DNA Ch 8 Standard 4

History of DNA 1. Hershey & Chase  proved DNA is the genetic material found in cells 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 Structure DNA is a double helix (twisted ladder)

DNA is made of nucleotides 3 nucleotide parts 1.Deoxyribose sugar 2.Phosphate 3.Nitrogen base - adenine (A) - thymine (T) - guanine (G) - cytosine (C)

Base Pair Rules: - Adenine binds only with Thymine (A  T) - Cytosine binds only with Guanine (C  G) ----Straight letters together Curvy letters together Curvy letters together

Deoxyribose Sugars phosphatesDeoxyribose Sugars & phosphates make up the sides of the ladder Phosphodiester bondsPhosphodiester bonds hold the sugars to the phosphates Nitrogen bases hydrogen bondsNitrogen bases are held together by hydrogen bonds 2 A  T = 2 hydrogen bonds 3 G  C = 3 hydrogen bonds Base pairsThe Base pairs make up the steps (rungs) of the DNA Ladder

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

Hydrogen Bonds H H H H O O H C C C C N N C Thymine H N H H N C C C C N N H N C Adenine H O N H C C C N N C Cytosine H H H N C C C C N N H N C Guanine N H O H Adenine Guanine Cytosine Thymine

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 Six Steps of DNA Replication 1) DNA is unzipped by the Helicase enzyme (breaks hydrogen bond) 2) DNA polymerase enzyme binds DNA begins attaching complimentary nucleotides 3) 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 jwanamaker/animations/DNA%2 0Lecture.html jwanamaker/animations/DNA%2 0Lecture.html jwanamaker/animations/DNA%2 0Lecture.html

Once more time….. Once more time…..

Protein Synthesis Protein Synthesis DNA  RNA  Proteins DNA  RNA  Proteins

DNA1.sugar=deoxyribose 2.bases = A, C, G, T 3.double strand 4.stays in nucleus RNA 1.sugar = ribose 2.Bases=A, C, G,U 3.single strand 4.leaves nucleus

3 Types of RNA 1. mRNA  made from DNA in nucleus “messenger” 2. 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 1. DNA is unzipped by Helicase all genes start with the code “TAC” all genes start with the code “TAC” 2. RNA polymerase adds RNA nucleotides to the DNA strand 3. mRNA is complete when it reaches a stop code on DNA 4. mRNA then leaves nucleus & carries code into the cytoplasm DNA never leaves the nucleus 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

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Translation Decoding the Message Steps 1. mRNA leave nucleus and enters ribosome 2. mRNA codons read & tRNA brings matching amino acid to the ribosome 3. Amino acids are strung together like beads on a necklace 4. Amino Acids are held together by peptide bonds or more Amino Acids = protein

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

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 ?

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

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

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

GENETIC VARIATION There are some variations in genes   ~every 1350 th bp (average)   Known as polymorphisms “different forms”   Different forms of genes are called alleles Effects   How well the protein works. EX: Melanin   How the protein interacts with another protein or substrate. EX: Enzymes

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

Gene Expression Gene Expression All cells within an organism have the same DNA and genes. 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. What makes cells different from each other is that different genes are turned on and turned off in different cells. Ex: Pigment in eyes or skin Ex: Pigment in eyes or skin Ex: Keratin in nails or hair Ex: 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 basesTwo 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.The more closely related two organisms are, the more alike the order of nucleotides in their DNA will be.