Unit 6: DNA & Protein Synthesis Ch. 9: Chemistry of the Gene Ch. 10: From Genes to Proteins DNA = Deoxyribonucleic Acid 300

Video PPT: Lies, Thieves, & DNA Lies, Thieves, & DNA How did each of the following scientists contribute to our knowledge of DNA and the genetic code? –Friedrich MiescherFriedrich Miescher –Frederick Griffith –Oswald Avery, Colin MacLeod, & Maclyn McCartyOswald Avery, Colin MacLeod, & Maclyn McCarty –Alfred Hershey & Martha ChaseAlfred Hershey & Martha Chase –P.A. Levene –Erwin ChargaffErwin Chargaff –Rosalind Franklin & Maurice WilkinsRosalind Franklin & Maurice Wilkins –James Watson & Francis CrickJames Watson & Francis Crick

Describing DNA Who first described the true shape of DNA? –James Watson & Francis CrickJames Watson & Francis Crick What shape did they use to describe DNA? –double helix

DNA is a Polymer… What is the monomer that repeats to make DNA? –nucleotide

What are the parts of a nucleotide? phosphate group sugar (deoxyribose) nitrogenous base –4 kinds: Adenine (A) Thymine (T) Guanine (G) Cytosine (C) –base gives name to nucleotide adenine, thymine, guanine, cytosine

4 kinds of nitrogen bases: –Purines (2 rings) Adenine Guanine –Pyrimidines (1 ring) Thymine Cytosine Always pair –A – T –G – C What are the parts of a nucleotide?

A Model of DNA Is DNA single or double stranded? –double-stranded 2 chains of nucleotides bonded together –shape = “double helix” (spiral staircase) DNA Structure Video nucleotide Purines Pyrimidines

A Model of DNA What parts make up the strands? –“backbone”/sides alternating sugars (deoxyribose) & phosphates –“rungs”/steps nitrogenous base pairs –A - T –G - C »held by hydrogen bond DNA Structure Video nucleotide Purines Pyrimidines

Strands are complementary (A-T & G-C) & antiparallel (opposite directions/upside down)

Where is DNA found in eukaryotic cells? DNA is contained in chromosomes (chromatin) within the nucleus sugar-phosphate “backbone” & nitrogenous base “rungs”

DNA Replication What is another word for replication? –copying Why must DNA replicate? –so when cell divides, each new cell gets a copy of DNA ple/giannini/flashanimat/m olgenetics/dna-rna2.swf

DNA Replication When does DNA replicate? –before the cell divides (before mitosis or meiosis) Where does DNA replicate? –inside the nucleus

1. “Helicase” enzyme unzips DNA molecule along H bonds ( between bases) forming two “parent strands”. What are the steps in DNA replication?

2. “Parent” strands act as templates… –“parent” strand’s base is paired up with complementary “new” nucleotide with help of “DNA Polymerase” enzyme forming complementary daughter strand –ex. “G” on “parent”  DNA polymerase brings “C” What are the steps in DNA replication? T C

3. Sections of nucleotides (Okazaki Fragments) are joined by enzyme DNA ligase. –Now, have 2 exact copies of original DNA molecule. & when cell divides, each “new” daughter cell gets a copy What are the steps in DNA replication?

DNA Replication Video T C What are the steps in DNA replication?

Let’s Practice… Predict the next base…

Let’s Practice… Finish the replications…

Deoxyribonucleic Acid vs. Ribonucleic Acid DNARNA sugar = deoxyribose sugar = ribose double stranded single stranded CANNOT leave nucleus Can move between nucleus & cytoplasm N bases = adenine, thymine, guanine, cytosine N bases = adenine, uracil, guanine, cytosine

The DNA Code & Protein Synthesis What is a gene? –section of DNA that codes for synthesis of a specific protein Which part of DNA carries the code for a protein? –the nitrogen bases & their order –change sequence  amino acid (usually) changes  & protein made (usually) changes

So, the big question is… –How does the DNA code in a cell’s nucleus get to the ribosomes where proteins are synthesized? transcription & translation The DNA Code & Protein Synthesis

Transcription What is transcription? –DNA code is “transcribed”/copied into mRNA codons When does transcription happen? –when a protein is needed

