Diffusion and Osmosis

Diffusion is when molecules move from high concentration to low concentration.

Let's think of this in terms of students in a classroom. If we were to fit 100 students in our classroom, and there was no one in the common area, student would naturally leave the classroom to spread out and stand in the common area so each student would have more space.

Food coloring is another good example of diffusion. When food coloring is first placed into a beaker of water, the coloring is highly concentrated in one area. Then, you will observe it spreading out and eventually becoming evenly spaced throughout the beaker. 

Diffusion doesn't cost the cell any energy- it happens naturally!

Osmosis is a special kind of diffusion, with water molecules only.This can be a little tricky. Just keep in mind that the water molecules always move from high concentration to low concentration- so they go from where there are many water molecules to where there are less (just like food coloring does).

Take a look at the diagram of osmosis above. The red molecules with white around them represent water (H2O- note that there are 2 hydrogens--white and 1oxygen--red in each). In the first diagram, there are many more water molecules on the left than on the right. Then, some of these molecules move over to the right, so that the water molecules are more evenly spaced out. 

If you look at the above diagram, you will note that the purple dots represent a solute (which is any molecule that dissolves in water- such as salt for example). If you look at the left side of this diagram, you can see that the left part of the tube has more water molecules and less solute molecules, while the right part of the tube has less water molecules and more solute molecules. So, water moves from the left to the right, as you can see in the diagram to the right of the arrow.

A few important terms when learning about osmosis are HYPERTONIC and HYPOTONIC. 

-HYPERTONIC means more solute, less water.

-HYPOTONIC means less solute, more water.

In the diagram below, you can see that the outside of the cell is HYPERTONIC to the inside of the cell..because there are many more solutes in the outside and less water.

You could also say that the inside of the cell is HYPOTONIC to the outside of the cell, because there are many less solutes and more water molecules.

So, in osmosis of this cell, water molecules will move from where there are more water molecules to less, meaning that they will move from inside the cell to outside the cell.

The opposite is true for the diagram below. The inside of the cell is HYPERTONIC to the outside of the cell (since there are more solutes and fewer water), or the outside of the cell is HYPOTONIC to the inside of the cell.

Therefore, in this example, water will move from outside the cell (where there are more water molecules) to inside the cell (where there are less water molecules)

Take a look at the following animation on osmosis

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

and a similar animation on diffusion 

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Transcription and Translation

Protein synthesis is very important for any living thing! Why???

-Proteins make up antibodies, which fight diseases

-Proteins make up your CELL STRUCTURE..so without proteins, you'd have no cells

-Proteins make up your muscles..without them you couldnt move. (Some people have disorderse where their protein synthesis doesn't work properly, and they have degenerative muscular disorders because of this--- example=alzheimers)

Where do you get proteins from??? -Meat, beans, a combination of vegetables, chickpeas, tofu, etc...


The steps of protein synthesis: 
1. DNA strand divides in 2
2. Transcription
3. Translation


Here is a diagram of what happens in protein synthesis overall.....

Now let me take you on a tour of protein synthesis.

1. The DNA divides in 2: remember that for protein synthesis to occur, the information from DNA is needed to make the proteins. By information, I mean the sequences (or order) of the bases. So... having a DNA strand with bases ATCGGGC would lead to a different protein than the bases TACGGCG. Even though the same bases are present, the sequences is different, so the protein is different.

..To get the information from DNA for our proteins, the strands need to be separated so only 1 strand at a time is read.

2. Transcription: This happens in the nucleus. Information from DNA is used to make an mRNA strand. mRNA stands for MESSENGER RNA..this is the messenger in the protein synthesis process. Remember that the bases in DNA are A,T,C,G and in RNA are A,U,C,G. A pairs with U (and vice versa), C pairs with G (and vice versa).

If I were to ask you to TRANSCRIBE the following DNA strand to an mRNA strand

ATCGGCATC

It would become...

UAGCCGUAG.

(Because A in DNA codes for U in RNA, then T in DNA codes for A in RNA, then C in DNA codes for G in RNA, then G in DNA codes for C in RNA, etc.)

3. The last step in making our protein is called TRANSLATION. In translation, the information in mRNA is used to make a protein.

First, the mRNA needs to leave the nucleus and attach to a ribosome (which is found in the cytoplasm)..take a look back up at the diagram to understand where in the cell we are right now.

Next, the mRNA is broken up into groups of 3 called CODONS. 

Let's go back to our mRNA strand: TACCCGUAG

The codons would be:  AUG CCG UAG

Remember that a protein is really just a long chain of AMINO ACIDS.

Here is an image of a protein (note that each ball represents 1 amino acid). 

Now that we have our codons, how do we figure out which amino acid strands they code for? 

Using this chart!

Our codons are AUG CCG UAG

Find AUG on the chart! You will see that it codes for Met.

CCG codes for Pro

UAG codes for Stop.

If you were to write the chain of amino acids, it would look like this:

Met-Pro-Stop

You have now made your protein.

Take a look at the following Protein Synthesis video:

http://www.youtube.com/watch?v=NJxobgkPEAo

And play the following game on Protein Synthesis 

http://learn.genetics.utah.edu/content/begin/dna/transcribe/

Mitosis

Mitosis is CELL DIVISION in eukaryotice (plant or animal) cells.

Why is mitosis important?

-By making new cells through mitosis, dead cells are replaced

-Through mitosis, living things are able to become multicellular organisms (this is how we went from being 1 cell to multiple cells).

--When mitosis goes wrong, cells can divide uncontrollably and a person can get cancer.

Below is a diagram of the phases of mitosis:

INTERPHASE is the stage before mitosis. This is just when the cell is growing (in G1 and G2 phases), and DNA is replicating. No cell division occurs at this point. You will notice that the nucleus is in tact, and the DNA is found in strands.

