CELLS - EUKARYOTIC VS. PROKARYOTIC CELLS

Add to your notes the following chart - COMPARISON BETWEEN PROKARYOTIC & EUKARYOTIC CELLS

Comparison Between Prokaryotic and Eukaryotic Cells
Characteristic	Prokaryotes	Eukaryotes
Size of cell	Typically 0.2-2.0 m m in diameter	Typically 10-100 m m in diameter
Nucleus	No nuclear membrane or nucleoli (nucleoid)	True nucleus, consisting of nuclear membrane & nucleoli
Membrane-enclosed organelles	Absent	Present; examples include lysosomes, Golgi complex, endoplasmic reticulum, mitochondria & chloroplasts
Flagella	Consist of two protein building blocks	Complex; consist of multiple microtubules
Glycocalyx	Present as a capsule or slime layer	Present in some cells that lack a cell wall
Cell wall	Usually present; chemically complex (typical bacterial cell wall includes peptidoglycan)	When present, chemically simple
Plasma membrane	No carbohydrates and generally lacks sterols	Sterols and carbohydrates that serve as receptors present
Cytoplasm	No cytosketeton or cytoplasmic streaming	Cytoskeleton; cytoplasmic streaming
Ribosomes	Smaller size (70S)	Larger size (80S); smaller size (70S) in organelles
Chromosome (DNA) arrangement	Single circular chromosome; lacks histones	Multiple linear chromosomes with histones
Cell division	Binary fission	Mitosis
Sexual reproduction	No meiosis; transfer of DNA fragments only (conjugation)	Involves meiosis

Complete the following:
CELL EUKARYOTES & PROKARYOTES

 CELL STRUCTURE & FUNCTION ACTIVITY

• Concept 1-4 & Self Quiz

CELLS - PLANT & ANIMAL CELL TUTORIALS

Plant and animal cells have several differences and similarities. For example, animal cells do not have a cell wall or chloroplasts but plant cells do. Animal cells are round and irregular in shape while plant cells have fixed, rectangular shapes.

COMPARISON CHART - DIFFERENCES IN ANIMAL & PLANT CELLS

Animal Cell	Plant Cell
Cell wall	Absent	Present (formed of cellulose)
Shape	Round (irregular shape)	Rectangular (fixed shape)
Vacuole	One or more small vacuoles (much smaller than plant cells).	One, large central vacuole taking up 90% of cell volume.
Centrioles	Present in all animal cells	Only present in lower plant forms.
Chloroplast	Animal cells don't have chloroplasts	Plant cells have chloroplasts because they make their own food
Plastids	Absent	Present
Plasma Membrane	only cell membrane	cell wall and a cell membrane
Lysosomes	Lysosomes occur in cytoplasm.	Lysosomes usually not evident.
Cilia	Present	It is very rare

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SIMILARITIES IN ANIMAL & PLANT CELLS

Animal Cell	Plant Cell
Cell wall	Absent	Present (formed of cellulose)
Shape	Round (irregular shape)	Rectangular (fixed shape)
Vacuole	One or more small vacuoles (much smaller than plant cells).	One, large central vacuole taking up 90% of cell volume.
Centrioles	Present in all animal cells	Only present in lower plant forms.
Chloroplast	Animal cells don't have chloroplasts	Plant cells have chloroplasts because they make their own food
Cytoplasm	Present	Present
Endoplasmic Reticulum (Smooth and Rough)	Present	Present
Ribosomes	Present	Present
Mitochondria	Present	Present
Plastids	Absent	Present
Golgi Apparatus	Present	Present
Plasma Membrane	only cell membrane	cell wall and a cell membrane
Microtubules/ Microfilaments	Present	Present
Flagella	May be found in some cells	May be found in some cells
Lysosomes	Lysosomes occur in cytoplasm.	Lysosomes usually not evident.
Nucleus	Present	Present
Cilia	Present	It is very rare

Follow the directions for the cell activity.  Click on the "tutorial" ; then game; then quiz.
Make sure you know the organelles structures  &  functions of the animal & plant cells.

