Chapter 3 Protein Structure and Function What Are the Building Blocks of Proteins The Structure of Amino Acids All proteins are made from just 20 amino acid building blocks All amino acids have a central carbon atom that bonds to NH2 COOH H and a variable side chain R group The Peptide Bond Condensation reactions bond the carboxyl group of one amino acid to the amino group of another to form a A chain of amino acids linked by peptide bonds is called a Within the polypeptide the peptide bonds form a backbone with three key characteristics 1 Side chains can interact with each other or water 2 Free amino group on the left is called the N terminus Free carboxyl group on the right is called the C terminus 3 Single bonds on either side of the peptide bond can rotate making the entire structure flexible Polypeptides Are Flexible What Do You Know About Protein Function Defense What Do You Know About Protein Function Movement Structure of actin filaments Muscle contraction and motility What Do You Know About Protein Function Catalysis Phosphofructokinase What Do You Know About Protein Function Signaling Angiotensin II What Do You Know About Protein Function Structure What Do Proteins Do Proteins are crucial to most tasks required for cells to exist enzymes speed up chemical reactions antibodies and complement proteins attack pathogens motor and contractile proteins move the cell or molecules within the cell proteins convey signals between cells structural proteins define cell shape and comprise body structures transport proteins carry materials membrane proteins control molecular movement into and out of the cell What Do Proteins Look Like Proteins can serve diverse functions in cells because they are diverse in size and shape as well as in the chemical properties of their amino acids All proteins have just four basic levels of structure Polypeptides Are Flexible Primary Structure A protein s primary structure is its Because the amino acid R groups affect a polypeptide s properties and function just a single amino acid change can radically alter protein function Secondary Structure Hydrogen bonds between the carbonyl group of one amino acid and the amino group of another form a protein s secondary structure A polypeptide must bend to allow this hydrogen bonding forming Secondary structure depends on the primary structure Some amino acids are more likely to be involved in helices others in pleated sheets The large number of hydrogen bonds in a protein s secondary structure increases its stability Tertiary Structure The tertiary structure of a polypeptide results from interactions between R groups or between R groups and the peptide backbone These contacts cause the backbone to bend and fold and contribute to the distinctive shape of the polypeptide R group interactions include hydrogen bonds hydrophobic interactions van der Waals interactions covalent disulfide bonds and ionic bonds Tertiary structures of proteins results from interactions with R groups Summary of R group Interactions That Form Tertiary Structures form between hydrogen atoms and the carbonyl group in the peptide bonded backbone and between hydrogen and negatively charged atoms in side chains within a protein increase stability of surrounding water molecules by increasing hydrogen bonding are weak electrical interactions between hydrophobic side chains form between sulfur containing R groups form between groups that have full and opposing charges
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