Transcript Slide 1

Proteins (aka polypeptides) 3.11-3.14
A. Polymer of amino acid
monomers
B. 1000s exist each with unique 3D structure that corresponds
to its function
C. Role in everything a cell
/organism does
D. Functions:
1. Enzymes- chemical catalyst
2. Structural proteins- hair and
fibers of connective tissues
3. Contractile proteins- muscle
4. Defensive proteins- antibodies
5. 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
E. Every amino acid (20) has the following
structure:
Amino
group
Carboxyl
group
F. Amino acids are classified as hydrophobic
or hydrophilic
–nonpolar R group hydrophobic
–polar R group hydrophilic
Leucine (Leu)
Hydrophobic
Serine (Ser)
Aspartic acid (Asp)
Hydrophilic
G. Amino acids are linked by dehydration
reaction.
Carboxyl
group
Amino acid
Amino
group
Amino acid
Carboxyl
group
Amino acid
Amino
group
Amino acid
Peptide
bond
Dehydration
reaction
Dipeptide
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
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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
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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
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Four Levels of Protein Structure
Primary structure
Amino acids
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
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix
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
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix
Tertiary structure
Polypeptide
(single subunit
of transthyretin)
Pleated sheet
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
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix
Tertiary structure
Quaternary structure
Polypeptide
(single subunit
of transthyretin)
Transthyretin, with
four identical
polypeptide subunits
Pleated sheet
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
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Nitrogenous
base
(adenine)
Phosphate
group
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.
Base
pair
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
Hydrogen
bond
Alpha helix
Secondary structure
Pleated sheet
Polypeptide
(single subunit
of transthyretin)
Tertiary structure
Transthyretin, with
four identical
polypeptide subunits
Quaternary structure