The document summarizes key aspects of cell structure and function according to the cell theory. It describes the basic components of cells, including the plasma membrane, nucleus, cytoplasm, and various organelles. It explains that cells are the basic structural and functional units of living organisms, and that their biochemical activities depend on their specific subcellular structures. The key cellular processes of protein synthesis and transport are also summarized.

1. cells

2. The Cell Theory
• A cell is the basic structural and functional unit of
living organisms.
• The activity of an organism depends on both the
individual and collective activities of its cells
• According to the principle of complementarity,
the biochemical activities of cells are dictated by
the specific subcellular structures of cells.
• Continuity of life has a cellular basis.

5. Parts of a cell
• Plasma membrane – boundary, maintains cell integrity
• Nucleus – contains chromosomes, has a double
membrane
• Nucleolus – organelle inside the nucleus, where
ribosomal subunits are manufactured
• Rough endoplasmic reticulum – extensive system of
membranes, contiguous with nucleus, studded with
ribosomes
• Ribosomes – small dark-staining granules composed of
protein and rRNA, some are located on the outer surface
of the RER and some are free in the cytoplasm, sites of
protein synthesis, each is composed of 2 subunits, each
subunit is made of rRNA (ribosomal RNA) + protein

6. Cell Anatomy
• After synthesis, proteins transported into lumen of RER
where they fold into their final 3 dim. shape, some are
modified by attachment of carb., packaged into transport
vesicles which carry them to Golgi complex (apparatus)
• Golgi apparatus – site of synthesis of most
carbohydrates, also where proteins are further
processed by addition of other CHO chains + packaged
into secretory granules (vesicles) for exocytosis or into
lysosomes in which intracellular digestion is performed.
• Smooth endoplasmic reticulum – where phospholipids,
steroids and some carbohydrates are synthesized;
processes exogenous chemicals (drugs)

9. Cell Anatomy cont.
• The Golgi complex is like the cell's packaging and
shipping department. It is made up of a stack of flattened
membrane sacs. Some of the protein being transported
through the canals of the endoplasmic reticulum ends up
in the Golgi complex. Here it may be joined with other
molecules before being "packaged". The packages are
little pieces of the Golgi complex which break off and
form "vesicles". The vesicles move to the cell membrane
and fuse with it. It may then squirt its contents outside of
the cell as a secretion, or the product assembled in the
Golgi complex may become a new piece of the cell
membrane itself. In that case the vesicle fuses with the
membrane and becomes a part of it
• Lysosomes and peroxisomes – types of vesicles, they
contain enzymes

10. Plasma membrane

11. Electron photomicrograph of
two adjacent plasma membranes

12. Fluid Mosaic Model
• The plasma membrane is composed of
– A lipid bilayer of phospholipids:
• The polar phosphate-containing heads are hydrophilic and
face the internal and external aqueous environments
• The non-polar fatty acid chains are hydrophobic and are
directed inward to the center of the membrane
– Cholesterol is embedded in the lipid portion of the
membrane
– Two populations of proteins are present:
• Integral proteins span the entire membrane
• Peripheral proteins are associated with the inner and outer
surfaces of the membrane

13. Other molecules associated
with cell membranes
• Glycolipids—externally facing
phospholipids with attached sugar groups
• Glycoproteins—branching sugar groups
associated with proteins on the external
surface of the cell. The glycoproteins
function as biological markers and are
important in cell recognition.

14. How do peripheral proteins differ
from integral proteins?

15. Functions of membrane
proteins
• Most integral proteins are transmembrane
proteins that span the entire membrane
and function in transport either as carriers
or by forming channels for the transport of
water-soluble molecules
• Peripheral proteins are not embedded in
the lipid bilayer—some support the
membrane, others function as enzymes

16. Phospholipid
molecule

17. Cholesterol
makes the
lipid bilayer
less
deformable
and
decreases its
permeability
to small
water-
soluble
molecules.

18. Cytoplasm
• The cellular material between the plasma
membrane and the nucleus
• Three major components
– Cytosol—the viscous fluid in which the other
cytoplasmic elements are suspended; mostly
water with proteins, salts, sugars and other
solutes
– Cytoplasmic organelles—tiny machines that
perform specific functions for the cell
– Inclusions—stored nutrients and pigments
found in some cells

19. Cell Organelles
• Mitochondria (sing. – mitochondrion) -
sites of ATP synthesis, the power plants of
the cell, they provide most of the cell’s
energy in the form of ATP. The more
metabolically active the cell, the greater
the # of mitochondria. They have a double
membrane. Inner membrane is folded.
Folds are called cristae. Interior of mito
called the matrix.

22. Cell Organelles
• Golgi apparatus: consists of stacked,
flattened membranous sacs and vesicles;
it modifies and packages the proteins
synthesized on the RER and lipids
manufactured in the smooth ER.
• Lysosomes: membrane-bound organelles
containing digestive enzymes, abundant in
phagocytes and necessary for intracellular
digestion.

27. Cellular Extensions
• Microvilli, cilia and flagella – 3 types of cell
membrane modifications
• Microvilli increase surface area of cell, function
to increase absorption, also called brush border
• Cilia: whip like, motile cellular extensions found
on some cells, cilia function in movement of
substances directionally along cell surfaces
• Flagella: much longer than cilia, only one per
cell—in the human body found only on sperm
cells; function in propelling the cells themselves

28. cilia

29. Name the
cellular
extensions
visible in
the photo.

30. Sperm cells
with flagella

31. Nucleus
• Control center of the cell
• All body cells are nucleated except mature
red blood cells
• Bound by a nuclear envelope with nuclear
pores
• Contains one or more nucleoli, sites where
ribosome subunits are made
• Contains DNA (the genetic material)
arranged in chromosomes

32. Name the
RNA
molecules
that travel
through the
nuclear
pores and
carry the
code for
protein
synthesis.

33. Protein Synthesis, 1
• A gene is a segment of a chromosome
(DNA molecule) that carries instructions
for creating a protein
• The code for building a protein is copied
by a messenger RNA molecule in a
process called transcription
• mRNA leaves the nucleus and attaches to
a ribosome where the code is “read” by
transfer RNA molecules

34. Protein Synthesis, 2
• tRNA molecules match amino acids to the
triplet codons of mRNA in a process
known as translation
• The newly synthesized protein may
remain in the cell or be packaged and
secreted for use in another location

37. Some Important Proteins
• Keratin remains within epidermal cells as
a structural protein
• Digestive enzymes are secreted by
exocytosis for extracellular functions
• Hemoglobin in produced by red blood cells
when they are forming in bone marrow; it
remains in the cells and functions in
transport of blood gases