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Download CH. 12.3 : DNA, RNA, and Protein
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Genes and Proteins • The sequence of nucleotides in DNA contains information. • This information is put to work through the production of proteins. • Proteins fold into complex, three-dimensional shapes to become key cell structures and regulators of cell functions. • Thus, by encoding the instructions for making proteins, DNA controls cells. Website upload 2015 Genes and Proteins • You learned earlier that proteins are polymers of amino acids. • The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein. Website upload 2015 DNA Proteins Cells Bodies DNA has the information to build proteins genes proteins cells bodies Website upload 2015 DNA gets all the glory, Proteins do all the work Cell organization • DNA – DNA is in the nucleus • genes = instructions for making proteins – want to keep it there = protected • “locked in the vault” nucleus Website upload 2015 cytoplasm Cell organization aa • Proteins – chains of amino acids – made by a “protein factory” in cytoplasm – protein factory = ribosome aa aa aa aa aa aa aa aa cytoplasm nucleus aa build proteins ribosome Website upload 2015 Passing DNA instructions: need RNA • RNA like DNA, is a nucleic acid. • RNA structure differs from DNA structure in three ways. • Has ribose sugar instead of deoxyribose (DNA). • Replaces thymine (T) with uracil (U). • Single stranded as opposed to double stranded DNA. Phosphate group Website upload 2015 Nitrogenous base (A, G, C, or U) Uracil (U) Sugar (ribose) Ribonucleic Acid (RNA) • RNA has a different function than DNA. • Whereas DNA provides the instructions for protein synthesis, RNA does the actual work of protein synthesis. • RNA takes from DNA the instructions on how the protein should be assembled, then—amino acid by amino acid—RNAs assemble the protein. Website upload 2015 Ribonucleic Acid (RNA) • 3 types of RNA – 1. Messenger RNA (mRNA), single, uncoiled strand which brings instructions from DNA in the nucleus to the site of protein synthesis. – 2. Ribosomal RNA (rRNA), globular form, makes up the ribosome –the construction site of proteins binds (site of protein synthesis); binds to the mRNA and uses the instructions to assemble the amino acids in the correct order. – 3. Transfer RNA (tRNA) single, folded strand that delivers the proper amino acid to the site at the right time. Website upload 2015 aa Passing DNA instructions • Need to get DNA gene instructions from nucleus to cytoplasm. – need a copy of DNA – messenger RNA cytoplasm aa aa aa aa aa aa aa aa aa build proteins mRNA nucleus ribosome Website upload 2015 Protein Synthesis Step #1-Transcription: DNA mRNA • In the nucleus, enzymes make an RNA copy of a portion of a DNA strand. The main difference between transcription and DNA replication is that transcription results in the formation of one single-stranded RNA molecule rather than a double-stranded DNA molecule. Step #2- Translation: mRNA Protein Process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein. Website upload 2015 aa From nucleus to cytoplasm aa aa aa aa aa nucleus transcription DNA mRNA aa aa aa protein aa translation cytoplasm trait Website upload 2015 Transcription • Making mRNA from DNA • DNA strand is the template (pattern). – match bases •U:A •G:C • Enzyme – RNA polymerase Website upload 2015 Matching bases of DNA & RNA • Double stranded DNA intact. T G G T A C A G C T A G T C A T CG T A C CG T Website upload 2015 Matching bases of DNA & RNA • Double stranded DNA unzips. T G G T A C A G C T A G T C A T CG T A C CG T Website upload 2015 Matching bases of DNA & RNA A • Match RNA bases to DNA bases on one of the DNA strands. G C G U C A C A C C RNA polymerase A U A G U AG U C G A U A RNA base ‘bank’ G T G G T A C A G C T A G T C A T CG T A C CG T Website upload 2015 U C Matching bases of DNA & RNA aa • U instead of T is matched to A. DNA aa aa TACGCACATTTACGTACGC aa aa aa mRNA AUGCGTGUAAAUGCAUGCG aa aa aa aa ribosome A C C A U G U C G A U C A