protein synthesis. protein synthesis proteinsthe production (synthesis) of proteins. 3 phases3...
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PROTEIN SYNTHESISPROTEIN SYNTHESIS
Protein SynthesisProtein Synthesis
• The production (synthesis) of proteinsproteins.
• 3 phases3 phases:
1.1. TranscriptionTranscription
2.2. RNA processingRNA processing
3.3. TranslationTranslation
• Remember:Remember: DNA DNA RNA RNA ProteinProtein
DNA DNA RNA RNA ProteinProtein
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Eukaryotic CellCell
TranscriptionTranscription
TranslationTranslation
DNA
mRNA
Ribosome
Protein
Prokaryotic CellProkaryotic Cell
DNA DNA RNA RNA ProteinProtein
Question:Question:
• How does RNARNA (ribonucleic acid) (ribonucleic acid) differ from DNA (deoxyribonucleic acid)DNA (deoxyribonucleic acid)?
RNARNA differs from DNADNA
1. RNARNA has a sugar ribosesugar ribose
DNADNA has a sugar deoxyribosesugar deoxyribose
2. RNARNA contains uracil (U)uracil (U)
DNADNA has thymine (T)thymine (T)
3. RNARNA molecule is single-strandedsingle-stranded
DNADNA is double-strandeddouble-stranded
1. Transcription1. Transcription
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Eukaryotic CellCell
1. Transcription1. Transcription
• The transfer of information in the nucleusnucleus from a DNADNA molecule to an RNARNA molecule.
• Only 1 1 DNADNA strand serves as the templatetemplate
• Starts at promoter DNADNA (TATA box)
• Ends at terminator DNADNA (stop)
• When complete, pre-RNApre-RNA molecule is released.
Question:Question:
• What What enzymesenzymes are responsible are responsible for the production of the RNA for the production of the RNA molecule?molecule?
Answer:Answer: Helicase Helicase andand RNA RNA PolymerasePolymerase
• HelicaseHelicase separates the DNADNA molecule by breaking the H-bonds between the bases.
• RNA PolymeraseRNA Polymerase moves along one of the DNA DNA strandsstrands and links RNARNA nucleotides together.
1. Transcription1. Transcription
DNADNA
pre-mRNApre-mRNA
RNA PolymeraseRNA Polymerase
Question:Question:
• What would be the complementary RNARNA strand for the following DNADNA sequence?
• DNA 5’-GCGTATG-3’DNA 5’-GCGTATG-3’
Answer:Answer:
• DNA 5’-GCGTATG-3’DNA 5’-GCGTATG-3’
• RNA 3’-CGCAUAC-5’RNA 3’-CGCAUAC-5’
2. RNA Processing2. RNA Processing
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Eukaryotic CellCell
2. RNA Processing2. RNA Processing
• Maturation of pre-RNApre-RNA molecules.
• Also occurs in the nucleus.nucleus.
• IntronsIntrons spliced out by splicesome-enzymesplicesome-enzyme and exonsexons come together.
• End product is a messenger RNA molecule messenger RNA molecule (mRNA)(mRNA) that leaves the nucleusnucleus to the cytoplasm.cytoplasm.
2. RNA Processing2. RNA Processing
pre-RNA molecule
intron
intronexon exon exon
exon exon exon
Messenger RNA moleculeMessenger RNA molecule
exon exon exon
intron intron
splicesome splicesome
Types of RNATypes of RNA
• Three types ofThree types of RNARNA:
A.A. messenger RNA (mRNA)messenger RNA (mRNA)
B.B. transfer RNA (tRNA)transfer RNA (tRNA)
C.C. ribosomal RNA (rRNA)ribosomal RNA (rRNA)
• Remember: all produced in theRemember: all produced in the nucleusnucleus!!
A. Messenger RNA (mRNA)A. Messenger RNA (mRNA)
• Carries the information for a specific proteinprotein.
• Made up of 500 to 1000 nucleotides nucleotides long.
• Made up of codons codons (sequence of three bases: AUG -
methionine).
• Each codoncodon, is specific for an amino acidamino acid.
