Steroids. Steroids. Proteins: Wide range of func6ons. lipids characterized by a carbon skeleton consis3ng of four fused rings

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1 Steroids Steroids lipids characterized by a carbon skeleton consis3ng of four fused rings 3 six sided, and 1 five sided Cholesterol important steroid precursor component in animal cell membranes Although cholesterol is essen3al in animals, high levels in the blood may contribute to cardiovascular disease Fig Proteins coded in DNA Proteins: Wide range of func6ons account for more than 50% of the dry mass of most cells Protein func3ons structural support storage transport cellular communica3ons movement defense against foreign substances

2 Polypep6des Polypep6des polymers built from the same set of 20 amino acids Amino acid monomers Protein consists of one or more polypep3des Folded into func3onal 3 D form Amino acids Amino Acid Monomers organic molecules with carboxyl and amino groups differ in their proper3es due to differing side chains called R groups Fig Nonpolar Glycine (Gly or G) Alanine (Ala or A) Valine (Val or V) Leucine (Leu or L) Isoleucine (Ile or I) Methionine (Met or M) Phenylalanine (Phe or F) Trypotphan (Trp or W) Proline (Pro or P) Polar Serine (Ser or S) Threonine Cysteine Tyrosine Asparagine Glutamine (Thr or T) (Cys or C) (Tyr or Y) (Asn or N) (Gln or Q) Electrically charged Acidic Basic Aspartic acid Glutamic acid (Asp or D) (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H)

3 Amino Acid Polymers pep6de bonds Covalent bond between C and N linking amino acids Polypep3des range in length from a few to more than a thousand monomers Amino acid sequence dictates type of polypep3de and ul3mately type of protein Fig Peptide bond (a) Peptide bond Side chains Backbone (b) Amino end (N-terminus) Carboxyl end (C-terminus) Protein Structure and Func6on func3onal protein consists of one or more polypep3des twisted, folded, and coiled into a unique shape

4 Fig Groove Groove (a) A ribbon model of lysozyme (b) A space-filling model of lysozyme Sequence of amino acids Protein Structure and Func6on determines a protein s three dimensional structure Protein s structure determines its func3on Fit substrate in in specific lock and key fashion Antibody protein Protein from flu virus Primary structure (1 ) Four Levels of Protein Structure sequence of amino acids Secondary structure (2 ) ini3al folding consists of coils (alpha(α) helices) and folds (beta(β) sheets) in the polypep3de chain Ter3ary structure (3 ) determined by interac3ons among various side chains (R groups) combina3ons of α helices and β sheets Quaternary structure (4 ) results when a protein consists of mul3ple polypep3de chains

5 Primary structure Four Levels of Protein Structure Sequence of amino acids Dictated by sequence of nucleo3des in DNA Codon set of three nucleo3des code for a specific amino acid secondary structure result from hydrogen bonds between amino acids α helices But between amino acid side chains, but between parts of the backbone coiled Between every fourth amino acid α kera3n hair β pleated sheet Accordian folds Fibrous proteins Four Levels of Protein Structure Fig. 5 21c β pleated sheet Secondary Structure Examples of amino acid subunits α helix

6 Ter6ary structure Four Levels of Protein Structure Combina3ons of helices and pleated sheets determined by interac3ons between R groups, rather than interac3ons between backbone cons3tuents hydrogen bonds ionic bonds hydrophobic interac6ons van der Waals interac3ons Strong covalent bonds called disulfide bridges may reinforce the protein s structure Quaternary structure results when two or more polypep3de chains form one Collagen macromolecule fibrous protein consis3ng of three polypep3des coiled like a rope Hemoglobin Four Levels of Protein Structure globular protein consis3ng of four polypep3des: two alpha and two beta chains Fig. 5 21e Tertiary Structure Quaternary Structure

7 Fig. 5 21g Polypeptide chain β Chains Iron Heme Collagen α Chains Hemoglobin Fig Primary Structure Secondary Structure Tertiary Structure Quaternary Structure β pleated sheet +H 3N Amino end Examples of amino acid subunits α helix What Determines Protein Structure? In addi3on to primary structure physical and chemical condi3ons can affect structure ph Denatura6on salt concentra3on Temperature other environmental factors can cause a protein to unravel loss of a protein s na3ve structure Now biologically inac3ve

