Franklin’s photo below proved model on left to be correct for DNA Crick Watson Franklin Wilkins Franklin’s photo below proved model on left to be correct for DNA Pauling

Most important scientific paper in Biology in last 100 years First time DNA double helix seen in print Most important scientific paper in Biology in last 100 years By Watson and Crick, 1953

2 April 1953 MOLECULAR STRUCTURE OF NUCLEIC ACIDS A Structure for Deoxyribose Nucleic Acid   “We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). This structure has novel features which are of considerable biological interest.” From the original Watson and Crick article – first published “double helix” diagram

Proof of double helix

Summary of a few people involved with DNA: Pauling and Corey – “telephone pole” model for DNA Franklin – x-ray photos proved Pauling wrong Wilkins – gave x-rays to Watson and Crick Watson, Crick, Wilkins – Nobel Prizes for DNA structure Watson & Crick Pauling and Corey

First to describe the physics to split the atom Rosalind Franklin 06 Lise Meitner Nobel Prize Otto Hahn Nobel Prizes Figure: 13-02a Title: DNA Investigator Caption: (a) DNA Investigator Rosalind Franklin, whose work in X-ray diffraction was important in revealing the structure of the DNA molecule. First to discover structure of DNA First to describe the physics to split the atom

Basic Terms: DNA Nucleotide (monomer) Subcomponents of nucleotide sugar = deoxyribose phosphate bases – 4 of them adenine (A) guanine (G) cytosine (C) thymine (T) Nucleic Acid (polymer) – chain of nucleotides Double helix – two chains of nucleic acids

DNA Nucleotide B B B B B S P S S S P S P P P B S P Nucleic acid (polymer) = chain of nucleotides (monomers) B B B B B S P S S S P S P P P B Base = A, G, C, T phosphate Nucleotide (DNA or RNA) S P sugar DNA Nucleotide

Double helix of nucleic acid Sugar phosphate base Double helix of nucleic acid Figure: 13-03b Title: Component Molecules of DNA Caption: The Structure of DNA Nucleotide

Base Pairing in DNA double helix G-C A-T C-G T-A

Only one base pairing is possible

Nucleosome = protein + DNA

Nucleosomes

Euchromatin = active DNA = decondensed Heterochromatin = inactive DNA = condensed Nucleosome DNA Euchromatin = active DNA = decondensed Fig. 13.11

DNA Replication

One double helix forms two identical double helices DNA replication: One double helix forms two identical double helices Figure: 13-04 Title: DNA Replication Caption: The result of DNA replication is two identical molecules of DNA, whereas the process began with one.

Double Helix separates New strands forms by base pairing Figure: 13-05 Title: How Life Builds on Itself Caption: Each newly synthesized DNA molecule is a combination of the old and the new. An existing DNA molecule unwinds, and each of the resulting single strands (the old) serves as a template for a complementary strand that will be formed through base pairing (the new).

Double helix separates C A T G C A G Double helix separates T A T

Base pairing New nucleotides are added to the “old” or original DNA nucleotides by base pairing with the help of enzymes (not shown here)

normal Mutant Fig. 11.08

Protein Synthesis

Review Protein gives life structure Protein gives life function Amino acid sequence gives protein its structure and function Question: How is amino acid sequence determined?

Gene = section of DNA that codes for amino acid sequence in a protein Yeast Fruit Fly Worm Green Plant 6034 genes 13,061 genes 19,099 genes 25,000 genes Gene = section of DNA that codes for amino acid sequence in a protein Figure: 14-13 Title: Not as Much Difference as We Thought Caption: At one time, scientists assumed that the human genome contained about 100,000 genes. Genome sequencing revealed, however, that the human genome probably contains about 30,000 genes. This is only about 11,000 more genes than the tiny roundworm C. elegans, and about 17,000 more than the Drosophila fruit fly. Scientists can make comparisons among genomes because, though the human genome has gotten most of the attention, the genomes of several other organisms have now been sequenced as well, including those shown here.

