M2: Biological Membranes Flashcards by Etin <3

2.1.5 Biological Membranes:

What are the 5 Functions of Membranes?

1) Keep all cellular components inside cell
2) Allow entry & exit of selective molecules in a cell
3) Isolate organelles from rest of cytoplasm
4) Site of biochemical reactions
5) Allows cell to change shape

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2.1.5 Biological Membranes: Fluid Mosaic Model

What’s the structure of the Fluid Mosaic Model?

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2.1.5 Biological Membranes: Fluid Mosaic Model

What’s the Fluid Mosaic Model?

When phospholipid molecles form a continuous double layer (bilayer)

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2.1.5 Biological Membranes: Fluid Mosaic Model

What’s the Phospholipic Bilayer?

Tails facing inwads

2 layers of a glycerol + 2 fatty acid tails + phosphate group

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2.1.5 Biological Membranes: Fluid Mosaic Model

Why’s the Fluid Mosaic Model described as Fluid?

Phospholipids are constantly moving

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2.1.5 Biological Membranes: Fluid Mosaic Model

Why’s the Fluid Mosaic Model described as a Mosaic?

Protein molecules are scattared through the bilayer like tiles in a mosaic

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2.1.5 Biological Membranes: Fluid Mosaic Model

How do Phospholipids form a Barrier to Dissolved Substances?

head = hydrophillic
tails = hydrophobic

Centre of bilayer is hydrophobic : membrane doesn’t allow water soluble substances (ions) through it but fat slubl substances (fat soluble vitamins) can dissolve in bilayer & pass directly through membrane

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2.1.5 Biological Membranes: Fluid Mosaic Model

What’s the function of Cholesterol?

Provides membrane stability

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2.1.5 Biological Membranes: Fluid Mosaic Model

How does Cholesterol perform its function?

Cholesterol mol fit between phospholipids
↳ bind to hydrophobic tails → pack more closely together making the membrane less fluid & more rigid

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2.1.5 Biological Membranes: Fluid Mosaic Model

What’s the affect of Cholesterol at Lower Temps?

Prevents phospholipids from packing too close together : increases membrane fluidity

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2.1.5 Biological Membranes: Fluid Mosaic Model

What are Channel Proteins?

Proteins that allows small or charged molecules through membrane

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2.1.5 Biological Membranes: Fluid Mosaic Model

What are Carrier Proteins?

Proteins that transport molecules & ions across membrabe through active transport or facilitated diffusion

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2.1.5 Biological Membranes: Fluid Mosaic Model

How do Proteins act as receptors in Cell Signalling?

When a mol binds to a protein, a chemical reaction is triggered inside the cel

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2.1.5 Biological Membranes: Fluid Mosaic Model

What are Glycolipids?

Carbonhydrate chains attached to lipids

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2.1.5 Biological Membranes: Fluid Mosaic Model

What are Glycoproteins?

Carbonhydrate chains attached to proteins

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2.1.5 Biological Membranes: Fluid Mosaic Model

What’s the main function for Glycolipids & Glycoproteins?

Stabilise the membrane by forming H bonds with sorrounding water mol

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2.1.5 Biological Membranes: Fluid Mosaic Model

What are the 3 other Functions for Glycolipids & Glycoproteins?

Site where drugs, hormones & antibodies bind
Act as receptors for cell signalling
Could be antigens

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2.1.5 Biological Membranes: Fluid Mosaic Model

Extrinsic Proteins

Intracts w hydrophillic parts of membrane

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2.1.5 Biological Membranes: Fluid Mosaic Model

Intrinsic Protein

Interacts w hydrophobic parts of membrabe

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2.1.5 Biological Membranes: Cell Signalling

What do cells use to Communicate w each other?

Messenger mol

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2.1.5 Biological Membranes: Cell Signalling

What are the 3 Steps for Cell Signalling?

A cell releases a messenger mol (e.g hormone)
This mol travels to another cell (e.g in blood)
Messenger mol is detected by cell
↳ binds to receptor on its cell membrane

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2.1.5 Biological Membranes: Cell Signalling

What are Membrane bound organelles?

Proteins in the cell membrane that act as receptors for messenger mol

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2.1.5 Biological Membranes: Cell Signalling

What do the Membrane bound organelles bind to?

Complementary messenger mols

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2.1.5 Biological Membranes: Cell Signalling

Why do Membrane bound organelles only bind to complementary messenger mol?

