Chapter 17 Memorization
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118 Terms
What is the main topic of Chapter 17?
Gene expression from gene to protein.
What is gene expression?
The process by which information in a gene is used to make a functional product.
What is the central dogma of molecular biology?
DNA to RNA to protein.
What molecule links genotype to phenotype?
Proteins.
What did Archibald Garrod propose about inborn errors of metabolism?
They result from inherited defects in enzymes.
What disease did Garrod study as an example of an inborn error of metabolism?
Alkaptonuria.
What did George Beadle initially suggest while studying fruit flies?
Genes control enzymes involved in metabolic pathways.
What organism did Beadle and Tatum use in their experiments?
Neurospora crassa.
What is Neurospora?
A bread mold.
Why was Neurospora useful for Beadle and Tatum?
It could grow on minimal medium if it made required nutrients.
How did Beadle and Tatum increase mutation rates in Neurospora spores?
They exposed spores to radiation.
What was the one gene-one enzyme hypothesis?
Each gene controls the production of one enzyme.
What is the revised one gene-one polypeptide hypothesis?
Each gene codes for one polypeptide.
Why was one gene-one enzyme revised to one gene-one polypeptide?
Some proteins contain multiple polypeptides and some genes produce functional RNA.
What are the monomers of DNA and RNA?
Nucleotides.
What are the monomers of proteins?
Amino acids.
What are three differences between RNA and DNA?
RNA has ribose, uracil, and is usually single-stranded.
What sugar is found in RNA?
Ribose.
What base is found in RNA instead of thymine?
Uracil.
What is transcription?
DNA-directed synthesis of RNA.
What is translation?
RNA-directed synthesis of a polypeptide.
What is the template for transcription?
DNA.
What is the product of transcription?
RNA.
Where does transcription occur in eukaryotic cells?
The nucleus.
What is the template for translation?
mRNA.
What is the product of translation?
A polypeptide.
Where does translation occur?
At ribosomes in the cytoplasm.
What is pre-mRNA?
The initial RNA transcript made in eukaryotic cells.
What is another name for pre-mRNA?
Primary transcript.
How many nucleotide bases are used in the genetic code?
Four.
How many common amino acids are used to make proteins?
Twenty.
What is a codon?
A three-nucleotide sequence in mRNA that specifies an amino acid or stop signal.
How many possible mRNA codons are there?
Sixty-four.
How many codons specify amino acids?
Sixty-one.
How many stop codons are there?
Three.
What are the three stop codons?
UAA, UAG, and UGA.
What is the usual start codon?
AUG.
What amino acid does AUG specify?
Methionine.
What does it mean that the genetic code is redundant?
More than one codon can specify the same amino acid.
What does it mean that the genetic code is not ambiguous?
Each codon specifies only one amino acid.
What is a reading frame?
The way nucleotides are grouped into consecutive codons.
Why is the genetic code nearly universal?
Almost all organisms use the same codon meanings.
What did Marshall Nirenberg's poly-U experiment show?
UUU codes for phenylalanine.
What is the template strand of DNA?
The DNA strand used by RNA polymerase to synthesize RNA.
What is the coding strand of DNA?
The non-template strand with the same sequence as mRNA except T replaces U.
What is another name for the coding DNA strand?
The non-template strand.
What enzyme makes RNA during transcription?
RNA polymerase.
Does RNA polymerase require a primer?
No.
What is a promoter?
A DNA sequence where transcription begins.
What is a transcription unit?
The DNA region transcribed into an RNA molecule.
What is the start point of transcription?
The first nucleotide transcribed into RNA.
What sequence signals the end of transcription in bacteria?
A terminator sequence.
What sequence is important for eukaryotic transcription initiation?
The TATA box.
Why is it called a TATA box?
It contains many T and A bases.
What are transcription factors?
Proteins that help RNA polymerase bind to DNA and begin transcription.
What is a transcription initiation complex?
RNA polymerase, transcription factors, and promoter DNA assembled together.
What are the three stages of transcription?
Initiation, elongation, and termination.
What happens during transcription initiation?
RNA polymerase binds the promoter and unwinds DNA.
What happens during transcription elongation?
RNA polymerase adds RNA nucleotides to the growing RNA strand.
What happens during transcription termination?
The RNA transcript is released and RNA polymerase detaches.
In what direction is RNA synthesized?
5′ to 3′.
In what direction does RNA polymerase read the DNA template?
3′ to 5′.
How does bacterial transcription terminate?
RNA polymerase reaches a terminator sequence and releases the RNA.
What sequence signals RNA processing in eukaryotic transcription termination?
The polyadenylation signal sequence.
What happens after RNA polymerase II transcribes the polyadenylation signal?
The transcript is released downstream of the signal.
What is RNA processing?
Modification of eukaryotic pre-mRNA before it leaves the nucleus.
What is a 5′ cap?
A modified nucleotide attached to the 5′ end of pre-mRNA.
What is a poly-A tail?
A long chain of adenine nucleotides added to the 3′ end of pre-mRNA.
What are introns?
Noncoding regions removed from pre-mRNA.
What are exons?
Expressed regions retained in mature mRNA.
Why are exons called exons?
They are the expressed regions of a gene.
What is RNA splicing?
Removal of introns and joining of exons.
What is a spliceosome?
A complex of proteins and small RNAs that removes introns.
What are small nuclear RNAs?
Small RNAs that help recognize splice sites in spliceosomes.
What is a ribozyme?
An RNA molecule that functions as an enzyme.
What discovery did ribozymes challenge?
The idea that all enzymes are proteins.
What is alternative RNA splicing?
Different combinations of exons are joined from the same pre-mRNA.
Why is alternative splicing important?
One gene can produce multiple different polypeptides.
What are the three main types of RNA involved in translation?
mRNA, tRNA, and rRNA.
What is the role of mRNA?
It carries codons from DNA to ribosomes.
What is the role of tRNA?
It delivers amino acids to the ribosome.
What is the role of rRNA?
It forms part of ribosomes and helps catalyze peptide-bond formation.
What is an anticodon?
A three-base tRNA sequence complementary to an mRNA codon.
What is aminoacyl-tRNA synthetase?
An enzyme that attaches the correct amino acid to a tRNA.
What is a charged tRNA?
A tRNA with its amino acid attached.
What is a ribosome?
A complex that reads mRNA and builds polypeptides.
What are the two ribosomal subunits?
A small subunit and a large subunit.
What are the three tRNA-binding sites in a ribosome?
A, P, and E sites.
What does the A site do?
It accepts an incoming charged tRNA.
What does the P site do?
It holds the tRNA carrying the growing polypeptide.
What does the E site do?
It is where empty tRNAs exit.
What are the three stages of translation?
Initiation, elongation, and termination.
What happens during translation initiation?
Ribosomal subunits assemble around mRNA and initiator tRNA at AUG.
What is the first amino acid in a new polypeptide?
Methionine.
What happens during codon recognition?
A charged tRNA anticodon pairs with an mRNA codon in the A site.
What happens during peptide-bond formation?
The growing polypeptide is transferred to the amino acid in the A site.
What happens during translocation?
The ribosome moves one codon along the mRNA.
What is a release factor?
A protein that binds a stop codon and ends translation.
What happens when a stop codon enters the A site?
A release factor binds instead of a tRNA.
What is a polyribosome?
Multiple ribosomes translating the same mRNA at once.