Biological membranes

Fluid mosaic model

Theory of cell membrane structure with proteins embedded in a sea of phospholipids

Glycolipid

Phospholipid chain with a. Chain of carbohydrate molecules attached

Glycoprotein

Protein with a chain of carbohydrate molecules attached

Plasma membrane

Cell surface membrane

Describe the plasmas membrane

Partially permeable

Roles of membranes at surface of cells

Separates cells components from external environment

Regulates transport of materials in and out of cell

Contains enzymes involved in specific metabolic pathways

Has antigens

Releases chemicals as signals to other cells

Why do plasma membranes have antigens at the surface of cells

So that immune system recognises the cell as itself

Purpose of plasma membranes inside cells

Chloroplasts-reactions of photosynthesis

Small intestine-digestive enzymes on plasma membrane

Why are there digestive enzymes on the plasma membrane of epithelial cells in the small intestine

Catalyse breakdown of sugars

What type of proteins are the channel and carrier proteins

Integral proteins

Why are glycocalyx on the outside of the membrane

Very hydrophilic and attract water with dissolved solutes helps cells interact with water environment

Glycocalyx definition

Carbohydrate molecules

Why is cholesterol in the plasma membranes

Gives mechanical stability and flexibility

What proteins are there in the plasma membrane

Peripheral

Carrier

Channel

Purpose of channel and carrier proteins

Their membranes interact with hydrophobic region of phospholipid bilayer

Inside channel protein

Water filled channel lined with hydrophilic amino acids

What are glycocalyx attached to

Either lipids or proteins

Neurones membrane

Protein channel and carrier proteins covering axon allow entry adn exit of ions for conduction of electrical impulses

What is the myelin sheath formed from

Flattened Schwann cells wrapped around axon

What forms the membrane in neurones

Myelin sheath

Maybe idk

Plasma membranes in white blood cells

Protein receptors -enables them to recognise antigens on foreign cells

Root hair cells membranes

Carrier proteins to actively transport nitrate ions from soil into cells

Diffusion

Movement of molecules from an area of high concentration to a low concentration

Doesn’t involve ATP

Facilitated diffusion

Movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane via protein channels or carrier proteins embedded

Doesn’t involve ATP

Name 2 Passive processes in the cell membrane

Removal of toxic carbon dioxide

Export Enzymes hormones

What are passive processes

Where use only kinetic energy of molecules and do not use ATP

What happens when molecules move down their concentration gradient

Still moving randomly

Remain evenly dispersed

No net diffusion

Reached equilibrium

In diffusion do molecules move up or down concentration gradient

Down

What determines the rate of diffusion

Concentration gradient

Diffusion distance

Surface area

Temperature

Size of diffusing molecule

What small molecules can pass through cell membranes by diffusion

Oxygen carbon dioxide

What large molecules can pass through the cell membranes

Fat soluble molecules e.g steroid hormones

Diffuse through cell membrane and dissolve in lipid bilayer

Down concentration gradient still

How is the concentration gradient maintained in cell membranes -oxygen

Oxygen diffuses into cytoplasm of respiring cells then diffuses into mitochondria for aerobic respiration

How is the concentration gradient maintained in cell membranes-co2

Co2 diffuses into palisade mesophyll cells of plant leaf then diffuses into chloroplasts for photosynthesis

Thylakoid

Inner membranes of chloroplasts that house chlorophyll

How does temperature affect rate of diffusion

Higher temp

More KE

Particles move faster

How does surface area affect rate of diffusion

More diffusion across larger surface area

How does size of diffusing molecule affect rate of diffusion

Smaller ions or molecules difffuse quicker than larger ones

How does concentration gradient affect rate of diffusion

Steeper concentration gradient faster rate of diffusion

What types of molecules are insoluble in lipids

Small molecules that have polarity such as ions As cannot interact with hydrophobic tails of lipid bilayer

How do polar molecules diffuse through the cell membrane

Transmembrane Water filled proteins channels Embedded in the membrane

How does cholesterol affect a cell membrane

Reduces the permeability of the membrane to small water soluble molecules

How do glucose molecules diffuse through the plasma membrane

Bind to transmembrane carrier proteins which pens to allow glucose to pass on other side

Carrier proteins are specific to the typ of molecule

Neurones plasma membrane

Ratio to transmembrane protein channels and transmembrane protein carriers

N

Many channels specific to sodium or potassium ions

Important for conduction of nerve impulses

Some Calcium and chloride ion channels

Plasma membranes of Epithelial cells

Transmembrane protein channels

Many chloride ion channels

Why do plasma membranes of epithelial cells have many chloride channels

To regulate composition of mucus to trap pathogens

Osmosis

Movement of water molecules down water potential gradient across a partially permeable membrane

Water potential

Tendency of water molecules to diffuse from one region to another

How do water molecule spass through the phospholipid bilayer

Directly through

Aquaporins

Protein channels in SOME membranes

Purpose of aquaporins

Allow water to pass through more rapidly

What are cell surrounded by

Extracellular tissue fluid

How do smaller ionic solute molecules have a greater effect on water molecules

Is solute molecules dissociate from e.g sodium chloride to sodium and chloride ions greater effect on relative number of water molecules

