Transcription and Translation Genes to Proteins Transcription and Translation

DNA  RNA  Protein DNA contains genes which provide the information necessary to make proteins Different versions of the same gene result in different versions or amounts of a protein, and the differences in the protein result in different characteristics Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein

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RNA How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)? RNA has a sugar ribose DNA has a sugar deoxyribose RNA contains uracil (U) DNA has thymine (T) RNA molecule is single-stranded DNA is double-stranded

Transcription The process that copies the message in a gene into a messenger RNA (mRNA) molecule that will provide the instructions for making a protein molecule Started and controlled by an enzyme called RNA polymerase. RNA polymerase binds to the DNA at a special point (start signal) RNA polymerase unwinds and separates the two DNA strands RNA polymerase adds and links complementary RNA nucleotides as it “reads” the gene until it reaches a “stop” signal RNA polymerase DNA mRNA

Transcription

Products of Transcription Ribosomal RNA (rRNA) – Carrier molecule on ribosomes – holds the tRNA and mRNA in place Transfer RNA (tRNA) - The molecule that physically couples nucleic acid codons with specific amino acids Messenger RNA (mRNA) - The messenger that carries information from genes on DNA to the protein manufacturing ribosomes

Translation The process that makes proteins Translation The process that makes proteins. The sequence of nucleotides in an mRNA molecule specifies the sequence of amino acids in a protein. This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. Codon= series of three nucleotides A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

Messenger RNA (mRNA) Primary structure of a protein Each codon translates into one of twenty amino acids or is a stop or start signal A U G C mRNA 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

The Genetic Code UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG GUU GUC GUA GUG UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG UAU UAC UAA UAG CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA GAG UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG Phenylalanine Leucine Valine Serine Proline Threonine Alanine Tyrosine Stop Histidine Glutamine Asparagine Lysine Glutamic Acid Cysteine Arginine Serine Glycine Stop Tryptophan Isoleucine Methionine

Note that 3rd Base Position is Variable

Eukaryotic Cell Protein Synthesis

Protein Synthesis occurs on Ribosomes

Protein Synthesis occurs on Ribosomes A ribosome on the rough endoplasmic reticulum attaches to the mRNA molecule. ribosome A U G G G C U U A A A G C A G U G C A C G U U

Along comes a Transfer RNA Molecule… amino acid attachment site U A C anticodon methionine amino acid

A U G G G C U U A A A G C A G U G C A C G U U Amino acid U A C tRNA molecule The tRNA brings an amino acid to the first three bases (codon) on the mRNA. The three unpaired bases (anticodon) on the tRNA link up with the codon. anticodon A U G G G C U U A A A G C A G U G C A C G U U

U A C C C G Another tRNA molecule comes into place, bringing a second amino acid. Its anticodon links up with the second codon on the mRNA. A U G G G C U U A A A G C A G U G C A C G U U

U A C C C G Peptide bond A peptide bond forms between the two amino acids. A U G G G C U U A A A G C A G U G C A C G U U

U A C C C G The first tRNA molecule releases its amino acid and moves off into the cytoplasm. A U G G G C U U A A A G C A G U G C A C G U U

C C G The ribosome moves along the mRNA to the next codon. A U G G G C U U A A A G C A G U G C A C G U U

C C G A A U Another tRNA molecule brings the next amino acid into place. A U G G G C U U A A A G C A G U G C A C G U U

C C G C C G A peptide bond joins the second and third amino acids to form a polypeptide chain. A U G G G C U U A A A G C A G U G C A C G U U

A C G G U C The process continues. The polypeptide chain gets longer. This continues until a termination (stop) codon is reached. The polypeptide is then complete. A U G G G C U U A A A G C A G U G C A C G U U

There is a tunnel through the large subunit of the ribosome that allows the growing polypeptide chain to pass out of the ribosome

Termination of translation is triggered by stop codons A release factor enters the A site and triggers hydrolysis of the peptidyl-tRNA bond leading to the release of the protein.

Release of the protein causes the disassociation of the ribosome into its constituent subunits.

Transcription And Translation In Prokaryotes 3’ 5’ 5’ mRNA RNA Pol. Ribosome Ribosome Everything happens in the nucleus

Eukaryotic Transcription DNA Cytoplasm Nucleus Nuclear pores RNA Transcription G AAAAAA RNA Processing mRNA Export G AAAAAA

Eukaryotic Translation

Transcription/Translation Quiz What is transcription? Production of RNA molecules by copying part of DNA into a complementary sequence of RNA Why is transcription necessary? Transcription makes messenger RNA (mRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm. Describe transcription. RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble mRNA. It uses the nucleotide bases except it replaces Thymine with Uracil

Transcription/Translation Quiz What is translation? The genetic message encoded in RNA is used to create a polypeptide with a specific amino acid sequence Describe translation. The cell uses information from mRNA and tRNA to produce proteins. Why is translation necessary? Translation assures that the right amino acids are joined together by peptides to form the correct protein. What are the main differences between DNA and RNA? DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil.