The Structure and Function of Macromolecules Chapter 5 The Structure and Function of Macromolecules Part B

Steroids Steroids Are lipids characterized by: A carbon skeleton consisting of four fused rings

One steroid, cholesterol Is found in cell membranes Is a precursor for some hormones HO CH3 H3C Figure 5.15

Proteins have many structures, resulting in a wide range of functions Have many roles inside the cell

An overview of protein functions Table 5.1

Enzymes: An enzyme is a type of protein that acts as a catalyst, speeding up chemical reactions Substrate (sucrose) Enzyme (sucrase) Glucose OH H O H2O Fructose 3 Substrate is converted to products. 1 Active site is available for a molecule of substrate, the reactant on which the enzyme acts. Substrate binds to enzyme. 2 4 Products are released. Figure 5.16

Polypeptides Polypeptides A protein Are polymers of amino acids Consists of one or more polypeptides

Amino Acid Monomers Amino acids Are the monomers (building blocks) of proteins Are organic molecules possessing both carboxyl and amino groups Differ in their properties due to differing side chains, called R groups

20 different amino acids make up proteins H H3N+ C CH3 CH CH2 NH H2C H2N Nonpolar Glycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile) Methionine (Met) Phenylalanine (Phe) Tryptophan (Trp) Proline (Pro) H3C Figure 5.17 S

Polar Electrically charged OH CH2 C H H3N+ O CH3 CH SH NH2 Polar Electrically charged –O NH3+ NH2+ NH+ NH Serine (Ser) Threonine (Thr) Cysteine (Cys) Tyrosine (Tyr) Asparagine (Asn) Glutamine (Gln) Acidic Basic Aspartic acid (Asp) Glutamic acid (Glu) Lysine (Lys) Arginine (Arg) Histidine (His)

Amino Acid Polymers Amino acids Are linked by peptide bonds OH DESMOSOMES OH CH2 C N H O Peptide bond SH Side chains H2O Amino end (N-terminus) Backbone (a) Figure 5.18 (b) Carboxyl end (C-terminus)

Determining the Amino Acid Sequence of a Polypeptide The amino acid sequences of polypeptides Were first determined using chemical means Can now be determined by automated machines

Protein Conformation and Function A protein’s specific conformation Determines how it functions

Four Levels of Protein Structure Primary structure Is the unique sequence of amino acids in a polypeptide Figure 5.20 – Amino acid subunits +H3N Amino end o Carboxyl end c Gly Pro Thr Glu Seu Lys Cys Leu Met Val Asp Ala Arg Ser lle Phe His Asn Tyr Trp Lle

Secondary structure Is the folding or coiling of the polypeptide into a repeating configuration Includes the  helix and the  pleated sheet O C  helix  pleated sheet Amino acid subunits N H R H Figure 5.20

Is the overall three-dimensional shape of a polypeptide Tertiary structure Is the overall three-dimensional shape of a polypeptide Results from interactions between amino acids and R groups CH2 CH O H O C HO NH3+ -O S CH3 H3C Hydrophobic interactions and van der Waals interactions Polypeptide backbone Hyrdogen bond Ionic bond Disulfide bridge

Quaternary structure Is the overall protein structure that results from the aggregation of two or more polypeptide subunits Polypeptide chain Collagen  Chains  Chains Hemoglobin Iron Heme

The four levels of protein structure +H3N Amino end Amino acid subunits helix

Sickle-Cell Disease: A Simple Change in Primary Structure Results from a single amino acid substitution in the protein hemoglobin

Sickle-cell hemoglobin Hemoglobin structure and sickle-cell disease Primary structure Secondary and tertiary structures Quaternary structure Function Red blood cell shape Hemoglobin A Molecules do not associate with one another, each carries oxygen. Normal cells are full of individual hemoglobin molecules, each carrying oxygen   10 m Hemoglobin S Molecules interact with one another to crystallize into a fiber, capacity to carry oxygen is greatly reduced.  subunit 1 2 3 4 5 6 7 Normal hemoglobin Sickle-cell hemoglobin . . . Figure 5.21 Exposed hydrophobic region Val Thr His Leu Pro Glul Glu Fibers of abnormal hemoglobin deform cell into sickle shape.

What Determines Protein Conformation? Depends on: the physical and chemical conditions of the protein’s environment

Is when a protein unravels and loses its native conformation Denaturation Is when a protein unravels and loses its native conformation Denaturing factors: pH and temperature Denaturation Renaturation Denatured protein Normal protein Figure 5.22

Nucleic Acids Nucleic acids: Are polymers of monomers (building blocks) called nucleotides. Are the information storage molecules. Provide the instructions for building proteins. There are two types of nucleic acids: DNA, deoxyribonucleic acid RNA, ribonucleic acid

Different from DNA in that: RNA, ribonucleic acid: Different from DNA in that: It is a single strand Its sugar (ribose) has an extra OH group. It has the base uracil (U) instead of thymine (T).

The genetic instructions in DNA Nucleic Acids The genetic instructions in DNA Must be translated from “nucleic acid language” to “protein language.” This process is called tanslation Genes Are the units of inheritance They specify the amino acid sequence of polypeptides Are segments of nucleic acids

Synthesis of mRNA in the nucleus Nuclear DNA Directs RNA synthesis Directs protein synthesis through RNA 1 2 3 Synthesis of mRNA in the nucleus Movement of mRNA into cytoplasm via nuclear pore Synthesis of protein NUCLEUS CYTOPLASM DNA mRNA Ribosome Amino acids Polypeptide Figure 5.25

The Structure of Nucleic Acids Exist as polymers called polynucleotides 3’C 5’ end 5’C 3’ end OH Figure 5.26 O (a) Polynucleotide, or nucleic acid

Each polynucleotide Consists of monomers called nucleotides Nitrogenous base Nucleoside O O O P CH2 5’C 3’C Phosphate group Pentose sugar (b) Nucleotide Figure 5.26

(c) Nucleoside components Nucleotide Monomers Nucleotide monomers Are made up of nucleosides and phosphate groups CH Uracil (in RNA) U Ribose (in RNA) Nitrogenous bases Pyrimidines C N O H NH2 HN CH3 Cytosine Thymine (in DNA) T HC NH Adenine A Guanine G Purines HOCH2 OH Pentose sugars Deoxyribose (in DNA) 4’ 5” 3’ 2’ 1’ Figure 5.26 (c) Nucleoside components

Nucleotide Polymers Nucleotide polymers Are made up of nucleotides linked by: the–OH group on the 3´ carbon of one nucleotide, and the phosphate on the 5´ carbon on the next

Each DNA nucleotide has one of the following bases: Adenine (A) Guanine (G) Thymine (T) Cytosine (C) The sequence of bases along a nucleotide polymer is: unique for each gene

Cellular DNA molecules The DNA Double Helix Cellular DNA molecules Have two polynucleotides (strands) The two strands spiral around an imaginary axis forming a double helix The double helix consists of two antiparallel nucleotide strands

The DNA double Helix Figure 5.27 3’ end Sugar-phosphate backbone Base pair (joined by hydrogen bonding) Old strands Nucleotide about to be added to a new strand A 5’ end New strands Figure 5.27

The nitrogenous bases in DNA Form hydrogen bonds in a complementary fashion: A binds with T only (thru two H bonds) C binds with G only (thru three H bonds)

DNA and Proteins as Tape Measures of Evolution Molecular comparisons: Help biologists sort out the evolutionary connections among species

Figure 3.30