Bio 124 Chapter 5

Need to add answers to last questions

What does a plasma membrane do? 

defines outer border of all cells and organelles, manages what enters and exits the cell, receives external signals and initiates cellular responses, adheres to neighboring cells

What gives the plasma membrane a fluid character?

a mosaic of components like phospholipids, cholesterol, proteins, and carbohydrates

Phospholipid:

amphiphilic lipid molecule

Hydrophobic tails: 

two fatty acid chains, nonpolar

Hydrophillic head:

glycerol molecule, phosphate group that is polar

Each fatty acid can be either _______

saturated or unsaturated

A saturated fatty acid is _______

unbent, straight

A unsaturated fatty acid is ________

bent, not straight

When are carbons saturated?

all single C-C bonds

When are carbons unsaturated?

at least one double C=C bond occurs

Phospholipids arrange themselves in a _______

bilayer

In a bilayer what faces outwards?

polar heads

In a bilayer what faces inwards?

hydrophobic tails

Proteins are the _________

second major component of membranes

Proteins function as ________

transporters, receptors, enzymes, or in binding and adhesion

Integral proteins:

integrated completely into the bilayer

Peripheral proteins:

occur only on the surfaces

Integral membrane proteins have _________

one or more regions, locations and number of regions determine how they arrange within the bilayer

The third major component are ________

oligosaccharide carbohydrates

Where are carbohydrates located? 

the plasma membrane, bound to either proteins, forming glycoproteins, or to lipids, forming glycolipids

What do carbohydrates do?

in cell recognition and attachment

Human immune system’s T cells have _______

CD4 receptor glycoproteins that recognize HIV as ‘self’

The membrane needs to be flexible but not so _______

fluid that it cannot maintain its structure

Fluidity is affected by _____

phospholipid type, temperature, cholesterol

(Fluidity)Phospholipid type:

phospholipids with saturated fatty acids can pack together more closely than those with unsaturated FA; therefore, more SFA, more rigid

(Fluidity)Temperature:

cold temperatures compress molecules making membranes more rigid

(Fluidity)Cholesterol:

located within the fatty acid layer, acts as a fluidity buffer; keeping membranes fluid when cold and from not getting too fluid when hot

Plasma membranes are _______

asymmetric, the inner surface differs from the outer surface

Interior proteins anchor _______

fibers of the cytoskeleton to the membrane

Exterior proteins bind to the _________

extracellular matrix

Glucoproteins bind to ________

substances the cell needs to import

The plasma membrane is selectively permeable, which means what? 

allows some molecules to pass through, but not others

Transport across a membrane can be either ________

passive, requiring no energy, or active, requiring energy

The simplest type of passive transport is _______

diffusion

Diffusion occurs when a _________

substance from an area of high concentration moves down its concentration gradient

In membranes how does diffusion occur?

through the lipid bilayer

Net movement ceases once ________

equilibrium is achieved

What type of molecules can diffuse through biological membranes?

small nonpolar molecules and lipid hormones

(Factor that affects diffusion rates)Concentration gradients:

greater difference, faster diffusion

(Factor that affects diffusion rates)Mass of the molecules:

smaller molecules diffuse more quickly

(Factor that affects diffusion rates)Temperature:

molecules move faster when temperatures are higher

(Factor that affects diffusion rates)Solvent density:

dehydration increases density of cytoplasm – reduces diffusion rates

(Factor that affects diffusion rates)Solubility:

more nonpolar, lipid-soluble, materials diffuse faster

(Factor that affects diffusion rates)Surface area:

increased surface area speeds up diffusion rates

(Factor that affects diffusion rates)Distance travelled:

the greater the distance, the slower the rates, important factor affecting upper limit of cell size

(Factor that affects diffusion rates)Pressure:

in some cells, blood pressure forces solutions through membranes, speeding up diffusion rates

Facilitated transport/diffusion:

moves substances down their concentration gradients through transmembrane, integral membrane proteins

What uses facilitated transport?

ions and small polar molecules

Two types of facilitated transport proteins include ________

channel and carrier proteins

Channel proteins:

some are open all the time, others are gated, only opening when a signal is received

Carrier proteins: 

all of these proteins are specific to a single substance, bind to that substance, change shape and carry it to the other side, many allow movement in either direction, as concentration gradients change

