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Cell Structure & Function
Chapter 3
The Diversity of Cells in the Human Body
There are over 200 different kinds of cells in the body
Figure 3-1
Anatomy of a representative cell
Parts of a “representative” cell

Plasma (Cell) Membrane
 Cytoplasm


Plasma (cell) membrane
Comprised primarily of:
 Phospholipids
 Proteins
 Carbohydrates
Plasma (cell) membrane
Phospholipids
 Arranged as bilayer
 Hydrophilic phosphate “heads”
 Hydrophobic fatty acid “tails”
 acts as a selective physical barrier between
extracellular fluid (interstitial fluid) and intracellular
fluid (cytosol)
Plasma (cell) membrane
Proteins


Plasma (cell) membrane
Functions of Membrane Proteins include:
•Receptors
•Channels
•Carriers
•Enzymes
•Anchors
•Identifiers
Plasma (cell) membrane
Carbohydrates
 act as receptors & identity markers
Functions of The Cell Membrane
Functions of the plasma membrane include:






Physical isolation
Regulation of exchange with the environment
(“selective permeability”)
Sensitivity to surrounding environment
Help maintain shape and structural support
between cells
Cell identification
Communication (signaling)
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Cytoplasm
Cytoplasm
All the “stuff” inside a cell
The “stuff”:
 Cytosol (a.k.a. intracellular fluid
ICF)
 Organelles
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Cytosol
Cytosol


Intracellular fluid that usually has a
__________ consistency
Contains water, dissolved nutrients (including
amino acids, sugars (glucose/glycogen) &
lipids), ions, proteins (enzymes), and wastes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid compartments of the body
• Intracellular fluid (ICF) – a.k.a. cytosol
• Extracellular fluid (ECF)
• interstitial fluid
• plasma
• lymph
ISF
Cell
(ICF)
ISF
Cell
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Transport Processes
between/within fluid compartments
Two types of processes of transport
(movement):
• Passive –
• Active –
Passive processes of transport
- No energy required for movement
- Movement occurs with (“down”) the concentration
gradient
Includes:
 Diffusion (simple & channel-mediated)
 Facilitated diffusion (carrier-mediated transport)
 Osmosis
 Filtration
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Diffusion
Random movement down a
concentration gradient (from higher to
lower concentration)
Movement continues until “equilibrium” is reached
Diffusion Across Cell Membranes
(simple diffusion)
(channel
mediated
diffusion)
Facilitated Diffusion
(carrier-mediated transport)
No ATP required but requires a carrier protein (transporter)
(GLUT-1)
Osmosis
Movement of water across a selectively permeable
membrane, down a water concentration gradient
(from higher H2O concentration to lower), due to
osmotic pressure
 Osmotic pressure – relates to the concentration of
solutes. The higher the concentration of solutes, the
higher the osmotic pressure.

Water will always move from _______ to _______
osmotic pressure
Osmotic Effects of Solutions on cells
Isotonic solution- same concentration solutes (equal
osmotic pressure)
 Cells maintain normal size and shape
Hypertonic solution- more solutes in solution (higher
osmotic pressure) therefore less H2O
 Cells lose water osmotically and shrink and shrivel
Hypotonic solution- less solutes in solution (lower
osmotic pressure) therefore more H2O
 Cells gain water osmotically and swell and may
burst.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Osmotic Flow across a RBC Cell Membrane
Hemolysis
Crenation
Filtration
Hydrostatic pressure ( _____ pressure in
the body) pushes on water
 Water crosses membrane (across
capillary endothelium in the body)
 If membrane is permeable to solutes,
solutes follow water movement

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Active processes of transport
- Cell must generate energy (ATP – adenosine triphosphate) for
movement
- Movement can occur against (“up”) the concentration gradient
- Larger substances can move in/out of the cell
-Includes:
• Active transport
•Vesicular transport
endocytosis
exocytosis
Active transport




Carrier-Mediated
Energy from ATP consumed by carrier protein
Molecular movement is independent of
concentration gradients (low  high concentration)
Ion pumps (e.g. Na-K exchange pump)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Vesicular Transport


Membranous vesicles requiring energy for
movement
Transport in both directions

Endocytosis - movement into cell
Receptor-mediated endocytosis
 Pinocytosis
 Phagocytosis


Exocytosis - movement out of cell
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Receptor-Mediated Endocytosis
Receptor-Mediated Endocytosis
EXTRACELLULAR FLUID
Exocytosis
Molecules bind
to receptors
Target molecules bind to receptors
in cell membrane.
Endocytosis
receptors
Coated
vesicle
Areas coated with bound molecules
form deep pockets in membrane
surface.
Pockets pinch off, forming vesicles.
Vesicles fuse with lysosomes.
CYTOPLASM
Molecules are removed and
absorbed into the cytoplasm.
Lysosome
Molecules
removed
Fused vesicle
and lysosome
The membrane containing the
receptor molecules separates from
the lysosome.
The vesicle returns to the surface
(Exocytosis).
Figure 3-10
Pinocytosis
 “_____________”
 Cell membrane folds inward “engulfing” ECF

No receptor proteins involved
Phagocytosis
Phagocytosis
Cell membrane
of phagocytic
cell
Lysosomes
A phagocytic cell comes in contact
with the foreign object and sends
pseudopodia (cytoplasmic
extensions) around it.
The pseudopodia approach one
another and fuse to trap the
material within the vesicle.
Vesicle
The vesicle moves into the
cytoplasm.
Lysosomes fuse with the vesicle.
Foreign
object
CYTOPLASM
This fusion activates digestive
enzymes.
Pseudopodia
(cytoplasmic extension)
EXTRACELLULAR FLUID
Exocytosis
The enzymes break down the
structure of the phagocytized
material.
Residue is then ejected from the
cell by exocytosis.
Figure 3-11
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Exocytosis
Exocytosis
The Organelles
Membranous organelles




