General Biology I ORGANIC CHEMISTRY AND CELLS Lecture 5

Proteins

Composed of carbon, hydrogen, oxygen, nitrogen, and small amounts of other elements, notably sulfur
Building blocks of proteins are amino acids

  • 20 different amino acids

  • Common structure with variable sidechain that determines structure and
    function

  • What do they do?
    ◦ Gene, expression and regulation, Motor proteins, Defense proteins, Metabolic proteins, Cell-Signaling proteins, Structural proteins, Transport proteins

Amino Acid Structure

Polypeptide formation

Amino acids joined by dehydration reaction

  • Carboxy + amino forms peptide bond

  • Polymers of amino acids known as polypeptides

  • The free amino group of a polypeptide is the N-terminus

  • The free carboxyl end is the C-terminus

  • Proteins may be formed from one or several polypeptides


Proteins have a Hierarchy of Structure

Four progressive levels:
◦ Primary
◦ Secondary
◦ Tertiary
◦ Quaternary

Primary Structure

  • Amino acid sequence

  • Determined by genes

  • Held together by peptide bonds

Secondary Structure

Chemical and physical interactions cause protein folding

  • α helices and β pleated sheets determinants of a protein’s characteristics

  • Random coiled regions” Not α helix and β pleated sheet Shape is specific and
    important to function

Tertiary structure

  • Folding gives protein complex 3D shape

  • This is the final level of structure for a single polypeptide chain


Quaternary structure

Made up of two or more polypeptides (proteins)

  • Individual polypeptide chains are protein subunits

  • Protein can be formed from several copies of the same polypeptide

Proteins
Atoms → Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur
Monomer → Amino Acid
Name of Covalent bond → Peptide
Examples → antibodies, motor proteins, transport proteins, cell-signaling proteins, Structural proteins, enzymes
Functions → immunity, muscle movement, cellular transport and signaling, gene
expression and regulation

Nucleic Acids

Responsible for the storage, expression, and transmission of genetic information

  • Deoxyribonucleic acid (DNA)
    ◦ Stores genetic information encoded in the sequence of nucleotide monomers

  • Ribonucleic acid (RNA)
    ◦ Decodes D N A into instructions for linking together a specific sequence of amino acids to form a polypeptide chain

Nucleic acid monomer is a nucleotide

  • Made up of phosphate group, a five-carbon sugar (either ribose or deoxyribose), and a single or double ring of carbon and nitrogen atoms known as a base

  • Purines: adenine (A) & guanine (G)

  • Pyrimidines: cytosine (C) & thymine(T)-Uracil

  • Nucleotides are linked into polymer by a sugar-phosphate backbone

DNA is Composed of Two Strands of Nucleotides

  • DNA molecule consists of two strands of nucleotides coiled around each other in a double helix

  • Held together by hydrogen bonds between a purine base in one strand and a pyrimidine base in the opposite strand

  • A pairs with T; C pairs with G

Nucleic Acids
Atoms → Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus
Monomer → Nucleotide
Name of Covalent bond → Covalent bond (regular)
Examples → DNA, RNA
Function → Genetic Information