homeostasis, transport & the cell membrane
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Homeostasis, Transport & The Cell Membrane. Chapter 4-2 ( pg 73 – 75) Chapter 5. Unit 5: Lecture 1. Topic: The Cell Membrane Covers: Chapter 5, pages 95 - 96 Chapter 4, pages 73 - 75. The Cell Membrane. The chemistry of living organisms involves the study of solutions. - PowerPoint PPT PresentationTRANSCRIPT
Homeostasis, Transport & The Cell Membrane
Chapter 4-2 (pg 73 – 75)Chapter 5
Unit 5:Lecture 1
Topic:◦The Cell Membrane
Covers:◦Chapter 5, pages 95 - 96◦Chapter 4, pages 73 - 75
The Cell Membrane
The chemistry of living organisms involves the study of solutions. ◦ A large portion of our body is water, and
the chemical reactions of life occur in aqueous (watery) solutions.
◦ Nutrients move through the watery matrix of your blood to deliver the nutrients to cells.
Cell membranes help organisms by controlling what substances may enter or leave the cells. ◦ Known as Selectively Permeable or
Semipermeable◦ Some substances can cross the cell
membrane without any input of energy, whereas other materials need ATP to help cross through the membrane.
The Cell Membrane It’s Selectively Permeable…HOW DOES IT DO THAT?
◦ Because of the membrane’s structure◦ Cell membrane is a PHOSPHOLIPID
BILAYER BILAYER - 2 LAYERS PHOSPHOLIPID - 2 PARTS
1. Phosphate head 2. Lipid tail
1. Phosphate head - Outer part of the bilayer◦ HYDROPHILIC - "Water loving”
2. Lipid Tail - Middle part of the bilayer◦ HYDROPHOBIC - "Water hating"
The phospholipids are not attached to one another, enabling the membrane to have “fluid” like properties
Because of the lipid bilayer’s chemical properties, not all types of molecules can cross through the membrane
Some substances can cross through on their own◦ Small, uncharged particles can squeeze between
phospholipids and can cross though the lipid layer Some substances need assistance to cross through the
membrane◦ Large molecules cannot fit between phospholipids◦ Charged particles (ions) cannot cross through the
lipid layer
Other Parts of the Cell Membrane
1. CHOLESTEROL (type of lipid)◦ Function: Helps to make the membrane "fluid",
not rigid◦ Location: Part of the the bilayer
2. PERIPHERAL PROTEINS◦ Function: Helps to keep the shape of the cell◦ Location: Inner layer of cell membrane,
connected to fibers of the cytoskeleton
Other Parts of the Cell Membrane
3. INTEGRAL PROTEINS◦ Function: Channel for molecules to come into
the cell◦ Location: Embedded in the membrane (goes
through membrane, from one side to the other)
◦ Some integral proteins have carbohydrates attached Known as Glycoprotein
Other Parts of the Cell Membrane
4. GLYCOPROTEINS◦ Location: Integral protein with a
carbohydrate attached Carbohydrate (glycogen) sticks out of the
cell, on outside of cell membrane◦ Functions:
Used in cell recognition Different cell types have different shaped glycoproteins attached
Used as a cell receptor Glycoprotein accepts proteins/substances meant for that specific cell type
End Lecture 1
Unit 5:Lecture 2Topics:
◦Transport across membranes◦Passive Transport (Diffusion,
Osmosis)
Covers:◦Chapter 5, pages 95 – 99
Transport AcrossCell Membrane
Many materials cross through the cell membrane (enter cell or leave cell)
The types of transport are grouped into two categories:◦ Passive Transport◦ Active Transport
The type of transport used to move the material depends on the concentration gradient as well as the type of molecule being transported
CONCENTRATION GRADIENT – when the solutions on either side of the membrane do not have the same concentration of solutes (one more concentrated than the other)
When the concentration is equal throughout the space/solution, the solution is said to be in EQUILIBRIUM
Due to kinetic energy, molecules are in constant motion, even when the solution is in a state of equilibrium
In the cell, molecules will diffuse in & out of the cell even when the cell is in equilibrium with its surroundings
Types of Transport:Passive
Passive Transport occurs naturally due to kinetic energy, so it does not require any additional energy from the cell. ◦ In passive transport, the molecules are said
to be moving "down the concentration gradient" because the molecules are moving to an area with a lower concentration.
Types of Passive Transport:◦ Diffusion◦ Osmosis◦ Facilitated Diffusion◦ Ion Channel
DIFFUSION: Movement of molecules from an area of high concentration to an area of lower concentration
EXAMPLES: Food coloring in water, Solute added to a solvent
Types of Passive Transport:◦ Diffusion◦ Osmosis◦ Facilitated Diffusion◦ Ion Channel
OSMOSIS Type of Passive Transport driven by kinetic
energy OSMOSIS is the diffusion of water!
