Monday, November 29, 2021

Mitosis: Closer Look

 Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Explore the process of mitosis understanding why mitosis happens, the main goal of mitosis, and the key terms involved in mitosis.

Article includes ideas, images, and content from Troy Smigielski (2021-11)

Mitosis: Closer Look
(Let's start with a review!)
Source, 2021-11

Review of Mitosis Basics

"Mitosis is a process where a single cell divides into two identical daughter cells (cell division). During mitosis one cell? divides once to form two identical cells. The major purpose of mitosis is for growth and to replace worn out cells" (Souce, 2021-11)

So, cells split… hmm…

Why does mitosis happen? Why is it necessary for cells to divide?

Three reasons cells divide:

1. Healing: to replace old or damaged cells. 
2. Growth: to help an organism’s growth in an orderly way.
3. Transport: to help efficiency of cellular transport.

Your cells will duplicate to make your body more efficient.

Simply put, mitosis is the process when a cell divides replicated DNA (from Interphase) into 2 cells that are both identical to the original cell.

How does this occur?

In order to do this, your cell uses centrioles, which are organelles that function to separate sister chromatids. They do this by using spindle fibers.




Mitosis occurs in steps.

Step 1: Prophase


In prophase, chromatin is organized into chromosomes. Chromatin is the stringy material that makes up a chromosome.

During this phase, centrioles begin to move to opposite sides of the cell. Lastly, the nuclear envelope begins to disappear.





Prophase






Step 2: Metaphase



At this point, the nuclear envelope is gone allowing chromatids to move freely. 

The free chromatids line up in the middle of the cell along the metaphase plate.









Metaphase





Step 3: Anaphase






Sister chromatids are pulled apart to opposite sides of the cell by centrioles using spindle fibers.












Anaphase




Step 4: Telophase


The nuclear envelope returns to surround each set of chromosomes.

The large cell prepares to divide into two separate cells in cytokinesis.









Telophase


During telophase, the cell begins the process of creating two separate cells. In animal cells, a cleavage furrow forms in the middle of the cell. In plant cells, a cell plate forms in the middle of the cell.




The last part of the process is called cytokinesis.

Cytokinesis


The cells divide to become two completely separate entities.




In other words, the cytoplasm divides.




At the end of mitosis, we have two brand new diploid cells. Wait! What is this thing, diploid?


Haploid vs. Diploid


Haploid - having one set of chromosomes (1n)

Diploid - having two sets of chromosomes (2n)



The cell cycle (mitosis) divides a diploid (2n) cell into two identical diploid (2n) cells called daughter cells. Each daughter cell has the same number of chromosomes as the original cell.



While most of the cells in your body divide, some do not. 

Blood Cells

Blood cells do not duplicate. Why?


In order to carry more oxygen, blood cells end up without a nucleus. This means they have no DNA. So, they cannot duplicate chromosomes in Interphase, which means they can’t undergo mitosis.


Brian and Never Cells


Because brain and nerve cells cannot duplicate, spinal and brain injuries typically cannot repair themselves.

In the process of cell division, recall that a certain organelle functions to pull sister chromatids apart from each other by using spindle fibers.

Neurons do not have centrioles, so they are unable to divide.



Regulating the Cell Cycle





Your body uses proteins called cyclins to regulate the cell cycle.

Cyclins function as checkpoints that decide if the cell cycle should continue or not.

Cyclin is a family of proteins that controls the progression of a cell through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes or group of enzymes required for synthesis of cell cycle.

For instance, if the DNA is damaged, the process will be stopped; the damaged DNA will not be replicated.





If your body cannot properly control cell growth, what may happen?

  • Cancer is a disease of the cell cycle.
  • Cancer cells do not respond to signals that regulate the cell cycle. So, they have potential to form masses of cells called tumors.
  • Occasionally, these masses can break loose and metastasize (spread).

Your body has innate immunity that has the ability to naturally fight these cells off.

These cells are called natural killer cells.

Your NK cell count is influenced by exercise and diet.


Overview of Mitosis

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Explore the process of mitosis understanding why mitosis happens, the main goal of mitosis, and the key terms involved in mitosis.

Article includes ideas, images, and content from Troy Smigielski (2021-11)

Overview of Mitosis
(Hmm… )
Source, 2021-11

"Mitosis is a process where a single cell divides into two identical daughter cells (cell division). During mitosis one cell? divides once to form two identical cells. The major purpose of mitosis is for growth and to replace worn out cells" (Souce, 2021-11)

So, cells split… hmm…

Why does mitosis happen? Why is it necessary for cells to divide?

