p.8
Regulation of Protein Synthesis in Prokaryotes
What role do histones play in gene transcription?
Histones nonspecifically repress transcription of genes.
p.1
Mutations and Their Effects on Proteins
What are frameshift mutations?
Mutations that occur when the number of bases added or deleted is not a multiple of three, shifting the reading frame.
p.1
Mutations and Their Effects on Proteins
What causes sickle cell anemia?
A point mutation (GAG to GTG) that causes valine to replace glutamate in the β-globin chain.
p.4
Protein Synthesis and Translation
What is required for the binding of aminoacyl-tRNA?
An elongation factor (EF-Tu in prokaryotes and eEF-1 in eukaryotes) and hydrolysis of GTP.
p.10
Operons and Gene Regulation
What happens when the repressor is activated in a repressible operon?
It binds to the operator, preventing RNA polymerase from binding to the promoter, leading to no transcription.
p.1
Mutations and Their Effects on Proteins
What is a silent mutation?
A mutation that does not affect the amino acid sequence of a protein.
p.5
Posttranslational Modifications
What modifications can proteins undergo after synthesis?
Proteins can be modified by phosphorylation, glycosylation, ADP ribosylation, hydroxylation, and addition of other groups.
p.4
Protein Synthesis and Translation
What determines which aminoacyl-tRNA will bind to the A site?
The mRNA codon at the A site.
p.1
Gene Expression and Transcription
What is the significance of the start codon (AUG) in protein synthesis?
It determines the reading frame for subsequent nucleotides.
p.11
Operons and Gene Regulation
What is the function of the lac operon?
To regulate the metabolism of lactose in bacteria.
p.4
Protein Synthesis and Translation
What occurs during translocation?
The peptidyl-tRNA moves from the A site to the P site, and the uncharged tRNA moves to the E site.
p.11
Operons and Gene Regulation
What is catabolite repression?
A mechanism where the operon is transcribed only when glucose is low.
p.11
Gene Expression and Transcription
What occurs if translation is slow in relation to transcription?
Transcription continues because the termination structure does not form.
p.7
Protein Synthesis and Translation
How are secretory proteins released from the cell?
By exocytosis from secretory vesicles.
p.2
Protein Synthesis and Translation
What does the term 'antiparallel binding' refer to in the context of aminoacyl-tRNA?
The binding of aminoacyl-tRNA to mRNA in opposite orientations.
p.9
Operons and Gene Regulation
What is the lac operon and when is it induced?
The lac operon is inducible and is induced in the absence of glucose.
p.13
RNA Processing and Stability
What role do nucleases play in mRNA regulation?
Nucleases can degrade mRNAs after synthesis in the nucleus, affecting their stability and translation.
p.11
Operons and Gene Regulation
What is the role of allolactose in the lac operon?
It acts as an inducer that inactivates the repressor.
p.7
Protein Synthesis and Translation
Where are secretory proteins synthesized in eukaryotic cells?
On ribosomes attached to the rough endoplasmic reticulum (RER).
p.14
Gene Expression and Transcription
What is the significance of the TATA box?
It is a core promoter element that helps initiate transcription.
p.7
Protein Synthesis and Translation
What happens to the signal sequence after the protein enters the RER?
It is cleaved from the N-terminus.
p.15
Regulation of Protein Synthesis in Eukaryotes
What are iron-response elements (IREs) and their role in mRNA regulation?
They regulate translation of mRNAs for ferritin and transferrin receptor based on iron levels.
p.4
Protein Synthesis and Translation
What is the first step in the elongation of a polypeptide chain?
Binding of aminoacyl-tRNA to the A site.
p.10
Operons and Gene Regulation
What is the role of the co-repressor in a repressible operon?
The co-repressor binds to the inactive repressor, activating it to bind to the operator and prevent transcription.
p.5
Protein Synthesis and Translation
What is a polysome?
A complex of mRNA with multiple ribosomes attached to it.
p.7
Protein Synthesis and Translation
Which sequences target specific proteins to the nucleus?
Highly basic sequences containing arginine and lysine.
p.13
Regulation of Protein Synthesis in Eukaryotes
How do small interfering RNAs (siRNA) contribute to gene silencing?
siRNA can block translation or induce degradation of target mRNAs, regulating gene expression.
p.6
Posttranslational Modifications
What is myristoylation?
