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cell and molec test1
activity answers and quiz answers
| Question | Answer |
|---|---|
| An 80S eukaryotic ribosome is made up of one large 50S subunit and one small 30S subunit. | false |
| Which of the following statements is (are) true and provide(s) evidence that a certain component of the ribosome catalyzes protein synthesis? | Ribosomes are inactive after RNase digestion. and Structural analysis shows that rRNA occupies the catalytic site where peptide bonds are formed. |
| In feedback inhibition, the inhibiting molecule is often the | end product of the pathway |
| A signal peptidase | removes a signal sequence from a polypeptide chain after it passes through a channel into the rough ER. |
| Eukaryotic ribosomes recognize and initially bind to what structure on the mRNA? | the 7-methylguanosine cap |
| A single mRNA can code for more than one polypeptide chain. | true |
| In translation, mRNAs are read in the _______ direction, and polypeptide chains are synthesized from the _______ends. | 5′ to 3′; amino to the carboxyl |
| Many chaperones are called heat-shock proteins because they | are expressed at higher levels after a heat shock than at normal growth conditions. |
| What happens to ubiquitin in proteosomes? | it is released and recycled |
| Eukaryotic mRNAS have a 7-methylguanosine cap on their 3′ end. | false |
| Phosphorylation of elongation factors 2 and 2B | blocks their exchange of bound GDP for GTP. |
| MicroRNAs can regulate translation by targeting proteins that can either cleave an mRNA or repress its translation. | true |
| One molecule of GTP is split in the process of loading one amino acid onto its tRNA. | false |
| SiRNAs act primarily to inhibit | translation, by inducing cleavage of a complementary mRNA. and translation, by binding to an mRNA. |
| The capacity for some tRNAs to recognize more than one codon in mRNA is explained by a phenomenon called | wobble |
| Ferritin levels can be regulated by IRE-binding proteins that bind to a site near the 5′ end of ferritin mRNAs and block translation of the RNA. | true |
| Prokaryotic and eukaryotic ribosomes are | 70S and 80S, respectively. |
| Proteins are often regulated by phosphorylation by enzymes called | protein kinases |
| The factor that escorts the amionacyl tRNA to the eukaryotic ribosome and then releases it with GTP hydrolysis following the correct codon–anticodon base pairing is | eEF-1α. |
| During translation, the codons on the mRNA are recognized by complementary base pairing to the anticodon on the | transfer RNA. |
| Oocytes store mRNAs with _______ and activate them by _______. | short poly-A tails; lengthening the tails |
| Cells contain 64 tRNAs, with one anticodon for each codon. | false |
| Monomeric G proteins, such as Ras and several elongation factors, are usually in the active state when a molecule of _______ is bound to them. | GTP |
| In a major protein degradation pathway, a short polypeptide called _______ is attached to a protein to target it for destruction. | ubiquitin |
| Cleaving of pre-rRNA produces | the 28S, 18S, and 5.8S rRNAs. |
| The nucleolus is the site where _______ is (are) assembled. | ribosomal subunits |
| Highly condensed, transcriptionally inactive chromatin is called | heterochromatin. |
| Export of RNAs from the nucleus occurs primarily by | selective transport through nuclear pore complexes. |
| Which of the following is not involved in the transport of RNAs out of the nucleus? | Small RNAs crossing by passive diffusion |
| The nuclear localization signal is typically a(n) _______, rich in the amino acids _______. | short sequence; Lys and Arg |
| The nuclear localization signal is recognized by and binds to which protein in the process of nuclear protein import? | importin |
| Eukaryotic ribosomes leave the nucleus as | 40S and 60S ribosomal subunits. |
| The eukaryotic 45S pre-rRNA transcript codes for the | The eukaryotic 45S pre-rRNA transcript codes for the |
| The nucleolus is the site of rRNA synthesis and processing, and of ribosomal subunit assembly. | true |
| SnoRNP particles contain RNA sequences complementary to rRNA sequences. | true |
| Chromatin domains appear to represent discrete functional units that independently regulate gene expression. | true |
| Ribosomal proteins are synthesized in the nucleolus and then assembled onto rRNAs. | false |
| For proteins that normally are nuclear, deletion of the nuclear localization signal and injection of the protein into the cytoplasm of cultured cells will result in localization | in the cytoplasm |
| Nuclear localization signals were first identified by Alan Smith and his colleagues in the protein | SV40 T antigen. |
| Which of the following is an example of the involvement of the nucleolus in the processing of non-rRNAs? | The base modification of tRNAs catalyzed by snoRNPs |
| Messenger RNAs are transported through the nuclear pores as ribonucleoprotein particles. | true |
