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THE MOLECULAR BIOLOGY OF THE GENE
THE MOLECULAR BIOLOGY OF THE GENE
• EXPERIMENTS HAVE SHOWN THAT DNA IS THE GENETIC MATERIAL– DNA HAS BEEN KNOWN ABOUT FOR OVER 100
YEARS; HOWEVER, KNOWLEDGE OF ITS ROLE AS GENETIC MATERIAL IS RELATIVELY NEW
– ORIGINALLY, IT WAS THOUGHT THAT PROTEIN WAS IN CHARGE OF TRAITS (WHY DO YOU THINK THEY BELIEVED PROTEINS WERE THE ANSWER?)
THE MOLECULAR BIOLOGY OF THE GENE
• GRIFFITH’S EXPERIMENT
THE MOLECULAR BIOLOGY OF THE GENE
• GRIFFITH’S SETUP– INVOLVED A TYPE OF BACTERIA (STREPTOCOCCUS)– UTILIZED HEAT SHOCK TO DENATURE PROTEINS
• GRIFFITH’S RESULTS– HARMLESS FORM (R FORM) WAS TURNED INTO
HARMFUL FORM (S FORM) WHEN HEAT-SHOCKED “S” WAS MIXED WITH NORMAL “R”
– IDENTIFIED DNA IS GENETIC CARRIER
THE MOLECULAR BIOLOGY OF THE GENE
• SCIENTISTS WERE RESISTANT TO GRIFFITH’S FINDINGS
• SCIENTISTS KNEW ABOUT CHROMOSOMES– CHROMOSOMES ARE MADE UP OF• PROTEINS (VERSATILE SUBSTANCES, 20 DIFFERENT
AMINO ACIDS)• NUCLEIC ACIDS (ONLY 5 DIFFERENT NUCLEOTIDES)
THE MOLECULAR BIOLOGY OF THE GENE
• HERSHEY AND CHASE EXPERIMENT
THE MOLECULAR BIOLOGY OF THE GENE
• HERSHEY AND CHASE SETUP– USED T2 BACTERIOPHAGES (PHAGE = VIRUS THAT
ATTACKS/EATS BACTERIA)– GREW PHAGES IN RADIOACTIVE ELEMENTS
• SULFUR FOR PROTEIN / PHOSPHOROUS FOR DNA
– TRACING RADIOACTIVITY ALLOWED THEM TO DETERMINE THE GENETIC CARRIER
• RESULTS– RADIOACTIVE PHOSPHOROUS ONLY WAS PRESENT IN
BACTERIAS; CONCLUSIVELY SHOWING THAT DNA (NUCLEIC ACIDS) ARE CONTROLLING TRAITS/GENETICS
THE MOLECULAR BIOLOGY OF THE GENE
• NOW THE RACE WAS ON TO STUDY DNA/RNA
• DNA / RNA– POLYMERS OF NUCLEOTIDES
• NUCLEOTIDE??• POLYNUCLEOTIDE??
– SUGAR-PHOSPHATE BACKBONE• REPEATING PATTERN
OF SUGAR (PENTOSE) AND PHOSPHATE
THE MOLECULAR BIOLOGY OF THE GENE
• DNA– DEOXYRIBONUCLEIC
ACID• DEOXYRIBOSE ??• NUCLEIC ??• ACID ??
– 4 TYPES OF BASES IN DNA (2 GROUPS)• PURINES (2 RINGS)
– ADENINE / GUANINE
• PYRIMIDINES (1 RING)
– CYTOSINE / THYMINE
• RNA– RIBONUCLEIC ACID
• RIBOSE ??• NUCLEIC ??• ACID ??