It is the addition of a lipid group to the amino group of N-terminal glycine (gly).
p.11
Regulation of Protein Synthesis in Prokaryotes
What is the role of cAMP in the lac operon?
It binds to CAP, facilitating the initiation of transcription by RNA polymerase.
p.12
Gene Expression and Transcription
What is the difference in genome size between mammals and E. coli?
The mammalian genome contains about 1,000 times more DNA than E. coli (10^9 vs 10^6 base pairs).
p.3
Protein Synthesis and Translation
How is the initiating methionine modified in bacteria?
It is formylated and carried by tRNA f Met.
p.3
Protein Synthesis and Translation
What sequence in prokaryotes binds to the 3' end of 16S rRNA?
The Shine–Dalgarno sequence.
p.12
Gene Expression and Transcription
What are Alu sequences?
Relatively short, repetitive DNA sequences dispersed throughout the eukaryotic genome that do not code for proteins.
p.2
Protein Synthesis and Translation
What is the role of aminoacyl-tRNA synthetase?
It catalyzes the formation of aminoacyl-tRNA by linking an amino acid to tRNA.
p.9
Operons and Gene Regulation
What is the role of a repressor protein in gene expression?
It binds to the operator, preventing RNA polymerase from binding and thus inhibiting transcription.
p.13
RNA Processing and Stability
How does alternative polyadenylation affect antibody production?
It allows lymphocytes to produce both membrane-bound and soluble forms of IgM antibodies at different developmental stages.
p.4
Protein Synthesis and Translation
What is the role of elongation factors in translocation?
They are required for the movement of peptidyl-tRNA from the A site to the P site.
p.15
Gene Expression and Transcription
What protein does the Apo B gene produce in the liver?
Apo B-100, which contains more than 4000 amino acids.
p.4
Protein Synthesis and Translation
What happens when a termination codon moves into the A site?
The elongation and translocation steps are repeated until termination occurs.
p.10
Regulation of Protein Synthesis in Prokaryotes
What is catabolite repression?
It is a mechanism where cells preferentially use glucose, leading to decreased expression of operons like lac and ara when glucose is present.
p.15
Gene Expression and Transcription
What is the role of miRNAs in gene expression?
They bind to target RNA and ablate its expression.
p.15
Gene Expression and Transcription
How can chemically synthesized double-stranded RNA molecules be used therapeutically?
They can generate siRNA in cells, which holds promise as a therapeutic tool.
p.10
Regulation of Protein Synthesis in Prokaryotes
What occurs during attenuation in bacterial cells?
Rapid translation of the nascent transcript can lead to the formation of a secondary structure that signals termination of transcription.
p.8
Regulation of Protein Synthesis in Prokaryotes
What processes can lead to changes in gene expression?
Genes can be deleted, amplified, rearranged, or modified (e.g., methylated).
p.13
Gene Expression and Transcription
What is the function of bromodomains in chromatin remodeling?
Bromodomains recognize acetylated histones and help bind ATP-driven chromatin remodeling complexes to DNA.
p.6
Posttranslational Modifications
What is ADP-ribosylation and which amino acids are involved?
It involves the addition of ADP-ribose to the nitrogen of arginine (arg) and glutamine (gln), and the sulfur of cysteine (cys).
p.7
Protein Synthesis and Translation
What sequence allows proteins to remain within the ER lumen?
The amino acid sequence KdE1 near the carboxy terminus.
p.14
Gene Expression and Transcription
What does the gene regulatory control region consist of?
The promoter region and additional gene regulatory sequences, including enhancers and hormone response elements (HRE).
p.14
Gene Expression and Transcription
What is the role of specific transcription factors?
They bind directly to DNA and can act as activators or repressors of transcription for specific genes.
p.10
Regulation of Protein Synthesis in Prokaryotes
How does glucose affect cAMP levels in cells?
Glucose decreases cAMP levels; when glucose is low, cAMP levels rise.
p.10
Regulation of Protein Synthesis in Prokaryotes
What is the function of the cAMP–protein complex in operon regulation?
It binds to a site near the promoter, facilitating the binding of RNA polymerase to the promoter.
p.12
Gene Expression and Transcription
How is DNA organized in eukaryotes compared to prokaryotes?
In eukaryotes, DNA is complexed with histones, while in prokaryotes, it is not.
p.12
Gene Expression and Transcription
What portion of the mammalian genome codes for proteins?
The major part of the genome does not code for proteins.
p.2
Protein Synthesis and Translation
How is the amino acid linked to tRNA?
