lecture 21 nucleic acids
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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. - PowerPoint PPT PresentationTRANSCRIPT
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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
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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 :
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A nucleotide is formed when a sugar combines with a base and phosphate
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Adding phosphate groups to AMP forms the diphosphate ADP and the triphosphate ATP.
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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
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An example of a partial structure of RNA
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In DNA, the amount of A always equals the amount of T; G equals the amount of C
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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
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When DNA unravels into a single strand, a duplicate copy of the departed strand can be reproduced
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In RNA uracil replaces thymine
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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.
The sequence in DNA is transmitted to messenger RNA
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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
aminoacid attached here
tRNA binds to -A-A-A on mRNA here which was TTT in DNA
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Where you see UUU, the DNA must have read AAA; UUC was AAG
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The activation of tRNAoccurs 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 ribosomethe 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
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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
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Phenyketonuria results when phenylalanine cannot be converted to tyrosine due to the lack of the enzyme phenylalanine hydroxylase
large amounts of phenylalanine and phenylpyruvate lead to mental retardation
A mutationalters the nucleotide sequence in DNAresults from mutagens such as radiation and chemicalsproduces one or more incorrect codons in the corresponding mRNAproduces a protein that incorporates one or more incorrect amino acidscauses genetic diseases that produce defective proteins and enzymes
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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-GCCmissense Val- His- Leu- Thr - Pro - Val -Glu - Lys - Ser - Alamutation: the sickle cell mutation
... ATG-GTG-CAC-CTG-ACT-CCT-GAG-GAG-TAG-TCT-GCCVal- His- Leu- Thr - Pro – Glu -Glu - STOP
nonsense mutation resulting in thalassemia
... ATG-GTG-CAC-CTG-ACC-CTG-AGG-AGA-AGT-CTG-CC...
Val- His- Leu- Thr - Leu– Arg -Arg - Ser - Leu ...
frameshift mutation also resulting in thalassemia
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Genetic diseases result from a mutation which results in a defective enzyme.