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!!