topic 2 - transport across the cell surface membrane

What does the cell surface membrane form

A boundary with the cells cytoplasm and the environment surrounding the cell

What is the role of the cell surface membrane

Controls what enters and leaves the cell

What is the cell surface membrane made of

Phospholipids which have a hydrophobic an a hydrophilic region

What are the three functions of phospholipids in the cell surface membrane

• allows lipid soluble substances to leave and enter easily

• Prevents water soluble substances leaving/entering easily

• Makes the membrane flexible and self sealing

What in the membrane helps cells adhere together

Proteins

What are the three functions of cholesterol in the membrane

• adds strength to it

• Prevents loss of water and dissolvable ions

• Limits phospholipids movements without making the membrane rigid

How does cholesterol prevent the loss of water and dissolved ions

It’s hydrophobic

How does cholesterol limit the movement of the membrane and how is this beneficial

• pulls the fatty acid tails of a phospholipid together

• Means the membrane is less fluid at high temperatures

What are glycolipids

Carbohydrates covalently bonded with lipids

What are four functions of glycolipids in the cell surface membrane

• A receptor for certain chemicals

• Maintains membrane stability

• Acts as a recognition site

• Helps cells adhere to create tissues

What part of the glycolipids acts as a receptor and how

• carbohydrate portion

• It’s hydrophilic and is able to extend into the water environment surrounding the cell

What is a glycoprotein

Carbohydrates attached to any extrinsic protein on the CSM

What are three functions of glycoproteins on the CSM

• act as receptors specifically for hormones and neurotransmitters

• Helps cells adhere together to create tissues

• Allows cells to recognise each other

What molecules can’t pass through the CSM (4)

• ones not soluble in lipids

• Ones that are too large to pass through

• One’s with the same char age as the protein channels

• Polar molecules

Why cant polar molecules pass through the CSM

Because they are electrically charged whilst the fatty acid tails are not (they’re non-polar)

What dose the fluid aspect of the fluid mosaic model suggest

That phospholipids can move relative to one another making the membrane flexible and allows the structure to change shape

What is the mosaic part of the fluid mosaic model

Proteins embedded in the membrane vary in shape ad size

How does temperature affect the cell surface membrane

Affects how much the phospholipids move which affects the membrane structure and permeability

How do temperatures below 0 degrees affect the CSM

• phospholipids have little kinetic energy so dont move much

• Phospholipids re rigid and tightly packed together

• Channel and carrier proteins denature increasing permeability

• Ice crystals may form and pierce the membrane increasing permeability

How does the denaturing of carrier and channel proteins increase permeability

Their change in shape could create gaps in the membrane

How do temperatures between 0 and 45 degrees impact the CSM

• phospholipids can move around and aren’t tightly caked - more flexible

• Partially permeable

What happens to CSM at temperatures above 45 degrees

• starts to melt and becomes more permeable

• Water in the cell starts expanding and puts pressure on the membrane

• Channel and carrier proteins denature and increases permeability

Is simple diffusion passive or active

Passive, particles rely on the natural kinetic energy they possess

Particles naturally —— themselves ——- throughout the vessel they’re in

Distribute. Evenly

What i simple diffusion

Net movement of molecules or ions from a region of high concentration to low concentration until evenly distributed

When is facilitated diffusion used

When substances cant pass through the CSM

What is used in facilitated diffusion

Carrier and channel proteins

Is facilitated diffusions passive or active

Passive

How do channel proteins control the entry and exit of ions

They open in the presence of a particular ion that binds to it and makes it change shape so the ion can pass through

What two things affect facilitated diffusions

• increased conc.g increases the RoFD

• No. Of channel and carrier proteins

What is osmosis

Diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of low water potential

What is water potential and what is it measured in

Pressure created by water molecules. Measured in kilapascals kPa

What is the partially permeable membrane permeable to

Water and a few small molecules

What are the standard conditions for pure water and what is the water potential of water at these conditions

25 degrees 100kPa water potential = 0

What does adding solutes to pure water do to the water potential

Decreases it

All solutions have what kind of water potential

Negative

A low water potential means there’s a —— water potential

High

What does isotonic mean

Two solutions with the same water potential

What happens to cells in an isotonic solution

Nothing, they wont lose or gain water by osmosis

What does hypotonic mean

Solutions with a higher water potential compared to the inside of a cell

What happens to cells placed into a hypotonic solution

Water draws into the cell via osmosis making it swell

What does hypertonic mean

Solutions with a lower water potential compared to the inside of a cell

What happens to a cell placed into a hypertonic solution

Water draws out of a cell into the solution via osmosis making the cell shrink

What three factors impact osmosis

• water potential gradient

• Thickness of exchnge surface

• Increased SA leads to a faster RoO

What is Clive transport

The movement of molecules or ions in or out of a cell against its concentration gradient from an area of low concentration to an area of high concentration using ATP and carrier proteins

What is the process of active transport (4 steps)

• ion binds to specific receptors on carrier protein

• ATP binds to protein and undergoes a hydrolysis reaction which releases energy

• Molecule/ion is released to other side

• Phosphate molecule is released from carrier protein and and protein returns to original shape

What is the hydrolysis reaction that takes place during active transport

ATP —- ADP + Pi

What happens to the Pi released during the hydrolysis reaction during active transport, what is this an example of

It remains on the carrier protein ATP binds

Example of phosphorylation

What does the Pi cause to happen on the carrier protein

Makes it change shape so the molecule/ion can pass through

What happens to the Pi once its released from the carrier protein

Recombined with ADP during respiration

What is co-transport and when does it happen

• ion/molecule moved in the same direction at the same time as another one using active transport

• Happens as on molecules is being removed and another is moving into a cell or organelle

An example of co transport

• sodium potassium pump

• Absorption of glucose or amino acids

What is the process of the absorption of glucose or amino acids using co transport

• sodium is actively transported out of epithelial cells by the NA+K+ pump

• Sodium diffuses down its conc.g back into the epithelial cells using a carrier protein

• At the same time AA or glucose is transported through that same carrier protein into the cell

• AA or glucose hen diffuses into the blood plasma via facilitated diffusion