THE MOLECULAR BIOLOGY OF THE GENE. EXPERIMENTS HAVE SHOWN THAT DNA IS THE GENETIC MATERIAL – DNA...

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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?)

• GRIFFITH’S EXPERIMENT

• 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

• 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)

• HERSHEY AND CHASE EXPERIMENT

• 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

• 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

• 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

• STRUCTURE DENOTES ____________– THEREFORE LEARNING THE STRUCTURE OF DNA

BECAME OF EXTREME IMPORTANCE

• 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

• 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

• DISCOVERED STRUCTURE SUGGESTED AN EXPLANATION OF DNA REPLICATION

• SPECIFIC BASE PAIRING IS HOW DNA IS COPIED

• WHILE THE CONCEPT OF REPLICATION IS SIMPLE, ACTUAL PROCESS IS COMPLEX

• DNA REPLICATION: A CLOSER LOOK– REPLICATION BEGINS AT SPECIFICS POINTS CALLED

ORIGINS OF REPLICATION (O.R.’S)

• 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!!

• DNA REPLICATION: A CLOSER LOOK– ENZYMES OF IMPORTANCE• DNA POLYMERASE

– ENZYME THAT ADDS NUCLEOTIDES TO GROW DAUGHTER STRAND

• 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

• 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 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!!

• 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

• 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

• 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

• 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

• TRANSCRIPTION : A CLOSER LOOK– OCCURS IN 3 STAGES• INITIATION• ELONGATION• TERMINATION

• TRANSCRIPTION : A CLOSER LOOK– INITIATION• ????

• TRANSCRIPTION : A CLOSER LOOK– ELONGATION• ????

• TRANSCRIPTION : A CLOSER LOOK– TERMINATION• ?????• TERMINATOR SPECIFIC SEQUENCE ON DNA THAT

SIGNALS THE RNA POLYMERASE TO DETACH

• 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

• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC mRNA PROCESSING• ONE TYPE OF PROCESSING IS ADDING A “CAP” AND

“TAIL”• WHY DOES THIS HAPPEN??

• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC mRNA PROCESSING

• SECOND TYPE OF PROCESSING IS REMOVAL OF NON-CODING REGIONS= RNA SPLICING

• TWO TYPES– EXONS

» ???– INTRONS

» ???

• TRANSCRIPTION : A CLOSER LOOK– EUKARYOTIC mRNA PROCESSING• RNA SPLICING

– REMOVAL OF INTRONS TO PRODUCE FINAL mRNA PRODUCT– SPLICEOSOMES (A.KA. snRNP’S = PRONOUNCED SNURPS)

• 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

• 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

• TRANSLATION : A CLOSER LOOK– CODONS• THREE NITROGENOUS

BASE “WORD” THAT SPECIFIES A PARTICULAR AMINO ACID

• 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)

• TRANSLATION : A CLOSER LOOK

• TRANSLATION : A CLOSER LOOK– TRANSLATION CAN BE DIVIDED INTO THREE

STAGES• INITIATION• ELONGATION• TERMINATION

• TRANSLATION : A CLOSER LOOK– INITIATION

• 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

• TRANSLATION : A CLOSER LOOK– ELONGATION• ADDS NUCLEOTIDES

TO POLYPEPTIDE CHAIN• 3 STEPS TO

ELONGATION– CODON

RECOGNITION– PEPTIDE BOND

FORMATION– TRANSLOCATION

• TRANSLATION : A CLOSER LOOK– TERMINATION• ELONGATION CONTINUES UNTIL A “STOP” CODON

ENTERS THE “A” SITE

• REVIEW

• 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

• SUBSTITUTIONS– A BASE SUBSITUTION

MAY CHANGE AN AMINO ACIDIN A POLYPEPTIDE, CHANGING THE PROTEIN

– “WOBBLE” HYPOTHESIS??

• INSERTIONS AND DELETIONS– CAN BE MORE SEVERE– THEY CHANGE THE

“READING FRAME”

• 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

• VIRUSES– IN A SENSE, VIRUSES ARE NOTHING MORE THAN

PACKAGED GENES

• 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?

• VIRUSES– TWO REPRODUCTIVE CYCLES• LYTIC CYCLE

• VIRUSES– TWO REPRODUCTIVE CYCLES• LYSOGENIC CYCLE **CAN LEAD TO A PROPHAGE

• EMERGING VIRUSES– AIDS (HIV)– FLU– EBOLA– HANTA

• HOW DO VIRUSES ARISE?– UNKNOWN!!!!– POSSIBLE THEORIES??

• AIDS– HIV IS A

RETROVIRUS (UNIQUE)

– MAKES DNA FROM AN RNA TEMPLATE

• 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 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. EXPERIMENTS HAVE SHOWN THAT DNA IS THE GENETIC MATERIAL – DNA...

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