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
RNA polymerase are unable to start a chain from scratch T or F?
F. they don’t need to add the first nucleotide onto a pre-existing primer
tHe first step of transcription is?
Initiation-
(1) RNA polymerase binds to the promoter
(2) DNA strands unwind
(3) Polymerase initiates RNA synthesis at the start point on the template strand
The second step of transcription is?
Elongation-
(1) polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5’—>3’
(2) in the wake of transcription the DNA strands reform the shape of a double helix
The third step of transcription is?
Termination-
(1) the RNA transcript is released, and the polymerase detaches from the DNA
TATA box
A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.
transcription factors
A regulatory protein that binds to DNA and affects transcription of specific genes
transcription intuition complex
The completed assembly of transcription factors and RNA polymerase bound to a promoter.
5’ cap
A modified form of guanine nucleotide added onto the 5’ end of a pre-mRNA molecule.
RNA processing
Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5′ and 3′ ends.
RNA splicing
After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons).
Poly-A tail
A sequence of 50–250 adenine nucleotides added onto the 3′ end of a pre- mRNA molecule.
introns
A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA pro- cessing; also refers to the region of DNA from which this sequence was transcribed.
exons
A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed
spliceosome
A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.
ribozymes
An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing.
alternative RNA splicing
A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produces from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.
domains
A taxonomic category above the kingdom level. The three domains are Archaea, Bacteria and Eukarya.
transfer RNA (tRNA)
An RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA
anticodon
A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on on mRNA molecule
Aminoacyl-tRNAsynthetases
An enzyme that joins each amino acid to the appropriate 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.
(allows some tRNA to bind to more than one codon)
Ribosomal RNA (rRNA)
RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA
A site
One of a ribosome’s three binding sites for tRNA during translation. The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain.
P site
One of a ribosome’s three binding sites for tRNA during translation. The P site hols the tRNA carrying the growing polypeptide chain
E site
One of a ribosome’s three binding sites for tRNA during translation. The E site is the place where discharges tRNAs leave the ribosome
Describe the process of translation (including initiation, elongation, and termination) and explain which enzymes, protein factors, and energy sources are needed for each stage.
Initiation: brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
Elongation: tRNA is base paired with mRNA, another tRNA binds to A site, ribosome creates covalent bond between amino acids, mRNA is moved the length of a codon, GTP is converted to GDP and energy is used
Termination: once an stop codon is reached, a release factor enters the A-site, a water is in place of an amino acid and the polypeptide is detached
In eukaryotic cells, transcription cannot begin until
several transcription factors have bound to the
promoter
Which of the following is not true of a codon?
(A) It may code for the same amino acid as another codon. (B) It never codes for more than one amino acid.
(C) It extends from one end of a tRNA molecule.
(D) It is the basic unit of the genetic code.
(c)
The anticodon of a particular tRNA molecule is
complementary to the corresponding mRNA codon
Which of the following is not true of RNA processing?
(A) Exons are cut out before mRNA leaves the nucleus.
(B) Nucleotides may be added at both ends of the RNA.
(C) Ribozymes may function in RNA splicing.
(D) RNA splicing can be catalyzed by spliceosomes.
(a)
Which component is not directly involved in translation? (A) GTP (C) tRNA (B) DNA (D) ribosomes
(B)
Which of the following mutations would be most likely to have a harmful effect on an organism?
(A) a deletion of three nucleotides near the middle of a gene
(B) a single nucleotide deletion in the middle of an intron
(C) a single nucleotide deletion near the end of the coding sequence
(D) a single nucleotide insertion downstream of, and close to, the start of the coding sequence
(d)
Describe the structure and functions of ribosomes.
Large subunit and small subunit. A-site, P-site, E-site. Made of protein and rRNA. Facilitate the pairing of tRNA anticodons to mRNA codons
Explain how RNA is modified after transcription
A modified guanine cap is placed on the 5’ end and a poly A tail goes on the 3’ end. Spliceosomes remove introns and splice together exons
translation can begin before transcription has completed T or F?
T
RNA synthesis is catalyzed by ________, which pries the DNA strands apart and joins together the RNA nucleotides
RNA polymerase
