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23 Nov 2019

In eucaryotic cells, disulfide bonds do not form in the cytosol. However, keratin intermediate filaments in the skin or in the hair are cross-linked by disulfide bonds. How can the disulfide bonds form in the keratin filaments? (In the perming of hair, the disulfide bonds in hair keratins are disrupted by reducing compounds. Then, the hair is styled in a desired shape and heat dried. In this process, new disulfide bonds are formed by oxidation that maintains the hairstyle.)

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Related questions

16.Globular proteins fold up into compact, spherical structures that have uneven surfaces. They tend to form

multisubunit complexes, which also have a rounded shape. Fibrous proteins, in contrast, span relatively large

distances within the cell and in the extracellular space. Which protein is not classified as a fibrous protein?

(a)elastase (b)collagen (c)keratin (d)elastin

17.You have two purified samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a

single amino acid substitution. When washed through the same gel-filtration column, mutant protein Y runs through

the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely

to explain this result?

(a)the loss of a binding site on the mutant protein surface through which protein Y normally forms dimers

(b)a change that results in the mutant proteinâs acquiring an overall positive instead of a negative charge

(c)a change that results in the mutant proteinâs being larger than the wild-type protein

(d)a change that results in the mutant proteinâs having a slightly different shape from the wild-type protein

18.Which of the following statements is true?

(a)Disulfide bonds are formed by the cross-linking of methionine residues.

(b)Disulfide bonds are formed mainly in proteins that are retained within the cytosol.

(c)Disulfide bonds stabilize but do not change a proteinâs final conformation.

(d)Agents such as mercaptoethanol can break disulfide bonds through oxidation.

19.Proteins bind selectively to small molecule targets called ligands. The selection of one ligand out of a mixture of

possible ligands depends on the number of weak, noncovalent interactions in the proteinâs ligand-binding site. Where

is the binding site typically located in the protein structure?

(a)on the surface of the protein (b)inside a cavity on the protein surface

(c)buried in the interior of the protein (d)forms on the surface of the protein in the presence of ligand

thanks

__________ are fairly small organelles that provide a safe place within the cell to carry out certain biochemical reactions that generate harmful, highly reactive oxygen species. These chemicals are both generated and broken down in the same location.

Lysosomes

Endosomes

Peroxisomes

Nucleosomes

Biologists cannot possibly study all living species. Instead, they try to understand cell behavior by studying a select subset of them. Which of the following characteristics are useful in an organism chosen for use as a model in laboratory studies?

rapid rate of reproduction

all of the above

ability to grow under controlled conditions

amenability to genetic manipulation

By definition, prokaryotic cells do not possess __________.

ribosomes.

a nucleus.

membrane bilayers.

replication machinery.

Cell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both standard fluorescence microscopy and confocal microscopy to observe specific details in the cell. Even though fluorescence permits better visualization, the resolving power is essentially the same as that of a standard light microscope because the resolving power of a microscope is limited by the __________ of light.

intensity

absorption

wavelength

filtering

Choose the phrase that best completes this sentence: Microtubules ____________ and are required to pull duplicated chromosomes to opposite poles of dividing cells.

generate contractile forces

can rapidly reorganize

are found in especially large numbers in muscle cells

are intermediate in thickness

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cell division

cell motility

vesicle transport

membrane support

DNA and RNA are different types of nucleic acid polymer. Which of the following is true of DNA but not true of RNA?

It contains thymine.

It has 5'-to-3' directionality.

It is single-stranded.

It contains uracil.

Double covalent bonds are both shorter and stronger than single covalent bonds, but they also limit the geometry of the molecule because they ____________________.

prevent additional bonds from being formed with the bonded atoms.

limit the rotation of the bonded atoms.

create a new arrangement of electron shells.

change the reactivity of the bonded atoms.

Drosophila melanogaster is a/an __________. This type of animal is the most abundant of all animal species, making it an appropriate choice as an experimental model.

mammal

amphibian

bird

insect

10.

If the isotope 32S has 16 protons and 16 neutrons, how many protons, neutrons, and electrons will the isotope 35S have, respectively?

16, 19, 17

16, 19, 15

16, 19, 16

16, 20, 15

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Living systems are incredibly diverse in size, shape, environment, and behavior. It is estimated that there are between 10 million and 100 million different species. Despite this wide variety of organisms, it remains difficult to define what it means to say something is alive. Which of the following can be described as the smallest living unit?

cell

organelle

protein

DNA

12.

Macromolecules in the cell can often interact transiently as a result of noncovalent interactions. These weak interactions also produce stable, highly specific interactions between molecules. Which of the factors below is the most significant in determining whether the interaction will be transient or stable?

the concentration of each molecule

the size of each molecule

surface complementarity between molecules

the rate of synthesis

13.

Many of the mechanisms that cells use for maintenance and reproduction were first studied at the molecular level in bacteria. Which bacterial species had a central role in advancing the field of molecular biology?

E. coli

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cholesterol

isoprene

triacylglycerol

palmitic acid

15.

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anaerobes.

viruses.

parasites.

endosymbionts.

16.

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17.

Polar covalent bonds are formed when the electrons in the bond are not shared equally between the two nuclei. Which one of these molecules contains polar bonds?