Answer:
DNA may be taken up by bacterial cells and be active.
Explanation:
To understand Avery, MacLeod, and McCarty's experiment, it is important to know Frederick Griffith's precursor experiment. The microbiologist worked at the British Ministry of Health's Pathology Laboratory with pneumococci (commonly known as the bacterium Streptococcus pneumoniae, then known as Pneumococcus, which causes pneumonia), which were previously classified into several types. When cultured in petri dishes in the laboratory, the pneumococci that synthesize their capsules generate 'smooth' colonies. Subcutaneous injection of liquid culture of these pneumococci into mice causes their death. However, in vitro culture also allows the emergence of rough colonies', whose bacteria have lost the ability to synthesize mucopolysaccharide (and therefore have no capsules). Rough mutants could no longer be classified with sera and, moreover, lost their virulence: mice inoculated with them remained alive, unlike inoculated with smooth pneumococci.
The nature of Griffith's transforming principle remained unclear until the work of Avery, MacLeod, and McCarty. They repeated the in vitro transformation of pneumococci at the Rockfeller Institute for Medical Research, but replaced heat-dead cells with a purified fraction of smooth bacterial extract (unable to cause disease alone) and treated the material with different enzymes, each capable of destroying a specific type of macromolecule. Experience has shown that this fraction retained its transforming capacity when treated with protein or RNA degrading enzymes, but lost that ability when treated with DNA degrading enzymes. These results indicated that the chemical nature of the 'transforming principle' was DNA.
Thus, we can conclude that in addition to identifying genetic material, Avery, MacLeod and McCarty experiments with different strains of Streptococcus pneumoniae demonstrated that DNA can be absorbed by bacterial cells and be active.
Answer:
Magma
Explanation:
This rock is made of cooled magma
The Nucleus & Its Structures
Therefore, the nucleus houses the cell's DNA and directs the synthesis of proteins and ribosomes, the cellular organelles responsible for protein synthesis. The nuclear envelope is a double-membrane structure that constitutes the outermost portion of the nucleus.
Answer:
(a) Microfilaments
(b) Microtubules
(c) Microtubules
(d) Microfilaments
(e) Intermediate filaments
(f) Microfilaments, intermediate filaments, microtubules
(g) Microfilaments, microtubules
(h) Microfilaments, intermediate filaments, microtubules
(i) Microtubules, microfilaments
(j) Microtubules
Explanation:
Microtubules (MTs) are dimers of the protein tubulin (alpha- and beta-tubulin subunits) and they are major components of the cytoskeleton. MTs play diverse cellular roles including, mechanical support (cytoskeleton), transport, motility, chromosome segregation, etc. Microfilaments (MFs) are protein filaments that also form part of the cytoskeleton in eukaryotic cells. MFs consist of G-actin monomers assembled in linear actin polymers, and their functions include mechanical support, cytokinesis, changes in cell shape, amoeboid movement, endocytosis and exocytosis, etc. MFs associate with the protein myosin to generate muscle contractions. Actin filaments/MTs assembly from monomeric actin/tubulin is caused due to energy expenditure, where ATP/GTP bound to actin/tubulin is hydrolyzed during polymerization. Finally, intermediate filaments (IFs) are a type of cytoskeletal element composed of a heterogeneous group of structural elements, and they are not found in all eukaryotes. The primary function of the IFs is to contribute to the mechanical support for the plasma membrane where these filaments come into contact with other cells and/or with the extracellular matrix. The IFs are not directly involved in cell movement. All 3 types of cytoskeletal elements (microfilaments, intermediate filaments, microtubules) can be visualized by fluorescence microscopy when cells express chimeric MT/IF/MF.–GFP fusion proteins.