◦ Water molecules are moving from an area of high concentration (of water) to an area of low concentration (of water)
◦ If water is diffusing into or out of a cell, the water molecules will be crossing through the cell membrane Cell is trying to reach EQULIBRIUM with its
surrounding environment
HYPOTONIC SOLUTION External solution has higher
concentration of water than inside the cell
Water moves into the cell Cell can burst!
HYPERTONIC SOLUTION External solution has a
lower concentration of water than inside the cell
Water moves out of the cell Cell shrivels up!
ISOTONIC SOLUTION Concentration of water
inside and outside the cell is and inside the cell are equal
Cell is in equilibrium with its surrounding environment!
How cells deal with osmosis...
HYPOTONIC SOLUTION In plants - vacuole fills with water creating turgor
pressure◦ Helps to support plant cell
In unicellular freshwater organisms - water constantly entering cell, these organisms must continuously pump the water out of the cell◦ Contractile Vacuole - Organelle that removes water
In Red Blood Cells – water fills up the RBC & the cell
can burst!◦ Known as CYTOLYSIS
HYPERTONIC SOLUTION In plants - when water leaves cell, turgor pressure
reduced and plants become wilted, Known as PLASMOLYSIS
In Red Blood Cells - cells can't compensate for extreme changes in concentration, so cells would shrivel◦ Known as CRENATION
End Lecture 2
Unit 5Lecture 3Topics:
◦Transport across membranes Passive Transport (Facilitated Diffusion, Ion
Channel) Active Transport
Covers:◦Chapter 5, pages 99 – 104
Types of Passive Transport:◦ Diffusion◦ Osmosis◦ Facilitated Diffusion◦ Ion Channel
FACILITATED DIFFUSION Type of passive transport that is driven by kinetic
energy◦ Moving molecules from high to low
concentration (“Down the gradient”) Transports molecules that can not diffuse on their
own◦ EX. - too big, not soluble in lipids, glucose,
polysaccharides These molecules are assisted across the
membrane by a type of integral protein known as a CARRIER PROTEIN
Many types of carrier proteins because each carrier protein can only assist ONE type of molecule
* REMEMBER - Form Fits Function! *
Types of Passive Transport:◦ Diffusion◦ Osmosis◦ Facilitated Diffusion◦ Ion Channel
ION CHANNEL* REMEMBER - An ION is an atom or molecule with a charge Type of passive transport that is driven by kinetic
energy◦ Moving molecules from high to low
concentration (“Down the gradient”) Ions are not soluble in lipids, so ions cannot cross
through the lipid bilayer (cell membrane) on their own
Ions cross through the cell membrane by traveling through a type of integral protein known as an ION CHANNEL
Many types of ion channels because each ion channel can only assist ONE kind of ion across the membrane
Sodium (Na+) - Potassium (K+) Calcium (Ca++) - Chlorine (Cl-)
ACTIVE TRANSPORT Unlike passive transport, ACTIVE TRANSPORT
requires the cell to use energy to move the molecules across the membrane◦ Energy supplied by the cell's mitochondria
in the form of ATP Active transport moves molecules from an
area of lower concentration to an area of higher concentration◦ Molecules moving "up the gradient” or
“against the gradient”, solution moving away from equilibrium
Types of Active Transport:◦ Membrane Pumps (Sodium-Potassium)◦ Endocytosis◦ Exocytosis
SODIUM - POTASSIUM PUMP Type of Active Transport, requires ATP to occur Membrane Pumps require a special type of
carrier proteins (a type of integral protein) Membrane Pumps transport molecules from an
area of low concentration to an area of high concentration
In the Sodium-Potassium Pump, sodium ions (Na+) are pumped out of the cell and potassium ions (K+) are pumped into the cell◦ 3 sodium leave cell for every 2 potassium that
enter Cell needs to have a high concentration of Na+
outside the cell and a high concentration of K+ inside the cell
Types of Active Transport:◦ Membrane Pumps ◦ Endocytosis◦ Exocytosis
ENDOCYTOSIS Type of Active Transport, requires ATP to occur
◦ Requires additional energy because the cell is making major structural changes
Endocytosis is how: ◦ Cells ingest large particles◦ Unicellular organisms ingest their food◦ Our body begins to get rid of bacteria and
viruses 2 Types of Endocytosis:
◦ PINOCYTOSIS - transport of fluids◦ PHAGOCYTOSIS - movement of large
particles or whole cells
Endocytosis:The Process
1. Cell membrane folds in and begins to form a pouch
2. Cell membrane encloses the external materials in a pouch
3. Pouch pinches off to form a VESICLE ◦ Vesicle - membrane bound organelle used to
transport molecules. Often combines with lysosomes to break down ingested materials
Types of Active Transport:◦ Membrane Pumps ◦ Endocytosis◦ Exocytosis
EXOCYTOSISType of Active Transport, requires ATP to
occur◦ Requires additional energy because the
cell is making major structural changesExocytosis is how:
◦ Cells release proteins after protein leaves the Golgi
◦ Cells release waste products
Exocytosis:The Process
1. Vesicle moves to the cell membrane2. Vesicle fuses with the cell membrane3. Contents gets released to the outside
of the cell
End Lecture 3