| The nuclear lamina is built of proteins called | lamins |
| The major pathway for molecules to pass into and out of the nucleus is through | nuclear pore complexes |
| The nuclear envelope is composed of a nuclear membrane and an underlying nuclear lamina. | false |
| Chromatin domains are loops of about _______ base pairs of DNA. | 100,000 |
| The nuclear lamina binds to | both the inner nuclear envelope membrane and the chromatin. |
| Export of RNAs from the nucleus occurs primarily by | selective transport through nuclear pore complexes. |
| Which of the following statements about snRNAs is true? | They are synthesized in the nucleus, move to the cytoplasm to pick up proteins to become functional, and then return to the nucleus. |
| The activity of some proteins is regulated based on whether they can (or cannot) be imported into the nucleus. | true |
| By restricting the traffic of proteins and RNA across the nuclear envelope, eukaryotic cells can regulate _______ in unique ways. | translation and transcription |
| Cajal bodies are thought to represent sites of | snRNA processing and assembly. |
| Looped chromatin domains can be seen by viewing _______ chromosomes with light microscopy. | amphibian oocyte |
| Individual chromosomes occupy discrete territories within the nucleus. | true |
| Vesicle formation is driven by the binding of clathrin or COP proteins. | true |
| The Golgi apparatus is the main site of intracellular drug detoxification. | false |
| Calreticulin assists in folding glycoproteins that contain one _______ residue. | glucose |
| The pH inside lysosomes is about | 5 |
| Gaucher disease is a failure of lysosomes in macrophages to hydrolyze | glycolipids |
| Which of the following lipids is/are synthesized in the Golgi apparatus? | glycolipids |
| In plant cells, vesicles transport proteins from the Golgi apparatus to | vacuoles |
| Clathrin coats are bound to specific receptors by a protein called | adaptor protein |
| Proteins that span the membrane multiple times have multiple _______ that alternate with multiple transmembrane stop-transfer sequences. | internal signal sequences |
| Which of the following is not a contiguous membrane domain? | secretory granules |
| The main method by which a cell gets rid of old, worn-out organelles is exocytosis. | false |
| Using radiolabeled amino acids, Palade and colleagues were able to define the pathway taken by secreted proteins. Which of the following represents that pathway? | Rough ER→Golgi→secretory vesicles→cell exterior |
| Which of the following polysaccharides is (are) synthesized in the Golgi apparatus? | pectin |
| The unfolding response involves | general inhibition of protein synthesis. increased synthesis of chaperones. increased activity of proteosomes. |
| The major site at which membrane lipids are synthesized is the | cytosolic side of the ER membrane. |
| Which of the following provides evidence for the signal hypothesis for the targeting of a secretory protein to the rough ER? | protein is lger when synthesized in vitro on free polysomes secretory protein ends up in cytosol when a short sequence is deleted by genetic engineering.normally cytosolic protein is secreted when a specific sequence is added to it by genetic engineering. |
| The ribosomes of the rough endoplasmic reticulum are targeted to the cytoplasmic side of the membrane via | a sequence within the protein being synthesized. |
| Lysosomal proteins are initially incorporated into _______ vesicles. | clathrin coated |
| The major site at which membrane lipids are synthesized is the | cytosolic side of the ER membrane. |
| Transport vesicles carrying acid hydrolases fuse with | late endosomes |
| ARF function on vesicles is regulated by | binding GTP |
| Phospholipids are synthesized in the cytosolic half of the ER membrane bilayer. | true |
| Griscelli syndrome, a disease caused by mutations in the gene encoding Rab27a, is characterized by an abnormal | transport of melanosomes. export of vesicles in T lymphocytes. |
| GPI-anchored proteins are synthesized | as transmembrane proteins, cleaved, and attached to the GPI group on the lumenal surface of the ER. |
| Which of the following is not one of the classes of proteins that regulates the activity of Rab GTPases? | GTF (Guanine nucleotide trypolysis factor) |
| Which of the following would you expect to find at high concentrations in lysosomes? | Degradative enzymes |
| A common abbreviation for genes that regulate secretion is “sec,” while a common abbreviation for genes that regulate autophagy is | atg |
| The initial site of N-linked glycosylation is the Golgi apparatus. | false |
| Newly synthesized membrane lipids are found in both halves of a membrane bilayer because they are | synthesized on one surface and flipped to the other surface by proteins called flippases. |
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