Transcript 8-5 ppt
8.5 Translation The student is expected to: 4B investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules and 6C explain the purpose and process of transcription and translation using models of DNA and RNA TEKS 4B, 6C Translation (In the cytoplasm) The mRNA made during transcription is used to make a protein. mRNA protein Click on the picture for video 8.5 Translation TEKS 4B, 6C Amino acids are coded by mRNA base sequences. • Translation converts mRNA messages into polypeptides. • A codon is a sequence of three nucleotides that codes for an amino acid. codon for methionine (Met) codon for leucine (Leu) Proteins Remember that proteins, which are sometimes called polypeptides, are macromolecules made of monomers called amino acids. Translation (In the cytoplasm) • During translation, ribosomes decode the mRNA message (made of nucleotides) to make polypeptide chains (made of amino acids). nuclear pore Step 1: Two subunits of the ribosome attach to the mRNA. Step 2 Ribosomes read the mRNA 5’ 3’. As each codon of the mRNA moves through the ribosome, the correct amino acid is brought to the ribosome by tRNA. The Genetic Code – In RNA, the nucleotides are read in “words” made of 3 nucleotide “letters”. Each “word” is called a codon and contains the genetic code for one amino acid. Move from the inside out! – – – The first “word” or start codon is always the same for every protein. It is always AUG. Using the genetic code wheel you can figure out which amino acid a codon represents. What amino acid is associated with the codon AUG? Methionine There are a total of 20 different amino acids that can be arranged in different ways to make different proteins. Step 3 Each tRNA molecule has a group of three nucleotides called the anticodon. These three nucleotides pair with the nucleotides in the codon. The tRNA molecule also has an amino acid attached. amino acid Anticodon (3 bases) Transfer RNA Step 4: Peptide bonds form between amino acids to form the polypeptide chain in a process called elongation (it makes the polypeptide chain longer.) Step 5: The ribosome continues to match the codons in the mRNA with anticodons in tRNA until it reads a codon in the mRNA that says “stop.” A tRNA for “stop” does not carry an amino acid. No peptide bond will form, so the ribosome releases the mRNA and the protein. Step 6: The newly formed polypeptide will start to coil and bend, forming the 3-D shape of proteins (recall the 4 levels of protein structure) Why are proteins important? Each protein has a specific function within living cells. Some functions of proteins are: 1. acting as enzymes, to speed up and regulate chemical reactions. 2. making pigments 3. determining your blood type. 4. regulating cell growth and development. Where in the cell does transcription occur? -Nucleus Where in the cell does translation occur? -Cytoplasm Activity 1 Transcription in nucleus AUG CGG Translation in cytoplasm Activity 1 Transcription in nucleus AUG CGG Translation in cytoplasm Met, Arg,