SC.912.L.16.5
Protein Synthesis: Transcription and
Translation
Replication, Replication, Transcription, Transcription,
TranslationTranslation
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)
DNA RNA
One More
Time!!..
Step 1: Hydrogen bonds between complimentary bases break
DNA “unzips”
Step 2: DNA strandspull apart from each other
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 completelytranscribed
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 mRNAleaves, 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 moleculeAttached 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 NucleusRibosomes (site of
protein synthesis) is in Cytoplasm
Need a Messenger to carry information held in nucleus to ribosome
SUMMARY
1. DNA unzips2. 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 acidChains of amino acids can make proteinsProteins=genes!!