- WELCOME TO THE NUCLEIC ACIDS PART THREE.
IN THIS PART OF THE SERIES WE WILL LOOK AT RNA
AND HOW THE PRIMARY STRUCTURE OF PROTEINS ARE SYNTHESIZED.
LET'S GET STARTED. ALL RIGHT.
SO WE REMEMBER THAT DNA HAS THE GENES THAT HOLD THE INSTRUCTIONS
FOR HOW TO SYNTHESIZE THE PROTEINS, RIGHT,
BUT THE ACTUAL SYNTHESIS OCCURS WITH RNA AND RIBOSOMES.
SO IT TURNS OUT THAT THERE ARE THREE MAJOR FORMS
AND THEY EACH HAVE DIFFERENT JOBS.
THEIR NAMES ARE VERY HELPFUL THOUGH, RIGHT.
SO THE rRNA IS DESCRIBED AS THE RIBOSOMAL RNA.
AND THIS--THESE TEND TO BE A LARGER.
THEY TYPICALLY HAVE A HUNDRED TO A THOUSAND NUCLEOTIDES.
AND THEN THE mRNA IS THE MESSENGER RNA
AND THEN THE LAST FORM IS THE TRANSFER RNA.
AND IT TENDS TO BE THE SMALLER ONE
WITH ONLY TYPICALLY 70 TO 100 NUCLEOTIDES. OKAY.
SO NOW REMEMBER, RIGHT, THAT THE NITROGENOUS BASES,
SO, FOR RNA WE HAVE THE ADENINE, CYTOSINE, AND THE GUANINE
BUT REMEMBER THAT URACIL, RIGHT?
REPLACES THYMINE. OKAY.
NOW, SO, WHAT'S THE SAME AND WHAT'S DIFFERENT?
SO WE'VE DONE A LOT TO LEARN ABOUT DNA
LET'S USE THAT TO COMPARE AND CONTRAST WITH RNA.
SO THE FIRST DIFFERENCE IS THE URACIL REPLACES THE THYMINE.
THE SECOND IS THAT RNA IS A SINGLE-STRANDED NUCLEIC ACID
VERSUS DNA WITH THE DOUBLE HELIX.
AND THEN REMEMBER FROM OUR INTRODUCTION, RIGHT?
RIBOSOMES ARE THE PROTEIN MAKING FACTORIES OF THE CELL
AND SO IN THIS TUTORIAL WE'RE GONNA FOCUS
ON TWO MAIN PROCESSES.
WE'RE GONNA LOOK AT TRANSCRIPTION.
THIS IS WHERE THE INSTRUCTIONS FROM A SECTION OF THE DNA
ARE COPIED TO THE MESSENGER RNA
AND THEN WE'LL LOOK AT TRANSLATION
WHERE A TRANSFER RNA DELIVERS AMINO ACIDS TO THE RIBOSOME
FOR THE PROTEIN SYNTHESIS. ALL RIGHT.
SO NOW, IF WE LOOK AT THE SCHEMATIC TRANSCRIPTION, RIGHT,
TRANSCRIPTION IS RIGHT HERE. IT'S GETTING THE MESSAGE, RIGHT?
THE INSTRUCTIONS TO BE ACTIVATED.
SO FROM THE DNA TO THE MESSENGER RNA.
AND THEN TRANSLATION WILL BE
WHERE THE ACTUAL PROTEIN SYNTHESIS OCCURS. ALL RIGHT.
AND THEN IF WE CAN TAKE THIS UNDERSTANDING TO THE CELL,
RIGHT? SO THE DNA IS IN THE NUCLEUS OF THE CELL
AND THEN TRANSCRIPTION THE DNA SHARES THE INFORMATION
WITH THE MESSENGER RNA, RIGHT?
THE DNA IS TRAPPED INSIDE THE CELL
BUT THE MESSENGER RNA CAN COME OUT
AND THEN IT CAN GIVE THE DIRECTIONS TO THE TRANSFER RNA
AND THE RIBOSOME AND THEN WE GET THE PROTEIN SYNTHESIZED.
