Chapter 3: The Cell (pgs. 3 –5, 8- 19)
•cells smallest living units in our bodies
• Cell theory:
1.) cells are building blocks of all plants & animals
2.) all cells come from the division of preexisting cells
3.) cells are the smallest units that perform all physiological functions
4.) each cell performs all the functions necessary to sustain life:
-obtain nutrients
-excrete
-replicate (mitosis)
-maintain homeostasis
•cytology:
•somatic vs sex cells
•cell size and shapes differ:
flat, disk shaped, spherical (adipose), branching
-shape reflects function
• cells bathed by watery fluid termed extracellular (interstitial) fluid
Intracellular fluid – within cell
•no one cell is exactly alike, all share 3 major parts:
1. cytoplasm w/ organelles
2. nucleus
3. plasma (cell) membrane
1. Cytoplasm
• material between cell membrane and nuclear envelope
• high in protein
• contains cytosol and organelles
Cytosol or intracellular fluid
-cytosol has high
concentrations and low
concentrations
cytosol also contains enzymes, amino acids, carbohydrates, ions.
-inclusions: glycogen, pigments
Organelles: little organs (see pages 4 & 5)
Nonmembranous vs. membranous (ER, Golgi apparatus, lysosomes,
peroxisomes, mitochondria)
A. Cytoskeleton protein structures:
1. microfilaments: smallest
actin
anchors cytoskeleton to transmembrane proteins
provide mechanical strength to cell
cause movement (with myosin)
2. Intermediate filaments:
provide strength and stability (stabilize organelles)
prevent cell from being torn
3. microtubules: largest diameter, formed from protein tubulin
provide cell strength & rigidity, anchor major organelles
important in changing shape of cell
form monorail system to move organelles within cell, form spindle
apparatus to move chromosomes during mitosis
make up bulk of structure in other organelles such as centrioles & cilia
4. thick filaments: formed from protein myosin
B. Microvilli
 finger-like projections from the cell membrane
 increase surface area – usually for absorption
C. Centrioles
 found as a pair of cylindrical (barrel shaped) structures
 formed by microtubules
 required for cell division (mitosis) (not found in RBC, skeletal & cardiac muscle
& neurons)
 centrosome: the cytoplasm/area of cell that contains centrioles
D. Cilia & Flagella
•cilia: hairlike cellular extensions
“beat” to move fluids or secretions across the cell surface
trachea & bronchi move mucus & dust up to throat
smoking paralyzes cilia
•flagella (um): longer projections
E. Ribosomes:
•site of protein synthesis
 consist of ribosomal RNA (rRNA) and protein subunits
one small (small ribosomal subunit) and one large (large ribosomal subunit) : these are separate
units
 the 2 subunits must join together with mRNA for protein synthesis to begin
 some float freely in cytoplasm others attached to membranes (fixed)
F. Proteasomes:
- contain proteases to break down proteins and recycle amino acids
- remove damaged, denatured or abnormal proteins (tagged for destruction)
G. Endoplasmic Reticulum: "network"
 network of intracellular membranes which attach to the nuclear envelope
Functions include:
1. synthesize proteins, carbohydrates and lipids
2. store molecules
3. transport materials
4. detoxify drugs or toxins
•Smooth (SER): no ribosomes attached to it
- synthesizes (and stores) phospholipids, cholesterol for membranes
-synthesis of steroid hormones
-synthesis of glycerides - synthesis & storage of glycogen
- in liver and kidney cells (hepatocytes & nephrons) responsible for detoxification of
drugs
•Rough (RER): has ribosomes attached to it:
- proteins are synthesized within it
- chemically modifies proteins (forms glycoproteins)
- protein folding occurs within RER
once protein is completed packaged into transport vesicle to go to Golgi apparatus
H. Golgi Apparatus
-flattened sac
- modifies & packages proteins for secretion from the cell via exocytosis (secretory vesicles)
- maintains cell membrane
- packages enzymes within vesicles for use in the cytosol
- synthesizes lysosomes
I. Lysosomes: "demolition crew"
- produced by golgi apparatus
• vesicles which contain hydrolytic enzymes to breakdown substances
Fuse to membrane of organelle, enzymes activated to destroy organelle
- used to destroy bacteria, debris from extracellular fluid
- cleanup/recycle within cell: inactive muscle proteins broken down
- autolysis: damaged or dead cells lysosomes disintegrate releasing enzymes into cytosol
lysosomal storage diseases: lack of specific lysosomal enzyme causes build up of
wastes/debris normally recycled by lysosome. See Applications Manual
J. Peroxisomes:
•membranous sacs contain different enzymes than lysosomes
- formed from existing peroxisomes
- absorb and break down fatty acids to form hydrogen peroxide (H2O2) which is then broken
down into O2 and H2
K. Mitochondria: generates ATP (pg. 77)
•sausage shaped
• enclosed by double membrane
 outer membrane surrounds organelle
 inner membrane contains folds called cristae
 matrix fluid filled contents of mitochondria
•generates the energy (ATP) for the cell:
•involved w/ cellular respiration (Krebs or TCA cycle and electron transport chain)
First step for metabolism is glycolysis :occurs in cytosol
10 steps begins with glucose and results in either:
1. 2 ATP molecules and 2 lactic acid, considered anaerobic
2. 2 ATP, 2 pyruvic acid molecules, 2 NADH + H (step 1 aerobic)
If aerobic, each pyruvic acid enters the mitochondria and is converted into acetyl CoA
Acetyl CoA enters the Krebs (TCA) cycle which produces CO2 and more NADH + H
molecules
NADH+ H molecules go to the electron transport chain (in mitochondria) where the H+
are used to create energy to synthesize ATP from ADP: End result = 36/38 ATP per
glucose
•muscle & liver cells
•contain DNA & RNA:
see Application’s Manual for mitochondrial DNA Disease
2. Nucleus: control center, usually centrally located - controls protein synthesis
•most cells are nucleated
anucleate
multinucleate
surrounded by nuclear envelope
contains nuclear pores
Contains:
1. nucleoplasm: contains ions, enzymes, RNA & DNA nucleotides
2. Nucleoli (little nuclei)
make rRNA and ribosome subunits and proteins (histones)
histones surround coiled DNA (supercoiled)
3. Chromatin or chromosomes
- chromatin appears threadlike
-histones
- chromatin coils and thickens to form chromosomes
during mitosis
- somatic cells contain 23 pairs of chromosomes
-chromosomes contain DNA (genetic code)
- a sequence of 3 bases in DNA is termed a triplet –
a series of triplets form a gene
Gene: contains all the triplets needed to produce a
specific protein
Humans have aprx. 30,000 genes
- “junk DNA” varies between individuals – DNA
fingerprinting used for ID