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Genes to Proteins
Transcription and
Translation
DNA RNA Protein• DNA contains genes
which provide the information necessary to make proteins
• Different versions of the same gene result in different versions or amounts of a protein, and the differences in the protein result in different characteristics
Nuclearmembrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Don’t let this happen to you!!
How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)?
1. RNA has a sugar ribose2. DNA has a sugar
deoxyribose
3. RNA contains uracil (U)4. DNA has thymine (T)
5. RNA molecule is single-stranded
6. DNA is double-stranded
RNA
Transcription• The process that copies the message in a gene into a
messenger RNA (mRNA) molecule that will provide the instructions for making a protein molecule
• Started and controlled by an enzyme called RNA polymerase.– RNA polymerase binds to the DNA at a special point (start
signal)– RNA polymerase unwinds and separates the two DNA
strands– RNA polymerase adds and links complementary RNA
nucleotides as it “reads” the gene until it reaches a “stop” signal
RNA polymerase
mRNA
DNA
Transcription
1 Ribosomal RNA (rRNA) – Carrier molecule on ribosomes – holds the tRNA and mRNA in place
2 Transfer RNA (tRNA) - The molecule that physically couples nucleic acid codons with specific amino acids
3 Messenger RNA (mRNA) - The messenger that carries information from genes on DNA to the protein manufacturing ribosomes
Products of Transcription
TranslationThe process that makes proteins. The sequence of nucleotides in an mRNA molecule specifies the sequence of amino acids in a protein.
A U G G G C U U A A A G C A G U G C A C G U U
mRNA molecule
Codon= series of three nucleotides
This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule.
Messenger RNA (mRNA)
methionine glycine serine isoleucine glycine alanine stopcodon
protein
A U G G G C U C C A U C G G C G C A U A AmRNA
startcodon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
Each codon translates into one of twenty amino acids or is a stop or start signal
The Genetic CodeUUUUUCUUAUUG
CUUCUCCUACUG
AUUAUCAUAAUG
GUUGUCGUAGUG
UCUUCCUCAUCG
CCUCCCCCACCG
ACUACCACAACG
GCUGCCGCAGCG
UAUUACUAAUAG
CAUCACCAACAG
AAUAACAAAAAG
GAUGACGAAGAG
UGUUGCUGAUGG
CGUCGCCGACGG
AGUAGCAGAAGG
GGUGGCGGAGGG
Phenylalanine
Leucine
Leucine
Valine
Isoleucine
Methionine
Serine
Proline
Threonine
Alanine
Tyrosine
Stop
Histidine
Glutamine
Asparagine
Lysine
Asparagine
GlutamicAcid
Cysteine
Arginine
Serine
Arginine
Glycine
StopTryptophan
Note that 3rd Base Position is Variable
Eukaryotic Cell Protein SynthesisEukaryotic Cell Protein Synthesis
Protein Synthesis occurs on Ribosomes
A U G G G C U U A A A G C A G U G C A C G U U
A ribosome on the rough endoplasmic reticulum attaches to the mRNA
molecule.
ribosome
Protein Synthesis occurs on Ribosomes
Along comes a Transfer RNA Molecule…
amino acidattachment site
U A C
anticodon
methionine amino acid
A U G G G C U U A A A G C A G U G C A C G U U
The tRNA brings an amino acid to the first three bases (codon) on the mRNA.
Amino acid
tRNA molecule
anticodon
U A C
The three unpaired bases (anticodon) on the tRNA link up with the codon.
A U G G G C U U A A A G C A G U G C A C G U U
Another tRNA molecule comes into place, bringing a second amino acid.
U A C
C C G
Its anticodon links up with the second codon on the mRNA.
A U G G G C U U A A A G C A G U G C A C G U U
A peptide bond forms between the two amino acids.
Peptide bond
C C G
U A C
A U G G G C U U A A A G C A G U G C A C G U U
The first tRNA molecule releases its amino acid and moves off into the cytoplasm.
C C G
U A
C
A U G G G C U U A A A G C A G U G C A C G U U
C C G
The ribosome moves along the mRNA to the next codon.
A U G G G C U U A A A G C A G U G C A C G U U
Another tRNA molecule brings the next amino acid into place.
C C G
A A U
A U G G G C U U A A A G C A G U G C A C G U U
A peptide bond joins the second and third amino acids to form a polypeptide chain.
C C G
C C G
• The process continues.
• The polypeptide chain gets longer.
• This continues until a termination (stop) codon is reached.
• The polypeptide is then complete.A U G G G C U U A A A G C A G U G C A C G
U U
G U C
A C G
There is a tunnel through the large subunit of the ribosome that allows the growing polypeptide chain to pass out of the ribosome
• Termination of translation is triggered by stop codons
• A release factor enters the A site and triggers hydrolysis of the peptidyl-tRNA bond leading to the release of the protein.
Release of the protein causes the disassociation of the ribosome into its constituent subunits.
3’
5’
5’
3’
Transcription And Translation In Prokaryotes
Ribosome
Ribosome5’
mRNA
RNAPol.
Everything happens in the nucleus
DNA
Cytoplasm
Nucleus
Eukaryotic Transcription
ExportG AAAAAA
RNA
Transcription
Nuclear pores
G AAAAAA
RNAProcessing
mRNA
Eukaryotic Translation
Transcription/Translation Quiz
What is transcription? Production of RNA molecules by copying part of DNA into a complementary sequence of RNA
Why is transcription necessary?Transcription makes messenger RNA (mRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm.
Describe transcription.RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble mRNA. It uses the nucleotide bases except it replaces Thymine with Uracil
Transcription/Translation QuizWhat is translation?
The genetic message encoded in RNA is used to create a polypeptide with a specific amino acid sequence
Describe translation.The cell uses information from mRNA and tRNA to produce proteins.
Why is translation necessary?Translation assures that the right amino acids are joined together by peptides to form the correct protein.What are the main differences between
DNA and RNA?DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil.
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