A Gene is a Segment of DNA When a gene is expressed, DNA is transcribed to produce RNA and RNA is then translated to produce proteins.
Transcription The process by which a molecule of DNA is copied into a complementary strand of RNA. 1 Strand DNA 2 Strands RNA DNA must be copied to messenger RNA (mRNA) mRNA goes from nucleus to the ribosomes in cytoplasm mRNA complements known as codons Only 3 nucleotide “letters” long Remember RNA has uracil (U) instead of thymine (T)
Step 3: RNA nucleotides in the cell match up with only one side of the “unzipped” DNA each “unzipped’ strands forms a template for a mRNA strand RNA nucleotide
Step 4: RNA nucleotides continue to match up with “unzipped” DNA until the message is completely transcribed mRNA strand One side of DNA strand
Step 4: mRNA strand breaks off from the DNA strand mRNA strand One side of DNA strand
Step 5: mRNA strand leaves the nucleus for the ribosome
Step 6: Once the mRNA leaves, the DNA “zips” back together
Protein Translation Modified genetic code is “translated” into proteins Codon code is specific, but redundant! 20 amino acids 64 triplet (codon) combinations
Translation The process in which the information in the nucleotide base sequence of mRNA is used to dictate the amino acid sequence of a protein. 1 Strand RNA Amino Acid Chain Protein
tRNA in cytoplasm has a codon attached to an amino acid
tRNA structure 3-base code (triplet) is an “anticodon” Protein molecule Attached amino acid that is carried from cytoplasm to ribosomes
RNA and Protein Synthesis RNA is a Single Stranded Nucleic Acid RNA Acts as a Messenger between DNA and Ribosomes Process Takes Amino Acids and Forms Proteins
Why Is It Necessary? DNA is in Nucleus Ribosomes (site of protein synthesis) is in Cytoplasm Need a Messenger to carry information held in nucleus to ribosome
SUMMARY 1. DNA unzips 2. mRNA made from DNA. 3. mRNA leaves nucleus and enters ribosome. 4. tRNA reads mRNA from “start” to “stop” 5. As tRNA reads mRNA, it brings the correct amino acids. DNA makes mRNA (complement) mRNA matches up with tRNA (complement) tRNA brings amino acid Chains of amino acids can make proteins Proteins=genes!!