Cells Anatomy and Physiology Summer, 2002

Cells -approx. 70trillion/ human; types: somatic and sex

A. Extracellular fluid - liquid medium which fills space between cells; consists
of plasma and interstitial fluids

B. Intracellular fluid - liquid medium within cells

II Cellular anatomy

A. Cell Membrane
1. Roles:

a. Physical barrier

Glycocalyx - consists of proteoglycans. glycoproteins or glycolipids

• Extends from outer cell membrane surface

• Acts as a lubricant, helps in cell anchoring, helps identify
normal cells, may act as receptors

B. Membrane Transportation Mechanisms - selective permeability

1. Diffusion - net movement of particles from an area of high concentration
to a lower one through a selectively permeable membrane; a
passive/natural process

a. implies a concentration gradient

b. factors as distance, magnitude of gradient, molecule size, temperature
and electrical forces

c. Osmosis -diffusion with water

• Osmotic pressure=osmotic gradient=concentration gradient

• Osmotic concentration = osmolarity

Isotonic = solute concentration = solvent concentration

Hypertonic = solute concentration >solvent concentration; e.g. RBC shrink and crenate

Hypotonic = solute concentration < solvent concentration; e.g. RBC swell and hemolysis

2. Filtration - movement of solvent and dissolved substances across
semipermeable membrane by gravity, mechanical or hydrostatic pressure
a. Kidney function - blood pressure from heart forces water/small

molecules into kidney tubules

3. Carrier mediated Transport - uses integral protiens to move material in
and out of cell

a. Facilitated Diffusion - extracellular molecules (i.e. glucose) bind to receptor on carrier protein. Binding alters shape of protein then release the molecule to diffuse into cell cytoplasm; a natural process.

2

b. Active Transport - net movement from an area of low concentration to area of high concentration through semi permeable membrane; needs energy to occur (ATP)

E.g. sodium potassium pump - regulates ion distribution and uses nearly 40% of all cellular ATP

4. Vesicular Transport- all need energy to occur

a. Endocytosis - segment of plasma membrane surrounds substance,
encloses and eventually engulfs it, bringing it into the cell; e.g.
phagocytosis

Pinocytosis- engulfed material is extracellular fluid rather than any solid parts

b. Exocytosis - export substances from inside cells; opposite of
endocytosis

C. Cytoplasm -area inside the cell membrane

1. Cytosol/Intracellular fluid - liquid matrix in which various cell component
are found

a. Components - mainly water (80-90%) with solid components which
tend to be suspended (colloids)

b. Functions

• Assist in chemical reactions

• Converts external raw materials into useable energy via
decomposition reactions

• Packages chemicals for transport

• Facilitates waste excretion

2. Organelles - specialized structures within the cell performing directed
functions

D. Cellular Organelles

1. Cytoskeleton- series of minute (micro) tubules and filaments which give shape, support and movement for cell; specialized forms include centrioles, cilia and flagella

a. Microfilaments - 3-12 nm dia; vary in length; seen in muscle
contractile elements; aid in cell movement and support

b. Microtubules - 18-30 nm dia; contains protein (Tubulin); aids in cell
movement and conduction channels within cytosol; forms cilia.
flagella, centrioles

• Centrioles composed of 9 triplet cluster: are paired and at right
angles with each other; assist in chromosomal movement during
cell division

• Cilia - short and numerous cytoplasmic projections for movement
or transportation; consist of 9 pairs of microtubules in a circle
around a central pair

3

• Flagella -long and few cytoplasmic projects for motility (e.g.
sperm); consist of 9 pairs of microtubules in a circle around a
central pair

c. Intermediate fiber - 7-11 nm dia; varies with protein types; provides structural reinforcement

2. Nucleus - largest, centrally located, usually 1 (RBC = 0, Skeletal muscle
= several);

• Prokaryotes =organisms without nucleus (bacteria

• Eukaryotes = organism with nucleus

a. Nuclear membrane -define nucleus; consist of double bilayer
membrane with openings (nuclear pores)

b. Nucleoplasm/karyolymph - gel like fluid which fills nucleus

c. Nucleoli - composed primarily of RNA fragments, DNA and proteins;
produce ribosomal RNA

d. Genetic Material - DNA

• Genes - all genetic information needed to produce a specific
protein. Specifically group of nucleotides on DNA which serves
as master mold for protein synthesis.

• Chromosome - contains genetic information or genes; 46 for
normal human cell.

Consist of two separate strands (Chromatids) which are held together by special proteins (Histones).

3. Ribosomes - tiny granules (<25nm); composed of r RNA + specific
ribosomal protein

a. Two subunits: one large (heavy) and one small (light)

b. Site for protein synthesis

Free Ribosomes - in cytoplasm, synthesis proteins for use within cell

Fixed Ribosome - associated with ER, synthesis proteins for export from cell

4. Endoplasmic Reticulum - system of pairs of parallel membranes enclosing
narrow cavities throughout the cell cytoplasm; is continuous with cell
membrane

a. Rough ER -studded with Ribosomes

b. Smooth ER - no associated ribosomes

c. Function

• Synthesis of macronutrients

• Act as storage area

• Mechanical support

• Transportation vehicle within cell

• Act as cellular detoxification area by containing enzymes

5. Golgi Apparatus - 5-6 flattened membrane disc called saccules.
a. Function

4

• Synthesize and package cell products and secretions

• Renews or modifies cell membrane

• Packages special enzymes for use in cytosol
b. Special Products

• Lysosomes -vacuoles that contain digestive enzymes; used in
phagocytosis or autolysis; Vit A overdose can increase lysosomal
activity