– 4 TYPES OF BASES IN RNA (2 GROUPS)• PURINES (2 RINGS)
– ADENINE / GUANINE
• PYRIMIDINES (1 RING)– CYTOSINE / URACIL
THE MOLECULAR BIOLOGY OF THE GENE
• STRUCTURE DENOTES ____________– THEREFORE LEARNING THE STRUCTURE OF DNA
BECAME OF EXTREME IMPORTANCE
THE MOLECULAR BIOLOGY OF THE GENE
• DNA IS A DOUBLE STRANDED HELIX– DOUBLE HELIX TWO STRANDS OF DNA, COILED
AROUND EACH OTHER (*TWISTED LADDER*)– EXPLAINED BY WATSON AND CRICK– USED DATA FROM WILKINS AND FRANKLIN• X-RAY CRYSTALLOGRAPHY
THE MOLECULAR BIOLOGY OF THE GENE
• WATSON AND CRICK EXPLAINED THE DOUBLE HELIX– USING DATA FROM
ERWIN CHARGAFF (EXPERIMENT THAT SHOWED # OF A’S AND T’S WAS ALWAYS EQUAL, AND # OF C’S AND G’S WAS ALWAYSEQUAL)
– AS WELL AS DATA THAT SHOWED DNA STRANDS WERE ALWAYS THE SAME DISTANCE APART
THE MOLECULAR BIOLOGY OF THE GENE
• DISCOVERED STRUCTURE SUGGESTED AN EXPLANATION OF DNA REPLICATION
• SPECIFIC BASE PAIRING IS HOW DNA IS COPIED
THE MOLECULAR BIOLOGY OF THE GENE
• WHILE THE CONCEPT OF REPLICATION IS SIMPLE, ACTUAL PROCESS IS COMPLEX
THE MOLECULAR BIOLOGY OF THE GENE
• DNA REPLICATION: A CLOSER LOOK– REPLICATION BEGINS AT SPECIFICS POINTS CALLED
ORIGINS OF REPLICATION (O.R.’S)
THE MOLECULAR BIOLOGY OF THE GENE
• DNA REPLICATION: A CLOSER LOOK– THERE ARE MULTIPLE
O.R.’S ALONG THE DNA STRAND (WHY IS THAT??)
– REPLICATION BUBBLES• WHERE DNA SPLITS AND
REPLICATION OCCURS IN BOTH DIRECTIONS (WHY IS THAT??)
– THE STRANDS OF DNA AREORIENTED IN OPPOSITE DIRECTIONS!!!• HOW WILL THIS AFFECT
REPLICATION? REMEMBER, ENZYMES HAVE SPECIFIC SHAPES!!
THE MOLECULAR BIOLOGY OF THE GENE
• DNA REPLICATION: A CLOSER LOOK– ENZYMES OF IMPORTANCE• DNA POLYMERASE
– ENZYME THAT ADDS NUCLEOTIDES TO GROW DAUGHTER STRAND
THE MOLECULAR BIOLOGY OF THE GENE
• DNA REPLICATION: A CLOSER LOOK• DNA LIGASE
– TIES/GLUES PIECES OF DNA TOGETHERINTO A SINGLE CONTINUOUS STRAND
• DNA HELICASE– UNZIPS THE DOUBLE STRANDED HELIX
• TOPOISOMERASE– RELIEVES THE PRESSURE/TENSION PLACED
ON PARTS OF DNA STRAND THAT ARE STILLED COILED
THE MOLECULAR BIOLOGY OF THE GENE
• DNA REPLICATION: A CLOSER LOOK– ENSURES THAT EXACT COPIES
OF DNA ARE PASSED ALONG TO ALL SOMATIC CELLS
– AMAZINGLY ACCURATE; ONLY ONE MISTAKE EVERY BILLION NUCLEOTIDES PLACED!!
THE MOLECULAR BIOLOGY OF THE GENE
• THE STRUCTURE OF DNA ALSO OFFERS AN EXPLANATION AS TO HOW IT CAN CONTROL YOUR TRAITS
• THE DNA GENOTYPE (NUCLEOTIDE MAKEUP) IS EXPRESSED AS PROTEINS, WHICH ACTS AS THE MOLECULAR MAKEUP FOR PHENOTYPIC EXPRESSION!!
