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.