Detailed summary of the book Essential cell biology, 9780393680362, for biology exam, Unicamillus University
Riassunto dettagliato del libro essential cell biology, 9780393680362, per esame di biologia, Università Unicamillus
Test Bank for Essential Cell Biology: with Norton Illumine Ebook, Smartwork, and Animations, 5th Edition by Alberts, 9780393680362, Covering Chapters 1-20 | Includes Rationales
Test Bank - Essential Cell Biology, 5th Edition (Alberts, 2020), Chapter 1-20 | All Chapters
Test Bank: Essential Cell Biology, 5th Edition (Alberts, 2020) | All Chapters
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UNITY AND DIVERSITY OF CELLS:
Cells are the fundamental units of life; cell biology is the study of cells and of their structure,
function and behavior. All living organisms are built from CELLS: small, membrane-enclosed
units filled with an aqueous solution of chemicals and with the ability to create copies of
themselves by growing and then dividing in two. Cells differ vastly in size, shape and
function, also they are diverse in their chemical requirements, some require oxygen to leave;
for others the gas is deadly. Although the cells are varied from the outside, they are similar
inside. In all organisms GENETIC INFORMATION, in the form of GENES, is carried in DNA
molecules. In every cell, long POLYMER CHAINS of DNA are made from the same set of
four monomers, called NUCLEOTIDES, put together in different sequences. The flow of
information is so fundamental to life that is referred to as the CENTRAL DOGMA.
Appearance and behavior of a cell are dictated by its protein molecules, which serves as
structural supports, chemical catalysis and much more. Proteins are built from AMINO
ACIDS, and all organisms use the same set of 20 amino acids to make proteins. The amino
acids are linked in different sequences, giving each protein molecule a different
tridimensional shape. One of the cells most commonly cited properties is their ability to
reproduce. For cells the process involves duplicating their genetic material and other
components, and dividing in two, producing a pair of daughter cells that are capable of the
same cycle of replication.
It is the relationship between DNA, RNA and proteins that makes these self replication
possible:
- DNA encodes (=codifica) information that directs the assembly of proteins (the
sequence of nucleotides in a molecule of DNA dictates the sequence of amino acids
in a protein);
- Proteins catalyze the replication of DNA and the transcription of RNA(it is transcribed
the information carried by the DNA) and they participate in the translation of RNA into
proteins(a linear sequence of amino acids). Proteins also catalyze the other chemical
reactions that keep the self replicating system running.
A cell can break down nutrients and use the products to both make the building blocks
needed to produce polynucleotides, proteins, and other cell constituents or to generate
energy needed to power these processes. Only living cells can perform this self replication.
VIRUSES also contain information in the form of DNA or RNA, but they do not have the
ability to reproduce by their own efforts. Instead, they parasite the reproductive machinery of
the cells that they invade, to make copies of themselves. When a cell replicates its DNA for
cell division, the copying is not always perfect. On occasion, the instructions are corrupted
by MUTATIONS that change the sequence of nucleotides in the DNA. For this reason,
daughter cells are not exact replicas of their parents. Mutation can create offspring (prole)
that are changed for the worse, for the better or in a natural way. The genes of the next
generation will be the genes of the survivors (evolution). All diseases can be explained by a
dysfunction at the cellular level. Some example of diseases: - Hypercholesterolemia
(defective uptake of lipoproteins);
- Cystic fibrosis (miss folding of a key protein);
- Hypertension (defective cell-cell adhesion in the kidney cells);
- Muscular dystrophy (defective attachment of the plasma membrane to the cytoskeleton); -
Cancer (error in the cell division, migration, growth, signaling).
A cell’s GENOME, (the entire sequence of nucleotides in an organism’s DNA), provides a
genetic program that instructs a cell how to behave. All these differentiated cell types are
generated during embryonic development from a single fertilized egg cell and they contain
,identical copies of the DNA of the species. Different cells express different genes. Each cell
is capable of carrying out a variety of biological tasks, depending on its environment and its
history, and it uses the information in its DNA to guide its activities.
