Unit 6: DNA & Protein Synthesis Ch 28: DNA—Life’s Code DNA = Deoxyribonucleic Acid

Describing DNA James Watson & Francis CrickJames Watson & Francis Crick –1st to describe DNA as a double helix shape

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

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

A Model of DNA DNA molecule –Double-stranded “backbone” = sugars & phosphates “rungs” = nitrogenous bases –Always paired as: »A - T »G - C DNA Structure Video

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

DNA Replication 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 cell divides (before mitosis) Where does DNA replicate? –in the nucleus

How does DNA replication occur? –1. DNA molecule unzips between bases DNA Replication

–2. “parent” strands act as templates… nucleotides are paired up with complementary base on “parent” strand –form complementary daughter strand »Ex. “G”  “C” DNA Replication T C

–3. 2 exact copies of original DNA molecule when cell divides each daughter cell gets a copy DNA Replication

DNA Replication Video T C

Predict the next base…

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 Gene –section of DNA that codes for synthesis of a protein Which part of DNA actually carries the code? –the nitrogen bases & their sequence change the sequence  change the amino acid  change the protein

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 Occurs: –when a protein is needed 20 different amino acids –but DNA has only 4 kinds of bases –in the nucleus DNA code is “transcribed” into mRNA code

Transcription Produces single-stranded messenger RNA (mRNA) from instructions in DNA 1.DNA unzips 2.Free RNA nucleotides pair w/ exposed bases on DNA until “stop codon” is reached 3.mRNA separates from DNA giannini/flashanimat/molgen etics/transcription.swf

mRNA 3 consecutive bases on mRNA –code for an amino acid called “codon” –a chart tells us amino acid for each codon

mRNA Codons & Amino Acids

Translation Occurs: –when mRNA from the nucleus & joins with ribosomes –in the cytoplasm

1.anticodon on tRNA: –joins with complementary mRNA codon –carries amino acid specified by the codon on mRNA to ribosome 2.Amino acids line up & bond to form a protein ashanimat/molgenetics/translation.swf Translation

tRNA anticodon DNA codon mRNA codon transcriptiontranslation mRNA codon

What would the mRNA strand look like?

What amino acids would be coded for using this mRNA?

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

Given the following DNA sequence determine: –The mRNA codon sequence –The amino acids that would be coded for by each codon Also determine the tRNA anticodon for each amino acid DNA = TAC CCA TTG GAT CCG ACT mRNA = A. A. = Anticodon =

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: Deletion & Insertion deletion –nucleotide left out insertion –nucleotide added in “frame shift” –different amino acid from that point on different protein

Types of Mutations: Point point mutation –one base is replaced by another

Sickle Cell Mutation affects hemoglobin –caused by point mutation changes one amino acid