DNA (m)RNA (copy) Protein Transcription Translation

Retire already!!! Overview Figure: 14-02 Title: The Two Major Stages of Protein Synthesis Caption: The Two Major Stages of Protein Synthesis

Sugar–phosphate backbone Base pairing is the genetic code G-C C-G A-T T-A

DNA double helix separates RNA nucleotides attach to DNA T replaced by U Figure: 14-04a Title: Transcriptions Works through Base Pairing Caption: Thanks to their chemical similarity, DNA and RNA can engage in base pairing, and this base pairing is how RNA transcripts are synthesized. The enzyme complex RNA polymerase undertakes two tasks in transcription: It unwinds the DNA sequence to be transcribed, and it brings together RNA nucleotides with their complementary DNA nucleotides, thus producing an RNA chain. Base pairing makes RNA copy of DNA

Transcription = (m)RNA copy of one side of DNA

Transcription of mRNA DNA mRNA transcript DNA Figure: 14-04b Title: Transcriptions Works through Base Pairing Caption: Thanks to their chemical similarity, DNA and RNA can engage in base pairing, and this base pairing is how RNA transcripts are synthesized. The enzyme complex RNA polymerase undertakes two tasks in transcription: It unwinds the DNA sequence to be transcribed, and it brings together RNA nucleotides with their complementary DNA nucleotides, thus producing an RNA chain.

Codon = three RNA nucleotides = code for particular amino acid

Translation – conversion of mRNA nucleotide sequence (codons) into amino acid sequence of protein Figure: 14-06 Title: Triplet Code Caption: Each triplet of DNA bases codes for a triplet of mRNA bases (a codon), but it takes a complete codon to code for a single amino acid.

Codon – group of three mRNA nucleotides Each amino acid has at least one specific codon. Alanine (Ala) has the codon GCU. Glycine has the codon GGU Tyrosine has the codon UAU Figure: 14-T01 Title: Amino Acids Caption: Amino Acids

review Codon = three RNA nucleotides = code for particular amino acid

Translation = mRNA codons place amino acids in proper order review Nontranscribed strand 5’ Transcription DNA 3’ Transcribed strand Codon 1 Codon 2 Codon 3 Codon 4 Codon 5 Codon 6 Polypeptide Translation

UV-A UV-B Sun screen products Human skin

Thymine Dimer mutation DNA from U.V. light A C G T T C C A T G C A A G G T Thymine Dimer mutation DNA from U.V. light UV light A C G T T C C A T G C A A G G T

Thymine dimer removed DNA repair enzymes New DNA replaces hole left by damaged DNA

Every cell in the body has the same DNA, but each specific type of cell makes proteins unique to those cells? In other words every cell in your body has the exact same book of blueprints but only certain pages are read in certain cells.

Human embryos are totipotent = can become any cell in the human body Why? because it has DNA to make every cell in the body. http://www.dynamist.com/aaa/blastocyst.gif

4 week old embryo is pluripotent – produce most cells 6 day old embryo is totipotent – produce all cells

Salamander – many tissues can be regenerated if damaged.

Salamander can re-grow new limbs because adult stem cells behave like embryonic cells. http://www.luc.edu/depts/biology/dev/regen.gif

Transcription of DNA to make new leg Heterochromatin - inactive Salamander leg cells damaged Nucleosome Euchromatin - active DNA Transcription of DNA to make new leg

Polymerase Chain Reaction

Small amount of DNA left at crime scene Polymerase Chain Reaction (PCR) DNA replication After 20 replications (a few hours) – over 1,000,000 helices formed

DNA DNA Restriction enzyme (Eco R1) cuts DNA into fragments

DNA fragments loaded into wells in gel (like Jell-O) Figure: 15-UNSB1 Title: Visualizing Lengths of DNA Caption: In gel electrophoresis, negatively charged DNA fragments travel through the porous gel toward the positive end of the tray when a charge is applied to the gel. Large fragments, however, do not travel as far in a given amount of time as small fragments. Thus the fragments separate out by size. The first ÅgstripeÅh at the top of a lane represents a collection of fragments of a given size, the second stripe a second collection of fragments of a smaller size, and so on. Fragments (-) migrate through gel because of electric current

DNA fragments have (-) charge (+)

DNA fingerprinting – compares fragments of DNA formed by restriction enzymes Like a barcode

Baby’s DNA Father #1 Father #2