WE'RE GOING TO START BY TALKING ABOUT PROTEIN STRUCTURE.

AND TO THE LEFT HERE,

WHAT YOU SEE IS A STRING OF AMINO ACIDS,

AND THESE ARE JUST THREE AMINO ACIDS.

AMINO ACIDS ARE THE BUILDING BLOCKS OF PROTEIN.

WE'RE GO INTO MORE DETAIL ABOUT THIS,

BUT THE STRUCTURE OF PROTEIN IS MUCH MORE COMPLEX

THAN THAT OF CARBOHYDRATES AND LIPIDS.

AND HERE, WHAT YOU CAN SEE IS THE BLUE

OR THE TURQUOISE REPRESENTS CARBON,

WHEREAS THE PURPLE REPRESENTS THE NITROGEN

AND THE RED CARBOXYL GROUP.

WHAT I WANT YOU TO KNOW ABOUT IS THAT THESE UNITS

HERE ARE REPRESENTING AMINO ACID.

SO YOU CAN SEE THREE AMINO ACIDS,

AND THEY'RE LINKED TOGETHER BY A VERY STRONG PEPTIDE BOND.

SO THEY'RE VERY, VERY TIGHTLY BOUND.

AND THEN THE NITROGEN REALLY MAKES THIS UNIQUE.

IF WE TAKE A CLOSER LOOK AT THE AMINO ACIDS YOU CAN SEE HERE

THE NITROGEN THAT I WAS TALKING ABOUT AND THEN THE BONDS.

YOU'RE NOT REQUIRED TO KNOW THE STRUCTURE.

THIS R JUST REPRESENTS THE SIDE CHAIN

OR THE SIDE UNIT OF THE AMINO ACIDS,

AS THERE ARE 20 STANDARD AMINO ACIDS

THAT WE'LL BE REFERRING TO.

THE CATEGORIES OF AMINO ACIDS ARE DIVIDED INTO ESSENTIAL,

NONESSENTIAL, AND CONDITIONALLY ESSENTIAL.

AND THESE ARE FOR THE STANDARD AMINO ACIDS.

THERE ARE ACTUALLY MANY AMINO ACIDS,

BUT THE ONES THAT WE'LL BE REFERRING TO.

AND I DON'T EXPECT YOU TO KNOW THE 20 AMINO ACIDS,

AND YOU ACTUALLY NEED TO KNOW WHICH

ONE ARE ESSENTIAL OR NONESSENTIAL,

BUT I DO WANT YOU TO KNOW THE DEFINITIONS AND WHAT THESE MEAN.

ESSENTIAL IS THE SAME DEFINITION WE'VE BEEN TALKING ABOUT.

THIS MEANS THAT THESE AMINO ACIDS,

AND THERE ARE NINE OF THEM, NEED TO BE SUPPLIED BY THE DIET.

AND THAT'S BECAUSE THE BODY CANNOT SYNTHESIZE THEM,

CANNOT MAKE THESE AMINO ACIDS.

THE NONESSENTIAL AMINO ACIDS ARE THE AMINO

ACIDS WHICH CANNOT BE MADE BY THE BODY.

SO THEY MUST--

EXCUSE, THEY CAN BE MADE BY THE BODY.

SORRY TO CONFUSE YOU.

SO THE NONESSENTIAL MEANS THAT THEY TAKE THE ESSENTIAL

AMINO ACIDS AND THE BODY CAN THEN CONVERT THOSE

INTO THE NONESSENTIAL AMINO ACIDS WHEN NEEDED.

AND IT DOESN'T NECESSARILY MEAN THAT SOME ARE

MORE IMPORTANT TO OTHERS IN THE BODY.

IT JUST MEANS THAT THERE IMPORTANT IN THE SENSE

THAT WE HAVE TO OBTAIN THOSE FROM THE DIET.

THEN THERE ARE THE CONDITIONALLY ESSENTIAL AMINO ACIDS,

AND AN EXAMPLE IS CYSTEINE, TYROSINE.

THESE ARE NECESSARY JUST FOR INFANTS AND

EVEN MORE IMPORTANT FOR PRETERM INFANTS.

SO IT'S ONLY UNDER A CERTAIN

CONDITION THAT THEY BECOME ESSENTIAL.

NORMALLY THE BODY CAN MAKE THEM, BUT AT TIMES--

REMEMBER THE DEFINITION OF ESSENTIAL IS THAT THE BODY

CANNOT MAKE OR CANNOT MAKE ENOUGH FOR ITS NEEDS AND THAT'S

WHY SOME OF THE NONESSENTIAL AMINO ACIDS WILL THEN BECOME

CONDITIONALLY ESSENTIAL UNDER CERTAIN CONDITIONS.

LET'S TAKE A LOOK AT THIS PICTURE,

AND WE'RE GOING TO START UP WITH THIS STRING OF AMINO ACIDS.

SO ALL THESE LITTLE BALLS HERE ARE

REPRESENTATIVE OF ONE AMINO ACID.

SO JUST LIKE WE TALKED ABOUT, YOU CAN SEE THE AMINO ACID.

THIS IS JUST A REPRESENTATIVE OF ONE.

AND WHEN WE LOOK AT THIS WE CAN SEE THE CHAIN OF

AMINO ACIDS THAT ARE ALL LINKED TOGETHER.

SO THIS IS GOING TO CREATE, ESSENTIALLY,

A POLYPEPTIDE, A CHAIN OF AMINO ACIDS.

THIS IS CALLED THE PRIMARY STRUCTURE.

