Chapter 12 Notes DNA RNA and Protein Synthesis

Chapter 12 Notes, DNA, RNA, and Protein Synthesis

THE DISCOVERY OF DNA BY THE EARLY 1900'S, SCIENTISTS KNEW THAT CHROMOSOMES WERE RESPONSIBLE FOR TRAITS BEING INHERITED. THE KEY COMPONENT OF THE CHROMOSOMES THAT ACTUALLY CONTAINED THE GENETIC INFORMATION REMAINED A MYSTERY. CHEMICAL ANALYSIS OF CHROMOSOMES TOLD THEM THAT THE GENETIC MATERIAL HAD TO BE EITHER PROTEINS OR NUCLEIC ACIDS (DNA). BUT THEY DIDN'T KNOW WHICH ONE WAS RESPONSIBLE FOR CARRYING THE GENETIC INFORMATION.

GRIFFITH'S EXPERIMENT IN 1928, BRITISH BACTERIOLOGIST FREDRICK GRIFFITH PERFORMED AN EXPERIMENT TO TRY TO DETERMINE WHAT THE GENETIC MATERIAL WAS. GRIFFITH INJECTED TWO DIFFERENT STRAINS OF BACTERIA INTO MICE. THE STRAIN OF BACTERIA IS KNOWN AS STREPTOCOCCUS PNEUMONIA. ONE STRAIN WAS COVERED IN A SUGAR COAT AND ONE WAS NOT. HE CALLED THE STRAIN THAT WAS COVERED IN THE SUGAR COAT THE SMOOTH OR S STRAIN. THE SMOOTH STRAIN WAS VIRULENT (HARMFUL).

THE RESULTS OF GRIFFITH'S EXPERIMENT THE SMOOTH STRAIN WAS THE VIRULENT (DISEASECAUSING) STRAIN. THE ROUGH STRAIN WAS THE NONVIRULENT (HARMLESS) STRAIN. THIS WAS THE RESULT OF HIS EXPERIMENTS MICE + SMOOTH STRAIN (VIRULENT) = DEAD MICE + ROUGH STRAIN (NONVIRULENT) = LIVE MICE + SMOOTH STRAIN KILLED WITH HEAT = LIVE MICE + ROUGH STRAIN+ HEAT KILLED SMOOTH STRAIN = DEAD MICE

EXPLANATION OF GRIFFITH'S EXPERIMENT GRIFFITH CONCLUDED THAT A DISEASE-CAUSING FACTOR WAS TRANSFORMING THE ROUGH STRAIN (NONVIRULENT) INTO THE SMOOTH STRAIN (VIRULENT) OF BACTERIA.

HERSHEY AND CHASE EXPERIMENT IN 1952, A BACTERIOLOGIST BY THE NAME OF ALFRED HERSHEY, AND A GENETICIST BY THE NAME OF MARTHA CHASE PROVIDED CONCLUSIVE EVIDENCE THAT DNA WAS THE TRANSFORMING FACTOR. THEIR EXPERIMENT INVOLVED A SPECIAL TYPE OF VIRUS CALLED A BACTERIOPHAGE IS A VIRUS THAT ATTACKS BACTERIA. THE BACTERIOPHAGE WAS IDEAL FOR THIS EXPERIMENT BECAUSE IT WAS MADE OF THE TWO KEY COMPONENTS (PROTEIN AND DNA) THAT WERE THOUGHT TO RESPONSIBLE FOR INHERITANCE. AND THEY WERE ALSO IDEAL BECAUSE VIRUSES CAN NOT REPRODUCE ON THEIR OWN.

HERSHEY AND CHASE EXPERIMENT HERSHEY AND CHASE USED A TECHNIQUE CALLED RADIOACTIVE LABELING TO TRACE BOTH THE PROTEIN AND THE DNA OF THE BACTERIOPHAGE AFTER IT INFECTED THE BACTERIA (E. COLI). AFTER THE VIRUS INFECTED THE BACTERIA WITH ITS OWN GENETIC MATERIAL, HERSHEY AND CHASE MONITORED WHICH RADIOACTIVE MATERIAL (PROTEINS OR DNA) WAS INHERITED BY THE BACTERIA. THIS WOULD IDENTIFY THE GENETIC MATERIAL AS PROTEINS OR DNA. AFTER THE TEST WAS COMPLETED, THEY DISCOVERED THAT THE E. COLI THAT WAS INJECTED WITH RADIOACTIVE DNA BECAME RADIOACTIVE. THUS THEY CONCLUDED THAT DNA IS THE GENETIC MATERIAL.

