BIOL1406 Lecture Week 4

Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements. -Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. -The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. -The diverse proteins found in and attached to membranes perform many important functions. -The kinky tails of some proteins help keep the membrane fluid by preventing the component molecules from packing solidly together. -Membranes include a mosaic, or mix, of carbohydrates embedded in a phospholipid bilayer.

-Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. -The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. -The diverse proteins found in and attached to membranes perform many important functions.

How many electron pairs does carbon share to complete its valence shell? -2 -3 -4 -8

4

Which of the following statements about osmosis is correct? -Osmotic movement of water into a cell would likely occur if the cell accumulates water from its environment. -If a cell is placed in an isotonic solution, more water will enter the cell than leaves the cell. -The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis. -If a solution outside the cell is hypertonic compared to the cytoplasm, water will move into the cell by osmosis. -Osmosis is the diffusion of water from a region of lower water concentration to a region of higher water concentration.

The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.

In facilitated diffusion, what is the role of the transport protein? -Transport proteins provide a hydrophilic route for the solute to cross the membrane. -Transport proteins organize the phospholipids to allow the solute to cross the membrane. -Transport proteins provide the energy for diffusion of the solute. -Transport proteins provide a low-resistance channel for water molecules to cross the membrane. -Transport proteins provide a protein site for ATP hydrolysis, which facilitates the movement of a solute across a membrane.

Transport proteins provide a hydrophilic route for the solute to cross the membrane.

Which of the following molecular movements is due to diffusion or osmosis? -The sodium-potassium pump pumps three sodium ions out of a neuron for every two potassium ions it pumps in. -Cells of the pancreas secrete insulin into the bloodstream. -When a plant cell is placed in concentrated salt water, water moves out of the cell.

When a plant cell is placed in concentrated salt water, water moves out of the cell.

According to the fluid mosaic model of cell membranes, phospholipids _____. -frequently flip-flop from one side of the membrane to the other -occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane -have hydrophilic tails in the interior of the membrane -can move laterally along the plane of the membrane

can move laterally along the plane of the membrane

The element present in all organic molecules is _____. -oxygen -hydrogen -nitrogen -carbon

carbon

Which two functional groups are always found in amino acids? -amino and sulfhydryl groups -hydroxyl and carboxyl groups -carbonyl and amino groups -carboxyl and amino groups

carboxyl and amino groups

A carbon atom is most likely to form what kind of bond(s) with other atoms? -ionic bonds, covalent bonds, and hydrogen bonds -ionic -covalent -hydrogen

covalent

Most organic compounds contain carbon and _____. -phosphate -oxygen -hydrogen -sulfur

hydrogen

Molecules that have the same chemical formula (same numbers of each atom) but different three-dimensional shapes are called _____. -hydrocarbons -isomers -functional groups -enantiomers -isotopes

isomers

White blood cells engulf bacteria using _____. -phagocytosis -receptor-mediated exocytosis -pinocytosis -osmosis

phagocytosis

Ions diffuse across membranes through specific ion channels down _____. -their electrochemical gradients -their concentration gradients -the electrical gradients -their chemical gradients

their electrochemical gradients

Which of the following best describes the structure of a biological membrane? -two layers of phospholipids (with opposite orientations of the phospholipids in each layer) with each layer covered on the outside with proteins -a fluid structure in which phospholipids and proteins move freely between sides of the membrane -two layers of phospholipids with proteins embedded between the two layers -two layers of phospholipids with proteins either crossing the layers or on the surface of the layers -a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot

two layers of phospholipids with proteins either crossing the layers or on the surface of the layers