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Cell Structure
1. Cell Membrane
cell is basic unit of all life; structural and functional
anything that is alive must contain at least a single cell
the function of an organism is the summation of
functions of its individual cells
phospholipids tend to arrange into a double
layered film
in human body
single fertilized egg ! 75–100 trillion cells (adult)
proteins “float” in this bilayer
fluid mosaic (1972 Singer & Nicholson)
[>10x’s more bacterial cells in body]
! proteins randomly arranged in lipid bilayer
not fixed
There are about 200 different kinds of cells in the
human body with a variety of sizes and shapes
some protein functions:
receptors (ie. docking sites) for specific
substances
junctions between cells
channel proteins: have pore, act as pumps and
gates to selectively move specific substances
through c.m.
enzymes: energy transforming enzymes
anchoring: bound to cytoskeleton
human cells range in size from:
human egg barely visible to naked eye to cells over 3 ft long
diversity in size and shape
!less diversity in function
the cell membrane is selectively permeable
some things enter freely
2. Cytoplasm (=Cytosol)
Basic Components of Most Cell:
a. cell membrane
- boundary
b. cytoplasm (=cytosol)
c. nucleus
d. organelles and
internal structures
– includes everything except
cell membrane
-genetic material
contains mostly water, ions, organic molecules etc
variety of enzymes eg. glycolysis
- highly organized, specialized
structures
Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
defines boundary
highly ordered
!phospholipids, proteins, cholesterol
3. Nucleus
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Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
contain enzymes for respiration and
produces most of cells ATP (=energy)
largest of internal cell structures
number varies: one to many
!use 02 in energy reactions
in humans
most cells have one nucleus
RBC’s have none
a few cells are multinucleate (2-50 nuclei)
typical cell has dozens to 100,000’s
!number related to cells activity
eg: muscle cells
liver cells
sperm cells
eg. liver, skeletal muscle cells and certain osteoblasts
and ‘thromboblasts’
100,000’s/cell
1000’s/cell
~25/cell
6. Ribosomes
contains genetic material:
replication and reproduction
daily metabolism
workbenches for protein synthesis
!protein factories
genetic material
=chromosomes
100’s times length of cell
humans ~3’ of DNA/cell
= DNA with chromatin =highly organized histones
up to 1000’s per cell
># ribosomes = > amount of protein synthesis
7. Endoplasmic Reticulum
4. Nucleolus
(= “little network within the cytoplasm”)
densely packed chromosome region within
nucleus
a single highly branched membranous tube, with
sacs and channels
site of RNA synthesis
two types:
most cells contain both types
5. Mitochondria
(in different proportions)
Rough ER:
power plants of cells:
Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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lots of ribosomes attached to surface
synthesizes carbohydrates and complex
organic molecules
protein synthesis and transport
esp those that are secreted or those
found in lysosomes
encloses chemicals in vesicles and takes them
to the cell membrane for secretion
especially in protein exporting cells
usually 1 to several 100 golgi bodies
eg. liver and pancreas
but can have up to 25,000/cell
Smooth ER:
!highest in secretory cells
no ribosomes
9. Lysosomes
lipid metabolism
membrane bound package of digestive enzymes
transports lipids throughout cell
several 100/cell
most cells have only a small amt of
smooth ER
contains at least 50 different enzymes
!capable of breaking almost every kind of
large organic molecule
most common in lipid synthesizing cells
esp liver cells
adrenal cortex (steroid hormones)
testes – steroid hormone synthesis
digestive system for cell:
destroys unwanted materials, cellular debris,
worn out organelles, eg. mitochondria
8. Golgi Bodies (Golgi Apparatus)
stack of membranes (flattened sacs)
used to destroy invading pathogens
eg WBC’s, neuroglial cells
packing and shipping
gets rid of worn out cells = suicide bags
Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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helps move things around in the cell
= apoptosis (programmed cell death)
12. Centrioles
eg. uterus at full term weighs ~900g, shrinks
to 60 g within 5 or 6 weeks after delivery
each cell has one pair – at right angles to each
other
10. Peroxisomes
functions in cell division: mitosis & meiosis
! helps form spindle
resemble lysosomes but with a different set of
enzymes
! contains oxidases
Structures found on the surfaces of some cells:
detoxification =removes poisons
13. Microvilli
eg. alcohol and other drugs
extensions of cell membrane that greatly
increase its surface area
eg. free radicals
several 100 per cell
best developed in cells specialized for
absorption
! intestinal lining
! nephric tubules (PCT)
! esp in liver and kidney cells
11. Cytoskeleton
1000’s/cell in intestine
! give cells 15 – 40 times more
surface area
microfilaments and microtubules
responsible for the overall shape & rigidity of each
kind of cell
14. Membrane Junctions
used in:
cell movement
phagocytosis
holds organelles in place
Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
formed by various proteins associated with the cell
membrane
a. tight junctions
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Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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eg. mainly in respiratory tract and uterine tubes
form impermeable barriers
16. Flagella
eg: keeps digestive enzymes in intestine
from leaking into blood
similar to cilia but much longer and only 1/cell
eg. prevents intestinal bacteria from invading
tissues
eg. flagella are found only on sperm cells
17. Membrane Surface Receptors
b. desmosomes
“guy wires” throughout sheet of cells
diverse molecular sites at which cells
chemically recognize and bind extracellular substances
especially in tissues subjected to stretching
proteins, glycoproteins, lipoproteins
!prevents sheets of cells from tearing
binding often causes metabolic changes
=> “activates” cell to do something
eg. skin, neck of uterus, heart muscle
also important in cell-to-cell identity
eg. surface markers
!defense against foreign cells and
tissues
c. gap junctions
create pores between cells
allows direct passage of small molecules and ions
between cells
eg. intercalated discs in cardiac muscle cells
15. Cilia
cilia are hairlike processes found in some cells
! some are able to move = motile cilia
beat in waves moving mucus or egg
cells along tubes
Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005
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