3.1 Intro to the Cell and Cell theory
What is a cell?
A cell is the basic unit of all living things. Meaning, if something is alive, it is made up of one or more cells.
There are many different types of cell. Animal cells and plant cells are very different. Even within our own bodies we have many different types (heart cell, skin cell, neurons, blood cells, muscle cells etc).
We’ve come a long way.
Scientists have studying living things for hundreds of years.
The development of microscopes has really helped our study and understanding of cells.
As part of this unit, we will work with microscopes!
Cell Theory:
There are three parts to the Cell Theory:
1. All living things are made of one or more cells
2. Cells are the basic units of structure and function in organisms
3. All cells arise from existing cells.
Cell Theory Part 1:
The first part of the cell theory was based on discoveries by Schleiden and Schwann
This happened in 1838 and both are German
Schleiden first discovered that every part of a plant was made up of cells
It was believed that only stems and roots were made of cells.
Schwann claimed that animals were also made of all cells
Together, they found that both plants and animals were made of cells
Cell Theory Part 2:
What was the second part of the cell theory?
Cells are the basic units of structure and function in organisms
So what does structure and function mean in terms of cell?
Structure: The way that the cells and it’s parts are built
Function: What the cell and it’s parts do
STRUCTURE determines FUNCTION
Cell Theory Part 3:
What is the third part of the cell theory?
All cells arise from existing cells
This was based on a discovery by Virchow
This idea may seem basic to us, but people in the 1800s believed that organisms could spontaneously generate
Rotten meat and maggots example
Cell Size:
Does anyone know how many cells are in the human body?
About 100 trillion
That’s more than 1,000 times the number of people on Earth!
So how big are cells?
Are they bigger than a penny? Hydrogen atom? DNA?
Most cells are 5-20 micrometers (µm), which is about 5,000 – 20,000 nanometers (nm)
Why are cells so small?
Small cells perform better than large cells
A bunch of small cells have more SURFACE AREA than a fewer number of large cells.
Cells have to move substances in and out all the time
Organic compounds to use for energy need to come in
Waste products need to move out
If a cell is smaller, it can get those substances in and out more quickly then a large cell
Ex. Think of boiling a large pot of water and small pot of water, which boils first?
Structure and Function:
Structure: Small Size
Remember structure determines function, so why are cells small?
Function: To move substances in and out more quickly
Uses less energy as well
3.2 Cell Organelle and Cytoplasm Overview (Complete)
A eukaryote, has special cells that have complex structures that are enclosed by membranes.
Animals and plants have eukaryotic cells.
Bacteria are different. They are more simple and they are called prokaryotes. (Don’t worry we’ll go more into this next week).
Vocab Preview
Eukaryote: More complex organism (plants/animals).
Eukaryotic cell: cell with a nucleus and organelles
Organelles: special structures in eukaryotic cells that do specific jobs to make the cell work
Cell Membrane:
Protective outer layer controlling what goes in and out of the cell
BOTH plant and animal cells have this.
Cytoplasm:
Liquid that fills the cell and acts as support. It has a “jello”-like consistency.
BOTH plant and animal cells have this.
Nucleus:
This is the “brain” or control center of the cell. You find it in the center of cell
Controls everything in a cell because holds DNA
BOTH plant and animal cells have this
Endoplasmic Reticulum (ER)
Folded tube-like structures attached to the nucleus
Helps transport proteins around cells
Smooth ER: no ribosomes
Rough ER: ribosomes attached
Ribosome:
Attached to endoplasmic reticulum or floating in cytoplasm
Makes proteins that help carry out cell functions
BOTH plant/animal cells have this
Nucleolus:
Small organelle inside the nucleus
Creates rRNA needed to make ribosomes
BOTH plant and animal cells have this
Mitochondira:
Creates the ATP or ENERGY for a cell to stay alive. It’s like the nuclear power plant of the cell.
BOTH plant and animal cells have this
Golgi Complex (or Apparatus or body)
Folded tube-like structure NOT attached to the nucleus
Packages, process, and transports things around cell
BOTH plant and animal cells have this
Lysosome:
Breaks down food and waste in cell. (It’s like the stomach)
BOTH plant and animal cells have this
Vaculoles:
Fluid-filled sac
Stores materials needed by the cell like water, food, or waste
BOTH plant and animal cells have this
Small in animal cells
Large in plant cells
Organelles found only in plants: Cell walls and chloroplasts
Cell wall:
Supportive layer that surrounds the cell membrane. Gives structure!
