NUCLEIC ACIDS AND PROTEIN SYNTHESIS
I.
STRUCTURE OF DNA
A.
A NUCLEIC ACID
B.
AN ORGANIC COMPOUND
C.
MADE UP OF REPEATING SUBUNITS CALLED NUCLEOTIDES
1.
EACH DNA MOLECULE (CHROMOSOME) CONSISTS OF 2 LONG CHAINS OF
NUCLEOTIDES
a.
EACH NUCLEOTIDE CONSISTS OF A:
i)
DEOXYRIBOSE SUGAR
ii)
A NITROGEN-CONTAINING BASE (ADENINE, GUANINE, THYMINE
OR CYTOSINE)
ii)
A PHOSPHATE GROUP (PO43-)
b.
D.
E.
THERE ARE FOUR DIFFERENT NITROGEN BASES
i)
ADENINE AND GUANINE ARE PURINES (HAVE 2 RINGS OF CARBON
AND NITROGEN ATOMS)
ii)
THYMIND AND CYTOSINE ARE PYRIMIDINES (HAVE 2 RING OF
CARBON AND NITROGEN ATOMS)
c.
ADENINE ALWAYS PAIRS WITH THYMINE (PURINEPYRIMIDINE)
d.
GUANINE ALWAYS PAIRS WITH CYTOSINE (PURINEPYRIMIDINE)
THE DOUBLE HELIX
1.
DISCOVERED IN 1953 BY JAMES WATSON AND FRANCIS CRICK
2.
DNA = 2 NUCLEOTIDE CHAINS WRAPPED AROUND EACH OTHER TO FORM A
DOUBLE HELIX
3.
ROSALIND FRANKLIN’S XRAY CRYSTALLOGRAPHY CONTRIBUTED TO THEIR
MODEL
a.
PROVIDED AN EXPLANATION FOR HOW COPIES OF DNA COULD BE MADE,
USED BY THE CELLS AND STORED
b.
INDIVIDUAL NUCLEOTIDES ARE CONNECTED BY COVALENT BONDS
BETWEEN THE SUGAR AND PHOSPHATE MOLECULES
c.
THE NITROGEN BASES ARE HELD TOGETHER BY WEAKER HYDROGEN
BONDS
REPLICATION OF DNA
1.
IS THE PROCESS OF COPYING DNA
2.
F.
EACH STRAND SERVES AS A TEMPLATE FOR A NEW STRAND
a.
ENZYMES CALLED HELICASES UNWIND THE DNA STRAND
3.
DNA POLYMERASE ENZYMES ADD THE PROPER COMPLEMENTARY BASE TO
EACH STRAND
ACCURACY AND REPAIR
1.
REPLICATION OCCURS WITH A HIGH DEGREE OF ACCURACY
a.
1 ERROR IN ABOUT EVERY 10,000 PAIRED NUCLEOTIDES
b.
ERRORS ARE CALLED MUTATIONS
i)
MAY HAVE SERIOUS EFFECTS ON CELLS; MOST ARE BAD AND
DON’T STAY IN THE GENE POOL
ii)
PROOFREADING AND REPAIR HELPS KEEP THE ERROR RATE TO
ABOUT ONE ERROR PER 1 BILLION NUCLEOTIDES
c.
SOME ERRORS OCCUR NATURALLY BUT ARE USUALLY REPAIRED
d.
SOME ERRORS ARE CAUSED BY EXTERNAL DAMAGE (CHEMICALS, UV
RADIATION FROM THE SUN)
WHAT YOU SHOULD KNOW AFTER STUDYING THIS SECTION:
1.
WHAT ARE THE MAIN FUNCTIONS OF DNA?
2.
IDENTIFY THE TYPES AND LOCATIONS OF COVALENT BONDS AND HYDROGEN BONDS IN
A DNA MOLECULE.
3.
LIST THE BASE-PAIRING RULES.
4.
WHAT ROLES DO ENZYMES PLAY IN DNA REPLICATION?
5.