Through an ester bond formed with the 2′- or 3′-hydroxyl of the terminal ribose.
p.2
Protein Synthesis and Translation
What interaction is crucial for the insertion of amino acids into a growing polypeptide chain?
Codon–anticodon interaction.
p.9
Operons and Gene Regulation
What happens when an inducer is present in an inducible operon?
It binds to and inactivates the repressor, allowing RNA polymerase to bind and initiate transcription.
p.6
Posttranslational Modifications
What is the significance of acetylation in protein modification?
It modifies the amino group of lysine (lys) and the N-terminus.
p.9
Gene Expression and Transcription
What proteins are produced by the genes of the lac operon?
Alpha-galactosidase, lactose permease, and transacetylase.
p.5
Antibiotics and Protein Synthesis Inhibition
What is the role of chloramphenicol in protein synthesis?
Chloramphenicol inhibits the peptidyl transferase activity of the 50S ribosomal subunit in prokaryotes.
p.5
Antibiotics and Protein Synthesis Inhibition
What is the mechanism of action of ricin?
Ricin acts as an N-glycosidase, cleaving a specific adenine base from the 28S rRNA, thereby inhibiting protein synthesis.
p.6
Posttranslational Modifications
What is prenylation?
It involves the addition of a lipid group to the sulfur of cysteine (cys).
p.2
Protein Synthesis and Translation
What is formed when an amino acid reacts with ATP?
An enzyme-aminoacyl-AMP complex and pyrophosphate (2 Pi).
p.6
Posttranslational Modifications
Which amino acids can undergo phosphorylation?
Serine (ser), threonine (thr), and tyrosine (tyr).
p.4
Protein Synthesis and Translation
What happens to the tRNA at the P site after peptide bond formation?
It becomes uncharged and does not contain an amino acid.
p.1
Mutations and Their Effects on Proteins
What are point mutations?
They occur when one base in DNA is replaced by another, altering the codon in mRNA.
p.6
Posttranslational Modifications
What is the difference between O-glycosylation and N-glycosylation?
O-glycosylation involves the hydroxyl groups of serine (ser), threonine (thr), and tyrosine (tyr), while N-glycosylation involves the amino group of asparagine (asn).
p.9
Operons and Gene Regulation
What is repression in the context of operons?
It is the process whereby a corepressor inhibits the transcription of an operon.
p.1
Mutations and Their Effects on Proteins
What is a nonsense mutation?
A mutation that results in a premature termination of the growing polypeptide chain.
p.1
Protein Synthesis and Translation
How are amino acids activated and attached to tRNAs?
By highly specific enzymes known as aminoacyl-tRNA synthetases.
p.14
RNA Processing and Stability
What is the role of the 5' cap in mRNA?
It protects the mRNA from degradation and assists in ribosome binding during translation.
p.3
Protein Synthesis and Translation
What completes the initiation complex in translation?
The large ribosomal subunit binds.
p.8
Regulation of Protein Synthesis in Prokaryotes
What is the function of inducers in gene transcription?
Inducers cause proteins to bind to DNA sequences and stimulate transcription of specific genes.
p.13
Gene Expression and Transcription
How do transcription factors interact with histones?
Transcription factors often have histone acetylase activity, facilitating the removal of histones from DNA for transcription.
p.7
Protein Synthesis and Translation
What targets cytoplasmic proteins to the peroxisomes?
The amino acid sequence SKL at the carboxy terminus.
p.6
Posttranslational Modifications
What is palmitoylation?
It is the addition of a lipid group to the internal sulfur of cysteine (cys).
p.9
Regulation of Protein Synthesis in Prokaryotes
What is catabolite repression?
It is a mechanism that inhibits the expression of the lac operon in the presence of glucose.
p.15
Gene Expression and Transcription
What is the major apoprotein of chylomicrons produced in intestinal cells?
Apo B-48, which contains only 48% of the amino acids of Apo B-100.
p.15
RNA Processing and Stability
What process generates a stop codon in intestinal mRNA for Apo B?
RNA editing, specifically the conversion of a C to a U.
p.7
Regulation of Protein Synthesis in Eukaryotes
How can eukaryotic protein synthesis be regulated?
By modification of DNA, transcription, mRNA processing, or translation.
p.8
Regulation of Protein Synthesis in Prokaryotes
How is gene regulation achieved during hnRNA processing?
