BIOCHEMISTRY TRANSES
Lecture/First Semester
THE CELL AND ITS CHEMISTRY
Cells
- Basic functional and structural unit of life
- All living things are composed of cells, cell parts,
or cell products
- Organisms may be:
- Unicellular: prokaryotes
- Multicellular: human
Cell theory
- All organisms are composed of one or more cells.
- Cells are the smallest living units of all living
organisms.
- Cells arise only by division of a previously existing
cell.
- Cells vary in size and shapes.
Cell Requirements
- Genetic material
-Single circular molecule of DNA in
prokaryotes
-Double helix located in nucleus in
eukaryotes
- Cytoplasm
-Fills cell interior (sugars, amino acids,
proteins, organelles)
- Plasma Membrane
-Encloses the cell
Cell Size
- Most cells are relatively small because as size
increases, volume increases much more rapidly.
- Cell size and shape are related cell functions.
A Scale of Visibility
Classification of Cells
There are two major types of cells
- Prokaryotic
-lacks a nucleus and does not have an
extensive system of internal membranes
- all bacteria and archaea have this cell
type
- Eukaryotic
- has a nucleus and has internal
membrane-bounded compartments
- all organisms other than bacteria or
archaea have this cell type
Prokaryotic Cells
Prokaryotes are the simplest cellular organisms. They
have a plasma membrane surrounding a cytoplasm without
interior compartments (some bacteria have additional outer
layers to the plasma membrane)
-Cell wall - comprised of carbohydrates to confer rigid
structure
-Capsule may surround the cell wall
-Cytoplasm is uniform with little or no internal support
framework
-Ribosomes (sites for protein synthesis) are scattered
throughout the cytoplasm
-Nucleoid region (an area of the cell where DNA is
localized)
- not membrane-bounded, so not a true nucleus
-Flagellum (plural, flagellae) is a threadlike structure
made of protein fibers that extends from the cell
surface
- may be one or many
- aids in locomotion and feeding
-Pilus (plural, pili) is a short flagellum
- aids in attaching to substrates and in
exchanging genetic information between cells
Eukaryotic Cells
Eukaryotic cells are larger and more complex than
prokaryotic cells. They have a plasma membrane encasing the
cytoplasm, internal membranes form compartments called
organelles. The cytoplasm is semi-fluid and contains a network
of protein fibers that form a scaffold called a cytoskeleton.
-Nucleus - a membrane-bounded compartment for DNA
that gives eukaryotes (literally, “true-nut”) their name
- Endomembrane system - gives rise to the internal
membranes found in the cell. Each compartment can
provide specific conditions favoring a particular
process.
- The cells of plants, fungi, and many protists have a cell
wall beyond the plasma membrane
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