Genetics

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DNA polymerase
the enzymes that link DNA nucleotides to a growing daughter strand; also carry out proofreading step that quickly removes nucleotides that have base-paired incorrectly during replication; also involved in repairing damaged DNA; responsible for forming new copies of DNA,
DNA ligase
enzyme that links (ligates) the pieces together into a single DNA strand; also involved in repairing damaged DNA
Semiconservative model
when a double helix replicates, each of the two daughter molecules will have one old strand, which was part of the parental molecule, and one newly created strand; half of the parental molecule is maintained
RNA polymerase
Enzyme that links RNA nucleotides; the RNA nucleotides follow the same base-pairing rules that govern DNA replication except that U pairs with A
phases of transcription
initiation (attachment of RNA polymerase to the promoter and the start of RNA synthesis)-RNA elongation; RNA peels away from DNA template, allowing the two separated DNA strands to come back together-termination (RNA polymerase reaches a sequence of bases in the DNA template called a terminator)
messenger RNA
the kind of RNA that encodes amino acid sequences; it conveys genetic information from DNA to the translation machinery of the cell; transcribed from DNA; short-lived
introns
(intervening sequences) internal noncoding regions in genes; stil transcribed from DNA to RNA
exons
coding regions of genes that are expressed as amino acids
RNA splicing
cutting and pasting process; before RNA leaves the nucleus, the introns are removed and the exons are joined to produce an mRNA molecule with a continuing coding sequence; in most cases, catalyzed by a complex of proteins and small RNA molecules, but sometimes the RNA transcript itself catalyzes the process
transfer RNA
a molecular interpreter that converts the three-letter word (codons) of nucleic acids to the one-letter amino acid words of proteins
ribosomal RNA
a ribsome consists of two subunits each made up of proteins and rRNA
initiation
1. an mRNA molecule binds to a small ribosomal subunit. a special initiator tRNA binds to the specific codon called the start codon; where translation begins 2. a large ribosomal subunit binds to the small one, creating a functional ribosome. The initiator tRNA fits into one of the two tRNA-binding sites on the ribosome. this site is called the P site and holds the growing polypeptide; the other tRNA binding site is called the A site and is ready for the next amino-acid-bearing tRNA
mutation
any change in the nucleotide sequence of DNA
base substitution
replacement of one nucleotide with another; some substitution mutations have no effect because there is no change in the protein product; may cause changes in a protein that prevent it from functioning normally; occasionally it leads to an improved protein
base deletion/insertion
often have disastrous effects; because mRNA is read as a series of nucleotide triplets (codons) during translation, adding or subtracting nucleotides may alter the reading frame
reading frame
triplet grouping of the message for a protein
mutagenesis
production of mutations; can occur during DNA replication or recombination (spontaneous)
mutagen
physical or chemical agent; most common in nature is radiation, such as X-rays and ultraviolet light
central dogma
DNA -> RNA -> proteins
transcription
the process of copying hereditary information in DNA to RNA
translation
the process of using the information in nucleic acids to synthesize proteins; messenger RNA is translated to proteins in ribosomes
genotype
determined by the sequence of bases in DNA
phenotype
a product of the proteins produced through translation
reverse transcriptase
viral enzyme that synthesizes a DNA version of the RNA genes (happens with HIV)
triplet code
three-base code (codon)
start codon
AUG; signals that protein synthesis should begin at that point on the mRNA molecule; specifies the amino acid methionine
stop codons
(UAA, UAG, UGA) signal that the protein is complete; do not code for amino acids; end translation
code rules
many codons code one amino acid, one codon never codes for more than one amino acid, the code is non-overlapping, the code is universal in all organisms, when several codons code for one amino acid, the first two bases in those codons are usually always identical
beneficial mutations
mutations that increase the fitness of the organism, such as with the light coated mice in beach habitats
neutral mutations
if a mutation has no effect on fitness; silent mutations are usually neutral
deleterious mutations
mutations that lower fitness; most point mutations fall under this category
silent mutations
change in nucleotide sequence that does not change the amino acid specified by a codon; no change in phenotype; neutral with respect to fitness
missense mutations
change in nucleotide sequence that changes the amino acid specified by the codon; change in the primary structure of protein; may be beneficial, neutral or deleterious
nonsense mutations
change in nucleotide sequence that results in an early stop codon; leads to mRNA breakdown or a shortened polypeptide; usually deleterious
frameshift mutations
addition or deletion of a nucleotide; reading frame is shifted, altering the meaning of all subsequent codons; almost always deleterious
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