Transcript Lecture 21
Lecture 21 Nucleic Acids Nucleic acids are molecules that store information for cellular growth and reproduction; deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are large molecules consisting of long chains of monomers called nucleotides The bases in DNA and RNA are pyrimidines C, T, and U and purines A and G In DNA, the bases are A: T G: C In RNA, U replaces T The sugars are : A nucleotide is formed when a sugar combines with a base and phosphate Adding phosphate groups to AMP forms the diphosphate ADP and the triphosphate ATP. The primary structure of RNA and DNA is the sequence of the four nucleotides A-T-G-C in DNA and A-U-G-C in RNA The nucleotides are combined in the sequence: phosphate-sugar-phosphate sugar - ... attached at the 3’ and 5’ locations of the sugar An example of a partial structure of RNA In DNA, the amount of A always equals the amount of T; G equals the amount of C The DNA structure is a double helix that consists of two strands of nucleotides that form a double helix structure like a spiral stair case; DNA has hydrogen bonds between the bases A–T and G–C; DNA has bases along one strand that complement the bases along the other When DNA unravels into a single strand, a duplicate copy of the departed strand can be reproduced In RNA uracil replaces thymine The sequence in DNA is transmitted to messenger RNA RNA has several types: Messenger RNA (mRNA) carries genetic information from DNA to the ribosomes. Transfer RNA (tRNA) brings amino acids to the ribosome to make the protein. Ribosomal RNA (rRNA) makes up 2/3 of ribosomes where protein synthesis takes place. aminoacid attached here Each tRNA has a triplet called an anticodon that complements a codon on mRNA; bonds to a specific amino acid at the acceptor stem; there is a transfer tRNA for every amino acid tRNA binds to -A-A-A on mRNA here which was TTT in DNA Where you see UUU, the DNA must have read AAA; UUC was AAG The activation of tRNA occurs when a synthetase uses energy from ATP hydrolysis to attach an amino acid to a specific tRNA each tRNA uses a triplet called an anticodon to complement a codon on mRNA For the initiation of protein synthesis, an mRNA attaches to a ribosome the start codon (AUG) binds to a tRNA with methionine the second codon attaches to a tRNA with the next amino acid a peptide bond forms between the adjacent amino acids at the first and second codons How is it known that for example, UUU or UUC only codes for phenylalanine If a synthetic mRNA with only the UUU is used, the protein that is synthesized is polyphenylalanine even though all other tRNA’s are present A mutation alters the nucleotide sequence in DNA results from mutagens such as radiation and chemicals produces one or more incorrect codons in the corresponding mRNA Phenyketonuria results when phenylalanine cannot be converted to tyrosine due to the produces a protein that incorporates one or more incorrect amino acids lack ofgenetic the enzyme phenylalanine causes diseases that producehydroxylase defective proteins and enzymes large amounts of phenylalanine and phenylpyruvate lead to mental retardation Hemoglobin is made up of 2 and 2 chains. Each carries a heme which contains the Fe+ gene DNA code ... ATG-GTG-CAC-CTG-ACT-CCT-GAG-GAG-AAG-TCT-GCC normal chain:Val- His- Leu- Thr - Pro – Glu -Glu - Lys - Ser - Ala ... ATG-GTG-CAC-CTG-ACT-CCT-GTG-GAG-AAG-TCT-GCC missense Val- His- Leu- Thr - Pro - Val -Glu - Lys - Ser - Ala mutation: the sickle cell mutation ... ATG-GTG-CAC-CTG-ACT-CCT-GAG-GAG-TAG-TCT-GCC Val- His- Leu- Thr - Pro – Glu -Glu - STOP nonsense mutation resulting in thalassemia ... ATG-GTG-CAC-CTG-AC C-CTG-AGG-AGA-AGT-CTG-CC... Val- His- Leu- Thr - Leu– Arg -Arg - Ser - Leu ... frameshift mutation also resulting in thalassemia Genetic diseases result from a mutation which results in a defective enzyme.