Membrane Proteins - ️️- Inserted into the phospholipid membrane
- associated with inner or outer sides or pass all the way through the membrane
- Functions to maintain structure, regulate cell function, allow transport across the
membrane, and facilitate signalling
Roles of the Plasma Membr...
PHGY 215 - Midterm
Membrane Proteins - ✔️✔️- Inserted into the phospholipid membrane
- associated with inner or outer sides or pass all the way through the membrane
- Functions to maintain structure, regulate cell function, allow transport across the
membrane, and facilitate signalling
Roles of the Plasma Membrane - ✔️✔️- Plays an active role in regulating the internal
fluid composition as it controls which molecules flow in and out
- Allows nutrients to enter cells and waste products to leave
Permits chemical signals released from other cells in the body to influence a cell
allowing cell to cell communication
- Participates in joining cells together to form tissues and organs
Physiology - ✔️✔️The scientific study of the functions of our body
Homeostasis - ✔️✔️The ability of a cell or organism to regulate and maintain its
internal environment regardless of the influences of the external environment
Set Point - ✔️✔️The range or point at which a variable physiological state tends to
stabilize
3 components of a homeostatic control system - ✔️✔️Sensor, Integrator, Effector
Sensor - ✔️✔️The sensor is responsible for detecting an environmental change
Integrator - ✔️✔️The integrator compares the variable being detected to its set point
Effector - ✔️✔️The effector is responsible for initiating the changes to restore the
variable back to the set point
Intrinsic Control - ✔️✔️The sensor, integrator, and effector are all located in a tissue so
that the tissue can regulate its own internal environment
Extrinsic Control - ✔️✔️The regulatory mechanisms are outside of the tissue or organ
Positive Feedback - ✔️✔️When the effector causes changes that amplify the initial
signal - not homeostatic
Negative Feedback - ✔️✔️A change in an environmental parameter causing the
effector to initiate a response in the opposite direction, restoring the parameter to the
set point - system stops signalling once set point is achieved
,Plasma Membrane - ✔️✔️The barrier that separates the cell's internal and external
environments that serves as protection and allows cells to maintain an internal fluid
composition different than the external fluid composition
Three primary functions of the plasma membrane - ✔️✔️- ensure the cell's survival
- maintain homeostasis
function cooperatively and in coordination with surrounding cells
Phospholipids in the Plasma Membrane - ✔️✔️- The lipid bilayer is comprised of
phospholipids
- A phospholipid has a polar head with a negatively charged phosphate group and two
non-polar fatty acid tails
- the head is hydrophilic and the tail is hydrophobic
Cholesterol in the Plasma membrane - ✔️✔️- Found tucked in between the
phospholipids
- Prevent the fatty acid chains from packing too tightly together and forming rigid
structures
- keeps the membrane fluid
Ion Channels - ✔️✔️Specialized membrane proteins that span the entire lipid
membrane and permit the entry and exit of ions
Carbohydrate Chains in the Plasma Membrane - ✔️✔️- Short chains of carbohydrates
that can be attached to proteins or the bilayer to form glycoproteins and glycolipids
- Involved in stabilizing membrane structure, act as cell surface receptors, participate in
transportation across the cell membrane
Cystic fibrosis - ✔️✔️- Caused by a defect in a particular chloride ion channel that is
involved in controlling the amount of fluid and mucous within the lungs
- Patients experience fluid build up in the lungs
Alzheimer's Disease - ✔️✔️- Results in oxidative stress which leads to the alteration
and degradation of phospholipids within brain cells
- Reduction in phospholipids compromises the integrity of the membrane, and thus
impacts neural function, resulting in memory loss and reduced cognitive function
Oxidative Stress - ✔️✔️The generation of reactive oxygen species that may result in
damage to cells
Extracellular Matrix - ✔️✔️- A network of fibrous proteins embedded in a gel-like
mixture of complex proteins
,- The ECM surrounds all cells in tissues and keeps them in place, even if they are not
physically contacting their neighbour
- The watery gel allows for diffusion of nutrients from the blood and the removal of
wastes from the cells