A. Messenger RNA (mRNA)A. Messenger RNA (mRNA)
methionine glycine serine isoleucine glycine alanine stopcodon
proteinprotein
A U G G G C U C C A U C G G C G C A U A AmRNAmRNA
startcodon
Primary structure of a proteinPrimary 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
B. Transfer RNA (tRNA)B. Transfer RNA (tRNA)• Made up of 75 to 80 nucleotides long.
• Picks up the appropriate amino acid amino acid floating in the cytoplasm (amino acid activating enzymeamino acid activating enzyme)
• Transports amino acids amino acids to the mRNAmRNA.
• Have anticodonsanticodons that are complementary to mRNAmRNA codonscodons.
• Recognizes the appropriate codonscodons on the mRNAmRNA and bonds to them with H-bonds.
B. Transfer RNA (tRNA)B. Transfer RNA (tRNA)
amino acidamino acidattachment siteattachment site
U A C
anticodonanticodon
methionine amino acidamino acid
C. Ribosomal RNA (rRNA)C. Ribosomal RNA (rRNA)
• Made up of rRNArRNA is 100 to 3000 nucleotides long.
• Important structural component of a ribosome.ribosome.
• Associates with proteins proteins to form ribosomes.ribosomes.
RibosomesRibosomes
• Large and small subunits.Large and small subunits.
• Composed of rRNA (40%) rRNA (40%) and proteins (60%).proteins (60%).
• Both units come together and help bind the mRNAmRNA and tRNA.tRNA.
• Two sites forTwo sites for tRNAtRNA
a. P siteP site (first and last tRNA will attachtRNA will attach)
b. A siteA site
RibosomesRibosomes
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
3. Translation3. Translation
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Eukaryotic CellCell
3. Translation3. Translation
• Synthesis of proteinsproteins in the cytoplasmcytoplasm
• Involves the following:Involves the following:
1. mRNA (codons)mRNA (codons)
2. tRNA (anticodons)tRNA (anticodons)
3. rRNArRNA
4. ribosomesribosomes
5. amino acidsamino acids
3. Translation3. Translation
• Three parts:
1. initiationinitiation: start codon (AUG)
2. elongationelongation:
3. terminationtermination: stop codon (UAG)
• Let’s make a PROTEIN!!!!PROTEIN!!!!.
mRNA Codon Translation Table
3. Translation3. Translation
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
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
C C U
G 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
C C U
G G A
5-tRNA
aa5
Ribosomes move over one codon
mRNAmRNA
C 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
End ProductEnd Product
• The end products of protein synthesis is a primary structure of a proteinprimary structure of a protein.
• A sequence of amino acid amino acid bonded together by peptide bondspeptide bonds.
aa1
aa2 aa3 aa4aa5
aa200
aa199
Question:Question:
• The anticodon The anticodon UACUAC belongs to a belongs to a tRNAtRNA that that recognizes and binds to a particular recognizes and binds to a particular amino amino acidacid..
• What would be the What would be the DNA base code DNA base code for this for this amino acid?amino acid?
Answer:Answer:
• tRNA tRNA - UAC (anticodon)- UAC (anticodon)
• mRNAmRNA - AUG (codon)- AUG (codon)
• DNA DNA - TAC- TAC
When things go wrong…• Mutations: changes in the DNA sequence,
that may be passed along to future generations.
• Point mutations: a single base substitutionTHE CAT SAW THE RATTHE CAT SAW THE HAT
• Deletion: a small DNA segment is lostTHE CAT SAW THE RATTHE ATS AWT HER AT
• Insertion: a segment of DNA is added THE CAT SAW THE HAT
THE CAT SAW THE BHAT
Mutations• Frame-shift mutation: modification of the reading
frame after a deletion or insertion, resulting in all codons downstreams being different.
For example:THE RAT SAW THE CAT AND RAN
If you take out the “R” in “RAT” and shift the frames, you get:
THE ATS AWT HEC ATA NDR AN
The resulting sentence (or mRNA message) is meaningless!
Mutations
• Somatic mutations: occur in body cells, or cells that do not lead to gametes.
• Somatic mutations that occur in leaves, roots or stems are usually not passed on to future generations… UNLESS the plant is reproduced asexually.
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