Parts of a cell
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What are the three components of a cell?
- Plasma membrane
What is the fluid mosaic model?
- A description of the plasma membrane in cells.
- Mosaic- art of creating images with an assemblage of small pieces of colored glass, stone, or other materials.
- The membrane is fluid: It is flexible and the phospholipids can move in the membrane like water in a lake.
- The membrane is mosaic: There are proteins embedded in the membrane that can float freely in it (boats in a lake), and some anchored to specific locations.
What is a plasma membrane? How does it interact with substances?
- A flexible yet sturdy barrier that surrounds and contains the cytoplasm of a cell.
- Membrane lipids allow some lipid soluble molecules through but block charged or polar ones
- Some proteins in the plasma membrane allow charged or polar substances through the membrane. Others can act as signal receptors or as molecules that link the plasma membrane to intracellular or extracellular proteins.
What is a lipid bilayer? Whats it made of and %?
- Basic structural framework of the plasma membrane
- Made of two back to back layers made of three kinds of lipids: Phospholipids (75%), Cholesterol (20%), and Glycolipids (5%) which are lipids that have attached carbohydrate groups.
Where do the lipids of the plasma membrane orient themselves?
- Phospholipids- amphipathic, line up tail to tail in a double row, hydrophilic heads at the ECF and cytosol while hydrophobic tails are inside.
- Cholesterol- weakly amphipathic, its -OH group (hydroxyl),only polar region of cholesterol, forms hydrogen bonds with the polar heads of phospholipids and glycolipids. The nonpolar steroid rings and hydrocarbon tail fit among the fatty acid tails of the phospholipids and glycolipids.
- Glycolipids- the carbohydrate groups of glycolipids form a polar head; their fatty acid tails are nonpolar. Glycolipids appear only in the membrane layer that faces the extracellular fluid, which is one reason the sides of the bilayer are asymmetric, or different.
What are the two types of proteins in the plasma membrane? What classifies them?
- Integral proteins
- Peripheral proteins
- ***Whether they are firmly embedded in the plasma membrane or not.
What are integral proteins? Their basic structure?
- Most are transmembrane proteins.
- Many are glycoproteins.
- Proteins that extend through or into the lipid bilayer among fatty acid tails, and are firmly embedded in it.
What are transmembrane proteins?
- Integral proteins that span the entire lipid bilayer and protrude into the cytosol and ECF.
- Amphipathic, hydrophilic portions protrudes into ECF or cytosol while hydrophobic extend into the fatty acid tails.
- Few have covalent bonds to fatty acids on one side of bilayer.
What are peripheral proteins?
- Proteins not firmly embedded in the membrane.
- Attached to polar heads of membrane lipids or integral proteins at the inner or outer surface of the membrane.
What are glycoproteins?
- Proteins with carbohydrate groups attached to the ends that protrude into the extracellular fluid.
- The carbohydrates are oligosaccharides (oligo- few) with 2-60 monosaccharides that can be strait or branched.
What is the glycocalyx?
- The carbohydrate portions of glycoproteins and glycolipids THAT FORM an extensive sugary coat around a cell.The pattern of carbohydrates in the glycocalyx varies from one cell to another and can be used as a molecular 'signature' that allows cells to recognize each other.
How is a cells glycocalyx used?
- The pattern of carbohydrates in the glycocalyx varies from one cell to another and can be used as a molecular 'signature' that allows cells to recognize each other.
- Enables cells to adhere to one another in some tissues.
- Protects cells from being digested by enzymes in the extracellular fluid.
- Attracts a film of fluid to the surface of many cells due to hydrophilic properties that aid movement (red blood cells) and protect some cells from drying out (airways and gastrointestinal tract).
What determines the majority of cellular membrane functions?
- The different proteins that made up part of the plasma membrane.
- Lipids are only slightly varied through out cell membranes while proteins have a vast assortment.
What are some of the types of membrane proteins and their classification? (also glyco-)
- Ion channels (integral proteins)
- Carriers (integral proteins)
- Receptors (integral proteins)
- Enzymes (integral and peripheral proteins)
- Linkers (integral and peripheral proteins)
- Cell identity markers (glycoproteins & glycolipids)
What are ion channels (channel proteins)? Are they integral or peripheral?
