Molecular Composition of Cells:

Carbohydrates, Lipids, Proteins, Nucleic Acids, Cell Membranes, Membrane Lipids

Membrane Proteins, Transport across Cell Membranes

 Carbohydrates: Include simple sugars (Glucose, Fructose etc.,), Disaccharides ( sucrose = glucoe + Fructose) and polysaccharides.

Polysaccharides-. Servers as a storage forms of sugars, structural components of cells, also serves as cell recognition marker.

Starch- Storage polysaccharides in plants, Glycogen - Storage polysaccharides in animals. Cellulose- structural polysaccharides plant cell walls.

Glycosidic bond-Two simple sugars joined by a dehydration reaction.

Lipids: Three major Roles in Cells: 1. Important form of energy storage 2. Major component of cell membrane 3. Roles in Cell Signalling ( Signalling both between and within cells)

Simplest lipids are Fatty Acids: Hydrophobic molecules-Fatty acids stored in the form of triacylglycerols or fats ( 3 fatty acids linked to a glycerol molecule).

Phospholipids- Amphipathic mplecules-Two fatty acids joined to a polar head group; Principal component of plasma membrane.

Glycerol Phospholipids contain two fatty acids joined to glycerol. The fatty acid may be different from each other and are designated as R1 and R2 . The 3^rd carbon of glycerol is joined to a phosphate group ( forming Phosphotidic acid ), which in turn joined to another small polar molecule

forming the following phospholipids; Phosphotidyl-ethanolamine, Phosphotidylcholine, Phosphotidylserine, Phosphotidylinositol.

Sphingomyelin-A non-glycerol phospholipid in cell membrane consists of two hydrocarbon chain linked to a polar head group formed from serine unlike other phospholipids where the head group is glycerol.

Glycolipids- Composed of two hydrocarbon chains linked to polar head groups that contain carbohydrates.

Cholesterol- Important component of animal cell membrane. Consists of 4 fused hydrocarbon rings with an attached functional groups (mostly OH group). Cholesterol is a precursor to testesterone, estrogen and progesterone.

Nucleic Acid- DNA and RNA, Polymers of Nucleotides. Principal informational molecule of the cell. Nucleic acids can self replicate by means of hydrogen bonding between complementary base pairs.

Proteins: Polymers of 20 different amino acids, each of which has very distinct side chain and a specific chemical properties.

Peptide bonds- Joining of alpha-amino group of one amino acid and the alpha COOH group of a second amino acid.

Polypeptides- Linear chains of amino acids which are usually hundred to thousand amino acid long.

Protein Structure- Frederick Sanger (1953) for the first time determined complete sequence of Insulin; which is consists of two polypeptide chains, one 21 and the other 30 amino acid. The two chain are joined by disulphide bonds.

Primary structure- Sequence of amino acids in a polypeptide chain.

Secondary Structure-

Alpha helix and the Beta sheet are the most common types of secondary structure.

Alpha helix : Hydrogen bonds forms between the CO group and the NH groups of a polypeptide chain which are seperated by four amino acid residues.

Beta Sheet- Hydrogen bonds connect two parts of a polypeptide chain lying side by side.

Forms due to folding of the polypeptide chains as a result of interactions between the side chains of amino acids lying in different regions of the primary sequence.

Domain- Folding of the polypeptide chain into a compact globular structure by a combination of alpha helices and bets sheet which are connected by a loop.

Consists of Interactions between different polypeptide chains in protein which are composed of more than one polypeptide; eg., Hemoglobin is composed of four polypeptide chain, each of which is bound to a heme group..Fourth level of protein structure .

Protein. Biological catalyst. All chemical reactions in cell are catalyzed by enzymes.

Mechanism of Enzymatic Catalysis- Substrate binding in proper position, Alters the conformation of substrates to approach transition state, Participate directly in chemical reaction.

Coenzyme-Function in conjunction with enzyme to carry chemical group between substrates.

Regulation of enzymatic activity- Can be controlled by binding of small molecules, by interaction with other proteins, and by covalent modification,

Feedback Inhibition- Product of a metabolic pathway inhibits the activity of an enzyme involved in its synthesis.

Allosteric regulation- Controlled by the binding of small molecules to regulatory sites on the enzyme. Feedback inhibition is one example.

Phosphorylation- A common mechanism for regulating enzyme activity.

Metabolic Energy:

Free Energy and ATP- ATP is a purine nucleotide which serves as a storage of free energy. ATP is used to drive the energy requring reactions within cells.

Glycolysis –Takes place in the cytosol in Eukaryotes. Initial stage in the breakdown of glucose , Occurs in the absence of oxygen and common to almost all cells.

Reactions of Glycolysis- A 10 step process where glucose is broken down to 2 molecules of pyruvate, with the net formation of 2 molecules each of ATP and NADH. Under anaerobic conditions NADH is reoxidized by the conversion of pyruvate to ethanol or lactate.

Under aerobic condition Pyruvate is further metabolized by the citric acid cycle.

Citric Acid Cycle- Takes place in Mitochondrial matrix. Pyruvate is oxidatively decaboxylated with coenzyme A (CoA) to form acetyl CoA.

A 2-C acetyl CoA group is transferred from acetyl CoA to oxaloacetate forming citrate. Two carbon of citrate are then oxidized forming citrate. Two carbons of citrate are then oxidized to Co2 and oxaloacetate is regenerated. Each turn of the cycle yields one molecule of GTP, three of NADH, and one FADH2.

Electron Transport Chain- Takes place in the mitochondrial matrix. Electrons from NADH and FADH2 are transferred to O2 through a series of protein carriers organized into four complexes in the inner mitochondrial membrane. the free energy derived from electron transport reactions at complexes I, III, IIV are used to drive ATP-synthetase to synthesize ATP.

Fats are more reduced than glucose so they provide a more efficient source of energy. Beta oxidation of fatty acids release energy from fats.

Photosynthesis: Ultimate source of energy required for synthesis of organic molecules comes from photosynthesis where plant harvest the solar energy through its photosystem of pigment molecules.

In light reaction of photosynthesis energy from sunlight is used to synthesize ATP and NADPH which is coupled to H2O and O2. In the dark reaction the ATP and NADPH are used to synthesize glucose from CO2 and H2O.

Gluconeogenesis-Glucose can be synthesized from other organic molecules using ATP and NADH.