1. The first real mitosis phase is PROPHASE. In this phase, the nuclear envelope breaks up, or dissolves, the DNA is in chromosomes and (those X-like structures), the spindle fibers begin to form.

2. METAPHASE comes next. The chromosomes line up in the middle of the cell, along the metaphase plate, and are attached to the spindle fibers.Note that the spindle fibers are attached to centrioles in the poles.

3. ANAPHASE: The spindle fibers pull apart the chromosomes to 2 separate sister chromatids. Now, you will find the sister chromatids separated along the 2 poles of the cell.

4. The last phase of mitosis is TELOPHASE. In this phase, the nuclear envelope re-forms and 2 nuclei are found in the long, extended cell.

After mitosis comes CYTOKINESIS. This is when the cytoplasm divide in 2, and 2 separate cells are formed.

-Cytokinesis is slightly different in plants and animals. In plants, a cell wall is formed along the middle of the cell, and then 2 cells are formed. In animals, the cytoplasm pinches in, and then 2 cells are formed.

Here is a diagram of animal cell cytokinesis (note the cleavage furrow that forms):

 

Here is a diagram of plant cell cytokinesis (note the cell wall that forms in the middle of the cell):

Here is an animation that takes you through all of the stages..

http://www.cellsalive.com/mitosis.htm

The end. :)

Cell Organelles

Our bodies are made up of BILLIONS of cells.
-Cells make up tissues, which make up organs, which make up organ systems.

A cell is made up of tiny structures called ORGANELLES, which each have special functions that contribute to the overall cell. Plants and animals have slightly different organelles. (remember, that humans have animal cells, because we are technically animals).

Below is a labeled animal cell diagram:

 And a plant cell:

Don't be alarmed that you see different kinds of cell diagrams- there are tons of ways to draw cells, so just pay attention to the overall structure of each organelle!


Now what do these organelles do?

1. Nucleus: This is found in both plant and animal cells. The nucleus is known as the "control center" of the cell, basically  controlling all cell functions. This is where DNA is found (more specifically, DNA is found inside the NUCLEOLIS, which is inside of the nucleus.)

2. Cell membrane: Also found in plants and animals. The cell membrane is selectively permeable, meaning that it selectively lets molecules into and out of the cell. The membrane is most likely to let in smaller molecules. Found in plants and animals.

3. Mitochondria: Known as the "power house" of the cell- this is where energy is made for the cell in the form of ATP. Found in plants and animals.

4. Golgi Apparatus: This is where molecules (such as proteins) are packaged and sent out of the cell. So, the golgi apparatus (also known as golgi body) is kind of like a post office. Found in plants and animals.

5. Ribosome: This is where proteins are made (as we will learn, through transcription and translation). Found in plants and animals.

6. Rough Endoplasmic Reticulum: This is where proteins are altered (so, sugars are added and the proteins are folded) so that they are ready for the body's use. From the rough endoplasmic reticulum, proteins are packaged in vesicles and sent out of the cell to be used by the body. Found in plants and animals.

7. Smooth Endoplasmic Reticulum: This is where lipids (also known as fats) are made. Found in plants and animals.

8. Vacuole: This is where food, water, and wastes are stored. It is found in both plants and animals, but is MUCH bigger in plants.

9. Lysosome: This is where food is digested, or where poisons are broken down. Found in plants and animals.

10. Cell wall: This is a rough outer surface of PLANT cells only. This is the reason why when you touch a stem it feels hard. The cell wall provides support for the plant.

11. Chloroplast: This is where photosynthesis occurs. It is found only in PLANT cells!

Here is a video that takes you through a tour of the cell!
http://www.youtube.com/watch?v=a6boqEbcJWI

The Origin of Life!!

How did life begin?! There are tons of different theories.. but the one I'm about to explain is according to Scientists. You may believe this, or your own theory, or some sort of hybrid of the two, and that's okay!!

According to scientists, when Earth was first formed, there was NO life. This Earth was really hot, and full of ammonium, some Carbon Dioxide, water, and some other gases all mixed up in a "soup". Take a look at the video below to understand better..

http://www.youtube.com/watch?v=jTCoKlB0s4Y

1. The first "cells" that evolved were called protocells (above). These LOOKED like real cells- they had a cell membrane and DNA inside- but they weren't alive! These protocells started replicating and eventually the first prokaryotic cells evolved.

2. The first REAL cells that appeared were PROKARYOTIC cells. These cells are very simple, only containing a DNA strand, ribosomes, a cytoplasm, and cell wall (and sometimes flagella for moving around- locomotion!). 


**These first prokaryotic cells were HETEROTROPHS (like the chicken below)... meaning that they DON'T make their own food, and need to eat other organisms for food.
-Because these heterotrophs were going through the process of fermentation (a type of cellular respiration) they were releasing Carbon Dioxide (CO2). Now, the atmosphere is full of too much Carbon Dioxide!

 3. Because there was too much Carbon Dioxide in the atmosphere, autotrophs evolved. Autotrophs are organisms that make their own food (such as through photosynthesis with plants). To do so, they take in Carbon Dioxide and release Oxygen.
-Now, the atmosphere is full of Oxygen, and has less Carbon Dioxide (just like today!).

                                                   This diagram is autotrophic bacteria (prokaryote)

 

Plants are another example of autotrophs (above)

4. Finally, these prokarytoic (simple) cells began to "eat" small bacteria. These bacteria turned into organelles of the new eukarytoic cells. Eukaryotic cells are COMPLEX cells containing specialized organelles with their own functions. Plants and animals (such as humans) have eukaryotic cells! (See diagram of eukaryote below!!).

*For prokaryotes to turn into eukaryotes, they go through a process called endosymbiosis (where they eat small organelles).