PROTEIN SYNTHESIS 1 DNA AND GENES DNA DNA

PROTEIN SYNTHESIS 1

DNA AND GENES

DNA ■ DNA contains genes, sequences of nucleotide bases ■ Genes have different alleles. ■ These genes code for polypeptides (proteins)

Genes & Proteins § Proteins are made of amino acids linked together by covalent bonds called peptide bonds § Dehydration synthesis or condensation reactions form the 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 copy 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 singlestranded DNA is double-stranded 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 codons 16

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 in the nucleolus ■ Associates with proteins to form ribosomes ■ Site of protein Synthesis 17

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 18

Transfer RNA amino acid attachment site U A C anticodon 19

Codons and Anticodons ■ The 3 bases of an anticodon are complementary to the 3 bases of a codon ■ Example: Codon ACU Anticodon UGA ACU 20

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 21

The Genetic Code • Use the code by reading from the center to the outside • Example: AUG codes for Methionine 22

Name the Amino Acids ■ GGG? ■ UCA? ■ CAU? ■ GCA? ■ AAA? 23

TRANSCRIPTION AND TRANSLATION

Pathway to Making a Protein DNA m. RNA t. RNA (ribosomes) Protein 25

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 26

DNA RNA Protein Eukaryotic Cell Nuclear membrane DNA Transcription Pre-m. RNA Processing m. RNA Ribosome Translation Protein 27

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 28

Question: § What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’ 29

Answer: ■DNA 5’-GCGTATG-3’ ■RNA 3’-CGCAUAC-5’ 30

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 31

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 32

RNA Polymerase 33

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 34

m. RNA Editing ■ Exons, segments of RNA 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 35

Result of Transcription CAP New Transcript Tail 36

m. RNA Transcript • m. RNA leaves the nucleus through its pores and goes to the ribosomes 37

Translation ■ Translation is the process of 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 38

Transcription Translation 39

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 40

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 41

Ribosomes Large subunit P Site A Site m. RNA Small subunit A U G C U A C U U C G 42

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 44

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 45

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 46

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 47

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 48

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 49

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 50

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 51

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 52

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 aa 4 aa 5 aa 6 peptide bonds 53