VII RNA and Protein Synthesis

Genes, segment of DNA, are coded DNA instructions that control the production of proteins. Genetic messages can be decoded and used in protein synthesis by copying part of the nucleotide sequence from DNA into mRNA. mRNA contains coded information for making proteins.

The Structure of RNA There are three main differences between RNA and DNA: The sugar in RNA is ribose instead of deoxyribose. RNA is generally single-stranded. RNA contains uracil in place of thymine.

Types of RNA There are three main types of RNA: messenger RNA ribosomal RNA transfer RNA

Types of RNA The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.

Ribosomes are made up of proteins and ribosomal RNA (rRNA). The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes. Ribosomes are made up of proteins and ribosomal RNA (rRNA).

Amino acid The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Transfer RNA During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.

Protein Synthesis DNA molecule DNA strand (template) 3¢ 5¢ TRANSCRIPTION mRNA 5¢ 3¢ Codon TRANSLATION Protein Amino acid

Transcription DNA is copied in the form of RNA This first process is called transcription. The process begins at a section of DNA called a promoter.

RNA RNA polymerase DNA During transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA.

RNA Editing Some DNA within a gene is not needed to produce a protein. These areas are called introns. The DNA sequences that code for proteins are called exons.

The introns are cut out of RNA molecules. Exon Intron DNA The introns are cut out of RNA molecules. The exons are the spliced together to form mRNA. Pre-mRNA mRNA Many RNA molecules have sections, called introns, edited out of them before they become functional. The remaining pieces, called exons, are spliced together. Then, a cap and tail are added to form the final RNA molecule. Cap Tail

The Genetic Code The genetic code is the “language” of mRNA instructions. The code is written using four “letters” (the bases: A, U, C, and G).

A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid. A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid.

The Genetic Code The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward.

Translation Translation is the decoding of an mRNA message into a polypeptide chain (protein) on ribosomes. During translation, the cell uses information from messenger RNA to produce proteins. Nucleus mRNA

The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA and the anticodons of tRNA match the mRNA codons. Lysine Phenylalanine tRNA Methionine Ribosome During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Start codon

Protein Synthesis Translation direction Lysine tRNA mRNA Ribosome During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Translation direction Ribosome

The process continues until the ribosome reaches a stop codon. Polypeptide Ribosome tRNA During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA

Amino acids within a polypeptide Codon Codon Codon DNA mRNA Protein Single strand of DNA Codon Codon Codon mRNA This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits. Alanine Arginine Leucine Amino acids within a polypeptide

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