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An Introductory Overview of Cells, Chemical Bonds & Energy Part-II

Lecture no.4. An Introductory Overview of Cells, Chemical Bonds & Energy Part-II. BCH 361/ Section: xxxxx. What We Will Be Covering-II?. Lecture no.4. Covalent and non-covalent bonds. The four macromolecules and their building blocks Chemical reactions and delta G

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An Introductory Overview of Cells, Chemical Bonds & Energy Part-II

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  1. Lecture no.4 An Introductory Overview of Cells, Chemical Bonds & EnergyPart-II BCH 361/ Section: xxxxx

  2. What We Will Be Covering-II? Lecture no.4 • Covalent and non-covalent bonds. • The four macromolecules and their building blocks • Chemical reactions and delta G • Coupling chemical reactions to ATP hydrolysis

  3. Chemical Hierarchy structure in living cells Lecture no.4 • Organization of molecules in cells: • Atoms. • Small molecules. • Macromolecules. • Supramolecular aggregates.

  4. Continue… Lecture no.4 Organization is the key to the chemistry of life.

  5. Atoms Lecture no.4 • Each atom has a nucleus (protons and neutrons) with electrons orbiting it. • H, C, O, and N make up 96.5% weight of a living organism. • Na, K, Cl, Ca, Fe, Zn are each present at less than 1%. • Two types of atomic interaction: Covalent & Non-covalent Bonds.

  6. Continue… Lecture no.4 Atomic Interaction Covalent Bonds Non-Covalent Bonds 1 2 1 Hydrogen Bonds Van der Waals 2 Polar interaction Non-polar interaction 3 4 Ionic interactions Hydrophobic effects

  7. Lecture no.4 • Hi, plz remember this regarding the covalent bonds: • It form the backbones of molecules. • Electrons are shared between atoms. • Single bonds allow rotation, • double bonds are rigid • Molecules are covalently bonded atoms, covalent bonds result from sharing electrons and depend on valence (C: +4, N: -3, O: -2, H:+1).

  8. Lecture no.4 Nonpolar Hormones Pass Through Cell Membranes; Polar Hormones Use Extracellular Receptor Proteins

  9. Lecture no.4 Covalent And Noncovalent Bonds Play Different Roles In Maintaining Molecular Structure • Covalent bonds assemble atoms into molecules, but noncovalent bonds determine the shape of large molecules and the way in which molecules interact with each other. • Covalent bond = approx. 350 kJ/mol and difficult to break, Noncovalent bond = 1- 30 kJ/mol and readily reversible by thermal movement or interactions with other molecules.

  10. Lecture no.4 Hydrogen Bonds In Biomolecules • Hydrogen has a low electronegativity (it has only one proton to attract electrons with). • Oxygen and nitrogen are highly electronegative. • When there is a bond between O and H, or N and H, the molecule forms a dipole -- the O or N will become δ- (hydrogen bond acceptor), and the H will become δ+ (hydrogen bond donor).

  11. Lecture no.4 Hydrogen Bonds Hold The DNA Double Helix Together • An AT pair has 2 H bonds, while a CG pair has 3 H bonds. • The helix is harder to unwind in a CG-rich region than in an AT-rich region. • H-bonds play pivotal roles in different aspects of the central dogma of MB DNA.

  12. Lecture no.4 Noncovalent Bonds Influence Molecular Structure--Hydrophobic Interactions • Lipids form micelles, in which the hydrophilic groups line the outside of the micelle and the hydrophobic groups cluster inside it, away from the water. • The first stage of lipid digestion involves breaking up huge globs of fat into smaller globs and micelles

  13. Lecture no.4 • They determine the shape of macromolecules (i.e. the double stranded helical shape of DNA is determined by hydrogen bonds between complementary base pairs A-T and G-C). • They produce reversible self-assembly of pre-synthesized subunits into specific structures (i.e. membrane lipid bi-layer, protein "polymers" like microtubules). • They determine the specificity of most molecular interactions (i.e. enzyme substrate specificity and catalysis). • Molecules or supramolecular aggregates denature (unfold) upon environmental changes (pH, temperature, or ionic strength) which affect the strengths of weak bonds.

