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
• RNA
– DEOXYRIBONUCLEIC
ACID
• DEOXYRIBOSE ??
• NUCLEIC  ??
• ACID  ??
– 4 TYPES OF BASES IN
DNA (2 GROUPS)
• PURINES (2 RINGS)
– ADENINE / GUANINE
• PYRIMIDINES (1 RING)
– CYTOSINE / THYMINE
– 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 ALWAYS
EQUAL)
– 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 ARE
ORIENTED 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 TOGETHER
INTO 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 AVAILABLE
IN THE CELL FROM
DIGESTED FOOD
– tRNA PICKS UP THE
APPROPRIATE
AMINO ACID AND
BRINGS IT TO THE
MATCHING 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 REVERSE
TRANSCRIPTASE
– TURNS HOST
CELL INTO A
“PROVIRUS”
– WHAT IS THE
DIFFERENCE
BETWEEN 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