Please enable JavaScript.
Coggle requires JavaScript to display documents.
16,17 (transcription (rnaprocessing (at the 3' end, an enzyme then…
16,17
transcription
promotor of a gene includes within it the transcription start point, the nucleotide where RNA synthesis begins
RNA polymerase binds to a specific location on the promoter determining where transcription starts and which strands of DNA helix is used as a template
-
the RNA polymerase moves along the DNA, untwisting the DNA, exposing DNA nucleotides for pairing with RNA nucleotides
-
the advancing wave of RNA synthesis, the new RNA molecule peels away from its DNA template, and the DNA reforms
-
-
the 5' end which is synthesized first, receives the a 5' cap a modified form of guanine nucleotide added onto the 5' end after transcription of the first 20-40 nucleotides
-
pre-mRNA is released soon after the polyadenylation signal, AAUAAA, is transcribed
at the 3' end, an enzyme then adds 50-250 more adenine nucleotides forming a poly-A trail
-
-
DNA replication
the ends of the replication bubble is a replication fork, it is Y-shaped where the parental strands are being unwound
-
helicases, are enzymes that untwist the double helix at the replication forks, to separate the parental strands
after the parental strands separate, single strand binding proteins bind to the unpaired DNA strands keeping them from repairing
-
initial nucleotide chain that is produced during DNA synthesis, is RNA
-
-
DNA is composed of a nitrogenous base, a pentose sugar, and a phosphate group
the base can be Adenine, thymine, guanine and cytosine
adenine always pairs with thymine, and guanine always pairs with cytosine
an X-ray crystallography was used to look at DNA. the X-rays were diffracted as they passed through aligned fibers of purified DNA
this confirmed that DNA was helical in shape, pattern in the photo suggests the helix was made of two strands called double helix
-
-
nitrogenous bases are paired, Adenine with Thymine, Guanine with Cytosine
Adenine and Thymine are purines that have two organic rings, while Guanine and Cytosine are pyrimidines, with single ring
-
-
-
-
after DNA poly III forms the Okazaki fragment, DNA poly I replace RNA nucleotides of the adjacent primer with DNA
DNA poly I cannot join the final nucleotide replacement DNA segment to the first DNA nucleotide of the adjacent Okazaki fragment
DNA ligase does the task by joining the sugar phosphate backbones of all Okazaki fragments into a continuous DNA strand
DNA mutations
-
-
small scale mutations of one or few nucleotide pairs including point mutations, a change in single nucleotide pair
a change of s single nucleotide in the DNA's template strand can lead to production of abnormal protein
-
-
silent mutation, change in nucleotide pair may transform one codon into another that is translated into the same amino acid
another mutation, called missense mutations change one amino acid to another one
nonsense mutations causes translation to be terminated prematurely, they lead to nonfunctional proteins
Watson and crick model predicts when a double helix replicates, each of the daughter molecules will have one old strand, from the parental molecule, and a newly made strand
ex; the semiconservative model, is distuingushed from the conservative model of replication
-
dispersive model, al four strands of DNA following replication have a mixture of old and new DNA
conservative model, the two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix
DNA polymerases can only add nucleotides to the free 3' and of the primer or growing DNA strand, never to the 5' end
in one strand DNA pol III synthesizes a complementary strand by elongating new DNA in the 5'-3' direction
DNA poly III stays in the fork on that template strand, adding new nucleotides a new strand
-
-
to elongate the other new strand DNA in the 5-'3' direction, poly III has to work along the other template in the direction away from the fork
this strand is the lagging strand, it is synthesized discontinuously as a series of segments called Okazaki fragments
-
telomeres
-
-
telomerase, catalyzes the lengthening of telomeres in eukaryotic germ cells
-
translation
codon recognition requires hydrolysis of one molecule of GTP it increases and efficiency of this step. one more GTP is hydrolyzed to provide energy for the translocation step
-
elongation cycle takes about less than tenth of a second in bacteria and is repeated as each amino acid is added to the chain until the polypeptide is completed
the empty tRNA's that are released from the E site return to the cytoplasm, where they will be reloaded with the appropiate amino acid
-
-
the bases UAG, UAA, UGA, do not code for amino acids but hey act as signals to stop translation
the release factor, a protein shaped like a aminoacyl tRNA binds directly to the stop codon in the A site
the release factor causes more addition of water molecules instead of the amino acid to the polypeptide chain
this reaction hydrolyzes the bond between the completed polypeptide and the tRNA in the P site, releasing the polypeptide through the exit tunnel of the ribosomes large subunit
the rest of this translation assembly comes apart, aided by other proteins, breaking down translation assembly requires the hydrolysis of two more GTP molecules
-
signal peptide
polypeptides of proteins destined for the endomembrane system or for secretion are marked by a signal peptide, it targets the protein to ER
the signal peptide, with about 20 amino acids at or near the leading end of the polypeptide, is recognized as it emerges from the ribosome by a protein -RNA complex called a signal recognition particle
-
-
the polypeptide synthesis continues there and the growing polypeptide snakes across the membrane into the ER lumen via a protein pore , the signal peptide is usually removed by an enzyme
some signal peptides are used to target polypeptides to mitochondria, chloroplasts, and the interior of the nucleus and other organelle that are not part of the endomembrane system
the replication of DNA starts at the origin of replication, short stretches of DNA having a specific sequence of nucleotides
-
-
enzymes called DNA polymerases, catalyze the synthesis of new DNA by adding nucleotides to a preexisting chain
in E.coli there are different polymerases, but there are two that are major in DNA replication, DNA polymerase III and DNA polymerase I
most DNA polymerase, require a primer and a DNA template Strand, with a complementary DNA nucleotides are lined up
E.coli DNA polymerase III, adds a nucleotide to the RNA primer and continues adding DNA nucleotides, complementary to the parental DNA strand, to the growing end of the DNA strand
each nucleotide to be added to a growing DNA strand consists of sugar attached to a base and to three phosphate groups
-
-
-
-
-