AND, SO, THIS IS-- THESE LITTLE BALLS
ARE REPRESENTING THE INDIVIDUAL AMINO ACIDS.
AND RIBOSOMES HAVE A VERY UNIQUE SHAPE.
YOU CAN SAY THEY HAVE, LIKE,
THE TWO LOBES THERE TO HELP YOU RECOGNIZE THEM. OKAY.
SO LET'S LOOK AT TRANSCRIPTION
AND THEN WE'LL MOVE ON TO TRANSLATION.
SO REMEMBER THAT WE HAVE A SEGMENT OF THE DNA
UNRAVELING TO EXPOSE THE NUCLEOTIDE SEQUENCE RIGHT?
THERE'S THE GENE. RIGHT?
THE NUCLEOTIDE SEQUENCE IS THE GENE THAT GIVES THE DIRECTIONS
FOR HOW TO SYNTHESIZE A PROTEIN. ALL RIGHTY.
SO THEN THE RNA POLYMERASE, RIGHT,
SO WE RECOGNIZE THAT AS ANOTHER ENZYME, RIGHT, CAN BUILD
A COMPLEMENTARY NUCLEOTIDE SEQUENCE OF MESSENGER RNA.
RIGHT? THE DNA FOLDS BACK UP,
IT'S SHARED THE INFORMATION IT NEEDED TO SHARE
AND NOW THE MESSENGER RNA CAN BE EXPORTED OUT OF THE NUCLEUS
AND CAN TRAVEL TO THE RIBOSOMES IN THE CYTOPLASM. RIGHT?
SO REMEMBER GENE EXPRESSION IS A GENE'S DNA,
IS USED AS A TEMPLATE FOR THE SYNTHESIS OF A SPECIFIC PROTEIN.
SO GENE EXPRESSION BEGINS WITH THE TRANSCRIPTION.
SO DNA MUST BE UNRAVELED TO EXPOSE THE NUCLEOTIDE SEQUENCE
AND THEN THE COPYING BEGINS AT THE NUCLEOTIDES
AND, SO, THERE ARE CODONS,
THERE ARE PATTERNS OF NUCLEOTIDES THAT SIGNAL
WHERE TO--WHERE A SEQUENCE STARTS AND STOPS. ALL RIGHT.
SO LET'S LOOK HERE. RIGHT.
SO THE WHOLE IDEA OF THE TEMPLATE STRAND OF DNA
IS REALLY IMPORTANT. ALL RIGHT.
SO LET'S LOOK DOWN HERE AT OUR DIAGRAM
AND HERE WE SEE THE TEMPLATE STRAND OF DNA. RIGHT?
SO IT HAS UNRAVELED AND THEN THE RNA POLYMERASE
COMES IN TO CREATE THE COMPLEMENTARY STAND--
STRAND OF RNA IN WHICH--YEAH, IS RIGHT THERE.
OKAY. SO THERE'S OUR COMPLEMENTARY STAND
OF MESSENGER RNA COMES, RIGHT.
AND, SO, WE COULD THINK OF THIS PART RIGHT HERE, RIGHT,
THIS IS--THIS IS WHERE WE HAVE THE GENE WITH INSTRUCTIONS
TO PRODUCE A PROTEIN. ALL RIGHTY.
OKAY. SO ONE THING TO KEEP IN MIND, RIGHT,
SO THE START CODONS THAT--RIGHT, SO THAT'S A SEQUENCE
OF NUCLEOTIDES TO SIGNAL THE BEGINNING
OF THE GENE OR THE BEGINNING OF THE INSTRUCTIONS.
OKAY. SO LET'S THINK ABOUT WHAT WE'VE LEARNED SO FAR
ABOUT THE NUCLEOTIDES.
