Macromolecules Part 3

Proteins

Proteins!

Functions of Proteins– Structural support– Storage– Transport– Cellular communications– Movement– Defense against foreign substances

Proteins• Monomer: amino acids

– 20 amino acids– Amine (NH2) and carboxyl (COOH) groups attached to

carbon– Only thing different is side chain…R-group

• Polymer: polypeptide chains (proteins)• Link between monomers is called: polypeptide

bond – Made by a dehydration reaction – (between amine group of one aa and carboxyl group

of another aa)• STRUCTURE of A.A.

– Amino group on one end (-NH2)– Carboxyl group on one end (COOH)– Hydrogen– R-group/side chain (changes)-------- ALANINE

• Proteins account for more than 50% of the dry mass of most cells

Polypeptide bonds

DEHYDRATION!!!

Some famous proteins…– Essential components of cell

membranes– Oxygen-carrying pigment

hemoglobin (hemoglobin) – Antibodies which attack and

destroy invading microorganisms

Protein Structure

• Primary structure 1’– Order of amino acids in a polypeptide chain

• Secondary structure 2’– Polypeptide chain folds because of interactions between

amino acids– HYDROGEN BONDING

• Tertiary Structure 3’– Gives proteins 3-D shape

• VERY IMPORTANT to function of protein– Beta pleated sheets and alpha helices fold based on

interactions between R-groups of a.a.– Hydrogen bonds, polar/non-polar interactions, acid/base

interactions, disulfide bonds, van der Waals forces• Quaternary Structure 4’

– the association of the polypeptide chains– some proteins contain more than one polypeptide chain– Each polypeptide chain in the protein is called a subunit– Two or more subunits come together for a specific

function– HEMOGLOBIN

• On Red blood cells• Its shape allows RBCs to carry oxygen all around your

body!

Primary Structure

• Sequence of AA in a long polypeptide chain

• AA= letters of alphabet• Sequence of AA= arrangement

of letters to make words• HUGE amount of different

primary structures• Changing ONE AA is polypeptide

chain GREATLY changes the properties of the polypeptide chain and PROTEIN

Secondary Structure• The order of AA in

polypeptide chain determine interactions between functional groups of AA

• Functional groups interact via HYDROGEN BONDS– Attraction between

oxygen in the –CO end of one AA and the hydrogen in the –NH end of another AA

– H-bond easily broken• Change pH and change

Temperature

– Three possible 2o structures• Determined by order R-

groups

– No particular arrangement– Alpha helix

• Polypeptide chains that coil tightly

– Beta pleated sheet• Looser, straighter shape

created by hydrogen bonds

Tertiary Structure• Secondary structure gets coiled

and folded• Precise 3D shape• Folding is determined by

interactions between R-groups– Hydrogen bonds

• Tryptophan• Arginine• Asparigine

– Disulphide bonds• Between 2 cystine molecules

– Ionic bonds• b/t R groups containing amine and

carboxyl groups

– Hydrophobic interactions• b/t R groups that are non-polar

(hydrophobic)

Quaternary Structure• Proteins are made up of multiple polypeptide

chains, sometimes with an inorganic component (for example, a haem group in haemoglogin)– Prosthetic Group (inorganic component of

protein)• These proteins will only be able to function if all

subunits are present• Made by same bonds found in tertiary structure• Interactions between R-groups

– Hydrogen bonds• Tryptophan• Arginine• Asparigine

– Disulphide bonds• Between 2 cystine molecules

– Ionic bonds• b/t R groups containing amine and carboxyl groups

– Hydrophobic interactions• b/t R groups that are non-polar (hydrophobic)

Denaturation

• Unraveling/unfolding of protein• Why would this be a problem?• When protein loses its 3-D shape and thus its specific

function• Caused by:

– Unfavorable changes in pH, temperature or other environmental condition

– Disrupts the interactions between side chains and causes loss of shape

• Examples:– Frying an egg– Straightening your hair

Enzymes!

Why do you think we can compare it to

this?

• A special type of protein…???• In order for a protein to work

at its SPECIFIC JOB, it must have….???

• Because an enzyme is a protein, it MUST have….???

• Can any key unlock the door to your house???

• Can any substrate/reactant fit into a specific enzyme?

• How many different enzymes do we have???

ENZYMES!!!

ENZYMES!!!• Proteins• Biological catalysts that

speed up the rate of chemical reactions

• They help make products faster!

• Never used up!• “Matchmaker”

Enzymes in Action

• Enzymes speed up chemical reactions that take place in cells

• They DECREASE ACTIVATION ENRGY– The energy needed to

get the reaction started (or energy needed to start making product)

Catal-ASE is an enzyme that helps

break up hydrogen peroxide

Proteins: Enzymes

• What is a chemical reaction?• Do they happen on their own?– If we stare at the piece of paper, are we going to

be able to make the oxygen molecules in the air collide with the cellulose in the paper?

– What do we need to do?• What are reactants?• What are products?

Factors that Effect the Rate of Reactions

• Temperature– Hot

• Breaks bonds that give proteins its tertiary structure DENATURES

– Cold• Slow down chemical reaction (formation of enzyme

substrate complex)

• pH– Acids and bases produce OH- and H+ ions

• too many ions are present, the enzyme may be denatured (twisted and pulled so out of shape that it can no longer function)

• Inhibitors– Non-competitive

• react with portions of the active site, changing of its shape

• Allosteric Inhibitors– Change shape of the enzyme– Attach to regulatory site (not active site) and change the

shape of the entire enzyme (specifically the active site)

– Competitive• look like substrate, bind to active site, but do not make

the intended product

Examples of endothermic reactions:Melting of ice absorbs energy Dissolving ammonium nitrate in water( the essence of commercial cold packs) PHOTOSYNTHESIS

Examples of exothermic reactions:Digestion of food releases energy (CELL RESPIRATION)All combustion reactions (fires) C + O2 CO2 + EAdding an alkali metal to water 2 Na + 2 H2O 2 NaOH + H2 + E

Condensation of water Explosion of bombs

Endothermic Reactionsthe reactants have less potential energy than do the products. Energy must be input in order to raise the particles up to the higher energy level.Energy + A + B --> AB

Exothermic Reactionsthe reactants have more potential energy than the products have. The extra energy is released to the surroundings. A + B --> AB + Energy

Enzymes• Enzyme– Catalyst

• Anything that speeds up the rate of a reaction by lowering the ACTIVATION ENERGY– Activ. E: energy required for a chem.

Rxn to start making products– used to regulate the rate (speed) of chemical

reactions– Protein that helps speed up a reaction that occurs

in a biological system– Name of enzymes end in –ASE

• all enzymes are proteins, but not all proteins are enzymes

• each chemical reaction in an organism requires its own specific enzyme

• enzymes are never changed by their reactions!

SubstrateMolecule/compound that attaches to enzyme

Active SiteSpecific location on enzyme for substrate to attachWhere the enzymatic reaction occurs

Enzyme-substrate complexWhen substrate binds to active site of enzyme

Productsmolecules produced at the end of an

enzymatic reaction

• Acetylcholinesterase– catalyzes the breakdown of the neurotransmitter

acetylcholine at several types of synapses as well as at the neuromuscular junction — the specialized synapse that triggers the contraction of skeletal muscle.

– One molecule of acetylcholinesterase breaks down 25,000 molecules of acetylcholine each second

– makes possible the rapid "resetting" of the synapse for transmission of another nerve impulse.

Lock and Key Model

Class work! Label Each box!

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