How Proteins are Made Biology I: Chapter 10

Decoding the Information in DNA Traits, such as eye color, are determined by proteins that are built according to instructions coded in DNA Proteins are not built directly from DNA RNA is involved

RNA (ribonucleic acid) A nucleic acid Made of linked nucleotides

RNA versus DNA Single Stranded Sugar Ribose Nitrogenous Bases Adenine (A) Guanine (G) Cytosine (C) Uracil (U) Double Stranded Sugar Deoxyribose Nitrogenous Bases Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

Transcription The process of synthesizing RNA by using one strand of DNA molecule as a template Prokaryotes Occurs in the cytoplasm Eukaryotes Occurs in the nucleus

Messenger RNA (mRNA) The form of RNA that carries the instructions for making a protein from a gene and delivers it to the site of translation

Transcription: Step 1 RNA polymerase binds to the gene’s promoter RNA polymerase: An enzyme that adds and links complementary RNA molecules during transcription Promoter: a specific sequence of DNA that acts as a “start” signal for transcription

Transcription: Step 2 RNA polymerase unwinds and separates the two strands of the double helix This exposes the DNA nucleotides on each strand

Transcription: Step 3 RNA polymerase adds and links complementary RNA nucleotides RNA polymerase moves along the nucleotides of the DNA pairing G and C and A and U (not T)

Codons RNA instructions A series of 3 nucleotide sequences on the mRNA

Codons: Amino Acids The codons make amino acids Linked amino acids: proteins! Genetic Code: the 64 possible mRNA codons with “start” and “stop” signals

Transcription: End RNA polymerase eventually reaches a “stop” signal in the DNA Stop signal: A sequence of bases Marks the end of each gene in eukaryotes Marks the end of a set of genes in prokaryotes

Protein Synthesis in Eukaryotes The human genome is about 30,000 genes Regulatory proteins are used to determine if transcription should occur “transcription factors”

Transcription Factors Help arrange RNA polymerases in the correct position on the promoter Enhancer: sequence of DNA that can be bound by a transcription factor that can activate transcription

Introns and Exons Introns: long segments of nucleotides that have no coding information “junk” Exons: the portions of a gene that are translated (expressed) in proteins

Spliceosomes After a eukaryotic gene is transcribed, the introns in the resulting mRNA are cut out Spliceosomes cut out introns and “stitch” exons together

Translation The transfer of genetic material in the form of DNA fragments from one cell to another or from one organism to another

Translation Eukaryotes and Prokaryotes Takes place in the cytoplasm

Transfer RNA (tRNA) Single strands of RNA that help in the synthesis of proteins Folded into a particular shape with an anticodon Anticodon: a 3-nucleotide sequence complementary to an mRNA codon

Ribosomal RNA (rRNA) RNA molecules that are part of the structure of ribosomes Ribosomes temporarily hold 1 mRNA and 2 tRNA

Translation The ribosomal subunits, the mRNA, and the tRNA carrying methionine (Met) bind together

Translation The tRNA carrying the amino acid specified by the codon in the A site arrives A peptide bond forms between adjacent amino acids The tRNA in the P site detaches and leaves its amino acid behind

Translation The tRNA in the A site move to the P site The tRNA carrying the amino acid specified by the A site arrives A peptide bond is formed The tRNA in the P site detaches and leaves its amino acid behind

Translation The process is repeated until a stop codon is reached The ribosome complex falls apart The newly made protein is released

Gene Expression The manifestation of the genetic material of an organism in the form of specific traits Also known as protein synthesis

Protein Synthesis in Prokaryotes Prokaryotes have about 2,000 genes Operator: on-off switch for protein synthesis Operon: the combined promoter and operator regions

Protein Synthesis in Prokaryotes lac operon: operon that controls the metabolism of lactose Repressor: protein that binds to an operator and blocks RNA polymerase from binding to the promoter site If lactose is present it binds to the repressor and changes the repressor’s shape The repressor falls off the operator and lactose can be metabolized

Protein Synthesis in Prokaryotes By producing the enzyme only when the nutrient is available, the bacterium saves energy

Mutations A change in the DNA of a gene Gene rearrangements Transposition or chromosomal rearrangement Point mutation A single nucleotide changes Insertion mutation A sizeable length of DNA is inserted into a gene Deletion mutation Segments of genes are lost, often during meiosis

Major Types of Mutations