- WELCOME TO PART SIX OF THE PROTEIN
AND ENZYME TUTORIAL SERIES.
THIS TUTORIAL FOCUSES ON TERTIARY STRUCTURE
VERY IMPORTANT PARTICULARLY
FOR THE GLOBULAR AND MEMBRANE PROTEINS
AND IT'S ALL ABOUT THE R GROUPS.
LET'S GET STARTED. ALL RIGHT.
SO TERTIARY, WE THE KNOW
THEY'RE SYMBOLIZED WITH THE THREE DEGREES
AND THERE ARE FIVE PRIMARY WAYS THAT R GROUPS,
REMEMBER THE SIDE CHAINS,
CAN INTERACT TO CREATE THE TERTIARY STRUCTURE.
AND REMEMBER THAT THESE INTERACTIONS
COULD OCCUR BETWEEN AMINO ACIDS
THAT ARE VERY FAR APART ON THE BACKBONE.
SO THAT DISTINGUISHES IT FROM THE SECONDARY STRUCTURE.
NOW, THE FIRST ONE IS A COVALENT INTERACTION
AND IT'S VERY RESTRICTED, RIGHT?
SO CYSTEINE, THE AMINO ACID WITH THE THIOL GROUP
UNDER MILD OXIDIZING CONDITIONS,
WE CAN GET A REACTION TO OCCUR HER--
OCCUR HERE THAT LEADS TO THE DISULFIDE BRIDGE.
AND SO THIS IS AN ACTUAL COVALENT BOND.
HOWEVER, IT'S A RELATIVELY WEAK COVALENT BOND AND SO WE--
AS WE KNOW IF WE'VE EVER HAD OUR HAIR PERMED OR STRAIGHTENED,
IT'S A BOND THAT WE CAN BREAK AND WE FORM CHEMICALLY.
SO-- BUT IT DOES ADD A BIT
OF RIGIDITY AND STIFFNESS TO A PROTEIN.
AND SO IT'S IMPORTANT.
NOW THE REST OF THESE ELEMENTS OF TERTIARY STRUCTURE,
THEY ARE CALLED NON-COVALENT INTERACTIONS,
RIGHT, SO THE DISULFIDE BRIDGE IS A COVALENT BOND.
THE REST OF THESE,
WE CAN THINK OF THEM AS INNER MOLECULAR FORCES
BUT SINCE THEY'RE HAPPENING WITHIN ONE GIANT MOLECULE,
THE MOST CORRECT TERM IS TO SAY NON-COVALENT INTERACTIONS.
RIGHT? REMEMBERING, RIGHT,
THAT WHEN A COVALENT BOND FORMS,
THERE'S ACTUAL ELECTRON SHARING.
SO LINKING BACK TO WHAT WE LEARNED EARLIER IN THE SEMESTER,
RIGHT, SO THERE IS A COVALENT BOND RIGHT THERE,
THE DISULFIDE BRIDGE.
FOR THESE OTHER INTERACTIONS, THERE'S NO COVALENT BOND.
SO, RIGHT, SO FOR H-BONDING,
WE COULD HAVE THE POLAR GROUPS ON THE SIDE CHAINS INTERACT
WITH OTHER R GROUPS OR WITH THE BACKBONE ITSELF, RIGHT.
SO THIS IS ALL ABOUT ELECTROSTATIC INTERACTIONS
OF PARTIAL PLUS AND MINUSES, RIGHT?
AND SO THE PARTIAL PLUS WE ALWAYS THINK OF AS HYDROGEN
AND THE PARTIAL MINUS WILL BE NITROGEN OR OXYGEN.
OKAY. AND THEN SALT BRIDGES,
THESE ARE AN IONIC BOND WHICH CAN
BE TECHNICALLY DESCRIBED AS A NON-COVALENT INTERACTION
AND THIS IS WHERE WE HAVE FULL CHARGES.
BECAUSE WE'VE SEEN IN OUR AMINO ACIDS, RIGHT,
THAT OUR BASIC SIDE CHAINS COULD HAVE A POSITIVE CHARGE
AND OUR ACIDIC SIDE CHAINS COULD HAVE A NEGATIVE CHARGE
AND SO THEY COULD ATTRACT TO EACH OTHER.
ANOTHER VERY IMPORTANT INTERACTION
IS THE HYDROPHOBIC INTERACTION
AND WE FIRST LEARNED ABOUT IT AS LONDON DISPERSION FORCE
AND THIS IS A HUGE DEAL FOR GLOBULAR PROTEINS.