CELL UNDER THE MICROSCOPE:
If a very thin slice is cut from a plant or an animal tissue, and viewed using a light
microscope(it uses visible light to illuminate and zoom in very small objects), it is apparent (è
evidente) that the tissue is divided into thousands of small cells. In some cases, the cells are
closely packed; in others, they are separated from one another by an extracellular matrix (a
dense material made of protein fibers embedded=incorporate in a gel of long sugar chains).
Each cell is typically about 5-20 μm in diameter. Typical animal cells visualized in these
ways have a distinct anatomy: they have a defined boundary=confine, indicating the
presence of an enclosing membrane, the plasma membrane and a large, round structure,
the nucleus. Around the nucleus, and filling the cell’s interior, is the cytoplasm, a transparent
substance. New types of light microscopes, called fluorescence microscopes, have been
developed; these use sophisticated methods of illumination and electronic image processing
to see fluorescently cell components in finer detail. For the highest resolution, there is the
electron microscope, which can reveal details down to a few nanometers. A tissue has to be
fixed (preserved in a reactive chemical solution), supported by embedding (=incorporato) in
a solid wax or resin, sectioned into much thinner slices than the light microscope, and
stained (=macchiato) before it is viewed and there is no possibility of looking at living cells. A
delicate membrane is visible enclosing the cell, and similar membranes form the boundary of
many of the organelles inside. The plasma membrane separates the interior of the cell from
its external environment, while internal membranes surround organelles. The type of
electron microscope used to look at thin sections is known as the transmission electron
microscope: this is similar to a light microscope, except that it transmits a beam of electrons
(= fascio di elettroni), rather than a beam of light, through the sample. Another type of
electron microscope is the scanning electron microscope, which is used to look at the
surface detail of cells and other structures. Even the most powerful electron microscopes
cannot visualize the individual atoms that make up biological molecules.
CELLULAR ORGANIZATION: the Prokaryotic and Eukaryotic cells
The presence or absence of a nucleus is used for a classification of all living things.
Organisms whose cells have a nucleus are called EUKARYOTES; organisms whose cells do
not have a nucleus are called PROKARYOTES. The bacteria have the simplest structure,
they contain no organelles other than ribosomes and no nucleus.
THE PROKARYOTIC CELL:
Prokaryotes are very small (few micrometer long) and have a tough protective coat, or cell
wall, surrounding the plasma membrane, which encloses a compartment containing the
cytoplasm and the DNA; the cell appears without any obvious organized internal structure
and it reproduces quickly by dividing in two. Population of prokaryotic cells can evolve fast,
rapidly acquiring the ability to use a new food source or to resist being killed by an antibiotic.
Most prokaryotes live as single-celled organisms, although some join together to form chains
or other organized structures. Members of this class exploit=sfrutta an enormous range of
habitats. Some are AEROBIC, using oxygen to oxidize easy food molecules; some are
ANAEROBIC and are killed by the slightest=minimo exposure to oxygen. Some prokaryote
can live on organic substances: they can get carbon from CO2 in the atmosphere, nitrogen
from atmospheric N2, and oxygen, hydrogen, sulfur and phosphorus from air, water and
inorganic minerals:
- Some of these cells, like plant cells, perform PHOTOSYNTHESIS, using energy from
sunlight to produce organic molecules from CO2;
,- Other cells derive energy from the chemical reactivity of inorganic substances in the
environment.
Prokaryotes are divided into two distinct domains:
○ 1) THE BACTERIA: most of the prokaryotes from everyday life are bacteria.
—> the structure can be “gram positive” or “gram negative”; this depends on
the organization of the wall.
○ 2) THE ARCHAEA: archaea are also found in environments that are hostile
for other cells, as the hot acid of volcanic springs=sorgenti vulcaniche
THE EUKARYOTIC CELL:
Eukaryotic cells are bigger and more elaborate than bacteria and archaea. Some live
independent lives as single-celled organisms; others live in multicellular assemblies. All
eukaryotic cells have a nucleus, and other organelles, most of which are membrane-
enclosed. The NUCLEUS is enclosed within two membranes that form the NUCLEAR
ENVELOPE (2 phospholipid bilayers) and it contains molecules of DNA. In the light
microscope these giant DNA molecules become visible as a CHROMOSOMES before a cell
divides into two daughter cells. MITOCHONDRIA are present in all eukaryotic cells,
individual mitochondria are enclosed in two separate membranes. They are generators of
chemical energy for the cell. They exploit the energy (=sfruttano l’energia) from the oxidation
of food molecules, such as sugars, to produce ATP (Adenosine Triphosphate). Because the
mitochondria consumes oxygen and releases CO2 in this activity, the process is called CELL
RESPIRATION. Without the mitochondria, animals, fungi and plants would be unable to use
oxygen to extract the energy they need from the food molecules that feed them.
