Chapter 5: The Structure and Function of Large Biological Molecules. 1. Polymers 2. Carbohydrates 3. Proteins 4. Lipids 5.

Transcription

1 Chapter 5: The Structure and Function of Large Biological Molecules 1. Polymers 2. Carbohydrates 3. Proteins 4. Lipids 5. Nucleic Acids

2 1. Polymers Chapter Reading pg. 67

3 What are Polymers? Polymers are chains of smaller molecules:

4 Dehydration Synthesis Building biological polymers involves the loss of H 2 O: (a) Dehydration reaction: synthesizing a polymer Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond Longer polymer

5 Hydrolysis of Polymers Breaking down polymers requires water: (b) Hydrolysis: breaking down a polymer Hydrolysis adds a water molecule, breaking a bond

6 2. Carbohydrates Chapter Reading pp

7 Overview of Carbohydrates Made of CH 2 O (1 Carbon : 2 Hydrogen : 1 Oxygen) Glucose (C 6 H 12 O 6 ) structural formula abbreviated structure simplified structure Functions: source of energy Examples of Carbohydrates: sugars cellulose structural support starch glycogen

8 Carbohydrate Monomers & Polymers monosaccharides, disaccharides & polysaccharides ( saccharide is Greek for sugar) 2 monosaccharides Glucose Glucose 1 disaccharide Important monosaccharides: GLUCOSE & FRUCTOSE Important disaccharides: Maltose SUCROSE, LACTOSE & MALTOSE

9 Linear and Ring Forms (a) Linear and ring forms Monosaccharides that can adopt the ring form have 5 carbons (pentoses) or 6 carbons (hexoses) (b) Abbreviated ring structure

10 Some Important Monosaccharides Aldose (Aldehyde Sugar) Ketose (Ketone Sugar) Trioses: 3-carbon sugars (C 3 H 6 O 3 ) Glyceraldehyde Dihydroxyacetone Aldoses have a terminal carbonyl (aldehyde) group Ketoses have an internal carbonyl (ketone) group Aldose (Aldehyde Sugar) Ketose (Ketone Sugar) Pentoses: 5-carbon sugars (C 5 H 10 O 5 ) Aldose (Aldehyde Sugar) Ketose (Ketone Sugar) Hexoses: 6-carbon sugars (C 6 H 12 O 6 ) Ribose Ribulose Glucose Galactose Fructose

11 Disaccharides 1 4 glycosidic linkage Glucose Glucose (a) Dehydration reaction in the synthesis of maltose Maltose 1 2 glycosidic linkage Glucose Fructose Sucrose (b) Dehydration reaction in the synthesis of sucrose

12 Polysaccharides Chloroplast Starch granules Amylopectin (a) Starch: a plant polysaccharide 1 m Amylose Mitochondria Glycogen granules (b) Glycogen: 0.5 m an animal polysaccharide Glycogen

13 & forms of Glucose (a) and glucose ring structures Glucose Glucose (b) Starch: 1 4 linkage of glucose monomers (c) Cellulose: 1 4 linkage of glucose monomers Starch and glycogen are polymers of glucose Cellulose is a polymer of glucose

14 Structure of Cellulose Cell wall Cellulose microfibrils in a plant cell wall Microfibril 10 m 0.5 m Cellulose molecules Glucose monomer

15 Chitin (a) The structure (b) Chitin forms the (c) of the chitin exoskeleton of monomer. arthropods. Chitin is used to make a strong and flexible surgical thread. Chitin is a polymer of an unusual nitrogen-containing sugar: found in exoskeletons of insects, cell walls of fungi

16 3. Proteins Chapter Reading pp

17 Overview of Proteins Proteins are polymers of amino acids and have a tremendous variety of functions. proteins carry out most of the activities toward maintaining homeostasis in cells and staying alive made from elements C, H, O, N & S

18 Functions of Proteins Proteins have a wide variety of functions and carry out most of the biochemical activities in cells: ENZYMATIC PROTEINS Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules. DEFENSIVE PROTEINS Function: Protection against disease Example: Antibodies inactivate and help destroy viruses and bacteria. Antibodies Enzyme Virus Bacterium STORAGE PROTEINS Function: Storage of amino acids Examples: Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo. TRANSPORT PROTEINS Function: Transport of substances Examples: Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes. Transport protein Ovalbumin Amino acids for embryo Cell membrane

