chapter 05. building proteins dna’s instructions are translated into thousands of proteins that do...
TRANSCRIPT
Chapter 05
Building Proteins
• DNA’s instructions are translated into thousands of proteins that do a cell’s work
• Protein molecules communicate and coordinate activities to perform life’s functions
Roles of ProteinsEnzymes:• Catalysts• Have specific
shapes that recognize specific molecules (active sites)
• Remain unchanged in reactions – can be used over again
Roles of Proteins
Transporters• Located in cell
membrane• Function as
tunnels and pumps – allow material to pass in and out of cell
Transport Proteins
Facilitated Diffusion (top) and Active
Transport (bottom)
Roles of ProteinsMovers
• Protein chains can change shape in response to energy (ATP)
Roles of ProteinsSupporters• Long chains of
folded or coiled proteins
• Form sheets or tubes
• Help support and shape the cell
Types of Support Fibers Found in Cells
Roles of ProteinsRegulators• Enzymes that
respond to feedback
• Notice when enough final product accumulates and stop assembly cycle
Roles of ProteinsDefenders• Antibodies –
recognize and bind to foreign substances so that scavenger cells can destroy them
Structure of an
Antibody Molecule
Roles of Proteins
Communicators
• Example – hormones
• Act as cell’s chemical messengers
How Peptide Hormones Work
Proteins at WorkExample: Actin and Myosin
• Make muscles work • Small molecular changes produce large effects
Proteins at Work
• Actin and myosin line up and use ATP to shorten and lengthen themselves
Proteins at Work
• Muscle contraction is collective action of millions of actin-myosin combinations
Actin Microfilaments
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
Proteins
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
Some Common
Amino Acids
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
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
Amino Acid Sequence
Determines Protein Shape
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
Nucleotide Triplets are Translated into Amino
Acids
How To Read the Genetic Code
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
Overview of Protein Synthesis
TranslationEnergizing Amino Acids and Linking Them to Transfer RNA
Key Players:• Amino Acid• Transfer RNA
(adaptor)• ATP• Activating Enzyme
Transfer RNA
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
TranslationEnergizing Amino Acids and Linking Them to Transfer RNA
2. The amino acid is energized
TranslationEnergizing Amino Acids and Linking Them to
Transfer RNA3. Transfer RNA (adaptor) docks at a nearby site on the enzyme
TranslationEnergizing Amino Acids and Linking Them to Transfer RNA
4. The transfer RNA and the amino acid are joined. The spent ATP is released.
TranslationEnergizing Amino Acids and Linking Them to Transfer RNA
5. The transfer RNA is released with the amino acid attached
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
TranslationAssembling the Protein Chain
1. Messenger RNA attaches to the smaller subunit of the ribosome
TranslationAssembling the Protein Chain
2. The first transfer RNA matches the messenger RNA’s first three nucleotides
TranslationAssembling the Protein Chain
3. The larger ribosome subunit joins with the smaller subunit
TranslationAssembling the Protein Chain
4. The second transfer RNA the second dock on the messenger RNA
TranslationAssembling the Protein Chain
5. The backbones of the first two amino acid link
TranslationAssembling the Protein Chain
6. The messenger RNA shifts to the right and the first transfer RNA drops off
TranslationAssembling the Protein Chain
7. The next transfer RNA arrives to add the next amino acid
TranslationAssembling the Protein Chain
8. One by one, triplets are read and the protein chain grows
TranslationAssembling the Protein Chain
9. The final triplet signals “stop”. No transfer RNA fits here.
TranslationAssembling the Protein Chain
10. The ribosome separates and drops off the messenger RNA
TranslationAssembling the Protein Chain
11. For efficiency, the messenger RNA is read by more than one ribosome simultaneously
Translation Overview
Overview of Protein Synthesis
The Flow of Information
DNA’s message is transcribed into
RNA and RNA is translated into
protein.
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
Examples of Nature’s 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 reptile’s jaw has evolved into a device in the ear for transmitting sound waves.