Biology Cytology Quiz 1

Front 1

Selective Permeability of the Plasma Membrane

Back 1

~ The plasma membrane is described as selectively permeable since it controls the passage of particles in and out of the cell

~ Particles can pass across depending on:

- Size of the particle

- The concentration gradient of the particle (ie. the difference in concentration of the particle on either side of the membrane)

- Solubility of the particle in the phospholipid bilayer (ie. whether or not a particle can easily pass through the fatty acid tails of the phospholipid bilayer)

Front 2

Particles that cannot easily pass through the fatty acid tails of the plasma membrane

Back 2

~ Polar molecules and Ions are lipid insoluble

Front 3

Mechanisms of Membrane Transport

Back 3

~ Mechanisms by which particles cross membranes can be classified as either passive or active transport.

Front 4

Passive Transport

Back 4

Mechanisms involve the movement of particles through the membrane without the use of energy (ie. No ATP required)

Front 5

Active Transport

Back 5

Mechanisms do require the energy stored in and released by ATP

Front 6

Passive Transport Mechanisms: Simple Diffusion

Back 6

~ The movement of particles from an area of high concentration to an area of low concentration (ie. down the concentration gradient)

~ Continues until equilibrium is reached, the movement in both directions is equal and there is no net movement

~ Energy is not required

~ Relies on the energy of molecular motion. The kinetic energy contained by the particles results in random molecular motion and molecular collision resulting in diffusion

~ Particles diffuse across the plasma membrane through fatty acid tails or protein channels

~ Ex) O2,CO2,N2,Glycerol, Steroids (non-polar, lipid soluble)

Front 7

Factors Affecting the Rate Of Diffusion: Temperature

Back 7

~ The higher the temperature (i.e. the more heat energy), the more kinetic energy the particles will have. This increases particle motion and therefore increases the rate of diffusion.

Front 8

Factors Affecting the Rate Of Diffusion: Particle Size

Back 8

~ At a given temperature, smaller particles move faster than large particles. Thus, for a given temperature, a smaller molecule will diffuse faster than a larger particle due to less resistance/ friction

Front 9

Factors Affecting the Rate Of Diffusion: Concentration Gradient

Back 9

~ Concentration gradient is the difference in concentration of a particular type of particle across the plasma membrane. The greater the concentration gradient, the greater the rate of diffusion.

Front 10

Factors Affecting the Rate Of Diffusion: Density of the Medium

Back 10

~ The medium is the material through which a diffusing particle moves and density refers to how tightly packed the medium particles are.

~ The higher the density of the medium, the greater the resistance to the movement of the diffusing particle.

~ Thus the higher the density of the medium, the slower the rate of diffusion

~ Therefore, particles will diffuse fastest in low density media such as gases and slowest in high density media such as solids

Front 11

Factors Affecting the Rate Of Diffusion

Back 11

1. Temperature

2. Particle Size

3. Concentration Gradient

4. Density of the Medium

Front 12

Passive Transport Mechanisms: Osmosis

Back 12

~ The diffusion of WATER across a selectively permeable membrane

~ During osmosis, water moves from an area of high water concentration to an area of low water concentration

~ Osmosis is passive; does not require energy

~ Water moves across the plasma membrane in two ways:

- Although water is polar, it is small enough to pass through the non polar fatty acid tails of the phospholipids in the bilayer since they are so loosely packed. Water does not cross quickly through the phospholipid bilayer.

- Water moves rapidly and in large quantities through channel proteins called aquaporins. The channels within the protein are hydrophilic

Front 13

Passive Transport Mechanisms: Facilitated Diffusion

Back 13

~ Movement of particles from an area of high concentration to low concentration.

~ Passive; does not require energy

~ Requires the use of specific protein carriers.

-This is a function of integral membrane proteins

~ There are two types of transport proteins: Carrier Proteins, Channel Proteins

~ Ex) Glucose, Amino Acids, Ions (Na+, K+,Ca +2)

Front 14

Passive Transport Mechanisms: Facilitated Diffusion: Carrier Proteins

Back 14

~ Have a specifically shaped binding site that fits only a specifically shaped molecule

~ When the molecule attaches, it causes a subtle change in the three dimensional shape of the transport protein that allows the binding and release of the molecule

~ A carrier protein can move the molecule in either direction. The direction of transport depends on the concentration gradient.

Front 15

Passive Transport Mechanisms: Facilitated Diffusion: Channel Proteins

Back 15

~These proteins provide a pathway that allows specific particles to cross

~ Some proteins are gated; they open when stimulated, allowing a specifically shaped molecule to cross

- Ex) Calcium (Ca+2) in a nerve cell

Front 16

Active Transport Mechanisms: Active Transport

Back 16

~ The movement of particles from an area of low concentration to high concentration (i.e. against the concentration gradient)

~ Active mechanism as it requires energy. ATP powers active transport by transferring its terminal phosphate group directly to the transport of protein. This results in a change in shape which allows the substance to be moved across.

~ Requires the use of specific protein carriers

- This is a function of integral proteins

~ Active transport does not achieve an equilibrium

~ This mechanism is commonly used to move ions

~ Ex)

1. Iodide into the cells of the thyroid gland

2. Sodium and Potassium across the neutron plasma membrane ( referred to as the sodium phosphate pump)

Front 17

Active Transport Mechanisms: Endocytosis

Back 17

~ The movement of large particles INSIDE OF THE CELL through the formation of a vesicle or vacuole by the plasma membrane

~ Active mechanism because energy is required

~ Two forms: Phagocytosis and Pinocytosis

Front 18

Active Transport Mechanisms: Endocytosis: Phagocytosis "cell eating"

Back 18

~ Used by a cell to engulf large particles

~ Ex) Bacteria, Virus, Yeast Cells

~ Extensions of the plasma membrane called pseudopods wrap around the particle and enclose it in a large vesicle or vacuole

~ Within the cell, a lysosome will fuse with the vesicle, allowing hydrolytic enzymes to digest the particle.

Front 19

Active Transport Mechanisms: Endocytosis: Pinocytosis

Back 19

~ Used by a cell to engulf moderately sized particles

~ Ex) Macromolecules such as proteins or polysaccharides

~ During pinocytosis, the plasma membrane indents drawing the particle and a small amount of surrounding fluid into a small pocket which pinches off forming a vesicle.

~ Within the cell, a lysosome will fuse with the vesicle, allowing hydrolytic enzymes to digest the particle

~ This is nonspecific because all dissolved solutes are taken in

Front 20

Active Transport Mechanisms: Exocytosis

Back 20

~ The movement of large particles to the outside of the cell by the fusing of a vesicle with the plasma membrane.

~ The contents of the vesicle are released outside of the cell

~ Active transport; requires energy

~ Particles have been released by exocytosis from the cell have often been packaged into secretion vesicles by the Golgi body

~ Ex) Pancreas releases insulin, ovaries release estrogen

Front 21

Iodine moves against the concentration gradient into the thyroid

Back 21

~ Through the use of a specific protein carrier which are attached to the membrane, to pump iodine, by attaching to the iodine, to the thyroid gland. This is through active transport.

Front 22

Water moves into a potato cell

Back 22

~ Through the process of osmosis, water moves from an area of high concentration to low concentration. It will pass through the fatty acid tails or protein channels.

Front 23

A bacterial cell is moved into a macrophage (white blood cells)

Back 23

~ Due to its large size, it must be moved through phagocytosis (pseudopods). It is a type of active transport. Fluidity allows the formation of pseudopods.