Cell Biology – Practice Questions

Biology Tutorial

Cell Biology - Practice Questions

Intro

These questions are meant for beginner students in undergraduate level cell biology. These are review questions based on material in the first four chapters in “Essential Cell Biology” – See link below.

Sample Problem

Question source

1. If you wanted to determine the diameter of the lumen in an endoplasmic reticulum, which type of microscopy would be best?

A) Light microscopy
B) Scanning electron microscopy
C) Transmission electron microscopy
D) No need for microscopy- just look at it

2. Which of the following orders the cytoskeletal elements from thinnest to the thickest, with thinnest on the left?

A) Intermediate filaments, actin filaments, microtubules
B) Microtubules, actin filaments, intermediate filaments
C) Actin filaments, intermediate filaments, microtubules
D) Actin filaments, microtubules, intermediate filaments
E) None of this is real

3. Draw your best representation of the two conformations of β-sheets

4. Which of the following statements is false?

A) Disulfide bonds are formed by the cross linking of cysteine residues
B) Disulfide bonds are formed mainly in proteins in the cytosol
C) Disulfide bonds stabilize but do not change a proteins final conformation
D) Reducing agents such as beta-mercaptoethanol can break disulfide bonds through reduction
E) Disulfide bonds are formed mainly in proteins that are found outside the cell

5. True or False: Phosphatase is an enzyme that adds a phosphate

6. True or False: Many co-enzymes are derived from external sources, such as nicotinamide being derived from the vitamin niacin, due to the fact the humans are not able to synthesize them

7.Bonding between __________________ is what causes secondary structures, such as α-helices and β-sheets to be formed

A) R groups on amino acids
B) C-termini
C) Peptide bonds
D) Side chains of amino acids
E) A and D

8. Which of the following organelles have an inner and outer membrane?

A) Nucleus
B) Mitochondria
C) Endoplasmic Reticulum
D) A and B
E) All of the above

9. Hemoglobin is an example of a protein performing what kind of role?

A) Transport Protein
B) Special Protein
C) Structural Protein
D) Gene Regulation Protein
E) Hemoglobin is a sugar, not a protein

Solution

1. If you wanted to determine the diameter of the lumen in an endoplasmic reticulum, which type of microscopy would be best?

First of all, you must think of the scale of the specimen. The lumen of the ER is inside an organelle, which is inside a cell. IF you can’t see the cell with the naked eye you would absolutely need some form of microscopy to measure the lumen of the ER. Light microscopy differs greatly from electron microscopy, especially at such great magnification (resolution basically means – shortest distance between two points on a specimen that can still be distinguished by the observer or camera system as separate entities). Because excellent resolution is needed to measure something so small, transmission electron microscopy (TEM) is the best option. TEM is a type of microscopy that allows us to see very small structures with a resolution at the nanometer sale (billionth of a meter). Scanning electron microscopy (SEM) also allows us to see these small structures, however SEM is typically used to look at peripheral structures of a cell. TEM generally includes the use of a microtome, which is basically a really fine deli slicer for your specimens. Slicing the tissues allows one to see beyond the outside of the cell. Light microscopy does not work in this instance because we could not get great enough magnification to confidently measure the lumen of the ER.

2. Which of the following orders the cytoskeletal elements from thinnest to the thickest, with thinnest on the left?

The answer here is C (Actin filaments, intermediate filaments, microtubules). Make sure to read the question carefully, as one may look for the “thickest to thinnest” rather than “thinnest to thickest”. These cytoskeletal elements are merely introduced at this point, but in later parts of the course you learn more about their structure and function inside cells. Stay tuned!

3. Draw your best representation of the two conformations of β-sheets

This is a question about protein structure. There are several scales of protein structure. From smallest to greatest, the different levels of protein structure are: primary, secondary, tertiary and quaternary. I encourage you to review the material in Ch 2 for descriptions of each one if you were totally lost in this question. β-sheets are apart of secondary structure in proteins, and they can either be parallel or anti-parallel. There are excellent images in the text book, but they consist of strings of amino acids (the primary structure) called beta strands (also β-strand) connected laterally by at least two or three backbone hydrogen bonds. A β-strand is usually 3 to 10 amino acids long.

4. Which of the following statements is false?

For this question we will take each possible response one-by-one. There is a lot that you need to know to be confident in your response here.

A) Disulfide bonds are formed by the cross linking of cysteine residues

This is a true statement. At this point in the game, you should only commit a few of the amino acids to memory. I would recommend at least methionine and cysteine. Cysteine is special because it has an -SH group that can connect with another -SH group to form a S-S (disulfide bond). Think back to chemistry… what kind of bond is this? This is a covalent bond, which is much stronger than a H-bond (what we typically see in proteins).

B) Disulfide bonds are formed mainly in proteins in the cytosol

This is a false statement, and therefore the correct answer. Remember OIL RIG.

Oxidation Is Loss of electrons Reduction Is Gain of electrons

This is easy to follow if you know that the electrons always bring a negative charge. So why is this relevant? Well the cytosol just happens to be filled with all sorts of reducing agents (such as NADH) that would hinder disulfide bond formation.

Note: Don’t forget that these are oxidation/reduction reactions. When molecule A reduces molecule B, molecule B is also oxidizing molecule A. Think of them as exchanging electrons.

C) Disulfide bonds stabilize but do not change a proteins final conformation

This is a true statement. Disulfide bonds significantly increase the integrity of a protein structure.

D) Reducing agents such as beta-mercaptoethanol can break disulfide bonds through reduction

This is also a correct statement. You do not need to know what beta-mercaptoethanol is to answer this question. Try not to get intimidated by that. The question tells you that it is a reducing agent, and you know that without an oxidizing environment these disulfide bonds will not form (think OIL RIG). Reducing agents like beta-mercaptoethanol are used frequently in biochemistry to specifically break covalent bonds in proteins.

E) Disulfide bonds are formed mainly in proteins that are found outside the cell

This is a correct statement. Antibodies are a classic example of proteins with strong covalent disulfide bonds. They can only maintain such strength outside the cell though (see explanation for answer B)

5. True or False: Phosphatase is an enzyme that adds a phosphate

False. A kinase adds a phosphate group and a phosphatase removes a phosphate group.

6. True or False: Many co-enzymes are derived from external sources, such as nicotinamide being derived from the vitamin niacin, due to the fact the humans are not able to synthesize them

True. A co-enzyme, or cofactor is a non-protein chemical compound (such as niacin) or metallic ion (such as zinc) that is required for a protein’s biological activity to happen. These proteins are commonly enzymes, and cofactors can be considered “helper molecules” that assist in biochemical processes.

7.Bonding between __________________ is what causes secondary structures, such as α-helices and β-sheets to be formed

The answer here is E. For this question you have to know that “side chains” and “R-groups” mean the same thing. An R-group or side chain can be something as simple as a single hydrogen or as complicated as a multiple ringed structure. The R-group/side chain is the only thing that distinguishes amino acids from one another.

8. Which of the following organelles have an inner and outer membrane?

The correct answer is D. The ER does not have an inner and outer membrane, or a bilayer.

9. Hemoglobin is an example of a protein performing what kind of role?

The correct answer here is A. To confidently answer this question you must understand that there are many types of proteins. Hemoglobin is a pretty common protein that is known to transport oxygen throughout the body for respiration to occur. As long as you are aware of that function it should be easy to come up with transport protein. Special proteins are like anti-freeze proteins that prevent frogs from freezing to death over winter. A structural protein could be like a microtubule. A gene regulatory protein example could be the sonic hedgehog protein (yes thats real) which is responsible for several aspect of development.



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