Three reasons cells divide:

1. Healing: to replace old or damaged cells. 
2. Growth: to help an organism’s growth in an orderly way.
3. Transport: to help efficiency of cellular transport.

Your cells will duplicate to make your body more efficient.

As a cell grows in size, its volume increases quicker than its surface area. Since cells rely on the surface area (the membrane) to get nutrients in to all of its parts, too much volume puts parts of the cell too far from the membrane.



For this reason, cells divide. If cells didn’t divide, the cell would have a massive volume. This would require your cell a great deal of energy to transport materials.


How do cells divide?


In eukaryotic cells, the 2 main stages of cell division are interphase and mitosis.

Prokaryotic cells undergo a process called binary fission.

The main goal of the cell cycle is to create 2 identical cells from one cell for the purpose of healing, growth, or to maximize the efficiency of cell transport.

To do this, your body must go through the cell cycle.

What are the 2 main phases of the cell cycle?


Interphase is a growth period that happens in between cell divisions. It takes up the majority of time in the cell cycle. Therefore, at any given time, ~90% of your cells will be in interphase. 

Interphase is the longest phase of the cell cycle.

There are 3 main phases of interphase.

G1 - cell growth
S - DNA replication in nucleus
G2 - preparation for division; small amounts of growth

What would that look like, say, for a human cell?

Pictures!





S phase stands for synthesis phase, and synthesis means “to create”. 

S phase synthesizes (creates) sister chromatids, which are identical copies of one chromosome.


Sister chromatids are attached at a region called the centromere.




Once Interphase is complete, the cell moves on to mitosis. What is the goal of this entire process?



Simply put, mitosis is the process when a cell divides replicated DNA (from Interphase) into 2 cells that are both identical to the original cell.




The original cell is referred to as the parent cell.

Both of the new cells are referred to as daughter cells.

Each daughter cell is a somatic cell, which means it is a body cell.




There are 4 main stages of mitosis:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Pass Me Another Taco

At the end of telophase, the cell divides into two separate cells in a process called cytokinesis.


In order to do this, your cell uses centrioles, which are organelles that function to separate sister chromatids. They do this by using spindle fibers.




Different types of cells go through mitosis at different rates based on how often they need to be replaced. 


Friday, November 12, 2021

Electron Transport Chain

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Model and understand aerobic respiration demonstrating the flow of matter and energy out of a cell and explain energy transfer systems. Also, compare aerobic respiration to alternative processes of glucose metabolism.

Article includes ideas, images, and content from Troy Smigielski (2021-10)

Electron Transport Chain
(Chains? So, no cycle and all that going around and around?)


So, how many names does this thing have?

At least three!

"The electron transport chain (ETC; respiratory chain) is a series of protein complexes that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. The electron transport chain is built up of peptides, enzymes, and other molecules…" (Source, 2021-11).

Am I supposed to understand any of that! 

Let's try to get a handle on that. So…

The electron transport chain is the final step in cellular respiration. 
  • It receives electron carriers from the Krebs cycle and uses them, along with oxygen (hence it is aerobic), to create ATP which is passed on to the cell to provide energy for cellular functioning.
  • The process takes place in the inner membrane of the mitochondria. 
  • It produces water as a byproduct.
Nice! Can we just stop now?

The whole process begins with glycolysis





that sends pyruvate (which is broken down into acetyl CoA first) to the Krebs cycle.



The Krebs cycle creates and sends electrons to the electron transport chain. The electron carriers are NADH and FADH2.

The Krebs cycle is considered to be anaerobic. Why? 

It is part of a system that includes the electron transport system that, we will see later, needs oxygen. So, because without oxygen, the ETC cannot use the electrons from NADH and FADH2. If they can’t drop off electrons, they can’t become NAD+ and FAD. Without NAD+ and FAD, the Krebs cycle cannot function. Therefore, the Krebs cycle indirectly requires oxygen.

At the end of the Krebs cycle, the are sent to the electron transport chain to be converted into ATP.


The ETC
is the final step of cellular respiration. We further discussed that it occurs in the mitochondria and that it is aerobic.

Okay… about those names…

It is also called oxidative phosphorylation.
Seriously! Stop!

“Oxidative” refers to oxidation, which is when a molecule loses an electron. Phosphorylation” refers to the attachment of a phosphate to ADP, which makes ATP.

Now, recall that the overall, main purpose of cellular respiration is to create ATP!

Source 2021-11
In discussing glycolysis and the Krebs cycle, we previewed the role of the electron transport chain and learned that it is responsible for the bulk of ATP produced. 
How? 

The ETC is located in the inner membrane of the mitochondrion.

