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Molecular Basis of Inheritance / gene expression (Flow of genetic…
Molecular Basis of Inheritance / gene expression
Flow of genetic information
genes specify proteins by transformation/translation
Transcription produces messenger RNA
Translation is the synthesis of polypeptide using information in the mRNA
transcription is the synthesis of RNA using information in DNA
ribosomes are the sites of translation
transcription
happena near the DNA to make RNA
initiation is after RNA polymerase binds to the promoter the DNA strands unwind polymerase initiates RNS synthesis at the start point on the template stand
elongation the polymerase moves downstream unwinding the DNA and elongating the RNA transcript 5' to 3' in the wake of transcription the DNA strands reform double helix
transcription at a eukaryotic promoter
several transcription factors one recognizing the TATA box must bind to DNA before RNA polymerase II can bind to correct position and orientation
additional transcription factors bind to DNA along with RNA polymerase II then unwinds the DNA double helix, and the RNA synthesis begins at the start point on template stand
translation
a small ribosomal subunit binds to a molecule of mRNA. In a bacteria cell, the mRNA binding site on this subunit recognizes a specific nucleotide sequence on the mRNA just upstream of the start condon
the arrival of a large ribosomal subunit completes the initiation complex. Proteins called initiation factors are required to bring all the translation components together.
codon recognition the anticodon of an incoming aminoacyl tRNA base pairs with the complementary mRNA codon in the A site. Hydrolysis of GTP increases the accuracy and efficiency of this step. Many different aminoacyl tRNAs are not present , but only the one with with the appropriate anticodon will bind and allow cycle to progress
peptide bond formation an rRNA molecule of the large ribosomal subunit catalyzes the formation of a peptide bond between the amino acid in the A site and the carboxyl end of the growing polypeptide in the P site. This step removes the polypeptide from the tRNA in the P site and attached to the amino acid on the tRNA in the A site
translocation the ribosome translocates the tRNA in the A site to the P site. At the same time the empty tRNA in the P site is moved to the E site where it is released the mRNA moves along with its bound tRNAs bringing the next codon to be translated into the A site
mutations
silent mutations have no observable effects on the phenotype
missense mutations change one amino acid to another
point mutations change a single nucleotide pair of a gene
nonsense mutation causes translation to be terminated prematurely; lead to non functional proteins
split genes and RNA splicing
RNA splicing where large portions of the RNA molecules are removed and the remaining portions are reconnected
the average length of a transcription unit along a human DNA is about 27,000 nucleotide pairs
tRNA
Transfer RNA is for transferring amino acids from cytoplasmic pool of amino acids to growing polypeptide
a cell keeps its cytoplasm stocked with 20 amino acids either by synthesizing them from other compounds or by taking them from surrounding solution
The ribosome a structure made of proteins and RNAs adds each amino acid brought to it by tRNA to the growing end of a polypeptide chain
life's operating instructions
proteins work together in DNA replication
because both strands of DNA are complementary each strand acts as a template for building a new strand
semiconservative model of replication predicts that when a double helix replicates each daughter molecule will have one old strand
relationship between structure an function is in the double helix
origins of replication where the two DNA strands are separated, opening up a replication bubble
pro
bacterial DNA proteins and their functions
helicase unwinds parental double helix at replication forks'
single strand binding protein binds to and stabilizes single stranded DNA until it is used as a template
topoisomerase relieves overwinding strain ahead of replication forks by breaking swiveling and rejoining DNA strands
primase synthesizes an RNA primer at 5' end of leading strand and at 5' end of each okazaki fragment of lagging strand
DNA pol III uses parental DNA strand by adding nucleotides to an RNA primer or pre existing DNA strand
DNA pol I removes RNA nucleotides of primer from 5' and replaces them with DNA nucleotides added to 3' end of adjacent fragment
DNA ligase joins okazaki fragments of lagging strand on leading strand joins 3' end of DNA that replaces primer to rest leading strand DNA
DNA is genetic material
transformation is defined as change in genotype and phenotype due to assimilation of foreign DNA
bacteriophages are used in molecular genetics research
a virus is DNA enclosed in a protective coat
DNA is a polymer of nucleotides
in 1950 Erwin Chargaff reported DNA composition varies from one species to the next
in any species the number of A and T bases is equal and number of G and C is equal
DNA consist of a nitrogenous base a sugar and a phosphate group
telomeres
special nucleotide sequences at their ends called telomeres
do not prevent shorting of DNA but they postpone the erosion of genes
telomeres are connected to aging
a chromosome consist of DNA molecule packed with proteins
in eukaryotic cells DNA is precisely combined with proteins in a complex called chromatin
protiens called histones are responsible for the first level of packing chromatin
unfolded chromatin resembles beads on a string with each bead being a nucleosome the basic unit of DNA packaging
loosely packed chromatin is called euchromatin
