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Transcript of The Cell
Section 2 -- The Plasma Membrane
aka The Cell Membrane
Holds the cell together
Controls what enters and what leaves the cell.
The Key is Selective Permeability
The membrane has the ability to let some things pass through, while others stay in or stay out.
The membrane is a phospholipid bilayer
-- two layers of lipids
with a phosphate group.
The hydrophilic polar heads are attracted to water while the hydrophobic nonpolar tails are repelled by water.
This allows the lipids to line up as a protective membrane.
The membrane contains a lot more than just lipids.
Cholesterol helps keep the lipids from sticking together so that the membrane has better fluidity.
Carbohydrates act as receptors for chemical signals.
Proteins in the membrane can act as anchors, signal transmitters, or contribute to the selective permeability of the membrane.
Proteins that span the entire membrane and move materials into or out of the cell are called
The plasma membrane is described by the fluid mosaic model -- it's made up of a lot of different stuff and it all moves around.
Inside the cell is a semi-fluid substance called Cytoplasm.
All of the cell's internal parts are called Organelles.
The organelles float in the cytoplasm, but they are held in place by a supportive framework of thin protein fibers called the Cytoskeleton.
The cytoskeleton is made up of microfilaments and microtubules that disassemble and reassemble to allow for movement.
The nucleus is the management
center of the cell.
It contains the DNA -- instructions for making all of the proteins needed to function.
The nucleus is surrounded by a double membrane called the Nuclear Envelope.
The Nucleolus is located within the nucleus, it is the site of ribosome production.
Ribosomes translate the DNA code and make the proteins as the DNA instructs.
Ribosomes make proteins!
They are made up of protein and RNA.
They do not have a membrane.
The Endoplasmic Reticulum
Also known as ER, the endoplasmic reticulum is where important macromolecules (carbohydrates, lipids, and proteins) are synthesized in the cell.
Some ER has ribosomes attached, which appear as bumps. This is called "Rough ER."
Endoplasmic Reticulum without ribosomes is called "Smooth ER."
The Golgi Apparatus
After proteins are put together in the ER, they are transported to the Golgi Apparatus for packaging.
Lysosomes contain digestive enzymes that can break down wastes.
Lysosomes can attach to vacuoles and breakdown the contents.
They also defend against invading bacteria and viruses by digesting them.
Centrioles are made of microtubules and they aid in pulling the cell apart during cell division.
The mitochondria are the "powerhouses" of the cell. They create the energy the cell needs to work.
A mitochondrion has both an
outer membrane and a highly
folded inner membrane.
The mitochondria harness energy by breaking down fuel molecules -- mostly sugars and creating new molecules that can take that energy to where it is needed in the cell.
Plants are made up of cells too, and they have most of the same organelles as animal cells...
Chloroplasts are like the solar panels of the plant.
They capture light energy and convert it into chemical energy through a process called photosynthesis.
Chloroplasts have a double
membrane and contain disks
filled with chlorophyll -- a
that traps the light.
The plant cell also has a
This is a rigid structure made up of a carbohydrate called cellulose that surrounds the plasma membrane.
The cell wall provides protection but also structure and support, making the plant cell less flexible.
Movement: Cilia and Flagella
Cilia are hair like projections on the outside of some cells.
A Flagellum is longer, and uses whip-like movements for motion.
Section 4 -- Cellular Transport:
How things move within a cell, or from cell to cell.
Diffusion of solutes across the membrane is called
(also known as passive transport)
It utilizes transport proteins to move molecules, but does not require any energy.
One method is...
-- particles move randomly from an area of high concentration to an area of low concentration.
Concentration is the amount of solutes in the solvent.
Osmosis: The diffusion of water across a selectively permeable membrane.
In the cell, water is the solvent, with many different solutes.
When osmosis occurs, water (the solvent) moves across the membrane, but the solutes do not.
Water diffuses, or moves from areas of high concentration (more water/less solutes) to areas of low concentration (less water/more solutes). This is referred to as "moving down the concentration gradient."
When water is entering and leaving a cell at the same rate, it is said to be in an Isotonic Solution.
In this case, the concentration on both sides of the membrane are the same.
-- Water (solvent)
-- Salt (solute)
Net movement of water is equal.
