Use the following key to answer questions 1-8. 1 & 2 are correct. & 2 are incorr

Question

Use the following key to answer questions 1-8. 1 & 2 are correct. & 2 are incorrect. 1) Cell membranes 1. contain both lipids and proteins. phosphatidylserine) from organelle to organelle. 2. vary in specific composition (eg 20 Peripheral membrane proteins constituents nucleic acids. membrane. 1. are covalently bound to membrane such as are embedded in the cell 2. contain a-helical regions of secondary structure that 3) Fluid mosaic model anchored cytoplasmic components readily move laterally 1. lipids and proteins that a not to within their lipid layer. two leaflets of the lipid bilayer. 2. lipids and proteins readily "flip-flop" between the 4) Simple diffusion of molecules across cell membranes 1. is an endergonic process (requires an input of concentration. 2. molecules move from an area of high concentration to low ATPase Pump 1. hydrolyzes ATP 2. actively transports Nat into and K out of the cell. 6) Endocytosis 1. may be receptor mediated. molecules by invagination and budding of the cell 2. would include internalization of food membrane to form intracellular vesicles. Water moves out of a cell via osmosis if A. the concentration of water is higher inside the cell B. the solute concentration is higher outside the cell 80 Active transport 1. requires an energy source such as ATP either directly or indirectly 2. active movement of solutes from an area of high concentration to an area o low concentration. ***Select the best answer (questions 9-24) likely 9. In the lists of molecules below, select the list that correctly orders the molecules from most across cell membranes to least likely to diffuse across cell membranes, via simple diffusion. A. H20, O2, CO2 B. N2, H2O, ATP D Glucose, ATP, CO2 E. Na ATP, H20

Explanation / Answer

1) C Both are correct.The cell membrane is primarily composed of a mix of proteins and lipids. lipids help to give membranes their flexibility, proteins monitor and maintain the cell's chemical climate and assist in the transfer of molecules across the membrane.Phosphatidylserine  is a phospholipid and is a component of the cell membrane. It plays a key role in cell cycle signaling and apoptosis.They are actively held facing the inner side of the cell membrane by the enzyme flippase. when a cell undergoes apoptosis, phosphatidylserine is no longer restricted to the cytosolic side by flippase. Instead scramblase catalyzes the rapid exchange of it between the two sides. When the phosphatidylserines flip to the outer surface of the cell, they act as a signal for macrophages to engulf the cells.

2) B 2 is correct. These proteins are covalently attached to different fatty acid acyl chains on the cytoplasmic side of the cell membrane.Peripheral proteins associate with lipid bilayers irreversibly and can form transmembrane alpha-helical or beta-barrel channels.

3) Phospholipids can be asymmetric through the active translocation of a phospholipid type from one leaflet of the membrane to the other. This process is controlled by flippase and scramblase enzymes.phospholipid molecules can, although they seldom do, migrate from one side of the lipid bilayer to the other (a process known as flip-flop). However, flip-flop might be enhanced by flippase enzymes.

4) B is correct.The simple diffusion of a substance down its concentration gradient is an exergonic process,because energy is not required.Simple diffusion is the movement of substances from high concentration to low concentration.

5) A 1 is correct.The pump, after binding ATP, binds 3 intracellular Na+ ions, and ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP.

The Na+/K+-ATPase enzyme is a solute pump that pumps sodium out of cells while pumping potassium into cells, both against their concentration gradients.

6) C Both are correct. Endocytosis pathways known as receptor-mediated endocytosis.

Macropinocytosis is the invagination of the cell membrane to form a pocket, which then pinches off into the cell to form a vesicle.The vesicle then travels into the cytosol and fuses with other vesicles such as endosomes and lysosomes.The actual budding process a pit is converted to a vesicle, is carried out by clathrin assisted by a set of cytoplasmic proteins, which includes dynamin and adaptors..

7) C both are correct. Solution in which there is a higher concentration of water molecules inside a cell than outside a cell membrane and solute concentration higher outside the cell.

8) A 1 is correct.The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

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