathways Intermediates Catabolic - energy Anabolic - synthesis Figure 4-18b: A group of metabolic pathways resembles a road map

Control of Metabolic Pathways Feedback inhibition Figure 4-19: Feedback inhibition

ATP Production Glycolysis Pyruvate Anaerobic respiration Lactate production 2 ATPs produced Figure 4-21: Overview of aerobic pathways for ATP Production

Pyruvate Metabolism Aerobic respiration In mitochondria Acetyl CoA and CO2 Citric Acid Cycle or Kreb’s Cycle or TCA Cycle Energy Produced from 1 Acetyl CoA 1 ATP 3 NADH 1 FADH2 Waste–2 CO2s

Figure 4-23: Pyruvate metabolism

Electron Transport High energy electrons Energy transfer ATP synthesized from ADP H2O is a byproduct- In a typical individual this amounts to approximately 400 ml/day

Electron Transport Figure 4-25: The electron transport system and ATP synthesis

Biomolecules Catabolized to make ATP Complex Carbohydrates Glycogen catabolism Liver storage Muscle storage Glucose produced Figure 4-26: Glycogen catabolism

Protein Catabolism Deaminated Conversion Glucose Acetyl CoA

Protein Catabolism Figure 4-27: Protein catabolism and deamination

Lipid Catabolism Higher energy content Triglycerides to glycerol Fatty acids Ketone bodies - liver

Fat mass, adipose tissue and energy stores Liver triglycerides = 450 kcal Muscle triglycerides = 3000 kcal Liver glycogen = 400 kcal Muscle glycogen = 2500 kcal Adipose tissue triglycerides = 120,000 kcal Data for a 70 kg lean subject.

Synthetic (Anabolic) pathways Glycogen synthesis Liver storage Glucose to glycogen Gluconeogenesis Amino acids Glycerol Lactate Figure 4-29: Gluconeogenesis

Figure 4-30: Lipid synthesis Lipogenesis Acetyl Co A Glycerol Fatty acids Triglycerides Figure 4-30: Lipid synthesis

Figure 4-30: Lipid synthesis Lipogenesis Figure 4-30: Lipid synthesis

Summary Energy: chemical, transport, mechanical work Reactions: reactants, activation energy, directions Enzymes: characteristics, speed & control pathways Metabolism: catabolic, anabolic ATP production: anaerobic, aerobic, glycolysis, citric acid cycle, & electron transport Synthesis of carbohydrates, lipids and proteins