MB207 Molecular Cell Biology

1. MB207 Molecular Cell Biology 2. Cell Chemistry and Biosynthesis

2. Cell Chemistry and Biosynthesis • Chemistry of life: - based majority on carbon compounds, organized into macromolecules that are require for cells growth and function. - cells are 70% water (life depends almost exclusively on chemical reactions that take place in aqueous solution) - cell chemistry is enormously complex: even the simplest cell is vastly more complicated in its chemistry than any other chemical system known.

3. Chemical component of a cell • Matter is made of combinations ofelements. Substances that cannot be broken down or converted into other substances by chemical means ie. Hydrogen or carbon • Smallest particle of an element is an atom • A molecule may consist of atoms of a single element or of different elements. • These elements are connected by chemical bonds that hold atoms together.

4. Cell are made from a few types of atoms • Cells are made from atoms. - Atom is the smallest particle of an element - consisting of a +ve charged nucleus (protons and neutrons), surrounded by a cloud of -ve charged electrons. - There are 92 naturally occurring elements, differing in protons and electrons in its atoms. • Atom - electron (held in a series of orbitals electrostatic attraction to the nucleus) - protons (positively charged, gives the atomic number) - neutron (uncharged) Atomic nucleus

5. Living organisms are made up of 4 main elements: C, H, N & O. This composition differs markedly from that of the nonliving inorganic environment. • Chemical bonds : 1) Covalent bonds (sharing of electrons) - strongly bonding 2) Non-covalent bonds: ionic, hydrogen bond, Van der Waals attraction and hydrophobic strength

6. 70% of a cell’s weight is water

7. Representations of a water molecule

8. Covalent bond and ionic bond 2 types of chemical bonds between atoms: a. Covalent bond: formed when 2 atoms have a pair of electrons b. Ionic bond: formed when electrons are donated by 1 atom to another

9. Cl2 & CO2 : examples of covalent bonds formation Chlorine molecule formed by 2 atoms sharing 1 pair of electrons Carbon dioxide molecule formed from 2 oxygen atom each sharing 2 pairs of electrons with a carbon atom

10. Sodium Chloride: ionic bond formation

11. Four types of noncovalent interactions help to bring molecules together in cells • Van der Waals interactions • interactions between two atoms that occur only if the atoms are very close to one another and are oriented appropriately. • Hydrogen bond • polar interactions of a electropositive hydrogen that is shared by two neighboring electronegative atoms. • Ionic bond • Interactions between two oppositely charged ions.

12. Hydrophobic forces • Pushing of non-polar surfaces out of the hydrogen-bonded water network.

13. Strong Weak Covalent > ionic > hydrogen > van der Waals

14. Cells contain 4 major families of small organic molecules • Are carbon-based compounds having molecular weights in the range 100 to 1000 and contain up to 30 or so carbon atoms. Function: monomer subunits - to construct polymeric macromolecules eg. proteins, nucleic acids, and large polysaccharides of the cell. energy sources - are broken down and transformed small molecules in intracellular metabolic pathways. 1) Sugar (2%)  polysaccharides 2) Fatty acids (2%)  Fats, lipids, phospholipids (membrane) 3) Amino Acids (15%)  polypeptides, proteins 4) Nucleotides (7%)  nucleic acids Others (4%) + H2O (70%)

15. Cells contain four major families of small organic molecules

16. Sugars • Simplest - monosaccharides. • General formula [CH2O]n where n is a number between 3 – 8. • Polysaccharides are large molecules composed of individual sugar units. • Can exist in either 2 forms, D-form and L-form, which are mirror images of each other. • Exist in either a ring or and open-chain form. Open –chain form: aldosugars or ketosugars • Main functions: • Energy source • Mechanical support e.g. cellulose • Covalently linked to protein and lipid  glycoprotein or glycolipids

19. Condensation and hydrolysis of disaccharide

20. Fatty Acids • Is a long, unbranched hydrocarbon chain with a carboxyl group at one end. • Amphipathic; carboxyl group renders one end polar whereas the hydrocarbon tail is nonpolar. • Variable but usually even number of carbon atoms ranging from 12 to 20 carbon atoms per chain. • Main functions: • long-term energy storage • Act as structural components e.g. the major building block in cell membranes • as "messengers" (hormones) that play roles in communications within and between cells

21. Saturated fatty acids Unsaturated fatty acids

22. Phospholipid structure and the orientation of phospholipids in membranes

23. Nucleotides • Nitrogen-containing ring compound linked to a five-carbon sugar. • Ribose: ribonucleotides Deoxyribose: deoxyribonuleotides • Pyrimidines: cytosine, thymine and uracil • Purines: guanine and adenine • Main functions: • Subunits for DNA & RNA, storage of genetic information • Short term carriers of chemical energy, e.g. ATP • Coenzyme & specific signaling molecules in the cells e.g. cAMP

27. The assembly of macromolecules

28. Energy is needed for the assembly of macromolecules, where can cells obtain such energy?

29. Cell Metabolism - Organized by enzymes • Chemical reactions: • catabolic pathways; • anabolic or biosynthetic pathways Catalysis & the use of energy by cells A set of enzyme-catalyzed reactions generates a metabolic pathway

30. Breaks large molecules into smaller molecules; usually releases energy. Builds large molecules from smaller ones; usually consumes energy.

31. The Carbon Cycle

33. How cells obtain energy from food??? - To produce ATP, NADH • Food Molecules Are Broken Down in 3 Stages: • Digestion (enzymatic breakdown of food molecules into monomer subunits) • Partial breakdown of simple molecules to provide some energy in the cytoplasm (Different metabolism pathways) • Complete oxidation through respiration at the mitochondria to provide more energy

34. Metabolism of Food & Energy production 1) Break down of large macromolecules to simple subunits (amino acids, simple sugars, fatty acids & gylcerol) 2) Further breakdown to Acetyl CoA, production of limited amount of ATP and NADH (Glycolysis and Kreb Cycle) 3) Complete oxidation of Acetyl CoA to H2O & CO2, production of large amount of NADH and ATP in mitochondria.

35. The 3 stages of cellular metabolism from food to waste products in animal cells 1st stage: Breakdown of large macromolecules to simple subunits outside cells Outside cell Digestion 2nd stage : Oxidation begin Cytosol

36. 1st stage Outside cells 2nd stage: Breakdown of simple subunits to acetyl CoA accompanied by production of limited amounts of ATP and NADH Cytosol Glycolysis Mitochondrial 3rd stage Mitochondrial

37. Glycolysis Glucose Pyruvate Cytosol Pyruvate dehydrogenase ATP NADP ATP CO2 ATP ATP CO2 + Carbon acetyl group + coenzyme A 3rd stage Aceyl CoA Citric acid cycle Oxidation phosphorylation O2 + H2O mitochondrion Waste products

38. 2nd stage Cytosol + mitochondrial 3rd stage: Complete oxidation of acetyl CoA to H2O and CO2 accompanied by production of large amounts of NADH and ATP Mitochondrial Waste product