BECAUSE WHAT HAPPENS IS THEY ARE POLAR GROUPS, RIGHT,
THEY POINT OUTWARDS TO GO WITH THE WATER,
RIGHT, BECAUSE THE POLAR GROUPS HAVE THE PARTIAL PLUS
AND THE PARTIAL MINUS AND SO,
THEY LOVE WATER WITH ITS PARTIAL PLUS AND MINUS.
AND SO THEN
WHAT THAT DOES THOUGH IS THE NON-POLAR SIDE CHAINS,
THEY MOVE INWARD AWAY FROM THE WATER.
AND SO EVEN THOUGH THE HYDROPHOBIC INTERACTION IS WEAK,
COLLECTIVELY,
WE CAN GET--
CREATE A TERTIARY STRUCTURE BECAUSE THERE'S A LOT
OF NON-POLAR R GROUPS AMONGST THE AMINO ACIDS.
SO WHAT THEY MAKE UP FOR IN STRENGTH OR WHAT--
THEY MAKE UP FOR THEIR LACK OF STRENGTH WITH NUMBERS.
AND THEN THE FINAL INTERACTION
IS A METAL-ION COORDINATION, RIGHT,
SO TRACE MINERALS WHICH ARE METAL CATIONS.
THEY CAN FROM BRIDGES TO THE ANIONIC SIDE CHAINS, RIGHT?
SO NOTICE THAT IT'S ALL ELECTROSTATIC.
THESE NON-COVALENT INTERACTIONS ARE ELECTROSTATIC IN ORIGIN.
SO IT'S ALL ABOUT RECOGNIZING POLARITY
AND DIFFERENCES IN ELECTRONEGATIVITY TO--
-AND SO NOW IF YOU LOOK AT THE BOTTOM OF THIS PAGE,
HERE IS SOME PRACTICE FOR YOU TO CLASSIFY
THESE DIFFERENT TERTIARY INTERACTIONS.
SO A LITTLE PAUSE THERE
FOR YOU TO ANSWER FOR YOURSELF AND NOW WE'LL LOOK.
DEFINITELY RIGHT HERE WITH THOSE HYDROXYL GROUPS,
H-BONDING HERE, NOW THE CHARGES ARE PRETTY LIGHT,
RIGHT, BUT NOTICE WE HAVE A FULL POSITIVE AND A FULL NEGATIVE.
SO THIS WOULD BE A SALT BRIDGE BECAUSE WE KNOW
THAT ANOTHER NAME FOR IONIC COMPOUNDS IS SALT.
THIS EXAMPLE, TWO NON-POLAR REGIONS,
SO THIS WOULD BE THE HYDROPHOBIC INTERACTION
WHICH WE ALSO CALL THE LONDON FORCE.
AND THEN LAST BUT NOT LEAST,
WE LOOK RIGHT HERE AND WE HAVE OUR METAL ION
WITH ITS POSITIVE CHARGE AND THEN
WE HAVE THE ACIDIC R GROUPS WITH THEIR NEGATIVE CHARGE
AND SO THIS CREATES THE METAL ION COORDINATION. OKAY.
SO THERE IS A--
AN OVERVIEW OF THE FIVE MAJOR FORMS OF TERTIARY STRUCTURE.
NOW LET'S PRACTICE THIS A LITTLE BIT.
SO ON THE NEXT PAGE,
THERE IS A DIAGRAM THAT SHOWS A PORTION OF A PROTEIN SEGMENT.
AND SO NOW LET'S BRING TOGETHER
WHAT WE'VE LEARNED ABOUT SECONDARY STRUCTURE AND ADD TO
THAT WHAT WE'RE LEARNING ABOUT TERTIARY STRUCTURE.
SO TAKE A MINUTE AND EVALUATE THIS DIAGRAM
AND PUT AS MUCH DETAIL.
SEE WHAT YOU KNOW ABOUT SECONDARY AND TERTIARY STRUCTURE
AND THEN COMPARE YOUR ANSWERS TO MINE.
ALL RIGHT. SO HERE--
AND THERE'S A LOT OF CLUES HERE,
THE PLEATED SHEET AND WE SEE THE H-BONDING.
SO WE RECOGNIZE THIS AS SECONDARY STRUCTURE
AND THIS IS OUR BETA SHEET.
AND THEN IF WE LOOK AT THE FAR RIGHT,
WE SEE THE HELICAL STRUCTURE,
THE ALPHA HELIX.
AND SO WE ALSO RECOGNIZE THAT AS SECONDARY STRUCTURE.
NOW, SO--
RIGHT, SO THAT'S ALL ABOUT THE INTERACTIONS
OF THE POLYPEPTIDE BACKBONE.
NOW WE'LL LOOK FOR THE TERTIARY STRUCTURE, RIGHT,
AND THIS COULD BE FROM AMINO ACIDS THAT ARE QUITE FAR APART.
