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BIOL. 233 TERM 121 CHAPTER 3 PART 2 Dr. Amjad Khalil 1 3.4 PROTEINS – DIVERSITY IN STRUCTURE AND FUNCTION Proteins are the most diverse biological molecules (examples: there are structural, nutritious, enzyme, transport, communication, and defense proteins) Cells build thousands of different proteins by stringing together amino acids according to the directions found in the DNA Key is the flexibility of proteins allowing them to perform many functions in the organism 2 PROTEINS AND AMINO ACIDS What is Protein? An organic compound composed of one or more chains of amino acids joined by peptide bonds 3 PROTEINS STRUCTURE An amino acid is a small organic compound with an amino group (-NH3+) , a carboxyl group (-COO-,the acid part ),a hydrogen atom , and one or more atoms called its R group . It is the R group that makes each of the 20 naturally occurring amino acids different In most cases ,these components are attached to the same carbon atom (Figure 3.15). 4 PEPTIDE BOND FORMATION AND POLY PEPTIDE Peptide Bond: A bond between the amino group of one amino acid and the carboxyl group of another. A peptide bond from as a condensation reactions joins the amino group of one amino acid and the carboxyl group of the next in line. 5 PEPTIDE BOND FORMATION AND POLY PEPTIDE Polypeptide: A chain of amino acids linked by peptide bonds. Each polypeptide chain consists of three or more amino acids .The carbon of this chain incorporates nitrogen atoms in this regular pattern: -N-C-C-NC-C- . 6 POLYPEPTIDES FROM AMINO ACIDS Protein synthesis involves the formation of chain of joined amino acids (also called a polypeptide) Polypeptide A chain of amino acids bonded together by peptide bonds in a condensation reaction between the amine group of one amino acid and the carboxyl group of another amino acid Remember: the condensation bond is made by extracting water from the two amino acids and thus linking them together 7 AMINO ACIDS CODED IN DNA Instructions coded in DNA specify the order in which any of the twenty kinds of amino acids will occur in a given protein. 8 PROTEIN STRUCTURE (PRIMARY & SECONDARY) Primary structure The unique amino acid sequence of a protein (just the list of amino acids contained in protein) Secondary structure The polypeptide chain can fold and it forms hydrogen bonds between the amino acids 9 PROTEIN STRUCTURE (TERTIARY & QUATERNARY) Tertiary structure (more complex) A secondary structure is compacted into structurally stable units called domains or unit. Forms a functional protein Quaternary structure (most complex) Some proteins consist of two or more folded polypeptide chains(units) in close association Example: hemoglobin 10 LEVELS OF PROTEIN STRUCTURE 3.5 WHY IS PROTEIN STRUCTURE SO IMPORTANT? Just one wrong amino acid….. Hemoglobin’s oxygenbinding properties depend on its structure. Each of the 4 globin chains in the hemoglobin protein forms a pocket that holds an iron containing heme group, figure 3.18. Hemoglobin made up of 4 globin units, 2 α and 2 β. ONE WRONG AMINO ACID CAUSE SICKLE CELL ANEMIA Phenotypic Basis Of Sickle Cell Anemia Glutamic acid carries a negative charge; valine carries no charge. This difference changes the protein so it behaves differently. At low oxygen levels, HbS molecules stick together and form rodshaped clumps that distort normally rounded red blood cells into sickle shapes. (A sickle is a farm tool that has a crescent-shaped blade.) sickled cell normal cell 14 Fig. 3-19c, p. 47 PROTEINS UNDONE – DENATURATION Proteins function only as long as they maintain their correct three-dimensional shape Heat, changes in pH, salts, and detergents can disrupt the hydrogen bonds that maintain a protein’s shape When a protein loses its shape and no longer functions, it is denatured; a breakfast egg with the “white” set around the yolk is a familiar example of denatured protein 15 KEY CONCEPTS: PROTEINS IN GENERAL Structurally and functionally, proteins are the most diverse molecules of life They include enzymes, structural materials, and transporters A protein’s function arises directly from its structure 16 3.6 NUCLEOTIDES, DNA, AND THE RNA Each nucleotide is made up of one 5 carbon sugar, phosphate group and one nitrogen base. ATP: Adenosine tri- phosphate. 17 NUCLEIC ACIDS – BLUEPRINT FOR LIFE Some nucleotides are subunits of nucleic acids such as DNA and RNA. Some nucleotides have roles in metabolism such as ATP and ADP in cell respiration and in photosynthesis via energy storage (that’s adenosine triphosphate and adenosine diphosphate). 18 NUCLEOTIDES Nucleotide A small organic molecule consisting of a sugar with a five-carbon ring, a nitrogen-containing base, and one or more phosphate groups ATP – adenosine triphosphate A nucleotide with three phosphate groups Important in phosphate-group (energy) transfer ATP is the “energy ATM” of the cell – it is used to store and release energy as needed 19 ATP STRUCTURE 20 NUCLEIC ACIDS Nucleic acids Polymers of nucleotides in which the sugar of one nucleotide is attached to the phosphate group of the next RNA and DNA are very useful nucleic acids 21 RNA – CARRIES OUT DNA INSTRUCTIONS RNA (ribonucleic acid) Contains four kinds of nucleotide monomers, including ATP Important in protein synthesis Is always at direction (and creation of) the DNA Is a single helix (helix simply means curved) 22 DNA – ARCHITECT FOR LIFE DNA (deoxyribonucleic acid) Two chains of nucleotides twisted together into a double helix with links of hydrogen bonds Contains all inherited information necessary to build/maintain an organism, coded in the order of the nucleotide bases, with each three base “letters” forming a genetic code “word” All living organisms have DNA 23 NUCLEOTIDES AND NUCLEIC ACIDS DNA MOLECULE Hydrogen bonds between base join the 2 strands along the length of a DNA molecule. DNA sequence of bases has heritable information on how to build all the proteins and RNAs that gives each cell the potential to grow and reproduce. KEY CONCEPTS: NUCLEOTIDES AND NUCLEIC ACIDS Nucleotides have major metabolic roles and are building blocks of nucleic acids Two kinds of nucleic acids, DNA and RNA, interact as the cell’s system of storing, retrieving, and translating information about building proteins 26 END OF CHAPTER 3 27