HERSHEY AND CHASE EXPERIMENT

THE STRUCTURE AND COMPOSITION OF DNA SCIENTISTS WERE NOW CONFIDENT THAT THEY HAD DISCOVERED WHAT THE GENETIC MATERIAL WAS, BUT QUESTIONS REMAINED ABOUT THE STRUCTURE OF DNA AND HOW DNA USES THE INFORMATION. WHAT THEY DISCOVERED IS THAT DNA IS MADE UP OF NUCLEOTIDES. A NUCLEOTIDE IS MADE OF A SUGAR MOLECULE, A PHOSPHATE MOLECULE, AND A NITROGEN BASE.

DNA STRUCTURE AND COMPOSITION IN THE DNA THERE ARE FOUR DIFFERENT NITROGEN BASES ADENINE GUANINE CYTOSINE THYMINE URACIL (IN RNA, URACIL REPLACES THYMINE)

CHARGAFF'S RULE IN THE 1950 S, ERWIN CHARGAFF DISCOVERED THAT IN EVERY ORGANISM THE AMOUNT OF GUANINE AND CYTOSINE, AND THE AMOUNT OF ADENINE AND THYMINE WAS NEARLY ALWAYS EQUAL. THIS PRINCIPLE IS KNOWN AS CHARGAFF'S RULE.

THE DOUBLE HELIX IN 1951, ROSALIND FRANKLIN USED X-RAYS TO PHOTOGRAPH DNA. PHOTO 51 SHOWED THAT THE DNA MOLECULE WAS IN THE SHAPE OF A TWISTED LADDER KNOWN AS A DOUBLE HELIX.

THE DOUBLE HELIX

WATSON AND CRICK JAMES WATSON AND FRANCIS CRICK USED DATA FROM CHARGAFF AND FRANKLIN'S PHOTO TO BUILD THE FIRST ACCURATE MODEL OF DNA.

THE STRUCTURE OF DNA IS LIKE A TWISTED LADDER MADE UP OF ALTERNATING STRANDS OF DEOXYRIBOSE AND PHOSPHATE. THE RAILS OF THE LADDER ARE JOINED BY THE BASES. (ADENINE, GUANINE,

COMPLEMENTARY BASE PAIRING EACH NITROGEN BASE PAIRS UP WITH ONLY ONE OTHER BASE IN WHAT IS KNOWN AS COMPLEMENTARY BASE PAIRING. PURINE BASES ALWAYS PAIR UP WITH PYRIMIDINE BASES. • • ADENINE AND GUANINE ARE CALLED PURINES. (DOUBLE– RINGS) CYTOSINE AND THYMINE ARE CALLED PYRIMIDINES. (SINGLE -RINGS) ADENINE ALWAYS PAIRS WITH THYMINE. GUANINE ALWAYS PAIRS WITH CYTOSINE.

PURINES AND PYRIMIDINES

COMPLEMENTARY BASE PAIRING

ORIENTATION OF THE DNA ANOTHER IMPORTANT FEATURE OF THE DNA STRUCTURE IS THE ORIENTATION OF THE DNA STRANDS. THE TWO STRANDS OF DNA ARE ANTIPARRELLEL, MEANING THEY RUN PARALLEL TO EACH OTHER, BUT THEY RUN IN OPPOSITE DIRECTIONS. THIS ORIENTATION IS IMPORTANT TO UNDERSTAND BECAUSE IT EXPLAINS HOW DNA REPLICATES (SEMICONSERVATIVE REPLICATION). ONE END OF THE DNA STRAND IS REFERRED TO AS THE 5' (FIVE-PRIME) END, AND THE OTHER END IS REFERRED TO AS THE 3' (THREE-PRIME) END.

