Cell membranes

What are plasma membranes

Membranes surrounding cells and cell organelles

What are cell surface membrane

The membrane surrounding the cell

Where are phospholipid bilayer found

Cell surface membrane

Structure of phospholipid membrane

Hydrophillic polar, phosphate group head that attracts water so face outwards

Hydrophobic tail made of fatty acids (non polar) that repels water so faces inwards

Functions of phospholipids in membrane

Allow lipid soluble substances to enter and leave the cell

Prevent water soluble substances entering and leaving the cell

Make the membrane flexible and self sealing

What are the function of proteins that are only on the inner or outer surface (peripheral)of phospholipid bilayer?

For mechanical strength

Connects glycoproteins that acts as receptors together with glycolipids

What are the function of integral proteins( spans the phospholipid bilayer from one side to the other)

Protein channels - facilitates diffusion of water of water soluble ions across the membrane

Carrier proteins - bind to large molecules and then change shape in order to move these molecules across the membrane

What is the function of cholesterol within the phospholipid bilayer?

Add strength to cell surface membrane

Hydrophobic so prevent water loss and dissolved ions from cell

Reduce lateral(side to side)movement of fatty acids of phospholipids, without not making the cell too rigid.

Makes membrane less fluid at high temperatures

Functions of glycolipids in the phospholipid bilayer

Acts as recognition sites

Helps maintain stability of the membrane

Helps cells to attach to one and other so form tissues

What are glycolipids and their functions

Carbohydrate chains attached to extrinsic proteins

Acts as recognition sites

Helps cells recognise each other to form tissues

Help lymphocytes recognise their own cells

What properties would prevent substances to pass through cell surface membrane?

Non lipid soluble substances(non polar)

Water soluble(polar molecules)

Electrically charged molecules.

Large molecules

Why is it called the fluid mosaic model?

Fluid- phospholipid molecules move relative to one another so constantly changing in shape

Mosaic- proteins embedded in the phospholipid bilayer vary in shape size and pattern

What affects the phospholipid bilayer to be more fluid

Higher temperature

More fatty acids

Shorter tails

What affects the phospholipid bilayer to be less fluid

More cholesterol

What does passive mean

Processes rely on inbuilt kinetic energy of the molecules not ATP released from respiration.

Do particles stop moving when they reach equilibrium

All particles are constantly in random motion due to the kinetic energy they possess

What is diffusion

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

What type of molecules can pass through cell surface membrane?

Small, non polar molecules such as oxygen and carbon dioxide.

Facilitated diffusion

Charged ions ands polar molecules can’t diffuse easily because of the hydrophobic nature of the tails, so they need protein channels and carrier proteins to get across the membrane.

Protein channels

Transports specific water soluble ions, through water filled hydrophillic channels.

Selective as it only opens in the prescience of a specific ions

Ion binds to protein, changing shape so it closes on one side of the membrane and opens it on the other side

Carrier proteins

Transports specific molecules e.g. glucose.

Specific molecules bind to proteins causing a change in shape. This causes particles to be released on the other side of the membrane

Osmosis

Net movement of water molecules or ions from an area of high water potential to an area of low after potential through a partially permeable membrane.

Why is there sometimes osmosis in the phospholipid bilayer

Water ions are weakly charged and is a small molecule

What is a solute

The substance that is being dissolved

What is the solvent

The substance the solute is being dissolved in

Solution

The solute dissolved in solvent

Aquaporins

Water selective Protein channels that facilitate diffusion of water

Water potential

Measure of pressure created by water molecules, units are kiloPascals.(kPa)

What happens to the water potential when a solute is added to pure water

It lowers and has a negative water potential because pure water has 0kPa.

What happens when more solute is added to pure water

The water potential lowers more because solution is more concentrated

Ie the more concentrated a solute the lower the water potential.

What prevents animal cells from bursting by osmsis?

Don’t have cell wall

Animals cells live in blood plasma which has the same water potential as the water potential inside red blood cell.

Active transport

Net movement of molecules or ions from an area of low concentration to high concentration using ATP and carrier proteins.

How is active transport selective

Carrier proteins have a specific tertiary structure and will only transport and bind to specific substances across the membrane. They have binding sites.

Outline the process of active transport

Molecule binds to a specific receptor site on one side of the carrier proteins

On the inside of the cell, ATP also binds to the protein

ATP is hydrolysed into ADP and a phosphate molecule, causing the protein to change shape and open on the other side of the membrane

Molecule is released to the other side

Phosphate molecule is release and the carrier proteins returns to its original shape. Phosphate is then combined with ADP to make ATP so process repeats.

What is ATP

ATP is the energy currency for the cell.ATP forms when a chemical reaction releases sufficient energy to bond to a third phosphate group to ADP. Energy is stored in bonds between three phosphate groups.

What happens when ATP is hydrolysed

ADP is formed and energy is released from bonds being broken. Energy is used for transport, movement etc.

What is sodium potassium pumps

Some carrier proteins actively transport more than one molecule or ion in the same or opposite way at the same time by active transport. For example, sodium potassium pumps take in potassium ions and remove sodium ions.

How are sodium and potassium ions transported by active transport : sodium potassium pump

Cytoplasmic sodium binds to sodium potassium pump

Na+ binding stimulates phosophorykation by ATP which is bonded to pump,so that it breaks down into phosphate group and ADP.

Phosphorylation causes the protein the change shape (conformation change),expelling Na+ to the outside.

Extra cellular K+ binds to the protein , triggering the release of the phosphate group, so it goes back to its original shape

K+ is released and Na+ sites are receptive again; the cycle repeats.

Where are villi and micro villi on ileum?

Villi line ileum

Micro villi line epithelial cells which line the ileum

What increases facilitated diffusion?

Increased surface area, more protein channels and carrier proteins, blood is constantly circling away so concentration gradient is maintained.

Why doesn’t facilitated diffusion remove all glucose from the ileum

Eventually equilibrium is reached so not all amino acids and glucose can be absorbed

Co- transport

Process by which 2 molecules are simultaneously transported across a membrane using one carrier proteins. Both molecules move along concentration gradient.