19 more Protein Functions HORMONAL PROTEINS Function: Coordination of an organism s activities Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration RECEPTOR PROTEINS Function: Response of cell to chemical stimuli Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells. High blood sugar Insulin secreted Normal blood sugar Signaling molecules Receptor protein CONTRACTILE AND MOTOR PROTEINS Function: Movement Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles. STRUCTURAL PROTEINS Function: Support Examples: Keratin is the protein of hair, horns, feathers, and other skin appendages. Insects and spiders use silk fibers to make their cocoons and webs, respectively. Collagen and elastin proteins provide a fibrous framework in animal connective tissues. Actin Myosin Collagen Muscle tissue Connective 100 m tissue 60 m

20 Amino Acids Amino acids are the monomers from which the polymers we call proteins are made. Side chain (R group) carbon Each amino acid has a central carbon atom to which is attached: an amino group a carboxyl group Amino group Carboxyl group a hydrogen atom a variable R group

21 NONPOLAR SIDE CHAINS HYDROPHOBIC Side chain Hydrophobic Amino Acids DG favors avoidance of H 2 O by non-polar R groups. * 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) Tryptophan (Trp or W) Proline (Pro or P)

22 Polar Amino Acids POLAR SIDE CHAINS HYDROPHILIC Serine (Ser or S) Threonine (Thr or T) * Cysteine (Cys or C) The R groups on all of these AAs are polar because they have polar chemical groups Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q) The R groups of these AAs mix well with water and other polar substances

23 Charged Amino Acids The R groups of these AAs are acidic or basic and as a result have a net charge at neutral ph. interact well with water, oppositely charged substances ELECTRICALLY CHARGED SIDE CHAINS HYDROPHILIC Acidic (negatively charged) Basic (positively charged) Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H)

24 Polypeptides Polypeptides are polymers of AAs Peptide bond New peptide bond forming Each AA is joined to the next by the loss of H 2 O (dehydration) Side chains Backbone Amino end (N-terminus) Peptide bond Carboxyl end (C-terminus) OH from the carboxyl group, H from the amino group Polypeptides have N-termini & C-termini

25 Primary (1 o ) structure Secondary (2 o ) structure Hydrogen bond Four Levels of Protein Structure Amino acids Protein Structure Protein function depends on its structure: Tertiary (3 o ) structure Quaternary (3 o ) structure Polypeptide (single subunit of transthyretin) Alpha helix Transthyretin, with four identical polypeptide subunits Pleated sheet ea polypeptide must be folded properly polypeptides in a protein must interact in the right way If this is not the case, proteins don t work!

26 Primary Protein Structure Amino acids PRIMARY STRUCTURE The 1 o structure of a protein is simply the AA sequence of each polypeptide it contains Higher orders of protein structure are dependent on the AA sequence changes in AA sequence (i.e., mutations) will affect overall protein structure Amino end Primary structure of transthyretin Carboxyl end

27 Higher Levels of Protein Structure Secondary (2 o ) structure Tertiary (3 o ) structure Quaternary (4 o ) structure helix pleated sheet Hydrogen bond strand Hydrogen bond Transthyretin polypeptide Transthyretin protein reflect 3-D arrangements on successively larger scales

28 Secondary Structure SECONDARY STRUCTURE helix Involves H-bonding between C=O & N H within the backbone of the polypeptide pleated sheet Hydrogen bond strand, shown as a flat arrow pointing toward the carboxyl end Hydrogen bond

29 Tertiary & Quaternary Structure 3 o structure overall 3-D shape of a single polypeptide due to R group interactions Tertiary Structure 4 o structure 3-D arrangement of multiple polypeptides in a single protein Quaternary Structure

30 R-group Interactions in Tertiary (& Quaternary) Structure Disulfide bridge Hydrogen bond Hydrophobic interactions and van der Waals interactions Ionic bond Polypeptide backbone

31 Modeling Protein Structure Groove Groove (a) A ribbon model of lysozyme (b) A space-filling model of lysozyme Ribbon models reveal the 2 o structure: coils = -helices arrows = -pleated sheets intervening regions = loops MHC

32 Variety in Protein Shape Polypeptide chain Chains Iron Heme Chains Collagen Hemoglobin

33 Mutations & Protein Structure Sickle-cell hemoglobin Normal hemoglobin Primary Structure Secondary and Tertiary Structures subunit Exposed hydrophobic region subunit Quaternary Structure Normal hemoglobin Sickle-cell hemoglobin Function Molecules do not associate with one another; each carries oxygen. Molecules crystallize into a fiber; capacity to carry oxygen is reduced. Red Blood Cell Shape 10 m 10 m

34 Denaturation of Proteins Denaturation Normal protein Renaturation Denatured protein Proteins can be denatured by: extreme temperature extreme ph high [salt] non-polar solvent

35 4. Lipids Chapter Reading pp

36 Lipids glycerol fatty acid Hydrophobic, made mostly of C & H. Functions: source of energy insulation hormones membranes Includes: fatty acids (FA) triglycerides phospholipids steroids triglyceride

37 Fatty Acid Saturation depends on whether or not C=C double bonds are present (a) Saturated fat (b) Unsaturated fat Structural formula of a saturated fat molecule Space-filling model of stearic acid, a saturated fatty acid Polyunsaturated fats have >1 C=C double bond Structural formula of an unsaturated fat molecule Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending.

