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Proteins (aka polypeptides) 3.11-3.14
A. Polymer of amino acid monomers
B. 1000s exist each with unique 3-D structure that corresponds to its function
C. Role in everything a cell /organism does
D. Functions:1. Enzymes- chemical catalyst2. Structural proteins- hair and fibers
of connective tissues3. Contractile proteins- muscle4. Defensive proteins- antibodies5. Signal proteins- chemical
messenger communication between cells
6. Receptor proteins- transmit signals into cells
7. Transport protein- help move molecules
8. Storage proteins- source of aa
Carboxylgroup
Aminogroup
E. Every amino acid (20) has the following structure:
F. Amino acids are classified as hydrophobic or hydrophilic–nonpolar R group hydrophobic–polar R group hydrophilic
Leucine (Leu)
Hydrophobic
Serine (Ser)
Hydrophilic
Aspartic acid (Asp)
Carboxylgroup
Amino acid
Aminogroup
Amino acid
G. Amino acids are linked by dehydration reaction.
Carboxylgroup
Amino acid
Aminogroup
Amino acid
Peptidebond
Dipeptide
Dehydrationreaction
3.13 A protein’s specific shape determines its function
• A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds– The amino acid sequence causes the polypeptide to
assume a particular shape– The shape of a protein determines its specific function
Copyright © 2009 Pearson Education, Inc.
Groove
Groove
3.14 A protein’s shape depends on four levels of structure
• A protein can have four levels of structure– Primary structure– Secondary structure– Tertiary structure– Quaternary structure
Copyright © 2009 Pearson Education, Inc.
3.14 A protein’s shape depends on four levels of structure
• primary structure- unique amino acid sequence– The correct amino acid sequence is determined by
the cell’s genetic information– The slightest change in this sequence affects the
protein’s ability to function
Copyright © 2009 Pearson Education, Inc.
Four Levels of Protein Structure
Amino acids
Primary structure
3.14 A protein’s shape depends on four levels of structure
• secondary structure- coiling or folding of the polypeptide as result of H bonds between areas of polypeptide chain– Coiling results in a helical structure called an alpha helix– Folding may lead to a structure called a pleated sheet
Copyright © 2009 Pearson Education, Inc.
Four Levels of Protein Structure
Amino acids
Primary structure
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
3.14 A protein’s shape depends on four levels of structure
• Tertiary structure- overall 3D shape of a protein– results from interactions between the R groups of
the various amino acids– Shape stabilized by clustering of hydrophobic R
groups, H bonds, and ionic & covalent bonds
Copyright © 2009 Pearson Education, Inc.
Four Levels of Protein Structure
Amino acids
Primary structure
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
Polypeptide(single subunitof transthyretin)
Tertiary structure
3.14 A protein’s shape depends on four levels of structure
Quaternary Structure- occurs in proteins with more than one polypeptide; described as globular or fibrous
Four Levels of Protein Structure
Amino acids
Primary structure
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
Polypeptide(single subunitof transthyretin)
Tertiary structure
Transthyretin, withfour identicalpolypeptide subunits
Quaternary structure
3.13 A protein’s specific shape determines its function
• If for some reason a protein’s shape is altered, it can no longer function– Denaturation will cause polypeptide chains to
unravel and lose their shape and, thus, their function– Proteins can be denatured by changes in salt
concentration and pH
Copyright © 2009 Pearson Education, Inc.
3.16 Nucleic acids are information-rich polymers of nucleotides
• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides– Nucleotides have three parts
– A five-carbon sugar called ribose in RNA and deoxyribose in DNA
– A phosphate group– A nitrogenous base
Copyright © 2009 Pearson Education, Inc.
Phosphategroup
Nitrogenousbase
(adenine)
Sugar
3.16 Nucleic acids are information-rich polymers of nucleotides
• a polynucleotide forms when the phosphate of one nucleotide bonds to the sugar of the next nucleotide
• DNA double helix-two polynucleotide strands wrap around each other– The two strands are associated because
particular bases always hydrogen bond to one another
– A pairs with T, and C pairs with G, producing base pairs
• RNA is usually a single polynucleotide strand
Copyright © 2009 Pearson Education, Inc.
Basepair
3.16 Nucleic acids are information-rich polymers of nucleotides
• A particular nucleotide sequence that can instruct the formation of a polypeptide is called a gene– Most DNA molecules consist of millions of base pairs
and, consequently, many genes– These genes, many of which are unique to the species,
determine the structure of proteins and, thus, life’s structures and functions
Copyright © 2009 Pearson Education, Inc.
3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution
• Mutations are alterations in bases or the sequence of bases in DNA– Lactose tolerance is the result of mutations– In many people, the gene that dictates lactose
utilization is turned off in adulthood– Apparently, mutations occurred over time that
prevented the gene from turning off– This is an excellent example of human evolution
Copyright © 2009 Pearson Education, Inc.
Amino acids
Primary structure
Amino acids
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
Polypeptide(single subunitof transthyretin)
Tertiary structure
Transthyretin, withfour identicalpolypeptide subunits
Quaternary structure