Molecules of Life

Chapter 2

Protein Functions Act as enzymes Structural- cytoskeleton (actin, tubulin, others) Mechanical- actin and myosin in muscle Cell signaling Immune responses Cell adhesion Cell cycle transport

The 20 amino acids

You don’tHave to memorize these

Proteins

Built from 20 common monomers called amino acids (aa)

polypeptide=polymer

Amino acid = monomerPeptide bond

aa aa aa aa aa aa aa

Polypeptide- A chain of amino acids bonded together by peptide bonds in a condensation reaction

Fig. 3-16a, p. 44

A DNA encodes the order of amino acids in a new polypeptide chain. Methionine (met) is typically the first amino acid.

B In a condensation reaction, a peptide bond forms between the methionine and the next amino acid, alanine (ala) in this example. Leucine (leu) will be next. Think about polarity, charge, and other properties of functional groups that become neighbors in the growing chain.

Peptide Bond Formation

Fig. 3-16b, p. 45

D The sequence of amino acid subunits in this newly forming peptide chain is now met–ala–leu–trp. The process may continue until there are hundreds or thousands of amino acids in the chain.

C A peptide bond forms between the alanine and leucine.

Tryptophan (trp) will be next. The chain is starting to twist and fold as atoms swivel around some bonds and attract or repel their neighbors.

Stepped Art

Globin Chains in Hemoglobin

Fig. 3-19a, p. 47

valine histidine leucine threonine prolineglutamic acid

A Normal amino acid sequence at the start of the hemoglobin beta chain.

glutamic acid

Molecular Basis of Sickle Cell Anemia

Fig. 3-19b, p. 47

valine histidine leucine threonine proline valine glutamic acid

B One amino acid substitution results in the abnormal beta chain of HbS molecules. The sixth amino acid in such chains is valine, not glutamic acid.

Molecular Basis of Sickle Cell Anemia

Nucleotides

Nucleotide (the monomer of nucleic acid)

Monomer

Two kinds of nucleic acids: RNA DNA

Four Nucleotides of DNA

Fig. 3-22, p. 49

covalent bonding in sugar–phosphate backbone

hydrogen bonding between bases

The DNA Molecule

Nucleic Acids- Informational Polymers

Nucleic acids

Proteins

Lipids

Summary: Organic Molecules in Living Things