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Proteinsynthesis [Autosaved]11111111.ppt
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- 2. 2 Protein Synthesis Protein Synthesis The production (synthesis) of The production (synthesis) of polypeptide chains polypeptide chains (proteins) (proteins) Two phases: Two phases: Transcription Transcription & & Translation Translation mRNA must be mRNA must be processed before it processed before it leaves the nucleus leaves the nucleus of eukaryotic cells of eukaryotic cells
- 3. 3 Transcription Transcription Translation Translation DNA mRNA Ribosome Protein Prokaryotic Cell Prokaryotic Cell DNA DNA RNA RNA Protein Protein
- 4. 4 DNA DNA RNA RNA Protein Protein Nuclear membrane Transcription Transcription RNA Processing RNA Processing Translation Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Eukaryotic Cell Cell
- 5. 5 Pathway to Makinga Pathway to Making a Protein Protein DNA DNA mRNA mRNA tRNA (ribosomes) tRNA (ribosomes) Protein Protein
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- 7. 7 DNA or Protein? DNAor Protein? Walter Sutton discovered Walter Sutton discovered chromosomes chromosomes were made of were made of DNA and Protein DNA and Protein However, scientists were However, scientists were NOT NOT sure which one (protein sure which one (protein or DNA) was or DNA) was the actual the actual genetic material of the cell genetic material of the cell
- 8. 8 DNA! DNA! Frederick Griffith FrederickGriffith in 1928 showed the in 1928 showed the DNA DNA was the cell’s was the cell’s genetic material genetic material Watson & Crick Watson & Crick in in the 1950’s built the the 1950’s built the 1 1st st model of DNA model of DNA
- 9. 9 Structure of DNA Structureof DNA DNA is made of subunits called DNA is made of subunits called nucleotides nucleotides DNA nucleotides are composed of DNA nucleotides are composed of a a phosphate phosphate, , deoxyribose deoxyribose sugar, sugar, and and a nitrogen-containing base a nitrogen-containing base The 4 bases in DNA are: The 4 bases in DNA are: adenine adenine (A), (A), thymine (T), thymine (T), guanine (G), guanine (G), and cytosine (C) and cytosine (C)
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- 11. 11 Base Pairing Rule BasePairing Rule • Watson and Crick showed that DNA Watson and Crick showed that DNA is a is a double helix double helix • A A (adenine) pairs with (adenine) pairs with T T (thymine) (thymine) • C C (cytosine) pairs with (cytosine) pairs with G G (guanine) (guanine)
- 12. 12 Nitrogen Rings Nitrogen Rings •Purines Purines have have single single rings of rings of carbon-nitrogen (G, A) carbon-nitrogen (G, A) • Pyrimidines Pyrimidines have have double double carbon- carbon- nitrogen rings (C, T) nitrogen rings (C, T) • This is called This is called complementary complementary base pairing base pairing because a because a purine purine is is always paired with a always paired with a pyrimidine pyrimidine
- 13. 13 . 5’ to 3’Sugars 5’ to 3’ Sugars When the DNA When the DNA double helix double helix unwinds, it unwinds, it resembles a ladder resembles a ladder The The sides sides of the ladder are of the ladder are the the sugar-phosphate backbones sugar-phosphate backbones The The rungs rungs of the ladder are of the ladder are the the complementary paired bases complementary paired bases The two DNA strands are The two DNA strands are anti- anti- parallel parallel (they run in opposite (they run in opposite directions) directions)
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- 16. 16 Steps in DNAReplication Steps in DNA Replication Occurs when Occurs when chromosomes duplicate chromosomes duplicate (make copies) (make copies) An An exact copy exact copy of the DNA is produced of the DNA is produced with the aid of the enzyme with the aid of the enzyme DNA DNA polymerase polymerase Hydrogen bonds Hydrogen bonds between bases between bases break break and enzymes “unzip” the molecule and enzymes “unzip” the molecule Each Each old strand old strand of nucleotides serves as of nucleotides serves as a a template template for each new strand for each new strand New nucleotides New nucleotides move into move into complementary positions are joined by complementary positions are joined by DNA polymerase DNA polymerase
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- 18. 18 Another View ofReplication Another View of Replication
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- 20. 20 RNA Differs fromDNA RNA Differs from DNA 1. 1. RNA RNA has a sugar has a sugar ribose ribose DNA DNA has a sugar has a sugar deoxyribose deoxyribose 2. 2. RNA RNA contains the base contains the base uracil uracil (U) (U) DNA DNA has has thymine (T) thymine (T) 3. 3. RNA RNA molecule is molecule is single- single- stranded stranded DNA DNA is is double-stranded double-stranded