HERE, ALL THOSE CARBONS AND HYDROGENS, RIGHT,
THERE'S OUR HYDROPHOBIC INTERACTION.
AND LET'S SEE.
AND WE HAVE THAT HERE AS WELL.
HERE'S ANOTHER HYDROPHOBIC INTERACTION, RIGHT,
ANY TIME WE SEE ALL CARBONS AND HYDROGENS,
WE CAN RECOGNIZE THAT AS BEING NON-POLAR AND HYDROPHOBIC.
AND THEN IF WE LOOK HERE,
WE SEE THERE'S A FULL POSITIVE CHARGE ON THIS AMINE
AND A NEGATIVE CHARGE ON THE CARBOXYLATE.
SO THERE'S OUR SALT BRIDGE
AND LAST BUT NOT LEAST, WHAT DO WE HAVE?
WHAT ELSE DO WE HAVE HERE? OKAY.
WE HAVE A DISULFIDE BOND, RIGHT.
SO THAT'S CALLED--
THAT'S ALSO TERTIARY--
OOPS, I WASN'T LABELING THOSE, RIGHT.
SO THE HYDROPHOBIC INTERACTIONS ARE TERTIARY.
THE SALT BRIDGE IS TERTIARY.
THIS DISULFIDE BRIDGE IS ALSO A TERTIARY INTERACTION,
PART OF THE TERTIARY STRUCTURE.
AND THEN LAST BUT NOT LEAST,
WE HAVE SOME H-BONDING GOING ON HERE.
AND THIS WILL USE THE DOUBLE CROSS, RIGHT,
SO ALL OF THESE ARE H-BONDING.
ALL RIGHTY. OKAY.
AND THEN ONE LAST LITTLE BIT ABOUT TERTIARY STRUCTURE,
SO WHERE SECONDARY STRUCTURE WAS VERY IMPORTANT
FOR FIBROUS PROTEINS,
IT'S THE TERTIARY STRUCTURE THAT'S IMPORTANT TO GLOBULAR,
THE MORE INTERESTING PART OF GLOBULAR PROTEINS,
BECAUSE THE HYDROPHOBIC EFFECT IS THE PROCESS
BY WHICH THE WATER SOLVENT ATTRACT THE POLAR
AMINO ACIDS TO THE OUTSIDE,
RIGHT, SO ALL OF THE POLAR, RIGHT,
THE POLAR R GROUPS ARE GOING TO BE ALL AROUND THE OUTSIDE
BECAUSE THEY LOVE INTERACTING WITH WATER.
BECAUSE WHEN WE LOOK AT WATER, WE CAN'T HELP IT,
WE HAVE TO SEE THOSE STRONGLY POLAR COVALENT BONDS.
AND THEN WHAT HAPPENS THEN ON THE INSIDE, RIGHT,
THIS IS THE NON-POLAR REGION,
THIS IS WHERE IT'S NON-POLAR OR HYDROPHOBIC.
SO THE HYDROPHOBIC INTERACTIONS TAKE PLACE
ON THE INSIDE OF THE GLOBULAR PROTEIN
AND THEN THE POLAR R GROUPS ARE ARRANGED ON THE OUTSIDE AND SO
THE TERTIARY STRUCTURE IS VERY IMPORTANT.
IT'S WHAT CREATES THE GLOBULAR PROTEINS.
ONE OTHER THING THAT'S--
I WANTED TO POINT OUT
TO YOU IS WE WOULD KNOW THAT THIS WOULD BE PART
OF A GLOBULAR PROTEIN BECAUSE WE SEE A MIX OF ALPHA HELIXES
AND BETA SHEETS WITHIN THE SAME PROTEIN.
SO REMEMBER THAT FOR THE FIBROUS PROTEINS,
WE ONLY HAD ALPHA OR BETA, NOT BOTH.
BUT WITH THE GLOBULARS,
WE CAN GET A MIX OF ALPHA AND BETA WITHIN THE SAME PROTEIN.
AND THEN HERE'S SOME EXAMPLES
OF SOME IMPORTANT GLOBULAR PROTEINS,
INSULIN FOR REGULATING GLUCOSE METABOLISM,
WE HAVE ENZYMES, IMMUNITY, TRANSPORT,
AND ALL KINDS OF USEFUL FUNCTIONS
THAT WERE DESCRIBED IN OUR INTRODUCTION VIDEO.
ALL RIGHTY.
SO THIS CONCLUDES TERTIARY STRUCTURE.
THIS WOULD BE A GREAT TIME
TO WORK THROUGH A FEW HOMEWORK PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.