Membrane Structure and Function Chap7

Question 1

How does the plasma membrane regulate inbound and outbound traffic? (p1)

Answer 1

Exocytosis: large molecules are secreted when a vesicle fuses with the plasma membrane.

Question 2

How does the plasma membrane regulate inbound and outbound traffic? (p2)

Answer 2

Bulk transport moves large molecules.

Question 3

How does the plasma membrane regulate inbound and outbound traffic? (p3)

Answer 3

Endocytosis: Large molecules are taken in when the plasma membrane pinches inward, forming a vesicle.

Question 4

How does the plasma membrane regulate inbound and outbound traffic? (p4)

Answer 4

Active transport of small molecules requires energy and a transport protein.

Question 5

How does the plasma membrane regulate inbound and outbound traffic? (p5)

Answer 5

Passive transport of small molecules doesn’t require energy: it may involve transport proteins.

Question 6

Cellular membranes…?

Answer 6

Cellular membranes are fluid mosaics of lipids and proteins.

Question 7

Phospholipid Bilayer

Answer 7

Contains two parts, Hydrophilic (water loving) outer head, and Hydrophobic (water fearing/hating) inner tail.

Question 8

Affecting factors of membrane fluidity.

Answer 8

Unsaturated versus saturated hydrocarbon tails. (unsaturated tails prevent packing) (saturated tails pack together) Cholesterol within the animal cell membrane. (Cholesterol reduces membrane fluidity at moderate temperatures by reducing phospholipid movement, but hinders solidification at low temperatures by disrupting packing.

Question 9

Membrane Proteins and functions

Answer 9

Glycolipid (extracellular), Peripheral proteins (intercellular), Integral proteins (goes through the bilayer).

Question 10

Functions of Membrane proteins

Answer 10

Transport of ATP, Enzymatic activity, Signal transduction, Cell-cell recognition, Intercellular joining, Attachment to the cytoskeleton and the extracellular matrix.

Question 11

Roles of membrane carbohydrates in cell-cell recognition (p1)

Answer 11

Cells recognize other cells by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane. These molecules may be glycolipids (carb bonded to lipids) or glycoproteins (carb bonded to proteins).

Question 12

Roles of membrane carbohydrates in cell-cell recognition (p2)

Answer 12

The arrangement and type of glycolipids and glycoproteins on the extracellular side of the cell varies between organisms as well as between cell types. These molecules create a specific “fingerprint” that can be used to identify cell types.

Question 13

Synthesis and sidedness of membranes (p1)

Answer 13

Endoplasmic reticulum: carbohydrates attached to the transmembrane proteins creating glycoproteins which are then transported via vesicle to the Golgi Apparatus. Golgi Apparatus: Glycoproteins carbohydrates are further modified, glycolipids are built. Vesicles transport glycoproteins, glycolipids, and secretory proteins to the cell membrane.

Question 14

Synthesis and sidedness of membranes (p2)

Answer 14

Cell membrane: vesicles from the Golgi apparatus fuse with the cell membrane, releasing contents to the outside of the cell. The inside face of the vesicle then becomes part of the extracellular side of the cell membrane while the outside face of the vesicle becomes part of the cytoplasmic side of the cell membrane. This process allows cells to create different arrangements of glycoproteins, glycolipids, and proteins on each face of the membrane.

Question 15

Membrane structure results in selective permeability

Answer 15

Emergent properties of the plasma membrane result in it being selectively permeable, meaning that some substances easily cross the membrane, while other do not. FORM FITS FUNCTION: The fluid mosaic model helps explain how membranes regulate the cell’s molecular traffic. No polar molecules are hydrophobic and therefore easily pass through the hydrophobic middle of the membrane and in some cases are not able to cross membranes independently.

Question 16

Transport proteins (p1)

Answer 16

Ions and polar molecules that cannot move through the cell membrane independently can avoid contact with the hydrophobic middle of the membrane by traveling through a transport protein.

Question 17

Transport proteins (p2)

Answer 17

Channel proteins are a type of transport protein which contain hydrophilic channels that act as tunnels through the membrane for the passage of ions or polar molecules. One example of a channel protein is an aquaporin, which allows for water molecules to pass more quickly through the membrane.

