B2.1 Cells Flashcards
What is the phospholipid bilayer?
Phospholipids are the basis of membrane structure.
Head is water loving
Tail is water hating
What are fatty acids composed of?
Fatty acids are chains of hydrogen and carbon atoms termed as a hydrocarbon chain
These hydrocarbon chains can be either saturated or unsaturated
Diffusion
Net movement of molecules from a region of high concentration to a region of low concentration. This directional movement along a concentration gradient is passive and will continue until molecules become evenly dispersed (equilibrium)
How do hydrophilic water molecules cross the hydrophobic interior of the bilayer?
Carrier proteins
Integral proteins
Penetrate the phospholipid bilayer to remain attached to the membrane
Peripheral proteins
Only temporarily associated with one side of a membrane
Membrane protein functions
Junctions - serve to connect and join two cells together.
Enzymes - fixing to membrane localises metabolic pathways
Transport - responsible for facilitated diffusion and active transport
Recognition - may function as markers for cellular identification
Anchorage - attachment points for cytoskeleton and extracellular matrix
Transduction - function as receptors for peptide hormones
Definition of osmosis
The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
What are aquaporins?
Aquaporins are integral membrane proteins that form channels that allow for the passage of water molecules.
What is facilitated diffusion?
Is the passive movement of molecules across a cell membrane via the aid of a membrane protein
What are channel proteins?
Integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other
Channel proteins are ion-selective and may be gated to regulate the passage of ions in response to certain stimuli
Channel proteins only move molecules along a concentration gradient (i.e. are not used in active transport)
Channel proteins have a much faster rate of transport than carrier proteins
What are carrier proteins?
Integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane
Carrier proteins will only bind a specific molecule via an attachment similar to an enzyme-substrate interaction
Carrier proteins may move molecules against concentration gradients in the presence of ATP (i.e. are used in active transport)
Carrier proteins have a much slower rate of transport than channel proteins (by an order of ~1,000 molecules per second
Direct active transport
Is where the energy released by a reaction (like the breakdown of ATP) is used to directly transport
Indirect active transport
Is where the movement of one solute down its concentration gradient drives the movement of the second solute against its concentration gradient.
Selectivity in membrane permeability
Let some things through but not others, similar to diffusion
Glycoproteins and glycolipids structure and function
Glycolaisation of a phospholipid results in a glycolic whiile glucoslation of a membrane protein produces a glycoprotein
Read book for functions
Fluid-mosaic model
Must be able to draw
Membrane fluidity
The membrane is “fluid” because the phospholipids can move around and switch positions within the bilayer
Importance of membrane fluidity
Enables molecules to diffuse through the membrane to where they are needed in the cell.
Facilitate the interaction between proteins, which is crucial for cell signaling
Allows membranes to fuse with one another during the vesicle formation, endo and exocytosis
Ensures the even distribution of membrane molecules between daughter cells during cytokinesis
How temperature affects membrane fluidity
Low temperature:
High viscosity
Densely packed
More rigid
Not permeable enough
High temperature:
More flexible
Less densely packed
Won’t hold shape
Too permeable
Structure of cholesterol
Is a lipid
Hydroxyl group at one end
Four linked hydrocarbon rings
Hydrocarbon tail linked to the other end
Contains hydrophilic and hydrophobic parts making it amphipathic
Function of cholesterol in the membrane
High temperatures - restrains the movement of the phospholipid fatty acids, stabilizing the membrane by making it less fluid and reducing its permeability to small molecules
What is bulk transport in cells?
Vesicles can be used for bulk transport of many molecules into (endo) or out of (exo) the cell at once
What is endocytosis?
The cell activity transports water and solutes into the cell by engulfing them into vesicles formed from the cell membrane
Process of endoyctosis
Plasma membrane folds inward, creating a cavity filled with extracellular fluid, dissolved molecules, food particles, foreign matter, pathogens, etc
The membrane folds back on itself, trapping fluid inside the vesicle
The vesicle is pinched off from the membrane, moving into the cytoplasm
The cell membrane shrinks
What is exocytosis?
The cell activity transports molecules out of the cell into the extracellular space.
What is the process of exocytosis?
Vesicles containing molecules are transported from within the cell to the cell membrane
The vesicle membrane attaches to the cell membrane
Fusion of the membrane with the cell membrane releases the vesicle outside the cell
Cell membrane has grown larger
What is a sodium potassium pump?
Sodium potassium pump proteins are integral proteins that generate an electrochemical gradient between the inside and outside of a nerve cell
They move 3 sodium ions out of the cell and 2 potassium ions into the cell using one ATP molecule to provide energy. The pumps are always moving against the concentration gradient via active transport
Steps of sodium potassium pump
- 3 sodium ions from inside the axon bind to the pump
- ATP attaches to the pump and transfers a phosphate to the pump (phosphorylation) altering the pumps shape
- The pump opens to the outside of the axon
- The three sodium ions are released out of the axon
- Two potassium ions from outside the axon bind to their sites
- The phosphate is released, the pump shape and the potassium ions are released inside the axon
Sodium-dependent glucose cotransporters as an example of indirect active transport
Glucose cotransport proteins, also known as glucose transporters, are essential in the small intestine and kidney nephron for efficient glucose absorption and reabsorption. In the small intestine they pump sodium ions out of the epithelial cells causing a concentration gradient that leads to sodium ions forming into cell from the lumen. They bring glucose molecules with them
Multicellularity definition
Multicellular organism are composed of more than one cell that are adhered together. In a multicellular organism, the cells specialise and lose the ability to live independently
Multicellularity exist in:
All animals
All plants
Most fungi
Most algae
What is a tissue and what are the 4 basic types?
Tissues are groups of cells in multicellular organisms that work together to perform a function, except blood, where cells must communicate to coordinate function.
4 basic types of tissue:
Connective tissue - binds and supports other tissues (bone)
Epithelial tissue - provides a covering (skin)
Muscle tissue - includes stirated muscles that move the skeleton (stomach)
Nerve tissue - made up of neurons. Carries electrical impulses to various places
What are cell adhesion molecules (CAMs)
Proteins embedded in the plasma membrane, bind cells with other cells or extracellular matrix, aiding cell adhesion and different forms are utilised for different cell junction types.
