This document summarizes the structure and functions of the basic unit of life - the cell. It describes the three main parts of the cell: the plasma membrane, cytoplasm and organelles, and nucleus. It then explains the roles and components of these structures, including transport mechanisms, energy production, protein synthesis, and cell death processes. The genetic material in the nucleus controls and directs the complex functions that allow cells to work together to form the human body.

1. Cell Structure and Genetic Control
Human
physiology

2. Cell
• Basic unit of structure and function of the body.
▫ Highly organized molecular factory.
• Great diversity of function.
▫ Organ physiology derived from complex functions of
the cell.
• 3 principal parts:
▫ Plasma membrane.
▫ Cytoplasm and organelles.
▫ Nucleus.

3. Plasma Membrane
• Is selectively permeable.
• Composition:
▫ Double layer of phospholipids due to hydrophobic/hydrophilic
parts.
 Restrict passage of H20 and H20 soluble ions.
▫ Proteins span or partially span the membrane.
 Provide structural support, transport molecules, serve as receptors.
▫ Negatively charged carbohydrates attach to the outer
surface.
 Involved with regulatory molecules.

4. Plasma Membrane (continued)

5. Cytoplasm, Organelles, Nucleoli
• Cytoplasm:
▫ Aqueous content of the cell.
• Organelles:
▫ Sub-cellular structures within the cytoplasm.
• Nucleus:
▫ Is a large spheroid body.
▫ Largest of the organelles.
▫ Contains the genetic material (DNA).
▫ Nucleoli:
 Centers for production of ribosomes.

6. Cytoplasm, Organelles, Nucleoli (continued)

7. Bulk Transport
• Phagocytosis:
▫ Phagocytic cells use pseudopods to surround and engulf particles.
▫ Pseudopods join, fuse, and surround ingested particle (food
vacuole).
 Lysosomes digest food vacuole.
▫ Protects from invading organisms.
▫ Removes debris.
• Endocytosis:
▫ Pinocytosis:
 Nonspecific process.
 Plasma membrane invaginates, fuses, vesicle containing ECF pinches off,
and vesicle enters cell.

8. Bulk Transport (continued)
• Receptor-mediated endocytosis:
▫ Interaction of molecules in ECF with specific membrane receptor
proteins.
▫ Membrane invaginates, fuses, pinches off and forms vesicle.
▫ Vesicle enters cell.
• Exocytosis:
▫ Process by which cellular products are secreted into extracellular
environment.
▫ Proteins and other molecules to be secreted are packaged in vesicles
by Golgi complex.
▫ Vesicles fuse with plasma membrane and release contents into
extracellular environment.

9. Cilia, Flagella, Microvilli
• Cilia:
▫ Tiny hair-like structures that project from the
surface of the cell.
 Stroke in unison.
 Respiratory tract, uterine tube.
• Flagella:
▫ Simple whip-like structure that propels sperm
through its environment.
• Microvilli:
▫ Numerous folds (finger-like projections) increase
surface area.
 Aid absorption.

10. Cytoplasm and Cytoskeleton
• Cytoplasm:
▫ Jelly-like matrix within
the cell.
▫ Includes organelles and
cytosol.
▫ Highly organized
structure with
microtubules and
microfilaments that
function as cytoskeleton.
• Cytoskeleton:
▫ Actin and myosin
(microfilaments).
▫ Spindle apparatus
(microtubules).

11. Lysosomes
▫ Primary:
 Contain only digestive enzymes.
▫ Secondary:
 Primary lysosome fuses with food vacuole or organelle.
 Contain partially digested remnants of other organelles and organic
material.
▫ Residual body:
 Contain undigested wastes.
▫ Autophagy:
 Process that destroys worn-out organelles, so that they can be
continuously replaced.
▫ Apoptosis (programmed cell death):
 Lysosomes release digestive enzymes into the cell.

12. Peroxisomes
• Membrane-enclosed organelles.
▫ Contain specific enzymes that promote
oxidative reactions.
▫ Oxidize molecules and form H202.
• Catalase: converts H202 H20 + 02.
• Oxidation of toxic molecules by peroxisomes
is an important function of liver and kidney
cells.

13. Mitochondria
• Sites for energy
production of all cells;
but mature RBCs.
• Contain own DNA, can
reproduce themselves.
• Structure:
▫ Outer membrane: smooth.
▫ Inner membrane: cristae.
▫ Cristae and matrix
compartmentalize
mitochondrion space.
 Have different roles in
energy generation.

14. Ribosomes
• Protein factories:
▫ Proteins produced according to genetic information
contained in mRNA.
▫ Located in cytoplasm and on the surface of
endoplasmic reticulum.
• rRNA molecules serve as enzymes (ribozymes)
required for protein synthesis.
▫ Contains 2 subunits composed of rRNA and
proteins.

15. Endoplasmic Reticulum (ER)
• Granular (rough) ER:
▫ Bears ribosomes on
surface, in cells active in
protein synthesis.
 Proteins enter cisternae
are modified for secretion.
• Agranular (smooth) ER:
▫ Provides site for enzyme
reactions in steroid
hormone production and
inactivation.
▫ Storage of Ca2+
in striated
muscle cells.

16. Golgi Complex
• Stacks of hollow, flattened
sacks with cisternae.
▫ One side of sack faces site for
entry of vesicles from ER that
contain cellular products.
▫ Other site faces towards
plasma membrane and
releases vesicles of chemically
modified products.
• Modifies proteins, separates
according to destination, and
packages into vesicles.

17. Cell Nucleus
Most cells have single nucleus.
Enclosed by inner and outer membrane
(nuclear envelope).
◦ Outer membrane is continuous with ER.
Nuclear pore complexes fuse inner and outer
membranes together.
◦ Selective active transport of proteins and RNA.
 Regulation of gene expression.
 Transport of mRNA out of nucleus to ribosomes.
Nucleoli:
◦ DNA contains the genes that code for the production
of mRNA.

18. Cell Death
• Pathologically:
▫ Cells deprived of blood supply swell, the membrane
ruptures, and the cell bursts (necrosis).
• Apoptosis:
▫ Cells shrink, membranes become bubbled, nuclei condense.
• Capsases (“executioner enzymes”):
▫ Mitochondria membranes become permeable to proteins
and other products.
• Programmed cell death:
▫ Physiological process responsible for remodeling of tissues
during embryonic development and tissue turnover in the
adult.