BME Exam 2 iClicker

Protein A has a binding site for ligand L with a Ka of 10^5 M–1. Protein B has a binding site for ligand L with a Ka of 10^8 M–1. Which protein has the higher affinity for ligand L?

Protein B

Protein A has a Ka = 6.0 μM–1 for binding ligand L, and the protein B has a Kd = 4.0 μM for binding ligand L. Based on this information, which statement is true?

The Ka of protein B for L is 0.25 μM–1

When the partial pressure of oxygen is equal to the P50 of myoglobin, what is the value of Y?

0.50

A newly discovered protein has multiple subunits, each with a single ligand-binding site. Binding of ligand to one site increases the binding affinity of other sites for the ligand. The Hill coefficient (nH) is

Greater than 1

Which biochemical principle is NOT true of immunoglobulins as examples of protein structure and function?

Because the antigen-binding domain has high affinity, there is no observed induced fit.

The molecular structure for which an individual antibody or T-cell receptor is specific is known as?

an epitope.

Polyclonal antibodies?

are used as analytic reagents in Western blot assays.

Which statement is false?

T lymphocytes produce immunoglobulins.

Which biochemical structure is NOT present in myosin

 a prosthetic group

Thin filaments?

assemble as successive monomeric actin molecules add to one end.

Which of the major proteins involved in muscle contraction hydrolyzes ATP?

myosin

An apoenzyme?

requires a cofactor for its activity

The conversion of sucrose to CO2 and water has a very large and negative ∆G′°. Why is the conversion NOT spontaneous?

There is a very large activation energy barrier.

How does the concept of “induced fit” support the current theory of substrate-enzyme interaction?

Enzyme conformation changes allow additional stabilizing interactions with the transition state and enhance the activity.

For a specific enzyme/substrate system, which condition will ALWAYS result in an increase in V0 (assuming nothing else changes)?

a decrease in Km and an increase in Vmax

If a first-order reaction for the unimolar reaction S → P has a rate constant k of 0.05 s–1, how is this interpreted qualitatively?

5% of the available S will be converted to P in 1 second.

Competitive inhibitors?

occupy the active site to exclude the substrate.

Which statement is false for an uncompetitive inhibitor?

Uncompetitive inhibitors affect the apparent Km, but not the Vmax.

Which statement is true about both mixed inhibitors and uncompetitive inhibitors?

Both inhibitors can bind to the enzyme-substrate complex. 

Which type of inhibitor binds to the active site of an enzyme and undergoes the initial steps of the reaction before combining irreversibly with the enzyme?

suicide inactivators 

Why is DNA more stable than RNA?

The 2′-hydroxyl groups in RNA (absent in DNA) are directly involved in the hydrolysis of oligonucleotides. 

In a sample of DNA isolated from an unidentified species of bacteria, adenine makes up 28% of the total bases. Which statement is false about the relative proportions of the bases in the DNA sample?

The DNA must contain 28% C. 

Which statement regarding bases in DNA is false?

Pyrimidines are aromatic; purines are not. 

A graduate student carefully heated DNA to about 80 °C and then prepared it for electron microscopy. She observed several small open loops of DNA. What conclusion did she CORRECTLY make from her observation?

The open loops contain DNA with a high A-T content. 

Which statement regarding mRNA is false?

It is always monocistronic. 

Which statement is false regarding a solution of DNA subjected to extremes of pH?

Covalent bonds in the DNA will be broken. 

The process of separating strands of a DNA double helix is known as?  

Denaturation

Which nucleoside is the one MOST commonly found as part of coenzymes?  

Adenosine

A gene can be defined as a segment of DNA that codes for?

A functional product 

1. All of the following are components of a gene EXCEPT? 

RNA

What would be the consequence(s) if all the DNA in the human genome coded for proteins?

There would be enough genes to code for approximately 10,000,000 proteins. 

What is a major difference between prokaryotic genes and eukaryotic genes?

Prokaryotic genes lack introns. 

Which of the following is the most likely explanation for the presence of different B-like globin genes?

Unequal crossing over 

A gene family is a?

set of related but slightly different genes present in one individual 

Synthesis of different proteins from the same gene is due to?

alternative splicing 

DNA polymerase in eukaryotes are used to?

Replicate DNA 

What role does primase play in DNA replication?

Primase synthesizes the RNA primer needed to initiate synthesis of Okazaki fragments 

Which of the following is TRUE of DNA replication?

Synthesis of the leading and lagging strands occurs concurrently 

What prevents RNA nucleotides from becoming incorporated into a growing DNA strand?

DNA polymerase discriminates against nucleotides containing the ribose sugar 

Which of the following are methods of DNA repair?

Base excision, Mismatch excision, homologous recombination, nonhomologous end joining  

Which type of DNA damage is considered the most deleterious to the stability of the genome?

Double-stranded breaks  

Antibody diversity relies on both gene rearrangement and?

Post-transcriptional RNA splicing 

1. Does gene rearrangemnet happen before or after transcription?  

1. Before

E. coli RNA polymerase differs from E. Coli DNA polymerase in that?

It does not need a primer sequence to initiation reading

The promoter sequence is transcribed first, followed by the DNA of the gene?

False

A segment of DNA template strand has the following sequence: 3'-T A C A T G G C C A T G T A C -5' Which of the following is the correct mRNA transcript?

C. 5'-A U G U A C C G G U A C A U G -3'

The sigma subunits is of the proper size to?

Span between and bind to both the -35 and -10 promoter elements

RNA editing can be the result of insertion/deletion editing. This results in?

Changes to the mRNA sequence after transcription

In order for a molecule of RNA to be self-splicing it must? Contain an intrinsic with ribozyme activity

Contain an intrinsic with ribozyme activity

Mammalian mRNAs have different lifetimes, ranging from less than 30 minutes to approximately 20 hours. This is a form of regulation of gene expression. One would expect the shorter -lived mRNAs to code for?

Regulatory proteins

The statement that the genetic code is degenerate but not ambiguous refers to which of the following?

Each amino acid can be specified by more than one codon, but one codon cannot specific more than one amino acid.

A particular triplet of bases in the codon of mRNA 5’-UUC-3’. What is the anticodon that binds this mRNA?

3’-AAG’5’

Chain elongation in eukaryotes occurs at which site of the ribosome?

A site

Ribosomes in bacteria, archaea, and eukaryotes are composed of?

rRNA

The three stop codons each specific a different amino acid?

False

Why is the lac operon under transcriptional regulation?

Transcriptional regulation allows the cell to economize by not investing energy in the synthesis of unnecessary mRNAs and proteins.

Discuss a potential answer to the “Lactose Paradox”: If lactose is needed to induce the synthesis of the lactose permease, which is needed for the cell to take up lactose, how does lactose get into an E. coli cell to activate the Lac operon?

Occasionally, transcription and translation of the Lac repressor gene generates a defective Lac repressor protein. This defective protein cannot repress the expression of the Lac operon, so a certain number of the permease proteins are always present.

Explain how the lac operon is regulated?

It is regulated by a repressor protein that must be removed from the operator to allow for transcription.

Explain why depressors inhibit but activators stimulate transcription?

Repressors bind to specific DNA sequences and inhibit transcription, while activators bind to downstream elements and stimulate transcription.