Practice Exam For Cell Biology

1.

Which of the following statements concerning prokaryotes is TRUE?

A.

They have no nucleus and hence no DNA
B.

They have no Golgi apparatus
C.

They include bacteria, yeast, and protozoans
D.

They are all able to live on inorganic energy sources
E.

Both (b) and (c) are correct

Correct Answer
B. They have no Golgi apparatus

Explanation
Prokaryotes are single-celled organisms that lack a nucleus and other membrane-bound organelles. They have a simple cell structure, with their DNA located in the cytoplasm rather than within a nucleus. The Golgi apparatus is a membrane-bound organelle involved in protein modification and transport, which is absent in prokaryotes. Therefore, the statement that prokaryotes have no Golgi apparatus is true.

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2.

The α helix and β sheet are found in many different proteins because they are formed by

A.

Hydrogen bonding between the amino acid side chains most commonly found in proteins
B.

Noncovalent interactions between amino acid side chains and the polypeptide backbone
C.

Ionic interactions between charged amino acid side chains
D.

Hydrogen bonding between atoms of the polypeptide backbone
E.

Hydrophobic interactions between the many nonpolar amino acids

Correct Answer
D. Hydrogen bonding between atoms of the polypeptide backbone

Explanation
The α helix and β sheet are formed by hydrogen bonding between atoms of the polypeptide backbone. In the α helix, the backbone forms a tightly coiled structure held together by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid, four residues away. In the β sheet, hydrogen bonds form between the carbonyl oxygen of one strand and the amide hydrogen of another strand, creating a sheet-like structure. These hydrogen bonds stabilize the secondary structures of proteins and are responsible for their stability and shape.

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3.

A.

Have conserved amino acid sequences
B.

Have conserved secondary structures
C.

Have similar functions
D.

Have conserved tertiary structures
E.

All of the above

Correct Answer
E. All of the above

Explanation
All of the above options are correct because proteins that have conserved amino acid sequences, conserved secondary structures, conserved tertiary structures, and similar functions are likely to be evolutionarily related. Conserved amino acid sequences indicate that these proteins have similar building blocks, which suggests a common ancestry. Conserved secondary structures and tertiary structures imply that these proteins have similar folding patterns, further supporting their evolutionary relationship. Additionally, proteins with similar functions are likely to have similar structures and sequences, as their function is determined by their structure. Therefore, all of the above options are valid explanations for the given answer.

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4.

Enzymes catalyze a chemical reaction by the activation energy, because they provide conditions favorable for the formation of a intermediate called the __ .

A.

Lowering; high-energy; transition state
B.

Increasing; high-energy; transition state
C.

Lowering; low-energy; transition state
D.

Increasing; low-energy; alternative state
E.

Lowering; high-energy; alternative state

Correct Answer
A. Lowering; high-energy; transition state

Explanation
Enzymes catalyze a chemical reaction by lowering the activation energy, which is the energy required to start the reaction. By lowering the activation energy, enzymes make it easier for the reactant molecules to reach the transition state, which is a high-energy intermediate that forms during the reaction. This transition state is crucial for the formation of the final product. Therefore, enzymes provide conditions favorable for the formation of this high-energy transition state, ultimately speeding up the reaction.

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5.

RNA in cells differ from DNA in that

A.

It contains the base uracil, which preferentially pairs with cytosine.
B.

It is single-stranded and cannot form base pairs.
C.

It is single stranded can can fold up into a variety of structures.
D.

The nucleotides are linked together in different way
E.

The sugar ribose contains fewer oxygen atoms than does deoxyribose

Correct Answer
C. It is single stranded can can fold up into a variety of structures.

Explanation
RNA in cells differ from DNA in that it is single stranded and can fold up into a variety of structures. Unlike DNA, which is typically double stranded, RNA exists as a single strand. This single-stranded nature allows RNA molecules to fold upon themselves and form intricate secondary and tertiary structures. These structures are crucial for RNA's various functions, such as catalyzing chemical reactions, regulating gene expression, and serving as a template for protein synthesis.

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6.

Which of the following statements about the genetic code are correct?

A.

One codon specifies more than one amino acid
B.

The genetic code consists of 64 codons
C.

All amino acids are specified by more than one codon
D.

The genetic code is different in prokaryotes and eukaryotes
E.

All codons specify an amino acid

Correct Answer
B. The genetic code consists of 64 codons

Explanation
The genetic code consists of 64 codons. This means that there are 64 different combinations of three nucleotides (A, T, G, and C) that can specify an amino acid or serve as stop signals. Each codon codes for a specific amino acid or a stop signal, allowing the correct sequence of amino acids to be determined during protein synthesis.

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7.

K_M is a measure of

A.

Substrate affinity of an enzyme
B.

Enzyme performance
C.

Catalytic rate of an enzyme
D.

Ratio of [enzyme-substrate complex] to[unbound enzyme][unbound substrate]
E.

Rate of enzyme degradation

Correct Answer
B. Enzyme performance

Explanation
The correct answer is "enzyme performance." KM, or Michaelis constant, is a measure of how well an enzyme performs in converting substrate into product. It represents the concentration of substrate at which the enzyme is working at half of its maximum velocity. A lower KM value indicates a higher affinity between the enzyme and substrate, resulting in better enzyme performance.

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8.

What is an example of a GTP-binding protein?

A.

Lysozyme
B.

Ef-Tu
C.

Myosin head
D.

M-phase promoting factor (MPF)
E.

Hemoglobin

Correct Answer
B. Ef-Tu

Explanation
Ef-Tu is an example of a GTP-binding protein. GTP-binding proteins, also known as G proteins, are involved in various cellular processes, including signal transduction and protein synthesis. Ef-Tu specifically plays a crucial role in protein synthesis by delivering aminoacyl-tRNA molecules to the ribosome during translation. It binds to GTP and undergoes conformational changes, allowing it to interact with other components of the translation machinery. Therefore, Ef-Tu is a prime example of a GTP-binding protein due to its involvement in protein synthesis and its ability to bind to GTP.

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9.

What are ways in which proteins can be regulated?

A.

Allosteric regulation
B.

Feedback regulation
C.

GTP-binding
D.

ATP-binding
E.

All of the above

Correct Answer
E. All of the above

Explanation
Proteins can be regulated through various mechanisms such as allosteric regulation, feedback regulation, GTP-binding, and ATP-binding. Allosteric regulation involves the binding of a molecule to a site on the protein, which causes a conformational change and alters its activity. Feedback regulation occurs when the end product of a metabolic pathway inhibits an earlier step in the pathway. GTP-binding and ATP-binding are examples of proteins binding to these nucleotides, which can regulate their activity. Therefore, all of the mentioned options are ways in which proteins can be regulated.

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Practice Exam For Cell Biology

Which of the following statements concerning prokaryotes is TRUE?

The α helix and β sheet are found in many different proteins because they are formed by

Enzymes catalyze a chemical reaction by __________ the activation energy, because they provide conditions favorable for the formation of a __________ intermediate called the __________ .

RNA in cells differ from DNA in that

Which of the following statements about the genetic code are correct?

KM is a measure of

What is an example of a GTP-binding protein?

What are ways in which proteins can be regulated?

Enzymes catalyze a chemical reaction by the activation energy, because they provide conditions favorable for the formation of a intermediate called the __ .

K_M is a measure of