LECTURE 21

DNA - DEOXYRIBONUCLEIC ACID

  1. DNA IS THE MOLECULAR BLUEPRINT; A RECORD OF PRECISE INSTRUCTIONS THAT DETERMINE WHAT INHERITABLE TRAITS A CELL CAN MANUFACTURE (STORAGE OF GENETIC INFORMATION)

2.  DNA IS "HERITABLE". IT’S MESSAGE CAN BE
    PASSED FROM GENERATION TO GENERATION

3.  DNA’S MESSAGE CAN BE EXPRESSED THE GENETIC
    CODE IS READ OR TRANSCRIBED

THE TRANSCRIBED CODE IS TRANSLATED TO BE EXPRESSED AS PROTEINS

DNA ---> mRNA ---> PROTEIN

DNA COMPOSITION

NUCLEOTIDES - ENCODE INFORMATION BY VIRTUE OF THEIR SEQUENCE

1. MADE UP OF:
       a. 5-CARBON SUGAR
            1. DEOXYRIBOSE
       b. A PHOSPHATE GROUP
       c. NITROGENOUS BASE
              1. ARE DIVIDED INTO PURINES AND
         PYRIMIDINES
                      a. PURINES ARE ADENINE AND GUANINE
                      b. PYRIMIDINES ARE CYTOSINE AND THYMINE
              2. PURINES BOND TO PYRIMIDINES (BASE
         PAIRING) MAKING A TWO STRANDED DNA
                      a. ADENINE PAIRS WITH THYMINE
                      b. CYTOSINE PAIRS WITH GUANINE

2. HAS A SUGAR-PHOSPHATE BACKBONE
       a. THE PHOSPHATE OF ONE OF THE NUCLEOTIDES
      BONDS
WITH THE SUGAR OF AN ADJOINING
      NUCLEOTIDE WITH A PHOSPHATE BOND

3. TWO STRANDS OF DNA FORM AND MAKE A LADDER.
       a. THE LADDER TWISTS TO FORM A DOUBLE HELIX

DNA REPLICATION

1. DNA DOUBLE HELIX UNWINDS
2. DNA STRANDS SEPARATE EXPOSING
THE NITROGENOUS
   BASES
3. DNA STRANDS ACT AS TEMPLATES
FOR THE NEW
   STRANDS OF DNA
       a. DNA POLYMERASE ASSEMBLES FREE NUCLEOTIDES
      AND ALIGNS
THEM WITH THE TEMPLATE STRAND
       b. DNA REPLICATION IS SEMI-CONSERVATIVE
              1. EACH NEW DOUBLE HELIX CONSISTS OF ONE
         NEW STRAND AND ONE OLD STRAND

GENE EXPRESSION

A GENE DICTATES THE FORMATION OF A SINGLE TYPE OF PROTEIN

"ONE GENE-ONE PROTEIN" HYPOTHESIS

THE ORDER OF NUCLEOTIDES IN DNA DETERMINES THE SEQUENCE OF AMINO ACIDS IN A PROTEIN WHICH DETERMINES THE STRUCTURE OF THE PROTEIN

STRUCTURE

PRIMARY - SEQUENCE OF AMINO ACIDS

SECONDARY - THE FOLDING OF THE PRIMARY STRUCTURE

TERTIARY - THE THREE- DIMENSIONAL STRUCTURE

QUATERNARY - THE ARRANGEMENT OF TERTIARY
             STRUCTURES

PROTEIN SYNTHESIS

1. INFORMATION MUST GET FROM THE NUCLEUS TO THE
   RIBOSOME (TRANSCRIPTION)
       a. THE DNA GETS TRANSCRIBED INTO RNA
              1. THE DNA MOLECULE UNWINDS SO IT CAN BE
         TRANSCRIBED
              2. ONLY ONE STRAND OF THE TWO DNA STRANDS
         IS READ
                       a. THE READ STRAND IS THE "SENSE STRAND"
                       b. THE UNREAD STRAND IS THE "NONSENSE
            STRAND"
              3. THE SENSE STRAND IS USED TO MAKE A
         STRAND OF mRNA
                       a. mRNA = MESSENGER RNA