The electron transport chain will use electrons that are dropped off by NADH and FADH2 to create ATP. 
  • Each NADH can produce 3 ATP.
  • Each FADH2 can produce 2 ATP.

Steps of the Electron Transport Chain

  • Electrons are brought to the ETC by NADH and FADH2.
  • When electrons are dropped off, the Hydrogen that they are attached to is dropped off too. 
  • Therefore, when electrons are dropped off, NADH becomes NAD+ and FADH2 becomes FAD.


NAD+ and FAD go back to glycolysis and Krebs Cycle to pick up more electrons and keep the process going.

As more H+ ions and electrons are dropped off, H+ ions start to build up in the intermembrane space. Naturally, they want to diffuse out, but they are charged. Therefore, they must exit through a transport protein via facilitated diffusion.


The transport protein that allows the H+ ions to leave is called ATP Synthase. When this happens, ATP Synthase spins which provides enough energy to create ATP. When this happens, ATP Synthase spins which provides enough energy to create ATP.

Meanwhile, the electrons travel down the ETC and release energy.

This energy is used to push more H+ ions out because the more H+ ions that go out, the more H+ ions must come back in through ATP Synthase. This forces your cell to produce more ATP.

At the end of the chain, the electrons are fresh out of energy. They are “accepted” by oxygen. 


In other words, oxygen is the final electron acceptor.

Some H+ ions attach to the electron and oxygen, which forms water.

The Totals

  • About 36-38 total ATP are made in cellular respiration.
  • Remember, 2 ATP were used in glycolysis.
  • The net gain of ATP in cellular respiration is 34-36 ATP.
  • Glycolysis: 2 ATP (anaerobic)
  • Citric Acid Cycle + ETC: ~34 ATP (aerobic)

Despite the entirety of the system, some energy is left in the original glucose molecule. The energy in glucose that is not used to make energy is lost as heat, which helps keep our bodies at homeostasis.



Tuesday, November 9, 2021

About Reactions

Biology Index

Where are we going with this? The information on this page should increase understanding related to the discussion of chemical reactions in biology.

About Reactions
(Hmm… this must be about reactions…)

Many topics in biology include the need to understand chemical reactions. So… let's discuss this!

A chemical reaction basically is taking some things and causing them become different things. More accurately, a chemical reaction is when an interaction involving substances and energy result in the production of one or more DIFFERENT substances.

Let's use the main photosynthesis reaction as an example.

Starting with carbon dioxide and water, light energy is used to produce glucose and oxygen.

There are, in any reaction two types of substances:

reactants and products.

So, let's take the above sentence and say it in a way that make it clear what are reactants and what are products. Also, let's add color!

Carbon dioxide and water react to produce glucose and oxygen.

So:
the reactants are carbon dioxide and water.
to produce indicates that a reaction occurred
glucose and oxygen are the products.

While there are chemical symbols for most reactions, in biology, the discussion sometimes is more conveniently carried on using the names of the substances. However, sometimes the chemical symbols are used. Let's look at that:

Carbon dioxide and water react to produce glucose and oxygen.
                                    CO2 + H2O ---> C6H12O6 + O2

Molecules are the string of letters and subscripts connected to each other without spaces. The letters come from the periodic table, are the atomic symbols. The little numbers are the subscripts which indicate how many of each type of atom are present in each molecule.  The ---> symbol indicates that the reaction took place.

Some sources will not make the subscripts small, so you might see something like this:

H20

In any case, the number in the middle or at the end of molecular notation applies ONLY to the element that comes immediately before it. Hence, in H2O, the 2 only applies to the H.

So, in H2O, there are 2 H atoms and 1 O atom.

To be most accurate, symbolic notations will include numbers called coefficients which indicate how many of each type of molecule is present. Let's have a look!

Carbon dioxide and water react to produce glucose and oxygen.
                                    6CO2 + 6H2O ---> C6H12O6 + 6O2

This notation means that it takes 6 molecules of carbon dioxide and 6 molecules of water make the reaction run.

Discussing biological reactions frequently attempt to describe what "goes in and what comes out."

So… Let's get our fancy color coded example again!



                                            PHOTOSYNTHESIS

Carbon dioxide and water react to produce glucose and oxygen.
                                 6CO2 + 6H2O  --->     C6H12O6 + 6O2
                                    Reactants   yield   Products
                                      Goes in       --->      Comes out



Monday, November 8, 2021

Krebs Cycle (Citric Acid Cycle)

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Model and understand aerobic respiration demonstrating the flow of matter and energy out of a cell and explain energy transfer systems. Also, compare aerobic respiration to alternative processes of glucose metabolism.