Bc number of particles in the solution doubles

How are root hair cells specialised for active transport

Have many carrier proteins to actively transport nitrate ions from the soil into hair cells

Proportion of lipids to protein in mitochondria and why

More protein as inner membranes contain electron carriers that are made of protein and hydrogen ion channels associated with ATP synthase enzymes

Diffusion

Movement of molecules from a high concentration to a low concentration

Facilitated diffusion

Movements of molecules form an area of high concentration to an area of low concentration across partially permeable membranes via protein channels or carriers

Doesn’t involve metabolic energy

How do fat soluble molecules go across membranes

Diffuse through cell membranes as they dissolve in teh lipid bilayer

Move down their concentration gradient

Why does diffusion occur

To evenly disperse particles

When is there no net diffusion and why

When molecules move down their concentration gradient they remain evenly dispersed so there is no net diffusion

They have reached equilibrium

How do water molecules pass through the plasma membrane and why

Polar and insoluble in lipids in phospholipid bilayer Move down

But in large concentrations it does direct diffusion

How are membranes that require lots of water specialised

Aquaporins

How is the concentration gradient maintained in a leaf

Carbon dioxide diffuses into palisade mesophyll cells then diffused into chloroplasts

Factors affecting rate of simple diffusion

Temperature

Diffusion distance

Surface area

Size of diffusing molecule

Concentration gradient

How does the size of the molecule affect rate of simple diffusion

Smaller ions diffuse more rapidly than larger molecules

What type of molecules are insoluble in lipids and why

Small molecules that have polarity

As cannot interact with hydrophobic tails of lipid bilayer

How do lipid insoluble molecules pass through the lipid bilayer

They diffuse through water filled protein channels embedded in the membrane

Why does glucose pass through the membrane differently

Too late to diffuse through water filled protein channels

Water potential

Measure of tendency of water molecules to diffuse from a one region to another

What type of water has the highest water potential

Pure water

What happens to water potential when solutes are addded

Lower water potential

Units of water potential

Kilopascals

Water potential of pure water value and units

0 KPa

What happens to the value of water potential when solutes molecules are addded

Water potential becomes more negative

How do animals cells act in solutions of pure water very high water potential

Burst open and are cytolysed

How do animals cells act in solutions of low water potential

Water moves out of the cells by osmosis down a concentration gradient

Animal cells shrink and

How do plant cells act in high water potential solutions

Cell wall prevents bursting

Cell is turgid as membrane pushes against the cell wall

How do plant cells act in low water potential solutions

Plant cell membrane pulls away from cell wall as water leaves the cell is plasmolysed

Active transport

Movement of substances Against their concentration gradient from low to high concentration

Using ATP and protein carriers

Endocytosis

Transport of molecules that are too large to pass through the cell membrane

Exocytosis

Transport of molecules of a cell

Too large to pass through a cell membrane

Describe the two specific regions of a carrier protein

Sites that combine reversible with certain solutes or ions

Sites that binds to and allows a molecules of ATP to release energy

What does energy in carrier proteins do

Allow it to change its conformation

To carry ion across cell membrane

Guard cells-active transport

ATP made by chloroplasts provides energy for active transport of potassium ions from surrounding cells by osmosis

Does Bulk transport require ATP

Yah

How are large particles brought in to a cell

Endocytosis

Segment of plasma membrane surrounds and encloses particle and brings it into the cell enclosed in a vesicle

Is Phagocytosis Endocytosis or exocytosis

A type of Endocytosis

Phagocytosis

Intake of solid mater

Phagosome

Phagocytic vesicle

Pinocytosis

Cells ingest liquids

Is Pinocytosis a type of endo or exocytosis

Endocytosis

What is needed to form vesicles

ATP

What is needed to move vesicles

Molecular motor proteins

Along cytoskeleton threads

Into the cell interior

NOT EQ

Exocytosis explain how it works

Vesicle containing the large molecule is moved towards and fuses with plasma membrane

Example of exocytosis at synapses

Chemicals in vesicle are moved by motor proteins along cytoskeleton threads to the presynaptic membrane

Vesicle membranes fuse with plasma membrane

Neurotransmitter chemicals released into synaptic cleft

Is energy needed in exocytosis Adn why

Yes

To fuse membrane together and movement of vesicle

How does a decrease in temperature affect the cell membrane

Saturated fatty acids become compressed

Unsaturated fatty acids push adjacent phospholipid molecules away

Maintains membrane fluidity

What determines the membranes fluidity at cold temperatures

Proportion of unsaturated to saturated fatty acids become acids

How does cholesterol reduce the effect of cold temperatures on the plasma membrane

Prevents phospholipid molecules from packing closely together as cholesterol molecules are in between groups of phospholipid molecules

When temperature increases what happens to the plasma membrane

phospholipids have more kinetic energy adn move around more increasing membranes fluidity

Permeability increases

Some Proteins in membrane change position which alters the rate of reactions they catalyse

What does an increase in membrane fluidity affect and how?-2-

Infolding of plasma membrane In phagocytosis

Changes ability of cells to signal to other cells by releasing chemicals by exocytosis