1. Complete labeling of the PLANT & ANIMAL cell diagrams
2. Complete the ORGANELLE TABLE

PLANT CELL TUTORIAL

ANIMAL CELL TUTORIAL

CELLS - ACTVITIES

ANIMAL & PLANT CELLS ORGANELLES - ACTIVITY  #1

CELL ORGANELLES - ACTIVITY #2

animal cell - interactive

CELLS - RIBOSOMES #20

Ribosomes - Protein Construction Teams

Cells need to make proteins. Those proteins might be used as enzymes or as support for other cell functions. When you need to make proteins, you look for ribosomes.  Ribosomes are the protein builders or the protein synthesizers of the cell. They are like construction guys who connect one amino acid at a time and build long chains. 

Ribosomes are found in many places around the cell. You might find them floating in the cytoplasm (cytosol). Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. Endoplasmic reticulum with attached ribosomes is called rough. It looks bumpy under a microscope. Those attached ribosomes make proteins that will be used inside the cell and proteins made for export out of the cell. 

Two Pieces Make the Whole

A ribosome is not just one piece. There are two pieces or subunits. Scientists named them 60-S (large) and 40-S (small). When the cell needs to make protein, mRNA is created in the nucleus. The mRNA is then sent into the cell and the ribosomes. When it is time to make the protein, the two subunits come together and combine with the mRNA. The subunits lock onto the mRNA and start the protein synthesis. 

The 60-S/ 40-S model works fine for eukaryotic cells. Prokaryotic cells have ribosomes made of 50-S and 30-S subunits. It's a small difference, but one of many you will find in the two different types of cells. Scientists have used this difference in ribosome size to develop drugs that can kill prokaryotic microorganisms that cause disease. 

Mixing and Matching Amino Acids

The process of making proteins is quite simple. We just explained that mRNA is made in the nucleus and sent into the cell. The mRNA then combines with the ribosome subunits. Another nucleic acid lives in the cell - tRNA, which stands for transfer RNA. tRNA is bonded to the amino acids floating around the cell. With the mRNA offering instructions, the ribosome connects to a tRNA and pulls off one amino acid. Slowly the ribosome makes a long amino acid chain that will be part of a larger protein. 


CELL ORGANELLES - QUIZ

CELLS - PEROXISOMES #19

Peroxisomes - Another Enzyme Package

There are many ways that peroxisomes are similar to lysosomes. They are small vesicles found around the cell. They have a single membrane that contains digestive enzymes for breaking down toxic materials in the cell. They differ from lysosomes in the type of enzyme they hold. Peroxisomes hold on to enzymes that require oxygen (oxidative enzymes). Lysosomes have enzymes that work in oxygen-poor areas and lower pH. 

Peroxisomes absorb nutrients that the cell has acquired. They are very well known for digesting fatty acids. They also play a part in the way organisms digest alcohol(ethanol). Because they do that job, you would expect liver cells to have more peroxisomes than most other cells in a human body. They also play a role in cholesterol synthesis and the digestion of amino acids. 

Creating Hydrogen Peroxide

Peroxisomes work in a very specific way. Their enzymes attack complex molecules and break them down into smaller molecules. One of the byproducts of the digestion is hydrogen peroxide (H₂O₂). Peroxisomes have developed to a point where they are able to contain that hydrogen peroxide and break it down into water (H₂O) and oxygen (O₂). The water is harmless to the cell and the oxygen can be used in the next digestive reaction. 

Mysteries of the Peroxisome

Peroxisomes have a single membrane that surrounds the digestive enzymes and dangerous byproducts of their work (hydrogen peroxide). The protein enzymes are usually created by lysosomes floating in the cell. They then insert the proteins into the peroxisome bubble. Peroxisomes continue to grow until they split in two. Where does the membrane come from? Scientists are still researching that answer. It may come from the endoplasmic reticulum, but it may be created in a way different from lysosomes. 