Osmosis:

diffusion of water across a membrane

Tonicity:

describes how an extracellular solution can change the volume of a cell by affecting osmosis

Tonicity is often correlated to _______

the osmolarity of a solution

Osmolarity describes the ______

total solute concentration of a solution, both permeable and non-permeable 

Hypertonic, isotonic, and hypotonic describe __________

the osmolarity of the cell to that of its extracellular fluid

A hypertonic extracellular fluid has _________

lower osmolarity than the cytosol – water leaves the cell

An isotonic extracellular fluid has _________

the same osmolarity than the cytosol – water does not move

A hypertonic extracellular fluid has _____________

higher osmolarity than the cytosol – water enters the cell

Animal cells function best when _________

extracellular fluids are isotonic

Osmoregulation: 

organisms who’s cells have cell walls prefer hypotonic extracellular solutions

What cells have cell walls? 

plants, fungi, bacteria and some protists

Hypertonic solutions causes ________

plasmolysis

Plasmolysis:

process in which cells lose water in a hypertonic solution

Turgor pressure:

force within the cell that pushes the plasma membrane against the cell wall

Freshwater protists, like  paramecia and  amoebas, use _______

contractile vacuoles, to pump water out of their cells so they do not burst

Marine invertebrates have internal _________

salt concentrations that match their environment

Fishes excrete diluted urine to __________

get rid of excess H2O or salts

Osmoreceptors of brain cells monitor ___________

solute concentrations in our blood, releasing hormones that affect kidney function

Primary active transport: 

where ATP provides the energy

Secondary active transport:

where an electrochemical gradient provides the energy

Electrochemical gradient:

arise from the combined effects of concentration gradients and electrical gradients

Electrical gradient:

the cytoplasm contains more negatively charged molecules, more neg ions and proteins than the extracellular fluid, is critical for proper cell functioning

Active transport occurs through __________

transmembrane, integral carrier proteins called pumps, there are three types of pumps

Uniporter: 

carries one molecule or ion

Symporter:

carries two different molecules or ions, in the same direction

Antiporter:

carries two different molecules or ions, in different directions

Primary active transport: 

moves an ion or molecule up its concentration gradient using energy from ATP hydrolysis

Secondary active transport _______

uses an electrochemical gradient created by primary active transport to move a different substance against its concentration gradaient

Bulk transport is a type of _______

active transport

Importing by bulk transport is called ________

endocytosis

Exporting by bulk transport is called _________

exocytosis

The types of endocytosis are called:

phagocytosis, pinocytosis, receptor mediated endocytosis

Phagocytosis:

the cell membrane surrounds a particle and engulfs it, cellular eating

Pinocytosis:

the cell membrane surrounds a small volume of fluid, and pinches off, cellular drinking

Receptor-mediated endocytosis: 

uptake of a specific substance is targeted by binding to receptors on the external surface of the membrane

In exocytosis, vesicles containing substances fuse ______

with the plasma membrane, the contents are then released to the exterior of the cell

Which plasma membrane component can be either found on its surface or embedded in the membrane structure?

protein

Which characteristic of a phospholipid contributes to the fluidity of the membrane?

double bonds in the fatty acid tail

What is the primary function of carbohydrates attached to the exterior of cell membranes?

identification of the cell

Water moves via osmosis _________

from an area with a high concentration of water to one of lower concentration

The principal force driving movement in diffusion is the __________

concentration gradient

What problem is faced by organisms that live in fresh water?

bodies tend to take in too much water

In which situation would passive transport not use a transport protein for entry into a cell?

oxygen moving into a cell after oxygen deprivation

Active transport must function continuously because __________

diffusion is constantly moving solutes in opposite directions

What is the combination of an electrical gradient and a concentration gradient called?

electrochemical gradient

What happens to the membrane of a vesicle after exocytosis?

fuses with and becomes part of the plasma membrane

Which transport mechanism can bring whole cells into a cell?

phagocytosis

In what important way does receptor-mediated endocytosis differ from phagocytosis?

brings in only a specifically targeted substance

Many viruses enter host cells through receptor-mediated endocytosis. What is an advantage of this entry strategy?

virus only enters its target host cell type