Campbell Biology Chapter 17

gene expression

The process by which DNA directs the synthesis of proteins or, in some cases, just RNAs. Includes 2 stages - transcription and translation

Garrod

scientist who was the first to say in 1909 that genes determine phenotype through the production of enzymes that catalyze chemical reactions; diseases caused by missing enzymes are "inborn errors of metabolism"

Beadle and Tatum

Exposed bread mold to X-rays, creating mutants. Showed that each gene encodes a particular substance ("one gene, one enzyme" concept, later restated "one gene one polypeptide").

transcription

process by which a DNA template is used to produce a single-stranded RNA molecule

messenger RNA

RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell

translation

Decoding of a mRNA message into a polypeptide chain

ribosomes

sites of translation

primary transcript

the initial RNA transcript from any gene, including those specifying RNA that is not translated into protein

triplet code

the normal version of the genetic code in which a sequence of three nucleotides codes for the synthesis of a specific amino acid

central dogma

Crick, 1956, theory that states that, in cells, information only flows from DNA to RNA to proteins

template strand

the strand of DNA that the RNA polymerase uses as a guide to build complementary mRNA

codon

a specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid (64 were deciphered by mid 1960s, 61 code for amino acids, 3 are stop signals)

reading frame

the way a cell's mRNA-translating machinery groups the mRNA nucleotides into codons

AUG

codon that initaties ("start" signal) and also codes amino acid Methionine

redundant

more than 1 codon may specify a particular amino acid

ambiguous

no codon specifies more than one amino acid

reading frame

the division of a sequence of DNA or RNA into a particular series of three-nucleotide codons. There are three possible reading frames for any sequence

RNA polymerase

enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription, they can start a chain without a primer.

promoter

A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA.

terminator

In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.

transcription unit

the stretch of DNA that is transcribed into an RNA molecule

3 stages of transcription

initiation, elongation, termination

initiation

the first phase of transcription; RNA polymerase binds to DNA @ the promoter, and unwinds the double helix

elongation

RNA polymerase slides along DNA in an open complex to synthesize RNA

termination

RNA polymerase falls off at the terminator (Bacteria) or falls off after the new RNA strand is removed

start point

In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA.

transcription factors

collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription

transcription initiation complex

the whole complex of transcription factors and RNA polymerase II bound to the promoter

TATA box

A promoter DNA sequence crucial in forming the transcription initiation complex.

RNA processing

Modification of RNA transcripts, including splicing out of introns, joining together of exons, and alteration of the 5' and 3' ends before it is released into the cytoplasm.

5' cap

The 5' end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.

poly-A tail

Modified end of the 3' end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.

RNA splicing

The removal of noncoding portions (introns) of the RNA molecule after initial synthesis.

introns

a non-coding, intervening sequence within a eukaryotic gene

exons

expressed sequence of DNA; codes for a protein

snRNPs

(small nuclear ribonucleoproteins) composed of RNA and protein molecules, recognize the splice sites, join with additional proteins to form a spliceosome

spliceosome

A complex assembly that interacts with the ends of an RNA intron in splicing RNA, releasing the intron and joining the two adjacent exons.

ribozymes

An RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing

alternative RNA splicing

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

domain

an independently folding part of a protein

exon shuffling

The variation in the patterns by which RNA may produce diverse sets of exons from a single gene.``

transfer RNA

An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA - tRNA.

anticodon

A sequence of three bases of a tRNA molecule that pairs with the complementary three-nucleotide codon of an mRNA molecule during protein synthesis.

aminoacyl-tRNA synthetases

family of enzymes that matches the correct amino acid to the correct tRNA

wobble

flexibility in the base-pairing rules in which the nucleotide at the 5' end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3' end) of a codon

ribosomal RNAs

RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.

P site

one of a ribosome's three binding sites for tRNA, holds the tRNA carrying the growing polypeptide chain.

A site

One of a ribosome's three binding sites for tRNA, holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (A stands for aminoacyl tRNA.)

E site

the place on a ribosome where discharged tRNAs leave the ribosome. exit site

initiation factors

proteins that bind to ribosomal subunits and mRNA that bring components together in the correct positions to start translation

elongation factors

one of a group of nonribosomal proteins required for continued translation of mRNA (protein synthesis) following initiation

release factor

proteins that can trigger termination of RNA translation when a ribosome reaches a stop codon.

polyribosomes

An aggregation of several ribosomes attached to one messenger RNA molecule.

signal peptide

A stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell.

signal recognition particle

SRP - A protein-RNA complex that recognizes a signal peptide as it emerges from the ribosome.

mutations

changes in the genetic material

point mutation

Mutation that affects a single nucleotide, usually by substituting one nucleotide for another

nucleotide-pair substitution

replacement of one nucleotide and its partner with another pair of nucleotides

silent mutation

A mutation that changes a single nucleotide, but does not change the amino acid created.

missense mutations

A base-pair substitution that results in a codon that codes for a different amino acid

nonsense mutation

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

insertion

A mutation involving the addition of one or more nucleotide pairs to a gene.

deletion

the loss of one or more nucleotides from a gene by mutation

frameshift mutation

mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide

mutagen

A chemical or physical agent that interacts with DNA and causes a mutation.