Exam 2-Mamana

An allosteric interaction between a ligand and a protein is one in which

Binding of a molecule to a binding site affects binding properties of another site on the protein

In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by:

Oxygen binding

In the binding of oxygen to hemoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:

Sigmoidal

which of the following is not correct concerning 2,3-diphosphoglycerate (BPG)?

It binds at a distance from the heme groups of hemoglobin

Identify the correct statements regarding the Bohr effect in hemoglobin.

B- The Bohr effect shifts the fractional O2 saturation curve to the right as pH increasesC- The Bohr effect favors O2 release in respiring tissues

Carbon monoxide (CO) is toxic to humans because:

It binds to the Fe in hemoglobin and prevents the binding of O2

Which equation describes correctly the fraction of occupied ligand binding sites (θ) and its value when [L] = Kd?

Θ = [L] / [L] + Kd; θ = 0.5

Which one of the following descriptions is true?

Myosin has six subunits: two heavy and four light chains. The two heavy chains are arranged as extended coiled-coil α-helices (similar to α-keratin) at their carboxyl termini and each has a large globular domain at its amino terminus.

Which of the following steps of the cycle of actin-myosin that leads to muscle contraction is not correct?

None, they are all correct

Which one of the following statements is true of enzyme catalysts?

They lower the activation energy for the conversion of substrate to product

Which of the following statements about a plot of Vo vs. [S] for an enzyme that follows Michaelis-Menten kinetics is false?

At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at a value equal to Km

What is true about the mechanism of an enzymatic reaction involving two substrates?

A double reciprocal plot of the Michaelis-Menten equation with parallel lines corresponds to the double-displacement or Ping-Pong mechanism

Allosteric enzymes:

Usually have more than one polypeptide chain and are regulated by allosteric modulators

The number of structurally different polysaccharides that can be made with 20 different monosaccharides is far greater than the number of different polypeptides that can be made with 20 different amino acids, if both polymers contain an equal number (say 100) of total residues. Why?

Because all peptides are linear, the variability of peptides is limited by the number of different subunits. Polysaccharides can be linear or branched, can be α- or beta-linked, and can be joined 1 → 4, 1 → 3, etc. The number of different ways to arrange 20 different sugars in a branched oligosaccharide is therefore much larger than the number of different ways a peptide could be made with an equal number of residues.

The reference compound for naming D and L isomers of sugars is:

Glyceraldehyde

When two carbohydrates are epimers:

They differ only in the configuration around one carbon atom

Which of the following pairs is interconverted in the process of mutarotation?

α-D-glucose and beta-D-glucose

The basic structure of a proteoglycan consists of a core protein and a:

Glycosaminoglycan

Glycosaminoglycans are linear polymers composed of repeating disaccharide units. One of the two monosaccharides is always __________________.

Either N-acetylglucosamine or N-acetylgalactosamine

Which of the following monosaccharides is not an aldose?

Fructose

When the linear form of glucose cyclizes, the produce is a(n):

Hemiacetal

In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues:

Asparagine, serine, or threonine

D-glucose is called a reducing sugar because it undergoes an oxidation-reduction reaction at the anomeric carbon. One of the products of this reaction is:

D-gluconic acid

The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is

Adenosine

The difference between a ribonucleotide and deoxyribonucleotide is:

A deoxyribonucleotide has an --H instead of an --OH at C-2

Ribofuranose rings in nucleotides can exist in four different puckered conformations. Which of the following options below is a possible puckered conformation of ribose?

C-2' endo

Myoglobin and Hemoglobin have:

Very similar tertiary structures but different primary structures

Kd=1/Kd

The larger Ka the smaller Kd