Biology, 17.03.2020 17:18 rightdimple3692

The cell membrane contains channels and pumps that help move materials from one side to the other. What are these channels and pumps made of?

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Answer from: sierratellman

The correct answer is: Proteins.

Explanation:

The plasma membrane of a cell form a selectively permeable barrier which regulates the flow of molecules, ions and other substances across it from the cell exterior to the cell interior and also from the cell interior to the cell exterior.The lipid bilayer of the plasma membrane is hydrophobic in nature and so it is permeable to diffusion of gases and small non-polar molecules (with which it can form hydrophobic interaction or Van-der-Waals forces of interaction) across it.However, the diffusion of small polar molecules and ions in restricted across the lipid bilayer. This is because these molecules form hydrogen bonds with water molecules and lipid molecules are incapable of forming hydrogen bonds and are water-hating in nature.In order to facilitate the movement of these small polar molecules and ions across the plasma membrane there is a need of proteins which remain integrated in the plasma membrane and form a link between the cell interior and cell exterior.These proteins are amphipathic in nature, that is, they are made up of both polar and non-polar amino acid residues.The non-polar amino acids face towards the lipid molecules in the bilayer thereby forming hydrophobic interactions with the lipid molecules. The polar amino acids face towards the channel or lumen across the lipid bilayer so that they can form hydrogen bonds with the polar molecules and ions which are transported across the plasma membrane. These proteins either form Channels or Pumps.Channel proteins form a continuous linkage in the form of a lumen between the cell interior and cell exterior across the lipid bilayer. However, they open this lumen only in response to the appropriate stimuli. They can remain open or closed, simultaneously, on either side of the membrane.Pumps are made up of carrier proteins which do not form a continuous linkage but form a double-gated linkage in between the cell interior and cell exterior. They cannot remain simultaneously open on either side of the membrane. When they open in the cell interior, they remain closed in the cell exterior and when they open in the cell exterior they remain closed in the cell interior. Their opening and closing is also regulated by appropriate stimuli.

Answer from: Quest

The awnser is b i believe

Answer from: Quest

the african cheetah.

this species has a relatively low level of genetic

variation because the population was reduced to a small size approxi-

mately 10,000 to 12,000 years ago.

chapter outline

24.1

genes in populations and the hardy-

weinberg equation

24.2

factors that change allele and genotype

frequencies in populations

24.3 sources of new genetic variation

population genetics

until now, we have primarily focused our attention on genes

within individuals and their related family members. in this

chapter and chapters 25 and 26 , we turn to the study of genes in

a population or species. the field of

population genetics

is con-

cerned with changes in genetic variation within a group of indi-

viduals over time. population geneticists want to know the extent

of genetic variation within populations, why it exists, and how it

changes over the course of many generations. the field of popu-

lation genetics emerged as a branch of genetics in the 1920s and

1930s. its mathematical foundations were developed by theoreti-

cians who extended the principles of gregor mendel and charles

darwin by deriving formulas to explain the occurrence of geno-

types within populations. these foundations can be largely attrib-

uted to three scientists: sir ronald fisher, sewall wright, and j. b. s.

haldane. as we will see, support for their mathematical theories

was provided by several researchers who analyzed the genetic com-

position of natural and experimental populations. more recently,

population geneticists have used techniques to probe genetic

variation at the molecular level. in addition, staggering advances

in computer technology have aided population geneticists in the

analysis of their genetic theories and data. in this chapter, we will

explore the genetic variation that occurs in populations and con-

sider the reasons why the genetic composition of populations may

change over the course of several generations

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