Chapter 2 Cell
Chapter 2 Cell
Chapter 2 Cell
LEVEL
OF ORGANIZATION
#Cell
Cell
is the basic living structural and functional unit of the body.
Cytology - It is a branch of
science concerned with a
study of cells
Eukaryotic Cell
Much larger, more complex with a
wider range of diversity and
differentiation
Arose perhaps a billion years after
the prokaryotes
Multicellular and provided with
nuclear membrane
Comparison
Prokaryotes
Organism
Bacteria
Organelles
DNA
RNA and Protein
Cell Division
Eukaryotes
Protist,
Fungi,
Plants,
Animals
Few or None
Nucleus, Mitochondria, ER,
etc.
Circular in Cytoplasm
Linear/ Circular bounded by
a membrane
RNA and Protein synthesize RNA synthesize in nucleus,
in same compartment
protein
synthesized
in
cytoplasm
Binary Fission
Mitosis/ meiosis
PARTS OF A CELL
Cytoplasm , Nucleus, Cell Membrane
Forms the cells flexible outer surface, separating the cells internal environment
(inside the cell) from the external environment (outside the cell). It is a selective
barrier that regulates the flow of materials into and out of a cell. This selectivity helps
establish and maintain the appropriate environment for normal cellular activities. The
plasma membrane also plays a key role in communication among cells and between
cells and their external environment.
The cytoplasm
consists of all the cellular contents between the plasma membrane and the nucleus.
This compartment has two components: cytosol and organelles. Cytosol, the fluid
portion of cytoplasm, contains water, dissolved solutes, and suspended particles.
Surrounded by cytosol are several different types of organelles. Each type of organelle
has a characteristic shape and specific functions. Examples include the cytoskeleton,
ribosomes, endoplasmic reticulum, Golgi complex, lysosomes, peroxisomes, and
mitochondria.
The nucleus
is a large organelle that houses most of a cells DNA. Within the nucleus, each
chromosome, a single molecule of DNA associated with several proteins, contains
thousands of hereditary units called genes that control most aspects of cellular
structure and function.
Cytosol
The cytosol (intracellular fluid) is the fluid portion of the cytoplasm that surrounds
organelles and constitutes about 55% of total cell volume.
Although it varies in composition and consistency from one part of a cell to another,
cytosol is 7590% water plus various dissolved and suspended components.
Among these are different types of ions, glucose, amino acids, fatty acids, proteins,
lipids, ATP, and waste products, some of which we have already discussed. Also
present in some cells are various organic molecules that aggregate into masses for
storage.
These aggregations may appear and disappear at different times in the life of a cell
The Cytoskeleton
MICROFILAMENTS
MICROFILAMENTS These are the thinnest elements of the cytoskeleton.
They are composed of the protein actin, and are most prevalent at the edge of a cell. Microfilaments
have two general functions: They help generate movement and provide mechanical support. With
respect to movement, microfilaments are involved in muscle contraction, cell division, and cell
locomotion, such as occurs during the migration of embryonic cells during development, the
invasion of tissues by white blood cells to fight infection, or the migration of skin cells during wound
healing.
Microfilaments provide much of the mechanical support that is responsible for the basic strength and
shapes of cells. They anchor the cytoskeleton to integral proteins in the plasma membrane.
Microfilaments also provide mechanical support for cell extensions called microvilli, non-motile,
microscopic fingerlike projections of the plasma membrane. Within each microvillus is a core Of
parallel microfilaments that supports it. Because they greatly increase the surface area of the cell,
microvilli are abundant on cells involved in absorption, such as the epithelial cells that line the small
intestine.
INTERMEDIATE FILAMENTS
INTERMEDIATE FILAMENTS As their name suggests, these filaments are thicker than
microfilaments but thinner than microtubules. Several different proteins can compose
intermediate filaments, which are exceptionally strong. They are found in parts of cells
subject to mechanical stress, help stabilize the position of organelles such as the
nucleus, and help attach cells to one another
MICROTUBULES
MICROTUBULES These are the largest of the cytoskeletal components and are long,
unbranched hollow tubes composed mainly of the protein tubulin. The assembly of
microtubules begins in an organelle called the centrosome (discussed shortly). The
microtubules grow outward from the centrosome toward the periphery of the cell.