8 Fig Denaturation Normal protein Renaturation Denatured protein Protein Folding in the Cell It is hard to predict a protein s structure from its primary structure Sequences of 1.2 million proteins known Only 8,500 3 D shapes known Most proteins probably go through several states on their way to a stable structure Chaperonins protein molecules that assist the proper folding of other proteins Fig Cap Polypeptide Correctly folded protein Hollow cylinder Chaperonin (fully assembled) Steps of Chaperonin Action: 1 An unfolded polypeptide enters the cylinder from one end. 2 The cap attaches, causing the 3 cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comes off, and the properly folded protein is released.

9 Nucleic Acids Store and transfer gene3c informa3on Gene unit of inheritance that codes for the amino acid sequence of a polypep3de Genes are made of DNA, a nucleic acid Two types of nucleic acids: DNA The Roles of Nucleic Acids Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) provides direc3ons for its own replica3on directs synthesis of messenger RNA (mrna) controls protein synthesis Protein synthesis occurs in ribosomes Fig DNA 1 Synthesis of mrna in the nucleus mrna NUCLEUS CYTOPLASM

10 Fig DNA 1 Synthesis of mrna in the nucleus mrna NUCLEUS CYTOPLASM 2 Movement of mrna into cytoplasm via nuclear pore mrna Fig DNA 1 Synthesis of mrna in the nucleus mrna NUCLEUS CYTOPLASM 2 Movement of mrna into cytoplasm via nuclear pore mrna Ribosome 3 Synthesis of protein Polypeptide Amino acids Polynucleo6des The Structure of Nucleic Acids Nucleic acid polymer Nucleo6de monomers of polynucleo3de consists of a nitrogenous base, a pentose sugar, and a phosphate group Nucleoside por3on of a nucleo3de without the phosphate group

11 Fig C 5 end Nitrogenous bases Pyrimidines 3 C Nucleoside Nitrogenous base Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA) Purines 5 C Phosphate group Sugar (pentose) 3 C (b) Nucleotide Adenine (A) Guanine (G) 3 end Sugars (a) Polynucleotide, or nucleic acid Deoxyribose (in DNA) Ribose (in RNA) (c) Nucleoside components: sugars Two families of nitrogenous bases: Nucleo6de Monomers Pyrimidines (cytosine (C), thymine (T), and uracil (U)) single six membered ring Purines (adenine (A) and guanine (G)) deoxyribose six membered ring fused to a fivemembered ring Sugar in DNA ribose Sugar in RNA Nucleo3de = nucleoside + phosphate group Nucleo3de Polymers Nucleo6de Polymers linked together to build a polynucleo3de Simply unfinished nucleic acid Adjacent nucleo3des joined by phosphodiester bonds (covalent) form between the OH group on the 3 carbon of one nucleo3de and the phosphate on the 5 carbon on the next Create a backbone of sugar phosphate units with nitrogenous bases as appendages The sequence of bases along a DNA or mrna polymer is unique for each gene

12 The DNA Double Helix Double helix two polynucleo3des spiraling around an imaginary axis, forming a DNA molecule Nitrogenous bases bond with one another in the middle in complementary fashion A T; C G An6parallel two backbones run in opposite 5 3 direc3ons from each other in the DNA double helix One DNA molecule includes many genes Equals one chromosome Fig ' end 3' end Sugar-phosphate backbones Base pair (joined by hydrogen bonding) 3' end Old strands Nucleotide about to be added to a new strand 5' end New strands 3' end 5' end 5' end 3' end DNA and Evolu6onary Rela6onships Sequences of nucleo3des in DNA passed from parents to offspring Two closely related species are more similar in DNA than are more distantly related species Determined by % divergence

13 You should now be able to: 1. List and describe the four major classes of molecules 2. Describe the forma3on of a glycosidic linkage and dis3nguish between monosaccharides, disaccharides, and polysaccharides 3. Dis3nguish between saturated and unsaturated fats and between cis and trans fat molecules 4. Describe the four levels of protein structure 5. Dis3nguish between the following pairs: pyrimidine and purine, nucleo3de and nucleoside, ribose and deoxyribose, the 5 end and 3 end of a nucleo3de