Chapter 3.1-3.2 Cell Membranes Flashcards
Cells are surrounded by a limiting barrier, the _____ (aka the ______ membrane) which covers the cell surface.
Cells are surrounded by a limiting barrier, the Plasma Membrane (aka the Cell membrane) which covers the cell surface.
The interior of the cell is divided into two regions:
1) the ______, sperical or oval structure usually near the centre
2) the ______, the region outside of (1)
The interior of the cell is divided into two regions:
1) the nucleus, sperical or oval structure usually near the centre
2) the cytoplasm, the region outside of (1)
The cytoplasm contains cell ______ and fluid surrounding them known as ______
The cytoplasm contains cell organelles and fluid surrounding them known as cytosol
All of the fluid inside a cell (i.e. the cytosol + fluid inside all organelles incl the nucleus) is known as?
Intracellular fluid
What is the largest intracellular fluid compartment?
The cytosol
Membranes perform a variety of functions.
The most universal of which is:
- to act as a ______ _____ to the _____ of ______
In addition, they also have 2 more functions:
Membranes perform a variety of functions.
The most universal of which is:
- to act as a Selective B__arrier to the passage of molecules (semi-permeable)
In addition, they also have 2 more functions:
- communication with other cells by detecting chemical signals from other cells
- anchoring cell to adjacent cells and to the cellular matrix of CT proteins
All membranes consist of a double layer of ______ molecules containing embedded ______
All membranes consist of a double layer of Lipid molecules containing embedded proteins
What type of lipid is most commonly found in membranes?
Phospholipid
Describe a phospholipid structure.
One end of the phospholipid has a _______ (head) region and the remainder which consists of ____ ____ ____ _____ _____, is _____. Thus, Phospholipids are _______
One end of the phospholipid has a charged (Polar) region and the remainder, which consists of two long fatty acid chains, is non-polar. Thus, phospholipids are amphipathic
What compartments constitute the entire intracellular fluid?
The intracellular fluid compartment includes all of the water in the cytoplasm plus the water in the nucleus
What two features of the phospholipid bilayer (plasma membrane) all cells to undergo moderate changes in shape without disrupting structural integrity?
- Flexibility: chemical bonds don’t link the phospholipids to each other or the the membrane proteins = free to move = fluidity
- Cells are filled with fluid
The plasma membrane contains _______ (steroid), whereas intracellular membranes contain very little
The plasma membrane contains cholesterol, whereas intracellular membranes contain very little
What feature of cholesterol makes it slightly amphipathic?
Cholesterol has a single polar hydroxyl group attached to its relatively rigid, nonpolar ring structure.
Like phospholipids, cholesterol is inserted into the lipid bilayer with its _____ region toward the bilayer surface and its ______ rings in the interior in association with the fatty acid chains
Like phospholipids, cholesterol is inserted into the lipid bilayer with its polar region toward the bilayer surface and its non-polar rings in the interior in association with the fatty acid chains
Table 3.1
What are four functions of the plasma membrane?
- Regulate the passage of substances into and out of the cells and between cell organelles and cytosol
- Detect chemical messengers arriving at the cell surface
- Link adjacent cells together by membrane juntions
- Anchor cells to the extracellular matrix
The polar hydroxyl groups (of cholesterol) are joined to the polar regions of phospholipids through _______
The polar hydroxyl groups (of cholesterol) are joined to the polar regions of phospholipids through hydrogen bonds
What effect does a highly ordered, tightly packed arrangement of cholesterol within the membrane have on membrane fluidity?
Would decrease membrane fluidity
What are the two classes of membrane proteins?
- Integral (intrinsic)
- Peripheral (extrinsic)
_______ membrane proteins are closely associated with the membrane lipids and cannot be extracted from the membrane without disrupting the lipid bilayer
i.e. embedded within the membrane (partially or span entire membrane)
_______ membrane proteins are closely associated with the membrane lipids and cannot be extracted from the membrane without disrupting the lipid bilayer
i.e. embedded within the membrane (partially or span entire membrane)
Integral proteins that span the entire plasma membrane are called:
Transmembrane Proteins
Like the phospholipids, the integral membrane proteins are ______: having ____ amino acid side chains in one region and _____ side chains clustered in a separate region
Like the phospholipids, the integral membrane proteins are amphipathic: having polar amino acid side chains in one region and nonpolar side chains clustered in a separate region
The _______ chains of many transmembrane proteins cross the lipid bilayer several times
The polypeptide chains of many transmembrane proteins cross the lipid bilayer several times
Functions of Integral proteins:
Some ________ proteins form channels through which ____ or _____ can cross the membrane.