It involves alternative start sites for transcription, alternative splice sites for intron removal, alternative polyadenylation sites, and RNA editing.
p.13
Gene Expression and Transcription
What is the role of histone acetylation in gene expression?
Histone acetylation facilitates transcription by allowing chromatin remodeling and nucleosome displacement.
p.13
RNA Processing and Stability
What are alternative splice sites and their significance?
Alternative splice sites can produce different mRNAs, leading to the production of different proteins from the same gene.
p.9
Operons and Gene Regulation
What is the inducer for the lac operon?
Allolactose, a metabolite of lactose.
p.5
Antibiotics and Protein Synthesis Inhibition
How do antibiotics like streptomycin affect protein synthesis?
Streptomycin binds to the 30S ribosomal subunit and causes misreading of mRNA, preventing the formation of the initiation complex.
p.1
Mutations and Their Effects on Proteins
What is a missense mutation?
A mutation that results in one amino acid being replaced by another.
p.7
Protein Synthesis and Translation
What causes a nascent secretory protein to enter the lumen of the RER?
A hydrophobic signal sequence at the N-terminus.
p.5
Antibiotics and Protein Synthesis Inhibition
What is the effect of diphtheria toxin on protein synthesis?
Diphtheria toxin inhibits translocation in eukaryotes by catalyzing the ADP-ribosylation of EF-2.
p.5
Antibiotics and Protein Synthesis Inhibition
What is the function of puromycin in protein synthesis?
Puromycin binds at the A site, forms a peptide bond with the growing peptide chain, and prematurely terminates synthesis.
p.1
Mutations and Their Effects on Proteins
What is β-thalassemia?
An imbalance in the synthesis of globin proteins, resulting in an excess of α subunits.
p.3
Protein Synthesis and Translation
What binds to the small ribosomal subunit during the initiation of translation in eukaryotes?
Methionyl-tRNA i Met binds to the small ribosomal subunit.
p.15
RNA Processing and Stability
What is the function of the Dicer complex in miRNA processing?
It processes pre-miRNA into double-stranded miRNA and selects the guide strand for RISC.
p.12
Gene Expression and Transcription
What is a key difference between eukaryotic and bacterial genes regarding introns?
Eukaryotic genes contain introns, while bacterial genes do not.
p.3
Protein Synthesis and Translation
How many initiation factors are present in prokaryotes?
Three initiation factors (IF-1, IF-2, IF-3).
p.8
Operons and Gene Regulation
What is the role of the operator in an operon?
It determines whether the genes are expressed or not by interacting with repressor proteins.
p.6
Posttranslational Modifications
What is the role of 4-Hydroxyproline in posttranslational modifications?
It is a modified amino acid derived from proline.
p.4
Protein Synthesis and Translation
What catalyzes the formation of a peptide bond?
Peptidyl transferase, which is an activity of the rRNA in the large ribosomal subunit.
p.1
Mutations and Their Effects on Proteins
How do mutations in DNA affect proteins?
Mutations can be transcribed into mRNA, causing changes in the encoded protein.
p.13
RNA Processing and Stability
What is RNA editing?
RNA editing involves the alteration of bases in mRNA after transcription, potentially changing the protein produced.
p.7
Regulation of Protein Synthesis in Prokaryotes
What is the role of operons in prokaryotic protein synthesis regulation?
They contain promoter regions that facilitate or inhibit RNA polymerase binding.
p.11
Regulation of Protein Synthesis in Prokaryotes
What factors affect RNA polymerase activity?
Factors such as sigma that bind to core RNA polymerase to increase its binding ability to specific promoters.
p.12
Gene Expression and Transcription
How are eukaryotic genes different from bacterial genes in terms of copies?
Some eukaryotic genes are unique, while others have many copies in the genome.
p.12
Regulation of Protein Synthesis in Eukaryotes
What effect does DNA methylation have on gene transcription?
Increased methylation generally reduces the transcriptional activity of a gene.
p.12
Regulation of Protein Synthesis in Eukaryotes
What are histones and their role in gene regulation?
Histones are proteins that associate with DNA in eukaryotes and act as nonspecific repressors.
p.5
Protein Synthesis and Translation
What happens when a termination codon occupies the A site during translation?
Release factors cause the newly synthesized polypeptide to be hydrolyzed from the tRNA and released from the ribosome.
p.10
Operons and Gene Regulation
What is the corepressor in the tryptophan operon?
