Biological membranes

Describe the membrane’s structure- Phospholipids

• contains a phospholipid bilayer, hydrophobic tails facing interior, hydrophilic heads facing exterior. The outer surface can interact with water

Describe why the term Fluid mosaic, is used to describe the membrane

Fluid- because the phospholipids are free to move within the layer relative to each other, giving flexibility

Mosaic- because of the proteins within the belayer wich range in shape size and position

What are the different components found in a membrane

• intrinsic proteins

• Extrinsic proteins

• Phospholipids

• Glycoproteins

• Glycolipids

• Cholesterol

what are some functions of the cell membrane

• can form vesicles to transport substances

• isolates potentially harmful enzymes

• partially permiable to control which substances can leave and enter

• sperates cells from environment

Explain the roles of Intrinsic proteins

Channel proteins= provide a hydrophilic channel for passive movement of polar ions down the concentration gradient

Carrier proteins= both passive and active transport, often involves shape of protein changing

They go through the whole of the bilayer

What are glycoproteins?

Are intrinsic proteins that have carbohydrates attached to them. play a role in cell adhesion and as receptors, involved in cell signaling, act as antigens,

What are glycolipids

Lipids with attached carbohydrates, they are antigens and are involved in the immune system, stablising

What extrinsic proteins

Are proteins that are present on one side of the bilayer, they can move between layers

Cholesterol in the membrane.

• regulates the fluidity of the membranes

• They are positioned between phospholipids wich helps to add stability to membranes

What is ATP

A molecule that severs as the main source of energy for cellular processes

How does temperature effect the membrane

The phospholipids have more kinetic energy and will move more, this makes the membrane more fluid and begin to lose its structure, eventually it wills break down completely.

The loose for structure increase permeability meaning it’s easier for particles to cross.

Carrier and channel proteins will denature

Organic Solvents effect on membranes

Organic solvents are less polar then water, or they are non polar. They can dissolve membranes disrupting cells. This is why alcohol is used in wipes, as they dissolve the membranes of bacteria, killing them

Alcohols affect on membranes

Alcohol solutions are toxic as they destroy cells in the body. Less alcoholic solutions wont dissolve the membrane but they can still damage it

Non polar alcohol molecules can enter the cell membrane and the presence of theses molecules between the phospholipids disrupt the membrane

What happens when the membrane is disrupted

It becomes more fluid and more permeable

Explain simple diffusion

Movement of particles down the concentration gradient, and will continue until equilibrium is reached. It happens because the particles have kinetic energy, the movement is random

Because the particles are always moving, they collide a lot, slowing down the overall movement so shorter distance = faster diffusion

What factors affect the rate of diffusion

Temperature- higher temperature means more kinetic energy, so faster diffusion

Concentration- the greater the difference in concentration, faster the rate of reaction

Explain diffusion across membrane

Involves particles passing through the phospholipid bilayer, this can only happen if membrane is permeable to the particles. Non polar molecules diffuse freely

Polar molecules can be repealed, making it harder to pass. Sometimes than can pass but at very slow rates, smaller molecules can pass easily

Ion diffusion rate:

• surface area- larger surface area= faster diffusion

• Thickness of membrane- thinner = faster

Explain Facilitated diffusion

Channel proteins allow polar or ion molecules to move through. Facilitated diffusion is the movement of particles through a protein channel

• Membranes with protein channels are selectively permeable

• Can also involve carrier proteins, which Change shape depending on the molecules

• The rate of facilitated diffusion is the same as simple diffusion, but the more channel proteins the faster diffusion

what does local signalling mean

signalling molecules travel short distances, paracrine signalling, nerve impulses

what does distance signalling mean

signalling molecules that travel long distances

endocrine secretion, neurosecretion

why do cells need to move molecules across membranes

• secretion (protein)

• metabolism (o2)

• excretion of toxic metobolic waste (Co2)

what is active transport

the passive movement of molecules or ions into or out of a cell from a region of lower conenctraion to high. Need carrier proteins

explain carrier proteins in active transport

act as pumps

• ions bind to recpetors in the inside of carrier

• then a phosphate molecule binds changing the shape of the protein

• ions relaesed into cell

• phosphate group leaves allowing for it to go back to its orignal shpae

what is meant by bulk transport

another term for acitve transport but for larger molecules becuase they cant fit through carrier or channel proteins

what does endocytosis mean

bulk transport of material into a cell

the membrane fuses forming vesicles

whats the difference between phagocytosis and pinocytosis

phagocytosis is endocytosis of solids

pinocytosis is endocytosis for liquids

what is exocytosis

reverse of endocytosis, vesicles fuse with the cell membrane and the content is emptied outisde the cell

what does osmosis mean

the net movement of water particles from an area of high water potential to an area of low water potenital

what is water potential

the pressure exerterted by water molecules as they collide with a membrane or container

what is cytolysis

when water is moving into an animal cell. The membrane isnt flexible to hold this new volume of water and the cell will burst

what is crenation

movemnt of water out of the animal cell, causing the membrane to pucker

what is turgor pressure

an increase in water in a plant cell. Stronger cell walls causing it to become turgid. The pressure within the cell wall is called turgor

what does plasmolysed mean

when plant cells are put in a water potential lower then their own, causing the cell membrane to pull away from the cell wall

name to examples of active transport

mineral ions, root hair cells

hydrogen ions, companion cells

explain how cell signaling works

• excocytosis of signalling molecules

• SM bind to a specific receptor on the target cell

• SM have complimentary shapes to membrane recptor

• receptors can be glycoproteins