When a cell is in a solution with a lower concentration of solutes outside the cell (higher water concentration outside), then it is said to be in a Hypotonic Solution.
In this case, there will be a net movement of water into the cell, causing it to swell, increasing the pressure.
Too much pressure can cause the cell to burst.
Plant cell walls protect them from bursting under pressure.
into the cell
out of the cell
Chapter 7 -- Cellular Structure and Function
Section 1 -- Cell Discovery and Theory
Relate advances in microscope technology to discoveries about cells.
Compare compound light microscopes with electron microscopes.
Summarize the principles of the cell theory.
Differentiate between a prokaryotic cell and a eukaryotic cell.
Section 2 -- The Plasma Membrane
Describe how a cell's plasma membrane functions.
Identify the roles of proteins, carbohydrates, and cholesterol in the plasma membrane.
Section 3 -- Structures and Organelles
Identify the structure and function of the parts of a typical eukaryotic cell.
Compare and contrast structures of plant and animal cells.
Section 4 -- Cellular Transport
Explain the processes of diffusion, facilitated diffusion, and active transport.
Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.
Discuss how large particles enter and exit cells.
Section 1 -- Cell Discovery and Theory
In 1665 Robert Hooke created a simple microscope and observed a piece of cork.
He thought it looked like it was made of tiny rooms -- he called them cells.
Today we know that the cell is the basic structural and functional unit of all living things.
A few years later, Anton von Leeuwenhoek found living things under the microscope -- also made up of cells.
After a lot of observations by a lot of different scientists, the Cell Theory was eventually created.
The Cell Theory:
1. All living organisms are composed of one or more cells.
2. Cells are the basic unit of structure and organization of all living organisms.
3. Cells arise only from previously existing cells, with cells passing copies of their genetic material on to their daughter cells.
We couldn't have done it without the Microscope!
A Compound Light Microscope combines the power of multiple lenses -- each multiplying the magnification.
10X + 10X = 100X
Up to 1,000X
In the 1940s the electron microscope was invented. It uses magnets to aim a beam of electrons at cells.
Transmission Electron Microscopes (TEM) transmit electrons through a thin slice of cells, producing a black and white 2D image.
Scanning Electron Microscopes (SEM) can scan the surface of an object, producing a 3D image.
The Scanning Tunneling Electron Microscope (STM) gets extremely close to the specimen and can even produce images of atoms.
It also has the benefit of being able to look at live specimens, unlike the TEM or SEM, which can only look at a dead specimen.
Two main types of cells:
-- have no nucleus or organelles with membranes.
-- have nucleus and membrane-bound organelles.
some single-celled organisms
It is believed that Eukaryotes came about when one Prokaryote engulfed another.
This is called The Endosymbiont Theory
The cell uses Vacuoles for packaging any products that need to be transported or stored. The vacuole can travel to the cell membrane and expel its contents out of the cell.
Channel Proteins are always open and allow molecules to flow through based on size.
Carrier Proteins change shape to let molecules through based on fit.
In other words, molecular movement causes a substance to spread out or disperse, until it reaches dynamic equilibrium
(...that means even on all sides, but still moving).
When a cell is in a solution with a higher concentration of solutes outside the cell (lower water concentration outside), then it is said to be in a Hypertonic Solution.
In this case, there will be a net movement of water out of the cell, causing it to shrivel up.
Cells in isotonic solution
Cells in hypotonic solution (swelling)
Cells is hypertonic solution (shriveling)
Sometimes a cell needs to move solutes across the membrane
the concentration gradient.
This requires energy and is called Active Transport.
Usually a carrier protein
called a pump is used.
Some pumps can only
move one type of solute,
others can moves two -- either in
the same direction or opposite directions.
The Sodium-Potassium ATPase Pump!
This transport protein is actually an enzyme that uses ATP to transport 3 sodium (Na+) ions out of the cell against the concentration gradient. It also transports 2 potassium (K+) ions back into the cell.
The Na+/K+ ATPase Pump also allows for
of sugar molecules.
The Na+ that has been pumped out of the cell can flow back in along the concentration gradient, and sugar can hitch a ride, allowing the sugar to flow against its gradient without using energy.
Larger molecules can enter the cell by becoming engulfed in part of the plasma membrane, and then pinching off on the other side -- this process is called
Waste particles can leave the same way -- this is called