DNA ORIENTATION WE WILL DISCUSS THE IMPORTANCE OF THIS ORIENTATION LATER

HOW DOES DNA FIT INSIDE A CELL? JUST ONE STRAND OF DNA IN ONE CHROMOSOME CAN BE UP TO 245 MILLION BASE PAIRS LONG! AND REMEMBER, HUMANS HAVE 46 CHROMOSOMES. IT HAS BEEN ESTIMATED THAT IF ALL THE DNA FROM JUST ONE CELL OF A HUMAN'S BODY WAS UNWOUND, IT WOULD STRETCH ABOUT 6 FT. LONG! THAT MEANS THE DNA IN ONE CELL IS ABOUT 100, 000 TIMES LONGER THAN THE CELL ITSELF! AND AMAZINGLY, IT ALL FITS INTO THE NUCLEUS, WHICH ONLY TAKES UP ABOUT 10% OF THE CELL'S VOLUME!

HOW DOES DNA FIT INSIDE A CELL? SO HOW DOES ALL THAT INFORMATION FIT INTO A CELL? DNA COILS TIGHTLY AROUND SMALL BALLS OR SPHERICAL STRUCTURES OF PROTEIN CALLED HISTONES AND PHOSPHATES FROM THE DNA COMBINE TOGETHER TO FORM STRUCTURES CALLED NUCLEOSOMES COMBINE TOGETHER TO FORM CHROMATIN FIBERS, AND THE CHROMATIN FIBERS COMBINE TOGETHER TO FORM THE CHROMOSOMES.

CHROMOSOMES AND HISTONES

SEMICONSERVATIVE REPLICATION WHEN WATSON AND CRICK CREATED THEIR MODEL OF THE DNA DOUBLE HELIX, THEY ALSO PROPOSED A POSSIBLE WAY THAT DNA MIGHT GET REPLICATED. THE WAY THEY PROPOSED DNA GETS REPLICATED IS CALLED SEMICONSERVATIVE REPLICATION. IN SEMICONSERVATIVE REPLICATION, ONE OF THE STRANDS ALWAYS GETS COPIED AND THE OTHER STRAND IS A COPY FROM THE ORIGINAL PARENT OR TEMPLATE STRAND. THE PROCESS IS SIMILAR TO HOW SOURDOUGH BREAD IS MADE. IN ORDER TO MAKE IT YOU NEED A STARTER BATCH (ORIGINAL TEMPLATE).

SEMICONSERVATIVE REPLICATION SEMICONSERVATIVE REPLICATION OCCURS IN THREE STAGES: UNWINDING, BASE PAIRING, AND JOINING TOGETHER. DURING UNWINDING, AN ENZYME CALLED DNA HELICASE UNZIPS OR UNWINDS THE DNA DOUBLE HELIX. AFTER THE STRANDS UNWIND, ANOTHER ENZYME CALLED DNA POLYMERASE, ADDS NUCLEOTIDES TO THE NEW STRAND IN COMPLEMENTARY BASE PAIRS.

SEMICONSERVATIVE REPLICATION BECAUSE THE STRANDS ARE ANTIPARALLEL, AND BASE PAIRS ALWAYS HAVE TO BE ADDED TO THE 3’ PRIME END, ONLY ONE OF THE STRANDS CAN BE REPLICATED CONTINUOUSLY AS ITS UNWOUND. THE SECTION OF DNA THAT IS REPLICATED CONTINUOUSLY IS CALLED THE LEADING STRAND. THE OTHER STRAND, CALLED THE LAGGING STRAND, HAS TO BE REPLICATED IN REVERSE ORDER, IN SECTIONS OF NUCLEOTIDES. THESE SECTIONS OF NUCLEOTIDES ARE CALLED OKAZAKI FRAGMENTS.