CELL ORGANELLES - QUIZ

CELLS - LYSOSOMES #18

Lysosomes - Little Enzyme Packages

You will find organelles called lysosomes in nearly every animal-like eukaryotic cell. Lysosomes hold enzymes that were created by the cell. The purpose of the lysosome is to digest things. They might be used to digest food or break down the cell when it dies. What creates a lysosome? You'll have to visit the Golgi complex for that answer. 

A lysosome is basically a specialized vesicle that holds a variety of enzymes. The enzyme proteins are first created in the rough endoplasmic reticulum. Those proteins are packaged in a vesicle and sent to the Golgi apparatus. The Golgi then does its final work to create the digestive enzymes and pinches off a small, very specific vesicle. That vesicle is a lysosome. From there the lysosomes float in the cytoplasm until they are needed. Lysosomes are single-membrane organelles. 

Lysosome Action

Since lysosomes are little digestion machines, they go to work when the cell absorbs or eats some food. Once the material is inside the cell, the lysosomes attach and release their enzymes. The enzymes break down complex molecules that can include complex sugars and proteins. But what if food is scarce and the cell is starving? The lysosomes go to work even if there is no food for the cell. When the signal is sent out, lysosomes will actually digest the cell organelles for nutrients. 

Why Don't They Digest the Cell?

Here's something scientists are still trying to figure out. If the lysosome holds many types of enzymes, how can the lysosome survive? Lysosomes are designed to break down complex molecules and pieces of the cell. Why don't the enzymes break down the membrane that surrounds the lysosome? 

CELLS - MICROTUBLES #17

Microtubules - Thick Protein Tubes

Microtubules are usually discussed with microfilaments. Although they are both proteins that help define cell structure and movement, they are very different molecules. While microfilaments are thin, microtubules are thick, strong spirals of thousands of subunits. Those subunits are made of the protein called tubulin. And yes, they got their name because they look like a tube. 

Elements of the Cytoskeleton

All of the microfilaments and microtubules combine to form the cytoskeleton of the cell. The cytoskeleton is different from cytoplasm (cytosol). The cytoskeleton provides structure. Cytoplasm is just a fluid. The cytoskeleton connects to every organelle and every part of the cell membrane. Think about an amoeba. All of the pieces work together so that the foot might reach out towards the food. Then lysosomes and peroxisomes are sent to begin digestion. The movement of the cell membrane, organelles, and cytoplasm is all related to the tubules and filaments. 

Moving Chromosomes

Microtubules have many more uses than just cell structure. They are also very important in cell division. They connect to chromosomes, help them with their first split, and then move to each new daughter cell. They are a part of a small pair of organelles called centrioles that have the specific purpose to help a cell divide. Once the cell has finished dividing, the microtubules are put to work in other places. 

Moving Organisms

Beyond the role they play in internal cell movement, microtubules also work together to form larger structures that work on the outside of the cells. They can combine in very specific arrangements to form cilia and flagella. Cilia are little hairs you might see on the outside of a paramecium or other protists. They flap back and forth to help the cell move. Flagella are long, thick tails. They whip around and sometimes twirl, pushing the cell along. 

CELLS - MICROFILAMENTS #16

Microfilaments - Stringy Proteins

You will find microfilaments in most cells. They are the partner of microtubules. They are long, thin, and stringy proteins (mainly actin) compared to the rounder, tube-shaped microtubules. We'd like to say you can find them here or there, but they are everywhere in a cell. They work with microtubules to form the structure that allows a cell to hold its shape, move itself, and move its organelles. 

Making the Cytoskeleton

All of the microfilaments and microtubules combine to form the cytoskeleton of the cell. The cytoskeleton is different from cytoplasm (cytosol). The cytoskeleton provides structure. Cytoplasm is just a fluid. The cytoskeleton connects to every organelle and every part of the cell membrane. Think about an amoeba. All of the pieces work together so that the foot might reach out towards the food. Then lysosomes and peroxisomes are sent to begin digestion. The movement of the cell membrane, organelles, and cytoplasm is all related to the tubules and filaments. 