Mitochondria contain their own DNA and reproduce by dividing; because they look like
bacteria in so many ways, they are taught to derive from bacteria that were engulfed by
ancestors of eukaryotic cells. CHLOROPLASTS are large and green organelles found in the
cells of plants and algae, but not in animals or fungi. These organelles have a more complex
structure than mitochondria: in addition to their two membranes, they possess internal
stacks=pile of membranes containing the green pigment CHLOROPHYLL. Chloroplasts
carry out=effettuano PHOTOSYNTHESIS, imprison the energy of the sunlight in their
chlorophyll molecules and using this energy to drive the production of sugar molecules; they
release the oxygen as a molecular by-product=sottoprodotto. Plant cells can extract these
chemical energy when they need it, by oxidizing these sugars and their breakdown products
(=prodotti di decomposizione), mainly in the mitochondria. Like mitochondria, chloroplasts
contain their own DNA, and they reproduce by dividing in two. The cytoplasm contains some
other organelles that are surrounded by single membranes. These structures are involved
with the cell’s ability to import raw materials=materia prima and to export useful substances
and waste products produced by the cell. The ENDOPLASMIC RETICULUM (ER) is divided
into the rough ER, in which the attachment of ribosomes to the membrane gives a rough
appearance and where synthesis of proteins is made, and the smooth ER, where there are
relatively few bound ribosomes and where lipids are synthesized, Ca+ is stored and
detoxification occurs. Stacks of flattened=pile di sacchi, membrane-enclosed sacs constitute
the GOLGI APPARATUS, which packages molecules made in the ER, destined to be either
secreted or transported to another compartment by the help of vesicles.
- LYSOSOMES are small and irregularly shaped organelles in which intracellular digestion
occurs, releasing nutrients from ingested food particles into the Cytosol and breaking down
unwanted molecules for recycling within=all’interno the cell or excretion from the cell. Many
of the molecules within the cell are being constantly broken down and remade.
- PEROXISOMES are small, membrane-enclosed vesicles that provide an environment for
, the reactions in which the hydrogen peroxide is used to inactivate toxic molecules.
Membranes form many types of small transport vesicles that carry materials between one
membrane-enclosed organelle and another. The cytosol is the part of the cytoplasm that is
not contained within intracellular membranes, it contains a host of large and small
molecules, crowded together so closely that it behaves more like a water-based gel than a
liquid solution. The cytosol is the site of many chemical reactions that are fundamental to the
cell’s existence. This system of protein filaments, called the cytoskeleton, is composed of
three major filament types: the thinnest of these filaments are the actin filaments; the thickest
filaments in the cytosol are called microtubules and the intermediate in thickness between
actin filaments and microtubules are the intermediate filaments. The cell interior is in
constant motion, motor protein uses the energy stored in molecules of ATP to trundle
(rotolare) along these tracks and cables, carrying organelles and proteins throughout the
cytoplasm. Eukaryotic cells are typically 10 times the length of prokaryotic cells, an example
of prokaryotic cell is the bacterium of Escherichia coli that is a small rod-shaped cell that
normally lives in the gut of humans and other vertebrates. Most of our knowledge of the
fundamental mechanisms of life, including how cells replicate their DNA and how they
decode these genetic instructions to make proteins, has come from studies of E. coli. E. coli
carries its genetic instructions in a single, circular, double-stranded molecule of DNA.
CAPITOLO 4:
Proteins are assembled mainly from a set of 20 different amino acids, each with different
chemical properties. A protein molecule is made from a long chain of these amino acids,
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