Difference cells have different types of receptors
↳ they respond to diff messenger mol

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# **2.1.5 Biological Membranes:** Cell Signalling What's a Target Cell?

A cell that responds to a particular messenger mol

# **2.1.5 Biological Membranes:** Cell Signalling How's Glucagon an Example of this?

* **Glucagon:** hormone released when there isn't enough glucose in blood It binds to receptors on liver cells ↳ causing liver cell to break down stores of glycogen into glucose

# **2.1.5 Biological Membranes:** Drugs use in Cell Signalling How do many drugs work?

By binding to receptors in cell membranes ↳ either trigger a response or block the receptor & prevent it from working

# **2.1.5 Biological Membranes:** Drugs use in Cell Signalling How are Antihistamines an Example of this?

Cell damage causes release of histamines ↳ binds to receptors on the surface of other cells causes inflammation

# **2.1.5 Biological Membranes:** Drugs use in Cell Signalling How do Antihistamines work?

By blocking histamines receptors on cell surfaces ↳ prevents histamines from binding to the cells & stops inflammation

# **2.1.5 Biological Membranes:** Factors Affecting Fluidity How do Temps below 0°C affect membrane fluidity?

* Phospholipids don't have much energy **:** don't move much ↳ they're packed closely together & membrane is rigid * Channel & carrier proteins in membrane **deform** ↳ increasing membrane permeability * Ice crystals may form & pierce the membrane ↳ highly permeable when it thaws

# **2.1.5 Biological Membranes:** Factors Affecting Fluidity How do Temps between 0°C & 45°C affect membrane fluidity?

* Phospholipids can move around but aren't packed as tightly together * Membrane = partially permeable ↳ as temp increases, phospholipids move around more, they have more Ke & permeability increases

# **2.1.5 Biological Membranes:** Factors Affecting Fluidity How do Temps above 45°C affect membrane fluidity?

* Phospholipid bilayer starts melting & membrane become permeable ↳ water inside cell expands → putting pressure on membrane ↳ channel & carrier proteins deform → can't control what enters & leaves cell ↳ increases permeability

# **2.1.5 Biological Membranes:** Factors Affefcting Fluidity What's the affect of Solvents on membrane fluidity? | (detergents/alcohol)

Sorrounding cells in a solvent increases permeability

# **2.1.5 Biological Membranes:** Factors Affecting Fluidity How do Solvents affect membrane permeability?

Solvents diffuse lipids in cell membranes **:** membrane loses its structure * some solvents increase permeability more than others (higher conc = increased permeability)

# **2.1.5 Biological Membranes:** Transport across Membranes What's Diffusion?

Passive process where particles move down the conc gradient through a selectively permeable membrane

# **2.1.5 Biological Membranes:** Transport across Membranes What's Osmosis?

Movement of water molecules from a dilute concentration to a more concentrated one through a selectively permeable membrane

# **2.1.5 Biological Membranes:** Transport across Membranes What's meant by Selectively Permeable Membrane?

Membrane that has small holes in it & allows small molecules through

# **2.1.5 Biological Membranes:** Transport across Membranes What's meant by Net Movement?

Overall movement of particles

# **2.1.5 Biological Membranes:** Transport across Membranes What's meant by Equilibrium?

When the rate is the same at either side

# **2.1.5 Biological Membranes:** Factors affecting Diffusion How does Conc gradient affect the rate of Diffusion?

Higher conc gradient = faster rate

# **2.1.5 Biological Membranes:** Factors affecting Diffusion How does Thickness of Exchange Surface affect the rate of Diffusion?

Thinner exchange surface (shorter distances) = faster rate

# **2.1.5 Biological Membranes:** Factors affecting Diffusion How does SA affected the rate of Diffusion?

Larger SA = faster rate

# **2.1.5 Biological Membranes:** Factors affecting Diffusion How does Temp affect the rate of Diffusion?

Warmer = more Ke **:** faster rate

# **2.1.5 Biological Membranes:** Diffusion What's meant by Simple Diffusion?

Diffusion of small non-polar molecules

# **2.1.5 Biological Membranes:** Diffusion What's meant by Facilitated Diffusion?

Diffusion of larger polar molecules

# **2.1.5 Biological Membranes:** Diffusion What's the role of Carrier Proteins in Facilitated Diffusion?

Move large mol into or out of cell 1. Large mol attaches to carrier protein in membrane 2. Protein changes shape ↳ releases mol onto opposite side of membrane

