Bio I - 6 Flashcards
What is the plasma membrane?
It is a boundary that separates the living cell from its surroundings
What is selective Permeability?
It means that the plasma membrane allows some substances to cross it more easily than others
What is the most abundant lipid in the plasma membrane?
Phospholipids
What does ampithetic molecule mean?
It contains hydrophobic and hydrophilic regions
What does the fluid mosaic model state?
That a membrane is a fluid structure with a mosaic of various proteins embedded in it
What are membranes made of?
Proteins and lipids
What is a freeze fracture study?
Freeze fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer
What did the phrase fracture study support?
The fluid mosaic model
True or false
Phospholipids in the plasma membrane can move within the bilayer. 
True
How do the lipids and proteins move in the bilayer?
They drift laterally
Does a molecule ever flip flop transversely across the membrane?
Rarely
What happens to the membrane when temperatures cool?
Membranes switch from a fluid state to a solid state
At What temperature does the membrane solidify?
It depends on the type of lipid
Are membranes rich and unsaturated fatty acids are _______ than those rich in saturated fatty acids. 
More fluid
True or false
Membranes must be more solid to work properly.
False. They must be more fluid
What is cholesterol?
It is a steroid
How does cholesterol affect the membrane?
At warm temperatures cholesterol restrains movement of phospholipids. At cool temperatures it maintains fluidity by preventing tight packing.
What do proteins determine?
Most of the membrane specific functions
What is a membrane composed of?
It is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
What are peripheral proteins?
They are proteins that are bound to the surface of the membrane
What are integral proteins?
They are proteins that penetrate the hydrophobic core
What are integral proteins called that span the membrane?
Transmembrane proteins
The Hydrophobic regions of an integral proteins consist of one or more stretches of _________ often coiled into __________
Non polar amino acids
Alpha helices
What are the six major functions of membrane proteins?
Transport
Enzymatic activity
Signal transduction
Cell cell recognition
Intercellular joining
Attachment to the cytoskeleton an extra cellular matrix
When is the asymmetrical distribution of proteins lipids and associated carbohydrates in the plasma membrane determined?
When the membrane is built by the ER and Golgi apparatus
True or false.
Hydrophobic nonpolar molecules such as hydrocarbons can dissolve in the lipid bilayer and pass through the membrane rapidly
True
Do polar molecules cross the membrane easily?
No
What do transport proteins do?
They allow for passage of hydrophilic substances across the membrane
What are channel proteins?
They are a type of transport proteins that have a hydrophilic channel that certain molecules or ions can use as a tunnel
What are aquaporins?
They are channel proteins that facilitate the passage of water
What are carrier proteins?
They are transport proteins that bind to molecules and change the shape to shuttle them across the membrane
What is a passive transport?
It is the movement of ions and other atomic or molecular substances across cell membranes without need of energy input
What is active transport?
It is the movement of ions or molecules across the cell membrane into a region of higher concentration assisted by enzymes and requiring energy
What is diffusion?
Diffusion is the tendency for molecules to spread out evenly into the available space
What is dynamic equilibrium?
At dynamic equilibrium as many molecules cross one-way as cross in the other direction
Diffusion follows the natural concentration gradient. What is the natural concentration gradient?
When a molecule moves from higher concentration to lower concentration of molecules
Does diffusion require input of energy And a carrier protein?
No
What is osmosis?
Osmosis is the diffusion of water across a selectively permeable membrane
Water diffuses across a membrane from the region of _____ to the region of _____
Lower solute concentration
Higher solute concentration
What is tonicity?
What is the ability of a solution to cause a cell to gain or lose water
What is a isotonic solution?
The solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
What is a hypertonic solution?
When the solute concentration is greater than the inside of the cell and therefore the cell loses water
What is a hypotonic solution?
The solute concentration is less than that inside the cell and therefore the cell gains water
What happens when a plant cell is in a hypotonic solution?
It swells until the wall opposes uptake; the cell is now turgid/ firm
What happens to a plant cell and an isotonic state?
There is no net movement of water into the cell; the cell becomes flaccid/ limp and the plant may wilt
What is facilitated diffusion?
It is when transport proteins speed the passive movement of molecules across the plasma membrane
What do channel proteins include?
Aqua Porins, for facilitated diffusion of water
Ion channels that open or close in response to a stimuli/gated channels
What to channel proteins provide?
They provide corridors that allow a specific molecules or ions across the membrane
What is active transport?
Active transport moves substances against their concentration gradient
Does active transport require energy?
Yes
The energy is usually in the form of ATP
What is active transport performed by?
The specific proteins embedded in the membranes
What does active transport allow cells to do?
It allows cells to maintain concentration gradients that differ from their surroundings
What is one type of active transport system?
The sodium potassium pump
What is bulk transport?
It Is the transport of larger molecules across the membrane
What does the bulk transport process require?
It is an active transport process that requires input of energy and a carrier protein
What are two bulk transport systems?
Exocytosis and endocytosis
What is exocytosis?
It is when transport vesicles migrate to the membrane, fused with it, and release their contents
What type of cells use exocytosis to export their products?
Secretory cells
What is endocytosis?
The cell takes in macromolecules by forming vesicles from the plasma membrane
What are the three types of endocytosis?
Phagocytosis – larger molecules (cellular eating), pinocytosis – smaller molecules (cellular drinking)
Receptor mediated endocytosis
