PROTEIN SYNTHESIS

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

DNA  RNA  Protein Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

DNA  RNA  Protein Prokaryotic Cell DNA mRNA Ribosome Protein Transcription Translation DNA mRNA Ribosome Protein Prokaryotic Cell

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

3.RNA molecule is single-stranded DNA is double-stranded

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

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 H-bonds 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 mRNA. RNA polymerase III transcribes tRNA and other short genes that are about 100 base pairs in length.

1. Transcription

Question: DNA 5’-GCGTATG-3’ 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 Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

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 mRNA 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 intron exon exon exon splicesome exon Mature RNA molecule A-A-A Poly A Tail

Types of RNA Three types of RNA: A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosome RNA (rRNA) Remember: all produced in the nucleus!

A. Messenger RNA (mRNA) 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, is specific for an amino acid.

A. Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2 start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

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

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

C. Ribosomal RNA (rRNA) Made up of rRNA 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 rRNA (40%) and proteins (60%). Both units come together and help bind the mRNA and tRNA. Two sites for tRNA a. P site (first and last tRNA will attach) b. A site

Ribosomes Large subunit P Site A Site mRNA A U G C Small subunit

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

3. Translation Synthesis of proteins in the cytoplasm Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. rRNA 4. ribosomes 5. amino acids

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

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

Initiation G aa2 A U U A C aa1 A U G C U A C U U C G A codon 2-tRNA anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA

Elongation peptide bond G A aa3 aa1 aa2 U A C G A U A U G C U A C U U 3-tRNA G A aa3 aa1 aa2 1-tRNA 2-tRNA anticodon U A C G A U A U G C U A C U U C G A hydrogen bonds codon mRNA

Ribosomes move over one codon aa1 peptide bond 3-tRNA G A aa3 aa2 1-tRNA U A C (leaves) 2-tRNA G A U A U G C U A C U U C G A mRNA Ribosomes move over one codon

peptide bonds G C U aa4 aa1 aa2 aa3 G A U G A A A U G C U A C U U C G 4-tRNA G C U aa4 aa1 aa2 aa3 2-tRNA 3-tRNA G A U G A A A U G C U A C U U C G A A C U mRNA

Ribosomes move over one codon peptide bonds 4-tRNA G C U aa4 aa1 aa2 aa3 2-tRNA G A U (leaves) 3-tRNA G A A A U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

peptide bonds U G A aa5 aa1 aa2 aa4 aa3 G A A G C U G C U A C U U C G 5-tRNA aa5 aa1 aa2 aa4 aa3 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A A C U mRNA

Ribosomes move over one codon peptide bonds U G A 5-tRNA aa5 aa1 aa2 aa3 aa4 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

Termination aa5 aa4 aa3 primary structure of a protein aa2 aa1 A C U C terminator or stop codon 200-tRNA A C U C A U G U U U A G mRNA

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. aa1 aa2 aa3 aa4 aa5 aa200 aa199

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

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

Answer: tRNA - UAC (anticodon) mRNA - AUG (codon) DNA - TAC