• Peroxisomes - absorb and neutralize toxins

6. Mitochondria - rod shaped structure; varies in # for cell type (eg. Muscle cell = high #)

a. Composition
Outer membrane

Inner membrane – Cristae

Matrix -area between membranes

b. Function - site for ATP production

c. Self Replicative - not produced by cell - gotten primarily from egg
cell and simple replicate itself: DNA is different from nuclear DNA

E. Extracellular Materials/Matrix - substances outside cell, includes interstitial fluids, plasma and secreted inclusions

1. Amorphous

a. Hyaluronic Acid - viscous fluid which binds cells, lubricates joints
and maintains shape (eyeball)

b. Chondroitin Sulfate -jelly like substance; provides support and
adhesiveness in cartilage, bone, heart vales, cornea of eye and
umbilical cord

2. Threadlike

a. Collagenous fibers - made of collagen protein; found in all connective
tissue types

b. Reticular fibers - collagen protein + glycoprotein coat: forms network
around fat, nerve, muscle and blood vessels; forms Stroma
(framework) for organs

c. Elastic fibers - made of elastin protein; gives elasticity to skin, tissue
and blood vessels

III Cell Physiology

A. Gene Activation and Protein Synthesis

• Gene - group of nucleotides on DNA molecule serving as a master mold
for Protein Synthesis

• Proteins -cellular product or expression of genes

• DNA molecule contains may individual genes which holds the
information needed to synthesize many proteins

5

1. Phases of Protein Synthesis - before a gene can be activated for PS, DNA
segments (gene) must be separated (DNA polymerase) and is bound to
RNA polymerase. DNA polymerase unzips and proofreads mRNA
sequence for accuracy.

Sense Strand (Coding Strand) - strand of DNA used as template

a. Transcription-production of RNA from a DNA template. RNA
polymerase uses genetic information to assemble a strand of mRNA

b. Translation - assembling of a function protein by a ribose, which use
the information carried by the mRNA strand.

• Small ribosomal subunit binds with mRNA and larger subunit
attaches

• This activates tRNA to pick up AA in cytosol of cell

Codon - triplet bases calling for particular AA (ref mRNA)

Anticodon- complement to codon (ref tRNA)

• Complementary tRNA attaches with 1^st codon; ribosome moves
along mRNA and next tRNA move into position

• Second adjacent AA binds together (via peptide bond) and tRNA
is released leaving AA affix to preceding AA. Sequence is exactly
copied.

• AA strand terminates with terminal codon

2. Rate of Protein Synthesis - 15 AA/sec; several ribosomes moving in
tandem along same mRNA permit production of several identified
proteins simultaneously.

a. SOS Genes- certain genes produce increased quantities of proteins
(enzymes) that operate together to repair genetic damage

b. Recombinant DNA - combine DNA from sources incorporated into
genome (e.g. bacteria).

B. Cell Division - process by which cells reproduce themselves; major focus: nuclear and cytoplasmic (cytokinesis)

1. Types

a. Mitosis - for somatic cells; simple duplication; generates two daughter
cells from one mother cell

b. Meiosis - for reproductive cells; introduces variability; generates 4 sex
cells (gametes) from one mother cell.

• Chromosomes-highly coiled DNA molecules partially covered
with protein (histones)

• Two chromatids/chromosome

• Centromere - connection point between two chromatids

• Chromatin = uncoiled DNA

6

2. Stages of Mitosis

a. Interphase (metabolic phase)- When cell is between division. Cell is
performing normal functions

• G1- rapid growth and metabolism activity; new organelles
synthesized

• S - Chromosomes duplicates (DNA synthesis)

• G2 - organelles for cell division are synthesized

b. Prophase

• Chromatin shortens and coils

• Chromosomes start to assemble near equatorial plane

• Nuclear membrane dissolves

• Spindle fiber and centrioles become visible and migrate to opposite
poles

c. Metaphase

• Centromeres line on equatorial line

• Microtubules form and attach centromeres to poles

d. Anaphase

• Centromeres divide and chromosomes separate into chromatids
and move to opposite sides of cell

e. Telophase

• Nuclear membrane reforms enclosing chromosomes, which uncoil

• Spindle fiber disappear

• Cytokinesis - cytoplasmic division of daughter cells; initiated in
late anaphase and completed during telophase.

Cleavage furrow - constricting ring; forms around equatorial plane; progresses inward and separates into two separate equal portions.

f. Mitotic Rate

• In general, the longer the life expectancy, the slower the mitotic rate

• Primarily control by hormones and growth factors

• Tumor- when rate of cell division and growth exceed rate of cell death

3. Stages of Meiosis- manufacture of sex cells (haploid or gametes)

• Homologous pair of chromosomes- 2 chromosomes that are homologues from each parent

a. Interphase I – same as Mitosis

b. Prophase I – Synapsis occurs – exchange of piece between
homologues pairs of chromosomes (crossing over)

c. Metaphase I - same as Mitosis; Independent assortment occurs

d. Anaphase I - same as Mitosis

e. Telophase I - same as Mitosis

f. Interphase II (interkinesis) -no Chromosome replication

7

g. Prophase II - same as Mitosis

h. Metaphase II - same as Mitosis

i. Anaphase II - same as Mitosis

j. Telophase II - same as Mitosis

4. Aging - progressive failure of body's homeostatic adaptive response; Senescence - process of growing old; Geriatrics- care of elderly

a. Features

• Extracellular components change: collagen fibers increase in # and
quantity, decrease in extensibility of arterial walls; elastic fibers
thicken and fragments + increase in association with Ca ions

• Cell types can't reproduce; nerve, and certain muscle types

b. Causes

• Genetic programming

• Increase in free radicals - highly reactive compounds which tie up,
destroy or weaken structural elements; causes DNA damage
Produced by pollution, radiation and diet