PROTEIN SYNTHESIS 1 DNA and Genes DNA DNA

PROTEIN SYNTHESIS 1

DNA and Genes

DNA • DNA contains genes, sequences of nucleotide bases • These Genes code for polypeptides (proteins) • Proteins are used to build cells and do much of the work inside cells

Genes & Proteins § Proteins are made of amino acids linked together by peptide bonds § 20 different amino acids exist 4

Amino Acid Structure 5

Polypeptides • Amino acid chains are called polypeptides 6

DNA Begins the Process • DNA is found inside the nucleus • Proteins, however, are made in the cytosol of cells by organelles called ribosomes • Ribosomes may be free in the cytosol or attached to the surface of rough ER 7

Starting with DNA • DNA ‘s code must be copied and taken to the cytosol • In the cytosol, this code must be read so amino acids can be assembled to make polypeptides (proteins) • This process is called PROTEIN SYNTHESIS 8

RNA

Roles of RNA and DNA • DNA is the MASTER PLAN • RNA is the BLUEPRINT of the Master Plan 10

RNA Differs from DNA • RNA has a sugar ribose DNA has a sugar deoxyribose 11

Other Differences • • RNA contains the base uracil (U) DNA has thymine (T) RNA molecule is single-stranded DNA is doublestranded DNA 12

Structure of RNA 13

. Three Types of RNA • Messenger RNA (m. RNA) copies DNA’s code & carries the 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 14

Messenger RNA • Long Straight chain of Nucleotides • Made in the Nucleus • Copies DNA & leaves through nuclear pores • Contains the Nitrogen Bases A, G, C, U ( no T ) 15

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 16 codons

Ribosomal RNA (r. RNA) • r. RNA is a single strand 100 to 3000 nucleotides long • Globular in shape • Made inside the nucleus of a cell • Associates with proteins to form ribosomes • Site of protein Synthesis 17

The Genetic Code • A codon designates an amino acid • An amino acid may have more than one codon • There are 20 amino acids, but 64 possible codons • Some codons tell the ribosome to stop translating 18

The Genetic Code • Use the code by reading from the center to the outside • Example: AUG codes for Methionine 19

Name the Amino Acids • • • GGG? UCA? CAU? GCA? AAA? 20

Remember the Complementary Bases On DNA: A-T C-G On RNA: A-U C-G 21

Transfer RNA (t. RNA) • Clover-leaf shape • Single stranded molecule with attachment site at one end for an amino acid • Opposite end has three nucleotide bases called the anticodon 22

Transfer RNA amino acid attachment site U A C anticodon 23

Codons and Anticodons • The 3 bases of an anticodon are complementary to the 3 bases of a codon • Example: Codon ACU Anticodon UGA ACU 24

Transcription and Translation

Pathway to Making a Protein DNA m. RNA t. RNA (ribosomes) Protein 26

Protein Synthesis § The production or synthesis of polypeptide chains (proteins) § Two phases: Transcription & Translation § m. RNA must be processed before it leaves the nucleus of eukaryotic cells 27

DNA RNA Protein Nuclear membrane DNA Transcription Eukaryotic Cell Pre-m. RNA Processing m. RNA Ribosome Translation Protein 28

Transcription • The process of copying the sequence of one strand of DNA, the template strand • m. RNA copies the template strand • Requires the enzyme RNA Polymerase 29

Template Strand 30

Question: § What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’ 31

Answer: • DNA 5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5’ 32

Transcription • During transcription, RNA polymerase binds to DNA and separates the DNA strands • RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA 33

Transcription • Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA • Called the TATA box • Specific base sequences act as signals to stop • Called the termination signal 34

RNA Polymerase 35

m. RNA Processing • After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional • Introns, non-functional segments of DNA are snipped out of the chain 36

m. RNA Editing • Exons, segments of DNA that code for proteins, are then rejoined by the enzyme ligase • A guanine triphosphate cap is added to the 5” end of the newly copied m. RNA • A poly A tail is added to the 3’ end of the RNA • The newly processed m. RNA can then leave the nucleus 37

Result of Transcription CAP New Transcript Tail 38

m. RNA Transcript • m. RNA leaves the nucleus through its pores and goes to the ribosomes 39

Translation • Translation is the process of decoding the m. RNA into a polypeptide chain • Ribosomes read m. RNA three bases or 1 codon at a time and construct the proteins 40

Transcription Translation 41

Ribosomes • 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 42

Step 1 - Initiation • m. RNA transcript start codon AUG attaches to the small ribosomal subunit • Small subunit attaches to large ribosomal subunit m. RNA transcript 43

Ribosomes Large subunit P Site A Site m. RNA Small subunit A U G C U A C U U C G 44

Step 2 - Elongation • As ribosome moves, two t. RNA with their amino acids move into site A and P of the ribosome • Peptide bonds join the amino acids

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 46

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 47

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 48

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 49

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 50

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 51

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 52

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 53

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 54

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 55

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