Question

All of the following is true regarding the cell (plasma) membrane Except:

a) It has amphipathic transmembrane protein

b) It contains glycolipids and glycoproteins

c) it has large pores to accommodate RNA movement in and out of the cell

d) the proteins can float in the membrane

e) cholesterol is in the membrane to increase the membrane’s fluidity

2) If you want to form protein from individual amino acids, you would

a) dephosphorylate the amino acids

b) use a negative feedback loop

c) add water between the adjacent amino acids

d) phosphorylate the amino acids

e) remove water from between adjacent amino acids

Answer 1

1.ans) option C-It has large pores to accommodate RNA movement in and out of the cell.

Explanation - As plasma membrane is bi-lipid layer and semi-permeable. It allows hydrophobic and some polar compounds in and out of the cell through the pores.

Plasma membrane do not allow large molecules like RNA which contains proteins and amino acids.

RNA is transported across the plasma membrane occurs by two mechanisms - endocytosis (intake of large molecules by the cells) and exocytosis (release of macromolecules from the cells to the outside).

Explanation for other options-

-option A- It has amphipathic(containing both hydrophobic and hydrophilic groups) transmembrane protein. These serve as channels, carriers, pumps and receptors.

Channels allows diffusion of ions and small soluble substances.

Carriers transport materials across the lipid layer.

Pumps actively transport ions across the lipid layer.

Receptors, which when activated initiate intracellular reactions.

Option B- plasma membrane consists of cholesterol, phospholipids, sphingolipids, carbohydrates and proteins.

Carbohydrates and proteins combine to form glycoproteins.

Phospholipids, sphingolipids and carbohydrates combine to form glycolipids.

Option D- As plasma membrane is bi-lipid layer, polar molecules like proteins are embedded and float in the plasma membrane.

Option E- The bimolecular lipid layer in the plasma membrane has the characteristics of a fliud due to presence of cholesterol.

This fluidity makes the membrane quite flexible, thus allows cells to undergo considerable changes in shape without disruption of their structural integrity.

2. ans) option E- remove water molecules from between adjacent amino acids

Explanation - protein are complex molecules built mainly from alpha-amino acid linked together in chains.

The linkage between the amino acids is called peptide bond.

Amino acids consists of amino group, carboxyl group, hydrogen and a side chain.

Peptide formed is between the amino acids by condensation reaction of carboxyl group of one amino acid and amino group of adjacent amino acid with removal of water molecule.

By this way, peptide bond is formed between amino acids,molecules built up from many amino acids are called polypeptides.

Proteins consists of several polypeptide chains, cross linked between specific amino acid units.

Other options are incorrect-

Explanation -

Option A- dephosphorylation of amino acids is removals of phosphate group, so it do not forms the peptide bond.

Option B- As negative feedback loop interrupts formation of mRNA (transcription) and translation process. So, proteins are not formed.

Positive feedback loop activates the transcription and translation process, so proteins are formed.

Option C- As adding water molecules to the amino acids causes hydration of amino acids, which do not forms proteins.

Option D- As phosphorylation of amino acids is addition of phosphate group to the amino acids,which causes some functions.

Example, addition of phosphate group to ADP forms ATP, which is used as energy reserve for muscle contraction.