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TEAS Test Questions on the Action of Enzymes

In looking through sample TEAS test questions to address for my pre-nursing students I came across these two, both on the topic of enzyme action:

Image

An enzyme processing a substrate A + B –> AB

 

1. Which of the following statements about enzymes is not true?

A. Enzymes are catalysts. 
B. Almost all enzymes are proteins. 
C. Enzymes operate most efficiently at optimum pH. 
D. Enzymes are destroyed during chemical reactions.

2. Which of the following is considered a model for enzyme action?

A. Lock and Key model 
B. Enzyme interaction model 
C. Transformation model 
D. Transcription model

Enzyme action is key to cell survival, indeed, it is the basis of all that a cell does.  Conventiently, Question #1 help define exactly what an enzyme is.

Which of the following statements about enzymes is not true?

Before answering the question, I have to stop and remind test-takers to read carefully. If I were to get this question, the first thing I would do is underline, box, or otherwise note the word ‘NOT’ so that it is clearly obvious and I will not later come back and ‘read through’ this word. Even if I can answer the question easily, I would still mark this. So, restated:

Which of the following statements about enzymes is NOT true?

Instead of a multiple-choice question, this should be approached as a series of T/F questions. I wouldn’t actually re-write these (the object is not to make more work for you, but, to make your questions clear)

  1. A.     Enzymes are catalysts. 


True –  An enzyme is a catalyst. The clearest definition of what an enzyme is, is… ‘Enzymes act as biological catalysts.’ To further emphasize this, let’s define a catalyst by skipping down to ‘D’.

D. Enzymes are destroyed during chemical reactions

False – A catalyst is defined as a substance that takes part in a reaction, but is not consumed (altered / changed) by the reaction. Therefore, if enzymes are catalysts, then this must be false. You could stop here, but just to be sure, I always read through the other answers to make sure that there is no other answer that also appears true.

B.     Almost all enzymes are proteins.

  1. Image

Well…. I have a difficult time with this one. ‘Almost’ is not the kind of word you want to see in a question like this. Many enzymes are proteins, but many are also ribozymes, meaning enzymes composed of RNA. The ribosome is an excellent example of a ribozyme, consisting of mostly rRNA and a small protein component as well.

Luckily, we have already seen that ‘D’ is clearly false, while this is merely a questionable answer.


C. Enzymes operate most efficiently at optimum pH. 


Image

Each enzyme may have its own optimal conditions

True – Enzymes, like all molecules, will have an optimal pH. This is because pH changes will result in changes in how a molecule folds. As I have mentioned many times before, ‘Form Dictates Function’ – if a molecule folds correctly, it will function correctly.; if it folds incorrectly, then it will (almost always) function incorrectly, or not at all.

Which of the following statements about enzymes is NOT true?

D. Enzymes are destroyed during chemical reactions

Next question…

2. Which of the following is considered a model for enzyme action?

A. Lock and Key model 
B. Enzyme interaction model 
C. Transformation model 
D. Transcription model

A.           Lock and Key model 
Image

The lock and key model describes how an enzyme and its substrate fit together precisely as a key fits a lock. This analogy describes both the precision of the fit as well as the specificity a key has for its lock.

 B.              Enzyme interaction model 


These are just words. They sound right, but that’s as far as it goes.

C.           Transformation model

Again, these are just words. In this case, not even the right words. ‘Transformation’ refers to either the transfer of DNA into a cell (as with plasmid DNA into a bacteria) or the mutation of DNA in a cell such that it ‘transforms’ into a cancer cell.


D. Transcription model

            ‘Transcription’ refers to the copying of genetic information from DNA to RNA as in the central dogma.

 

 
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Posted by on January 1, 2014 in Uncategorized

 

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DNA –> RNA –> Protein (in greater detail)

I emphasize the importance of ‘the central dogma’Image pretty regularly throughout the semester in General Biology. This idea represents one of the core theories of biology and helps to explain an enormous amount about life. This ‘dogma’ explains how the information contained in DNA is replicated prior to cell division – and used to make drafts of that information (RNA) that can guide the construction of proteins that get the work of the cell done.

In the current unit, we are expanding this theory and examining the processes and the molecules they create more closely. Fortunately, each of these processes is elegantly illustrated in a set of animations available on the HHMI website.

The first video presents a model of replication. The model (as shown) is correct in its idea, but is not intended to be a model of HOW replication occurs, only how, in the words of Watson and Crick, “… [T]he specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”

http://www.hhmi.org/biointeractive/media/DNAi_replication_schematic-lg.mov

The actual mechanism of DNA replication is complicated by the anti-parallel arrangement of the paired DNA strands and the fact that DNA Polymerase, the enzyme responsible for copying the DNA, can work only in one direction.

