1. Unit 4A DNA Structure and replication
Click the star for the DNA Structure Video!!
Unit 4A DNA Structure and replication

2. DNA (Deoxyribonucleic Acid)
A nucleic acid
Made up of nucleotides

3. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, T, C, or G)
CH2 O C1 C4 C3 C2 5
5-C Sugar
(deoxyribose)

4. DNA is a molecule that must sometimes be copied.
When/why does the DNA need to be copied?

5. What do pyrimidines have in common? __________________
How many different types of nitrogenous bases are found in DNA? __________________
What do pyrimidines have in common? __________________
What do purines have in common? _____________________
If each nucleotide contains 1 nitrogen base, how many different types of DNA nucleotides can be formed? ______
NOTE: Another type of nucleotide, Uracil (U), will replace the Thymine nucleotide in RNA molecules.
4 total in 2 categories

6. Here is an example of a nucleotide:
We normally draw a nucleotide using symbols/letters to represent the parts.
What does the "A" stand for?
What other letters could be used in that position?___________
What does the "S" stand for?___________________________
What does the "P" stand for?___________________________ A S

7. Notice that each nucleotide bonds with a nucleotide above and below it
Notice that each nucleotide bonds with a nucleotide above and below it. This forms a strand of DNA.
The two strands run in opposite directions. This is called antiparallel.
The two strands are then twisted into a spiral shaped, double stranded structure called a double helix.
Phosphate Group P

8. The bonds that hold the nucleotides in a strand of DNA together are covalent bonds (highlight)
The bonds in between the nitrogenous bases that connect the two strand are hydrogen bonds
(draw in color)
Phosphate Group P

9. Circle a nucleotide on the drawing to the left
What does each nucleotide have in common?
How do nucleotides differ from each other?
How many strands make up a molecule of DNA? ____
Adenine (A) pairs with _________
Cytosine (C) pairs with _________
Phosphate Group P

10. If the sequence of nucleotides in one strand of a DNA molecule is T-A-C-G-G-T-C-A-A, what would be the complementary base pairs on the other strand? ______________________________

11. Who discovered the structure of DNA?
Erwin Chargaff (1950)
Determined that the percent of A was about equal to the percent of T in any DNA molecule.
Likewise, the percent of C was about equal to the percent of G.
This is known as Chargaff’s Rule
Why did he see this consistency?

12. Using Chargaff’s Rule Source of DNA A T C G Human 30
Percentage of Bases in Human DNA
Source of DNA A T C G
Human 30

13. Rosalind Franklin (1952) Used X ray diffraction
Her image hinted that DNA was two stranded and in a helical shape

14. James Watson and Frances Crick (1953)
Won the Nobel Prize for determining the structure of DNA
Used info from Chargaff and Franklin
James Watson
Francis Crick

15. Human Genome Project (1990-2003)
Genome: the entire set of genetic information that makes up the DNA of an organism
Completed in 2003, the Human Genome Project (HGP) was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health.

16. Goals of the Human Genome Project
identify all of the approximately 20,000-25,000 genes in human DNA
determine the sequence of the 3 billion base pairs that make up human DNA
store this information in databases for use by scientists everywhere
address the ethical, legal, and social issues (ELSI) that may arise from the project.

17. DNA Sequencing
the laboratory technique used to determine the exact sequence of A’s, T’s, C’s, and G’s in an individuals entire genome.

18. Human Genome Project
What were three surprises for scientists after they sequenced the human genome?
Fewer genes are in the human genome than once thought (20,000-25,000)
Only 2% of the genome is actually genes
Hasn’t helped to cure all diseases; DNA is not the only thing that dictates illness
What were two good things that came from sequencing the human genome?
New fields in biology were created to study genes (ex: genomics)
Has given clues to our evolutionary history. (We still have the gene for a tail even though it is not used!)

19. Forms of DNA and How it is Organized
Where is DNA located?
Prokaryotic cytoplasm
Eukaryotic nucleus
Every body cell has a complete copy of DNA

20. Forms of DNA Prokaryotic- 1 circular loop
Eukaryotic- multiple linear (straight) strands found in 2 forms depending on the situation.
1. Chromosomes
2. Chromatin

21. Forms of DNA (cont.)
1. Chromosome: tightly packed, or “condensed” strands of DNA. DNA forms these structures when the cell is dividing. Usually shown as an X-shape or doubled chromosome.
Histones - Proteins which act like spools for thread. DNA is wound around the histones.

22. Karyotypes
A picture of all of the chromosomes from one cell of an organism.
How many total chromosomes are in the karyotype?
These chromosomes are from a _________________.

23. Number of Chromosomes in each cell.
Every species of eukaryotic organisms have a specific number of chromosomes in each cell:
Organism
Number of Chromosomes in each cell.
goldfish 94
chicken 78
horse 64
sand dollar 52
chimpanzee 48
dog
human
brown bat 44
corn plant 20
housefly 12
fruit fly 8

24. How many chromosomes do humans have? _______ 
How long is the DNA in one human cell?__________
How does that much DNA fit into a cell?
1-3 meters

25. Forms of DNA (cont.)
2. Chromatin - loosely packed, or “working” form of DNA. The strands are loose and exposed so that the code or protein “recipes” can be read and proteins can be synthesized.

28. Why have 2 different forms of DNA in your cells?
Chromosomes are useful because 
they are condensed and easy to sort and move when cells are dividing to make new cells.
Chromatin is useful because  
it is loose/open so genes can be read to make proteins (like an open book)
Why is the number of chromosomes different for different organisms?
Chromosomes are different sizes
Chromosomes have different numbers of genes
3) Organisms need different proteins and amounts for different functions.

29. DNA Replication
DNA must be copied before cell division so that any new cells will have an IDENTICAL copy of the DNA from the original cell.

30. Steps in DNA replication:
1. The enzyme DNA helicase unwinds and unzips the double helix and the 2 DNA strands are separated between the complementary nitrogenous bases.

31. 2. The enzyme DNA polymerase helps to link free floating DNA nucleotides with the complementary nitrogenous bases on each of the two strands

32. 3.) Covalent bonds join the nucleotides above and below each other on the new strands. And, the hydrogen bonds are formed between the complementary nitrogenous bases (from one strand to another).

33. 4.) Each new DNA strand formed contains ONE parent (original) strand and ONE daughter (new) strand.

34. Summary of Replication
DNA double helix splits into two strands
Each strand becomes a template for new nucleotides to bind
Base pairing allows for the correct sequence to be created on the new “complementary” strand
Replication

35. If an error is made during replication it is called a mutation.