PLANT CELL ONLY
Chloroplast:
Where photosynthesis happens in plants to provide energy from sunlight
Gives plants their green color
PLANT CELL ONLY
3.4 Distinguish between prokaryotes and eukaryotes
Review:
Remember, you are a eukaryote!
There are two categories of eukaryotes:
1.) Plants
2.) Animals (that means you!)
Today, we’ll be learning about prokaryotes and how they differ from eukaryotes!
All Cells…
A. Tend to be microscopic
B. Have a few key structures:
i. are enclosed by a membrane.
ii. are filled with cytoplasm.
Prokaryotic Cells
A. Are the most basic cells
B. Unicellular (made of ONE cell)
C. Lived at least 3.5 billion years ago
D. Example: Bacteria (causes infections and food to spoil).
E. Contain simple structures
- Cell membrane
- cytoplasm
- genetic material (DNA) just floats around in the cell
- Organelles that do not have a membrane (like ribosomes)
- They have a cell wall surrounding the cell membrane for structure and support
Eukaryotic Cells
A. Contain simple structures of Prokaryotes
B. Contain a nucleus which holds the DNA
C. Have many organelles with membranes
D. Unicellular or Multicellular (made of many cells)
E. They are more complex than prokaryotes
F. Example: Plant or Animal cells
Review:
1. Eukaryotic cells have membrane-bond organelles
- Prokaryotic cells do NOT have membrane-bound organelles.
2. Eukaryotes have a nucleus
- Prokaryotes do NOT have a nucleus.
3. Eukaryotes do NOT have a cell wall
Prokaryotes have a cell wall
3.5: Cell Membrane Structure and Function
Cell Membrane
· Who remembers what the “job” of the cell membrane is?
o Support
o Protection
o Controls movement of materials in/out of cell
o Barrier between cell and its environment
o Maintains homeostasis
§ What is homeostasis?
· The cell membrane is the outer case of the cell
· It keeps the inside of the cell separated from the outside environment
· It is selectively permeable – it only allows certain substances in out and out
o 
What does it mean to be “selective”? “Permeate”?
· The cell membrane is made up of lipids.
· Who remembers what lipids are?
o Lipids are fats, waxes, and steroids
o They are non-polar and DO NOT dissolve in water
· Phospholipid bilayer – is another name for the cell membrane
· It is made up of two layers of lipids
· The cell membrane is NOT rigid and stiff like a cell wall
· Instead it is fluid and can move because it is made of lipids
· This allows the cell membrane to be selectively permeable
o What does that mean?
· Selectively permeable – the cell membrane only allows certain substances in and out of the cell
o It can do this because it is made up of lipids
· What is another name for the cell membrane?
o The phospholipid bilayer
· So what is the cell membrane made of?
Parts of the Cell Membrane
· The membrane is made up of phospholipids
· Phospholipids are made up of two parts:
o Hydrophilic Heads
o Hydrophobic Tails
· Hydrophilic heads = water loving
· Hydrophobic tails = water fearing
Phospholipid Bilayer
· The head of the lipid molecule is polar
· Polar – opposite ends of the molecule have opposite charges
o Think of water
· Water is able to dissolve polar and ionic molecules
o Both have charges
o Water has charges so it can bind to polar and ionic molecules
· The tails of the phospholipid molecule are non-polar
· Non-polar means that it can NOT be dissolved by water
o This is similar to most lipids – Ex. Oil
Hydrophobic
· Let’s break it down
· Hydro means water
· Phobic means a fear of
· Hydrophobic – repelled away from water
· The non-polar tails of phospholipids are hydrophobic
Hydrophilic
· If hydrophobic means a fear of water, then what do you think hydrophilic means?
· Hydro means water
· Philic means a love of
· Hydrophilic – attracted to water molecules
· The polar heads of phospholipids are hydrophilic
Phospholipid Bilayer
· So let’s think about this now…
o We know that there are two layers of lipids, we just have to figure out how they are going to align themselves
· Where is the water?
o This will tell us how the heads and tails of the phospholipids line up
· Because there is water both inside and outside the cell, the polar heads line up towards the water
· That means the non-polar tails make up the inside of the cell membrane
· So based on what we know, which part of the cell membrane is going to be hydrophobic?
o The TAILS!
