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Everything Else (Steps of Transcription: After a RNA polymerase binds to…
Everything Else
Steps of Transcription: After a RNA polymerase binds to the promoter, the DNA strands unwind and the polymerase initiates RNA synthesis at the start point of the template strand
Elongation: The polymerase moves downstream unwinding the DNA and elongating the RNA transcript 5'-3'
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Eukaryotic promoter: commonly includes a TATA sequence about 25 nucleotides upstream from the transcriptional start point
Several transcription factors, one recognizing the TATA box must bind to the DNA before RNA polymerase II can bind in the correct position and orientation
Additional transcription factors bind to the DNA along with RNA polymerase II, forming the transcription initiation complex. RNA polymerase II then unwinds the DNA double helix and RNA synthesis begins at the start point on the template strand
Transcription elongation, RNA polymerase moves along the DNA template strand, joining complementary RNA nucleotides to the 3' end of the growing RNA transcript. Behind the polymerase the new RNA peels away from the template strand, which reforms a double helix with the nontemplate strand
Step 1: The DNA strand must be separated, in order to do this Helicase unwinds the parental strand in two
The replication fork that is made from this process is were the template for replication will begin. This separation also causes a lagging and leading strand which is accommodated by different processes.
Step 2: A primase is then attached to the leading strand 3' to 5'. This leading strand is continueous in its replecation process making it the simplest way to replecate DNA
The lagging strand begins replication by binding with multiple primers. Each primer is only several bases apart. DNA polymerase then adds pieces of DNA, called Okazaki fragments, to the strand between primers. This process of replication is discontinuous as the newly created fragments are disjointed.
Step 4: an enzyme called exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases. Another exonuclease “proofreads” the newly formed DNA to check, remove and replace any errors. Another enzyme called DNA ligase joins Okazaki fragments together forming a single unified strand.
TELOMERASE act as protective caps at the end of chromosomes to prevent nearby chromosomes from fusing. A special type of DNA polymerase enzyme called telomerase catalyzes the synthesis of telomere sequences at the ends of the DNA.
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Ribosome subunit binds to mRNA, the sub-unit recognizes a specific nucleotide sequence. An initiator tRNA, with the anticodon UAC, base pairs with AUG, THis tRNA carries the amino acid methionine
Large ribosome sub-unit completes the initiation complex. initiation factor bring translation components together. hydrolysis of GTP provides energy for assembly.initiator tRNA is in the P site; the A site is available to the tRNA bearing the next amino acid
Codon recognition: the anticodon of tRNA pairs withe with complementary mRNA in A site. Hydolysis of GTP increases efficiency of this step.
Peptide bond formation: rRNA of large ribosomal subunit catalyzes the formation of a peptide bond between amino group of new amino acid in A site & corboxyl end of the growing polypeptide in the P 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 were it is released. mRNA moves along with bound tRNAs bringing the next codon to be translated at A site
DNA Structure
All DNA has a sugar-phosphate backbone that is attached by a covalent bond which alternates between phosphate and sugar hence the name
A polynucleotide had directionality, starting from the 5' end and ending at the 3' end. These numbers 5' & 3' are just the placement(numbering) of the carbon atoms in the pentose form, 5' being at the top end connected to the phosphate group and 3' being at the bottom connected to the -OH group.
The 1' carbon in the sugar pentose or deoxyribose is attached by a covalent bond to the nitrogen in the nitrogenous base. Adenine, Thymine, Gaunine, or Cytosine.
PURINE, nitrogenous bases with two organic rings
PYRIMIDINE, nitrogenous bases with one organic ring.
Purines can only connect with a pyrimidine specifically A-T and G-C. That is because to maintain a specific uniform diameter adenine only pair with thymine & Gaunine only pairs with Cytosine.
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Prokaryotes have only one origin of replication, creating two replication forks that unwind the parental DNA, turning them into two template strands.
Eukaryotes, have linear chromosome instead of the circle chomosomes of prokaryotes. Along this linear chomosome multiple sites of origin replication can occur during the S phase of interphase. These multiple bubbles expand till they merge with others creating two daughter DNA molecules
RNA SPLICING: a form of RNA processing in which a newly made precursor messenger RNA transcript is transformed into a mature messenger RNA. During splicing, introns are removed and exons are joined together
Structure of tRNA: Four base paired regions and three loops, the base sequence of the amino acid attachment site at the 3' end are characteristics of tRNA. the anticodon triplet is unique to each tRNA type
The signal recognition particle (SRP) is an abundant, cytosolic, universally conserved ribonucleoprotein (protein-RNA complex) that recognizes and targets specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes.
A polyribosome is a complex of an mRNA molecule and two or more ribosomes that act to translate mRNA instructions into polypeptides
Table Functions
Helicase, unwinds parental double helix at replication forks
Single-strand binding protein, binds to and stablizes single strand DNA
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 of each okazki fragment
DNA pol III, Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA PRimer or pre-existing DNA strand
DNA pol I Removes RNA nucleotides of primer from 5' end 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 of leading strand DNA