DNA Ch 8 Standard 4

History of DNA 1. Hershey & Chase  proved DNA is the genetic material found in cells

Erwin Chargaff DNA composition all 4 bases not in equal quantity bases present in characteristic ratio A = T ~ 40% G = C ~ 60% varies from species to species

Rosalind Franklin  took x-ray photos of DNA that showed it’s 3-D structure

Watson & Crick made the first 3-D model of DNA in 1953 Won the Nobel Prize in 1962

Why is DNA important? It stores genetic information in cells & this information is used to make proteins

DNA is a double helix (twisted ladder) DNA Structure DNA is a double helix (twisted ladder)

DNA is made of nucleotides 3 nucleotide parts Deoxyribose sugar Phosphate Nitrogen base - adenine (A) - thymine (T) - guanine (G) - cytosine (C)

Adenine binds only with Thymine Cytosine binds only with Guanine ----Straight letters together Curvy letters together-------

Sugars & phosphates make up the sides of the ladder, the nitrogen bases are the steps (rungs) Phosphodiester bonds

Difference in their shapes causes the DNA to twist Base Pair Shape Pyrimadine Single ring bases (Thymine or Cytosine) Purine Double ring bases (Adenine or Guanine) Difference in their shapes causes the DNA to twist

Hydrogen Bonds Adenine Thymine Thymine Adenine Guanine Cytosine

A T G G A C T A C T A C C T G A T G Practice If one side of DNA has this base sequence, what does the other side have? A T G G A C T A C T A C C T G A T G

DNA Replication

How Does DNA Replicate Process discovered by Meselson & Stahl Semi-conservative replication Half old strand, Half new strand Anti-parallel New strands are made in opposite directions

When does DNA replicate? During the cell cycle before mitosis & meiosis

Why does DNA replicate? So new cells will have their own copy of DNA

Six Steps of DNA Replication DNA is unzipped by the Helicase enzyme (breaks hydrogen bond) DNA polymerase enzyme binds DNA begins attaching complimentary nucleotides Same thing happens on the other side, but in opposite direction

4) Bonds Reform Helicase reforms Hydrogen bonds (between bases) Ligase reforms Phosphodiester bonds (sugar & phosphate) 5) DNA polymerase “proofreads” checking each strand for errors. 6) DNA rewinds itself into two identical double helix strands Let’s watch http://www.lpscience.fatcow.com/jwanamaker/animations/DNA%20Lecture.html

Protein Synthesis DNA RNA Proteins

DNA sugar = deoxyribose bases = A, C, G, T double strand stays in nucleus RNA sugar = ribose bases = A, C, G, U single strand leaves nucleus

3 Types of RNA mRNA  made from DNA in nucleus “messenger” tRNA  brings amino acids to the ribosomes; found in cytoplasm “transfer” 3. rRNA  part of the ribosome; this is where proteins are made “ribosomal”

DNA vs. RNA

TRANSCRIPTION How RNA is made from DNA

Transcription Steps DNA is unzipped by Helicase all genes start with the code “TAC” RNA polymerase adds RNA nucleotides to the DNA strand mRNA is complete when it reaches a stop code on DNA mRNA then leaves nucleus & carries code into the cytoplasm DNA never leaves the nucleus

Don’t Confuse Replication with Transcription! DNA Replication A – T C – G G – C T - A Transcription A – U C – G G – C T - A

Transcribe this…… TACGTATTCCGG | | | | | | | | | | I AUGCAUAAGGCC

Translation Decoding the Message Steps mRNA leave nucleus and enters ribosome mRNA codons read & tRNA brings matching amino acid to the ribosome Amino acids are strung together like beads on a necklace Amino Acids are held together by peptide bonds 1000 or more Amino Acids = protein

WHEN WE DECODE DNA Example: AUG= Methylamine (Start) Use the “Genetic Code”  Convert mRNA 3 letter groupings called codons Example: AUG= Methylamine (Start) The mRNA Code tells us what amino acid each codon codes for.

Transcribe and Translate this DNA Strand without looking at your notes TACAGTACCATAATC NOW, Label the DNA, mRNA, tRNA, rRNA Which part is transcription Which is translation ?

rRNA MET-SER-TRP-TYR-STOP DNA TACAGTACCATAATC mRNA AUGUCAUGGUAUUAG tRNA UACAGUACCAUAAUC rRNA MET-SER-TRP-TYR-STOP

DNA RNA Protein Transcription Translation A, T, C, G A, U, C, G Amino Acids Double Strand Single Strand Codons & Anti-codons In Cytoplasm In The Nucleus

Is it all DNA? There are different parts of the chromosome Entire chromosome is made of DNA Humans~ 3 billion base pairs Only part of the DNA codes for Genes Gene: The DNA that codes for a Protein. There are different parts of the chromosome Exons and Introns Introns are cut out before translation Exons are left, and get Translated to make Proteins

GENETIC VARIATION There are some variations in genes Effects ~every 1350th bp (average) Known as polymorphisms “different forms” Different gene forms are called alleles Effects How well the protein works. EX: Melanin How the protein interacts with another protein or substrate. EX: Enzymes Click and type your text here 3 2

Proteins do the work of the cell Proteins are chains of amino acids. The amino acids are coded by the bases that make up that gene Each gene codes for a different protein.

Gene Expression All cells within an organism have the same DNA and genes. What makes cells different from each other is that different genes are turned on and turned off in different cells. Pigment in Eyes or Skin Keratin in Nails or Hair

How can organisms be different from each other if their DNA is made of the same nucleotides? Two individuals DNA are different because of the order of nitrogen bases The more closely related two organisms are, the more alike the order of nucleotides in their DNA will be.