1. DNA

2. BEGIN THE CONSTRUCTION OF YOUR DNA MODEL…
As you work, make note of any patterns or trends you can see structurally or chemically; list at least 5.
Begin model here on the back of coloring worksheet 1. 2. 3. 4. 5.

3. EUKARYOTIC CELLS E D C B A A: DOUBLE HELIX
COILS AROUND PROTEINS CALLED
B: HISTONES
HISTONES COIL MOLECULE INTO
C: SUPER COILS
SUPER COILS WIND UP TO FORM
D: CHROMOSOMES
CHROMOSOMES IN
NUCLEUS FORM
E: CHROMATIN E D C B A

4. PRIMARY FUNCTION STORES GENETIC INFORMATION IN BASE CODE SEQUENCES
TRANSMITS GENETIC CODE FROM GENERATION
TO GENERATION
CHEMICALLY CONTROLS THE SYNTHESIS OF ALL PROTEINS
CHEMICAL PROCESSES
PHYSICAL STRUCTURES

5. DeoxyriboNucleic Acid
Made of repeating monomers: NUCLEOTIDES
5-carbon sugar
Phosphate functional group
1 of 4 Nitrogen containing bases
Adenine
Cytosine
Guanine
Thymine

6. NITROGEN BASES PURINES PYRIMIDINES BASES WITH TWO CARBON RINGS
BASES WITH ONE CARBON RING Uracil only found in RNA

7. ONE PURINE BONDS WITH ONE PYRIMIDINE FORMING A COMPLIMENTARY BASE PAIR
BASE PAIR BONDING
ONE PURINE BONDS WITH ONE PYRIMIDINE FORMING A COMPLIMENTARY BASE PAIR
ADENINE ALWAYS BONDS
WITH THYMINE FORMING
A-T OR T-A
GUANINE ALWAYS BONDS
WITH CYTOSINE FORMING
G-C OR C-G

8. The ANTIPARALLEL structure of the DNA molecule….5’ 3’ 3’ 5’

9. THAT’S INTERESTING! NATURE LOVES EFFICIENCY!
DNA LOOKS LIKE A LADDER
SUGAR AND PO4 MAKES THE “FRAME”
BASES FORM THE “RUNGS”
ONE SIDE OF MOLECULE MUST “FLIP” IN ORDER FOR HYDROGEN BONDS TO FORM BETWEEN BASES, THE SIDES ARE ANTIPARALLEL
ALL BASE PAIRS, NO MATTER THE ORDER, HAVE THE SAME STRUCTURAL SHAPE(isometric) THEY STACK ON TOP OF EACH OTHER THEN TWIST FORMING THE CHARACTERISTIC DOUBLE HELIX
SINCE A ALWAYS BONDS WITH T, AND C WITH G, THEIR AMOUNTS MUST BE EQUAL TO EACH OTHER(Chargaff Principle)
If 40% of the molecule is A-T, then how much of each base makes up the molecule?
NATURE LOVES EFFICIENCY!
DNA’S STRUCTURE ALLOWS THE MOLECULE TO
BE REPLICATED QUICKLY
CODE THE SYNTHESIS OF ALL PROTEINS
PASS THE GENETIC CODE TO FUTURE GENERATIONS
THE SAME WAY EVERY SINGLE TIME in ALL ORGANISMS.
20% A & 20% T, 60% C-G with 30% C & 30% G

10. Who figured all this out?
Rosalind Franklin and Maurice Wilkins
Maurice Wilkins and Rosalind Franklin were the first to obtain very good x-ray diffraction images of the DNA .
At the time, little was known about the structure of DNA; though their x-ray photos didn't show the structure of the DNA, there were patterns on those images that could be used to determine the position of DNA’s nucleotides.
From these photos, Franklin determined that the nitrogen bases were ‘inside’ the structure and molecule must be long, thin and possibly a helix

11. James Watson and Francis Crick
Using the X-ray diffraction photos of DNA taken by Wilkins and Franklin, they also saw that they showed an ‘X’ shape...which does illustrate the signature of a helix.
In April of 1953, using this information, together with the base pair’s isometric structure, they identified DNA’s double helix configuration Watson: basepairing

12. DNA REPLICATION

13. DNA Replication - Occurs during S phase of interphase
One strand of DNA has all of the information needed to construct the other strand through the mechanism of complimentary base pairing: A-T, T-A, C-G, G-C.
During DNA replication, the DNA molecule is used to produce two new complementary strands. Each strand of the double helix serves as a template for each new strand.
*Even though the DNA in
eukaryotes is linear
and circular in prokaryotes;
the replication process is the
same for both.

14. OLD REPLICATION MODELS
“LADDER” MODEL
DNA molecule “pried” apart
Bases added
Then sugar and
phosphate added
to hold bases in
place

15. “ZIPPER” MODEL Enzymes “unzip” molecule down entire length
Enzymes attach to each side
Another enzyme attaches complimentary bases
New strands build simultaneously in same direction until duplicate strands are formed

16. The ANTIPARALLEL structure of the molecule makes those models of
replication impossible … 5’ 3’ 3’ 5’
That’s because polymerase enzymes can only work
in one direction placing nucleotides “right-side up” 5’ to 3’

17. DNA Replication Step 3: DNA polymerase III attaches to
Step 1: A portion of the parental DNA double helix is unwound and separated by the enzyme DNA helicase. This occurs in several places along the strand at replication bubbles
Step 2: Proteins attach to the outside of the replication fork to stabilize the molecule
Step 3: DNA polymerase III attaches to
the leading(3’-5’) and lagging(5’-3’)
strands with the help of an enzyme
primase and an RNA primer.

18. Step 4: DNA polymerase III begins synthesis of the leading strand
Step 4: DNA polymerase III begins synthesis of the leading strand. As the nucleotides are placed right side up…this strand is replicated continuously.

19. Step 5: The lagging strand must be assembled discontinuously in segments called Okazaki fragments because DNA Polymerase can only place nucleotides right side up and in one direction.
Once a section is complete, a new enzyme
DNA polymerase I removes the RNA primer and the two sides of the molecule are bonded together by DNA ligase.
DNA ligase also ‘proof-reads’
the new strands and corrects
errors

20. ‘Semiconservative’ Replication
OLD NEW NEW OLD
DNA replication is “semiconservative”.
This means that one-half of each new molecule of DNA is old; one-half new.