Functions of Plasma Membrane

1. physically separates interior from exterior environment
2. recieves info about changes in the environment
3. regulates passage of materials in and out of the cell
4. communicates with other cells
5. forms compartments to allow sep. functions
6. participates in biochemical reactions

Fluid Mosaic Model

• cell membrane consists of a fluid bilayer of phospholipid molecules in which proteins are embedded
• like tiles in mosaic picture

Functions of Lipid Bilayer:

• flexible and self-sealing
• fuses with other membranes
• -->allows transport of materials within cell
• forms vessicles
• -->bud from one cell membrane
• -->fuse with another cell membrane

Properties of Lipid Bilayer:

• lipids of the bilayer
• -->fluid or liquid-crystaline state
• proteins move within the membrane

How are the plasma membrane and lipid bilayer alike?

• both can communicate with other cells
• fluid model
• hae transport of materials within the cell

Integral Membrane Proteins

• embedded in the bilayer
• can go all the way through or only partway

Transmembrane Proteins:

• extend completely through the membrane

Peripheral Membrane Proteins:

• at surface of the bilayer
• bound to exposed integral proteins

Functions of Membrane Proteins:

• transport materials
• act as enzymes or receptors
• -->cell-to-cell communication
• recognize cells
• -->self or non-self
• structurally link cells

Selectively Permeable Membranes:

• allow passage of some substances but not others
• controls volume and internal composition of cell's ions and molecules

Carrier Proteins

• transport proteins that can change as they bind and transport a specific solute

Channel Proteins

• allow water and certain ions through the membrane

Simple Diffusion

• molecules/ions move diretly through the membrane
• down their concentration gradient
• small non-polar (oxygen and some water) directly through the phospholipid bilayer
• ions and water through protein channels
• no metabolic energy directly used for transport

Facilitated Diffusion

• specific transport proteins move solutes (glucose) across a membrane
• down their concentration gradient
• no metabolic energy directly used for transport

Osmosis

• kind of diffusion that involves the net movement of water through a selectiely permeable membrane from a region of higher concentration to a region of lower concentration

Isotonic Solution

• water molecules pass in and out of the cell
• net movement of water molecules is zero
• equal solute concentration

Hypertonic Solution

• net movement of water molecules out the cell
• cell becomes dehydrated and shrinks

Hypotonic Solution

• net movement of water into the cell
• cell swells up and may even burst

Active Transport

• requires input of energy
• cell uses metabolic energy
• -->to move ions/molecules across membrane
• -->against a concentration gradient
• Ex: sodium-potassium pupu
• -->uses ATP to pump sodium ions out and potassium ions in
• independent of gradients

Exocytosis

• materials exit the cell
• membrane surface area increases
• secretory pathways
• helps with cell growth

Endocytosis

• materials enter the cell
• membrane surface area decreases

3 Types of Endocytosis:

• phagocytosis: cell ingests large solid particles (bacteria and food)
• pinocytosis: cell takes in dissolved materials, pinch off into the cytosol as tint vessicles
• receptor-mediated: specific molecules combine w/receptor proteins in the plasma membrane
• main way cell take in macromolecules
• vesicles fuse w/lysosomes and contents digested and released

Anchoring Junctions

• b/w cells in sheets of tissue
• don;t affect passage of materials between adjacent cells
• 2 common types-
• -->desmosomes:spot weld animal cells together
• --->adhering junctions:formed by cadherins and cement cells together

Tight Junctions

• tight connections between membranes of adjacent cells
• seal membranes together (nothing slips through)
• prevent movement between cells
• Ex: stomach

Gap Junctions

• composed of connexin (protein)
• formed channels
• allow communication between cells (direct communication)
• form large pores
• can be open or closed
• Ex: cardiac muscle cells

Plasmodesmata

• openings in cell walls
• channels connect plasma membranes
• allow certain ions and molecules to pass

Cell Signaling

1. synthesis, release, transport of signaling molecules;neurotransmitters, hormones, etc.;lignand bonds to a specific receptor
2. reception of info. by target cells
3. signal transduction; receptor converts extracellular signal to intracellular one; causes changes in the cell
4. response by the cell

Local Regulators

• target cell not very far from signaling cell
• direct contact
• Examples:
• histamine
• growth factors:affect cells close by
• prostaglandines: pain response
• nitric oxide: reg. circulatory system

Neurotransmitters

• local regulators
• chemical signals
• -->released by neurons (nerve cells)
• diffuse across synapses (tiny gaps between neurons)

Hormones

• move much larger distances to target cell
• chemical messangers
• -->in plants and animals
• secreted by endocrine glands (in animals)
• transported by blood to target cells

Receptors

• specific shape
• -->only matching signal molecule affects cell
• -->different cells, different receptors
• same cells make different receptors
• -->different stages
• -->different conditions
• cells can alter the number of receptors
• important to determing the specificity of cell communication

3 Responses Cells Make to Signals:

• ion channels open or close
• Ex:ion channel-linked receptor
• -->signaling molecule binds to ion channel-linked receptor
• -->ion channel opens or closes (gated channel)
• enzyme activity is altered
• -->leads to metabolic changes and other effects
• -->activate or inhibit enzymes
• alter activity of specific genes