Download THE CELL THEORY A. All living organisms are made up of one or

The Cell
CELL STRUCTURE & FUNCTION
THE CELL THEORY
A. All living organisms are
made up of one or more
cells
B. The cell is the basic
unit of life
C. All cells come from the
division of pre-existing
cells
The Cell Membrane
• functions in transport of materials in and out of cell, cell
recognition, maintaining cell integrity, and homeostasis.
• is called selectively permeable (also known as semipermeable and differentially permeable)
- means that the membrane will let some
substances cross but not others of the same
size
The Fluid Mosaic Model:
Cell notes.docx — Page 1
• Cells are
surrounded by a
thin membrane
of lipid and
protein.
• Scientists
today agree
Please Label this Diagram
upon The Fluid
Mosaic Model of cell membrane structure. The cell
membrane is a remarkable structure that has
properties of a solid and a liquid.
• The solid part (the “mosaic”) is the different proteins
embedded in the bilayer. The fluid part is the lipids and
how they give the membrane flexibility.
• Membranes made mostly of phospholipids molecules.
Phospholipids have two ends with different properties
in water. The phosphate head is HYDROPHILIC
“water-loving” while the lipid (fat) tail is
HYDROPHOBIC “water-fearing”. The cell Membrane
consists of two phospholipids layers called a BILAYER.
• There are proteins embedded in the phospholipid
bilayer and they form a mosaic pattern. These
proteins have different functions.
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o Receptor Sites – some proteins on the surface
serve as a receptor site so certain molecules can
attach to the surface.
o Protein Channels – these proteins provide the
mechanisms for lipid insoluble materials to cross
the membrane. (e.g. water)
o Channels with ATP – some substances (ions,
amino acids, glucose) actually bond to the
proteins and are propelled through the
membrane with the expenditure of ATP energy.
• The carbohydrates strung together in chains are
attached to proteins ("glycoproteins") or lipids
("glycolipids") of membrane. These carbs function
as identification markers for cell recognition (allows
the immune system to identify which cells belong to
the body and which are invaders).
The Nucleus:
• is a large, centrally located
organelle surrounded by the nuclear
envelope. The nuclear envelope is a
double membrane (2 phospholipid
bilayers) that has pores, called
nuclear pores, in it for molecules to
enter and exit. The envelope is a
continuation of the membrane of the
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endoplasmic reticulum.
• controls all of the cellular functions (metabolism,
growth, differentiation, structure, and reproduction)
in the cell
• contains the DNA and it is the site of RNA production.
The DNA is contained in a number of chromosomes,
which consist of long strands of DNA tightly wound into
coils with proteins called histones. Chromosomes
function in the packaging of DNA during nuclear
division and the control of gene expression.
• contains one or more DARK CIRCLES, known as the
NUCLEOLUS. The nucleolus is the site of
RIBOSOMAL RIBONUCLEIC ACID (rRNA)
SYNTHESIS. rRNA is one of two components that is
needed to produce a ribosome.
Endoplasmic Reticulum (ER)
• is a system of
MEMBRANOUS TUBULAR
CANALS that begin just
outside the nucleus and
branches throughout the
cytoplasm.
Rough
E.R.
Smooth E.R.
• When ribosomes are
Cell notes.docx — Page 4
attached to the ER, it is called Rough Endoplasmic
Reticulum (RER). The Rough ER is the site of protein
synthesis.
• If no ribosomes are attached to the ER, it is called
Smooth Endoplasmic Reticulum (SER). The
function of smooth ER is to synthesize lipids (Lipids
are required for the growth of the cell membrane and
for the membranes of the organelles within the cell and
are often used to make hormones). The smooth ER is
also used to detoxify drugs and chemicals in the cell
(takes place in peroxisome vesicles which are often
attached to smooth ER).
• The channels of the reticulum provide both storage
space for products synthesized by the cell and
transportation routes through which material can
travel through to other parts of the cell. Phospholipids
and cholesterol, the main components of membranes
throughout the cell, are synthesized in the smooth ER.