Tryptophan itself acts as the corepressor.
p.10
Operons and Gene Regulation
How does the presence of tryptophan affect the trp operon?
It represses the operon since the cell does not need to synthesize tryptophan when it is already present.
p.10
Operons and Gene Regulation
What is positive control in gene regulation?
It refers to mechanisms that activate transcription, such as the binding of arabinose to the repressor of the ara operon, turning it into an activator.
p.14
Gene Expression and Transcription
What is the function of the basal transcription complex?
It contains RNA polymerase and general transcription factors, binding to the TATA box to initiate gene transcription.
p.14
RNA Processing and Stability
What is alternative splicing?
It is the process by which the same transcript can be spliced differently to produce different protein products.
p.14
Gene Expression and Transcription
What protein is produced from the calcitonin gene in brain cells?
Calcitonin gene-related protein (CGRP).
p.15
Regulation of Protein Synthesis in Eukaryotes
How does heme regulate protein synthesis?
By preventing the phosphorylation and inactivation of eIF-2, a factor involved in initiation.
p.15
Regulation of Protein Synthesis in Eukaryotes
What effect does interferon have on protein synthesis?
It stimulates the phosphorylation of eIF-2, causing inhibition of initiation.
p.12
Gene Expression and Transcription
What is the ploidy level of most mammalian cells?
Most mammalian cells are diploid.
p.3
Protein Synthesis and Translation
What are the three sites in the ribosome during translation initiation?
P (peptidyl), A (acceptor), and E (ejection) sites.
p.12
Operons and Gene Regulation
How are bacterial genes organized?
Bacterial genes are organized in operons, controlled by a single promoter.
p.3
Protein Synthesis and Translation
What is the ribosomal subunit composition in eukaryotes?
80S ribosome (40S and 60S subunits).
p.12
Regulation of Protein Synthesis in Eukaryotes
What is the difference between heterochromatin and euchromatin?
Heterochromatin is transcriptionally inactive, while euchromatin is transcriptionally active.
p.5
Antibiotics and Protein Synthesis Inhibition
How does tetracycline inhibit protein synthesis?
Tetracycline binds to the 30S ribosomal subunit and inhibits the binding of aminoacyl-tRNA to the A site.
p.15
Gene Expression and Transcription
What happens to target mRNA when the guide strand of RISC binds to it?
It leads to either degradation of the mRNA or inhibition of translation.
p.11
Regulation of Protein Synthesis in Eukaryotes
How do eukaryotic and prokaryotic cells differ in gene expression regulation?
Eukaryotic cells undergo differentiation and have separated transcription and translation, while prokaryotes perform both simultaneously.
p.14
Gene Expression and Transcription
What are mediator proteins?
They are co-activators or co-repressors that interact with specific transcription factors and general transcription factors.
p.8
Regulation of Protein Synthesis in Prokaryotes
What are regulatory elements in DNA sequences?
They control the expression of genes that produce proteins, including the basal promoter, enhancers, and silencers.
p.8
Regulation of Protein Synthesis in Prokaryotes
How can protein synthesis be regulated at the translation level?
Through the degradation of mRNA by silencing RNA (miRNAs).
p.8
Operons and Gene Regulation
What is an operon?
A set of genes that are adjacent in the genome and are coordinately controlled.
p.8
Operons and Gene Regulation
What happens during the process of induction in gene expression?
An inducer stimulates the transcription of an operon by inactivating the repressor.
p.3
Protein Synthesis and Translation
What is the ribosomal subunit composition in prokaryotes?
70S ribosome (30S and 50S subunits).
p.3
Protein Synthesis and Translation
What is required for the formation of the initiation complex?
Initiation factors, ATP, and GTP.
p.12
Regulation of Protein Synthesis in Eukaryotes
What can result from changes in genes during differentiation?
Genes can be lost or partially lost, preventing the production of functional proteins.
p.12
Regulation of Protein Synthesis in Eukaryotes
How does the drug methotrexate affect gene expression?
It causes amplification of the gene for dihydrofolate reductase, leading to drug resistance.
p.8
Operons and Gene Regulation
What is a polycistronic mRNA?
A single mRNA that codes for all the proteins of an operon.
p.12
Regulation of Protein Synthesis in Eukaryotes
How do inducers like steroid hormones affect gene expression?
Inducers enter cells, bind to receptors, and activate specific genes by interacting with chromatin.
