Biological Membranes

What is the structure of a cell surface membrane called?

The fluid mosaic model.

What are the tole of membranes within a cell

partially permeable barriers between the cell and its environment

between organelles and the cytoplasm and within organelles

sites of chemical reactions

• sites of cell communication (cell signalling).

What are the main components of a cell membrane?

Phospholipids, proteins, cholesterol, glycoproteins, and glycolipids.

What do phospholipids form in the membrane?

A bilayer

Which part of a phospholipid is hydrophobic?

The fatty acid tails.

Which part of a phospholipid is hydrophilic?

The phosphate head.

What is the main function of the cell membrane?

To control what enters and leaves the cell.

What does “partially permeable” mean?

Only some substances can pass through.

What is the role of cholesterol in membranes?

It strengthens the membrane and reduces fluidity at high temperatures.

Maintains/ regulates fluidity

what are glycoprotein?

protein molecules with a carbohydrate part attached.

what are the role of glycoproteins?

• Cell signalling

• Cell recognition (e.g. antigens)

• Receptors for hormones

What are the roles of proteins in the membrane?

they transport molecules ‘carrier proteins’

act as receptors

act as enzymes

forms ‘channel proteins’

What are glycolipids?

phospholipid molecules with a carbohydrate part attached?

What are the roles of glycolipids in the membrane?

act as recognition sites

provide energy

support the structure

membrane stability

What is the role of a Phospholipid?

Form bilayer which is a barrier to water soluble substances

What type of molecules can diffuse directly through the membrane?

Small and non-polar molecules

Explain why the structure of the lenten is referred to as the fluid mosaic model?

The fluid represent how the phospholipids can move freely in the membrane

The mosaic refers to the different proteins embedded in the the phospholipids

What substances can diffuse through the phospholipid bilayer and why?

Small, non-polar, uncharged molecules

What makes the cell membrane “partially permeable”?

The bilayer blocks hydrophilic substances, while transport proteins selectively allow specific molecules through.

What is the role of cholesterol in the membrane

• Maintains fluidity at different temperatures

• Prevents membrane from becoming too rigid at low temps

• Prevents membrane from becoming too fluid at high temps

Name two intrinsic proteins and their main role

carrier protein

channel protein

transport

Role of extrinsic proteins?

act as receptors

involved in cell recognition

many are glyco proteins

What is simple diffusion?

The movement of molecules from an area of high to and area of low concentration

Does diffusion require energy?

No it is passive

What is facilitated diffusion?

Diffusion through channel or carrier proteins for larger or charged molecules.

Does facilitated diffusion require energy?

No, it is a passive process.

What if the difference between facilitated and simple diffusion?

facilitated: movement of large or polar molecules such as Ca+ where as simple is non polar or smaller molecules O2.

spike is through the phospholipid bi layer where as as facilitated through aid of carrier protein or protein channel

What is osmosis?

The movement of water molecules from a dilute to a concentrated solution through a partially permeable membrane.

How to increase rate of diffusion?

concentration gradient

increase temp

greater arcade area

thinner membrane

What is fucks law?

Ficks law if the rate of which a substance can diffuse

what is the equation for rate of diffusion

rate of diffusion =

surface area x concentration difference/ distance

What is meant by “water potential”?

is the pressure exerted by water molecules as they collide with a membrane or container.

what is the water potential of pure water

0kPa

What happens to an animal cell in a solution with lower water potential (hypertonic)?

Water moves out of the cell by osmosis, the cell shrinks/ shrivels and crenates / cremation because it loses water.

What happens to an animal cell in a solution with higher water potential (hypotonic)?

Water moves into the cell by osmosis; the cell swells and may burst (lysis)

What happens to a plant cell in a hypotonic solution?

Water potential higher outside the cell

Water move into the cell,

the vacuole expands,

and the cell becomes turgid.

(The cell wall prevents it from bursting.)

What happens to a plant cell in a hypertonic solution?

Water potential is lower outside the cell

Water moves out the cell,

the vacuole shrinks,

and the cytoplasm pulls away from the cell wall

the cell becomes plasmolysed.

What happens a to both animals and plant cells in isotonic solution?

Water potential inside and outside the cell are equal

no net eminent of water

equilibrium

Adaptions for alveoli for gas exchange

thin - shirt diffusion distance to diffuse

large surface area increasing rate of diffusion

large capillary network food ventilation and maintains concentration gradient

moist gases like o2 dissolve in water burger effusion cantos s membrane which adds to the the process

Define active transport

Active transport is the movement of molecules to a region of lower concentration to a region of higher concentration against their concentration gradient which require energy in the form of ATP

How does active transport differ from diffusion?

Active transport requires energy (ATP) and moves substances against the gradient, while diffusion is passive and moves substances down the gradient.

why does active transport require energy

The ATP is used to change the shape of the carrier protein

ATP is hydrolysed into ADP and phosphate

the phosphate binds to thecarrier proteik to change its shape

the phosphate is released and its original shaped is restored

What is endocytosis

the process where cells engulf materials from their environment allowing large molecules or particles to enter the cell

What are the two main types of endocytosis?

• Phagocytosis: for large solids (e.g. bacteria).

• Pinocytosis: for liquids or small particles.

What is exocytosis?

Exocytosis is when the substances be related dis contained in vesicles

vesicles inside the cell fuse with the plasma membrane, releasing their contents (e.g. hormones, enzymes) outside the cell

It requires ATP.

How does temperature affect membrane permeability?