PROTEIN SYNTHESIS 1 Protein Synthesis The production synthesis

PROTEIN SYNTHESIS 1

Protein Synthesis § The production (synthesis) of polypeptide chains (proteins) § Two phases: Transcription & Translation § m. RNA must be processed before it leaves the nucleus of eukaryotic cells 2

DNA m. RNA Protein DNA Transcription m. RNA Ribosome Translation Protein Prokaryotic Cell 3

DNA m. RNA Protein Nuclear membrane DNA Transcription Eukaryotic Cell Pre-m. RNA Processing m. RNA Ribosome Translation Protein 4

Pathway to Making a Protein DNA m. RNA Protein 5

Nucleic Acids 6

DNA or Protein? § Walter Sutton discovered chromosomes were made of DNA and Protein § However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell 7

DNA! § Frederick Griffith in 1928 showed the DNA was the cell’s genetic material § Watson & Crick in the 1950’s built the 1 st model of DNA 8

Structure of DNA § DNA is made of subunits called nucleotides § DNA nucleotides are composed of a phosphate, deoxyribose sugar, and a nitrogen-containing base § The 4 bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C) 9

DNA Nucleotide 10

Base Pairing Rule • Watson and Crick showed that DNA is a double helix • A (adenine) pairs with T (thymine) • C (cytosine) pairs with G (guanine) 11

Nitrogen Rings • Purines have single rings of carbon-nitrogen (G, A) • Pyrimidines have double carbonnitrogen rings (C, T) • This is called complementary base pairing because a purine is always paired with a pyrimidine 12

. 5’ to 3’ Sugars When the DNA double helix unwinds, it resembles a ladder The sides of the ladder are the sugar-phosphate backbones The rungs of the ladder are the complementary paired bases The two DNA strands are anti -parallel (they run in opposite directions) 13

Anti. Parallel Strands of DNA 14

DNA Replication 15

Steps in DNA Replication Occurs when chromosomes duplicate (make copies) An exact copy of the DNA is produced with the aid of the enzyme DNA polymerase Hydrogen bonds between bases break and enzymes “unzip” the molecule Each old strand of nucleotides serves as a template for each new strand New nucleotides move into complementary positions are joined by DNA polymerase 16

Two New, Identical DNA Strands Result from Replication 17

Another View of Replication 18

RNA 19

RNA Differs from DNA 1. RNA DNA 2. RNA DNA 3. RNA DNA has a sugar ribose has a sugar deoxyribose contains the base uracil (U) has thymine (T) molecule is single-stranded is double-stranded 20

Structure of RNA 21

. Three Types of RNA • Messenger RNA (m. RNA) carries genetic information to the ribosomes • Ribosomal RNA (r. RNA), along with protein, makes up the ribosomes • Transfer RNA (t. RNA) transfers amino acids to the ribosomes where proteins are synthesized 22

Making a Protein 23

Genes & Proteins § Proteins are made of amino acids linked together by peptide bonds § 20 different amino acids exist § Amino acids chains are called polypeptides § Segment of DNA that codes for the amino acid sequence in a protein are called genes 24

Two Parts of Protein Synthesis § Transcription makes an RNA molecule complementary to a portion of DNA § Translation occurs when the sequence of bases of m. RNA gives the sequence of amino acids in a protein 25

Overview of Transcription § During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves as a template for m. RNA formation § RNA polymerase joins the RNA nucleotides so that the codons in m. RNA are complementary to the triplet code in DNA 26

Transcription Translation 27

Steps in 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 promoter DNA (TATA box) § Ends at terminator DNA (stop) § When complete, m. RNA molecule is released 28

Transcription 29

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What is the enzyme responsible for the production of the m. RNA molecule? 31

RNA Polymerase § Enzyme found in the nucleus § Helicase separates the two DNA strands by breaking the hydrogen bonds between the bases § Then RNA Polymerase moves along one of the DNA strands and links RNA nucleotides together 32

DNA RNA Polymerase m. RNA 33

Question: § What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’ 34

Answer: • DNA 5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5’ 35

Processing Pre-m. RNA • Also occurs in the nucleus • Pre-m. RNA made up of segments called introns & exons • Exons code for proteins, while introns do NOT! • Introns spliced out by splicesomeenzyme and exons re-join • End product is a mature RNA molecule that leaves the nucleus to the cytoplasm 36

