DNA & PROTEIN SYNTHESIS

CHAPTERS 9 &10

Main Idea

How are proteins made in our bodies?

WHAT MAKES UP DNA?

•IT IS A MOLECULE COMPOSED OF CHEMICAL SUBUNITS CALLED NUCLEOTIDES

NUCLEOTIDES •ARE COMPOSED OF THREE SUBUNITS

•A FIVE CARBON SUGAR•A PHOSPHATE GROUP•A NITROGEN-CONTAINING BASE

NITROGENOUS BASES

•THERE ARE FOUR NITROGENOUS BASES IN DNA

•ADENINE

•CYTOSINE

•THYMINE

•GUANINE

•ADENINE AND GUANINE ARE PURINES

•THEY ARE MADE OF TWO RINGS OF NITROGEN AND CARBON ATOMS

•THYMINE AND CYTOSINE ARE PYRIMIDINES

•THEY CONTAIN A SINGLE RING OF CARBON AND NITROGEN ATOMS

•THE DNA HAS TWO MAIN SIDES

•THE SIDES ARE LIKE THE UPRIGHT PARTS OF A LADDER

•THE SIDES ARE MADE OF THE SUGAR AND THE PHOSPHATE GROUP (ACID)

•THEY ALTERNATE ALONG THE SIDES

•THE RUNGS OF THE LADDER ARE MADE OF NITROGEN BASES

•THERE ARE WEAK HYDROGEN BONDS BETWEEN THE BASE PAIRS

CHARGAFF’S OBSERVATIONS

•THE AMOUNT OF ADENINE EQUALS THE AMOUNT OF THYMINE

•THE AMOUNT OF CYTOSINE EQUALS THE AMOUNT OF GUANINE

•THE AMOUNTS VARY AMONG ORGANISMS

DNA MODEL

•WATSON & CRICK USED THE INFORMATION FROM CHARGAFF AND THE PHOTOGRAPHS FROM WILKINS AND FRANKLIN AND THEIR KNOWLEDGE OF CHEMICAL BONDING TO COME UP WITH A MODEL

