1. DNA
The BIG show!
All animations are from Virtual CellAnimation Collection

2. Watson and Crick 1953 the structure of DNA was finally described
Based on Roselind Franklin and Maurice Wilkins’ crystallography of DNA (Wilkins shared in Nobel prize 1962 – Franklin had died)

3. Double Stranded Helix DNA is comprised of
two strands of nucleic acids - bases
6 carbon sugar – phosphate backbone
helix – twists around each other, like the stripes of a peppermint stick

4. Structure of DNA Primary Secondary Tertiary Quaternary
Sequence of base pairs along one strand – ATGC
Secondary
DNA is wrapped around histones
Tertiary
Histones are grouped into bundles
Quaternary
DNA located on pairs of Chromosomes

5. Nucleotides
DNA is made up of subunits which scientists called nucleotides.
Each nucleotide is made up of a sugar, a phosphate and a base.
There are 4 different bases in a DNA molecule:
adenine (a purine)
cytosine (a pyrimidine)
guanine (a purine)
thymine (a pyrimidine)
The number of purine bases equals the number of pyrimidine bases
The number of adenine bases equals the number of thymine bases
The number of guanine bases equals the number of cytosine bases
The basic structure of the DNA molecule is helical, with the bases being stacked on top of each other

6. What does that mean? Adenine is hydrogen bonded to Thymine
Guanine is hydrogen bonded to Cytosine
DNA is directional from 5’ to 3’

7. Directional?
The DNA is “read” from the 5’ to the 3’ end, just like we read words from left to right
When DNA is replicated, it is read from 5’ to 3’
The two strands unzip to allow room for replication factors

8. Why is that important Double stranded adds stability to DNA
Easy to find errors in copying or transcribing to RNA or mutations
Easy to find T with a G or C with an A

9. Genes Areas of DNA have readable sequences which code for genes
Many parts of the genome are “junk DNA”
Genes can have differences in the AT and GC, which form alleles
If not detrimental, the mutation will continue
If advantageous, the allele will become more common

10. Questions?
BJ Shaw Panochthus frenzelianus American Museum of Natural History 2004

11. DNA to RNA to Protein

12. Overview
How it works
DNA – double stranded to protect and reduce the mutations
RNA – unstable, and breaks down quickly in the cell

13. Types of RNA mRNA (messenger RNA) is transcribed from DNA
tRNA (transfer RNA) is the molecule that carries amino acids
rRNA (ribosomal RNA) reads mRNA and matches tRNA to build the protein in the correct sequence

14. Types of RNA
cRNA (catalytic RNA) catalyses many reactions in the cytoplasm of the cell.
snRNA (small nuclear RNA) have various roles in the processing of the other classes of RNA.
snoRNA (small nucleolar RNA) over 100 of them found in the nucleolus where they are involved in several functions including making ribosomes

15. Amino Acids
Four nucleotides (Adenine, Thymine, Guanine, and Cytosine) translate into 20 different amino acids
If 1 nucleotide = 1 amino acid, only 4 amino acids
If 2 nucleotides = 1 amino acid, then 16 amino acids (still short)
If 3 nucleotides = 1 amino acid, then 64 amino acids (too many)

16. Amino Acids Closer look…
AUG = methionine, the start of the protein sequence
UAA = stop
UAG = stop
UGA = stop
Other codes allow for “wobble” room
For example, serine starts with a UC, and any other nucleotide

17. Protein Synthesis DNA unzips
Similar to replication, DNA is copied (transcription)
Uracil is the molecule that pairs with Adenine rather than Thiamine

18. Protein Synthesis mRNA is edited mRNA is spliced
mRNA exits the nucleus of the cell and is associate with the small subunit of rRNA (a ribosome) for translation
The protein is constructed one amino acid at a time

19. Proteins Complex molecules
One of the four major types of molecules found within the cell
DNA, RNA, and lipids are the other three
These comprise the variation found within populations
The amount of melanin will determine the color of the iris – or it is at least 74% responsible

20. Questions?
BJ Shaw Megatherium americanum Museo de La Plata 2008