Article includes ideas, images, and content from Troy Smigielski (2021-10)


Krebs Cycle (Citric Acid Cycle)
(This sounds like something off of Sponge Bob!)

Source, 2021-11

So, this process has three names, actually!

Krebs Cycle = Citric Acid Cycle = tricarboxylic acid cycle
(Must be important!)

Also, I head this guy on YouTube call it the Hans cycle, because that was Krebs' first name… Hans Krebs. So, yeah… That…

The Krebs cycle is a part of cellular respiration by which adenosine triphosphate (ATP) is produced. It's… complicated! 

It "is a central driver of cellular respiration. It takes acetyl CoA—produced by the oxidation of pyruvate and originally derived from glucose—as its starting material and, in a series of redox reactions, harvests much of its bond energy in the form of NADH, FADH2, and ATP molecules. The reduced electron carriers—NADH and FADH2—generated in the TCA cycle will pass their electrons into the electron transport chain and, through oxidative phosphorylation, will generate most of the ATP produced in cellular respiration (Source 2021-11).

Source, 2021-11
The whole goal of cellular respiration is to produce ATP that can be used to power cellular functioning. 


The Krebs cycle is one of the three steps, the middle step, in cellular respiration. 

Although it is complicated at a bio-chemical process, let's see if we can break it down into less complex steps!


If, in cellular respiration, we take a step backward from the Krebs cycle, we are in glycolysis.
Glycolysis is an anaerobic reaction taking place in the cytosol. If there is no oxygen present, then fermentation occurs. But!!! If oxygen is present, then it passes two 3-carbon pyruvate (pyruvic acid) on to the Krebs cycle.

aerobic - with oxygen

anerobic - without oxygen

Recall that glycolysis begins with glucose.
And… recall that glucose (along with oxygen) is produced by photosynthesis.

As discussed above, glucose is a six carbon molecule that is broken down in glycolysis. The process produces a net gain of 2 ATP, then passes 2 pyruvate to the Krebs cycle. 

Whereas glycolysis is anaerobic (and… you know… takes place in the cytosol), the Krebs cycle takes place in the mitochondria and is aerobic.

In between glycolysis and the Krebs cycle, the pyruvate (the pyruvic acid molecules) breaks down to produce one NADH and one CO2, leaving behind a 2-carbon molecule.

This 2-carbon molecule is called Acetyl CoA, and this is what is taken into the Krebs cycle. 





At this point, we are ready to start looking at the Krebs cycle.




Source 2021-11

The Krebs cycle occurs in the mitochondrion. Specifically, the Krebs Cycle takes place in the matrix inside the mitochondrion.

The matrix is the space inside the organelle… kinda like a curvy track.

Recall that between glycolysis and the Krebs cycle, the pyruvate molecules are turned into acetyl CoA, a 2-carbon molecule.

Before the Citric Acid Cycle begins, one pyruvate (3-C) from glycolysis is converted into Acetyl CoA (2-C) so the cycle can begin. This creates one CO2 that will go into the atmosphere. This also creates one NADH.

So, just getting ready to start the Krebs cycle, on of the electron carriers, NADH, and on CO2 have been created.


Source, 2021-11

The most important function of the Krebs cycle is to energize the electron carriers and send them to the electron transport chain. The electron transport chain will use the electron carriers to produce… a lot of ATP!

There are two electron transport molecules in cellular respiration. They are usually called electron carriers. Why? Because the… carry electrons! 

One of the two electron carriers in cellular respiration might remind you of the electron carrier in photosynthesis. It is NADH. (In photosynthesis, the electron carrier is NADPH.) The other electron carrier in cellular respiration is called FADH2. So, for cellular respiration, the electron carriers are NADH and FADH2.




The Krebs cycle is the source for most of the NADH and FADH2 that will be used in the electron transport chain.

Next, entering the Krebs cycle, Acetyl CoA (2-C) combines with oxaloacetate (4-C) to form citric acid (6-C).

After rearrangement, citric acid releases two of its Carbons as CO2 into the atmosphere.

As each CO2 leaves, one NADH is also produced. So, if 2 CO2 are released, then 2 NADH are also produced.

These CO2  molecules are exhaled and released into the atmosphere. They are byproducts not needed by the cell.

The remaining four carbons go through reactions to regenerate oxaloacetate so that the cycle can repeat. In the regeneration process, one ATP, one NADH, and one FADH2 are made.

One round of the Krebs cycle produces:
  • 2 CO2
  • 3 NADH
  • 1 FADH2
  • 1 ATP
These numbers are for one round. One round started with only one pyruvate. Remember, one glucose at the beginning makes 2 pyruvate. Therefore, we need to multiply these numbers by 2 to see the total number of each product that are made by one glucose molecule.