- Transmembrane (integral) proteins that form pores or holes that allow the passage of a specific ion type through along with water.
- They are selective meaning they only allow entry to a specific ion type.
- No energy (atp) required because it works off of concentration gradient AKA passive transport.
What are carriers (carrier proteins/transporters)? Are they integral or peripheral?
- Integral proteins that can selectively bind to a polar substance or ion to move it in or out of a cell.
- Sometimes requires ATP when it goes against the concentration gradient AKA active transport.
What are receptors (receptor proteins)? Are they integral or peripheral?
- Integral proteins that serve as cellular recognition sites.
- Receptors recognize and bind to specific molecules *** called a ligand of that receptor.
What do integral enzymes do? Are they integral or peripheral?
- Catalyze specific chemical reactions at the inside or outside surface of the cell.
- There are integral and peripheral proteins.
What are linkers (linker proteins)? Are they integral or peripheral?
- Proteins that anchor proteins in the plasma membranes of neighboring cells to one another or to protein filaments inside and outside the cell.
- There are integral and peripheral linkers.
What are cell identity markers and their uses?
- Membrane glycoproteins and glycolipids
- Enable cells to recognize cells of the same kind during tissue formation
- Recognize and respond to potentially dangerous foreign cells
- EX: Red blood cells clumping after a blood transfusion of the wrong blood type.
What are some uses of peripheral proteins?
- Help support the plasma membrane
- Anchor integral
- Participate in mechanical activities such as moving materials and organelles within
- Changing cell shape in dividing cells and muscle cells
- Attaching cells to one another
What three factors does membrane fluidity depend on and way?
- Temperature, phospholipids will move closer together when cold, farther when warm.
- Unsaturated fatty acids, the amount of kinks in fatty acids, this increases fluidity by preventing the lipids from stacking closely together.
- Cholesterol concentration, which strengthen the membrane but lessens its fluidity (at normal temp, at a lower it does opposite) by filling the spaces the kinks in fatty acids form, as well as hydrogen bonding their hydroxyl group (-OH) to the polar heads of phospholipids and glycolipids.
What is the importance of membrane fluidity?
- Membrane fluidity is a compromise of rigidness and fluidity
- If the membrane is to rigid it it lacks mobility
- If the membrane is to fluid it lacks the structural organization and mechanical support required from the cell
What cellular functions does membrane fluidity effect?
- Allows interactions to occur within plasma membrane, such as assembly of membrane proteins
- Enables movement of cell components responsible for cell movement, secretion (proteins), growth, devision, and formation of cellular junctions (physical cell connections)
- Self heal of the lipid bilayer if torn or punctured instead of bursting (like a needle (CLONE))
What is selective permeability?
Blocking certain particles while selecting others to cross the plasma membrane
How is the plasma membrane selectively permeable?
- The lipid bilayer is permeable to uncharged non-polar molecules (O,CO2,steriods), but blocks charged and polar substances passage while sometimes allowing small polar molecules such as water and urea (waste product of breakdown of amino acids) through (gaps in a chain link fence)
- Proteins such as ion channels and carriers (transporters) are able to selectively bind to ions and polar molecules, each its own ion or polar molecule
What is a concentration gradient?
- A difference in chemical concentration from one place to another, such as intra- and extracellular environments
- Many ions and molecules are more concentrated in either the cytosol (CO2 molecules, (K^+) or the extracellular fluid (oxygen molecules, (Na^+))
- A substance can move across the plasma membrane down the concentration gradient, to a place of lower concentration to reach equilibrium.
What is an electrical gradient? (membrane potential)
- A difference in electrical charges between two regions (each side of plasma membrane) known as membrane potential
- Plasma membrane creates a difference in distribution of positively and negatively charged ions between the two sides of the plasma membrane
- Inner surface of membrane usually more negatively charged, while outer surface more positively charged
- **positively charged substances tend to move towards negatively charged areas, and reverse as well
What is the electrochemical gradient and why is it important?
- The combined influence of the concentration and electrical gradient on movement of a particular ion.
- They each help move substances across the plasma membrane
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