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142 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Proteins are the links between what two things? |
Genotype and Phenotype |
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What is the bridge between genes and the proteins for which they code? |
RNA |
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What is transcription? |
Synthesis of RNA using information in DNA |
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What does transcription produce? |
Messenger RNA (mRNA) |
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What is translation? |
Synthesis of a polypeptide, using information in the mRNA |
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In prokaryotes, when does translation occur? |
Translation of mRNA can begin before transcription has finished |
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In eukaryotes, what does the nuclear envelope do? |
Separates transcription from translation |
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What is a primary transcript? |
The initial RNA |
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What is the central dogma? |
The concept that cells are governed by a cellular chain of command |
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How many amino acids are there and how many nucleotides are in the DNA? |
20 amino acids 4 nucleotides |
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What is the flow of information from gene to protein called? |
Triplet code |
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What is the triplet code? |
Non overlapping, three nucleotide words |
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How does transcription work in the words of a gene? |
Transcribed into complementary non overlapping, three nucleotide words of mRNA |
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How does translation occur in words of a gene? |
Words in mRNA are translated into amino acids, forming a polypeptide |
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What does the template strand do? |
Provides a template for the sequence of complementary nucleotides in an mRNA transcript |
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What does the non template strand do? |
Called the coding strand Nucleotides of this strand are identical to the codons, except U in RNA in place of T in the DNA |
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What do codons do during translation? |
The mRNA triplets (codons) are read in the 5’ —> 3’ |
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What does each codon do? |
Specifies the amino acid to be added in a growing polypeptide |
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The flow of information goes from what to what? |
Gene (DNA sequence) to protein (Polypeptide sequence) |
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Of the 64 triplets, how many code for amino acids? |
61 triplets |
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What do the other 3 triplets do? |
The 3 triplets are “stop” codons to end translation |
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Why is the genetic code considered redundant? |
More than one codon may specify a particular amino acid |
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Why, though, is the genetic code not ambiguous? |
No codon specifies more than one... |
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Why must codons be read in the correct reading frame? |
To produce the specified polypeptide |
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Because the genetic code is shared by the simplest bacteria and the most complex animal means that the genetic code is nearly... |
Universal |
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Which stage of gene expression is transcription? |
The first stage of gene expression |
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DNA is directing what in transcription? |
DNA directed RNA synthesis |
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What are the 3 stages of transcription? |
Initiation Elongation Termination |
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What catalyzes RNA synthesis? |
RNA polymerase |
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What does RNA polymerase do? (3/5) |
- Catalyzes RNA synthesis - Opens DNA strands and joins RNA nucleotides together - Does not need primer |
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What does RNA polymerase do? (2/5) |
Follows the same base-pairing rules as DNA, excepts that uracil substitutes for thymine Produces RNA that is complementary to the DNA template strand |
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What is the Promoter? |
DNA sequence where RNA polymerase attaches |
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What is the terminator? |
In bacteria, the sequence signalling the end of transcription |
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What is a transcription unit? |
The stretch of DNA that is transcribed is called a transcription unit |
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What are the characteristics of promoters? |
Transcriptional start point Usually extend several dozen nucleotides upstream of the start point |
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What does the TATA box do in transcription? |
Crucial in forming the initiation complex in eukaryotes |
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What do transcription factors do in transcription initiation? |
Mediate the binding of RNA polymerase and the initiation of transcription |
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In elongation (transcription) What happens as RNA polymerase moves along DNA? |
It untwists the double helix, 10-20 bases at a time |
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How fast does transcription progress in eukaryotes? |
40 nucleotides per second |
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Can a gene be transcribed simultaneously by several RNA polymerases? |
Yes |
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The mechanisms of termination are the same in bacteria and eukaryotes, true or false? |
FALSE |
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What is the mechanism for termination in bacteria? |
The polymerase stops transcription at the end of the terminator. MRNA can be translated without further modification |
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What is the mechanism for termination in eukaryotes? |
RNA polymerase transcribes the polyadenylation (polyA) signal sequence |
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Post transcription, What is RNA processing? |
Enzymes in the eukaryotic nucleus modify pre-mRNA Transcripts are then transported to the cytoplasm |
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In eukaryotes, What transcribes the the polyadenylation (polyA) signal sequence? |
RNA polymerase |
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In RNA processing, what happens to the primary transcript? |
Both ends of the primary transcript are altered. |
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What is splicing? |
Sections of mRNA (introns) are removed and remaining sections (Exons) are spliced |
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In RNA processing, Each end of a pre-mRNA molecule is modified. What does this involve? |
