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Nucleic Acid Function:
DNA Replication, Transcription & Translation
CLASS NOTES from Science Prof Online
Genetic Replication – Copying DNA
Before a cell divides (the parent cell), it must make a copy of its DNA so that both daughter cells have a complete copy of the genetic information. Copying the double-stranded DNA molecule is called replication; a process that takes place in the nucleus of eukaryotic cells and the nucleoid region in prokaryotes.
Each DNA strand holds the same genetic information, so both strands can serve as templates for the reproduction of the opposite strand. Each template strand is preserved and each new strand is assembled from nucleotides. This is called semi-conservative replication. The resulting double-stranded DNA molecules are identical.
Article Summary: Nucleic acids, such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the vital genetic blueprints, messengers and builders of the cellular world.
DNA Replication, Transcription & Translation
Genetic Translation – Making Proteins
Ribosomes make proteins from the messages encoded in mRNA. Each three nucleotide group along the mRNA is called a codon, and calls for a specific amino acid. This is the Genetic Code. In other words, the triplet code of genetic instructions for a protein is “written” in mRNA as a series of 3-nucleotide “words,” each coding for an amino acid.
Transfer RNA (tRNA), then brings the amino acid that was coded for. Amino acids are monomers that, when linked together with peptide bonds, ultimately become a protein molecule, the end product of translation.
To learn more about molecular genetics see the following animations and SPO Class Note Articles:
Animations
- DNA Structure Cell Biology Animation from John Kyrk.
- Build a DNA Molecule from University of Utah.
- DNA Replication animation and review questions.
- DNA Replication Process animated video by FreeScienceLectures.com.
- DNA Replication step-through animation by John Kyrk.
- DNA Transcription step-through animation by John Kyrk.
- DNA Transcription and Protein Assembly animated movie by RedAndBrownPaperBag.
- Transcription & Translation animated movie, PBS production “DNA: The Secret of Life.
- DNA Replication, Transcription & Translation animated movies from HHMI
Class Notes
- Deoxyribonucleic Acid Structure – What Is DNA?
- Genetic Replication – Copying of DNA
- Ribonucleic Acid Structure & Function – What Is RNA and What Does It Do?
Sources
- Bauman, R. (2005) Microbiology. Pearson Benjamin Cummings.
- Park Talaro, K. (2008) Foundations in Microbiology, McGraw-Hill.
- Campbell, N. & Reece, J. (2002) Biology, 6th Edition, Benjamin Cummings.
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Genetic Transcription – Making RNA
This is the process by which a DNA sequence is copied to produce a complementary strand of RNA. In other words, it is the transfer of genetic information from DNA into RNA, similar to replication, but in this case, RNA is being built, rather than DNA. Transcription is the beginning of the process that ultimately leads to the translation of the genetic code into a protein.
There are three types of RNA that can be transcribed from DNA:
- Messenger RNA (mRNA) – a copy of the DNA “blueprint”
- Ribosomal RNA (rRNA) – part of the structure of a ribosome
- Transfer RNA (tRNA) – function as little trucks that can each carry an amino acid
There are four different types of nitrogenous bases found in an RNA molecule: adenine (A), guanine (G), cytosine (C) and uracil (U). Adenine and guanine are larger, double ring nitrogenous bases called purines. Cytosine and uracil are smaller, single ring nitrogenous bases called pyrimidines.
The three main activities that nucleic acids are involved in include:
- Replication: Copying of the DNA genetic material.
- Transcription: Transferring the genetic code of DNA into RNA molecules.
- Translation: RNA following DNA’s instructions to building proteins from amino acid monomers.
Page last updated: 5/2013
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When RNA bases are laid down to build an RNA molecule, DNA is unzipped, and the new RNA molecule made is compliment of the DNA template. For example, if the DNA strand has the following bases, in this order, CTGACGGATCAGCCGCAA, the new RNA molecule being made will have the base sequence GACUGCCUAGUCGGCGUU. After the RNA segment is made, the DNA zips back up and the RNA floats off to carry out its function in the cell.
