Replication and Transcription DNA Replication and Transcription

DNA Structure: the backbones: -Consist of two five carbon sugar/phosphate backbones that are covalently bonded to create the rungs of the twisted ladder -Each of the backbones is antiparallel (they run in opposite ways). -One strand is the 3’ (the phosphate bonds on the third carbon), the other is the 5’ (the phosphate bonds to the fifth carbon). The sugars are oriented in opposite directions.

DNA Structure: the rungs Each deoxyribose sugar is covalently bonded to a nitrogen base The bases in between the sugars are bonded through a hydrogen bond -Adenine bonds to Thymine -Cytosine bonds to Guanine

DNA REPLICATION The copying of 1 DNA double helix to create 2 identical double helixes.

Steps of DNA REPLICATION Helicase (enzyme) separates the double helix by breaking the hydrogen bonds between the bases. 5’ 3’ 5’ 3’ ↑ Enzyme cuts here

Steps of DNA REPLICATION G A G T C Spare nucleotides pair up with bases in the original chain.

Steps of DNA REPLICATION G A G T C DNA Polymerase binds new nucleotides to the 3’ end of the new chain.

-DNA polymerase can ONLY add nucleotides in the 5’ direction, so it must start from the 3’ end of the parent chain. The leading strand is the orginal strand that has the 3’ end and adds nucleotides continuously The lagging strand is the original strand that has the 5’ end, therefore DNA polymerase starts in the middle of the strand and creates fragments as it moves. These Ozaki Fragments are later put together by the enzyme DNA ligase.

Overview of Replication

END RESULT The new strands of DNA combine with histones (proteins) to form nucleosomes that condense to form chromatin, that form chromosomes.

Transcription DNA chains are separated just enough to copy 1 gene RNA nucleotides H bond to exposed DNA bases RNA nucleotide includes the sugar ribose, phosphate, and a RNA base RNA polymerase binds the single stranded mRNA together

Transcription mRNA leaves the nucleus through pores in the nucleus and travels to the ribosome

Translation End of mRNA binds to the ribosome at the start codon START CODON: AUG Each set of 3 nucleotides on the mRNA= 1 codon

Translation tRNA is in the cytoplasm and contains: The anticodon to the mRNA strand with the matching RNA nucleotides A bonding site that is specific for an amino acid within the cytoplasm tRNA will pick up the correct amino acid and take it to the ribosome to be used to build protein

Translation As the mRNA moves along the ribosome, the corresponding tRNAs are drawn in. The tRNA drop off their amino acids and a peptide bond forms between the amino acids After dropping of the amino acid, the tRNA leaves the ribosome and goes to pick up more amino acids to continue the process

Translation Ribosome moves down the mRNA one codon at a time, bringing in tRNAs to match. They drop off their AA until the stop codon is reached. Once the stop codon is reached, the protein is released into the cytoplasm.

Helpful animations: http://learn.genetics.utah.edu/content/begin/dna/transcribe/ http://www.johnkyrk.com/DNAtranslation.htm

Identifying Amino Acid Chains Each mRNA carries a code that calls for a specific amino acid. The sequence of amino acids bond together to form proteins Use a mRNA codon chart to name the different amino acids in the protein chain. START: AUG (everything before that doesn’t matter!)