Name ________________________ Date _________ Period ______
THE NUCLEIC ACIDS and PROTEIN SYNTHESIS NOTES
History of DNA

Griffith’s experiment? INJECTED MICE WITH 2 PNEUMONIA BACTERIA;
R (ROUGH) HARMLESS AND S (SMOOTH) DEADLY; MIXED DEAD S
WITH LIVE R (THOUGHT MOUSE WOULD LIVE) BUT THE MICE DIED
OF PNEUMONIA; PNEUMONIA GENE WAS TRANSFERRED FROM S
TO R BACTERIA; CALLED TRANSFORMATION
CHARGAFF’S RULE --- A GOES
WITH T AND C GOES WITH G

Erwin Chargaff’s contribution?

Watson & Crick contribution?

Rosalind Franklin’s contribution?
BUILT FIRST MODEL OF DNA
(DOUBLE HELIX); WON NOBEL PRIZE
TOOK X-RAY PICTURES OF DNA
PICTURES WHICH WERE STOLEN AND USED BY WATSON
& CRICK
What are nucleic acids?

One of the 4 major organic MACROMOLECULES found in living things


They just have one function – to make PROTEINS.
There are 2 main types of Nucleic Acids.
 DNA
 RNA
Structure of Nucleic Acid (what are they made of?)


A NUCLEIC
ACID is made of many MONOMERS joined together
Nucleic acids are polymers made of many monomers called NUCLEOTIDES.
Parts of a nucleotide
Composed of (1) PHOSPHATE
(PO4); (2) NITROGEN BASE (A, T, C, G,
and U) (3) 5-CARBON SUGAR (RIBOSE or DEOXYRIBOSE)
1
Label a nucleotide and number the carbons on the sugar
PHOSPHATE
BASE
DEOXYRIBOSE SUGAR
DNA


DEOXYRIBONUCLEIC ACID
The structure of DNA is a DOUBLE HELIX (2-stranded spiral)
 “Deoxy” means ONE oxygen has been WITHOUT OXYGEN
 Deoxyribose – the type of 5-carbon SUGAR found in DNA (remember
sugars end in -OSE).
Stands for

Where is DNA found? NUCLEUS

Can DNA leave the nucleus?
NO WHY or WHY NOT? TOO LARGE
2

In the NUCLEUS of the cell, CHROMOSOMES are structures that are
made of DNA wrapped tightly around PROTEINS called HISTONES.
One Strand of DNA

DNA is a DOUBLE stranded molecule.

One strand of DNA has millions of nucleotides.

The backbone or

SIDES of the molecule is alternating SUGARS and
PHOSPHATES.
In the center, the RUNGS are the nitrogenous BASES
Label the DNA strand (phosphate, sugar, nitrogen base)
SUGAR
PHOSPHATE
NITROGEN BASE
3
Four Nitrogenous bases
DNA has 4 different bases




A
T
C
G
- ADENINE
- THYMINE
- CYTOSINE
- GUANINE
Two kinds of bases in DNA


PYRIMIDINES are the single ring bases
PURINES are double ring bases
The pyrimidines

CYTOSINE and THYMINE each have one ring
of carbon and nitrogen atoms
The purines

ADENINE and GUANINE each have 2 rings
of carbon and nitrogen atoms
Chargaff’s Rule:


ADENINE – A and THYMINE - T always join together
CYTOSINE - C and GUANINE - G always join together
Two Stranded DNA
DNA has 2 strands that fit together something like a

The “teeth” or rungs are the NITROGEN
together?
LADDER or ZIPPER.
BASES but why do they stick
HYDROPHOBIC CHARGES
Hydrogen Bonds

The bases attract each other because of
4
HYDROGEN BONDS.

Hydrogen bonds are WEAK but there are millions of them in a single molecule of
DNA.

When making hydrogen bonds, cytosine always pairs up with

Adenine always pairs up with TYHMINE.
GUANINE.
Why do we study DNA?
We study DNA for many reasons:

Its central importance to all life on earth because it codes for all PROTEINS.

Medical benefits such as cures for

Better
DISEASES.
AGRICULTURAL crops.
RNA
RIBONUCLEIC ACID
 Composed of NUCLEOTIDES
 Has only URACIL instead of THYMINE like DNA
 RNA COPIES the codes from DNA and MAKES the protein.
 Adenine bonds with URACIL on RNA
 Is made of ONE strand of nucleotides
 The 3 types are mRNA, rRNA, and tRNA
 RNA is involved in the process of PROTEIN SYNTHESIS

Stands for
RNA Structure

Also has 4 nitrogen bases like DNA

ADENINE
URACIL
CYTOSINE
GUANINE
Has the sugar RIBOSE instead of deoxyribose




DNA Replication



Occurs in the NUCLEUS during the S
or SYNTHESIS stage of interphase.
Makes a(n) EXACT copy of DNA before a cell DIVIDES.
Uses special proteins called ENZYMES with an –ASE ending
5
Steps in DNA Replication
1. The enzyme HELICASE UNCOILS the DNA strands and then weakens the
2.
HYDROGEN bonds between nitrogen bases causing them to separate.
DNA POLYMERASE (enzyme) molecules attach to each STRAND of the DNA
molecule.
3. Y-shaped RELICATION
4.
5.
6.
7.
FORKS forms.
DNA polymerase adds NUCLEOTIDES to the 3’ end of each DNA strand.
The LEADING strand is synthesized in one piece, while the LAGGING strand
is made in pieces called OKAZAKI fragments which must be JOINED or
GLUED together by the enzyme LIGASE.
HELICASE rejoins the two strands making EXACT copies of the DNA.
The two DNAs contain one old and one NEW strand which is known as SEMICONSERVATIVE replication.
Steps in Protein Synthesis
Step 1: Transcription
Location:
NUCLEUS
Purpose: to copy the DNA code (order of bases) onto
mRNA.
Events:
1.) DNA is unwound and HELICASE unzips DNA strand.
2.)
mRNA reads the complementary base and RNA POLYMERASE adds
new nucleotides to the DNA strand.
3.) Editing enzymes clip out INTRONS
4.)
(non-coding sections) and leave
and rejoin EXONS (coding sections)
NEW mRNA is made; it leaves the nucleus to go to ribosome.
6
Step 2: Translation
Location:
RIBOSOMES in the
CYTOPLASM
Purpose: to convert the instructions of
mRNA into amino acids, to make
POLYPEPTIDES or PROTEINS.
Events of translation:
1.) The first three bases of mRNA (codon) join the ribosome. Usually (AUG
2.)
3.)
–
CONSIDERED THE START CODON).
tRNA brings the “amino acid” down to the ribosome. The three bases on tRNA
called an ANTICODON match the complementary bases on mRNA CODON.
Each tRNA has an AMINO ACID, which is determined by its anticodon.
Ex: codon (AUG) Amino Acid - methionine
4.) The amino acids are joined by
PEPTIDE
bonds.
5.) The resulting chain of amino acids is called a
Codons & Anticodons
CODON – segment of 3 bases on mRNA
Start codon: AUG
Stop Codons: UAA,
UAG, UGA
ANTICODON - segment of three bases on tRNA
that is complementary to the
mRNA codon.
7
POLYPEPTIDE .