Protein Synthesis: An Overview SBI 4UI – 5.2

Where is the DNA? Cytoplasm? Nucleus? Outside the cell?

Central Dogma DNA is too important to leave the nucleus Plus, there are only 2 copies of DNA in a somatic cell Plus, ribosomes often need to make large amounts of protein Plus, DNA would then have to reenter the nucleus What to do?

Central Dogma Messenger RNA (mRNA) DNA is transcribed into mRNA mRNA can travel to ribosomes to translate into polypeptide chains This process in known as the central dogma of molecular genetics

Transcription DNA  mRNA Transcription is like making a carbon copy

Translation Ribosomes mRNA  amino acid sequences Translation is like translating

Ribonucleic Acid DNA RNA Carries genetic information Deoxyribose sugar Adenine pairs with thymine Adenine pairs with uracil Double stranded Single stranded Resides in nucleus Resides in nucleus and cytoplasm

Messenger RNA Varies in length Intermediary between DNA and ribosomes Like a blueprint for protein production Contains codons

Transfer RNA Delivery system of amino acids to ribosomes as they make proteins Very short (70-90 base pairs) Contains anticodons

Ribosomal RNA Central component of the ribosome Varies in length Protein manufacturing machinery Varies in length

Transcription Initiation Elongation Termination RNA polymerase binds to the promoter Elongation Begins adding ribonucleotides  mRNA Termination “Stop” signal ends transcription and mRNA is released

Translation Initiation Elongation Termination Ribosome recognizes a sequence on mRNA and binds to it Ribosome moves along mRNA 3 nucleotides at a time (3 nucleotides = 1 amino acid) Elongation tRNA delivers appropriate amino acid Termination 3 base nucleotide codes as “stop” signal and polypeptide is released

Genetic Code 20 amino acids, but only 4 bases Triplet(3) of nucleotides = codon 43 = 64 possible combinations Start codon signals initiation Stop codon signals termination

To Do: Section 5.2 Understanding Concepts #1-11