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CENTRAL DOGMA OF BIOLOGY
Basically states that DNA codes for RNA while RNA codes for proteins. The genotype is make up of all the genes and alleles that go with them. The phenotype is observable appearance of genes that have been expressed. Hence, genotypes determine phenotypes.
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Exception to the Central Dogma
- -Viruses
- -use reverse transcriptase to produce messenger RNA that flows back into the nucleus.
- -This allows the virus to be able to reproduce by using the cell’s machinery against itself
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RNA molecules as another exception to Central Dogma
-RNA molecules that are never translated into proteins. -MicroRNA is a good example because after it is transcribed, it immediately starts performing its function.
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THE GENETIC CODE
mRNA molecules are read by the codons that ribosomes can recognize. Codons specify a particular amino acid with a group of three bases.
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Things to know about codons:
- - They are redundant, all but two amino acids can be coded by more than one codon
- - A single codon never codes for more than one amino acid
- - The “language” is the same is all organisms
- - If a mutation occurs in the third base like Uracil and is replaced by Cytosine in a GGU codon, it will still most likely still code for the same amino acid. In this case Glycine.
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MUTATIONS
The ultimate source of new alleles; this results in the permanent alteration of an individuals genotype, which we know now, will affect the same individuals phenotype.
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Types of mutations:
- -Silent
- -replacement
- -nonsense
- -and frameshift
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Silent Mutation
usually very harmless
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Replacement mutations
may be detrimental if the mutation happened at a crucial place of the protein.
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Nonsense mutation
makes shorter than normal protein chain, therefore they can be detrimental if the protein is an essential one for the cell's functions.
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Frameshift Mutations
cause the protein to change completely because of the addition of wrong bases after the point of mutation.
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Anueploidy
- having the wrong number of homologs in one set of chromosomes.
- -such as having three homologs for chromose 21 in down syndrome individuals.
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Poliyploidy
- having more than two homologs for all the chromosomes.
- -such as 3n, 4n, 6n, etc.
- -instead of normal 2n number.
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Inversions
cause chunks of chromosomes to break and rejoin in inverted position.
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Translocations
cause chunks of chromosomes to break from one chromosome and join another.
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Beneficial Mutation
Beneficial mutations are those that increase the fitness of the individual, allowing the organism to survive better, or produce more offspring
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Deleterious Mutations
which are more likely to occur since organisms are already adapted to their environment, result in the individuals fitness being decreased
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Neutral Mutation
like silent mutations, there is no benefit or harm done on the individual that receives these mutations
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