Question 18

Transport proteins (p3)

Answer 18

Carrier proteins are another type of transport protein which attach to the molecules being transported and change shape as they transport them across the membrane.

Question 19

Transport proteins (p4)

Answer 19

Transport proteins are specific to the molecules they transport which contributes to the selective permeability of the plasma membrane.

Question 20

Passive transport is diffusion of a substance across a membrane with no energy investment.

Answer 20

The thermal energy of molecules due to their constant motion results in diffusion, the movement of particles of any substances so that they spread out into the available space.

Question 21

Passive transport

Answer 21

A substance will diffuse from HIGH concentration to LOW concentration, down the concentration gradient. Each substance diffuses down its own concentration gradient, unaffected by the concentration gradients of other substances.

Question 22

Diffusion

Answer 22

Diffusion is a type of passive transport because it requires no energy. Remember that only substances that can pass through the cell membrane can diffuse into or out of a cell.

Question 23

Osmosis

Answer 23

Osmosis is the diffusion of free water molecules across a semipermeable membrane. Hydrophilic solutes are attracted to the charges on water molecules so they form hydrogen bonds, the higher the solute concentration, the lower the free water concentration.

Question 24

Water balance

Answer 24

Hypotonic: Solutions have less solutes than the solution they are being compared to. If a cell is placed into a hypotonic solution, water enters the cell causing the cells to swell. Hypertonic: Solutions have more solutes than the solution they are being compared to. Cell placed into a hypertonic solution, water leaves the cell, the cell will shrivel and die. Isotonic results in NO NET MOVEMENT OF WATER. Water molecules ARE moving, BUT they are moving equally back and forth.

Question 25

Facilitated Diffusion: Passive Transport Aided By Proteins (p1)

Answer 25

Transport proteins help transport polar molecules and ions through the plasma membrane in a process known as facilitated diffusion. Most transport proteins are very specific and transport some substances but not others.

Question 26

Facilitated Diffusion: Passive Transport Aided By Proteins (p2)

Answer 26

Channel proteins have hydrophilic channels, Carrier proteins change shape to move a specific solute across the membrane.

Question 27

Facilitated Diffusion: Passive Transport Aided By Proteins (p3)

Answer 27

Facilitated diffusion does NOT require energy because the molecules being transported are moving down their concentration gradients from high concentration to low concentration.

Question 28

Active transport

Answer 28

Active transport uses energy to move solutes against their concentration gradient. Active transport utilizes specialized carrier proteins which use energy (often in the form of ATP) to pump specific molecules across the membrane against the concentration gradient.

Question 29

Cotransport

Answer 29

Transport protein couples the downhill diffusion of one solute with the uphill transport of a second substance against its concentration gradient. Plant cells use the concentration gradient created by proton pumps to drive the active transport of amino acids, sugars, and nutrients into the cell. In animal cells, a similar cotransporter moves Na+ into intestinal cells together with glucose, which is moving down its concentration gradient into the cell.

Question 30

Bulk transport

Answer 30

Bulk transport across the plasma membrane occurs by exocytosis and endocytosis. Large molecules cannot cross the plasma membrane by diffusion or through transport proteins. They MUST be packaged in vesicles and transported into or out of the cell.

Question 31

Exocytosis

Answer 31

Exocytosis is the process through which the cell releases large molecules by vesicles fusing with the plasma membrane.

Question 32

Endocytosis

Answer 32

Endocytosis is the process through which cells take in large molecules and substances.

Question 33

Phagocytosis

Answer 33

Cell extends pseudopodia around the material being taken into the cell and surrounds the material in a membrane sac, called a food vacuole. This food vacuole fuses with a lysosome, whose enzymes break down the large particle.

Question 34

Pinocytosis

Answer 34

Cell engulfs extracellular fluid into vesicles by infoldings in the cell membrane. In this process, the cell engulfs molecules dissolved in the droplets of fluid.

Question 35

Receptor-mediated endocytosis

Answer 35

A type of pinocytosis that uses protein receptors embedded in the plasma membrane to bind specific solutes. The protein receptors then cluster into pits and form vesicles that contain the specifically bound solute molecules.