Building Proteins

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Chapter 05
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Building Proteins

• DNAs instructions are translated into thousands
  of proteins that do a cells work
• Protein molecules communicate and coordinate
  activities to perform lifes functions

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Roles of Proteins

• Enzymes
• Catalysts
• Have specific shapes that recognize specific
  molecules (active sites)
• Remain unchanged in reactions can be used over
  again

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Roles of Proteins

• Transporters
• Located in cell membrane
• Function as tunnels and pumps allow material to
  pass in and out of cell

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Transport ProteinsFacilitated Diffusion (top)
and Active Transport (bottom)
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Roles of Proteins

• Movers
• Protein chains can change shape in response to
  energy (ATP)

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Roles of Proteins

• Supporters
• Long chains of folded or coiled proteins
• Form sheets or tubes
• Help support and shape the cell

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Types of Support Fibers Found in Cells
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Roles of Proteins

• Regulators
• Enzymes that respond to feedback
• Notice when enough final product accumulates and
  stop assembly cycle

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Roles of Proteins

• Defenders
• Antibodies recognize and bind to foreign
  substances so that scavenger cells can destroy
  them

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Structure of an Antibody Molecule
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Roles of Proteins

• Communicators
• Example hormones
• Act as cells chemical messengers

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How Peptide Hormones Work
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Proteins at WorkExample Actin and Myosin

• Small molecular changes produce large effects

• Make muscles work

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Proteins at Work

• Actin and myosin line up and use ATP to shorten
  and lengthen themselves

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Proteins at Work

• Muscle contraction is collective action of
  millions of actin-myosin combinations

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Actin Microfilaments
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Proteins

• Chains of amino acids linked by strong covalent
  bonds
• 20 different amino acids
• Shape and function of protein are determined by
  amino acid sequence

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Proteins
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Amino Acids

• All twenty contain carbon, hydrogen, oxygen, and
  nitrogen
• Two contain sulfur
• Ten have electrically charged side groups that
  are attracted to water cluster on surface of
  protein
• Ten have no electrical charge cluster on inside
  of protein

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Some Common Amino Acids
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Protein Folding

• Weak bonds between amino acids in a chain allow
  protein to fold
• Weak bonds are easily broken and reformed
  provide flexibility and mobility

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Protein Folding

• Water environment fat-liking amino acids fold
  inside protein molecule, water-liking amino acid
  face out
• Fat environment water-liking amino acids inside,
  fat-liking amino acids face out

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Amino Acid Sequence Determines Protein Shape
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Translation

• DNA is a chain of nucleotides
• Nucleotide triplets are translated into one of
  twenty different amino acids
• Average gene 1200 nucleotides translates into
  protein 400 amino acids long

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Nucleotide Triplets are Translated into Amino
Acids
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How To Read the Genetic Code
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Overview of Protein Synthesis

• Copy nucleotide sequence of a gene into messenger
  RNA (transcription)
• Attach amino acids to transfer RNA
• Bring transfer RNA with amino acids and messenger
  RNA to ribosome (protein synthesis factory)
• Ribosome links amino acids to make a protein

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Overview of Protein Synthesis
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TranslationEnergizing Amino Acids and Linking
Them to Transfer RNA

• Key Players
• Amino Acid
• Transfer RNA (adaptor)
• ATP
• Activating Enzyme

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Transfer RNA
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TranslationEnergizing Amino Acids and Linking
Them to Transfer RNA

• 1. ATP and an amino acid dock on the activating
  enzyme and bond with each other

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TranslationEnergizing Amino Acids and Linking
Them to Transfer RNA

• 2. The amino acid is energized

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TranslationEnergizing Amino Acids and Linking
Them to Transfer RNA

• 3. Transfer RNA (adaptor) docks at a nearby site
  on the enzyme

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TranslationEnergizing Amino Acids and Linking
Them to Transfer RNA

• 4. The transfer RNA and the amino acid are
  joined. The spent ATP is released.

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TranslationEnergizing Amino Acids and Linking
Them to Transfer RNA

• 5. The transfer RNA is released with the amino
  acid attached

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TranslationAssembling the Protein Chain

• Key Players
• Ribosomes-
• Organelles where proteins are manufactured
• Consists of two subunits
• Some attached to rough endoplasmic reticulum,
  others bound to cytoskeletal fibers

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TranslationAssembling the Protein Chain

• 1. Messenger RNA attaches to the smaller subunit
  of the ribosome

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TranslationAssembling the Protein Chain

• 2. The first transfer RNA matches the messenger
  RNAs first three nucleotides

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TranslationAssembling the Protein Chain

• 3. The larger ribosome subunit joins with the
  smaller subunit

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TranslationAssembling the Protein Chain

• 4. The second transfer RNA the second dock on
  the messenger RNA

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TranslationAssembling the Protein Chain

• 5. The backbones of the first two amino acid link

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TranslationAssembling the Protein Chain

• 6. The messenger RNA shifts to the right and the
  first transfer RNA drops off

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TranslationAssembling the Protein Chain

• 7. The next transfer RNA arrives to add the next
  amino acid

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TranslationAssembling the Protein Chain

• 8. One by one, triplets are read and the protein
  chain grows

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TranslationAssembling the Protein Chain

• 9. The final triplet signals stop. No
  transfer RNA fits here.

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TranslationAssembling the Protein Chain

• 10. The ribosome separates and drops off the
  messenger RNA

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TranslationAssembling the Protein Chain

• 11. For efficiency, the messenger RNA is read by
  more than one ribosome simultaneously

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Translation Overview
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Overview of Protein Synthesis
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The Flow of InformationDNAs message is
transcribed into RNA and RNA is translated into
protein.
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The Unity of Biology

• All living creatures -
• Use DNA and RNA to store and replicate
  information
• Make nucleotides using similar pathways
• Translate nucleotide chains into proteins using
  the same twenty amino acids and the same genetic
  code
• Use similar translation apparatus
• Have similar proteins

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Examples of Natures Unity

• Locomotion
• The cilia that propel many single cell creatures
  also serve to protect our lungs by sweeping up
  dirt particles.

• Bones
• A bone that was once part of a reptiles jaw has
  evolved into a device in the ear for transmitting
  sound waves.