1. Structure and Replication
DNA

2. Central Dogma DNA  RNA  Protein
DNA is the molecule of heredity that passes from parents to offspring
DNA contains the instructions for building RNA and proteins (which make up the structure of the body and carry out most of its functions)
What are the functions of proteins? What are their monomers? Their elements?

3. HISTORY OF DNA
In 1952, Rosalind Franklin used X-rays to photograph DNA molecules, but she could not interpret the photograph.
Franklin’s photograph helped James Watson and Francis Crick figure out the structure of DNA in 1953.
The structure is called a double helix, or twisted ladder.

4. HISTORY OF DNA

5. THE STRUCTURE OF DNA
DNA is made of nucleic acids, which are made up of the subunit nucleotides
Consists of a phosphate group, a 5 carbon sugar (deoxyribose), and one of four nitrogenous bases

6. THE STRUCTURE OF DNA
The two sides of the “ladder” (called backbones), are made from the sugar (deoxyribose) and phosphate, joined by phosphate bonds
Across the “ladder” are pairs of nitrogenous bases connected by hydrogen bonds
The sequence of these bases is what determines your traits/characteristics

7. THE STRUCTURE OF DNA
DNA has 4 kinds of nitrogenous bases: Adenine, Guanine, Cytosine and Thymine
The bases on one side of the “ladder” pair up with the bases on the other side
Adenine only pairs with Thymine (2 H-bonds)
Guanine only pairs with Cytosine (3 H-bonds)
A/T + G/C = 100%
*The sequence of these bases determines your traits
The two sides of the ladder run in opposite directions (antiparallel)
One side runs 5’  3’
The other side runs 3’  5’

8. THE STRUCTURE OF DNA

9. Practice Pairing
GATTACA

10. Practice Pairing
GATTACA CTAATGT

11. Vocabulary
DNA: the molecule that carries the genetic instructions for the characteristics and traits of an individual
Base-pairs: the part of the DNA nucleotides that constitute the blueprint
Gene: a section of DNA that codes for a specific RNA or protein; a specific sequence of bases
Chromosome: a single molecule of coiled (organized) DNA
Genome: an organism’s complete set of DNA, including all genes

12. Why is DNA Important?
There are approximately 20,000-30,000 genes on a human chromosome, and each gene has about 6 billion base pairs (seemingly infinite combinations)
ALL your cells contain a complete copy of your ENTIRE genome
Humans have 23 pairs of chromosomes (or 46 total) in each cell
One set of 23 chromosomes from your mom (egg), and another set from your dad (sperm)

13. Why is DNA Important?
ALL organisms (animals, plants, fungi, protists, and bacteria) have DNA made out of the same components
Sugar, phosphate, and the 4 bases (A, C, G, and T)
There are only two differences in the DNA of different organisms
Different organisms have different number of chromosomes
The order of bases is different for each organism

14. DNA Replication

15. DNA Replication
In DNA replication, the enzyme helicase splits the double helix down the middle by cutting the hydrogen bonds
Once separated, each side is used as a template strand
The enzyme DNA polymerase adds the matching bases to each template
The enzyme ligase seals the bonds between the bases
The end result is two IDENTICAL molecules of DNA – identical to each other and identical to the original

16. DNA Replication
Once replication is finished, there are two complete double helix molecules of DNA
Each new double-helix molecule has one “old” strand and one “new” strand
The “old” strand is said to have been “conserved”
Semi = half
Therefore, this type of replication is known as semi-conservative

17. Steps of DNA Replication
1. The double helix unzips
This unzipping is caused by the
enzyme helicase

18. Steps of DNA Replication
2. The two strands are separated

19. Steps of DNA Replication
3. Each side is now a template
The addition of new
DNA bases onto the
two original strands
of DNA is performed
by the enzyme DNA
polymerase
The bonds between the old and new bases is sealed by the enzyme ligase

20. Steps of DNA Replication
4. The result is two IDENTICAL strands of DNA

21. Semi-Conservative Replication
One strand is the original strand (PARENT)
One strand is the new strand (DAUGHTER)

22. Semi-Conservative Replication
One strand is the original strand (PARENT)
One strand is the new strand (DAUGHTER)

23. DNA Replication Details
When does DNA replication happen?
Once the DNA is unwound by helicase, the enzyme RNA primase adds an RNA primer to each strand of DNA
The DNA polymerase adds bases onto each side of the unzipped DNA
The leading strand is made as nucleotides are added smoothly to the 3’ end
The lagging strand is made as nucleotides are added in the 3’  5’ direction with small pieces called Okazaki fragments
DNA polymerase then removes the RNA primers and replaces them with DNA nucleotides, which are sealed with ligase

24. DNA Replication Details

25. Gene Expression Gene Expression All cells contain ALL your DNA
However, different genes are turned on in different cells
This means different proteins are made in each cell – whatever the cell needs to make in order to do its job
This is a regulated process

26. Cell Differentiation Cell Differentiation
All cells start as “stem” cells - undifferentiated
Different cells have different jobs, so stem cells have certain genes that get turned “on” – the ones that help the cell do its job
Examples – animal cells
Blood: carries oxygen to cells (RBC) and fights infection (WBC)
Muscle: allows movement (skeletal, smooth, cardiac)
Epithelium: skin, secreting mucus, & absorbing nutrients
Examples – plant cells
Root: absorb water and minerals from the soil
Stem: carry substances between roots and leaves
Leaves: capture sunlight and perform photosynthesis