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There are 2 types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The building blocks of DNA and RNA are nucleotides, which are made up of three parts: a 5-carbon sugar, phosphate group, and nitrogenous base. There are also 4 types of nitrogenous bases in DNA. Adenine (A) and guanine (G) are double-ringed purines, and cytosine (C) and thymine (T) are smaller, single-ringed pyrimidines. RNA contains the same nitrogenous bases, though excludes thymine. Instead of thymine, RNA contains Uracil (U).
The function of DNA is to store all of the genetic information that an organism needs to develop, function, and reproduce. Essentially, it is the biological instruction manual found in each of your cells.
DNA contains the instructions needed for an organism to develop, survive and reproduce. To carry out these functions, DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies.
1. Helicase unwinds the parental double helix
2. Single strand binding proteins stabilize the unwound parental DNA
3. The leading strand is synthesized continuously in the 5' to 3' direction by DNA polymerase.
4. The lagging strand is synthesized discontinuously. Primase synthesizes a short RNA primer, which is extended by DNA polymerase to form an Okazaki fragment.
5. After the RNA primer is replaced by DNA, DNA ligase joins the Okazaki fragment to the growing strand.
Step 1: Initiation
Initiation is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands. The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases.
Step 2: Elongation
Elongation is the addition of nucleotides to the mRNA strand. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs. There is a brief time during this process when the newly formed RNA is bound to the unwound DNA. During this process, an adenine (A) in the DNA binds to an uracil (U) in the RNA.
Step 3: Termination
Termination is the ending of transcription, and occurs when RNA polymerase crosses a stop (termination) sequence in the gene. The mRNA strand is complete, and it detaches from DNA.
Translation Steps
During translation, which is the second major step in gene expression, the mRNA is "read" according to the genetic code, which relates the DNA sequence to the amino acid sequence in proteins. Each group of three bases in mRNA constitutes a codon, and each codon specifies a particular amino acid (hence, it is a triplet code). The mRNA sequence is thus used as a template to assemble—in order—the chain of amino acids that form a protein.
1. The ribosome binds to mRNA at a specific area.
2. The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.
3. Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain.
4. The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA.
5. The polypeptide forms into its native shape and starts acting as a functional protein in the cell.