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- 22. 22 . Three Types ofRNA Three Types of RNA • Messenger RNA (mRNA) Messenger RNA (mRNA) carries carries genetic information to the genetic information to the ribosomes ribosomes • Ribosomal RNA (rRNA) Ribosomal RNA (rRNA), , along along with protein, makes up the with protein, makes up the ribosomes ribosomes • Transfer RNA (tRNA) Transfer RNA (tRNA) transfers transfers amino acids to the ribosomes amino acids to the ribosomes where proteins are synthesized where proteins are synthesized
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- 24. 24 Genes & Proteins Genes& Proteins Proteins Proteins are made of are made of amino amino acids acids linked together by linked together by peptide peptide bonds bonds 20 20 different amino acids different amino acids exist exist Amino acids chains are called Amino acids chains are called polypeptides polypeptides Segment of DNA that codes for Segment of DNA that codes for the amino acid sequence in a the amino acid sequence in a protein are called protein are called genes genes
- 25. 25 Two Parts ofProtein Two Parts of Protein Synthesis Synthesis Transcription Transcription makes an RNA makes an RNA molecule complementary to a molecule complementary to a portion of DNA portion of DNA Translation Translation occurs when the occurs when the sequence of bases of mRNA sequence of bases of mRNA DIRECTS DIRECTS the the sequence of amino sequence of amino acids acids in a polypeptide in a polypeptide
- 26. 26 Genetic Code Genetic Code DNA contains a DNA contains a triplet code triplet code Every three bases on DNA stands Every three bases on DNA stands for for ONE amino acid ONE amino acid Each three-letter unit on Each three-letter unit on mRNA mRNA is is called a called a codon codon Most amino acids have more than Most amino acids have more than one codon! one codon! There are There are 20 amino acids 20 amino acids with a with a possible 64 different triplets possible 64 different triplets The code is nearly The code is nearly universal universal among among living organisms living organisms
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- 29. 29 Overview of Transcription Overviewof Transcription During During transcription transcription in the in the nucleus, a segment of DNA nucleus, a segment of DNA unwinds and unzips, and the unwinds and unzips, and the DNA DNA serves as a serves as a template for mRNA template for mRNA formation formation RNA polymerase RNA polymerase joins the RNA joins the RNA nucleotides so that the nucleotides so that the codons in codons in mRNA are complementary mRNA are complementary to the to the triplet code in DNA triplet code in DNA
- 30. 30 Steps in Transcription Stepsin Transcription The transfer of information in the The transfer of information in the nucleus nucleus from a from a DNA DNA molecule to an molecule to an RNA RNA molecule molecule Only 1 Only 1 DNA DNA strand serves as the strand serves as the template template Starts at promoter Starts at promoter DNA DNA (TATA box) (TATA box) Ends at terminator Ends at terminator DNA DNA (stop) (stop) When complete, When complete, pre-RNA pre-RNA molecule is molecule is released released
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- 33. 33 What is the Whatis the enzyme enzyme responsible for the responsible for the production of the production of the mRNA molecule? mRNA molecule?
- 34. 34 RNA Polymerase RNA Polymerase Enzyme Enzyme found in the nucleus found in the nucleus Separates Separates the two DNA the two DNA strands by strands by breaking the breaking the hydrogen bonds hydrogen bonds between the between the bases bases Then moves along one of the Then moves along one of the DNA strands and DNA strands and links RNA links RNA nucleotides nucleotides together together
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- 36. 36 Question: Question: What wouldbe the What would be the complementary RNA strand complementary RNA strand for the following DNA for the following DNA sequence? sequence? DNA 5’- DNA 5’-GCGTATG GCGTATG-3’ -3’
- 37. 37 Answer: Answer: • DNA 5’-GCGTATG-3’ DNA5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5 RNA 3’-CGCAUAC-5’ ’
- 38. 38 Processing Pre-mRNA Processing Pre-mRNA •Also occurs in the Also occurs in the nucleus nucleus • Pre-mRNA Pre-mRNA made up of segments made up of segments called called introns & exons introns & exons • Exons code for proteins, while introns Exons code for proteins, while introns do NOT! do NOT! • Introns spliced out by Introns spliced out by splicesome- splicesome- enzyme enzyme and exons re-join and exons re-join • End product is a End product is a mature RNA mature RNA molecule molecule that leaves the nucleus to the that leaves the nucleus to the cytoplasm cytoplasm
- 39. 39 RNA Processing RNA Processing pre-RNAmolecule intro n intron exon exon exon exon exon exon Mature RNA molecule Mature RNA molecule exon exon exon intron intron splicesome splicesome
