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The Cell and Cellular transport
The Cell
Cell theory (1838):
1.
All organisms are composed of one or more cells, and the life processes of
metabolism and heredity occur within these cells.
Cells are the smallest living things, the basic units of organization of all organisms.
Cells arise only by division of a previously existing cell.
2.
3.
Common to ALL types of cells…
DNA for the genetic code
RNA for transcription of the code during
protein synthesis
Enzymes
(for metabolic reactions)
Cell membrane
(controls the movement of
things in and out of the
cell)
Cytoplasm or cytosol
(intracellular fluid)
ATP
ATP
Ribosomes
(for protein
synthesis)
Energy currency
(to provide energy for
metabolic processes)
How many types of cells?
Unicellular or (most of them)
multicellular organisms
Eukaryotic
Prokaryotic
‰
Unicellular
organisms
Æ bacteria
Interior of the cell
‰ Only cytoplasm
‰ Only ribosomes, NO other organelles.
Ribosomes are different in structure to
those of eukaryotes
‰
Interior of the cell
‰ Composed of Nucleus + Cytoplasm
‰
Several specialized organelles
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The Cell and Cellular transport
What is the size of a cell?
Most of them smaller than 50µm (0.0020 inches)
Why cells are not bigger?
‰
Practical reasons! Æ communication
‰ the different regions of a cell need to communicate with one another for the cell
as a whole to function effectively
ƒ Cell surface
ƒ responsible for the
interaction with the
environment
ƒ small cells have
bigger surface area
per unit of volume
than large ones
ƒ control is more
effective (ex: 3 vs.
0.30)
Cell membranes
ƒ Two layers of
phospholipids and
proteins
Ratio: Surface Area
Volume
Cell radius (r)
1cm
Increases with 12
Increases with 13
10cm
Surface Area
(4πr2)
12.57 cm2
1,257 cm2
Volume
(4/3)πr3
4.189 cm3
4,189 cm3
1000 times
more
volume!
Extracellular side
integral protein (inside
the membrane)
ƒ Also cholesterol
and proteins
phospholipids
Fatty
Acids tails
(hydrophobic)
Cholesterol
Cytoplasm
Peripheral
protein
(surface)
ƒ Fluid-mosaic model
Phospholipids
heads
(hydrophilic)
ƒ Molecules in the membrane are able to flow
and move around
ƒ Interaction of molecules with its surroundings
allows the membrane to maintains its forms
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The Cell and Cellular transport
Cellular Organelles in Animal Cells
(Eukaryotic cells)
Ribosomes
Endoplasmic
reticulum (ER)
Nucleus
Mitochondria
nucleolus
Golgi apparatus
Cytoskeleton
1) “Membrane” organelles
Exclusive
of animals
cells
Lysosomes
Centrioles
Nuclear membrane: Protects the DNA inside the
cell.
nuclear membrane
Inner
membrane
Mithocondrion
cristae
•Aerobic cellular
respiration
• Glu+O2 Æ CO2+H2O
•Energy conversion
and release (in the
form of ATP)
pores allow molecules to pass from
one side to the other
Nucleolus: site of ribosome manufacture
Endoplasmatic reticulum (ER): folded membranes and tubes
Æ huge surface area Æ many chemical reactions in a small place!
vesicles
Rough ER
Ribosomes associated to
the membrane Æ proteins
synthesis
Smooth ER
Lipids synthesis, destruction of
toxic substances
Golgi Apparatus: 5 to 20 membranous and smooth
sacs Æ modification of products (ex: activation of
enzymes) from the ER, packing and export to the
cytoplasm or extracellular space of certain molecules
Lysosomes: Vesicles
generated in the Golgi apparatus
containing hydrolytic enzymes.
Are use to degrade molecules
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The Cell and Cellular transport
2) “Protein” organelles
Ribosomes:
•Two subunits composed of RNA
and proteins
•Responsible for proteins synthesis
•Associated to the Rough ER or free
in cytoplasm
Cytoskeleton:
•Microtubules, microfilaments, and intermediate filaments Æ proteins!
•Interconnect and attach to the membrane cell
Centrioles:
•Arrangement of two sets
of microtubules
(proteins!) at right angles
•Organize microtubules
assembly for cell division
(chromosomes attach to
microtubules)
flagella
Cilia and Flagella:
cilia
• hairlike structures used for locomotion
Eukaryotic cilia
and flagella
•Made of microtubules (two types of proteins in
Eukaryotes and only one type in Prokaryotes) with
a specific arrangement
•Energy is needed to move microtubules and cause
movement
Cellular transport
ƒ Movement of particles across the cell membrane.
ƒ allow the cell to carry out the metabolic processes needed to live
ƒ Passive: NO energy is required
ƒ Active: Energy is used (ATP)
Diffusion:(passive)
ƒ Movement of molecules down a
concentration gradient Æ from where
are in higher concentration to where
are in lower concentration.