# **2.1.5 Biological Membranes:** Diffusion What's the role of Channel Proteins in Facilitated Diffusion?

Form pores in membrane for polar mol to diffuse through

# **2.1.5 Biological Membranes:** Active Transport What's Active Transport?

Movement of molecules from an area of low to high conc using ATP & carrier proteins

# **2.1.5 Biological Membranes:** Active Transport What are the steps that occur in Active Transport?

1. Mol attaches to carrier protein ↳ protein changes shape releasing mol across membrane 2. Energy is used to move solute against conc gradient

# **2.1.5 Biological Membranes:** Active Transport When is Bulk Transport used?

When extremely large substances need to be moved across a plasma membrane

# **2.1.5 Biological Membranes** Active Transport What's Endocytosis?

Bulk transport of large material into the cell via carrier & channel proteins

# **2.1.5 Biological Membranes:** Active Transport Why does Endocytosis require ATP?

To form the vesicles & move them around

# **2.1.5 Biological Membranes:** Active Transport What are Examples of Endocytosis?

* Phagocytosis: engulfing cells * Pinoendocytosis: if cells ingest liquids

# **2.1.5 Biological Membranes:** Active Transport What's the Mechanism of Endocytosis?

Segment of the plasma membrane sorrounds & closes particle & brings into the cell enclosed in a vesicle

# **2.1.5 Biological Membranes:** Active Transport What's Exocytosis

Bulk transport of large material out of the cell via carrier & channel proteins

# **2.1.5 Biological Membranes:** Active Transport Why does Exocytosis require ATP?

* Vesicle pinches off sacs of Golgi Apparatus & moves towards plasma membrane * Vesicle fuses w plasma membrane & release their contents outside cell

# **2.1.5 Biological Membranes:** Active Transport What's the Mechanism of Exocytosis?

Vesicle containing substance is moved towards & fuses w plasma membrane

# **2.1.5 Biological Membranes:** Active Transport What's an Example of Exocytosis?

**Synapses:** * Chemicals in vesicles are moved by motor proteins along cytoskeleton threads to presynaptic membrane * Vesicle membranes & plasma membrane fuse releasing neurotransmitted chemicals

# **2.1.5 Biological Membranes:** Osmosis What's meant by the term Turgid? | (hard)

Cell is filled w water

# **2.1.5 Biological Membranes:** Osmosis What's meant by the term Flaccid? | (soft)

Cell lacks water

# **2.1.5 Biological Membranes:** Osmosis What's meant by the term Plasmolysed?

Process where water is loss

# **2.1.5 Biological Membranes:** Osmosis What's Osmosis in terms of WP?

Movement of water mol from an area of high WP to an area of lower WP

# **2.1.5 Biological Membranes:** Osmosis What's Water Potential? | (measured in kPa)

Tendency of water molecules in a system to move into or out of a solution

# **2.1.5 Biological Membranes:** Water Potential What's the WP of Pure water?

Has the highest potential ( value of 0 kPa)

# **2.1.5 Biological Membranes:** Water Potential What's the WP of Solutions?

Have a lower WP than pure water ( negative WP)

# **2.1.5 Biological Membranes:** Water Potential What's meant when a solution is described to be Higher in solutes?

Its less water concentrated

# **2.1.5 Biological Membranes:** Solute Potential What's meant by Solute Potential? | Affected by the amount of solute it contains

The greater the amount of solute, the lower the solute potential ↳ water molecules bind to solute molecules ↳ reducing number of water molecules that are free to diffuse

# **2.1.5 Biological Membranes:** Pressure Potential What's meant by Pressure Potential? | Affected by the pressure applied to it

The greater the pressure, the higher the pressure potential

# **2.1.5 Biological Membranes:** Osmotic Concentration What's meant by the term Osmotic Concentration?

Relates to the amount of dissolved solutes in a solution

# **2.1.5 Biological Membranes:** Osmotic Concentration What's an Isotonic Solution?

Solutions that have the same OC as the cytoplasm of the cell

# **2.1.5 Biological Membranes:** Osmotic Concentration What's a Hypertonic Solution?

Solutions that have a higher OC than the cytoplasm of the cell

# **2.1.5 Biological Membranes:** Osmotic Concentration What's a Hypotonic Solution?

Solutions have a lower OC than the cytoplasm of the cell