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

Pathway to Making a Protein DNA m. RNA t. RNA (ribosomes) Protein 3

RNA 4

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 5

Structure of RNA 6

. 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 7

Making a Protein 8

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 9

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 DIRECTS the sequence of amino acids in a polypeptide 10

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 11

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Transcription Translation 13

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 14

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 § When complete, pre-RNA molecule is released 15

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RNA Polymerase § Enzyme found in the nucleus § Separates the two DNA strands by breaking the hydrogen bonds between the bases § Then moves along one of the DNA strands and links RNA nucleotides together 17

Question: § What would be the complementary RNA strand for the following DNA sequence? DNA - GCGTATG 18

Answer: • DNA - GCGTATG • RNA - CGCAUAC 19

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 enzyme and exons re-join • End product is a mature RNA molecule that leaves the nucleus to the cytoplasm 20

RNA Processing pre-RNA molecule exon intron exon splicesome exon Mature RNA molecule 21

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 22

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 23

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 24

Transfer RNA (t. RNA) amino acid attachment site methionine amino acid U A C anticodon 25

Ribosomal RNA (r. RNA) • Made up of r. RNA is 100 to 3000 nucleotides long • Made inside the nucleus of a cell • Associates with proteins to form ribosomes 26

Translation • Synthesis of proteins in the cytoplasm • Involves the following: 1. m. RNA (codons) 2. t. RNA (anticodons) 3. ribosomes 4. amino acids 27

Translation • Three steps: 1. initiation: start codon (AUG) 2. elongation: amino acids linked 3. termination: stop codon (UAG, UAA, or UGA). Let’s Make a Protein ! 28

m. RNA Codons Join the Ribosome Large subunit m. RNA A U G Small subunit C U A C U U C G 29

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 30

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 31

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 32

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 33

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 34

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 35

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 36

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 37

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 38