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PROTEIN SYNTHESIS. Protein Synthesis. The production (synthesis) of proteins . 3 phases : 1. Transcription 2. RNA processing 3. Translation Remember: DNA RNA Protein. Nuclear membrane. DNA. Transcription. Pre-mRNA. RNA Processing. mRNA. Ribosome. Translation. Protein.
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Protein Synthesis • The production (synthesis) of proteins. • 3 phases: 1. Transcription 2. RNA processing 3. Translation • Remember: DNA RNA Protein
Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein DNA RNA Protein Eukaryotic Cell
DNA Transcription mRNA Ribosome Translation Protein DNA RNA Protein Prokaryotic Cell
Question: • How does RNA(ribonucleic acid) differ from DNA (deoxyribonucleic acid)?
RNA differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains uracil (U) DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded
Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 1. Transcription Eukaryotic Cell
1. Transcription • The transfer of information in the nucleus from a DNA molecule to an RNA molecule. • Only 1 DNA strand serves as the template • Starts at promoterDNA (TATA box) • Ends at terminatorDNA (stop) • When complete, pre-RNA molecule is released.
Question: • What enzymes are responsible for the production of the RNA molecule?
Answer: Helicase and RNA Polymerase • Helicase separates the DNA molecule by breaking the H-bonds between the bases. • RNA Polymerase moves along one of the DNA strands and links RNA nucleotides together.
DNA RNA Polymerase pre-mRNA 1. Transcription
Question: • What would be the complementary RNA strand for the following DNA sequence? • DNA 5’-GCGTATG-3’
Answer: • DNA 5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5’
Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 2. RNA Processing Eukaryotic Cell
2. RNA Processing • Maturation of pre-RNA molecules. • Also occurs in the nucleus. • Introns spliced out by splicesome-enzyme and exonscome together. • End product is a messenger RNA molecule (mRNA) that leaves the nucleus to the cytoplasm.
pre-RNA molecule exon intron exon exon intron intron intron exon exon exon splicesome splicesome exon exon exon Messenger RNA molecule 2. RNA Processing
Types of RNA • Three types ofRNA: A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosomal RNA (rRNA) • Remember: all produced in thenucleus!
A. Messenger RNA (mRNA) • Carries the information for a specific protein. • Made up of 500 to 1000 nucleotides long. • Made up of codons (sequence of three bases: AUG - methionine). • Each codon, is specific for an amino acid.
start codon A U G G G C U C C A U C G G C G C A U A A mRNA codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 stop codon protein methionine glycine serine isoleucine glycine alanine Primary structure of a protein aa2 aa3 aa4 aa5 aa6 aa1 peptide bonds A. Messenger RNA (mRNA)
B. Transfer RNA (tRNA) • Made up of 75 to 80 nucleotides long. • Picks up the appropriate amino acid floating in the cytoplasm (amino acid activating enzyme) • Transports amino acids to the mRNA. • Have anticodons that are complementary to mRNAcodons. • Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds.
amino acid attachment site methionine amino acid U A C anticodon B. Transfer RNA (tRNA)
C. Ribosomal RNA (rRNA) • Made up of rRNA is 100 to 3000 nucleotides long. • Important structural component of a ribosome. • Associates with proteins to form ribosomes.
Ribosomes • Large and small subunits. • Composed of rRNA (40%) and proteins (60%). • Both units come together and help bind the mRNA and tRNA. • Two sites fortRNA a. P site(first and last tRNA will attach) b. A site
mRNA A U G C U A C U U C G Ribosomes Large subunit P Site A Site Small subunit
Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 3. Translation Eukaryotic Cell
3. Translation • Synthesis of proteins in the cytoplasm • Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. rRNA 4. ribosomes 5. amino acids
3. Translation • Three parts: 1. initiation: start codon (AUG) 2. elongation: 3. termination: stop codon (UAG) • Let’s make a PROTEIN!!!!.
mRNA A U G C U A C U U C G 3. Translation Large subunit P Site A Site Small subunit
aa2 aa1 2-tRNA 1-tRNA G A U U A C Initiation anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA
aa3 3-tRNA G A A Elongation peptide bond aa1 aa2 1-tRNA 2-tRNA anticodon U A C G A U A U G C U A C U U C G A hydrogen bonds codon mRNA
aa3 3-tRNA G A A aa1 peptide bond aa2 1-tRNA U A C (leaves) 2-tRNA G A U A U G C U A C U U C G A mRNA Ribosomes move over one codon
aa4 4-tRNA G C U peptide bonds aa1 aa2 aa3 2-tRNA 3-tRNA G A U G A A A U G C U A C U U C G A A C U mRNA
aa4 4-tRNA G C U peptide bonds aa1 aa2 aa3 2-tRNA G A U (leaves) 3-tRNA G A A A U G C U A C U U C G A A C U mRNA Ribosomes move over one codon
aa5 5-tRNA G G A peptide bonds aa1 aa2 aa4 aa3 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A C C U mRNA
aa5 5-tRNA G G A peptide bonds aa1 aa2 aa3 aa4 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A C C U mRNA Ribosomes move over one codon
aa5 aa4 Termination aa199 aa200 aa3 primary structure of a protein aa2 aa1 terminator or stop codon 200-tRNA C C U C A U G U U U A G mRNA
aa5 aa4 aa3 aa2 aa199 aa1 aa200 End Product • The end products of protein synthesis is a primary structure of a protein. • A sequence of amino acid bonded together by peptide bonds.
Question: • The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid. • What would be the DNA base code for this amino acid?
Answer: • tRNA - UAC (anticodon) • mRNA - AUG (codon) • DNA - TAC
When things go wrong… • Mutations: changes in the DNA sequence, that may be passed along to future generations. • Point mutations: a single base substitution THE CAT SAW THE RAT THE CAT SAW THE HAT • Deletion: a small DNA segment is lost THE CAT SAW THE RAT THE 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.