RNA Processing pre-RNA molecule exon intron exon splicesome exon Mature RNA molecule 37

Messenger RNA (m. RNA) • Carries the information for a specific protein • Made up of 500 to 1000 nucleotides long • Sequence of 3 bases called codon • AUG – methionine or start codon • UAA, UAG, or UGA – stop codons 38

Messenger RNA (m. RNA) start codon m. RNA A U G G G C U C C A U C G G C A U A A codon 1 protein methionine codon 2 codon 3 glycine serine codon 4 isoleucine codon 5 codon 6 glycine alanine codon 7 stop codon Primary structure of a protein aa 1 aa 2 aa 3 peptide bonds aa 4 aa 5 aa 6 39

Genetic Code § DNA contains a triplet code § Every three bases on DNA stands for ONE amino acid § Each three-letter unit on m. RNA is called a codon § Most amino acids have more than one codon! § There are 20 amino acids with a possible 64 different triplets § The code is nearly universal among living organisms 40

Translation • Synthesis of cytoplasm at proteins in the ribosome • Involves the following: 1. m. RNA (codons) 2. t. RNA (anticodons) 3. ribosomes 4. amino acids 41

Transfer RNA (t. RNA) • Made up of 75 to 80 nucleotides long • Picks up the appropriate amino acid floating in the cytoplasm • Transports amino acids to the m. RNA • Have anticodons that are complementary to m. RNA codons • Recognizes the appropriate codons on the m. RNA and bonds to them with H -bonds 42

Transfer RNA (t. RNA) amino acid attachment site methionine amino acid U A C anticodon 43

Ribosomes • Site of protein synthesis • Made of a large and small subunit • Composed of r. RNA (40%) and proteins (60%) • Have two sites for t. RNA attachment --- P and A 44

Ribosomes Large subunit P Site A Site m. RNA Small subunit A U G C U A C U U C G 45

Translation • Three steps of translation: 1. initiation: start codon (AUG) 2. elongation: amino acids linked 3. termination: stop codon (UAG, UAA, or UGA). Let’s Make a Protein ! 46

m. RNA Codons Join the Ribosome Large subunit P Site A Site m. RNA A U G Small subunit C U A C U U C G 47

Initiation aa 1 1 -t. RNA anticodon hydrogen bonds U A C A U G codon aa 2 2 -t. RNA G A U C U A C U U C G A m. RNA 48

Elongation peptide bond aa 1 aa 3 aa 2 3 -t. RNA 1 -t. RNA anticodon hydrogen bonds U A C A U G codon 2 -t. RNA G A U C U A C U U C G A m. RNA 49

aa 1 peptide bond aa 3 aa 2 1 -t. RNA 3 -t. RNA U A C (leaves) 2 -t. RNA A U G G A A G A U C U A C U U C G A m. RNA Ribosomes move over one codon 50

aa 1 peptide bonds aa 2 aa 4 aa 3 4 -t. RNA 2 -t. RNA A U G 3 -t. RNA G C U G A A C U U C G A A C U m. RNA 51

aa 1 peptide bonds aa 4 aa 2 aa 3 2 -t. RNA 4 -t. RNA G A U (leaves) 3 -t. RNA A U G G C U G A A C U U C G A A C U m. RNA Ribosomes move over one codon 52

aa 1 peptide bonds aa 5 aa 2 aa 3 aa 4 5 -t. RNA U G A 3 -t. RNA 4 -t. RNA G A A G C U A C U U C G A A C U m. RNA 53

peptide bonds aa 1 aa 5 aa 2 aa 3 aa 4 5 -t. RNA U G A 3 -t. RNA G A A 4 -t. RNA G C U A C U U C G A A C U m. RNA Ribosomes move over one codon 54

aa 4 aa 5 Termination aa 199 aa 3 primary structure aa 2 of a protein aa 200 aa 1 200 -t. RNA A C U terminator or stop codon C A U G U U U A G m. RNA 55

End Product –The Protein! • The end products of protein synthesis is a primary structure of a protein • A sequence of amino acid bonded together by peptide bonds aa 2 aa 1 aa 3 aa 4 aa 5 aa 199 aa 200 56

Messenger RNA (m. RNA) • Carries the information for a specific protein • Made up of 500 to 1000 nucleotides long • Sequence of 3 bases called codon • AUG – methionine or start codon • UAA, UAG, or UGA – stop codons 57

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