- 40. 40 Messenger RNA (mRNA) MessengerRNA (mRNA) • Carries the information for a Carries the information for a specific protein specific protein • Made up of Made up of 500 to 1000 500 to 1000 nucleotides nucleotides long long • Sequence of 3 bases called Sequence of 3 bases called codon codon • AUG AUG – methionine or – methionine or start start codon codon • UAA, UAG, or UGA UAA, UAG, or UGA – – stop stop codons codons
- 41. 41 Messenger RNA (mRNA) MessengerRNA (mRNA) methionine glycine serine isoleucine glycine alanine stop codon protein protein A U G G G C U C C A U C G G C G C A U A A mRNA mRNA start codon Primary structure of a protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1
- 42. 42 Transfer RNA (tRNA) TransferRNA (tRNA) • Made up of Made up of 75 to 80 nucleotides 75 to 80 nucleotides long long • Picks up the appropriate Picks up the appropriate amino acid amino acid floating in the cytoplasm floating in the cytoplasm • Transports Transports amino acids amino acids to the to the mRNA mRNA • Have Have anticodons anticodons that are that are complementary to complementary to mRNA codons mRNA codons • Recognizes the appropriate Recognizes the appropriate codons codons on on the the mRNA mRNA and bonds to them with and bonds to them with H-bonds H-bonds
- 43. 43 Transfer RNA (tRNA) TransferRNA (tRNA) amino acid amino acid attachment site attachment site U A C anticodon anticodon methionine amino acid amino acid
- 44. 44 Ribosomal RNA (rRNA) RibosomalRNA (rRNA) • Made up of rRNA Made up of rRNA is is 100 to 3000 100 to 3000 nucleotides nucleotides long long • Made inside the Made inside the nucleus nucleus of a cell of a cell • Associates with Associates with proteins to form proteins to form ribosomes ribosomes
- 45. 45 Ribosomes Ribosomes • Made ofa large and small subunit • Composed of rRNA (40%) and proteins (60%) • Have two sites for tRNA attachment --- P and A
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- 47. 47 Translation Translation • Synthesis ofproteins Synthesis of proteins in the in the cytoplasm cytoplasm • Involves the following: Involves the following: 1. 1. mRNA (codons) mRNA (codons) 2. 2. tRNA (anticodons) tRNA (anticodons) 3. 3. ribosomes ribosomes 4. 4. amino acids amino acids
- 48. 48 Translation Translation • Three steps: Threesteps: 1. 1. initiation initiation: start codon (AUG) : start codon (AUG) 2. 2. elongation elongation: amino acids linked : amino acids linked 3. 3. termination termination: stop codon : stop codon (UAG, UAA, or UGA). (UAG, UAA, or UGA). Let’s Make a Protein ! Let’s Make a Protein !
Editor's Notes
- #10 Notice that the 3’ and 5’ refer to a numbering system for the carbon atoms that make up the sugar.
- #14 On the left is the DNA double helix. When the helix is unwound, a ladder configuration shows that the uprights are composed of sugar and phosphate molecules and the rungs are complementary bases. Notice that the bases in DNA pair in such a way that the phosphate-sugar groups are oriented in different directions. This means that the strands of DNA end up running antiparallel to one another, with the 3’ end of one strand opposite the 5’ end of the other strand.
- #16 DNA polymerase is an enzyme.
- #17 Replication is called semiconservative because each new double helix is composed of an old (parental) strand and a new (daughter) strand.
- #18 Use of the ladder configuration better illustrates how complementary nucleotides available in the cell pair with those of each old strand before they are joined together to form a daughter strand.
- #21 Like DNA, RNA is a polymer of nucleotides. In an RNA nucleotide, the sugar ribose is attached to a phosphate molecule and to a base, either G, U, A, or C. Notice that in RNA, the base uracil replaces thymine as one of the pyrimidine bases. RNA is single-stranded, whereas DNA is double-stranded.
- #26 The fact that the genetic code is about universal in living things suggests that the code dates back to the first organisms on earth and that all living things are related.
- #27 Notice that in this chart, each of the codons (white rectangles) is composed of three letters representing the first base, second base, and third base. For example, find the rectangle where C for the first base and A for the second base intersect. You will see that U, C, A, or G can be the third base. CAU and CAC are codons for histidine; CAA and CAG are codons for glutamine.
- #28 Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein.
- #32 During transcription, complementary RNA is made from a DNA template. A portion of DNA unwinds and unzips at the point of attachment of RNA polymerase. A strand of mRNA is produced when complementary bases join in the order dictated by the sequence of bases in DNA. Transcription occurs in the nucleus, and the mRNA passes out of the nucleus to enter the cytoplasm.