ALL RIGHT. SO ON OUR TEMPLATE STRAND RIGHT HERE.
OOPS, I WANTED TO USE GREEN.
AND, SO, IF WE HAVE OUR TEMPLATE, RIGHT,
SO OUR TEMPLATE IS FROM THE DNA
AND IF IT HAS A SEQUENCE G, A, T, C, A, T, ALL RIGHT,
WHAT WOULD BE THE COMPLEMENT? ALL RIGHT.
SO THE COMPLEMENT WILL BE ON THE MESSENGER RNA. ALL RIGHT.
SO THIS IS WHERE WE HAVE TO THINK ABOUT WHAT'S THE SAME
AND WHAT'S DIFFERENT ABOUT THE NITROGENOUS BASES.
SO FOR THE G, EVERYTHING IS THE SAME.
CYTOSINE MATCHES GUANINE
BUT THEN RIGHT ON RNA THERE IS NO THYMINE.
SO WE WOULD USE A U FOR URACIL,
ADENINE, GUANINE, URACIL, ADENINE.
SO YOU WANT TO BE ABLE TO MATCH THE BASES UP
BETWEEN THE TEMPLATE FROM THE DNA
AND THE COMPLEMENT ON THE MESSENGER RNA. OKAY.
SO THAT'S PRETTY MUCH ALL WE NEED TO KNOW
ABOUT TRANSCRIPTION FOR OUR CLASS.
THERE'S A LOT MORE TO LEARN BUT THAT'S ENOUGH FOR US.
AND NOW WE'LL GO ON--SO ONCE THE MESSENGER RNA
HAS THE INSTRUCTIONS, HOW DO WE ACTUALLY SYNTHESIZE A PROTEIN?
WELL, WE NEED TO LOOK AT TRANSLATION. OKAY.
SO WHAT HAPPENS HERE, RIGHT,
IS THE RIBOSOMES THEN WILL TAKE THE INFORMATION
FROM THE MESSENGER RNA AND READ IT
AND THEN WE WILL THEN BUILD A POLYPEPTIDE
BY LINKING THE AMINO ACIDS, RIGHT,
THE PRIMARY STRUCTURE OF PROTEINS. ALL RIGHTY.
SO IT'S INTERESTING TO NOTE
THAT WE SAW THIS BEFORE THE START CODONS.
SO WHAT IS IT--WHAT IS IT ABOUT THESE CODONS?
WELL, EVERY GROUP OF THREE NUCLEOTIDES
ON THE MESSENGER RNA IS KNOWN AS A CODON
BECAUSE IT CODES FOR ONE OF THE 20 AMINO ACIDS.
SO IF WE THINK ABOUT,
HERE IS OUR DNA AND THEN WE HAVE THE NUCLEOTIDE SEQUENCE
AND SO WE CAN SEE HERE, RIGHT, SO THESE THREE NUCLEOTIDES CODE,
RIGHT, FOR ONE AMINO ACID
AND THEN THE NEXT THREE NUCLEOTIDES CODE
FOR THE SECOND AMINO ACID AND THEN SO ON.
AND THEN THE THIRD FOR A THIRD AMINO ACID.
SO THE SEQUENCE OF NUCLEOTIDES
DESCRIBES A PARTICULAR AMINO ACID. IT'S THE CODE FOR IT.
HOWEVER, THERE ARE 64 POSSIBLE CODONS
AND THERE'S ONLY 20 AMINO ACIDS AND THIS IS REALLY GOOD
BECAUSE WE--WHEN WE TALKED ABOUT REPLICATION IN THINGS,
WE SAW THAT THERE IS A VERY SMALL PERCENTAGE OF ERRORS.
AND, SO, BY ABLE TO HAVE MORE THAN ONE CODON
FOR EACH AMINO ACID THIS HELPS TO MINIMIZE EFFECTS
FROM MUTATIONS OR MISTAKES.
SO HERE WE HAVE, THERE'S THE GENETIC CODE.