- Referred to as interstitial fluid
- The ECM composition is different in every tissue to allow specialized function
- The majority of the ECM is secreted by fibroblast located within the interstitial space
Fibroblasts - ✔️✔️A type of cell that synthesizes the cellular matrix and collagen
cell adhesion molecules (CAMs) - ✔️✔️- Four main categories: cadherins, selectins,
NCAMs, and integrins
- Usually transmembrane proteins
- The intracellular side of the protein interacts with the cytoskeleton, while the
extracellular side interacts with the extracellular matrix CAMs from other cells
- CAMs are involved in protein-protein interactions, as they bind with other cells or with
the ECM
Types of cell junctions - ✔️✔️desmosomes, tight junctions, gap junctions
Desmosomes - ✔️✔️- Used to anchor together two adjacent cells that are not
otherwise in direct contact
- Composed of dense intracellular thickenings known as plaques that are connected by
glycoprotein filaments containing cadherins to attach the neighbouring plaques together
- Other cytoskeletal anchoring proteins can also attach to the plaque and are combined
to allow for a network of strong fibres extending through the tissues and cells
- This feature allows the desmosome containing cells to have stretch
Cadherins - ✔️✔️Play important roles in cell adhesion by forming adherens functions to
bind cells within tissues together
Tight Junctions - ✔️✔️- Creates a tight seal between cells, preventing movement of
molecules from cell to cell
- Long strings of junctional proteins in the plasma membrane between the neighbouring
cells align and adhere to form a tight junction
- the area where opposing junctional proteins from neighbouring cells meet is called a
kiss site
- this type of junction is found primarily in epithelial tissues
Epithelial Tissues - ✔️✔️Line the cavities and surfaces of blood vessels and organs
throughout the body
Gap Junctions - ✔️✔️- Within a plasma membrane, six connexin protein subunits form
one half of a gap junction (a connexon)
, - When connexons of adjacent cells align a tunnel forms that connects their intracellular
spaces and allows them to communicate directly
- One small water soluble substance can pass through the junction and these tunnels
can be opened and closed as needed to control cell communication
- Common in cardiac and smooth muscle cells that rely on these junctions to spread the
wave of excitation
- Allow the spread of secondary messengers between connected cells which provides a
mechanism for cells to act in a cooperative manner
Permeable, Impermeable, Semi-permeable - ✔️✔️- If a substance can freely cross the
membrane, the membrane is said to be permeable
- If a substance cannot cross the membrane it is said to be impermeable
- the plasma membrane is semi-permeable, which means that some substances may
pass freely while others cannot
2 Factors that determine membrane permeability - ✔️✔️Size and Solubility
Size - Membrane Permeability - ✔️✔️- Small substances like ions can enter through
the membrane spanning ion channels
- Larger substances require a transport protein to move it across the membrane
Solubility - Membrane Permeability - ✔️✔️- A principal factor which determines
membrane permeability is how lipophilic the substance is
- Uncharged or non-polar molecules are usually very lipophilic and can readily cross the
plasma membrane
Charged or polar substances are lipophobic and cannot pass through he plasma
membrane unaided
Lipophilic - ✔️✔️Tending to combine with or dissolve in lipids or fats
Lipophobic - ✔️✔️Compounds that are not soluble in lipids or other non-polar solvents
Passive transport - ✔️✔️- A mechanism used to transport impermeable molecules
across the membrane that does not require cellular energy
- Includes Diffusion and Facilitated Diffusion
Active transport - ✔️✔️- A mechanism used to transport impermeable molecules
across the membrane that requires cellular energy
- Includes carrier mediated transport and vesicular transport
Diffusion Down a Concentration Gradient - ✔️✔️- when molecules in a solution have a
high density they frequently collide and bounce off each other which causes molecules
to spread from areas of high density to low density, or down a concentration gradient
- this is known as diffusion and occurs until no concentration gradient exists and the
movement of substances are said to be in dynamic equilibrium
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