notes: ch 5, part 2 - proteins & nucleic acids. 5.4 - proteins have many structures, resulting...
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NOTES: Ch 5, part 2 - Proteins & Nucleic Acids
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5.4 - Proteins have many structures, resulting in a wide range of functions
● Proteins account for more than 50% of the dry mass of most cells
● Protein functions include:
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Functions of ProteinsFunctions of Proteins ● structural support
● storage
● cell-to-cell communication / signaling
● movement
● transport
● response
● defense
● catalysis of reactions (enzymes)
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● an enzyme is a type of protein that acts as a catalyst, speeding up chemical reactions
Substrate(sucrose)
Enzyme(sucrose)
Fructose
Glucose
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● consist of 1 or more polypeptide chains folded and coiled into specific conformations
● Polypeptide chains = polymers of amino acids – arranged in specific linear sequence– linked by PEPTIDE BONDS– range in length from a few to 1000+
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AMINO ACIDSAMINO ACIDS
● building blocks of proteins
● structure of an amino acid – central carbon– hydrogen atom– carboxyl group– amino group– variable R group (side chain)
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Amino Acid Monomers
● Cells use 20 amino acids to make thousands of proteins
Aminogroup
Carboxylgroup
carbon
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● linked together by PEPTIDE BONDS (links the carboxyl group of 1 amino acid to the amino group of another; requires dehydration / condensation)
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PROTEIN STRUCTURE
● a protein’s function depends on its specific conformation (3-D shape)
● Four levels of protein structure:
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1. Primary structure
● unique, linear sequence of amino acids (forms the “backbone” of a protein) – determined by genes– a slight change can affect a
protein’s conformation and function (e.g. sickle-cell hemoglobin)
– can be sequenced in the laboratory (insulin)
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2. Secondary structure
● regular, repeated coiling and folding of a protein’s polypeptide backbone
● stabilized by H-bonds between peptide linkages in protein’s backbone (NOT the amino acid side chains)
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● ALPHA HELIX = helical coil stabilized by H-bonding between every 4th peptide bond (3.6 amino acid/turn)
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● BETA PLEATED SHEET = sheet of antiparallel chains folded into “accordion” pleats
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Spiders secrete silk fibers made of a structural protein containing beta-pleated sheets…able to stretch & recoil!
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3. Tertiary Structure
● irregular contortions of protein due to bonding between side chains (R groups) resulting in 3-D shape
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Hydrophobicinteractions andvan der Waalsinteractions
Polypeptidebackbone
Disulfide bridge
Ionic bond
Hydrogenbond
Tertiary Protein
Structure
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4. Quaternary Structure
● association of 2 or more protein subunits to form a single functioning molecule (i.e. hemoglobin and collagen)
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Chains
ChainsHemoglobin
Iron
Heme
CollagenPolypeptide chain
Polypeptidechain
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Protein Form and Function
● A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape
● The sequence of amino acids determines a protein’s three-dimensional formation
● A protein’s formation determines its function
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Protein ConformationProtein Conformation● determined by physical and chemical
environmental conditions
● DENATURATION: process that alters a protein’s native conformation and hence its biological activity – heat– salt concentration– chemical agents that disrupt H-bonding– transfer to an organic solvent– pH changes
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(SDS is a detergent that denatures
proteins.)
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Protein Denaturation:
● A denatured protein is misshapen and therefore biologically inactive
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The Protein-Folding Problem
● It is hard to predict a protein’s conformation from its primary structure
● Most proteins probably go through several states on their way to a stable conformation
● Chaperonins are protein molecules that assist the proper folding of other proteins
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Chaperonin(fully assembled)
Hollowcylinder
Cap
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Polypeptide
Correctlyfoldedprotein
An unfolded poly-peptide enters thecylinder from oneend.
Steps of ChaperoninAction:
The cap comesoff, and theproperly foldedprotein is released.
The cap attaches, causingthe cylinder to changeshape in such a way that it creates a hydrophilicenvironment for thefolding of the polypeptide.
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5.5 - Nucleic acids store and transmit hereditary information
● The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a GENE
● Genes are made of DNA, a nucleic acid
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● Two types of nucleic acids:
1) DNA
2) RNA
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The Roles of Nucleic Acids
● There are two types of nucleic acids:
-Deoxyribonucleic acid (DNA)
-Ribonucleic acid (RNA)
● DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis
● Protein synthesis occurs in ribosomes
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1. DNA = Deoxyribonucleic acid
● encodes the instructions for amino acid sequences of proteins
● is copied and passed from one generation of cells to another
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2. RNA = Ribonucleic acid
● functions in the actual
synthesis of proteins
coded for by DNA
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● carries the encoded information to the ribosomes; carries the amino acids to the ribosome; a major component of ribosomes
DNA RNA Protein
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Structure of Nucleic AcidsStructure of Nucleic Acids
● polymers of monomers called NUCLEOTIDES
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● Each nucleotide consists of:
1. Pentose (5-carbon sugar)
-deoxyribose in DNA
-ribose in RNA 2. Phosphate group (attached to #5 carbon
on sugar) 3. Nitrogenous base
-purines (double ring) -pyrimidines (single ring)
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The Structure of Nucleic Acids
● The portion of a nucleotide without the phosphate group is called a nucleoside
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● nucleotides are joined together by phosphodiester linkages (between phosphate of one nucleotide and the sugar of the next)
● results in a backbone with a repeating pattern of sugar-phosphate-sugar-phosphate...
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5 end
3 end
Nucleoside
Nitrogenousbase
Phosphategroup
Nucleotide
Polynucleotide, ornucleic acid
Pentosesugar
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The DNA Double Helix● A DNA molecule has two polynucleotides
spiraling around an imaginary axis, forming a double helix
● One DNA molecule includes many genes● The nitrogenous bases in DNA form
hydrogen bonds in a complementary fashion: A always with T, and G always with C
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DNA & Proteins as Tape Measures of Evolution● genes and their products (proteins)
document the hereditary background of an organism
● linear sequences of DNA are passed from parents to offspring; 2 siblings have greater similarity in their DNA than do unrelated individuals…
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DNA & Proteins as Tape Measures of Evolution● it follows, that 2 closely related species
would share a greater proportion of their DNA & protein sequences than 2 distantly related species would…
● that is the case!!!
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DNA & Proteins as Tape Measures of Evolution
● example: the β chain of human hemoglobin:
● this chain contains 146 amino acids-humans & gorillas differ in 1 amino acid-humans & frogs differ in 67 amino acids
● Molecular biology has added a new “tape measure” with which we can study evolutionary relationships!!
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