AND EVEN THOUGH IT MIGHT HAVE ALL THE AMINO ACIDS NECESSARY,

IT DOESN'T FUNCTION AT ALL WHEN IT'S JUST

IN A STRING OR JUST A CHAIN LIKE THIS.

NOW THE SECONDARY STRUCTURE--

AND WE CAN SEE TWO DIFFERENT TYPES OF STRUCTURES,

IS EITHER, ONE, THIS A COIL.

IF YOU CAN THINK OF SOMETHING COILING AROUND.

THE AMINO ACIDS ARE THEN BONDED TOGETHER IN THIS

COIL OR THEY BECOME SHEETS SO THEY ARE PLEATED LIKE THIS.

AND THAT'S THE SECONDARY STRUCTURE.

NOW THE TERTIARY STRUCTURE IS WHEN THESE--

YOU CAN THIS COIL OR THESE SHEETS

AND IT THEN FOLDS ON ITSELF.

SO IF WE HAVE SOMETHING THAT'S COILED,

THEN THAT FOLDS AND THEN FOLDS AGAIN,

AS YOU CAN SEE HERE.

THIS IS GOING TO BE OUR TERTIARY STRUCTURE.

AT THIS POINT THE PROTEIN CAN BECOME FUNCTIONAL

ONCE IT GETS TO THIS TERTIARY STRUCTURE,

BUT IT MORE OFTEN FUNCTIONS AS THE QUATERNARY STRUCTURE,

WHICH IS WHEN THESE UNITS HERE JOIN TOGETHER,

AND THEN THIS IS GENERALLY AT OUR FULLY FUNCTIONAL PROTEIN.

SO A KEY POINT HERE IS THAT A PROTEIN

SHAPE DETERMINES ITS FUNCTION.

THIS RIGHT HERE, THIS PRIMARY STRUCTURE,

EVEN THE SECONDARY THERE.

THIS PROTEIN HAS ALL THE AMINO ACIDS.

IT'S NOT GOING TO FUNCTION.

IT HAS TO COIL AND THEN FOLD ON ITSELF AND THEN

GENERALLY JOIN OTHER UNITS TO MAKE A FUNCTIONAL PROTEIN.

AND I MENTIONED THIS EARLIER,

BUT I WANT TO GO BACK AND EMPHASIZE THIS AGAIN.

A PROTEIN'S STRUCTURE IS MUCH MORE COMPLEX

THAN THAT OF CARBOHYDRATES OR LIPIDS.

AND LET'S GO BACK.

LET'S REMEMBER CARBOHYDRATES AND IF

EACH OF THESE REPRESENTED A CARBON,

YOU CAN REMEMBER THIS SHAPE AS BEING GLUCOSE, RIGHT?

THIS IS GOING TO REPRESENT OUR, YOU KNOW,

SIMPLE CARBOHYDRATE GLUCOSE, SIMPLE SUGAR.

WE KNOW THAT LIPIDS EXIST IN THESE CHAINS

OF CARBON AND IF THEY HAVE THE HYDROGEN,

FULLY HYDROGENATED, IT'S A SATURATED FAT,

AND IF WE HAD A DOUBLE BOND IN HERE IT WOULD

EITHER BE MONO OR POLYUNSATURATED FAT,

BUT IT'S JUST CARBON AND HYDROGEN.

WELL NOW I GET TO PROTEIN,

AND WE HAVE THESE AMINO ACIDS WITH THEIR SIDE CHAINS,

THEY'RE LINKED TOGETHER.

THEY'VE GOT CARBOXYL UNITS AND IMPORTANTLY, NITROGEN.

THESE ARE MUCH MORE COMPLEX.

AND IF WE LOOK AT A BIGGER IMAGE WE CAN

LOOK AT OUR GLUCOSE LINKING TOGETHER TO FORM STARCH,

OUR LONGER CHAINS OF SATURATED MONO,

POLYUNSATURATED FATTY ACIDS.

AGAIN, THIS WOULD EACH BE A LITTLE CARBON HERE.

BUT THEN LOOK AT PROTEIN.

THIS IS SO MUCH MORE COMPLEX.

THINK OF IT COILING AND THEN FOLDING AND THEN JOINING,

AND NOT ONLY BECAUSE OF ITS BASIC MOLECULAR STRUCTURE,

BUT ALSO ITS MORE ADVANCED STRUCTURE,

THIS TERTIARY AND QUATERNARY STRUCTURE.

SO THAT'S A VERY IMPORTANT PART OF UNDERSTANDING PROTEINS.

NOW WE ALREADY TALKED ABOUT THE AMINO

ACIDS AND HOW THEY JOIN TOGETHER.

THEY USUALLY JOIN HERE TO FORM A VERY STRONG PEPTIDE BOND.

SO THAT INITIAL BOND THAT THEY HAVE IS REALLY STRONG.

AND I MEAN THAT'S HARDER TO BREAK APART A PROTEIN

COMPARED TO WHEN WE TALK ABOUT STARCH,

HOW EASY IT IS TO HYDROLYZE OR JUST REMOVE THOSE

CARBON FRAGMENTS AND UTILIZE THAT FOR ENERGY.

THIS HAS A VERY STRONG BOND SO IT'S MUCH MORE

DIFFICULT TO LIBERATE THESE AMINO ACIDS.

AND WHAT I'M SHOWING HERE AS FAR AS THE

STRUCTURE IS JUST SIMPLY THIS CIRCLE HERE.

WHEN WE GET INTO DIGESTION AND ABSORPTION I'M GOING TO

BE REPRESENTING ONE AMINO ACID JUST AS A SIMPLE CIRCLE.

AND THAT'S THE END OF OUR SECTION

ON THE STRUCTURE OF PROTEIN.