RNA = RIBONUCLEIC ACID

1. DIFFERS FROM DNA IN THREE WAYS
       a. NUCLEOTIDES IN RNA CONTAIN RIBOSE FOR THE
              SUGAR
       b. CONTAIN FOUR DISTINCT NUCLEOTIDES, ADENINE,
               CYTOSINE, GUANINE AND URASIL
              1. URASIL (IN RNA) PAIRS WITH ADENINE IN
         THE DNA
       c. RNA IS SINGLE STRANDED

2. INFORMATION MUST GET READ AT THE RIBOSOME
   (TRANSLATION)
      a. THE STRAND OF mRNA EXITS THE NUCLEUS AND
     GOES TO A RIBOSOME FOR TRANSLATION

THE mRNA IS TRANSLATED IN GROUPS OF THREE CALLED CODONS THAT CODE FOR ONE AMINO ACID
     a. THERE ARE 20 AMINO ACIDS
     b. THERE ARE 64 DIFFERENT CODONS

LECTURE 22

TRANSLATION - FROM mRNA TO PROTEINS

mRNA IS A LINEAR SEQUENCE OF NUCLEOTIDES

NUCLEOTIDE BASES ARE RECOGNIZED THREE AT A TIME (TRIPLETS)

THE THREE BASE TRIPLETS ARE CALLED CODONS

EACH CODON CODES FOR A DIFFERENT AMINO ACID

THERE ARE 20 AMINO ACIDS

THERE ARE 64 CODONS

THIS MEANS THAT THERE IS  MORE THAN ONE CODON FOR
EACH AMINO ACID

AUG IS THE START CODON

UGA IS A STOP CODON (UAA &

UAG ARE ALSO STOP CODONS)

THE 64 DIFFERENT CODONS ARE THE GENETIC CODE

ROLES OF tRNA AND rRNA

tRNA = TRANSFER RNA

tRNA CARRIES THE AMINO ACID AND HAS AN ANTICODON

THE ANTICODON PAIRS WITH THE CODON

THE CODON AND ANTICODON PAIR UP LIKE COMPLIMENTARY STRANDS OF DNA

A PAIRS WITH U

C PAIRS WITH G

THE FIRST TWO BASES OF A CODON PAIR UP BUT THE THIRD IS NOT THAT SPECIFIC.

CCU, CCC, CCA, AND CCG ALL SPECIFY PROLINE SO, IT DOESN’T MATTER WHAT PAIRS UP WITH THE THIRD BASE

THIS IS CALLED "WOBBLE"

tRNA’S AND mRNA’S INTERACT AT THE RIBOSOME

RIBOSOMES HAVE TWO SUBUNITS AND ARE ASSEMBLED IN THE NUCLEUS FROM rRNA AND PROTEINS AND TRANSPORTED INTO THE CYTOPLASM SEPARATELY

