Coding
and Information
The Genetic Code
Overview of Transcription
and Translation
Mechanics
of Transcription
Mechanics
of Translation
| Now we know that proteins are essential tools
.......... they perform the metabolic functions which keep cells alive,
with a "normal" phenotype.
|
| CODE | ELEMENTS | No. of ELEMENTS | GROUPING |
| Telephone | digits | 10 ( 0-9) | area code, exchange |
| English | arabic letters | 26 (a, b, c, d, .... etc.) | words, sentences |
| Greek | greek letters | 26 (a, b, c, d, .... etc.) | words, sentences |
| Chinese | ideographic symbols | thousands (each symbol = a word) | sentences |
| Spoken English | phonetic sounds, tones | thousands | words, sentences |
| Audio recording | magnetized "bits" | 2 ('magnetized or unmagnetized) | |
| Computer | bits | 2 (0 and 1) | bytes |
| Genetic | chemicals | 4 (A, T, G, C) | codons, genes |
In each of these codes, it is not the elements of the code which are important ........ it is the SEQUENCE of the elements!
| The elements of the genetic
code are not letters, digits or sounds - they are chemicals - Adenine,
Guanine, Thymine and Cytosine. The sequence of these
chemicals codes the information for the primary structure of proteins.
Remember the double stranded structure of DNA ............ what is the 5' ---> 3' sequence of bases? |
The Genetic Code (the sequence of bases in RNA)
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1. DNA Replication. The entire length of both DNA strands is copied into new DNA molecules. Neither the medium or the information is changed. 2. Transcription. Only the information on the coding strand in the coding regions (the genes!) of the DNA molecule is copied into a different medium (RNA). The new molecule is called messenger RNA (mRNA). The mRNA migrates from the nucleus to the cytoplasm where protein synthesis takes place. 3. Translation. mRNA carries
information for the primary structure of proteins in the base sequence
of the ribonucleotides. The ribosomes "read"
this information 3 bases at a time (or 1 codon at a time). Each codon
specifies an amino acid. The ribosome uses the sequence of codons to
link the correct amino acids together in the correct order (sequence).
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One strand of the DNA double helix
is used as a template by the RNA polymerase to synthesize a messenger RNA
(mRNA). Ribonucleotides (nucleotides containing ribose sugars
instead of
deoxyribose) are linked into a single RNA strand.
This is a polymerization reaction (forming a long chain of identical
or similar subunits). RNA polymerase is a
complex assemblage of many proteins which polymerizes the individual
ribonucleotides. The mRNA migrates from the nucleus to the cytoplasm.
Remember from above that there are 2 other kinds of RNA as well:
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In order to translate the information in mRNA
into a sequence of amino acids, a "reading machine" is needed. The
"reading machine" has two components: 1.) transfer
RNA (tRNA) 2.) the ribosome. Translation proceeds
as follows:
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| The
entire process of protein synthesis looks like this:
|
This is an electron micrograph
of translation being carried out in a living bacterial cell.
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| At the top of the page we asked: "Where do proteins come from? Now we know how the cell constructs proteins. The base sequence of DNA is really a book of instructions which tells the cell how to construct the primary structure of a protein |
Review
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Where
do proteins come from?
