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The Molecules of Life

The Molecules of Life. Proteins and Nucleic Acids Chapter 3. Proteins. A protein is a polymer constructed from amino acid monomers Proteins are the workhorse of the cell - they perform most of the tasks the body needs to function - there are 10s of 1000s of different kinds of proteins

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The Molecules of Life

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  1. The Molecules of Life Proteins and Nucleic Acids Chapter 3

  2. Proteins • A protein is a polymer constructed from amino acid monomers • Proteins are the workhorse of the cell - they perform most of the tasks the body needs to function - there are 10s of 1000s of different kinds of proteins - each has a unique 3-D shape

  3. Structural Proteins Storage Proteins Contractile Proteins Transport Proteins Defensive Proteins Receptor Proteins Enzymes Hormonal Proteins Sensory Proteins Gene Regulatory proteins Proteins

  4. a) Provide support b) Provide a source of amino acids for developing organisms c) Found primarily in muscle d) Include hemoglobin the iron-containing protein in blood Fig 3.19

  5. The Monomers: Amino Acids • All proteins are constructed from a common set of building blocks called amino acids • All 20 kinds of amino acids have a common backbone - consists of a central carbon atom bonded to 4 covalent partners • 3 are common to all - a carboxyl group, an amino group, and a hydrogen atom • The variable component, the unique side group (aka the radical group) is attached to the 4th bond

  6. General structure of an amino acid (aa) The 20 aa vary only in their side groups Fig 3.20

  7. Proteins as Polymers • Cells link amino acids together by dehydration reactions - the bond between adjacent amino acids is called a peptide bond • Proteins consist of 100 or more amino acids to form a chain called a polypeptide

  8. Figure 3.21

  9. Primary Structure • Your body has tens of thousands of different kinds of proteins made from just 20 amino acids - arrangement of amino acids makes each one different - protein alphabet • Primary structure – the specific sequence of amino acids in a protein

  10. Lysozyme • Primary structure • 129 amino acids - with its 3 letter abbreviation Figure 3.22

  11. Sickle-cell Hemoglobin • One ‘letter’ change in the primary structure affects a proteins ability to function • Example: the hemoglobin protein - hemoglobin transports oxygen from the lungs in RBCs - the substitution of one amino acid for another in hemoglobin affects its shape - RBCs are normally disc-shaped - the abnormal hemoglobin molecules tend to crystallize, causing the cells to sickle

  12. Figure 3.23

  13. 4 Levels of Protein Structure • Primary – linear sequence • Secondary – alpha helix and pleated sheets reinforced by hydrogen bonds • Tertiary – overall 3-D shape reinforced by chemical bonds between the amino acid side groups • Quaternary – some proteins consist of 2 or more polypeptide chains that are joined together by weak bonds

  14. Figure 3.24

  15. What Determines Protein Structure? • A protein’s shape is sensitive to the surrounding environment - unfavorable temperature and pH changes can cause a protein to unravel and lose its shape - this process is called denaturation • Example – boil an egg - egg white becomes opague (protein denaturation) - denatured proeins become insoluble in water to form a white solid • Why are high fevers dangerous

  16. Nucleic Acids • Nucleic acids are information storage molecules - provide the directions for building proteins • Called nucleic because they are located in the nucleus of the cell • 2 types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) • DNA is the genetic material inherited from the parental organism

  17. Translation • The genetic instructions in DNA are called genes - stretches of DNA that determine the amino acid sequences (primary structure) of proteins - DNA chemical code must be translated from ‘nucleic acid language’ to ‘protein language’ • RNA molecules help make this translation

  18. Figure 3.25

  19. Nucleotides • Nucleic acids are polymers - the building blocks (monomers) are called nucleotides • Each nucleotide is composed of 3 parts - at the center is a 5-carbon sugar, deoxyribose in DNA and ribose in RNA - attached to the sugar is a negatively charged phosphate group - also attached to the sugar is a nitrogen-containing (nitrogenous) base made of one or two rings

  20. A DNA Nucleotide - only the base varies Figure 3.26

  21. DNA Bases • Each DNA nucleotide has one of the following bases: • Adenine (A) • Guanine (G) • Thymine (T) • Cytosine (C) • All genetic information is written using this four-letter alphabet

  22. Figure 3.27

  23. DNA Strands • Nucleotide monomers are linked into long chainscalled polynucleotides, or DNA strands • Nucleotides are joined together by covalent bonds between the sugar of one nucleotide and the phosphate of the next - creates a sugar-phosphate backbone • Polynucleotides vary in length and may contain many genes, each having 100s or 1000s of nucleotides

  24. A DNA Strand • A nucleotide polymer with a sugar-phosphate backbone • Each strand has a specific sequence of DNA bases Figure 3.28a

  25. DNA Double Helix • A molecule of DNA is double stranded - 2 polynucleotide strands joined together to form a double helix • In the central core of the helix, the bases on one DNA strand hydrogen-bond to bases along the other strand • Base pairing is specific: - base A can pair only with T - base C can pair only with G

  26. DNA Structure • 2 DNA strands held together by bonds between bases • H-bonds are weak but they zip the 2 strands together giving the double helix its stability Figure 3.28b

  27. RNA • Ribonucleic acid, is different from DNA - RNA has a sugar with an extra -OH group and has the base uracil (U) instead of thymine (T) - RNA is usually found as a single-strand while DNA usually exists as a double helix

  28. Figure 3.29

  29. Evolution Connection • DNA and proteins as evolutionary tape measures • How can we access evolutionary relationships between organisms? - genes (DNA) and their products (proteins) are historical documents passed from parent to offspring - molecular genealogy extends to relationships between species - biologists use molecular analysis of DNA and protein sequences to test evolutionary hypotheses

  30. Evolutionary Hypotheses • If 2 species are closely related, then they should share a greater proportion of their inherited DNA and protein sequences than with more distantly related species • Testable hypothesis: - analyze and compare DNA and protein sequences from the 2 species

  31. Fig 3.30

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