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![Page 1: Proteins have many structures, resulting in a boat load of functions Proteins account for more than 50% of the dry mass of most cells Protein functions.](https://reader035.fdocuments.net/reader035/viewer/2022062409/5697bffa1a28abf838cc04a8/html5/thumbnails/1.jpg)
• Proteins have many structures, resulting in a boat load of functions
• Proteins account for more than 50% of the dry mass of most cells
• Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances
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• Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions
• Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life
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• Polypeptides are polymers built from the same set of 20 amino acids
• A protein consists of one or more polypeptides
• Amino acids are organic molecules with carboxyl and amino groups
• Amino acids differ in their properties due to differing side chains, called R groups
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Fig. 5-UN1
Aminogroup
Carboxylgroup
carbon
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• Amino acids are linked by peptide bonds
• A polypeptide is a polymer of amino acids
• Polypeptides range in length from a few to more than a thousand monomers
• Each polypeptide has a unique linear sequence of amino acids
• A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape
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• Name and explain 1 of the roles proteins may play in the human body… let’s get 3 examples.
• How do enzymes function?
• Describe the general formula for an amino acid.
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Fig. 5-19
A ribbon model of lysozyme(a) (b) A space-filling model of lysozyme
GrooveGroove
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• The sequence of amino acids determines a protein’s three-dimensional structure
• A protein’s structure determines its functionAntibody protein Protein from flu virus
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• The primary structure of a protein is its unique sequence of amino acids
• Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain
• Tertiary structure is determined by interactions among various side chains (R groups)
• Quaternary structure results when a protein consists of multiple polypeptide chains
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Fig. 5-21
PrimaryStructure
SecondaryStructure
TertiaryStructure
pleated sheet
Examples ofamino acidsubunits
+H3N Amino end
helix
QuaternaryStructure
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• Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word
• Primary structure is determined by inherited genetic information
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• The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone
• Typical secondary structures are a coil called an helix and a folded structure called a pleated sheet
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• Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents
• These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions
• Strong covalent bonds called disulfide bridges may reinforce the protein’s structure
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Fig. 5-21f
Polypeptidebackbone
Hydrophobicinteractions andvan der Waalsinteractions
Disulfide bridge
Ionic bond
Hydrogenbond
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• Quaternary structure results when two or more polypeptide chains form one macromolecule
• Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
• Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains
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Fig. 5-21e
Tertiary Structure Quaternary Structure
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amino acids amino acids polypeptides polypeptides protein protein
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• A slight change in primary structure can affect a protein’s structure and ability to function
• Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
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Fig. 5-22
Primarystructure
Secondaryand tertiarystructures
Quaternarystructure
Normalhemoglobin(top view)
Primarystructure
Secondaryand tertiarystructures
Quaternarystructure
Function Function
subunit
Molecules donot associatewith oneanother; eachcarries oxygen.
Red bloodcell shape
Normal red bloodcells are full ofindividualhemoglobinmoledules, eachcarrying oxygen.
10 µm
Normal hemoglobin
1 2 3 4 5 6 7
Val His Leu Thr Pro Glu Glu
Red bloodcell shape
subunit
Exposedhydrophobicregion
Sickle-cellhemoglobin
Moleculesinteract withone another andcrystallize intoa fiber; capacityto carry oxygenis greatly reduced.
Fibers of abnormalhemoglobin deformred blood cell intosickle shape.
10 µm
Sickle-cell hemoglobin
GluProThrLeuHisVal Val
1 2 3 4 5 6 7
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• In addition to primary structure, physical and chemical conditions can affect structure
• Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel
• This loss of a protein’s native structure is called denaturation
• A denatured protein is biologically inactive
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Fig. 5-23
Normal protein Denatured protein
Denaturation
Renaturation
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• It is hard to predict a protein’s structure from its primary structure
• Most proteins probably go through several states on their way to a stable structure
• Chaperonins are protein molecules that assist the proper folding of other proteins