PROTEIN SYNTHESIS Protein Synthesis The production synthesis of

PROTEIN SYNTHESIS

Protein Synthesis • The production (synthesis) of proteins • 3 phases: phases 1. Transcription 2. RNA processing 3. Translation • Remember: DNA RNA Protein

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

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

Question: • How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)? acid)

RNA differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose

2. RNA contains uracil (U) DNA has thymine (T)

RNA molecule is singlestranded DNA is doublestranded 3.

The Genetic Code There are 20 amino acids found in proteins but only four different bases in messenger RNA. To code for all 20 amino acids, a sequence of three nucleotides must be used for each amino acid. Each triplet of nucleotides is called a codon. The use of three nucleotides results in 64 different possible combinations (4364), which easily code for the 20 amino acids that exist.

The Genetic Code

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

1. 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, pre-RNA molecule is released.

Promoter • Consists of a base-pair pattern, one that is high in adenine and thymine bases. • Adenine and thymine share only two hydrogen • It takes less energy to break two bonds; therefore, the RNA polymerase expends less energy opening up the DNA helix if it possesses a high concentration of adenine and thymine base pairs.

Question: • What is the enzyme responsible for the production of the RNA molecule?

Answer: RNA Polymerase • Separates the DNA molecule by breaking the Hbonds between the bases. • Then moves along one of the DNA strands and links RNA nucleotides together.

DID YOU KNOW ? • There are three forms of the RNA polymerase in eukaryotes: • RNA polymerase I transcribes ribosomal RNA. • RNA polymerase II transcribes m. RNA. • RNA polymerase III transcribes t. RNA and other short genes that are about 100 base pairs in length.

1. Transcription

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

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

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

2. RNA Processing • Maturation of pre-RNA molecules. • Also occurs in the nucleus. • Introns spliced out by splicesome-enzyme and exons come together. • End product is a mature RNA molecule that leaves the nucleus to the cytoplasm.

5 cap • This 5 cap consists of 7 -methyl guanosine, which forms a modified guanine nucleoside triphosphate • The cap protects the m. RNA from digestion by nucleases and phosphatases as it exits the nucleus and enters the cytoplasm • It also plays a role in the initiation of translation.

poly-A tail. • 200 adenine ribonucleotides is added to the 3 end by the enzyme poly-A polymerase. • The 3 end is known to contain a poly-A tail. • This whole process is known as capping and tailing.

2. RNA Processing pre-RNA molecule exon intron exon splicesome exon Mature RNA molecule A-A-A Poly A Tail

Types of RNA • Three types of RNA: RNA A. messenger RNA (m. RNA) B. transfer RNA (t. RNA) C. ribosome RNA (r. RNA) • Remember: all produced in the nucleus!

A. Messenger RNA (m. RNA) • Carries the information for a specific protein • Made up of 500 to 1000 nucleotides long. • Made up of codons (sequence of three bases: AUG - methionine). • Each codon, codon is specific for an amino acid

A. 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 Primary structure of a protein aa 1 aa 2 aa 3 peptide bonds aa 4 aa 5 aa 6 codon 7 stop codon

B. Transfer RNA (t. RNA) • Made up of 75 to 80 nucleotides long. • Picks up the appropriate amino acid floating in the cytoplasm (amino acid activating enzyme) enzyme • 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.

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

C. Ribosomal RNA (r. RNA) • Made up of r. RNA is 100 to 3000 nucleotides long. • Important structural component of a ribosome. • Associates with proteins to form ribosomes.

Ribosomes • Large and small subunits. • Composed of r. RNA (40%) and proteins (60%). • Both units come together and help bind the m. RNA and t. RNA. • Two sites for t. RNA a. P site (first and last t. RNA will attach) attach b. A site

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

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

3. Translation • Synthesis of proteins in the cytoplasm • Involves the following: 1. m. RNA (codons) 2. t. RNA (anticodons) 3. r. RNA 4. ribosomes 5. amino acids

3. Translation • Three parts: 1. initiation: initiation start codon (AUG) 2. elongation: elongation 3. termination: termination stop codon (UAG) • Let’s make a PROTEIN!!!!

3. Translation Large subunit P Site A Site m. RNA A U G Small subunit C U A C U U C G

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

Elongation peptide bond aa 3 aa 1 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

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

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

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

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

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

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 m. RNA terminator or stop codon C A U G U U U A G

End Product • 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

Polyribosome • Groups of ribosomes reading same m. RNA simultaneously producing many proteins (polypeptides). incoming large subunit 1 incoming small subunit 2 3 4 polypeptide 5 6 7 m. RNA

Question: • The anticodon UAC belongs to a t. RNA that recognizes and binds to a particular amino acid. • What would be the DNA base code for this amino acid?

Answer: • t. RNA • m. RNA • DNA - UAC (anticodon) - AUG (codon) - TAC