38 Triglycerides (triacylglycerol) Fatty acid (palmitic acid) Glycerol (a) Dehydration reaction in the synthesis of a fat Ester linkage 3 fatty acids connected via ester linkages to a molecule of glycerol (b) Fat molecule (triacylglycerol)

39 Phospholipids Phospholipids are the major component of biological membranes. Hydrophobic tails Hydrophilic head Choline Phosphate Glycerol Fatty acids Hydrophilic head Hydrophobic tails (a) Structural formula (b) Space-filling model (c) Phospholipid symbol

40 Membrane Structure Phospholipids in water will form a phospholipid bilayer. Hydrophilic head WATER Hydrophobic tail WATER

41 Steroids All steroids contain the same core 4 ring structure. cholesterol Important Steroids: estradiol cholesterol estrogens testosterone testosterone

42 5. Nucleic Acids Chapter Reading pp ,

43 Overview of Nucleic Acids The main function of Nucleic Acids is to store and express Genetic Information: includes DNA & RNA DNA & RNA are linear polymers of nucleotides made from elements C, H, O, N & P

44 Nucleic DNA Acids & Gene 1 Synthesis of mrna in the nucleus mrna Expression DNA is used to store genetic information 2 NUCLEUS Movement of mrna into cytoplasm via nuclear pore mrna CYTOPLASM Ribosome RNA is used in gene expression & regulation 3 Synthesis of protein Polypeptide Amino acids

45 All nucleotides have this basic structure. Nucleotides nitrogenous base (adenine) phosphate group sugar

46 Sugars in Nucleotides SUGARS * * Deoxyribose (in DNA) Ribose (in RNA) (c) Nucleoside components: sugars Deoxyribose and Ribose differ only in what is attached to the 2 carbon.

47 Purines & Pyrimidines NITROGENOUS BASES Pyrimidines Pyrimidines have 1 ring Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA) Purines Purines have 2 rings Adenine (A) Guanine (G) (c) Nucleoside components: nitrogenous bases

48 DNA & RNA: Nucleotide Polymers 5'C 3'C 5' end Nucleotide polymers or strands are connected through an alternating sugar-phosphate backbone 5'C Nucleoside Nitrogenous base 5 end has a free phosphate group 5'C 3'C 3' end Phosphate group (b) Nucleotide 3'C Sugar (pentose) 3 end has a free hydroxyl group (a) Polynucleotide, or nucleic acid

49 DNA & RNA Structure DNA is double-stranded and RNA is single-stranded. 5 3 Sugar-phosphate backbones Hydrogen bonds Base pair joined by hydrogen bonding 3 5 (a) DNA Base pair joined by hydrogen bonding (b) Transfer RNA

50 Structure of Double-stranded DNA the 2 strands are anti-parallel and interact via base pairs C G G C C G 5 end Hydrogen bond 3 end G C T A T A 3.4 nm G C G C C G A T 1 nm T A C G C G G C C G A T A T 3 end T A A T 0.34 nm 5 end (a) Key features of DNA structure (b) Partial chemical structure (c) Space-filling model

51 DNA Base-Pairing Base pairs are held together by hydrogen bonds. Why only A:T and C:G? Sugar Adenine (A) Sugar Thymine (T) the position of chemical groups involved in H-Bonds the size of the bases (purine & pyrimidine) Purine purine: too wide Sugar Guanine (G) Sugar Cytosine (C) Pyrimidine pyrimidine: too narrow Purine pyrimidine: width consistent with X-ray data

52 Key Terms for Chapter 5 polymer, monomer, dehydration synthesis, hydrolysis carbohydrate; mono-, di-, polysaccharide aldose, ketose, triose, pentose, hexose lipid, fatty acid, triglyceride, phospholipid, sterol protein, amino acid, polypeptide, denatured nucleic acid, nucleotide, purine, pyrimidine, antiparallel, base pair Relevant Chapter Questions 1-9