  14. Lecture no.4 Disrupting Noncovalent Bonding Causes Sickle-Cell Anemia • Hemoglobin is a heterotetramer-2 alpha globin chains plus 2 beta-globin chains. • Glutamic acid (negative charge) is replaced by valine (uncharged) in the beta-globin polypeptide. • If beta-globin shape changes, hemoglobin's solubility decreases, hemoglobin precipitates into rod-like aggregates in red blood cells.

  15. Continue… Lecture no.4 Hemoglobin aggregation causes sickling of the red blood cell, and the aggregates punctures the cell when it gets squeezed through capillaries

  16. The Molecules of Life Lecture no.4 • Cells are 70% water, nearly 30% carbon compounds.

  17. Continue… Lecture no.4 All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids.

  18. Overview: The Molecules of Life Lecture no.4 • Concept 1: Macromolecules are polymers, built from monomers. • Concept 2: Carbohydrates serve as fuel and building material. • Concept 3: Lipids are a diverse group of hydrophobic molecules. • Concept 4: Proteins include a diversity of structures, resulting in a wide range of functions. • Concept 5: Nucleic acids store, transmit, and help express hereditary information

  19. Monosaccharide Lecture no.4 • The simplest carbohydrates form. • It serve as a major fuel for cells and raw material for building molecules • Polysaccharides, polymers composed of many sugar building blocks. • Monosaccharides are classified by: • The location of the carbonyl group (as aldose or ketose). • The number of carbons in the carbon skeleton.

  20. Lipids Lecture no.4 • Lipidsare the one class of large biological molecules that do not form polymers. • The unifying feature of lipids is having little or no affinity for water. • Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bond. • The most biologically important lipids are fats, phospholipids, and steroids.

  21. Amino acids Lecture no.4 • Subunits of proteins. • 20 major types of amino acids. • Side groups of amino acids dictate protein structure (non-polar, polar, and charged subgroups).

  22. Nucleotides Lecture no.4 • Made up of 5 carbon sugar, phosphate & nitrogenous base (adenine, cytosine, thymosine, guanine, Uracil). • Subunits of DNA and RNA. • ATP - the main energy source.

  23. Summary Lecture no.4

  24. Lecture no.4 The Adenosine triphosphate (ATP) • Adenosine-5'-triphosphate (ATP) is a multifunctional nucleotide used in cells as a coenzyme. • ATP transports chemical energy within cells. • ATP is produced by phosphorylation and cellular respiration and used by enzymes and structural proteins in many cellular processes, including: • Metabolism, synthesis, and active transport. • Roles in cell structure and locomotion. • Cell signaling.

  25. Continue… Lecture no.4 • The phosphoryl groups, starting with the group closest to the ribose, are referred to as the (α), (β), and (γ) phosphates. • ATP molecule as it exists in the intact cell is highly charged at pH 7, the three phosphate groups are completely ionized (4 negative charges) near the linear phosphate structure.

  26. Continue… Lecture no.4 • Metabolic processes that use ATP as an energy source convert it back into its precursors. • ATP is therefore continuously recycled in organisms.

  27. Lecture no.4 Ionization in biological systems • ATP has several negatively-charged groups in neutral solution, it canchelatemetals with very high affinity. • ATP forms stable complexes with certain divalent cations as Mg2+. Most of ATP in the cell present as Mg2+-complex Mg2+.

  28. Product Energy supplied Energy must be supplied. Reactant Energy released Reactant Energy is released. Product Gibbs Free Energy (G) Lecture no.4 • Gibbs Free Energy (G) The energy associated with a chemical reaction that can be used to do work. • Reactions can also be classified as: exergenic (G < 0) orendergenic (G > 0). 

  29. Continue… Lecture no.4 • Example: • the phosphorylation of glucose to glucose 6-phosphate:Glucose + phosphate G-6 phosphate                                  ΔG°' = +3.3 kcal/mol (unfavorable) • Consider the hydrolysis of ATP:ATP  ADP + Pi                                                        Δ G°' = - 7.3 kcal/mol (favorable) • Summing these reactions together:ATP + glucose ADP + G- 6-phosphate                             Δ G°' = +3.3 + (-7.3) = -4kcal/mol (still favorable)

  30. Continue… Lecture no.4

  31. Continue… Lecture no.4 The energy released in the formation of noncovalent bonds is on the order of 1-5 kcal per mol

  32. Lecture no.4 Time to relax ... Later we will start with the main part of the course “Nucleic acids”.. Good luck

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