Proteins, Enzymes and Nucleic Acids

Structure of a Fat

molecule

Proteins

Protein Functions

Proteins-1

• Proteins are made of amino acids• There are 20 different amino acids found in

living things• Amino acids have

– An amine group– A carboxyl group– Both are attached to the end carbon of a

carbon chain

Amino Acids

Connecting Amino Acids

• Dehydration synthesis reaction resulting in a polypeptide

Primary Structure of

a Protein

Secondary Structure

of a Protein

Tertiary Structure

of a Protein

Quaternary Structure of

a Protein

Protein Structure

Proteins & Evolutionary Relationships

Enzymes

Enzyme Characteristics-1• All enzymes are proteins• Most enzymes are named after their substrate

and end in –ase• Enzymes are specific- they work on only one

substrate• Enzymes must physically fit together with

their substrate- this is what makes them so specific

• Enzymes have an active site- this is where the reaction takes place

Enzyme reaction

Enzyme Characteristics

• Enzymes are denatured by high temperatures and by a pH that is too high or too low, relative to their optimal pH

• Denatured enzymes lose their shape, so they no longer fit with their substrate

How Enzymes Work• Enzymes are catalysts– they speed up reactions

– They are not consumed in the reaction– They are not changed in any way at the end of the

reaction– They can work in small quantities, because they

can be used over and over– They do NOT make reactions occur that would not

occur by themselves- they merely speed them up

• Lock and Key Hypothesis• Induced Fit Hypothesis

Some substances can make enzymes inactive

Metabolic Control

• Competitive inhibitors- block the substrate from entering active sites

• Noncompetitive inhibitors- impede enzymatic reactions by binding to another part of the enzyme which causes the enzyme to change shape, making the active site unreceptive to substrate.

• Allosteric regulation- similar to reversible noncompetitive inhibitors.– Allosteric site- a receptor site on the enzyme remote from the

active site– Causes inhibition or stimulation of enzyme activity– Enzyme activity changes due to fluctuating concentrations of the

regulators.

Energy in reactions

• Potential energy- – stored energy– Example: Energy in the chemical bonds

• Kinetic energy– Energy of motion or work– Example: Energy used to make chemical bonds

Endergonic/Exergonic Reactions

Activation energy

Activation energy of

an enzymatic reaction

Enzyme Helpers- necessary for catalysis

• Cofactors- nonprotein helpers – May be bound tightly to the active site

– May bind loosely and reversibly along with the substrate

– Some are inorganic: zinc, iron, copper

• Coenzyme- protein helper– Most vitamins are coenzymes or

– Some vitamins are raw materials from which coenzymes are made

Nucleic Acids

Nucleic Acid Structure• Nucleic acids are made of Nucleotides

• Nucleotides are made of:– A Phosphate group– A Sugar: either ribose or deoxyribose– A Base: A, T, G, C, U

• A= adenine

• T= thymine

• G= guanine

• C= cytosine

• U= uracil

Nucleic Acids- DNA & RNA

• There are only two nucleic acids: – DNA: deoxyribonucleic acid– RNA: ribonucleic acid

• Functions: control cell function and heredity– DNA makes RNA– RNA makes proteins

Comparison of DNA and RNA StructureDNA RNA

Sugar deoxyribose Ribose

Bases ATGC AUGC

Strands DOUBLE

helix

Single

helix

Structure of one strand of

a DNA molecule

Structure of DNA