IT'S THE KEY FOR THE CODONS AND THEIR AMINO ACIDS.
SO HERE WE SEE THE FIRST LETTER
AND THEN HERE'S THE SECOND LETTER.
AND THEN YOU CAN SEE HOW PRETTY MUCH EACH AMINO ACID
HAS SEVERAL DIFFERENT CODONS TO REPRESENT IT.
FOR EXAMPLE LEUCINE, THERE ARE FOUR DIFFERENT WAYS
THAT WE COULD CODE--PARDON ME, FOR LEUCINE.
SO THE MAIN POINT HERE IS THE MULTIPLE CODONS, RIGHT?
HELP TO MINIMIZE EFFECTS OF GENETIC MUTATIONS.
OKAY. THAT ALL FITS. GREAT. OKAY.
NOW THIS CHART, WE'RE GOING TO COME BACK TO BUT WE NEED TO GO
A LITTLE BIT FURTHER INTO THE STORY.
AND THE MAIN THING TO THINK ABOUT
IS WHEN YOU HEARD THE WORD CODON,
YOU'RE ALWAYS THINKING ABOUT MESSENGER RNA, RIGHT? OKAY.
SO NOW, LET'S BRING THIS ALL TOGETHER
TO SEE HOW WE SYNTHESIZE PROTEINS.
SO HERE'S OUR DIAGRAM DOWN AT THE BOTTOM.
SO THIS IS HAPPENING--
AND WE'LL HAVE ANOTHER DIAGRAM ON THE NEXT PAGE, RIGHT?
SO CODON, THINK ABOUT THE MESSENGER RNA
AND WE'LL BE THINKING ALWAYS
IN TERMS OF THREE NUCLEOTIDES AT A TIME.
ALL RIGHT. SO THEN THIS CLOVER LEAF STRUCTURE,
THIS REPRESENTS THE TRANSFER RNA. ALL RIGHT.
SO THE TRANSFER RNA IS VERY INTERESTING.
SO HERE WE HAVE THE ANTICODON.
SO WHENEVER YOU SEE ANTICODON, THINK ABOUT THE TRANSFER RNA.
WHEN YOU THINK ABOUT THE CODON,
YOU'RE THINKING ABOUT THE MESSENGER RNA. ALL RIGHT.
AND THEN THIS IS THE COOL PART, ALL RIGHT.
SO THIS CODON IS GIVING THE CODE FOR THIS AMINO ACID.
ALL RIGHT. SO THE TRANSFER RNA KNOWS, RIGHT, SO THE--
ONLY THE TRANSFER RNA THAT HAS THE CORRECT ANTICODON
CAN COME IN TO INTERACT WITH THE CODON OF THE MESSENGER RNA
SO THAT THE TRANSFER RNA BRINGS THE CORRECT AMINO ACID.
ALL RIGHTY. SO LET'S GO BACK UP TO THE NOTES A LITTLE BIT
AND SEE WHAT'S GOING ON HERE. ALL RIGHT.
SO I'VE PRETTY MUCH JUST EXPLAINED THAT, RIGHT?
SO THE TRANSFER RNA MATCHES THE CODON ON THE MESSENGER RNA
WITH THE CORRESPONDING AMINO ACID.
THE CLOVER SHAPED TRANSFER RNA
HAS TWO IMPORTANT REGIONS, RIGHT?
THE ANTICODON LOOP. SO THAT'S RIGHT HERE.
SO THE ANTICODON LOOP, RIGHT?
THAT'S WHERE IT'S THE COMPLIMENTARY.
WELL, IT'S COMPLEMENTARY TO THE MESSENGER RNA CODON. ALL RIGHT.
AND REMEMBER TO FOCUS THAT IT TAKES ONLY THREE AMINO ACIDS,
OKAY. AND THEN THE THREE PRIME END IS WHAT IS LINKED, RIGHT?
TO THE AMINO ACID. OKAY.