ONCE IN THE CYTOPLASM THE TWO SUBUNITS RECOMBINE TO FORM A FUNCTIONAL UNIT

STAGES OF TRANSLATION

TRANSLATION OCCURS IN THE CYTOPLASM AND IS MADE UP OF THREE STAGES

STAGE 1 - INITIATION

1. THE INITIATOR tRNA BINDS WITH THE SMALL
   RIBOSOMAL SUBUNIT

2. THE START CODON (AUG) OF A mRNA BINDS TO THE
   SAME
SMALL RIBOSOMAL SUBUNIT

3. THE LARGE RIBOSOMAL SUBUNIT BINDS TO THE SMALL
   SUBUNIT

STAGE 2 - ELONGATION

1. mRNA STRAND PASSES BETWEEN THE TWO RIBOSOMAL
   SUBUNITS

2. AMINO ACIDS ARE JOINED TOGETHER WITH PEPTIDE
   BONDS

STAGE 3 - TERMINATION

1. THE STOP CODON IS REACHED

2. THE mRNA AND POLYPEPTIDE CHAINS FALL OF THE
   RIBOSOME

THE mRNA CAN BE READ AGAIN AND AGAIN TO MAKE MORE PROTEIN

WHEN THERE IS MORE THAN ONE RIBOSOME ON A mRNA IT IS CALLED A POLYSOME

MUTATION AND PROTEIN SYNTHESIS

WHEN AN EXTRA BASE IS INSERTED IN THE DNA SEQUENCE OR IF ONE IS DELETED, THE AMINO ACIDS MADE WILL BE DIFFERENT - THIS IS A GENE MUTATION

MUTATIONS MAY BE CAUSED BY:

1. EXPOSURE TO MUTAGENS
       a. ULTRAVIOLET LIGHT
       b. IONIZING RADIATION
       c. CHEMICALS IN CIGARETTE SMOKE

2. MAY BE SPONTANEOUS
       a. MISMATCHED BASE PAIRS

3. FRAMESHIFT MUTATIONS
       a. HAPPEN WHEN BASES ARE ADDED OR DELETED

4. JUMPING GENES (TRANSPOSONS)
       a. WHOLE PIECES OF DNA CAN MOVE WITHIN A
      CHROMOSOME OR BETWEEN CHROMOSOMES

SOME MUTATIONS ARE LETHAL

LECTURE 23

DNA REPLICATION

TWO NUCLEOTIDE STRANDS ARE HELD TOGETHER BY HYDROGEN BONDS

ENZYMES BREAK THESE HYDROGEN BONDS BETWEEN THE STRANDS

THE STRANDS SEPARATE AND FREE NUCLEOTIDES ARE BROUGHT IN

ENZYMES USED:

DNA POLYMERASE - BRINGS IN NUCLEOTIDES

DNA LIGASE - JOINS THE NUCLEOTIDES

DNA POLYMERASES ALSO READ THE NEW STRAND OF DNA TO INSURE THAT IT COMPLIMENTS THE OLD STRAND

ANY ERRORS ARE CUT OUT AND THE PROPER BASES BROUGHT IN TO FIX THE ERROR

ONE STRAND OF DNA IS CONTINUOUSLY READ WHILE THE OTHER IS DISCONTINUOUSLY READ

WHY?

THE DNA STRANDS ARE JOINED TOGETHER IN A 5’ TO 3’ DIRECTION

WHEN THE STRANDS UNZIP, ONE STRAND HAS A 5’ END EXPOSED AND THE OTHER HAS A 3’ END EXPOSED

5’ A C G T T A C C G A G G T 3’

3’ 5’

 

TRANSCRIPTION

DONE IN A 5’ TO 3’ DIRECTION

ONLY A SELECTED SECTION ON ONE STRAND OF DNA IS USED FOR TRANSCRIPTION

RNA POLYMERASES ADD THE BASES IN RNA SYNTHESIS

TRANSCRIPTION ONLY RESULTS IN A SINGLE STRAND OF RNA BEING PRODUCED

THE STRAND GETS MODIFIED BEFORE IT IS USED FOR TRANSLATION

MODIFICATIONS

1. A CAP IS ATTACHED TO THE 5’ END
       a. THE CAP CONSISTS OF A NUCLEOTIDE WITH A
      METHLY GROUP AND PHOSPHATE GROUP ATTACHED
       b. AIDS IN ATTACHMENT TO THE RIBOSOME

2. A TAIL OF 100-200 ADENINE-CONTAINING
   NUCLEOTIDES ADDED
TO THE 3’ END (POLY-A TAIL)
       a. IS DIGESTED SLOWLY BY ENZYMES THAT WILL
      EVENTUALLY DIGEST THE mRNA

EXAMPLE: mRNA

5’A U G C C U A A G G G C G C C U G A 3’

. .

NUCLEOTIDE SEQUENCE

 

AMINO ACID SEQUENCE:

 

tRNA