The action of the DNA polymerase, along with some additional enzymes (Helicase and Ligase) is illustrated mechanistically in the following animation:

http://www.hhmi.org/biointeractive/media/DNAi_replication_vo2-lg.mov

Screen Shot 2013-04-30 at 6.36.15 PMOnce DNA is replicated, during S Phase of the cell cycle, the cell is ready to divide and provide one complete copy of the DNA to each of the two daughter cells. In this way, DNA replication allows for the continuity of genetic information from one generation (of cells or whole organisms) to the next.

Throughout the cell’s life, it is necessary to produce proteins to accomplish the work of that particular cell. Again, the information contained in the DNA is copied, this time to a messenger RNA (mRNA) strand, and the instructions to make the protein are carried into the cytoplasm. This process, called Transcription, is carried out primarily by the enzyme, RNA polymerase, as illustrated below:

http://www.hhmi.org/biointeractive/media/DNAi_transcription_vo2-lg.mov

Once an mRNA is constructed, it is transported from the nucleus (where the DNA resides) into the cytoplasm. There, a Ribosome will coordinate the recruitment of transfer RNAs (tRNA) bearing specific Amino Acid building blocks called for to synthesize the protein. This process, called translation, is illustrated by HHMI below:

http://www.hhmi.org/biointeractive/media/DNAi_translation_vo2-lg.mov

 
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Posted by on April 29, 2013 in Uncategorized

 

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This week in General Bio

This week we are studying the cell.

We have already discussed the importance of the cell in defining life (The Cell Theory) and talked about why this is a meaningful definition of life. I also spent a little time discussing viruses and how they defy this definition, but are often included or excluded depending upon the view or purpose of the investigator / student. (i.e. Viruses fail to be alive if the Cell Theory is used as the definition, but they are often considered alive by microbiologists for the purpose of classification, discussion of evolution, etc).

We began by recalling when in history people first realized that there was a microscopic world existing at all. This led into a talk about classification and how life falls into two major groups of cells, Prokaryotic and Eukaryotic. There are a number of key differences between these types of  cells, but I focus on just a few: 

1. Prokaryotic cells tend to be smaller

2. Prokaryotic cells have closed circles of DNA, Eukaryotic cells have linear chromosomes

3. Prokaryotic and Eukaryotic ribosomes are different from one another

4. Prokaryotic cells lack membrane-bound organelles (most notably, the nucleus)

We discussed other features, but I think these are the hallmark differences. Prokaryotic cells span two domains of life, the bacteria (which I tend to focus on) and the archae (which are more ancient and often extremophiles). Eukaryotic cells fall into four kingdoms: animalia, plantae, fungi and protista. With a quick discussion about some differences between these groups, I shelved all but animals and said that this was the group we would focus on for the remainder of the semester (with some exceptions such as photosynthesis).

What makes these four kingdoms similar is their Eukaryotic cell type. As I stated above, one feature of Eukaryotic cells is their membrane-bound organelles. These organelles are how the cell divies up its many tasks into separate functions and gets each of them done by some specific structure. In addition to discussing true organelles, we also discussed other structures and their functions (Ribosomes, plasma membranes, cytoplasm, cytoskeleton)

We finished up Tuesday’s class after just introducing all of the players. Today we will be putting some of them together to show how they function as parts of a larger organization. The three things I have in mind to walk through are: 

1. Energy Pathway – how solar energy gets converted into chemical energy, how that energy is stored (not getting into this part much) and then how that energy is brought back out and converted into a more usable form (ATP) that is put to work to make cells do things.

2. The Central Dogma – fleshed out this time with names of some of the processes. Initially focusing on how information is transformed into something that can actually do work (proteins). Then discussing how these proteins are made in a little more detail (cytoplasmic vs secretory proteins). This lets us talk about the ER, Golgi, Ribosomes and even ends with exocytosis.

3. Phagocytosis – I’m an immunologist, so I think about how macrophages attack cells and other foreign particles all the time. This is a good way to reverse the process of exocytosis and talk about endocytosis. Following endocytosis, we can then bring lysosomes and peroxisomes into play and discuss how they function to break down these ‘non-self’ items so that they become harmless (I’ll end by quickly tying this into the immune system’s antigen display mechanism – but without any detail).

That may be enough for them today. Depending upon questions, things can either go much quicker or drag out for the balance of the class. I expect that we will finish this material with enough time to at least get started with the next chapter – membranes. I like this chapter anyway and I think it’s the chapter that puts the students into the ‘mind’ of the cell the best. If you focus on a membrane and how it handles transport and diffusion, you are zoomed in so close, that suddenly, the cell feels large and familiar.

Lastly, I am really hoping to find an great animation of cellular processes that made the email loop of Penn a couple years ago. Cross your fingers – I have no idea where I might get a copy.

 
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Posted by on September 6, 2012 in Uncategorized

 

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