Cell Function Chapter 4

Enzyme

Catalyzes covalent bond breakage or formation

Structural Protien

Provides mechanical support to cells and tissues

Transport Protein

Carries small molecules or ions

Motor Protein

Generates movement in cells and tissues

Storage Protein

Stores small molecules or ions

Signal Protein

Carries from cell to cell

Peptide Bonds

When amino acids are joined together by amide linkage

Proteins

Long polymers of amino acids linked by peptide bonds, and they are always written with the N-terminus toward the left

Denature

Disrupting the non covalent interaction holding the folded chain together

Renature

Folding back into its original conformation when denaturant is removed

Levels of Protein Structures

Primary, secondary, tertiary, quaternary

Primary Structures

The unique sequence of amino acids in each polypeptide chain that makes up a protein

Secondary Structure

Hydrogen bonding of the peptide backbone causes the amino acid to fold into a repeating pattern

- Contains an a (alpha) helix and b (beta sheet)

Tertiary Structure

Three-dimensional folding pattern of a protein due to side chain interactions

- Determined by hydrophobic interactions, ionic bonding, hydrogen bonding, and disulfide linkages

- Stabilized by numerous weak interactions between amino acid side chains

- Fibrous and globular (water or lipid soluble) are the two major classes

Quaternary Structure

Protein consisting of more than one amino acid chain

- How the subunits of the protein is oriented and arranged with respect to one another

- Only applies to subunit proteins (proteins made from more than one polypeptide chain)

Helix

- Right (preferred) or left handed

- H-bond between every 4th amino acid linking the carbon oxygen double bonds of one peptide bond to the N-H of the other

Turns every 3.6 amino acids

Abundant in proteins located in cell membranes (transport proteins and receptors)

B (beta) Sheets

- Hydrogen bonds formed between segments of polypeptide chains lying side by side (parallel and anti-parallel)

Gives a rigid, pleated structure (silk fibers, amyoid plaque)

Fibrous Proteins

- Long and narrow

- Structural

- Repetitive amino acid sequence

- Less sensitive to changes in pH, temperature, etc.

- Ex: Collagen, myosin, fibrin, actin, keratin, elastin

- Insoluble in water

Globular Proteins

- Round/spherical shape

- Functional

- Irregular amino acid sequence

- More sensitive to changes in pH, temperature, etc.

Ex: Enzymes, hemoglobin, insulin, immunoglobulin, Soluble in water

Hemoglobin

Contains 2 copies of one polypeptide chain (aplha-globin) and 2 copies of another polypeptide chain (beta-globin)

Each polypeptide chains contains a heme molecule

Elastin

Loose and unstructured polypeptide chains covalently cross-linked into rubbber-like elastic meshwork

Phosphorylation

Attachment of phosphate group to side chains of amino acids (carried out by protein kinases and ads negative charges to protein and causes conformational change)

- Reversible method (1/3 rd) of all proteins in cell use this for regulation

- Phosphate group removed by protein phosphates

Protein Phosphorylation

- Transfer of ATP to serine, threonine or tyrosine side chain

- Phosphorylation can either stimulate or inhibit protein activity

Factors that Affect Enyme Activity

- Environmental conditions

- Cofactors and coenzymes

- Enzyme Inhibitors

Protein Domain

Segment of polypeptide chain hat can fold independently into stable structure