HOW WOULD THE DEOXYRIBOSE SUGAR-PHOSPHATE BACKBONE OF NUCLEOTIDE
CHAINS LOOK IF PURINES PAIRED ONLY WITH PURINES AND PYRIMIDINES PAIRED ONLY
WITH PYRIMIDINES?
6.
(DEMONSTRATE UNDERSTANDING) A DNA MOLECULE (LABELED AS A) REPLICATES TO
PRODUCE TWO NEW DNA MOLECULES (LABELED AS B). BOTH OF THE B DNA
MOLECULES THEN REPLICATE TO FORM FOUR NEW DNA MOLECULES LABELED AS C).
ARE ANY NUCLEOTIDE CHAINS FROM A PRESENT IN THE C DNA MOLECULES? EXPLAIN
YOUR ANSWER. IF YOU BELIEVE THE ANSWER IS YES, HOW MANY OF THE A DNA
NUCLEOTIDE CHAINS ARE PRESENT IN THE C DNA MOLECULES?
II.
RNA
A.
RNA STRUCTURE
1.
ALSO A NUCLEIC ACID MADE UP REPEATING NUCLEOTIDES
2.
THE SUGAR MOLECULE IS A RIBOSE SUGAR
3.
CONTAINS URACIL INSTEAD OF THYMINE
4.
IS SINGLE-STRANDED
B.
TYPES OF RNA
1.
MESSENGER RNA (mRNA)
a.
CONSISTS OF A SINGLE, UNCOILED CHAIN
b.
CARRIES GENETIC INFO FROM THE DNA IN THE NUCLEUS TO THE
CYTOPLASM IN A EUKARYOTIC CELL
2.
TRANSFER RNA (tRNA)
a.
CONSISTS OF A SINGLE CHAIN FOLDED INTO A HAIRPIN SHAPE
b.
BINDS TO SPECIFIC AMINO ACIDS
c.
ABOUT 45 DIFFERENT VARIETIES OF TRANSFER RNA
3.
RIBOSOMAL RNA (rRNA)
a.
IS THE MOST ABUNDANT FORM OF RNA
b.
CONSISTS OF RNA NUCLEOTIDES IN A GLOBULAR FORM
i)
C.
JOINED BY PROTEINS, IT MAKES UP THE RIBOSOMES WHERE
PROTEINS ARE MADE
TRANSCRIPTION
1.
IS THE PROCESS BY WHICH DNA INFO IS COPIED TO RNA
2.
THE BASE-PAIRING RULES ARE IDENTICAL, EXCEPT ADENINE PAIRS WITH URACIL
INSTEAD OF THYMINE (BECAUSE RNA DOESN’T USE THYMINE)
3.
THE PRODUCTS ARE CALLED TRANSCRIPTS
a.
INCLUDE ALL THE TYPES OF RNA MOLECULES
b.
EVEN THOUGH mRNA CARRIES THE DNA MESSAGE, ALL TYPES OF RNA
ARE INVOLVED IN THE SYNTHESIS OF PROTEINS
4.
RNA POLYMERASE IS THE ENZYME RESPONSIBLE
a.
SYNTHESIZES RNA COPIES OF A DNA SEQUENCE
b.
ATTACHES NUCLEOTIDES TO THE DNA TEMPLATE
c.
RELEASES THE DNA MOLECULE AND THE NEWLY-FORMED RNA
TRANSCRIPT
WHAT YOU SHOULD KNOW AFTER STUDYING THIS SECTION:
1.
DEFINE TRANSCRIPTION. LIST THE MAIN STEPS INVOLVED IN THIS PROCESS.
2.
IN WHAT WAYS DOES THE STRUCTURE OF RNA DIFFER FROM THAT OF DNA?
3.
DESCRIBE THE STRUCTURE AND FUNCTION OF EACH OF THE THREE TYPES OF RNA.
4.
LIST THREE ROLES OF RNA POLYMERASE IN TRANSCRIPTION.
5.