SEMICONSERVATIVE REPLICATION THE OKAZAKI FRAGMENTS ARE THEN GLUED TOGETHER BY ANOTHER ENZYME CALLED DNA LIGASE

SEMICONSERVATIVE REPLICATION

SEMICONSERVATIVE REPLICATION

THE CENTRAL DOGMA OF BIOLOGY DNA CONTAINS A CODE THAT IS TRANSCRIBED AND TRANSLATED BY ANOTHER NUCLEIC ACID CALLED RNA (RIBONUCLEIC ACID). RNA GUIDES THE SYNTHESIS OF PROTEINS. THIS PROCESS IS KNOWN AS THE CENTRAL DOGMA OF BIOLOGY. DNA IS TRANSCRIBED (COPIED) BY MESSENGER RNA CARRIES INFORMATION TO THE RIBOSOMES (AND THE RIBOSOMAL RNA) AND THE TRANSFER RNA TRANSLATE THE CODE TO MAKE THE PROTEINS.

THE CENTRAL DOGMA

WHAT IS RNA? RNA IS SIMILAR TO DNA. SOME DIFFERENCES ARE THAT RNA CONTAINS THE SUGAR RIBOSE INSTEAD OF DEOXYRIBOSE. ANOTHER DIFFERENCE IS THAT RNA USES THE NITROGEN BASE URACIL IN PLACE OF THYMINE. ANOTHER DIFFERENCE BETWEEN RNA AND DNA, IS THAT RNA IS SINGLE-STRANDED WHILE DNA IS DOUBLESTRANDED. THERE ARE THREE MAIN TYPES OF RNA THAT PLAY A ROLE IN PROTEIN SYNTHESIS. THEY ARE CALLED MESSENGER RNA, RIBOSOMAL RNA, AND TRANSFER RNA.

DNA VS. RNA

MESSENGER RNA THE JOB OR ROLE OF MESSENGER RNA (MRNA) IS TRANSCRIPTION IS THE PROCESS OF COPYING THE DNA CODE. MESSENGER RNA ENTERS THE NUCLEUS, A SMALL PORTION OF THE DNA STRAND IS COPIED. THEN THE MESSENGER RNA LEAVES THE NUCLEUS AFTER COPYING DOWN A PART OF THE CODE TO MAKE A PROTEIN.

MESSENGER RNA AND TRANSCRIPTION AFTER THE DNA IS UNWOUND IN THE NUCLEUS, AN ENZYME CALLED RNA POLYMERASE COMES ALONG TO ASSIST IN BASE PAIRING. RNA POLYMERASE ASSISTS THE MESSENGER RNA IN RECORDING INFORMATION FOUND ON A PORTION OF THE DNA STRAND. MESSENGER RNA RECORDS THE CODE IN COMPLEMENTARY BASE PAIRS, SIMILAR TO REPLICATION, EXCEPT WHEN THE BASE PAIR ADENINE IS PAIRED, ADENINE PAIRS WITH URACIL INSTEAD OF THYMINE.

MESSENGER RNA AND TRANSCRIPTION AFTER THE MESSENGER RNA IS TRANSCRIBED, IT CAN LEAVE THE NUCLEUS THROUGH NUCLEAR PORES AND ENTER INTO THE CYTOPLASM TO FIND TRANSFER RNA AND THE RIBOSOMES (AND THE RIBOSOMAL RNA).

TRANSLATION AND TRANSCRIPTION

RIBOSOMES, TRANSFER RNA, AND TRANSLATION AFTER A MESSENGER RNA FINDS A RIBOSOME, THE CODE IS READ AND TRANSLATED IN COMPLEMENTARY BASE PAIRS BY TRANSFER RNA INTERPRETS THE CODE BY READING THE BASES IN GROUPS OF THREE CALLED CODONS. TRANSFER RNA MOLECULES EACH HAVE THEIR OWN ANTICODON THAT ONLY MATCHES WITH A SPECIFIC CODON ON THE MESSENGER RNA. EACH TRANSFER RNA HAS AN AMINO ACID ATTACHED TO IT, THAT IT DEPOSITS WHEN IT ATTACHES TO THE MESSENGER RNA. THE AMINO ACIDS ARE LINKED TOGETHER TO FORM A PROTEIN.

RIBOSOMES, TRANSFER RNA, AND TRANSLATION

THE CODE THE DNA CODE IS READ IN GROUPS OF THREE. EACH CODON ONLY MATCHES WITH A SPECIFIC ANTICODON. BY JOINING MULTIPLE AMINO ACIDS TOGETHER,