Chapter 24 The Chemistry of Life

Molecules of Life Many of the most important molecules in our body are polymers. Proteins (amino acids), polysaccharides– (monosaccharides) and nucleic acids (nucleotides), lipids are not polymers, no repeating units (monomers)

Molecules of Life In our diet, we need relatively large amts of proteins, carbohydrates, and lipids. Organic cpds Nucleic Acids Biomolecules for heredity and protein synthesis.

Biochemistry Biochemistry study of the chemistry of living things. explores the substances involved in life processes and the rxns they undergo. Other than H2O (about 80 % or more of the weight of an organism), most of the molecules of life—the biomolecules—are organic.

elemental composition of living things % By mass

Biochemistry more than 95 % of the atoms in our bodies are H, O, C and N. All 4 of these elements can form the strong covalent bonds found in organic molecules.

Biochemistry S and P → proteins

Proteins A protein: an organic polymer composed of amino acids bonded together in one or more chains. Monomer: amino acids An amino acid has a central C atom, to which are bonded a carboxyl group (-COOH acid), an amino group (-NH2), a H atom, and a variable side chain designated as R.

Amino Acids

structural proteins: skin, hair, nails, and muscles A protein A peptide with more than about 100 amino acids. structural proteins: skin, hair, nails, and muscles ‘Functional’ proteins: enzymes, hormones needed for almost all chem rxns that take place in the body.

Proteins Amino Acids in a Peptide Chain Peptides form 3-d shapes. a) This is a representation of amino acids in a peptide chain. b) The chain may coil into a helix. c) Two peptide chains may become arranged in a pleated, sheet-like structure.

Amino Acids An amino acid cpd that contains an amino group (—NH2) and a carboxyl group (—COOH) in the same molecule.

Structure of an Amino Acid Amino acids bond to each other by forming a peptide bond

Structure of an Amino Acid 2 amino acids linked by a peptide bond form a dipeptide.

Structure of an Amino Acid A Peptide: A chain of 2 or more AAs linked by peptide bonds . Polypeptide: a chain of 10 or more AAs. Proteins may have 1 or several polypeptide chains, each chain must have an exact sequence of AAs.

Protein synthesis

Enzymes Enzymes proteins catalyze biochemical rxns speeding up rxns lower Ea

Enzymes Substrates The reactants in an enzyme-catalyzed process. bind to the enzyme’s active site, forming an enzyme-substrate complex. enables the substrate(s) to react with a much lower Ea than …

The Nature of Enzyme Catalysis ● Enzyme provides a catalytic surface ● This surface stabilizes transition state ● Transformed transition state to product B A B A Catalytic surface Juang RH (2004) BCbasics

Enzyme Stabilizes Transition State Energy change ST Energy required (no catalysis) Energy decreases (under catalysis) EST S ES P EP Reaction direction T = Transition state

Carbohydrates Familiar carbohydrates include glucose, sucrose, starches, and cellulose. Simple carbohydrates consist of a chain of C atoms hydroxyl (–OH) groups and a carbonyl gp, often in the form of an (alkanal) aldehyde gp.

Monosaccharides monosaccharides The simplest carbohydrates (simple sugars) e.g. glucose, ribose, fructose, deoxyribose

Monosaccharides

Polysaccharides Polysaccharide A polymer of many monosaccharides bonded into a chain. e.g. Starch consists only of glucose units.

Polysaccharides Plants also link glucose units together in a different way to form the polysaccharide cellulose

Polysaccharides Glycogen Animals store glucose as a polysaccharide

Lipids Lipids Fats and oils—produced by living things. not polymers, Digestion → fatty acids and glycerol chem structures vary widely.

Triglycerides Lipids: Fats, oils, and other water-insoluble cpds. Moderate levels of dietary fats and oils are essential to health.

Fatty Acids The most familiar lipids : plant oils and animal fats. These lipids are esters of fatty acids, which are alkanoic acids with long, straight hydrocarbon chains between 12 and 24 C atoms.

Saturated Fatty Acid The simplest fatty acids are the saturated fatty acids, no C ═ C double bonds between C atoms. Stearic acid is found in pork and beef tissue.

Monounsaturated Fatty Acid Many other fatty acids have 1 or more double bonds between C atoms → unsaturated fatty acids. Oleic acid is a major component of olive oil.

Triglycerides Animal fats and plant oils are made up primarily of triglycerides, molecules in which 3 fatty acids are bonded to a glycerol molecule (by ester linkages).

The Functions of Lipids long-term storage of energy is usually in the form of lipids. (more effective than carbohydrates.) an important component of our skin and cell membrane.

DNA and RNA nucleic acids polymers found primarily in cell nuclei. monomer: nucleotide 2 kinds: deoxyribonucleic acid (DNA) ribonucleic acid (RNA)

nucleotides. Each consists of a DNA and RNA nucleotides. Each consists of a phosphate group, a five-carbon sugar, and a nitrogen base.

Nucleic Acids

Nucleic Acids 2 types of nucleic acids DNA contains the sugar deoxyribose RNA contains the sugar ribose. DNA exists as a pair of polymer chains backbone of each chain consists of alternating phosphate and deoxyribose units. The bases stick out from the backbone.

The Structure of DNA A single DNA molecule contains many thousands of nucleotides.

Base Pairing the N bases of 1 chain are H-bonded to the N bases of the other chain. the chains wind into a spiral called a double helix.

Base Pairing 4 different N bases are found in DNA: adenine, guanine, cytosine, and thymine. Adenine— thymine (H-bond) Guanine— cytosine.

DNA and RNA

Base Pairing The order of these 3 N bases along 1 of the DNA chains provides the informn for the sequences of AAs in proteins. Cell mechanisms “read” the DNA sequence in gps of three bases called triplets. Each triplet codes for a specific AA or tells the cell to start or stop making a protein.

The Genetic Code A gene a segment of DNA carries the instructions for making 1 peptide chain. The products of genes are the peptides and proteins.

Question 1 Label the amino group and the carboxyl group of the dipeptide.

Answer

Question 2 Draw an arrow pointing to the peptide bond.

Answer

Question 3 Draw a square around each variable side chain.

Answer

Question 4 Glucose is a(n) a. polysaccharide. b. amino acid. c. part of cellulose. d. 5-carbon sugar.

Answer The answer is C, part of cellulose.

CST problem 1 Which substance is made up of many monomers joined together in long chains? A salt B protein C ethanol D propane

CST problems 2 Some of the molecules found in the human body are NH2CH2COOH (glycine), C6H12O6 (glucose), and CH3(CH2)16COOH (stearic acid). The bonds they form are A nuclear. B metallic. C ionic D covalent

CST problem 3 Proteins are large macromolecules composed of thousands of subunits. The structure of the protein depends on the sequence of A lipids B monosaccharides C amino acids D nucleosides

The End