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The Language of Life
Chetan Vaity
March 2007
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The Cell
 A eukaryotic cell
 Nucleus
 Chromosomes
 Very long, continuous
piece of DNA
 Endoplasmic Reticulum
 Ribosomes
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DNA
 All living things on the
planet contain DNA
 They store information
 Information to do what?
 Genes
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Nucleobases
 In genetics, these are
simply called bases
 Adenine, Thymine, ,
Guanine, Cytosine or A, T,
G, C
 Nucleotides pair in a
specific way - called the
Base-Pair Rule
 Adenine pairs to Thymine
 Guanine pairs to Cytosine
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RNA


DNA remains in the nucleus, but in
order for it to get its instructions
translated into proteins, it must
send its message to the
ribosomes, where proteins are
made. The chemical used to carry
this message is Messenger RNA
RNA is similar to DNA except:
1. has on strand instead of two
strands.
2. has uracil instead of thymine
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Transcription
 The codons of a gene are copied into
messenger RNA
 Transcription proceeds in a particular direction
 A section of DNA double helix is uncoiled and
only one of the DNA strands serves as a
template
 Note that the new RNA is identical to non
coding DNA with the exception of uracil where
thymine was located in DNA
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Amino Acids
 The general formula is NH2CHRCOOH
 These are molecules where the amino and
carboxylate groups are attached to the same
carbon atom
 The various alpha amino acids differ in which side chain (R group) is attached to their
alpha carbon.
 R = H (Hydrogen atom) : Glycine
 R = CH3 (Methyl group) : Alanine
 R = CH2C8H6N : Tryptophan
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More about Amino Acids
 Humans can produce 10 of the 20 amino acids. The others must be
supplied in the food.
 Failure to obtain enough of even 1 of the 10 essential amino acids,
those that we cannot make, results in degradation of the body's
proteins—muscle and so forth—to obtain the one amino acid that is
needed.
 Unlike fat and starch, the human body does not store excess amino
acids for later use—the amino acids must be in the food every day.
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The Genetic Code
 Since there are 4 bases in 3-letter
combinations, there are 64 possible
codons (4^3 combinations). These
encode the twenty standard amino
acids.
 Most amino acids, therefore, have more
than one possible codon.
 There are also three ‘STOP' codons
signifying the end of the coding region
 These are TAA, TGA and TAG
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Genetic Code and Translation into proteins
 mRNA copy is decoded by a
ribosome that reads the RNA
sequence by base-pairing the
messenger RNA to transferRNA (tRNA), which carries
amino acids.
 In proteins, amino acids are
joined together in a chain by
peptide bonds between their
amino and carboxylate groups.
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Proteins are a chain of amino acids
 Peptide bond
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Protein Synthesis
 The overall picture
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Example of a protein in action
 Haemoglobin
 Oxygen transport in red blood cells
 Sickle-cell anemia is caused by a point mutation
 Replace the amino acid glutamic acid with valine at the sixth position of
the β chain.
 Causes distortion of red blood cells and a tendency for them to lose their
elasticity.
 The link with Malaria
 The malaria virus attacks the red blood cells
 This mutation is prevalent in Africa
 If one inherits this gene from one of you parents, one is almost immune to
malaria
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