Cell structure
Lecture 2
A. Cell Membrane
a. The cell membrane regulates what enters and leaves the
cell and also provides protection and support
b. Takes in water and food and eliminates waste
c. The membrane is a double-layered sheet called a lipid
bi-layer
i. Polar heads face outwards and non-polar tails face
inwards
d. Embedded in the membrane are protein
channels/pumps and carbohydrates
B. Cell Wall
a. Where is it found?
i. Found in almost all prokaryotes
ii. Found in plants, fungi, and algae
iii. NOT found in animals
b. Lies outside of the cell membrane
c. Allow for movement of certain molecules
i. Water, carbon dioxide, oxygen and some other
substances
d. The main function of the cell wall is to provide support
and protection to the cell
e. Cell walls are made of carbohydrates produced by the
cell
i. Plants use cellulose
C. Nucleus
a. Discovered by a botanist named
Robert Brown in 1831
b. The nucleus controls most cell
processes and contains the
hereditary information of DNA
c. Consists of 4 parts
i. Nucleolus – small densely packed
region where ribosomes are
created
ii. Nuclear Envelope – double
membrane layer surrounding the
nucleus
iii. Nuclear Pores – a perforations
within the nuclear membrane
iv. Chromatin – this is the granular
material within the nucleus
1. Chromosomes – the
condensed form of chromatin
just before a cell divides
D.Cytoskeleton
a. A network of protein filaments that helps the
cell keep its shape, also used in many forms of
cell movement
b. Made up of microtubules and microfilaments
i. Microtubule – hollow tubes of protein which
also serve as tracks for organelles to move
ii. Microfilament – Long thin fibers that
function in the movement and support of the
cell
E. Organelles
a. Ribosomes
i. Ribosomes
assemble
proteins following
the coded
instructions that
come from the
nucleus
ii. Ribosomes are
made of protein
and RNA
b. Endoplasmic Reticulum
i. The organelle in which components of the cell
membrane are assembled and some proteins are
modified
ii. Smooth ER – contains collections of enzymes that
perform specialized tasks, such as the synthesis of
lipids
iii. Rough ER – the part that is involved in the synthesis
of proteins; has ribosomes embedded in the
membrane
c. Golgi Apparatus
i. Proteins made
by the ER move
to the Golgi
apparatus where
enzymes attach
carbohydrates
and lipids
ii. Discovered by
Camillo Golgi
d. Lysosomes
i. Are small
organelles filled
with enzymes
ii. Main function is to
break down lipids,
carbohydrates and
proteins into
particles that can
be used by the cells
iii. Also helps to break
down old
organelles, remove
debris from the cell
e. Vacuoles
i. Storage for the
cell
1. Stores
materials such
as water, salts,
proteins and
carbohydrates
ii. Plants have a
single large
vacuole
iii.Vesicles are the
animals cell
equivalent to
vacuoles
f. Chloroplasts
i. Found in
photosynthetic
organisms
ii. Use energy from
sunlight to make
energy-rich food
molecules in a
process known as
photosynthesis
iii. Enclosed by two
envelope membranes
iv.Contains thylakoids
and chlorophyll
v. Contains its own
DNA
g. Mitochondria
i. Releases energy
from stored food
molecules in a
process called
cellular respiration
ii. Enclosed by two
envelope
membranes
iii. Found in nearly all
cells
iv. Contains its own
DNA
h. Organelle DNA
i. Lynn Margulis
suggested that
mitochondria and
chloroplasts were
originally
prokaryotic
organisms that
were enveloped by
a eukaryotic cell
ii. The DNA in
mitochondria
comes almost
exclusively from
the mother
F. Movement through the membrane
a. Facilitated diffusion
i. Molecules such as glucose that cannot cross the cell membrane’s lipid
bilayer directly can move through protein channels from an area of high
concentration to an area of low concentration with the concentration
gradient
b. Active transport
i. When a molecule has to move against the concentration gradient
ii. Uses energy
iii. Each pump is used to move a specific molecule across the membrane
1. Example: sodium potassium pump moves sodium out and
potassium in
iv. Endocytosis
1. The process of taking materials into the cell by means of infolding
or pockets of the cell membrane
2. The resulting pocket breaks loose from the outer portion of the
membrane creating a vesicle within the cytoplasm
3. Phagocytosis is then used to break up the vesicle and use the
molecules inside
v. Exocytosis
1. The removal of large amounts of material from a cell
2. The membrane of the vesicle surrounding the material fuses with
the cell membrane forcing the contents out of the cell