Nucleotides, Hydrolysis, and Proteins

nucleotide

• Hydrolysis

• This is a type of reaction in which a macromolecule is broken down into smaller molecules.

• It is the reverse of condensation.

Proteins

• Composed of Amino Acids– Consist of a Carboxyl group, an amine group,

and a variable (“R” group)– The R group is the defining group for the 20

different types of amino acids

• Polypeptide chains are put together using Dehydration Synthesis.

Proteins

• When two amino acids are added together, they are always joined in the same way.

• The carboxyl group of one amino acid is connected to the amine group of the other amino acid.

• This bond is called a peptide bond

Proteins • Importance of proteins• enzymes (chemical reactions)• hormones• storage (egg whites of birds, reptiles; seeds)• transport (hemoglobin)• contractile (muscle)

Proteins

• protective (antibodies)

• membrane proteins (receptors, membrane transport, antigens)

• structural

• toxins (botulism, diphtheria)

Proteins

• Each protein has a unique shape.

• This shape (form) determines how the protein functions.

• 4 levels of protein structure– Primary– Secondary– Tertiary– Quaternary (Not all proteins)

Proteins

• Primary Structure – refers to the order of the amino acids in the polypeptide chain– A change in 1 amino acid can have drastic

consequences. Ex. Sickle Cell Anemia

• Secondary Structure – results from hydrogen bonding within the polypeptide molecule.

Proteins

• 2 types of secondary structure:– Alpha helix– Beta pleated sheet

• Proteins exhibiting these structures are called fibrous proteins– Wool, claws, beaks, collagen, ligaments

Proteins

• Tertiary Structure – 3-D shape of a protein– Determines the specificity

• Factors that affect the tertiary structure:– H-Bonding between R groups– Ionic bonding between R groups– Hydrophobic interactions– Van der Waals interactions– Disulfide bonds between cysteine

Proteins

• Quaternary Structure– Proteins that consist of more than one

polypeptide chain– Ex. Hemoglobin – Alpha + Beta

Form vs. Function

• It is not understood how proteins spontaneously fold into unique shapes.

• Proteins interact with each other to control cellular processes.

• The shape of a protein determines its function.

Enzymes

• Enzymes are globular proteins – Exhibit tertiary structure

• Lower the activation energy of a reaction

• Enzymes are substrate specific– An enzyme will on work on a specific

substrate.

• Enzymes are not used and remain unchanged during a chemical rxn.

Induced-Fit Model

• As a substrate enters the active site, it causes a slight change in the shape of the enzyme. This change in the shape of the enzyme causes the substrate to fit better.

Enzymes

• Named based on their substrate.

• Name ends in “-ase”– Ex. Lactase, Sucrase, Ligase, Helicase

• Catalyze reactions in both directions– Ex. Sucrase helps to break down and form

Sucrose

• Often require cofactors (inorganic) or coenzymes (vitamins)

Enzymes

• Enzymes are not only substrate specific but are temperature and pH specific.

• When the temp. or pH is too high/low, an enzyme will begin to denature.

• Ex. Gastric enzymes are effective at a low pH (~2)

Inhibition of Enzymes

• Competitive Inhibition– Occurs when a compound resembles the

normal substrate for an enzyme

Inhibition of Enzymes

• These competitive inhibitors reduce the productivity of the enzyme.

• Prevents the substrate form combining with the enzyme.

• Can be reversible or irreversible.

Inhibition of Enzymes

• Non-competitive inhibition– Enzymes contains more than 1 active site– Substrates do not resemble each other– When one substrate binds to one active site,

the other substrate cannot bind to the enzyme– Concentration of the substrates has a large

effect on which one binds to the enzyme

Inhibition of Enzymes

• Allosteric inhibition– Involves 2 active sites

• 1 substrate• 1 inhibitor

– Enzyme ocscillates between two conformations

– When the inhibitor binds, the enzyme becomes inactive.

Allosteric Inhibition

• Example – phosphofructokinase (PFK)– Found in glycolysis– Inhibited by ATP, which is a product of

glycolysis– Example of Feedback inhibition

• Pathway is switched off by its end-product