· Which part of the cell membrane is going to be hydrophilic?
o The HEADS!
Putting it all together
· So the inside of the cell membrane, which is composed of tails, doesn’t like water
o It is hydrophobic and non-polar
· That means that lipids and non-polar molecules can pass through the middle of the membrane
o Only let’s through substances that are similar to it
· However, the outside of the cell membrane, which is made up of polar heads does like water
o It’s hydrophilic and polar
· That means that ions and polar molecules can pass through the edges of the cell membrane
o Only lets through substances that are similar to it
Problem
· The problem comes when you try to move things through the cell membrane
· So is there anything that is both polar (hydrophilic) and non-polar (hydrophobic) that can move through the cell membrane?
· The answer to the problem is membrane proteins!
3.6: Cell Membrane Proteins
Yesterday
· We discussed the structure and function of the cell membrane
· We left yesterday with a problem – What was it?
o How can anything get through the cell membrane if it needs to be polar to get through the heads and non-polar to get through the tails?!?!
Membrane Proteins
· The solution to this problem comes in the form of membrane proteins!
· What are the building blocks of proteins?
o Amino Acids
· So membrane proteins are actually composed of both hydrophobic and hydrophilic amino acids
· Membrane Proteins – Proteins that are located in the phospholipid bilayer of a cell
· So let’s think about where each type of amino acid would have to be…
· Amino acids that are hydrophobic would be located near which part of the phospholipid bilayer?
o The TAILS which are inside of the cell membrane where there is no water
o The tails are hydrophobic
· That means that the amino acids that are hydrophilic are located near the heads of the phospholipid bilayer
o The heads are polar and like water, which makes them hydrophilic
· With different types of amino acids, you can have one protein that span the entire length of the cell membrane
o Goes from outside the cell to inside the cell
Classes of Membrane Proteins
· The cell membrane contains many proteins
· There are two classifications of membrane proteins
o Integral proteins
o Peripheral proteins
· Integral proteins are permanently connected to the cell membrane because they are embedded in the lipid bilayer
· Peripheral proteins sit on the surface of the membrane
Integral Proteins
· Integral proteins extend through the lipid bilayer meaning that one end of the protein contacts the exterior of the cell while the other end touches the interior of the cell
· These proteins can pass through the membrane one time or many
Peripheral Proteins
· Peripheral proteins sit on the surface of the membrane
· They can be on the inside of the cell or the outside of the cell
Membrane Proteins
· There are different types of proteins within the two classes
· There are four different types of membrane proteins that all have different functions
o Their structures are all different, but they have the same building blocks – What are they?
· Types of membrane proteins
1. Marker Proteins
2. Receptor Proteins
3. Enzymes
4. Transport Proteins
Marker Proteins
· Marker Proteins – membrane proteins that are actually attached to a carbohydrate
· They are peripheral proteins because they sit on the surface
· They allow other cells to know what type of cell it is
· For example: A liver cell would have a different marker protein than a heart cell
Receptor Proteins
· Receptor Proteins – Recognizes and binds to specific substances outside of the cell
· They are also peripheral proteins
· A signal could be sent from other cells and received by the receptor protein
· Example: When your brain signals the release of adrenaline (epinephrine), what happens to the rest of your body?
o Your cells start to work faster!
Enzymes
· We all know what enzymes do…
· Enzymes speed up chemical reactions by reducing the activation energy
· Even at the cell membrane there are important chemical reactions going on that need to move as quickly as possible
· Enzymes can be either peripheral or integral proteins depending on what their job is
Transport Proteins
· What does it mean to transport?
· Transport proteins – membrane proteins that aid in the movement of substances in to and out of the cell
· These are the proteins that really solve our initial problem of getting substances in to and out of the cell through the polar and non-polar parts of the cell membrane
· These are always integral proteins – they span the entire width of the membrane
3.7: Passive Transport: Diffusion
Phospholipid Bilayer
· Who remembers what the function of the cell membrane is?
o It allows certain substances in and out of the cell
· If you remember, what types of membrane proteins allow substances to move in and out of the cell?
o HINT: The proteins are made of both hydrophilic and hydrophobic amino acids
· Transport Proteins!!
