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Samenvatting Essential Cell Biology, ISBN: 9780393680393 Cell Biology-Histology
Samenvatting Cell Biology
[Meer zien]Voorbeeld 4 van de 45 pagina's
Voorbeeld 4 van de 45 pagina's
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Summary – Cell biologyChapter 1 – Cells: The Fundamental Units of Life
Unity and diversity of cells
Cell – The basic unit from which a living organism is made; an aqueous solution of chemicals, enclosed
by a membrane, that has the ability to self-replicate.
→ Differences in size, shape, and chemical requirements often reflect differences in cell function.
Every animal or plant is a vast colony of individual cells, each of which performs a specialized function
that is integrated by intricate systems of cell-to-cell communication.
The inside of cells is fundamentally similar:
- Same sorts of molecules
- Same types of chemical reactions
- Genetic information in form of genes, and carried in DNA molecules
- Reproduces in the same way
DNA – Double-stranded polynucleotide formed from two separate chains of
covalently linked deoxyribonucleotide units. It serves as the cell’s store of
genetic information that is transmitted from generation to generation.
RNA – Molecule produced by the transcription of DNA; usually single-stranded,
it is a polynucleotide composed of covalently linked ribonucleotide subunits.
Serves a variety of informational, structural, catalytic, and regulatory functions
in cells.
Central dogma – The flow of information: DNA → RNA → Protein
This feedback loop between proteins and polynucleotides underlies the self-reproducing behavior of
living things.
Viruses also contain information in the form of DNA or RNA, but they do not have the abilitiy to
reproduce by their own efforts. Instead, they parasitize the reproductive machinery of the cells that
they invade to make copies of themselves. So, viruses are not truly considered living.
Mutations can create offspring that are changed for the worse (in that they are less able to survive and
reproduce), changed for the better (in that they are better able to survive and reproduce), or changed
in a neutral way (in that they are genetically different but equally viable). The struggle for survival
eliminates the first, favors the second, and tolerates the third. The genes of the next generation will
be the genes of the survivors.
,Evolution – Process of gradual modification and adaptation that occurs in living organisms over
generations.
Present-day cells are so similar in their fundamentals, because they have all inherited their genetic
instructions form the same common ancestral cell.
Genome – The total genetic information carried by all the chromosomes of a cell or organism; in
humans, the total number of nucleotide pairs in the 22 autosomes plus the X and Y chromosomes.
Cells under the microscope
Microscope – Instrument for viewing extremely small objects. Some use a focused beam of visible
light and are used to examine cells and organelles. Others use a beam of electrons and can be used
to examine objects as small as individual molecules.
Cell theory – All living cells are formed by the growth and division of existing cells.
Extracellular matrix – A dense material often made of protein fibers embedded in a gel of long sugar
chains.
The plasma membrane encloses the cell. Inside the cell is the nucleus, this is a large round structure
near the middle of the cell. Around the nucleus is and filling the cells interior is the cytoplasm.
Ribosome – A large macromolecular complex in which RNAs are translated into proteins.
View through an electron microscope.
Different organelles are present:
- Plasma membrane
- Nucleus
- Endoplasmic reticulum
- Mitochondrion
- Lysosome
- Peroxisome
- Ribosomes
- Mitochondria
The prokaryotic cell
Bacteria have the simplest structure; it does not contain organelles other than ribosomes.
Eukaryotes – Organisms whose cells have a nucleus.
Prokaryotes – Organisms whose cells do not have a nucleus.
Prokaryotes:
- Typically spherical, rodlike or corkscrew-shaped
- Small, a few micrometers long
- Tough protective coat, or cell wall, surrounding the plasma membrane, which encloses a
single compartment containing the cytoplasm and the DNA.
, - Cells reproduce quickly by dividing in two
- Most live as single-celled organisms
- Prokaryotes can live entirely on inorganic substances: carbon from CO2 in the atmosphere,
nitrogen from atmospheric N2, and oxygen, hydrogen, sulfur, and phosphorus from air, water
and inorganic materials. Some of these prokaryotic cells, like plant cells, perform
photosynthesis, using energy from sunlight to produce organic molecules from CO2 others
derive energy from the chemical reactivity of inorganic substances in the environment
Two domains in the world of the prokaryotes: Bacteria and Archaea.