Others are associated with the transmission of ______ across the membrane or the ______ of extracellular and intracellular ____ _____ to the plasma membrane
Functions of Integral proteins:
Some transmembrane proteins form channels through which ions or water can cross the membrane.
Others are associated with the transmission of chemical signals across the membrane or the anchoring of extracellular and intracellular protein filaments to the plasma membrane
Peripheral Membrane Proteins are NOT ______, and do not associate with the ____ regions of the lipids in the membrane
Peripheral Membrane Proteins are NOT amphipathic, and do not associate with the nonpolar regions of the lipids in the interior of the membrane
Peripheral membrane proteins are located at the membrane ____\_ where they are bound to the _____ regions of the _______ and also (in some cases) to the ______
Peripheral membrane proteins are located at the membrane surface where they are bound to the polar regions of the integral membrane proteins and also (in some cases) to the charged polar regions of the membrane phospholipids
Most of the peripheral proteins are on the ____ surface of the plasma membrane
Most of the peripheral proteins are on the cytosolic surface of the plasma membrane
What are some examples of peripheral membrane functions: (3)
- some are enzymes that mediate metabolism
- Others involved in local transport of small molecules along or between the membrane
- Associated with cytoskeletal elements that influence cell shape and motility
The extracellular surface of the plasma membrane contains small amounts of ______ covalently linked to some of the membrane lipids and proteins
The extracellular surface of the plasma membrane contains small amounts of carbohydrate covalently linked to some of the membrane lipids and proteins
Carbohydrates on the extracellular surface of the plasma membrane consist of short, branched chains of _______ that extend from the cell surface into the extracellular fluid where they form a layer known as the _______
Carbohydrates on the extracellular surface of the plasma membrane consist of short, branched chains of monosaccharides that extend from the cell surface into the extracellular fluid where they form a layer known as the glycocalyx
Surface carbohydrates enable:
Cells to identify and interac with each other
What are Lipid Rafts
Cholesterol-rich regions of decreased membrane fluidity that are believed to serve as organizing centers for the generation of complex intracellular signals
The way that cells become organized into tissues and organs depends, in part, on the ability of ______ (transmembrane protein) to bind to specific proteins in the extracellular matrix and link them to the membrane proteins on adjacent cells
The way that cells become organized into tissues and organs depends, in part, on the ability of integrins (transmembrane protein) to bind to specific proteins in the extracellular matrix and link them to the membrane proteins on adjacent cells
What are three types of junctions?
- Desmosome
- Gap Junction
- Tight Junction
______ consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm
Desmosomes consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm
Desmosomes are characterized by accumulations of protein known as ______ along the cytoplasmic surface of the plasma membrane
Desmosomes are characterized by accumulations of protein known as “dense plaques” along the cytoplasmic surface of the plasma membrane
Dense plaques (of desmosomes) serve as anchoring points for _____
Dense plaques (of desmosomes) serve as anchoring points for cadherins
What are cadherins?
Proteins that are extend from the cell into the extracellular space where they link up and bind with cadherins from an adjacent cell
What does the presence of numerous desmosomes between cells provide?
Structural integrity of tissues.
Common in areas subject to considerable stretching (eg the skin)
Other proteins in desmasomes, such as ______ filaments, anchor the cytoplasmic surface of desmosomes to interior structures of the cell
Other proteins in desmasomes, such as keratin filaments, anchor the cytoplasmic surface of desmosomes to interior structures of the cell
A ________ forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them
A Tight Junction forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them
Most epithilial cells are joined by tight junctions near their _____ surfaces
Most epithilial cells are joined by tight junctions near their apical surfaces
Tight junctions are found in epithelial tissue specialized for_______ (kidney, intestine) and functionally, for nearly _______ junctions
Tight junctions are found in epithelial tissue specialized for molecular transport (kidney, intestine) and functionally, for nearly impermeable junctions
What is important about the movement of organic nutrients near tight junctions?
Prevent any molecules from moving through the interstitial space between cells - all molecules must go through the cells rather than between them = control types/amounts of substances absorbed
The ________ consists of protein channels linking the cytosols of adjacent cells
The gap junction consists of protein channels linking the cytosols of adjacent cells
In the region of the gap junction, two opposing plasma membrances come within 2-4nm of each other which allows specific proteins called _______ from the two membranes to join forming small transmembrane channels linking the two cells
In the region of the gap junction, two opposing plasma membrances come within 2-4nm of each other which allows specific proteins called connexins from the two membranes to join forming small channels linking the two cells
A variety of cell types possess gap junctions: name two
- Heart muscle = transmision of electrical activity between cells - depolarization
- Bone cells
Gap junctions ______ and ______ couple cells
Gap junctions electrically and metabolically couple cells
What type of substances could move through gap junctions of cells?
Small water-soluble molecules and ions