· Many substances move in and out of the cell membrane without the use of transport proteins
· They do this through a process called molecular transport
o Break it down “Molecular” + “Transport”
· There are two different types of molecular transport
o Passive transport
o Active transport
Passive vs. Active Transport
· Passive transport – movement across the cell membrane that does NOT require energy
o Ex. Diffusion, Osmosis, Facilitated Diffusion
· Active transport – movement across the cell membrane that DOES require enrgy
o Ex. Sodium-Potassium Pump
· What is the difference between an active and passive person?
Passive Transport: Thought Experiment
· Imagine there are 100 bouncing rubber balls in my room
· We open the door to the prep room
· What is going to happen?
Passive Transport
· This is exactly how passive transport works, except that the door we opened is really the selectively permeable cell membrane
· A substance wants to reach equilibrium
o What word is in equilibrium?
· Equilibrium – the concentration of a substance is equal throughout a space
o In our case, there is equal amounts of a substance inside and outside of a cell
Concentration Gradient
· In order for this to reach equilibrium, what has to happen?
· The substance must move from a higher concentration, where there is more, to a lower concentration where there is less
· Concentration Gradient – a difference in the concentration of a substance across a space
See-Saw Diagram
· A substance is said to move DOWN it’s concentration gradient when it’s reaching equilibrium
o Note: This has nothing to do with the actual direction that the molecules are moving
· You can represent a concentration gradient with a see-saw diagram
o Let’s draw one together to show how substances move down
Diffusion
· Diffusion – movement of a substance from higher concentration to lower concentration caused by the random movement of particles
o This eventually leads to equilibrium
· Now we’ll do a demonstration with water and food coloring
· Many molecules and ions that are dissolved in the cytoplasm move in and out of the cell by diffusion
o Why would a substance diffuse out of a cell?
o There is a higher concentration inside the cell
o Why would a substance diffuse in to a cell?
o There is a higher concentration outside the cell
· The process of diffusion across the cell membrane can only occur for very small or non-polar molecules
Osmosis
· Osmosis is the diffusion of water through a selectively permeable membrane
· How do molecules move in diffusion?
· From higher concentration to a lower concentration
o Down its concentration gradient (see-saw)
· This means that osmosis is a form of passive transport
· Osmosis can get tricky…
· It’s not really a measure of how many water molecules are inside or outside of a cell
· We are more interested in the other substances (like salt) that are dissolved in the water
· If there is a high concentration of salt, then there is a low concentration of water.
· If there is an area with a low concentration of it’s because there is a high concentration of water
· So the water will diffuse from the high concentration of water (with low amounts of salt) to the low concentration of water (with high amounts of salt).
Osmosis: Key Points
· It’s all about the diffusion of FREE water molecules from a higher concentration to a lower concentration
· More substances being dissolved means less free water molecules – a lower concentration of free water
· So water moves from a low concentration of dissolved substances to a high concentration of dissolved substances
· Osmosis is a form of passive transport and does not require energy
3.7: Passive Transport: Osmosis
Passive Transport
· Yesterday we learned about two kinds of passive transport
o Diffusion & Osmosis
· We said that passive transport is movement of substances across the membrane that does NOT require energy
· Diffusion is the movement of a substance from high concentration to low concentration
· Osmosis is the diffusion of water through a selectively permeable membrane
Osmosis in Cells
· Let’s take a closer look at osmosis in cells!
· The movement of water in and out of cells is obviously crucial to life
· There are three different ways this happens:
o Water moves out of a cell (hypertonic)
o Water moves in to a cell (hypotonic)
o Water stays the same (isotonic)
· It all depends on how many free water molecules there are inside or outside the cell.
Hypertonic
· Why would water diffuse out of a cell?
· Water diffuses out of a cell because the fluid outside as LESS free water molecules
· Hypertonic Solution – fluid outside of the cell that has less free water or MORE dissolved substance than the cytoplasm
· So if the cytoplasm, inside of the cell, has more free water than the fluid outside of the cell, water will move outside the cell
· Remember there are fewer free water molecules outside of the cell, so which way will water move?
· What happens to the cell?
· It SHRINKS because water is leaving the cell
Hypotonic
· Why would water move into a cell?