- the 5 end receives a modified nucleotide 5 cap The 3 end gets a poly-A tail |
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In RNA processing, Modifications share several functions. What functions? |
Facilitating the export of mRNA to the cytoplasm Protect mRNA from hydrolytic... |
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What do most eukaryotic genes contain? |
Long non coding stretches of nucleotides between coding regions |
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What are introns? |
Non coding regions |
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What are exons? |
Coding regions, expressed, usually translated into amino acid sequences |
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What does RNA splicing do? |
Removed introns and joins exons Creates an mRNA molecule with a continuous coding sequence RNA splicing is carried out by the spliceosome |
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What is a spliceosome? |
A variety of proteins and several small RNAs that recognize the splice sites |
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What do the RNAs of the spliceosome do? |
Also catalyze the splicing reaction and function as a ribozyme |
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What is a ribozyme? |
Catalytic RNA molecules that function as enzymes and can splice RNA |
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All biological catalysts are proteins, true or false? |
False |
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What is the first property of RNA that enable it to function as an enzyme |
Can form a 3D structure because of its ability to base-pair with itself. |
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What is the second property of RNA that enables it to function as an enzyme |
Some bases in RNA contain functional groups that may participate in catalysis |
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What is the third property of RNA enables it to function as an enzyme? |
RNA may hydrogen bond with other nucleus acid molecules |
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Some (what?) contain sequences that may regulate gene expression |
Introns |
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What happens in alternative splicing? |
Some genes can encode for more than one polypeptide, depending on which exons get included during splicing |
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Is the number of proteins produced equal to the number of genes? |
No. The number of proteins is greater. |
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What are domains? |
Protein’s modular architecture consisting of discrete regions |
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Different exons code for the different domains in a protein, T or F? |
True |
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What may result in the evolution of new proteins? |
Exon shuffling |
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Genetic information flows from mRNA to protein through which process? |
Translation |
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What does translation create? |
Polypeptide from the mRNA information |
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How does a cell translate an mRNA message into protein? |
Transfer RNA. (tRNA) |
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What do tRNAs do? |
Transfer amino acids to the growing polypeptide in a ribosome |
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What does each tRNA molecule enable? |
Translation of a specific mRNA codon into a certain amino acid |
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What does each tRNA carry? |
Specific amino acid on one end |
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What does each tRNA molecule have on the opposite end |
An anticodon |
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How long is a single RNA strand? |
About 80 nt long |
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What makes tRNA 3D? |
Hydrogen bonding twists tRNA into a 3D molecule |
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What is the shape of the tRNA and what are the orientations of the end? |
Roughly L-shaped with the 5’ and the 3’ ends both located near one end of the structure |
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What does the protruding 3’ end of tRNA act as? |
An attachment site for an amino acid |
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What catalyzes the correct match between tRNA and an amino acid? |
Aminoacyl-tRNA sythetase |
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What are the two steps involved in translation? |
1. Correct match between a tRNA and an amino acid 2. Correct match between the tRNA anticodon and an mRNA codon |
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What is the wobble hypothesis? |
Flexible pairing at the third base of a codon allows some tRNA to bind to more than one codon |
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What catalyzes the correct match between tRNA and an amino acid? |
Aminoacyl-tRNA sythetase |
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What do ribosomes do? |
Facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis |
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What is the wobble hypothesis? |
Flexible pairing at the third base of a codon allows some tRNA to bind to more than one codon |
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What are the two ribosomal subunits? |
Large and small Made of proteins and ribosomal RNA rRNA |
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How many binding sites does a ribosome have for tRNA |
3. A, P or E |
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What does the A site do? |
Holds the tRNA that carries the next amino acid to be added to the chain |
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What does the P site do? |
Holds the tRNA that carries the growing polypeptide chain |
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What does the E site do? |
The exit site, where discharged tRNAs leave the ribosome |
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What are the three stages of translation? |
Initiation Elongation Termination |
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Is energy required to build a polypeptide? |
Energy is required or some steps |
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In initiation, the start codon signals what? |
The start of translation |
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What does the small ribo unit bind to in initiation? |
Small ribo subunit binds w mRNA and a special initiator tRNA |
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What does the small subunit do after binding to mRNA? |
Moves along the mRNA until it reaches the start codon MET? |
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What do initiation factors do? |
They bring in the large subunit that completes the translation initiation complex |
Requires energy |
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During elongation, what happens with amino acids? |
Amino acids are added one by one to the C-terminus of the growing chain |
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During elongation, what does each addition involve? |
