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Proteins are the links between _________ and ____________.
genotype and phenotype
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What is a gene?
a region of DNA that can be expressed to produce a final functional product, wither a polynucleotide or an RNA molecule.
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What is gene expression? What are the two stages?
- the process by which DNA directs protein synthesis
- includes two stages: transcription and translation
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RNA is the ___________ between genes and the proteins for which they code.
intermediate
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What is transcription and what does it produce?
- is the synthesis of RNA under the direction of DNA
- produces messenger RNA (mRNA)
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What is translation and where does it take place?
- synthesis of polypeptide, which occurs under the direction of mRNA
- takes place in the ribosomes
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What is the central dogma?
- concept that cells are governed by a cellular chain of command
- DNA-->RNA-->protein
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What happens to mRNA produced by transcription in Prokaryotes?
it's immediately translated without more processing
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In eukaryotic cell, what separates transcription and translation?
nuclear envelope
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What is a primary transcript?
the initial RNA transcript from any gene (pre-mRNA)
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Define triplet code.
series of non-overlapping, three nucleotide words
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How many possible codons are there?
64
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During transcription, what does the template strand do?
provides a template for ordering the sequence of nucleotides in an RNA transcript
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What bond is formed between the amino acids?
peptide bonds
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During translation, the mRNA base triplets, called ___________, are read in the _______ direction.
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What happens in RNA synthesis and what is catalyzed by?
catalyzed by RNA polymerase, which pries opens the DNA strands apart and hooks together the RNA nucleotides
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What direction is DNA synthesized?
5' to 3'
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What direction is mRNA read for translation?
5' to 3'
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What direction is the DNA template strand read?
3' to 5'
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What direction is mRNA transcript synthesized?
5' to 3'
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The DNA sequence where RNA polymerase attaches is called ___________.
the promoter: signals the initiation of RNA synthesis
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what is the TATA box?
a nucleotide sequence that is crucial in forming the initiation complex in eukaryotes
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What are the 2 functions of transcription factors?
they settle the binding of RNA polymerase and the initiation of transcription
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What is the transcription initiation complex?
complete assembly of transcription factors and RNA polymerase 2 bound to a promoter.
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What is the function of RNA polymerase in transcription?
moves along the DNA, it untwists the double helix
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In bacteria, how does termination occur?
In bacteria, the polymerase stops transcription at the end of the terminator.
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In eukaryotes, how does termination occur?
In eukaryotes, proteins associated with the RNA transcript cut it free from the polymerase, the polymerase eventually falls off the DNA.
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Enzymes in the eukaryotic nucleus _____________ before the genetic messages are dispatched to the cytoplasm.
modify pre-mRNA
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How is each end of a pre-mRNA molecule modified before being dispatched to the cytoplasm? (2)
- 5' end receives a modified nucleotide 5' cap
- 3' end get a poly-A tail
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What functions to theses modifications provide for the pre-mRNA? (3)
- facilitate the export of mRNA
- protect mRNA from hydrolytic enzymes
- help ribosomes attach to the 5' end
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What are non-coding regions in the RNA transcripts called?
intervening sequences or introns
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What are the regions of RNA transcript that are usually expressed/ translated into amino acid sequence called?
exons
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What is RNA splicing?
removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence.
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What is alternative RNA splicing?
some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during RNA splicing.
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What does alternative RNA splicing produce?
the number of different proteins an organism can produce is much greater than its number of genes
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In many cases different exons code for the _____________ in a protein.
different domains
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What may result in the evolution of new proteins?
exon shuffling
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What are ribozymes?
catalytic RNA molecules that function as enzymes and can splice RNA
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What are the 3 properties of RNA that enable it to function as a n enzyme?
- it can form a three-dimensional structure because of its ability to base pair with itself
- some bases in RNA contain function groups
- RNA may hydrogen-bond with other nucleic acid molecules
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A cell ____________ an mRNA message into protein with the help of ____________.
- translates
- transfer RNA (tRNA)
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What makes the molecules of tRNA unique? (2)
- each carries a specific amino acid on one end
- each has an anticodon on the other end
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What does anticodon do?
it base-pairs with a complementary codon on mRNA
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What does tRNA consist of?
a single RNA strand that is about 80 nucleotides long
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What are the two steps to accurate translation?
- first: correct match between a tRNA and an amino acid done my the enzyme aminoactyl-tRNA synthase
- second: a correct match between the tRNA anticodon and mRNA codon
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What is wobble?
flexible paring at the third base of a codon, which allows some tRNAs to bind to more than one codon
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What is the function of ribosomes in protein synthesis?
facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
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What are the two ribosomal subunits made of?
proteins and ribosomal RNA
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What are the 3 binding sites for tRNA in order?
- A site: holds the tRNA that carries the next amino acid to be added to the chain
- P site: holds the tRNA that carries the growing polypeptide chain
- E site: exit site, where discharged tRNAs leave the ribosome
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Each addition of amino acids involves proteins and elongation factors and occurs in three steps:
- codon recognition
- peptide bond formation
- translocation
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How does termination in translation occur? (2)
- termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
- A site accepts a proton called a release factor, which causes the addition of a water molecule instead of an amino acid
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What is mutations?
changes in the genetic material of a cell or virus
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What mutations occur during DNA replication, recombination or repair?
spontaneous mutations
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What are mutagens?
physical or chemical agents that can cause mutations
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What are point mutations?
chemical changes in just one base pair of a gene
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What are the two main categories that point mutations are divided into?
- base-pair substitutions
- base-pair insertions or deletions
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What is silent mutation?
have no effect on the amino acid produces by a codon because of redundancy in the genetic code
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Which mutation still codes for an amino acid, but not necessarily the right amino acid?
missense mutation
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What is a nonsense mutation?
change an amino acid into a stop codon, nearly always leading to a non-functional protein
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What are the three mutations in base-pair substitutions?
- silent mutation
- missense mutation
- nonsense mutation
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Insertion or deletion of nucleotides may alter the reading frame, producing what?
frame shift mutation
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what will a single nucleotide insertion close to the start of the coding sequence cause?
frameshift mutation, immediate nonsense
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What will a single nucleotide deletion near the end of a coding sequence cause?
frameshift mutation, extensive missense
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What will a deletion of three nucleotides near the middle of a gene cause?
no frameshift, but one amino acid missing
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