DNA REPLICATION DNA Replication – process in which a DNA strand is copied • DNA polymerase is an enzyme that unzips the double stranded DNA. • Free nucleotides come in and pair with bases. • Two new double strands of DNA are made.
DNA replication DNA polymerase
DNA replication • Original DNA strands • Left strand copies going down, right strand copies going up
DNA replication • Newly assembled DNA strands
DNA replication • Let’s build our own DNA model and simulate DNA replication
RNA – Ribonucleic Acid • Chemically, RNA is very similar to DNA. There are 3 main differences: • RNA uses the sugar ribose instead of deoxyribose • RNA tends to be single-stranded (DNA-double) • RNA uses the base Uracil (U) instead of Thymine (T) Example: A-U (NOT A-T) Question: Is Uracil a single or double ring and why?
Transcription • Transcription – DNA must be copied to messenger RNA (mRNA) • Messenger RNA (mRNA) carries a code for a specific protein from the DNA in the nucleus to the ribosomes in cytoplasm. • CODON – a group of 3 bases on the mRNA that codes for a specific amino acids.
Transcription Cont’d 1. 4 Bases – A, G, U, C (no T) and 64 triplet codons (43) 2. The order of the codons on the strand of mRNA codes the order in which amino acids will be put together to create a protein. 3. Initiation (start) codon – AUG (methionine) Termination (end) codon – UAA, UAG, UGA
Transfer RNA (tRNA) • tRNA combines with amino acids in the cytoplasm and carries them (the amino acid) to the mRNA on the ribosomes. • Anticodon – 3 nucleotide bases on the tRNA • Codes for a specific amino acid • Complements the codon. • Translation – amino acids are assembled according to the instructions on mRNA. It occurs at the ribosomes.
Ribosomal RNA - rRNA • Molecules are incorporated in ribosomes. • Ribosomes are chemical workbenches where amino acids are linked to one another to synthesize proteins.