RNA and Protein Synthesis
How does a gene work? Gene – sequence of DNA that codes for a protein and thus determines a trait. Genes are instruction manuals for our bodies
The Structure of RNA RNA, like DNA is made of a long chain of nucleotides. Each nucleotide is made up of a ribose sugar, a phosphate, and a nitrogenous base.
Differences between DNA and RNA DNA has: deoxyribose sugar double stranded A,T,G,C RNA has: ribose sugar single stranded A, U, G, C U = uracil
Three types of RNA Transfer RNA (tRNA) Ribosomal RNA (rRNA) Messenger RNA (mRNA)
Transcription (to copy) Transcription is copying part of a nucleotide sequence of DNA into a complementary sequence of RNA.
RNA polymerase (an enzyme) During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
How does RNA polymerase know where to start and stop making an RNA copy of DNA? RNA polymerase only binds to regions of DNA called promoters, which have specific base sequences.
RNA must be edited before it can go to work. DNA of eukaryote genes contains sequences of nucleotides called introns, that are not involved in coding for proteins.
The DNA sequence that codes for the protein is called the exon. Introns are cut out before the mRNA leaves the nucleus. The remaining exons are spliced back together to form the final mRNA.
The Genetic Code Proteins are made of long chains of amino acids called polypeptides. There are 20 different amino acids. The type of protein is determined by the order of the amino acids. The order of the amino acids is determined by the order of the nitrogenous bases.
The language of mRNA is the genetic code. The code is read three bases at a time. Each three-base “word” in mRNA is called a codon. UCGCACGGU = UCG-CAC-GGU codon
There are 64 possible 3-base codons. Each amino acid can have more than one codon. UAC = Tyr How many codons code for Leucine?
Translation – the decoding of the mRNA message into a polypeptide chain (protein). nucleus mRNA leaves the nucleus Attaches to a ribosome in the cytoplasm mRNA Ribosome
Transfer RNA (tRNA) As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA. tRNA
Each tRNA molecule carries only one kind of amino acid. tRNA has three unpaired bases. These bases are called the anticodon. Anticodon is complementary to the mRNA codon.
AUG = start codon start
Ribosome moves along mRNA, tRNA brings in correct amino acids.
The process continues until the ribosome reaches a stop codon. The result is a complete polypeptide (protein) PROTEIN = long chain of amino acids.
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