SO THAT'S ABOUT ALL WE NEED TO SAY THERE.
LET'S MAKE SURE, RIGHT? SO THE CG--ALL RIGHT.
SO WE HAVE GCC, OKAY.
SO NOW LET'S GO BACK TO THE PREVIOUS PAGE AND LOOK.
ALL RIGHT. IF WE LOOK AT THE CODONS.
SO WE'RE LOOKING FOR GCC. OOPS, YEAH, SO SURE ENOUGH, RIGHT.
THERE'S GCC RIGHT THERE, RIGHT.
SO THAT'S THE CODE FOR THE ALANINE, SO, RIGHT.
REMEMBER THE GCC IS ON THE mRNA
AND THE ALANINE IS ON THE TRANSFER RNA.
OOPS, YOU CAN'T SEE WHAT I'M WRITING, SORRY. OKAY. ALL RIGHT.
SO THE GCC, THAT WAS THE CODON
THAT TELLS THE TRANSFER RNA TO BRING IN THE ALANINE.
ALL RIGHT. SO THAT'S RIGHT THERE.
SO THERE'S OUR CODON AND OUR ANTICODON AND OUR AMINO ACID.
SO NOW LET'S LOOK AT HOW THIS ALL FITS TOGETHER
TO SYNTHESIZE PROTEINS.
BUILDING A PROTEIN. ALL RIGHTY.
SO NOW, WE'LL EVEN HAVE THE RIBOSOME STRUCTURE THERE.
ALL RIGHTY. SO LET'S LOOK AT THAT. OKAY.
SO AT THE RIBOSOME AND MESSENGER RNA CODON
IS READ AND A MATCHING TRANSFER RNA MOLECULE ARRIVES
WITH THE CORRESPONDING AMINO ACID.
SO WE SAW THAT ON THE PREVIOUS SLIDE.
THE BASE PAIRS H-BOND TEMPORARILY
BETWEEN THE ANTICODON OF THE TRANSFER RNA
AND THE CODON OF THE MESSENGER RNA.
THE NEXT TRANSFER RNA ARRIVES WITH ITS AMINO ACID
AND THE TRANSFER RNA BASE PAIRS UP, RIGHT?
ALL THROUGH H-BONDING BETWEEN THE ADJACENT CODONS
WE GET AN AMIDE BOND FORMING
BETWEEN THE ADJACENT AMINO ACIDS ON THE TWO TRANSFER RNAs.
SO LET'S SEE IF WE CAN LOOK AT THAT PART FIRST
BEFORE WE GET TOO FAR. ALL RIGHT.
SO IT'S A LITTLE DARK BUT I THINK--RIGHT?
SO HERE'S THE MESSENGER RNA, RIGHT.
SO THAT WOULD BE OUR CODON, RIGHT.
TO SPECIFY AND THEN WE SEE, RIGHT?
SO HERE'S THE TRANSFER RNA.
AND IT HAS IT'S CORRESPONDING AMINO ACID.
AND NOW THE SECOND--SO THEN WE HAVE OUR SECOND CODE
AND HERE IS THE SECOND MOLECULE OF TRANSFER RNA
BRINGING IN A SECOND AMINO ACID.
EVERYTHING IS HELD TOGETHER WITH H-BONDS
AND NOW WE SEE THAT THESE TWO AMINO ACIDS, RIGHT?
ARE GOING TO, RIGHT?
AN AMIDE BOND FORMS BETWEEN THEM TO LEAD GLYCINE TO ISOLEUCINE.
AT THIS POINT NOW THE GLYCINE TRANSFER RNA,
YEAH, IT CAN LEAVE AND WE SEE
THE ISOLEUCINE'S HELD IN SPACE HERE
AND SO NOW WE COULD BRING IN A THIRD AMINO ACID
AND THE PROCESS JUST REPEATS OVER AND OVER.
AND THEN IT'S LIKE PUTTING BEADS ON A NECKLACE.
