cells Flashcards
do mature red blood cells have a nucleus
NO and therefore the cell cannot reproduce and will live in the bloodstream for 3-4 months before being broken down.
Plasma membrane structure and function
Structure:
* A phospholipid bilayer with embedded proteins arranged as a fluid mosaic.
Function:
* Physical barrier
* Selective permeability
* Communication
* Cell recognition
Three main components in plasma membrane
Lipids, proteins and carbohydrates
what are phospholids
lipids
Polar hydrophilic head (water lover)
Non-polar hydrophobic tail (water repeller)
Cholesterol function
- Stiffens the membrane
- Also decreases the water solubility of the membrane
Integral proteins
- Embedded in the lipid bilayer
Peripheral proteins
- Attached loosely to the membrane
Carbohydrates in the plasma membrane
- Glycolipids (attached to a lipid)
- Glycoproteins (attached to a protein)
what are the types of diffusion
- Simple (passive)
- Facilitated
What is simple (passive) diffusion
- The movement of molecules from an area of high concentration to an area of low concentration
- No energy required
- No assistance from transport proteins
What is facilitated diffusion
- Area of high concentration to an area of low concentration
- The passive movement of molecules across the membrane with the help of transport proteins.
- No energy is required, but molecules need protein channels or carriers to cross the membrane.
What are the two types of facilitated diffusion
Channel-Mediated Diffusion (leakage channels)
Carrier-Mediated Diffusion
what is channel mediated diffusion (leaky channels)
- Uses channel proteins that create a pore for specific molecules (e.g., ion channels for sodium, potassium).
what is carrier mediated diffusion
- Uses carrier proteins that change shape to transport molecules across the membrane (e.g., glucose transporter).
Active membrane transport
uses energy
may be needed for substances that are too big or moving against conc gradient
two major means of active membrane transport:
- Vesicular transport
- Active transport
Vesicular transport
moves substances across membrane in vesicles
Endocytosis: Transport of substances into the cell.
Exocytosis: Transport of substances out of the cell.
Primary Active Transport
- Active transport moves solutes against the concentration gradient. low to high
- Requires energy (ATP) to function.
Sodium potassium pump
type of primary active transport
* For each molecule of ATP used, the sodium potassium pump drives 3 Na+ out of the cell and pumps 2 K+ back in.
There are 3 main forms of gated channels:
- Voltage gated – opens and closes in response to a change in the membrane potential
- Chemically gated – open in response to a specific chemical (in neurons, it is a neurotransmitter)
- Mechanically gated – opens in response to physical deformation of the receptor (eg, touch and pressure)
Resting membrane potential
-70mV
Changes in the resting membrane potential can produce two types of signals:
Graded potentials
* Usually incoming signals (dendrites and cell bodies) operating over short distances that have variable (graded) strength
Action potentials
* Signals occurring at the axons, over long distances that always have the same strength
What is the role of proteins in the plasma membrane?
Can play a role in transport, communication and joining cells.
What is the role of carbohydrates in the plasma membrane?
They play a crucial role in cell-to-cell recognition, adhesion, and signalling
