Chapter 12 DNA

DNA History Griffith – Experimented on mice and observed some harmless strains of bacteria could change into harmful strains. He called this transformation. Avery – Discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation to the next.

More DNA History Hershey-Chase – Concluded that the genetic material in bacteria was DNA not proteins Watson & Crick – created the double helix model for DNA.

DNA Length E. Coli have about 4,639,221 base pairs. It is about 1.6mm in length. This sounds small until you realize the bacteria is only 1.6µm in diameter. Thus DNA must be wrapped tightly to fit into cells. Imagine fitting 900 yards (300m) of rope into a backpack.

DNA DNA – Deoxyribonucleic Acid It’s structure was determined by the scientists Watson and Crick in 1953 Nucleotide Structure: 5-Carbon Sugar – Deoxyribose Phosphate Group Nitrogen Base – Adenine (A), Thymine (T), Guanine (G), or Cytosine (C)

DNA Phosphate Group 5-Carbon Sugar Nitrogen Bases

1’. 4 nitrogen bases: a’. Adenine b’. Thymine c’. Cytosine d’. Guanine

Nucleotide DNA and RNA are made of thousands of nucleotides

DNA Each nucleotide is bonded to another nucleotide to make a strand Two (2) stands of nucleotides are held together with HYDROGEN bonds to form a DOUBLE HELIX (“Twisted Ladder”) shape

DNA The 5-carbon sugars and phosphates alternate as a backbone or as the sides of the ladder

DNA Double Helix

Prokaryotes & DNA In prokaryotes, DNA molecules are located in the cytoplasm of the cell. Most prokaryotic DNA is a single circular molecule that contains nearly all the cell’s genetic information.

Chargaff’s Rules Chargaff discovered how the nitrogenous bases bond together. He discovered that Adenine always bonds with Thymine and that Cytosine always bonds with Guanine.

So each new daughter cell gets a copy Remember Mitosis? What happens in prophase? DNA Replication-a cell must duplicate it’s DNA before dividing. WHY? So each new daughter cell gets a copy

DNA Replication DNA is able to make copies of itself through the process of replication a) the DNA double helix unwinds and unzips b) the original strands serve as templates for new nucleotides to join DNA polymerase (enzyme) moves along each strand: adds nucleotides according to base pairing rules proofreads new strands c) 6000 sites on one molecule can be replicated as the same time Result= 2 new strands identical to original each strand has old strand and new strand

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G T

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G T A

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G T A A

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G T A A G

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G T A A G T

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: A T T C A G T A A G T C

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: G C C T A G A C T A G G C A A C T G

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: G C C T A G A C G G A T C T C T A G G C A A C T G

DNA Practice What is the sequence of bases on the complementary strands of each tDNA below: G C C T A G A C G G A T C T C T A G G C A A C T G G A T C C G T T G A C

DNA Replication How long does it take to replicate one DNA molecule? a few minutes Why is it so fast? Enzymes speed it up Where does replication occur? Nucleus of cell When does replication occur? Before the cell divides

RNA RNA – Ribonucleic Acid Structure: 5-Carbon Sugar – Ribose Phosphate Group Nitrogen Base – Adenine (A), Uracile (U), Guanine (G), or Cytosine (C) Only one (1) strand of nucleotides RNA is like a disposable copy of DNA Genes contain instructions for assembling amino acids into proteins

RNA

Types of RNA Messenger RNA (mRNA) Transfer RNA (tRNA) Ribosomal RNA (rRNA)

mRNA Messenger RNA (mRNA) - single, uncoiled strand that provides information from DNA during protein synthesis

tRNA Transfer RNA (tRNA ) - single, folded strand that delivers amino acids to the ribosomes during synthesis

rRNA Ribosomal RNA (rRNA) - globular RNA that makes up the structure of the ribosome

Protein Synthesis Transcription - process by which RNA is made from the information stored in the DNA How does it happen? DNA unwinds/unzips and RNA nucleotides pair up with the DNA nitrogen bases to form a strand of mRNA Where does it occur? Nucleus

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C A

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C A U

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C A U U

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C A U U G

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C A U U G C

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? G T A A C G A C A U U G C U

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? A C C T G A G C C G A T A T G

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? A C C T G A G U G G A C U C C C G A T A T G

Transcription Practice Given the cDNA strand below, what mRNA sequence will form? A C C T G A G U G G A C U C C C G A T A T G G G C U A U A C

Protein Synthesis Translation - process by which protein is made from the info in mRNA Where does it occur? In the cytoplasm on the rRNA (Ribosomes) How does translation happen? tRNA delivers amino acids to the ribosomes according to the codon’s directions Codon - sequence of 3 nitrogen bases on mRNA that code for an amino acid (there are 20 amino acids that build proteins) example: GAU Anticodon - sequence of 3 nitrogen bases on tRNA that is complementary to the codon example: CUA

Translation Overview again: mRNA attaches to ribosome Start codon (AUG) signals beginning of protein chain 2. Start codon (AUG) signals beginning of protein chain 3. tRNA has ANTICODON (bases complimentary to codon on mRNA) -AUG (codon) binds UAC(anticodon) UAC tRNA molecule carries the amino acid Methionine (Met) 4.Continues until stop codon reached

The codon codes for the anti-codon which is “attached” to the amino acid

Codon (mRNA) Wheel

Protein Synthesis Gene – region of DNA that directs the formation of a protein. The genetic code is determines by the sequence of nitrogen bases

Summary

Mutations

Mutations Frameshift Mutations- shift the “reading frame” of the genetic message b. Insertions-base added c. Deletion- base removed Point mutations are changes in single bases substitutions silent mutations occur when the amino acid that it codes for doesn't change due to the DNA mutation missense mutations cause an amino acid substitution (sickle-cell anemia),  these mutations may reduce or disable protein function codon has a point or shift change that causes the translation process to be terminated too early

Chromosomal Mutations- Deletion

Chromosomal Mutation- cont.

Chromosomal Mutations cont.

Chromosomal Mutations- cont.

Mutations and Causes of Cancer Mutagen- any chemical or physical agent that induces a genetic mutation or increases the mutation rate Carcinogen- a substance or agent that causes the development or increases the incidence of cancer More than 80% of cases of cancer are attributed to cigarette smoking, exposure to carcinogenic chemicals, ionizing radiation, and ultraviolet rays; overexposure to the sun is the major cause of skin cancer.

Mutations can be detrimental, neutral or occasionally beneficial Think Evolution and Natural Selection- DNA mutations are necessary for this to occur!