THE MOLECULAR BIOLOGY OF THE GENE
• DNA RNA PROTEIN = PHENOTYPE– TRANSCRIPTION• PROCESS BY WHICH DNA IS CONVERTED TO RNA
– TRANSLATION• PROCESS BY WHICH RNA IS CONVERTED TO PROTEIN• PROTEINS CONTROL THE PHENOTYPE (TRAITS) OF AN
ORGANISM
THE MOLECULAR BIOLOGY OF THE GENE
• BEADLE AND TATUM EXPERIMENT– SHOWED THAT MUTANT
MOLD, DEFICIENT IN ONLY ONE GENE; COULDN’T GROW ON MEDIA THAT IT COULD GROW ON WITH NORMAL GENE
– ONE GENE : ONE POLYPEPTIDE HYPOTHESIS
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– PRODUCES GENETIC MESSAGES
IN THE FORM OF RNA– ONLY OCCURS IN THE NUCLEUS
(WHY??)– SIMILAR TO REPLICATION• 2 STRANDS SPLIT• BUT; ONLY STRAND SERVES AS
TEMPLATE
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– REQUIRES THE FOLLOWING:• RNA POLYMERASE
– ENZYME THAT PLACES AND LINKS NUCLEOTIDES BEING TRANSCRIBED
• PROMOTER– SPECIFIC REGION OF DNA FOR RNA POLYMERASE TO BIND
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– OCCURS IN 3 STAGES• INITIATION• ELONGATION• TERMINATION
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– INITIATION• ????
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– ELONGATION• ????
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– TERMINATION• ?????• TERMINATOR SPECIFIC SEQUENCE ON DNA THAT
SIGNALS THE RNA POLYMERASE TO DETACH
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC RNA IS PROCESSED BEFORE LEAVING
THE NUCLEUS• mRNA = MESSENGER RNA; CARRIES MESSAGE OF DNA
TO RIBOSOME FOR PROTEIN SYNTHESIS• IN EUKARYOTES, THE mRNA MUST BE PROCESSED
(CLEANED UP) BEFORE IT CAN LEAVE
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC mRNA PROCESSING• ONE TYPE OF PROCESSING IS ADDING A “CAP” AND
“TAIL”• WHY DOES THIS HAPPEN??
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC mRNA PROCESSING
• SECOND TYPE OF PROCESSING IS REMOVAL OF NON-CODING REGIONS= RNA SPLICING
• TWO TYPES– EXONS
» ???– INTRONS
» ???
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC mRNA PROCESSING• RNA SPLICING
– REMOVAL OF INTRONS TO PRODUCE FINAL mRNA PRODUCT– SPLICEOSOMES (A.KA. snRNP’S = PRONOUNCED SNURPS)
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– RIBOSOMES BUILD POLYPEPTIDES– RIBOSOMES ARE COMPOSED OF
PROTEINS AND rRNA– RIBOSOMES COORDINATE mRNA,
tRNA, AND AMINO ACIDS TO ALLOW PROTEIN SYNTHESIS
– RIBOSOME STRUCTURE• TWO SUBUNITS (LARGE VS SMALL)• P SITE = PEPTIDYL – tRNA BINDING• A SITE = AMINOACYL – tRNA BINDING
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– tRNA MOLECULES SERVE AS INTERPRETERS DURING
TRANSLATION– AMINO ACIDS ARE
READILY AVAILABLEIN THE CELL FROM DIGESTED FOOD
– tRNA PICKS UP THEAPPROPRIATEAMINO ACID AND BRINGS IT TO THEMATCHING CODON OF THE mRNA
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– CODONS• THREE NITROGENOUS
BASE “WORD” THAT SPECIFIES A PARTICULAR AMINO ACID
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– CODONS– 4 “UNIQUE” CODONS• AUG START CODON, ALSO CODES FOR METHIONINE• 3 STOP CODONS SIGNAL END OF TRANSLATION
– “WOBBLE” HYPOTHESIS• MORE THAN ONE CODON CAN CODE FOR THE SAME
AMINO ACID (OVERLAP)
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– TRANSLATION CAN BE DIVIDED INTO THREE
STAGES• INITIATION• ELONGATION• TERMINATION
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– INITIATION
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– INITIATION• 2 STEPS
– mRNA BINDS TO SMALL SUBUNIT OF RIBOSOME; tRNA WITH THE STARD CODON BINDS (MET = AUG)
– LARGE RIBOSOMAL SUBUNIT ATTACHES, CREATING A FUCNTIONAL RIBOSOME; INITIATOR tRNA FITS INTO “P” SITE
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– ELONGATION• ADDS NUCLEOTIDES
TO POLYPEPTIDE CHAIN• 3 STEPS TO
ELONGATION– CODON
RECOGNITION– PEPTIDE BOND
FORMATION– TRANSLOCATION
THE MOLECULAR BIOLOGY OF THE GENE
• TRANSLATION : A CLOSER LOOK– TERMINATION• ELONGATION CONTINUES UNTIL A “STOP” CODON
ENTERS THE “A” SITE
THE MOLECULAR BIOLOGY OF THE GENE
• REVIEW
THE MOLECULAR BIOLOGY OF THE GENE
• MUTATIONS CAN CHANGE THE MEANING OF GENES– MUTATION ANY RANDOM CHANGE IN THE
NUCLEOTIDE SEQUENCE OF DNA– CAN BE CLASSIFIED 3 WAYS• SUBSTITUTIONS• INSERTIONS (ADDITIONS)• DELETIONS
THE MOLECULAR BIOLOGY OF THE GENE
• SUBSTITUTIONS– A BASE SUBSITUTION
MAY CHANGE AN AMINO ACIDIN A POLYPEPTIDE, CHANGING THE PROTEIN
– “WOBBLE” HYPOTHESIS??
