Lecture #7Date _________ n Chapter 17~ From Gene to Protein.
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Transcript of Lecture #7Date _________ n Chapter 17~ From Gene to Protein.
![Page 1: Lecture #7Date _________ n Chapter 17~ From Gene to Protein.](https://reader035.fdocuments.in/reader035/viewer/2022062413/5a4d1b5d7f8b9ab0599abb4d/html5/thumbnails/1.jpg)
Lecture #7 Date _________
Chapter 17~ From Gene to Protein
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Protein Synthesis: overview
One gene-one enzyme hypothesis (Beadle and Tatum)
One gene-one polypeptide (protein) hypothesis
Transcription: synthesis of RNA under the direction of DNA (mRNA)
Translation: actual synthesis of a polypeptide under the direction of mRNA
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The Triplet Code
The genetic instructions for a polypeptide chain are ‘written’ in the DNA as a series of 3-nucleotide ‘words’
Codons ‘U’ (uracil) replaces ‘T’
in RNA
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Transcription, I RNA polymerase:
pries DNA apart and hooks RNA nucleotides together from the DNA code
Promoter region on DNA: where RNA polymerase attaches and where initiation of RNA begins
Terminator region: sequence that signals the end of transcription
Transcription unit: stretch of DNA transcribed into an RNA molecule
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Transcription, II
Initiation~ transcription factors mediate the binding of RNA polymerase to an initiation sequence (TATA box)
Elongation~ RNA polymerase continues unwinding DNA and adding nucleotides to the 3’ end
Termination~ RNA polymerase reaches terminator sequence
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mRNA modification 1) 5’ cap: modified guanine; protection; recognition site for
ribosomes 2) 3’ tail: poly(A) tail (adenine); protection; recognition;
transport 3) RNA splicing: exons (expressed sequences) kept,introns
(intervening sequences) spliced out; spliceosome
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Translation, I
mRNA from nucleus is ‘read’ along its codons by tRNA’s anticodons at the ribosome
tRNA anticodon (nucleotide triplet); amino acid
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Translation, II
rRNA site of mRNA codon & tRNA anticodon coupling
P site holds the tRNA carrying the growing polypeptide chain
A site holds the tRNA carrying the next amino acid to be added to the chain
E site discharged tRNA’s
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Translation, III Initiation~ union
of mRNA, tRNA, small ribosomal subunit; followed by large subunit
Elongation~ •codon recognition •peptide bond formation •translocation
Termination~ ‘stop’ codon reaches ‘A’ site
Polyribosomes: translation of mRNA by many ribosomes (many copies of a polypeptide very quickly)
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Mutations: genetic material changes in a cell Point mutations…. Changes in 1 or a few base
pairs in a single gene Base-pair substitutions: •silent
mutations no effect on protein •missense ∆ to a different amino acid (different protein) •nonsense ∆ to a stop codon and a nonfunctional protein
Base-pair insertions or deletions: additions or losses of nucleotide pairs in a gene; alters the ‘reading frame’ of triplets~frameshift mutation
Mutagens: physical and chemical agents that change DNA
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Disorders Nondisjunction- when the chromosomes don’t split
from each other giving one cell more than the other. Autosomal- these are all of your chromosomes except
for your sex chromosomes. You have 44 autosomal chromosomes.
Down syndrome- produces mild to severe mental retardation. (nondisjunction)
Albinism- lack of pigment (recessive) Cystic fibrosis- excess mucus in lungs, digestive tract,
liver; increased susceptibility to infections (recessive) Galactosemia- accumulation of galactose (sugar) in
tissue, mental retardation; eye and liver damage (recessive)
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Phenylketonuria PKU- accumulation of phenylalanine in tissue; lack of normal skin pigment; mental retardation (recessive)
Tay-Sachs disease- lipids accumulation in brain cells; mental deficiency; blindness; death in early childhood (recessive)
Achondroplasia- Dwarfism (dominant) Hunington’s disease- mental deterioration
and uncontrolled movements (dominant) Hypercholesterolemia- excess cholesterol in
blood; heart disease (dominant) Sickle cell- misshapen, or sickled, red blood
cells; damage to many tissue (co-dominant)