* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download From DNA to Protein
Cell-penetrating peptide wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
Community fingerprinting wikipedia , lookup
Bottromycin wikipedia , lookup
Non-coding DNA wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Gene regulatory network wikipedia , lookup
RNA interference wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
List of types of proteins wikipedia , lookup
RNA silencing wikipedia , lookup
Molecular evolution wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Biochemistry wikipedia , lookup
Polyadenylation wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Point mutation wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Non-coding RNA wikipedia , lookup
Gene expression wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Expanded genetic code wikipedia , lookup
Messenger RNA wikipedia , lookup
Chapter 14 Ricin (found in castor-oil plant used in plastics, paints, cosmetics) is toxic because it inactivates ribosomes, the organelles which assemble amino acids into proteins, critical to life processes Each strand of DNA consists of a chain of four kinds of nucleotides: A, T, G and C The sequence of the four bases in the strand is the genetic information DNA Sugar = Deoxyribose Double stranded Bases Cytosine Guanine Adenine Thymine RNA Sugar = Ribose Single Stranded Bases Cytosine Guanine Adenine URACIL (U) These chemical differences make it easy for the enzymes in the cell to tell DNA and RNA apart Messenger Carry a copy of the instructions from the nucleus to other parts of the cell Ribosomal RNA (rRNA) Makes up the structure of ribosomes Transfer RNA (mRNA) RNA (tRNA) Transfers amino acids (proteins) to the ribosomes to be assembled A cell’s DNA sequence (genes) contains all the information needed to make the molecules of life Gene expression A multistep process including transcription and translation, by which genetic information encoded by a gene is converted into a structural or functional part of a cell or body In transcription, a strand of mRNA is assembled on a DNA template using RNA nucleotides Uracil (U) nucleotides pair with A nucleotides RNA polymerase adds nucleotides to the transcript RNA polymerase and regulatory proteins attach to a promoter (a specific binding site in DNA close to the start of a gene) RNA polymerase moves over the gene in a 5' to 3' direction, unwinds the DNA helix, reads the base sequence, and joins free RNA nucleotides into a complementary strand of mRNA Transcription Fig. 14-5b, p. 219 Many RNA polymerases can transcribe a gene at the same time In eukaryotes, RNA is modified before it leaves the nucleus as a mature mRNA Introns = Nucleotide sequences that are removed from a new RNA Exons = Sequences that stay in the RNA Alternative splicing Allows one gene to encode different proteins Some exons are removed from RNA and others are spliced together in various combinations After splicing, transcripts are finished with a modified guanine “cap” at the 5' end and a poly-A tail at the 3' end mRNA carries protein-building information to ribosomes and tRNA for translation Codon A sequence of three mRNA nucleotides that codes for a specific amino acid The order of codons in mRNA determines the order of amino acids in a polypeptide chain Genetic code Consists of 64 mRNA codons (triplets) Some amino acids can be coded by more than one codon Some codons signal the start or end of a gene AUG (methionine) is a start codon UAA, UAG, and UGA are stop codons tRNAs deliver amino acids to ribosomes tRNA has an anticodon complementary to an mRNA codon, and a binding site for the amino acid specified by that codon Ribosomes, which link amino acids into polypeptide chains, consist of two subunits of rRNA and proteins Translation = mRNA to protein Occurs in the cytoplasm on the ribosomes Translation occurs in three stages Initiation Elongation Termination Translation An initiation complex is formed A small ribosomal subunit binds to mRNA The anticodon of initiator tRNA base-pairs with the start codon (AUG) of mRNA A large ribosomal subunit joins the small ribosomal subunit The ribosome assembles a polypeptide chain as it moves along the mRNA Initiator tRNA carries methionine, the first amino acid of the chain The ribosome joins each amino acid to the polypeptide chain with a peptide bond Fig. 14-12d, p. 223 When the ribosome encounters a stop codon, polypeptide synthesis ends Release factors bind to the ribosome Enzymes detach the mRNA and polypeptide chain from the ribosome Many ribosomes may simultaneously translate the same mRNA, forming polysomes If the nucleotide sequence of a gene changes, it may result in an altered gene product, with harmful effects Mutations Small-scale changes in the nucleotide sequence of a cell’s DNA that alter the genetic code Tay Sachs – One wrong letter - from PBS Cracking the Code of Life – 9:38 and 57:00 Base-pair-substitution May result in a premature stop codon or a different amino acid in a protein product Example: sickle-cell anemia Deletion or insertion (frame shift) Can cause the reading frame of mRNA codons to shift, changing the genetic message Example: Huntington’s disease Transposable Segments of DNA that can insert themselves anywhere in a chromosomes Spontaneous mutations Uncorrected errors in DNA replication Harmful elements environmental agents Ionizing radiation, UV radiation, chemicals Ionizing radiation damages chromosomes, nonionizing (UV) radiation forms thymine dimers Mutations in somatic cells (the cells that are not sperm or eggs) of sexually reproducing species are not inherited Mutations in a germ cell or gamete may be inherited, with evolutionary consequences