Ribosome:
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• consist of rRNA and proteins
• each ribosome is made of 2 non-identical subunits
• rRNA is produced in the nucleolus and joined with
proteins -- then migrate through the nuclear pore to the
cytoplasm for final assembly
• Ribosomes attach themselves to the endoplasmic
reticulum
• The ribosome and the Rough Endoplasmic Reticulum
are both sites for PROTEIN SYNTHESIS.
Polysomes:
• free-floating structures within the cytoplasm
• generally produce proteins that will be used inside the
cell
• consist of clusters of ribosomes bunched together,
each of which is transcribing the same type of protein
Golgi Apparatus
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• The Golgi
Apparatus (“X” in
diagram), named after an Italian
anatomist of the nineteenth century,
are stacks of flattened, hollow
cavities enclosed by membranes,
which are often continuous with the
membrane of the endoplasmic
reticulum.
• The stack is made of a half-dozen or
more saccuoles. Looks like a flattened
stack of hollow tubes. Each sac in the
organelle contains enzymes that modify
proteins as they pass through.
• Thus, the Golgi apparatus functions in modification,
assembly, packaging, storage and secretion of
substances.
• The Golgi apparatus receives newly manufactured
protein (from the ER) on its inner surface. Within the
Golgi apparatus, the proteins are sorted out, labeled,
and packaged into vesicles. These vesicles can then
be transported to where they are needed within the cell,
or can move to the cell membrane for export to the
outside of the cell by exocytosis.
Vacuoles and Vesicles: Storage Depots
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• A VESICLE is a small vacuole.
• vacuoles and vesicles are formed by:
1) pinching off from the Golgi apparatus
2) endocytosis of the cell membrane
3) extension of the ER membrane
• Vesicles and vacuoles are used for transport and
storage of materials.
Lysosomes: Cellular “Stomachs”
• Special vesicles which are formed by the Golgi
apparatus.
• The three main functions are:
1) Cellular digestion
2) Autodigestion or disposal of damaged cell
components like mitochondria
3) Breakdown of a whole cell (by releasing their
contents into the cell cytoplasm). For this reason, they
are sometimes called “suicide sacs.”
• Lysosomes help destroy invading bacteria.
Mitochondria: the Cell’s Powerhouse
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• are the 2nd largest
organelles in an animal
cell, after the nucleus
a.________________
b.________________
• Are sausage-shaped or filamentous structures
surrounded by a double-layered membrane.
• has two membranes: an outer and an inner. The
inner is convoluted into shelf-like folds called cristae.
The enzymes responsible for cellular respiration are
arranged, in assembly-line fashion, on the cristae.
This is where energy is produced.
• main function is to perform CELLULAR
RESPIRATION. Cellular respiration is when the cell
converts glucose (a carbohydrate)into ATP, the cell's
primary energy molecule. The overall formula for
cellular respiration is:
Carbohydrate + O2 CO2 + H2O + ENERGY (i.e. ATP)
• In the end, 38 molecules of ATP are formed for every
molecule of sugar that is used up in respiration.
Cell notes.docx — Page 9
THE SURFACE AREA TO VOLUME RATIO & CELL SIZE
• Cells cannot get too large. When cells get too large,
they must divide. One of the main reasons that cells do
this is because of the way that a cell's volume changes
with respect to its cell surface area.
• As the size of a cell increases, its surface to volume
ratio decreases. This means that, as a cell gets
larger, each cubic unit of cytoplasm is serviced by
proportionally less cell membrane.
Cell Size
1
2
4
8
Surface area
6
24
96
384
Volume
1
8
64
512
SA:V ratio
6:1
3:1
1.5:1
0.75:1
• How do cells get around the limits of the surface to
volume ratio?
1. Divide.
2. Get long and thin rather
then round and fat. e.g. nerve cell
3. Folds in the cell membrane: e.g. microvilli of
intestine.
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