· Water moves into a cell because there is more free water outside of the cell than in the cytoplasm
· Hypotonic Solution – fluid outside of the cell that has more water, or less dissolved substance than the cytoplasm
· So if the cytoplasm, inside of the cell, has less free water than the fluid outside of the cell, water will move inside the cell
· Remember, there are more free water molecules outside of the cell, so where will they move?
· What happens to the cell?
· It SWELLS because water moves in to it
Isotonic
· What happens when the fluid outside of the cell and the cytoplasm have the same concentration of free water molecules?
· Isotonic Solution – fluid outside of the cell that has the same amount of water and dissolved substance inside of the cell
· Water will diffuse out of the cell at the same rate
o This is EQUILIBRIUM!!
· What would the flow of water be?
· What would happen to the cell
· A cell would stay the same size!!
Passive Transport
· So far we’ve looked at these types of molecular transport:
o Diffusion – moves small or non-polar molecules in and out of the cell
o Osmosis – move water, a polar molecule, in and out of the cell
· Both are forms of passive transport
· What about the larger molecules? How do they get across the cell membrane?
Facilitated Diffusion
· When larger molecules, like amino acids or sugars try to get through the cell membrane they are blocked
o What type of membrane proteins do they need to use?
o TRANSPORT PROTEINS!!
· Facilitated Diffusion – uses transport proteins, called carrier proteins, to move large molecules down their concentration gradient across the cell membrane
1. Facilitated diffusionThe carrier protein binds a specific molecule on one side of the cell membrane
2. A change in the shape of the carrier protein exposes the molecule to the other side of the cell membrane
3. The carrier protein shields the molecule from the interior of the lipid bilayer
4. The molecule is then released from the carrier protein, which returns to its original shape
· Where is there a higher concentration of amino acids?
Ion Channels
· The last type of passive transport is an exception to the rule
· What is passive transport?
· Passive transport does not require any energy because molecules are moving down their concentration gradient
o They want to reach equilibrium
· This is not always the case with charged particles
o Anyone remember which types of molecules are charged?
· The two types of charged particles are polar and ionic molecules
o Remember water is polar
o Ions have either lost or gained an electron
§ What are their charges?
· When it comes to charged particles, opposites attract
· The inside of the cell has a negative charge and the outside of the cell has a positive charge
· If opposites attract, positively charged ions will want to move where?
· Positively charged ions will want to move INSIDE of a cell
· Negatively charged ions will want to move to?
· Negatively charged ions are attracted OUTSIDE of a cell
· OPPOSITES ATTRACT
3.8 & 3.9: Active Transport
Review
· We have gone over many different kinds of passive transport
· Do you remember what they are?
o Diffusion
o Osmosis
o Ion Channels
o Facilitated Diffusion
· Diffusion – the movement of a substance from high concentration to low concentration
· Osmosis – the diffusion of water through a selectively permeable membrane
· Ion Channels – help move charged particles down their concentration gradient
· Facilitated Diffusion – uses transport proteins, called carrier proteins, to move large molecules down their concentration gradient across the cell membrane
Active Transport
· But sometimes charged particles can move UP their concentration gradient
· Since opposites attract this can happen on its own
· But sometimes the cell needs important sugars and amino acids that have a lower concentration outside the cell
· If molecules are not charged can they still move UP their concentration gradient??
o YES!!!
· Active Transport – moves molecules against their concentration gradients
o Active transport requires the use of energy
· Cells move substances from a low concentration to an area of high concentration
· This means that the cell needs more sugars or amino acids even if there aren’t many outside the cell
· Active transport is usually performed by transport proteins called ‘pumps’
· The energy for active transport most often comes in the form of ATP
· Sodium-Potassium Pump: transports 3 sodium ions (Na+) out of the cell and 2 potassium ions (K+) in to the cell
Review
· So we have now talked about many different types of transport systems that the cell uses
· Diffusion
· Osmosis
· Ion Channels
· Facilitated Diffusion
· Active Transport
· Could there possibly be any more????????
Movement in Vesicles
· YES!! There is one more way!! VESICLES!!
· Many substances such as proteins and polysaccharides (large sugars) are too large to be transported by carrier proteins
· These substances move across the cell membrane by the use of vesicles
Types of Vesicles
· There are two types of vesicles:
o Endocytosis
o Exocytosis
· Endocytosis – the movement of a substance in to the cell
· Exocytosis – the movement of a substance out of the cell