Proteins called elongation factors |
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What are the 3 steps in elongation? |
1. Codon recognition 2. Peptide bond formation 3. Translocation |
First and third step require energy |
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During elongation Translation proceeds in which direction? |
Along the mRNA in a 5 to 3 direction |
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Do the ribosome and mRNA move relative to each other? |
Yes. Codon to codon |
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In elongation, what stops it? |
It continue until a stop codon in the mRNA reaches the A site of the ribosome |
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In termination, what does the A site accept? |
A protein called a release factor |
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What does the release factor do? |
Causes the addition of a water molecule instead of an amino acid |
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What splits the bond between tRNA and polypeptide in termination? |
Hydrolysis |
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What does the reaction do? |
Releases the polypeptide, and the translation assembly comes apart |
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What does the polypeptide chain spontaneously do during translation? |
Spontaneously fold into 3D molecule |
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What does a gene determine? |
Primary structure, and a primary structure in turn determines shape |
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Are polypeptide changes modified before or after translation? |
After translation or targeted to specific sites in the cell |
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What are post-translational modifications? |
May be required before the protein can begin doing its particular job in the cell |
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What are examples of post translational modification? |
Protein cleavage, phosphorylation, acetylation |
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Where are ribosomes located? |
Free ribos in the cytosol Bound ribos attached to the ER |
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What do free ribos do? |
Mostly synthesize proteins that function in the cytosol |
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What do bound ribosomes do? |
Make proteins of the endomembrane system and proteins that are secreted from the cell |
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Are ribos stuck as either free or bound? |
No. They’re identical and can switch |
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Where does polypeptide synthesis begin? |
In the cytosol |
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Where does synthesis finish? |
In the cytosol. Unless the polypeptide signals the ribo to attach to the ER |
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How do the polypeptides destined for the ER or for secretion know where to go? |
They’re marked by a signal peptide |
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What is a Signal-recognition particle? |
Binds to the signal peptide on N terminus |
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What does the SRP do to the ribo? |
Escorts the ribo to a receptor protein built into the ER membrane |
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When synthesis resumes, what happens? |
It sends polypeptides into the ER lumen |
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What is a polyribosome? |
Multiple ribos can translate a single mRNA simultaneously |
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What do polysomes enable cells to do? |
Make many copies of a polypeptide very quickly |
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How does a bacterial cell ensure a streamlined process? |
By coupling transcription and translation Occur at the same time |
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What are mutations? |
Changes in the genetic information of a cell |
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What can mutations of one or a few nucleotides affect? |
Protein structure and function |
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What are point mutation? |
Changes in just one nucleotide pair of a gene |
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What two categories can point mutations within a gene be divided into? |
Single nucleotide pair substitutions Nucleotide pair insertions or deletions |
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What are nucleotide pair substitutions? |
Replaces one nucleotide and its partner with another pair of nucleotides |
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What are silent mutations? |
No effect on the amino acid produced by a codon because of redundancy in the genetic code |
Due to wobble |
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What is a missense mutation? |
Still code for an amino acid, but not for the correct amino acid |
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What are nonsense mutations? |
Change an amino acid codon into a stop codon Most lead to a non functional proteins |
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What are insertions or deletions? |
Additions or losses of nucleotide pairs in a gene |
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What happens when there is an insertion or deletion? |
Often alters the reading frame, producing a frame shift mutation Depends if in/del is a multiple of three |
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How do proteins respond to environmental changes? |
Regulating transcription |
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How do proteins regulate transcription? |
They regulate enzymatic activity or enzymatic processes |
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What is the bacterial operon model? |
A cluster of functionally related genes: can be controlled together by a single on-off switch |
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What is the operator? |
The switch. A segment of DNA, usually positioned within the promoter |
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What is an operon? |
The entire stretch of DNA including the operator, the promoter, and the genes they control. |
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What is a repressor? What does it do? |
A protein repressor that can switch off an operon Prevents gene transcription by binding to the operator and blocking RNA polymerase |
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What is the repressor a product of? |
A separate regulatory gene, located some distance from the operon itself |
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What is a corepressor? |
A molecule that cooperates with a repressor protein to switch an operon off |
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(The trp operon) What happens when tryptophan is present? |
Tryptophan binds to the trp repressor protein, which turns the operon off |
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Trp is what kind of operon? Lac is what kind of operon? |
Trp is a repressible operon (usually on) Lac is an inducible operon (usually off) |
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