protein synthesis protein synthesis section 12.3
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PROTEIN SYNTHESISPROTEIN SYNTHESIS
Section 12.3Section 12.3
How your cell makes How your cell makes (“synthesizes”) proteins(“synthesizes”) proteins
• General stepsGeneral steps: :
DNA DNA RNA RNA ProteinProtein
• Occurs in 2 phasesOccurs in 2 phases:
1.1. TranscriptionTranscription (DNA (DNA RNA) – RNA) – occurs in the occurs in the nucleusnucleus
2.2. TranslationTranslation (RNA (RNAProtein) – Protein) – occurs on the occurs on the ribosomeribosome in the cytoplasm in the cytoplasm
DNA DNA RNA RNA ProteinProtein
RNARNA is DIFFERENT from DNADNA
1. RNARNA has a sugar sugar riboseribose
DNADNA has a sugar sugar deoxyribosedeoxyribose
2. RNARNA contains uraciluracil (U) (U)
DNADNA has thyminethymine (T) (T)
3. RNARNA molecule is single-strandedsingle-stranded
DNADNA is double-strandeddouble-stranded
3 types of RNA3 types of RNA
A.A. messenger RNA (mRNA)messenger RNA (mRNA)
B.B. transfer RNA (tRNA)transfer RNA (tRNA)
C.C. ribosomal RNA (rRNA)ribosomal RNA (rRNA)
mRNA – the “Messenger”
• Carries instructions from DNA to the ribosome.
• Gives the ribosome the “recipe” for making a specific protein
rRNA
• Part of the structure of a ribosome
• Helps in protein production
tRNA
“go-getter” Gets the right parts (amino acids) to make the right protein according to mRNA instructions
Phase 1: Transcription Phase 1: Transcription • mRNA is produced by copying part of
DNA into a complementary sequence of RNA
• Occurs inside the nucleus because DNA CANNOT leave the nucleus
Question:Question:
• What would be the complementary RNARNA strand for the following DNADNA sequence?
GCG TATGCG TAT
ANSWER:
•DNA: GCG TATGCG TAT
•RNA: CGC AUA
CODONS
• Bases are read in groups of 3, called codons.
• Each codon stands for 1 amino acid.
DNA: TAC CTT GTG CAT GGG ATC
mRNA AUG GAA CAC GUA CCC UAG
A.A MET G.A HIS VAL PRO STOP
Another RNA Chart
PHASE 2: Translation - making PHASE 2: Translation - making proteinsproteins
-mRNA lays across the ribosome-mRNA lays across the ribosome
-bases are read one -bases are read one CODONCODON (3 bases) at a time (3 bases) at a time
-tRNA molecules with complementary -tRNA molecules with complementary ANTICODONSANTICODONS deliver the appropriate amino deliver the appropriate amino acid to the ribosomeacid to the ribosome
-amino acids are linked together in a long chain to -amino acids are linked together in a long chain to form a protein (“polypeptide”form a protein (“polypeptide”
PHASE 2: Translation - making PHASE 2: Translation - making proteinsproteins
3 Steps:3 Steps:
1.1.InitiationInitiation2.2.ElongationElongation3.3.TerminationTermination
Translation
InitiationInitiation
mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogenbonds codon
mRNAmRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodon
hydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3
ElongationElongation
mRNAmRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codon
mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codon
mRNAmRNA
A C A U G U
aa1
aa2
U
primaryprimarystructurestructureof a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator or stopor stop codoncodon
TerminationTermination
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Transcription & Translation
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