WE BRING TOGETHER THE AMINO ACIDS TO CREATE THE POLYPEPTIDE.
SO--AND THAT'S JUST SUMMARIZED FOR YOU HERE, RIGHT.
THE FIRST TRANSFER RNA IS RELEASED
AND THEN AN ADDITIONAL TRANSFER RNA CAN COME IN
AND THIS PROCESS KEEPS GOING UNTIL WE HIT A STOP CODON.
RIGHT. AND AT THIS POINT WE'RE STILL CALLING IT A POLYPEPTIDE
BECAUSE THE SECONDARY, TERTIARY,
AND POSSIBLY THE QUATERNARY STRUCTURE
HAS TO MANIFEST BEFORE WE CALL IT A PROTEIN, RIGHT?
BECAUSE A PROTEIN HAS BIOLOGICAL FUNCTION
AND A POLYPEPTIDE IS SIMPLY A POLYMER OF AMINO ACIDS.
ALL RIGHT. SO IF YOU LOOK BACK AT YOUR CHART
YOU'LL SEE FOR THIS FIRST--OOPS, EXCUSE ME.
IF YOU LOOK BACK AT OUR CODON CHART YOU'LL SEE
THAT GGG CORRESPONDS TO THE AMINO ACID GLYCINE.
AND IF WE LOOK AUC IS ISOLEUCINE. OKAY.
SO NOW LET'S HAVE ONE LAST PAGE TO WRAP UP
AND PRACTICE OUR UNDERSTANDING,
MAKE SURE THAT WE HAVE THIS UNDERSTOOD BEFORE WE--
BEFORE I SET YOU FREE ON HOMEWORK.
LET'S LOOK AT--LET'S LOOK AT THIS PROCESS ONE LAST TIME.
SO WE'LL USE THE GENETIC CODE TABLE AT THE BOTTOM OF THE PAGE
TO HELP US IDENTIFY THE AMINO ACID ATTACHED TO THE RNA.
ALL RIGHT. SO IF WE LOOK HERE. ALL RIGHT.
SO WHERE ARE WE GOING TO LOOK? WELL, RIGHT, THIS IS OUR CODON,
THIS IS WHERE WE NEED TO LOOK, RIGHT?
BECAUSE THIS IS THE CODON TABLE.
SINCE WE'RE HERE, RIGHT,
REMEMBER THIS WOULD BE CALLED THE ANTICODON, RIGHT?
THAT HAS TO DO WITH THE TRANSFER RNA.
THE CODON'S ALWAYS THE MESSENGER RNA.
AND THEN NOTICE RIGHT, THIS CODON LINKS TO THIS AMINO ACID.
SO THE QUESTION IS WHAT AMINO ACID IS IT?
WHERE DO WE LOOK? WE LOOK AT THE CODON.
SO WE WOULD LOOK AT GCC. ALL RIGHT. SO WE LOOK AT OUR TABLE.
AND WE GO G AND C. SO IF WE LOOK GCC, THERE IT IS, VOILA. RIGHT?
SO ALANINE. SO WE CAN NOW RECOGNIZE THAT THIS IS ALANINE.
IT'S THE AMINO ACID THAT WILL BE TRANSFERRED WITH THIS tRNA.
OKAY. SO THAT WRAPS UP OUR TUTORIAL ON RIBONUCLEIC ACIDS
AND THEIR ROLLING PROTEIN SYNTHESIS, RIGHT?
THE TRANSCRIPTION AND THE TRANSLATION
ARE TWO KEY PROCESSES.
YOU WANT TO BE ABLE TO FIND
THE COMPLEMENTS OF THE NITROGENOUS BASES
AND BE ABLE TO INTERPRET THE CODON TABLE.
SO PLEASE TAKE SOME TIME NOW
TO REINFORCE YOUR UNDERSTANDING WITH THE FEW HOMEWORK PROBLEMS.