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DNA (16.1 (Dna is the genetic material. Dna is a double helix. two…
DNA
16.1
- Dna is the genetic material. Dna is a double helix. two antiparallel sugar-phosphate chains wind around the outside of the molecule.
- The Nitrogenous bases project into the interior where they hydrogen bond in specific pairs. A with T, and G with C
- Dna replication is semi conservative: the parent molecule unwinds, and each strand then serves as a template for the synthesis of a new strand according to base-pairing.
- Structure- Each DNA nucleotide monomer consist of a nitrogenous base, the sugar deoxyribose, and a phosphate group.
- The phosphate group of one nucleotide is attached to the sugar of the next by a covalent bond, forming a "backbone" of alternating phosphates and sugars from which the bases project.
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Single-strand binding protein- Binds to the stabalized single- stranded dna until it is used as a template
Topoisomerase- an enzyme that helps relive this strain 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- using parental DNA as a template synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand
DNA poly 1- Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides added to the 3' end of adjaent fragments
DNA ligase- joins okazaki fragments of lagging strand, on leading strand, jois a 3' end of DNA that replicates primer to rest of leading DNA strand.
replication
Begins at sites called "origins of replication", short stretches of DNA that have a specific sequence of nucleotides. At the end of each replication bubble is a replication fork, a y-shaped region where the parental strands of dna are being unwound
helicase are enzymes that untwist the double helix at the replication forks, separating the two parental strands and making them available as template strands.
Next, single strand binding proteins bind to the unpaired dna strands, keeping them from re-pairing. The untwisting of the double helix causes tighter twisting and strain ahead of the replication fork
Topoisomerase is an enzyme that helps relive this strain by breaking,swiveling, and rejoining DNA strands.
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Synthesis
RNA chain is called a primer and is synthesized by the enzyme primase. Primease starts a complementary RNA chain with a single RNA nucleotide and adds RNA nucleotide one at a time, using the parental dna strand as a template.
Enzymes called DNA polymerase catalyze the synthesis of new DNA by adding nucleotide to the 3' end of a pr-existing chain.
leading strand get synthesized first, the dna strand elongating is called the lagging strand.
Translation
Translation involves “decoding” a messenger RNA (mRNA) and using its information to build a polypeptide, or chain of amino acids. For most purposes, a polypeptide is basically just a protein (with the technical difference being that some large proteins are made up of several polypeptide chains).
Transcrpition
Transcription of a gene takes place in three stages: initiation, elongation, and termination. Here, we will briefly see how these steps happen in bacteria. You can learn more about the details of each stage (and about how eukaryotic transcription is different) in the stages of transcription article.
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1.Initiation. RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning of a gene. Each gene (or group of co-transcribed genes, in bacteria) has its own promoter. Once bound, RNA polymerase separates the DNA strands, providing the single-stranded template needed for transcription.
- Elongation. One strand of DNA, the template strand, acts as a template for RNA polymerase. As it "reads" this template one base at a time, the polymerase builds an RNA molecule out of complementary nucleotides, making a chain that grows from 5' to 3'. The RNA transcript carries the same information as the non-template (coding) strand of DNA, but it contains the base uracil (U) instead of thymine (T).
- Termination. Sequences called terminators signal that the RNA transcript is complete. Once they are transcribed, they cause the transcript to be released from the RNA polymerase. An example of a termination mechanism involving formation of a hairpin in the RNA is shown below.