BASE-PAIRING RULES

•A PURINE ALWAYS PAIRS WITH A PYRIMIDINE

•THE STRICTNESS OF BASE PAIRING RULES PRODUCES COMPLIMENTARY BASE PAIRS

•ADENINE BONDS WITH THYMINE

•CYTOSINE BONDS WITH GUANINE

•THE ARRANGEMENT OF NUCLEOTIDES IS WHAT MAKES US DIFFERENT

•THE ORDER OF BASES MAKE UP THE GENETIC CODE

•A SINGLE HUMAN CELL CONTAINS 6.6 BILLION BASE PAIRS OF DNA

•THIS WOULD BE 600,000 PRINTED PAGES WITH 500 WORDS EACH

DNA REPLICATION

•DNA MUST MAKE AN IDENTICAL COPY OF ITSELF DURING REPLICATION

•DNA HELICASES (ENZYME) BREAKS THE HYDROGEN BONDS BETWEEN THE NITROGEN BASES

•THE MOLECULE BEGINS TO UNWIND

•ONCE STRANDS ARE SEPARATED, PROTEINS ATTACH TO EACH STRAND TO HOLD THEM APART

•AREAS WHERE THE DOUBLE HELIX SEPARATE ARE CALLED REPLICATION FORKS

DNA POLYMERASE (ENZYME) SWEEPS ALONG BONDING NEW NUCLEOTIDES TO EACH SIDE OF THE PARENT CHAIN

•THE PROCESS CONTINUES UNTIL ALL DNA HAS BEEN COPIED

•TWO NEW IDENTICAL DNA MOLECULES ARE FORMED

•DNA POLYMERASE “PROOF-READS” THE STRAND

•NUCLEOTIDES ARE ADDED AND INCORRECT ONES ARE CORRECTED

REPLICATION RATE

•EACH CHROMOSOME IS REPLICATED IN 100 SECTIONS WITH 100,000 NUCLEOTIDES

•WITH MULTIPLE REPLICATION FORKS, THIS TAKES ABOUT 8 HOURS IN A HUMAN

RNA•A NUCLEIC ACID FOUND IN THE NUCLEUS AND CYTOPLASM

•COMPOSED OF A SINGLE CHAIN OF NUCLEOTIDES

•CONTAINS RIBOSE

•CONTAINS URACIL INSTEAD OF THYMINE

TRANSCRIPTION•THE INSTRUCTIONS FOR

MAKING A PROTEIN ARE TRANSFERRED FROM A GENE TO AN RNA MOLECULE

•WE CALL THIS PROCESS TRANSCRIPTION

•IT INVOLVES THE FORMATION OF RNA

•RNA POLYMERASE BONDS TO THE START SIGNAL OF DNA

•THE DOUBLE HELIX UNWINDS

•RNA POLYMERASE ADDS AND LINKS COMPLEMENTARY NUCLEOTIDES TO THE DNA TEMPLATE WITH COVALENT BONDS

•RNA MATCHES UP UNTIL A STOP SIGNAL IS REACHED

•THE SINGLE-STRANDED MOLECULE BREAKS AWAY FROM THE DNA CHAIN

•THE DOUBLE HELIX REFORMS

•THE RNA FORMED IS CALLED MESSENGER RNA (mRNA)

•mRNA CODES FOR PROTEIN PRODUCTION

•THE mRNA LEAVES THE NUCLEUS AND GOES TO THE RIBOSOME

• http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/transcription.htm

CODING FOR PROTEINS

•3 BASES IN A ROW CODES FOR A PARTICULAR AMINO ACID (CODON)

•MORE THAN ONE SET OF CODES CAN REPRESENT AN AMINO ACID

•THERE ARE STOP CODONS THAT DO NOT CODE FOR AN AMINO ACID

•THEY READ ONLY IN ONE DIRECTION

•THE CODE IS UNIVERSAL FROM ORGANISM TO ORGANISM

•INTRONS ARE LONG SEGMENTS OF NUCLEOTIDES THAT HAVE NO CODING INFORMATION

•EXONS ARE THE PORTIONS OF THE GENES THAT ARE TRANSLATED INTO PROTEINS

•AFTER TRANSCRIPTION, THE INTRONS ARE CUT OUT

•THE EXONS ARE STITCHED BACK TOGETHER AND TRANSLATED

THE GENETIC CODE

•IN 1961 MARSHALL NIRENBERG DECIPHERED THE CODE FOR PHENYLALANINE

•VARIOUS SCIENTISTS DECIPHERED THE REST OF THE CODE

TRANSLATION•THE PROCESS BY WHICH THE INSTRUCTIONS ON THE RNA MOLECULE ARE READ AND AN AMINO ACID CHAIN (PROTEIN) IS PRODUCED

•TRANSFER RNA (tRNA) TEMPORARILY CARRIES A SPECIFIC AMINO ACID

•PROTEINS ARE MADE OF CHAINS OF AMINO ACIDS

•AN ANTICODON IS A THREE-NUCLEOTIDE SEQUENCE ON A tRNA THAT IS COMPLEMENTARY TO AN mRNA CODON

•RIBOSOMAL RNA MOLECULES AND PROTEINS MAKE UP RIBOSOMES

•THE CYTOPLASM CONTAINS THOUSANDS OF RIBOSOMES

•EACH RIBOSOME TEMPORARILY HOLDS ONE mRNA AND TWO tRNA MOLECULES

STEP 1

mRNA WITH THE START CODON “AUG” BINDS TO THE ANTICODON OF TRNA CONTAINING METHIONINE

STEP 2

THE tRNA WITH THE COMPLEMENTARY ANTICODON BONDS TO THE NEXT CODON.

STEP 3 ENZYMES FORM A PEPTIDE BOND BETWEEN THE ADJACENT AMINO ACIDS

STEP 4THE MOLECULES THEN MOVE

AS A UNIT AND THE NEW CODON RECEIVES THE NEXT TRNA AND ITS AMINO ACID

STEP 5THE AMINO ACID BONDS TO

THE GROWING PROTEIN CHAIN

•STEPS 2 THOUGH 5 CONTINUES UNTIL A “STOP” CODON IS REACHED

MUTATIONS•MUTATIONS ARE MISTAKES IN THE REPLICATION OF GENETIC MATERIAL

•DAUGHTER CELLS CONTAIN DIFFERENT MATERIAL FROM THAT OF ITS PARENT

GENE REARRANGEMENTS

•CAUSED WHEN AN ENTIRE GENE IS MOVED TO A NEW LOCATION

GENE ALTERATIONS

•USUALLY RESULT IN THE PLACEMENT OF THE WRONG AMINO ACID DURING PROTEIN ASSEMBLY

•DELETION - A NUCLEOTIDE IS LEFT OUT ALTERING THE AMINO ACID SEQUENCE

•INSERTION - AN EXTRA NUCLEOTIDE IS ADDED ALTERING THE AMINO ACID SEQUENCE

•POINT MUTATION - ONE NUCLEOTIDE IS SUBSTITUTED FOR ANOTHER RESULTING IN ONE AMINO ACID CHANGE