Chapter 17 Flashcards
Gene expression
The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs
Archibald Garrod
First to suggest that genes dictate phenotypes through enzymes
One gene-one enzyme hypothesis
each chemical reaction in a sequence is catalyzed by a specific enzyme
Describe Beadle and Tatum’s experiments with Neurospora
Neurospora can grow on a minimal medium (MM): sucrose, salts, + biotin
Can synthesize all other biomolecules: amino acids, nitrogen bases, etc.
Biomolecules are made stepwise by a series of enzymes
Beadle and Tatum collected mutants that required arginine in their MM
Intermediates in the pathway were known
Intermediates: precursor→ornithine→citrulline→arginine
Mutants can be grouped by which intermediate cures them
Concluded that each group of mutants LACK a different enzyme in the pathway
DNA provides the instructions to build proteins. What builds the proteins directly?
RNA
Explain how RNA differs from DNA.
Uracil instead of thymine
Usually single-stranded
Transcription
The synthesis of RNA using info from DNA
Translation
synthesis of a polypeptide using info from mRNA
Messanger RNA (mRNA)
type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein
Difference between Transcription and Translation
Transcription = DNA bases → RNA bases by complementarity Translation = RNA bases → amino acid sequence
Ribosomes
A complex of RNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus
Primary transcript
An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene
Central Dogma
Cells are governed by a molecular chain of command with a directional flow of genetic information
Triplet Code
A genetic information system in which a series of three-nucleotide-long words specifies a sequence of amino acids for a polypeptide chain
Template strand
The DNA strand that provides the pattern, or template, for ordering, by complementary base pairing, the sequence of nucleotides in an RNA transcript
codons
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code
coding strand (non-template strand)
Nontemplate strand of DNA, which has the same sequence as the mRNA except it has thymine (T) instead of uracil (U)
reading frame
On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis
Consider this statement: “The red dog ate the bug.” Group the letters incorrectly by starting at the wrong point, and the result will probably be gibberish: for example, “her edd oga tet heb ug.”
RNA polymerase
An enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand.
Promoter
A specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.
(The DNA sequence where RNA polymerase attaches and initiates transcription)
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
(the sequence that signals the end of transcription)
Transcription unit
A region of DNA that is transcribed into an RNA molecule.
Start point
In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA
like DNA polymerase, RNA polymerase can assemble a polynucleotide only in the 5’—3’ direction. adding on to the 3’ end T or F?
T