Lower
concentration
Higher
concentration
Equal Concentrations
(dynamic equilibrium)
Osmosis: (passive)
ƒ Net movement of water through a selectively permeable membrane.
Red blood cell (RBC) is…
1) Osmosis is a special type
Hypertonic
Hypotonic
Isotonic
of diffusion in which the
diffusing substance can be
only water
2) The regions of different
concentrations are separated
by a membrane permeable
to water but not to the solute
less solutes in
the RBC
more solutes
in the RBC
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The Cell and Cellular transport
Carrier
Proteins
Facilitated diffusion
controlled
methods of
transporting
molecules
(passive) movement of
molecules down a concentration
gradient through the membrane
by combining with specific
carrier proteins.
concentration
+
-
Active transport
(active)
ƒ Movement of molecules up a
concentration gradient. An input of energy
(ATP) is needed to move the molecule
against its concentration gradient.
ATP
ADP+Pi
Endocytosis & Exocytosis:
ƒ Transport of materials into and out of the cell by
formation of vesicles of cell membrane containing
the particles, food, or materials
Pinocytosis: molecules engulfed are
dissolved in water Æ liquids
Phagocytosis: solid materials, the
sac is named phagosome (ex:
viruses, food, bacteria, lipoproteins)
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The Cell and Cellular transport
Special proteins that acts as catalysts in chemical reactions
Enzymes between
substances
Speed up reactions but are
not used in the reaction
Why do we need to speed up
reactions using enzymes?
Energy is stored in covalent
bonds of nutrients we
incorporate with the food
Molecules synthesis/breakdown and energy conversion
require energy to initiate the breakdown of nutrients
Energy of Activation (Ea)
Energy
Energy
Extra energy required to destabilize existing chemical bonds and initiate a chemical reaction
between two or more molecules
(Products have less energy
Do not occur
spontaneously
Ea
than reactants)
Exergonic reaction
Spontaneously
would take
millions of years!
Ea
product
reactants
E
stored
time
reactants
time
E
released
product
Endergonic reaction
(Products have more energy than reactants)
Energy used
Summary…
Ea
No enzyme
(uncatalyzed)
Ea
enzyme
(catalyzed)
2. Enzymes are substrate specific
Æ Only speed up the reaction
of one type of molecule
3. Enzymes remain unchanged
Æ Because they are not
used in the reaction
reactants
Energy releases
1. Enzymes lower the energy of
activation (Ea)
Æ Reactions occur very fast
product
4. Enzymes can be reused
billions of times
Æ One single enzyme can
convert millions of
substrate molecules per
second!
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The Cell and Cellular transport
How do enzymes speed reaction rates?
Three-dimensional shape of the enzyme allows it to combine with reactants, lower the
Ea and accelerate the reaction
Ex: dipeptide
(two amino acids)
Ex:dehydration
Ex: hydrolysis
Ex: amino acid 1
Ex: amino acid 2
Enzyme-substrate complex
ACTIVE SITE:
‰ Is the part of the ENZYME where the chemical reaction takes place,
‰ where the energy of activation is lowered by the enzyme so the reaction can happen
Cofactors & coenzymes: enzyme helpers”
ƒ ions or molecules that attach to the enzyme and help to speed up the reaction
1) Cofactors help removing one of the end products or bring in part of the substrate
2) Enzymes are substrate specific Æ but coenzymes can work with several different
enzymes
3) Cofactors ARE inorganic ions (zinc, iron, magnesium).
Coenzymes are organic molecules
4) As in the case of some fatty acids and amino acids, some coenzymes cannot be
produced by the body and need to be obtained with the diet. Cells need vitamins in order
to have coenzymes.
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The Cell and Cellular transport
What environmental factors affect the enzymes activity?
1) Temperature
ƒ Optimum (temperature range at which
the speed of product generation is
maximum) is around human body normal
temperature
ƒ The speed of the reaction, or the
number of molecules of substrate that
one enzyme can react with in a given
time, decreases as temperature moves
right or left of the optimum range.
ƒ At higher or lower temperatures than the optimum, Enzymes can lose their
configuration (be completely unfolded and only retain the primary structure) and be
no longer active
Enzyme
Denatured
Enzyme
(1ry structure =
sequence of
amino acids)
Denaturation
Lost of the structures of a protein, only the
primary structure remains
2) pH
ƒ Is important in defining the final shape of proteins
ƒ each enzyme reaches it maximum activity level at a given pH
ƒ Changes in pH determine
the number of H+ ions
available in the enzyme
environment
ƒ these H+ may interact with
exposed side-chains of the
polar enzyme molecule
ƒ enzyme activity changes
Denaturation
Lost of the structures of a
protein, only the primary
structure remains
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