proteins big idea 4: biological systems interact
TRANSCRIPT
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Proteins
Big Idea 4: Biological Systems Interact
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Essential Knowledge• Essential knowledge 4.B.1: Interactions
between molecules affect their structure and function.
• a. Change in the structure of a molecular system may result in a change of the function of the system.
• b. The shape of enzymes, active sites, and interaction with specific molecules are essential for basic functioning of the enzyme.
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• Structural support, storage, transport, cellular communications, movement, and defense
against foreigners• Make up more than 50% of dry mass of cells
Protein Functions!
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Example: Hemoglobin
• Iron-containing protein found in red blood cells.
• Transports oxygen to body
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Antibodies
• Defensive protein fights bacteria and viruses
Example: Antibodies
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Example: Lactase, an Enzyme
• Enzyme that helps break down sugar lactose into galactose and glucose. Speeds up reactions rates:
• Lactose intolerant: Mutation of Chrom. 2.• Cramps, bloating, flatulence
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• Hormonal protein: regulates sugar in blood (tells cells to take it in), pancreas
Example: Insulin
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Polypeptides• Polymers built
from same set of 20 amino acids
• A protein consists of one or more polypeptides
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Amino Acid Monomers
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Amino Acid Polymers• Amino acids are linked by peptide bonds
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Protein Structure and Function
• Consists of 1/more polypeptides twisted, folded, and coiled into a unique shape (determined by amino acid sequence)
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Four Levels of Protein Structure
• Primary, Secondary,
Tertiary, Quartenary!
• Watch Videos!
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Hollowcylinder
Cap
Chaperonin(fully assembled)
Polypeptide
Steps of ChaperoninAction:
An unfolded poly-peptide enters thecylinder from one end.
1
2 3The cap attaches, causing thecylinder to change shape insuch a way that it creates ahydrophilic environment forthe folding of the polypeptide.
The cap comesoff, and the properlyfolded protein isreleased.
Correctlyfoldedprotein
• Chaperonins are protein molecules that assist the proper folding of other proteins
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Sickle-Cell Disease: A Change in
Primary Structure
• A change in primary structure can affect a protein’s structure and ability to function
• Ex: Sickle-cell disease: results from a single amino acid substitution in protein
hemoglobin
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Fig. 5-22a
Primarystructure
Secondaryand tertiarystructures
Function
Quaternarystructure
Molecules donot associatewith oneanother; eachcarries oxygen.
Normalhemoglobin(top view)
subunit
Normal hemoglobin
7654321
GluVal His Leu Thr Pro Glu
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Fig. 5-22b
Primarystructure
Secondaryand tertiarystructures
Function
Quaternarystructure
Molecules interact with one another andcrystallize into a fiber; capacity to carry oxygenis greatly reduced.
Sickle-cellhemoglobin
subunit
Sickle-cell hemoglobin
7654321
ValVal His Leu Thr Pro Glu
Exposedhydrophobicregion
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Fig. 5-22c
Normal red bloodcells are full ofindividualhemoglobinmolecules, each carrying oxygen.
Fibers of abnormalhemoglobin deformred blood cell intosickle shape.
10 µm 10 µm
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Messing Up Proteins?• Alterations in pH, salt concentration, temp., or
other environmental factors can cause a protein to unravel denaturation inactive
protein
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• Acts as a catalyst to speed up chemical reactions
• Can perform functions repeatedly workhorses!
Enzyme Proteins!
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Cofactors
• A non-protein chemical compound required for enzyme activity Ex: Fe
• “Helper Molecules" that assist in biochemical transformations.
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Coenzymes
• A protein chemical compound required for enzyme activity
• “Helper Molecules" that assist in biochemical transformations.
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Cofactors and Coenzymes
• Work together to regulate enzyme function.• Usually the interaction relates to a structural
change that alters the activity rate of the enzyme
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Competitive Inhibitors
• Binding of inhibitor molecule to active site of enzyme prevents binding of the
substrate and vice versa.
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Allosteric Competition
• Binding of inhibitor to another (allosteric) site of enzyme (rather than active site) prevents binding of substrate
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Model Interpretations
• The change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/ or presence of a competitive inhibitor.