BIO 93 Final (Chapter 17)
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What is GENE EXPRESSION?
process by which DNA directs protein synthesis; includes transcription and translation
What is GENOTYPE?
genetic makeup or set of alleles of an organism; encoded on sequence of bases
What is PHENOTYPE?
physical and physiological traits of an organism, which are determined by genotype
What is TRANSCRIPTION?
synthesis of RNA under the direction of DNA; first stage of gene expression.
What is mRNA?
genetic message carrier from DNA to protein synthesizing machinery of cells
What is TRANSLATION?
synthesis of a polypeptide, which occurs under the direction of mRNA
What are RIBOSOMES?
complex particles that facilitate the orderly linking of amino acids into polypeptide chains; sites of translation
What is a CODON?
a three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid sequence of a polypeptide or termination signal; the basic unit of the genetic code
What is the TRIPLET CODE?
set of three-nucleotide-long words that specify the amino acids for polypeptide chains
Describe the TRIPLET CODE.
For each gene, one DNA strand functions as a template for transcription. The base-pairing rules for DNA synthesis also guide transcription, but Uracil (U) takes the place of thymine (T) in RNA. During translation, the mRNA is read as a sequence of base triplets, called codons. Each codon specifies an amino acid to be added to the growing polypeptide chain. The mRNA is read in the 5' --> 3' direction.
What is the TEMPLATE STRAND?
the DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript
What are the STAGES OF TRANSCRIPTION?
(1) Initiation --> After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.
(2) Elongation --> The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5' --> 3'. In the wake of transcription, the DNA strands re-form a double helix.
(3) Termination --> Eventually, the RNA transcript is released, and the polymerase detaches from the DNA.
Where do transcription and translation occur in the cell?
In prokaryotes --> transcription and translation are coupled, in which ribosomes attach to the leading end of mRNA while transcription is still in progress.
In eukaryotes --> almost all transcription occurs in the nucleus and translation occurs mainly at ribosomes in the cytoplasm.
What is a PROMOTER?
a specific DNA sequence upstream of the gene.
What is a TERMINATOR?
the sequence that signals the end of transcription.
What are TRANSCRIPTION FACTORS?
a collection of proteins in eukaryotes that mediate the binding of RNA polymerase and the initiation of transcription.
What is a TRANSCRIPTION UNIT?
a region of a DNA molecule that is transcribed into an RNA molecule.
What are the steps of the INITIATION OF TRANSCRIPTION AT A EUKARYOTIC PROMOTER?
(1) eukaryotic promoter includes a TATA box.
(2) several transcription factors must bind to the DNA before RNA polymerase II can do so.
(3) additional transcription factors bind to DNA along with RNA polymerase II, forming the transcription initiation complex.
What is the TRANSCRIPTION INITIATION COMPLEX?
the completed assembly of transcription factors and RNA polymerase bound to the promoter.
In a prokaryote, how does RNA polymerase know where to start transcribing a gene?
RNA polymerase recognizes the gene's promoter and binds to it.
In eukaryotes, how does RNA polymerase know where to start transcribing a gene?
transcription factors mediate the binding of RNA polymerase to the promoter.
What is PRIMARY TRANSCRIPT?
serves as a precursor to mRNA, rRNA, or tRNA and may be processed by splicing or cleavage.
How is the primary transcript produced by a prokaryotic cell different from that produced by a eukaryotic cell?
a prokaryotic primary transcript is immediately usable as mRNA, but a eukaryotic primary transcript must be modified before it can be used as mRNA.
What is a 5' cap?
the 5' end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.
What is a poly-A tail?
the modified end of the 3' end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.
What is RNA SPLICING?
the removal of introns; done by ribosomes.
What is an INTRON?
a noncoding, intervening sequence within a eukaryotic gene; A PORTION OF A DNA OR PRIMARY TRANSCRIPT THAT DOES NOT CODE FOR PROTEIN.
What is an EXON?
a coding region of a eukaryotic gene; exons are separated from each other by introns; exons are joined together after introns are removed.
What is the benefit of having a cap and tail on mRNA?
(1) keeps mRNA from degrading too quickly.
(2) it helps export mRNA out of nucleus.
(3) it helps ribosomes attach to 5' end.
What are some properties that a transcription factor must have in order to work?
(1) it must bind to DNA.
(2) it has to be in the nucleus.
(3) it must be able to promote or inhibit transcription.
What are RIBOZYMES?
RNA molecules that function as enzymes; CATALYTIC RNA MOLECULES.
What is the role of ribosomes in TRANSLATION?
ribosomes convert the information in the coding region of the mRNA (language of nucleotides) into polypeptide information (language of amino acids); ribosomes have binging sites for mRNA and tRNA.
What is a tRNA?
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; includes a loop that contains an anticodon and an attachment site at the 3' end for an amino acid.
What is an ANTICODON?
a specialized base triplet at one end of a tRNA molecule that recognizes a particularly complementary codon on an mRNA molecule.
What are the 3 steps of TRANSLATION?
(1) initiation: mRNA binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon; the start codon reads AUG and codes for methionine; the first tRNA has the anticodon UAC.
a large ribosomal subunit joins the small subunit, allowing the ribosome to function.
(2) elongation: addition of amino acids to the growing polypeptide chain; links amino acids together via peptide bonds.
(3) termination: stop codon- no amino acid to bind.
What is a POLYRIBOSOME (POLYSOME)?
an aggregation of several ribosomes attached to one messenger RNA molecule.
What is a SIGNAL PEPTIDE?
a stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell.
What is a SIGNAL RECOGNITION PARTICLE (SRP)?
a protein-RNA complex that recognizes a signal peptide as it emerges from the ribosome.
What is rRNA?
ribosomal RNA, plays structural and catalytic (ribozyme) roles in ribosomes.
What are MUTATIONS?
changes in the sequence of DNA.
What are POINT MUTATIONS?
change in the DNA sequence by one nucleotide.
- -base-pair substitution mutation.
- -insertion or deltion mutation.
What are BASE-PAIR SUBSTITUTION MUTATIONS?
a point mutation in which there is no change in the number of nucleotides.
What are MISSENSE MUTATIONS?
substitution mutation in which the altered codon still codes for an amino acid and thus makes sense.
What is a NONSENSE MUTATION?
substitution mutation in which a codon for an amino acid is changed into a stop codon; causes translation to be terminated prematurely.
What are INSERTION or DELETION MUTATIONS?
point mutations in which there is a change in the number of nucleotides.
What is a FRAMESHIFT MUTATION?
an insertion or deletion mutation in which there is a regroup of the codons of the gene which occurs if the insertion or deletion is not a multiple of three nucleotides.
Which type of mutation is most likely to drastically affect a protein's sequence?
insertion of 1 nucleotide because every amino acid changes.
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