G U A G C A U G G C A Website upload 2015 RNA Processing Not all the nucleotides in the DNA of eukaryotic cells carry instructions—or code—for making proteins. Genes usually contain many long noncoding nucleotide sequences, called introns, which are scattered among the coding sequences. Regions that contain coding nucleotide sequences are called exons because they are expressed. Website upload 2015 RNA Processing When mRNA is transcribed from DNA, both introns and exons are copied. The introns must be removed from the mRNA before it can function to make a protein. Enzymes in the nucleus cut out the intron segments and paste the mRNA back together. The mRNA then leaves the nucleus and travels to the ribosome. Website upload 2015 RNA Processing: simplified • Noncoding segments called introns are spliced out ( coding segment = exon). Website upload 2015 Translated Sequences • Transfer of DNA to mRNA uses “language” of nucleotides. – Letters: nitrogen bases of nucleotides (A,T,G,C) – Words: codons ≡ triplets of bases ( ex. AGC) – Sentences: polypeptide chain – The codons in a gene specify the amino acid sequence of a polypeptide. Website upload 2015 The Genetic Code The nucleotide sequence transcribed from DNA to a strand of messenger RNA acts as a genetic message, the complete information for the building of a protein. Virtually all organisms share the same genetic code. Website upload 2015 Translation: From mRNA to Protein • Translation occurs in the ribosomes in the cytoplasm. Translation involves 3 types of RNA: 1. Messenger RNA (mRNA) = carries the blueprint for construction of a protein. 2. Ribosomal RNA (rRNA) = the construction site where the protein is made. 3. Transfer RNA (tRNA) = the truck delivering the proper amino acid to the site at the right time. Website upload 2015 Transfer RNA are interpreters • In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide (protein). • The process is aided by transfer RNAs. • Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other. • Anticodon base pairs with codon of mRNA. Website upload 2015 aa aa aa aa aa nucleus aa cytoplasm protein aa aa aa aa ribosome A C C A U G U C G A U C A G U A G C A U G G C A Website upload 2015 trait How does mRNA code for proteins? • mRNA leaves nucleus. • mRNA goes to ribosomes in cytoplasm. • Proteins built from instructions on mRNA. How? mRNA A C C A U G U C G A U C A GU A GC A U G GC A aa aa aa aa aa Website upload 2015 aa aa aa How does mRNA code for proteins? TACGCACATTTACGTACGCG DNA ribosome AUGCGUGUAAAUGCAUGCGC mRNA ? Met Arg Val Asn Ala Cys Ala protein aa aa aa aa aa aa aa How can you code for 20 amino acids with upload 2015 only 4Website DNA bases (A,U,G,C)? aa mRNA codes for proteins in triplets DNA TACGCACATTTACGTACGCG codon mRNA AUGCGUGUAAAUGCAUGCGC AUGCGUGUAAAUGCAUGC ribosome ? protein Met Arg Val Asn Ala Cys A Codon = block of 3 mRNA bases that code for each amino acid Website upload 2015 The Genetic code • For ALL life! – strongest support for a common origin for all life. • Code has duplicates – several codons for each amino acid. – mutation insurance! Website upload 2015 The Genetic code • For ALL life! • Start codon • AUG methionine • Stop codons • UGA, UAA, UAG Website upload 2015 Codons for Amino Acids DNA mRNA TACGCACATTTACGTACGCGG AUGCGUGUAAAUGCAUGCGCC UAC tRNA amino acid Met codon GCA Arg CAU anti-codon Val Websitebases upload 2015that are opposites of codons Anti-codon = block of 3 tRNA mRNA to protein = Translation • The working instructions mRNA • The reader ribosome • The transporter transfer RNA (tRNA) ribosome mRNA A C C A U G U C G A U C A GU A GC A U G GC A U GG tRNA aa aa aa U A C tRNA aa A G tRNA aa C U AG tRNA aa Website upload 2015 From gene to protein aa nucleus transcription DNA cytoplasm translation aa aa protein aa mRNA aa aa aa ribosome A C CA U GU C G A U C A GU A GC A U GGC A tRNA Website uploadaa 2015 trait aa protein transcription nucleus cytoplasm translation aa aa aa aa aa aa aa aa aa aa trait Website upload 2015 From gene to protein protein transcription translation Website upload 2015