EPOB 1210 Lecture 7, 1996
Proteins and Nucleic Acids

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    OUTLINE:

    PROTEINS (cont.)

    PROTEIN CONFORMATION

    LEVELS OF CONFORMATION

    primary, secondary, tertiary, quaternary

    FACTORS DETERMINING CONFORMATION

    NUCLEIC ACIDS

    OVERVIEW OF FUNCTION

    NUCLEOTIDES

    POLYNUCLEOTIDES

    THE DOUBLE HELIX: INTRODUCTION

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    A. PROTEIN CONFORMATION = 3-D SHAPE

    Consequence of sequence of a.a.s

    Native Conformation = Conf. in cell

    function depends on conformation

    LEVELS OF CONFORMATION

    primary, secondary, tertiary, quaternary

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    1. PRIMARY = Sequence of a.a.s

    a. Determined by Genes

    b. Can be sequenced in the lab

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    2. SECONDARY STRUCTURE = FOLDING of Polypeptide

    Stabilized by H-bonds between carbonyl and amino groups of diff. a.a.s

    2 main types:

    alpha helix

    Beta pleated sheet

    ALPHA HELIX

    (Fig. 5.20)

    Common in fibrous proteins (keratin, collagen) and parts of many proteins

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    BETA PLEATED SHEET = "Accordion pleats"

    (Fig. 5.20)

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    3. TERTIARY STRUCTURE = Irregular Contortions

    a. Weak interactions,

    H-bonding between polar side chains

    Ionic bonds between charged side chains

    Hydrophobic interactions

    (Fig. 5.22)

    b. Covalent Linkage

    Disulfide bridges Ss from 2 cysteines

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    4. QUATERNARY STRUCTURE = GROUPING of several polypeptides (= subunits).

    Example: Collagen and Hemoglobin

    (Fig. 5.23)

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    SUMMARY: 4 levels of protein structure

    (Fig. 5.24)

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    FACTORS DETERMINING CONFORMATION

    Micro-environment pH, temp. etc.

    Proteins can denature if environment altered:

    Solvent change

    Chemicals that disrupt bonds

    Excessive Heat

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    B. NUCLEIC ACIDS = Polymers of Nucleotides (= monomers)

    OVERVIEW ---- 2 TYPES:

    1. DNA = DEOXYRIBONUCLEIC ACID

    Make up GENES = instructions for polypeptide synthesis. Self-replicating

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    2. RNA = RIBONUCLEIC ACID

    mRNA = Messenger RNA

    tRNA = Transfer RNA

    rRNA = Ribosomal RNA

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    Flow of information in cells: DNA ---> RNA ---> protein

    (Fig. 5.26)

    NUCLEOTIDES = building blocks of Nucleic acids

    Nucleic Acid = Polymer of Nucleotides (e.g. DNA)

    NUCLEOTIDES are made up of:

    (Fig. 5.27)

    1. PENTOSE

    RIBOSE (in RNA) or DEOXYRIBOSE (in DNA)

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    2. NITROGENOUS BASE (N.B.)

    2 types:

    Pyrimidine = six sided ring

    Cytosine, Thymine (in DNA)

    Uracil (in RNA)

    Purine = double ring (6 + 5)

    Adenine and Guanine

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    3. PHOSPHATE attached to the no. 5 carbon of the pentose

    Nucleotide = pentose + N.B. + Phosphate

    Nucleoside = pentose + N.B.

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    POLYNUCLEOTIDES = Polymer of nucleotides joined by

    PHOSPHODIESTER LINKAGES

    Results in repeating backbone of: Pent.-Phos.-Pent.-Phos.

    With the N.B.s sticking out from this "backbone"

    Show structure and DOUBLE HELIX

    (Fig. 5.28)

    DNA and protein sequences can be used to infer evolutionary relationships between organisms.

    (see Table 5.2)