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- Isolated compartments
Nucleus
Mitochondria
Endoplasmic reticulum (smooth & rough ER)
Golgi apparatus
Lysosomes
Peroxisomes
Nonmembranous organelles
- In direct contact with cytosol
 Cytoskeleton (including microvilli, centrioles, cilia, flagella)
 Ribosomes
The Nucleus
Figure 3-16
DNA/Chromosomes/Chromatin/Genes
DNA = deoxyribonucleic acid
Gene
Adenine
Guanine
Cytosine
Uracil (RNA only)
Thymine
Nucleoli


Nucleoli are non membranous organelles within
the nucleus
Synthesize ribosomal RNA (rRNA) – building
block that creates ________________
RNA = ribonucleic acid
Ribosomes

Made of ribsosomal RNA & protein subunits
 Found free in cytoplasm (free ribosomes) or attached
to rough endoplasmic reticulum (ER) (fixed ribosomes)
 Participates in protein synthesis by manufacturing of
polypeptides (translation)
Protein Synthesis
Two step process:
 Transcription –
 Translation –
Protein Synthesis
Transcription — the production of RNA from a
single strand of DNA

Occurs within nucleus with production of
messenger RNA (mRNA)
mRNA exits through nuclear pore to go to
ribosome
DNA
RNA
polymerase
Complementary
triplets

Gene
4
mRNA
strand
RNA
nucleotide
KEY
Adenine
Guanine
Cytosine
Uracil (RNA)
Protein Synthesis
Translation — the
NUCLEUS
mRNA
The mRNA strand binds to the small
ribosomal subunit and is joined at the
start codon by the first tRNA, which
carries the amino acid methionine.
Binding occurs between complementary base pairs of the codon and
anticodon.
The small and large ribosomal
subunits interlock around the mRNA
strand.
Amino acid
KEY
Adenine
Small
ribosomal
subunit
tRNA
Anticodon
tRNA binding sites
Guanine
Cytosine
Uracil (RNA)
Thymine
Start codon
A second tRNA arrives at the
adjacent binding site of the
ribosome. The anticodon of the
second tRNA binds to the next
mRNA codon.
mRNA strand
The first amino acid is detached
from its tRNA and is joined to the
second amino acid by a peptide
bond. The ribosome moves one
codon farther along the mRNA
strand; the first tRNA detaches as
another tRNA arrives.
Peptide bond
Large
ribosomal
subunit
The chain elongates until the stop
codon is reached; the components
then separate.
Small ribosomal
subunit
Completed
polypeptide
Stop
codon
Large
ribosomal
subunit
assembling of a
polypeptide
(“potential” protein)
on ribosomes
•Transfer RNAs
(tRNA) bring
specific amino
acids based on
transcribed
“message” of
mRNA
• Occurs within
cytoplasm
The Endoplasmic Reticulum
Network of intracellular
membranes primarily
for molecular synthesis,
storage & intracellular
transport
Rough ER (RER)
 Contains ribosomes on
surface of membrane
 Stores, modifies (folds) &
transports newly made
________________
Smooth ER (SER)
 Lacks ribosomes
 Synthesizes, stores
& transports
________ & ______
Golgi apparatus



Receives new proteins from RER & lipids from SER
Modifies proteins by adding carbohydrates and
lipids
Packages proteins & lipids in vesicles
Secretory vesicles (for exocytosis)
 Membrane renewal vesicle


Synthesizes Lysosomes
Golgi apparatus
Endoplasmic reticulum
EXTRACELLULAR
CYTOSOL FLUID
Lysosomes
Cell
membrane
Secretory
vesicles
Transport
vesicle
Golgi apparatus
(a)
Membrane renewal
vesicles
(b) Exocytosis
Vesicle
Incorporation in
cell membrane
Figure 3-14
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Lysosomes and Peroxisomes
Lysosomes:
Produced by golgi apparatus
Vesicles containing digestive enzymes
Clean-up cellular debris & recycle worn out organelles
Defend against bacteria
Peroxisomes:
contain digestive enzymes to break down fatty acids & other
organic compounds
Mitochondria
 Site of ___________________ production
 Double layered membrane with inner folds (cristae) enclosing
metabolic enzymes for cellular respiration (aerobic
metabolism)
Figure 3-15
The Cytoskeleton
Internal protein
framework to provide
strength & structural
support, movement of
cellular structures &
materials
Includes:
 Microfilaments (actin)
 Microtubules (tubulin)

The Cytoskeleton
Microfilaments
 myofilaments of muscle cells –
muscle contraction
 microvilli – increase cell surface
area
The Cytoskeleton
Microtubules
 centrioles - move chromosomes during mitosis
 cilia - move substances across cell surface
 flagella - moves cell through fluid (sperm)
Cell division
Somatic Cell division - The reproduction of body cells;
necessary for growth & repair. Results in the formation
of 2 genetically identical “daughter” cells
 Mitosis - nuclear (chromosomal) division of
somatic cells (after chromosomal replication has
occurred).
 Cytokinesis - division of cytoplasmic contents
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Interphase
Nucleus
Early prophase
Mitosis
begins
Spindle
fibers
Centrioles
(two pairs)
Metaphase
Late prophase
Centromeres
Anaphase
Chromosome
with two
sister chromatids
Telophase
Separation
Daughter
chromosomes
Cytokinesis
Metaphase
plate
Cleavage
furrow
Daughter
cells
Figure 3-22
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Cell Diversity and Differentiation
Somatic (Body) Cells
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All have same genes
Some genes inactivate during development
Cells thus become functionally specialized. This
specialization is known as “differentiation” of cells
Specialized (differentiated) cells form distinct
tissues in the body