2.2 Membrane Structure & Function Flashcards
fluid mosaic model
the idea that a biological membrane consists of a fluid phospholipid bilayer in which proteins are embedded and float freely
how is our current view of membrane structure based on the fluid mosaic model?
This model proposes that membranes are not rigid, with molecules locked into place. Instead, membranes consist of lipid molecules in which proteins are embedded and float freely. Membranes are described as a fluid because the lipid and protein molecules are generally free to move laterally within the two layers.
glycolipid
any membrane lipid that is bound to a carbohydrate
glycoprotein
a membrane component that contains a sugar, or carbohydrate, bound to an amino acid
what are the dominant lipids found in membranes?
phospholipids
phospholipid
contains 2 fatty acids tails, which are usually linked to glycerol, a phosphate group and a compound (e.g. choline)
why is the composition of phospholipids important?
This composition is important for membrane function. The fatty acid tails of a phospholipid are very hydrophobic (nonpolar), whereas the phosphate-containing head group is charged and hydrophilic (polar).
when added to an aqueous solution, what do phospholipids form?
phospholipids form a bilayer or a structure that is 2 lipid molecules thick
what is the dynamic nature of the lipid bilayer dependent on?
how densely the individual lipid molecules can pack together
sterol
a type of steroid with an OH group at one end and a non-polar hydrocarbon chain at the other
integral membrane protein
a protein that is embedded in the lipid bilayer
peripheral membrane protein
a protein on the surface of the membrane
When comparing the outside and inside halves of a cell membrane’s phospholipid bilayer, the composition of lipids on the two surfaces is asymmetrical.
(a) Describe how membranes are asymmetric
(b) Why is membrane asymmetry an important characteristic in cell membranes?
(a) The membranes are asymmetrical because the proteins and other components of
one half of the lipid bilayer differ from those that make up the other half.
(b) Membrane asymmetry reflects the differences in functions performed by each half of
the membrane.
How does the structure of the plasma membrane facilitate its function?
The phospholipids on the bilayer are oriented so that their hydrophilic heads point
outwards towards the aqueous external environment and inward towards the aqueous
cytosol of the cell.
The hydrophobic tails point towards the interior of the membrane.
This prevents most polar or ionic substances from diffusing through.
what is meant by membrane fluidity
“Membrane fluidity” is the dynamic nature of the membrane, which allows for it to be flexible. That is, membrane lipids undergo free movement on their side of the bilayer.
explain the 4 functional categories of membrane proteins
Transport proteins help substances move through the plasma membrane.
Enzymatic proteins help with respiration and photosynthesis.
Triggering signal proteins bind specific chemicals used in cellular communication.
Attachment and recognition proteins act as attachment points for structural elements such as the cytoskeleton or as recognition sites for foreign substances such as microbes.
How are protein receptors and enzymes similar?
They both detect molecules and perform an action in response. They both recognize and bind only to specific molecules at a specific time, changing shape after binding.
If proteins were rigid, how would this affect their ability to act as receptors?
When a receptor binds to a chemical signal, it changes shape. This shape change is critical because it affects how receptors interact with other molecules. If proteins were rigid, receptors would not be able to change shape and would lose functionality.
Describe what is meant by integral and peripheral membrane proteins. How do they differ in their chemical makeup and their arrangement of amino acids?
Integral proteins are embedded in the lipid bilayer of the membrane and peripheral proteins are positioned on the surface of the membrane. Integral proteins interact with the hydrophobic core of the membrane and contain non-polar amino acids as well as polar amino acids.
Peripheral proteins interact with hydrophilic regions of the membrane or exposed portions of integral proteins and are composed of polar amino acids.
the fluid mosaic model
– states that membrane proteins float freely throughout the phospholipid bilayer
Membranes are not rigid with molecules locked into place
Membranes contain a mosaic (wide assortment) of proteins
glycolipid
a membrane
lipid attached to a
carbohydrate group
glycoprotein
a membrane protein attached to a
carbohydrate group
Both are involved in cell
recognition/interaction
role of phospholipids
Make up the majority of the cell membrane
Hydrophobic tails and Hydrophilic head form bilayer in water (forms spontaneously)
sterols
Sterols (commonly Cholesterol) help to stop
membranes from becoming too rigid in cold
temperatures and hold membranes together at
higher temperatures
integral membrane proteins
Embedded in lipid bilayer
Has areas that interact with water/lipids
peripheral membrane proteins
On the surface of the membrane
Don’t interact with hydrophobic core of bilayer
transport (membrane proteins)
transport substances
across the membrane (ones that
cannot simply diffuse)
Ex. May move larger amino acids
across the membrane
enzymatic activity
help with
cellular respiration/photosynthesis
Ex. ATP Synthase is used to create
ATP
triggering signals
bind to chemicals and
cause changes within the cell
Ex. Hormones bind to membrane protein
causing chemical changes inside the cell
attachment
proteins can help anchor
parts of the cytoskeleton
Ex. Proteins attach to microtubules
recognition
allows cells to recognize
one another and invading pathogens
(diseases)
Ex. Neighboring cells can recognize one
another based on specific proteins