THE MOLECULAR BIOLOGY OF THE GENE
• INSERTIONS AND DELETIONS– CAN BE MORE SEVERE– THEY CHANGE THE
“READING FRAME”
THE MOLECULAR BIOLOGY OF THE GENE
• MUTAGENESIS– THE FORMATION OF MUTATIONS– 2 COMMON WAYS
• SPONTANEOUS MUTATION– ERRORS IN DNA REPLICATION/TRANSCRIPTION– UNKNOWN ORIGINS
• MUTAGEN– PHYSICAL (RADIATION) OR CHEMICAL AGENT
• *WHILE MUTATIONS ARE USUALLY HARMFUL; THEY CAN ALSO BE EXTREMELY USEFUL– PROMOTES EVOLUTION– IN THE LAB, PROVIDES A USEFUL TOOL FOR GENETIC RESEEARCH
THE MOLECULAR BIOLOGY OF THE GENE
• VIRUSES– IN A SENSE, VIRUSES ARE NOTHING MORE THAN
PACKAGED GENES
THE MOLECULAR BIOLOGY OF THE GENE
• VIRUSES USE HOST CELL MACHINERY TO REPRODUCE– HOW CAN THIS LEAD TO
DISEASE?– WHY ARE VIRUSES DIFFICULT
TO TREAT WITH ANTI-BIOTICS?– HOW DO WE TREAT VIRUSES?
THE MOLECULAR BIOLOGY OF THE GENE
• VIRUSES– TWO REPRODUCTIVE CYCLES• LYTIC CYCLE
THE MOLECULAR BIOLOGY OF THE GENE
• VIRUSES– TWO REPRODUCTIVE CYCLES• LYSOGENIC CYCLE **CAN LEAD TO A PROPHAGE
THE MOLECULAR BIOLOGY OF THE GENE
• EMERGING VIRUSES– AIDS (HIV)– FLU– EBOLA– HANTA
• HOW DO VIRUSES ARISE?– UNKNOWN!!!!– POSSIBLE THEORIES??
THE MOLECULAR BIOLOGY OF THE GENE
• AIDS– HIV IS A
RETROVIRUS (UNIQUE)
– MAKES DNA FROM AN RNA TEMPLATE
THE MOLECULAR BIOLOGY OF THE GENE
• AIDS– REQUIRES THE USE
OF REVERSETRANSCRIPTASE
– TURNS HOST CELL INTO A“PROVIRUS”
– WHAT IS THEDIFFERENCEBETWEEN AIDS &HIV??
– WHY IS HIV SO DIFFICULT TO TREAT?
THE MOLECULAR BIOLOGY OF THE GENE
• THE STRUCTURE OF DNA CAN TELL US HOW IT COPIES ITSELF AND HOW IT CAN GET CONVERTED INTO PROTEIN; BUT HOW COME IF EVERY CELL HAS THE SAME DNA, THEY CAN ALL LOOK DIFFERENT THAN EACH OTHER? YOU JUST HAVE TO STICK AROUND TO FIND OUT MORE!!
THE MOLECULAR BIOLOGY OF THE GENE