Bacterium – Microscopic organism that is a member of one of the two divisions of prokaryotes; some
species cause disease. The term is sometimes used to refer to any prokaryotic microorganism,
although the world of prokaryotes also includes archaea, which are only distantly related to each
other.
Archaeon – Microscopic organism that is a member of one of the two divisions of prokaryotes; often
found in hostile environments such as hot springs or concentrated brine.
The eukaryotic cell
Eukaryotic cells, in general, are bigger and more elaborate than bacteria and archaea. Some live
independent lives as single-celled organisms, such as amoebae and yeasts; others live in multicellular
assemblies. All of the more complex multicellular organisms—including plants, animals, and fungi—
are formed from eukaryotic cells.
Organelles eukaryotic cell:
- Nucleus
- Mitochondria
- Chloroplasts (only in plants and algaes)
- Endoplasmic Reticulum
- Golgi Apparatus
- Lysosomes
- Peroxisomes
Secretory vesicles
All eukaryotic cells have a nucleus, and thus other organelles which are membrane-enclosed.
Nucleus – The prominent, rounded structure that contains the DNA of a eukaryotic cell. It is enclosed
within two concentric membranes that form the nuclear envelope and it contains molecules of DNA.
Chromosome – Long, threadlike structure composed of DNA and proteins that carries the genetic
information of an organism; becomes visible as a distinct entity when a plant of animal cell prepares
to divide.
, Mitochondria – Membrane-enclosed organelle, about the size of a bacterium, that
carries out oxidative phosphorylation and produces most of the ATP in eukaryotic
cells. Because mitochondria consume oxygen and release CO2 during this activity,
the entire process is called cell respiration. Mitochondria have their own DNA and
reproduce by dividing.
Chloroplast – Specialized organelle in algae and plants that contains
chlorophyll (green pigment) and serves as the site for photosynthesis. They
contain their own DNA, reproduce by dividing in two, and are thought to
have evolved from photosynthetic bacteria.
The process by which plants, algae and some bacteria use the energy of sunlight to drive the
synthesis of organic molecules from carbon dioxide and water, is called photosynthesis.
Other organelles present in the cytoplasm of a cell are: Endoplasmic reticulum, the Golgi apparatus,
Lysosomes, Peroxisomes, and secretory vesicles:
Endoplasmic Reticulum (ER) – Labyrinthine membrane-enclosed
compartment in the cytoplasm of eukaryotic cells where lipids and
proteins are made.
Golgi Apparatus – Membrane-enclosed organelle in eukaryotic cells that modifies
and packages the proteins and lipids made in the ER and sorts them for transport to
either the outside of the cell or to other compartments of the cell.
Lysosomes – Membrane-enclosed organelle
that breaks down worn-out protein and
organelles and other waste materials, as well as
molecules taken up by endocytosis; contains
digestive enzymes that are typically most active
at the acid pH found inside these organelles.
Peroxisomes – small membrane-enclosed
organelle that contains enzymes that degrade
lipids and destroy toxins.
Secretory vesicle – Membrane-enclosed
organelle in which molecules destined for
secretion are stored prior to release.
→ Endocytosis – Process by which cells take in materials through an invagination of the plasma
membrane, which surrounds the ingested material in a membrane-enclosed vesicle.
→ Exocytosis – Process by which most molecules are secreted from a eukaryotic cell. These
molecules are packaged in membrane-enclosed vesicles that fuse with the plasma
membrane, releasing their contents to the outside.
Cytosol – Contents of the main compartment of the cytoplasm, excluding membrane-enclosed
organelles such as endoplasmic reticulum and mitochondria. The cell fraction remaining after
membranes, cytoskeletal components, and other organelles have been removed. The cytosol is the
site of many chemical reactions that are fundamental to the cell’s existence.
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