You will also find many microfilaments in muscle tissue. They are called myofibrils when you find them in muscles. The two proteins myosin and actinwork together to help the muscle cells relax and contract. The two proteins need each other and together they are called actomyosin. Combine those protein threads with some ions in the muscle cell and you get a huge contraction. The groups of actomyosin contracting are called sarcomeres. All of the muscle cells work together to make a muscle contract. 

A Role in Cell Movement

Cells move in a variety of ways. We just talked about the contraction of a muscle cell. That is an extreme example. When you learn about single-celled organisms, you will understand that they need to move. They may need to glide from one area to another. The microfilaments are often found anchored to proteins in the cell membrane. Sometimes microfilaments are found floating free and connected to other filaments and tubules. Those binding proteins allow the microfilaments to push and pull on the cell membrane to help the cell move. 

CELLS - VACUOLES #15

Vacuoles - Storage Bins to the Cells

Vacuoles are storage bubbles found in cells. They are found in both animal and plant cells but are much larger in plant cells. Vacuoles might store food or any variety of nutrients a cell might need to survive. They can even store waste products so the rest of the cell is protected from contamination. Eventually, those waste products would be sent out of the cell. 

The structure of vacuoles is fairly simple. There is a membrane that surrounds a mass of fluid. In that fluid are nutrients or waste products. Plants may also use vacuoles to store water. Those tiny water bags help to support the plant. They are closely related to objects called vesicles that are found throughout the cell. 

In plant cells, the vacuoles are much larger than in animal cells. When a plant cell has stopped growing, there is usually one very large vacuole. Sometimes that vacuole can take up more than half of the cell's volume. The vacuole holds large amounts of water or food. Don't forge that vacuoles can also hold the plant waste products. Those waste products are slowly broken into small pieces that cannot hurt the cell. Vacuoles hold onto things that the cell might need, just like a backpack. 

Helping with Support

Vacuoles also play an important role in plant structure. Plants use cell walls to provide support and surround cells. The size of that cell may still increase or decrease depending on how much water is present. Plant cells do not shrink because of changes in the amount of cytoplasm. Most of a plant cell's volume depends on the material in vacuoles. 

Those vacuoles gain and lose water depending on how much water is available to the plant. A drooping plant has lost much of its water and the vacuoles are shrinking. It still maintains its basic structure because of the cell walls. When the plant finds a new source of water, the vacuoles are refilled and the plant regains its structure. 

CELLS - GOLGI APPARATUS #14

Golgi Apparatus - Packing Things Up

The Golgi apparatus or Golgi complex is found in most cells. It is another packaging organelle like the endoplasmic reticulum (ER). It was named after Camillo Golgi, an Italian biologist. It is pronounced GOL-JI in the same way you would say squee-gie, as soft a "G" sound. While layers of membranes may look like the rough ER, they have a very different function. 

Foundation of Vesicles

The Golgi complex gathers simple molecules and combines them to make molecules that are more complex. It then takes those big molecules, packages them in vesicles, and either stores them for later use or sends them out of the cell. It is also the organelle that builds lysosomes (cell digestion machines). Golgi complexes in the plant may also create complex sugars and send them off in secretory vesicles. The vesicles are created in the same way the ER does it. The vesicles are pinched off the membranes and float through the cell. 

The Golgi complex is a series of membranes shaped like pancakes. The single membrane is similar to the cell membrane in that it has two layers. The membrane surrounds an area of fluid where the complex molecules (proteins, sugars, enzymes) are stored and changed. Because the Golgi complex absorbs vesicles from the rough ER, you will also find ribosomes in those pancake stacks. 

Working with the Rough ER

The Golgi complex works closely with the rough ER. When a protein is made in the ER, something called a transition vesicle is made. This vesicle or sac floats through the cytoplasm to the Golgi apparatus and is absorbed. After the Golgi does its work on the molecules inside the sac, a secretory vesicle is created and released into the cytoplasm. From there, the vesicle moves to the cell membrane and the molecules are released out of the cell.