One molecule of glucose produces:
  • 4 CO2
  • 6 NADH
  • 2 FADH2
  • 2 ATP
The energy in these electrons that are carried by NADH and FADH2 will go the the ETC (Step 3 of the cellular respiration process) to help produce many more molecules of ATP.

Wednesday, November 3, 2021

Glycolysis

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Model and understand aerobic respiration demonstrating the flow of matter and energy out of a cell and explain energy transfer systems. Also, compare aerobic respiration to alternative processes of glucose metabolism.


Article includes ideas, images, and content from Troy Smigielski (2021-10)

Glycolysis
(Someone should come up with a spicer name for this!)


Glycolysis is the first step in cellular respiration. Of the three steps it is different in a couple of ways:
  • It does not require oxygen, which makes it anaerobic.
  • It occurs in the cytoplasm (the cytosol) of the cell; not the mitochondrion.

In cellular respiration, you’ll notice that if the process is anaerobic, then it will happen outside of the mitochondrion.

Conversely, if it is aerobic, it will happen in the mitochondria.

Before we get too far, let's recall a few things. Keep in mind that…

… glucose is one of the reactants of cellular respiration. Where does the glucose come from? You will recall that plants make glucose as a product of photosynthesis

Don't forget the main purpose of cellular respiration (of which glycolysis is a step) is to convert the energy stored in glucose into energy stored as ATP. In other words, cellular respiration breaks down glucose and turns it into ATP.

If this process breaks down glucose, what does our starting material have to be?

Glycolysis starts with one glucose molecule.

Okay… fancy word… Lysis means to break.

So, glycolysis means “glucose broken”.


Using 2 ATP, the glucose molecule is broken into two 3-C molecules. (Wait! I thought we were trying to MAKE ATP. Are we doing this backwards?)

Next, 4 ATP and electrons are extracted from the two 3-C molecules. The electrons are placed onto NAD+, and this creates NADH, which is one of the electron carriers in cellular respiration.

(So… NADH… is that like the NADPH in photosynthesis?)

Just as the NADPH in photosynthesis carried electrons, the NADH carries electrons throughout cells as needed. NADH, is an electron carrier.

Electron carriers function to carry electrons around the cell. It is these NADH molecules that are used to transport electrons to the ETC (Step 3).

This extraction of ATP and electrons turns the 3-C molecules into pyruvate (pyruvic acid).

In basic terms, glycolysis turns glucose into 2 pyruvate.

But, it also makes some ATP and and NADH.

Staring with one glucose molecule at the beginning, by the end of glycolysis, the following have been produced:
  • 2 pyruvate (2 pyruvic acid)
  • 2 NADH
  • 2 ATP (2 where used up and 4 were created, so you end up with a net gain of 2, because math. )


During glycolysis, 2 ATP molecules are used. However, by the end of the process, 4 ATP molecules are created. So, if you lose 2 but gain 4, there is a net gain of +2 ATP.



What happens after glycolysis?


Normally, your body uses oxygen after glycolysis to go on to the Krebs Cycle. However, when oxygen is not available, your body resorts to fermentation.


Fermentation

Since fermentation happens in the absence of oxygen, is it aerobic or anaerobic?

Since fermentation happens when no oxygen is available, that makes this process anaerobic. Considering it does not require oxygen, this also happens in the cytoplasm of the cell. If a process is anaerobic, it will happen in the cytoplasm.

But… why? Why is this a thing?

In order for an organism to survive, it needs energy. The goal of fermentation is to keep glycolysis going so your body can still get at least 2 ATP because you have no other source of ATP without oxygen.

To do this, fermentation converts NADH back into NAD+ so that glycolysis can start again in order to produce those 2 ATP. 

If the NADH molecules cannot go to the ETC, then they are essentially useless. So, your body finds a use for them.

There are 2 main types of fermentation in nature:
  • Alcoholic - occurs in bacteria and yeast
  • Lactic acid - occurs in humans (animals)
In humans, the lactic acid pathway provides your body with small amounts of ATP during intense exercise. Remember, this is anaerobic, so it happens when your muscles’ oxygen demand is greater than the oxygen supply.

So, if skeletal muscles are used (such as during vigorous exercise) when there is not enough oxygen, they produce lactic acid instead of carbon dioxide.

Because this process only produces 2 ATP, this cannot keep you going for a long time.

As this pathway continues, lactic acid builds up in the body. This gives you a burning sensation and can cause nausea and vomiting.

Um… I suppose there must be some way to get rid of lactic acid build up?

To get rid of this lactic acid buildup, you simply need to rest and breathe.