Transcript Protein Synthesis: Transcription and Translation

Protein Synthesis:
Transcription and Translation
SC.912.L.16.5
Replication, Transcription,
Translation
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 strands
pull 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 completely
transcribed
mRNA strand
One side of DNA strand
mRNA strand
Step 4:
mRNA strand
breaks off from
the DNA 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!!