WHAT BASIC PRINCIPLE ENSURES THAT THE TRANSCRIBED RNA MOLECULE IS CARRYING
THE RIGHT GENETIC MESSAGE?
6.
(DEMONSTRATE UNDERSTANDING) DOES IT MATTER WHICH OF THE SEPARATED DNA
CHAINS IS USED FOR TRANSCRIPTION? DISCUSS YOUR ANSWER.
III.
PROTEIN SYNTHESIS (THE PRODUCTION OR “BUILDING” OF PROTEINS)
A.
PROTEIN STRUCTURE AND COMPOSITION
1.
ARE POLYMERS MADE UP OF ONE OR MORE POLYPEPTIDES
2.
CONSIST OF SPECIFIC AMINO ACID SEQUENCES LINKED BY PEPTIDE BONDS
3.
MAY CONSIST OF HUNDREDS OR THOUSANDS OF THE 20 DIFFERENT AMINO
ACIDS (a.a.) ARRANGED IN A PARTICULAR SEQUENCE
a.
a.a. SEQUENCE DETERMINES HOW THE POLYPEPTIDES TWIST AND FOLD
4.
THE FUNCTION OF THE PROTEIN DEPENDS ON ITS ABILITY TO BIND WITH OTHER
MOLECULES WITHIN A CELL (WHICH DEPENDS ON THE AMINO ACID SEQUENCE)
B.
THE GENETIC CODE
1.
IS A CORRELATION BETWEEN A NUCLEOTIDE SEQUENCE AND AN AMINO ACID
SEQUENCE
a.
THE “CODE” IS CONTAINED IN A 3-AMINO ACID SERIES CALLED A CODON
(IN THE mRNA MOLECULE)
b.
EACH CODON CODES FOR A SPECIFIC AMINO ACID (see p. 194)
C.
D.
TRANSLATION
1.
IS THE PROCESS OF ASSEMBLING POLYPEPTIDESFROM INFORMATION CODED
WITHIN THE mRNA
2.
tRNA HAS A 3-NUCLEOTIDE SEQUENCE CALLED AN ANTICODON
a.
PICKS UP MATCHING AMINO ACIDS FLOATING IN THE CYTOPLASM
b.
FOLLOWS THE SAME BASE-PAIRING RULES AS IN DNA SYNTHESIS OR
TRANSCRIPTION
RIBOSOMES
1.
ARE COMPOSED OF rRNA AND PROTEINS
2.
USUALLY FLOAT FREE IN THE CYTOPLASM AND ARE ATTACHED TO THE
ENDOPLASMIC RETICULUM (FORMING ROUGH ER)
3.
FREE-FLOATING RIBOSOMES TEND TO FORM PROTEINS TO BE USED WITHIN THE
CELL
4.
PROTEINS TO BE USED IN THE CELL MEMBRANE OR EXPORTED FOR USE OUTSIDE
THE CELL ARE FORMED ON RIBOSOMES ATTACHED TO THE ROUGH ER
WHAT YOU SHOULD KNOW AFTER STUDYING THIS SECTION:
1.
COMPARE TRANSCRIPTION WITH TRANSLATION.
2.
DISTINGUISH A CODON FROM AN ANTICODON, AND EXPLAIN THE SIGNIFICANCE OF
EACH.
3.
HOW DOES THE STRUCTURE OF tRNA RELATE TO ITS FUNCTION IN TRANSLATION?
4.
USING THE INFORMATION TABLE IN 10-1 IN YOUR TEXT (OR THE ONE ABOVE), LIST THE
AMINO ACIDS THAT ARE CODED FOR BY THE CODONS AGU, GGG, CCU, AND GUG.
5.
EXPLAIN THE SIGNIFICANCE OF THE START CODON AND THE STOP CODONS. DO ALL
POLYPEPTIDES BEGIN WITH THE AMINO ACID CODED FOR BY THE START CODON?
6.
(DEMONSTRATE KNOWLEDGE) WHAT WOULD TRANSLATION OF THE mRNA
TRANSCRIPT UAACAAGGAGCAUCC PRODUCE?