Transcription Where does transcription happen? –in the nucleus What does transcription make? –A single-stranded messenger RNA (mRNA) made from instructions/order of the bases in the DNA

Steps of Transcription When a protein is needed: –1. DNA near needed gene gives signal (“start codon”) –2. DNA unzips (w/ help of RNA polymerase) /people/giannini/flash animat/molgenetics/t ranscription.swf

Steps of Transcription 3. RNA polymerase pairs complementary RNA nucleotides with unzipped DNA strand until reach a “stop codon” 4. Nucleotides bond to form single RNA strand of mRNA (messenger RNA) 5. The 2 DNA strands rejoin & mRNA moves out of nucleus into cytoplasm /people/giannini/flash animat/molgenetics/t ranscription.swf

Steps of Transcription 3. RNA pairs complementary RNA nucleotides with unzipped DNA strand until reach a “stop codon” 4. Nucleotides bond to form single RNA strand of mRNA (messenger RNA) 5. The 2 DNA strands rejoin & mRNA moves out of nucleus into cytoplasm /people/giannini/flash animat/molgenetics/t ranscription.swf

mRNA Carries DNA’s Code Using “Codons” What is a codon? –3 consecutive bases on mRNA that codes for a particular amino acid 64 possible combos –Some amino acids have more than one codon

mRNA Carries DNA’s Code Using “Codons” How can we figure out the amino acid coded for by a codon? –a codon chart What amino acid does the AUG codon code for?

It must be in this row It must be in this square It must be in this amino acid mRNA Codons & Amino Acids What amino acid does the AUG codon code for?

mRNA Codons & Amino Acids

Translation What is translation? –process of reading mRNA codons to synthesize proteins with help of tRNA (transfer RNA) & ribosomes When does translation occur? –when mRNA from the nucleus joins with ribosomes Where does translation happen? –at ribosomes in the cytoplasm

1.mRNA comes from the nucleus & joins with ribosome in cytoplasm 2.Ribosome “reads” the codon until it finds the start codon (AUG) 3.tRNA (with complementary anticodon) joins to the mRNA codon –tRNA carries the amino acid specified by the mRNA codon people/giannini/flash animat/molgenetics/tr anslation.swf Steps of Translation

4.Ribosome moves along mRNA reading each codon until “stop” codon is reached –tRNA brings each amino acid 5.Amino acids line up & bond to form polypeptide 6.Polypeptide chain forms protein (3-D) –Shape of protein is related to its function people/giannini/flash animat/molgenetics/tr anslation.swf Steps of Translation

tRNA anticodon DNA codon mRNA codon transcriptiontranslation mRNA codon

Let’s Practice… What would the mRNA strand made during transcription look like?

What amino acids would be coded for using this mRNA?

What would the anticodons on the tRNA be for each amino acid?

Let’s Practice… Given the DNA sequence below, determine the: 1.mRNA codon sequence 2.amino acids that would be coded for by each codon 3.anticodons on each tRNA which allowed it to “bring” that amino acid (using the mRNA codons) DNA = TAC CCA TTG GAT CCG ACT mRNA codon = amino acid = anticodon (on tRNA) =

Mutations What are mutations? –mistakes/changes in a gene on a chromosome can occur spontaneously during replication can be caused by mutagens (such as radiation, high temperatures, or chemicals) often corrected, but not always –once occurs, copied as if correct –can cause different protein

Types of Mutations What are the 3 types of mutations? 1.deletion What happens in a deletion mutation? –a nucleotide (base) is left out »causes “frame shift” ~moves nucleotides after the deletion to the left causing a different protein to be formed

2.insertion What happens in an insertion mutation? –a nucleotide (base) is added in »causes “frame shift” ~moves nucleotides after the insertion to the right causing a different protein to be formed Types of Mutations

3.point (base substitution) What happens in a point mutation? –one nucleotide (base) is replaced by another »affects only 1 amino acid & does not cause “frame shift” »sometimes amino acid & protein can be the same (“silent mutation”) »protein may be able to function normally or nearly normally

Sickle Cell Mutation What does the sickle cell mutation do? –affects hemoglobin (protein in blood  carries O 2 ) What type of mutation causes sickle cell? –point mutation changes one amino acid –changes the protein

“Silent” mutation (no change in polypeptide) (point mutation)