2.3 Transport across membranes

Where are plasma membranes found

In all living cells

Is the basic structure of all cell membranes the same?

Yes

Describe 3 functions of a plasma membranes

1. Forms a barrier between 2 environments

2. Allows different conditions to be maintained

3. Controls the movement of substances between environment

Name the 6 component of a cell membrane

1. Phospholipid bilayer

2. Extrinsic proteins

3. Intrinsic proteins

4. Cholesterol (only in animal cells)

5. Glycoprotein

6. Glycolipids

How wide is a cell surface membrane

7 nm

What bonds together a glycerol molecule and a fatty acid

Ester bond

What makes a phospholipid different to a triglyceride

Has a phosphate group and a phosphoester bond joins this to the glycerol instead of another fatty acid

What does hydrophobic mean

Repels water

What is meant by hydrophobic

Attracts water

Explain the fluid meaning of the fluid mosaic model

Refers to the lateral movement of phospholipids and sm proteins

Gives membrane flexibility

Wha does the fluid mosaic model describe

How the molecules are arranged within the membrane

What does the term mosaic mean in the fluid mosaic model

Reflects the scattered arrangement of the proteins within the bilayer

What does the fluid mosaic model explain

Membrane is

• partially permeable

• Site for cell signalling/cell recognition/communication

• Controlling the exchange of substances

Wha are the two regions of a phospholipid

1. Phosphate head —> hydrophilic (polar)

2. Fatty acid tails x2 —> hydrophobic (nonpolar)

Can a fatty acid tail dissolve in water

No

It’s hydrophobic

So no polar

So insoluble in water

Wha type of molecules/substances can pass through the phospholipid bilayer

• lipid soluble molecules

• Small

• Non charged (nonpolar)

What molecules can’t pass through the pl bilayer

• water soluble

• Large

• Charged

What part of the bilayer faces inwards and what does this form

The hydrophobic tails

With the hydrophilic heads facing outwards

Forms a selectively permeable barrier

What if the phospholipid bilayer studded with

Proteins

How far can a extrinsic protein extend

Only half way

Or

On the top membrane

How far can an intrinsic protein extent

All the way on both sides

Name three functions of an extrinsic protein

1. Structural component and mechanical support

2. Antigens for cell to cell recognition

3. Receptors

Name three functions of an intrinsic protein

1. Transport protein

• carrier protien

• Protein channel - water filled tubes —> water soluble

• Gated channel protein

• Each transport protein is specific to a specific ion/ molecule

What is a glycoprotien

Carb + protien

What is a glycolipid

Carb + lipid

Name 2 functions of glycoproteins and glycolipids

1. antigens —> cell to cell recognition

2. Cell surface receptors

   —> signalling receptors to bind to hormones

   —> endocytosis receptors

   —> cell adhesion receptors

What type of biological molecule is cholesterol

Lipid

Name the 3 functions of cholesterol in cell membrane

1. strength to membrane

   —> less lateral movement

2. Less fluid at a high temp

3. Less loss of water

Name the four processes that substances can be transported across the plasma membrane

1. Diffusion (simple)

2. Osmosis

3. Active transport

4. Facilitated diffusion

Define simple diffusion

The passive net movement of molecules

from an area of high conc

to an area of low conc

What does passive mean

Energy comes from the natural kinetic energy of the particles

What does conc gradient mean

The difference in conc in two regions

Name the four factors of diffusion

1. Conc gradient

2. Diffusion distance

3. Area of diffusion

4. Temp

Explain how conc gradient affects the diffusion rate

• the more conc differnec of particles

• The more fast diffusion

• So less conc gradient = increase

Explain how the diffusion distance affect the diffusion rate

• the more thin the exchange surface

• The faster diffusion

• As more successful collisions occur thro membrane

• Eg one cell thick

Explain how does the area of which diffusion occurs in affect the diffusion rate

• more SA = more diffusion

• As more successful collisions occur thro membrane

Explain how the temp affects the rate of diffusion

• more kinetic energy

• More diffusion

What’s the definition of facilitated diffusion

Diffusion of polar/non-lipid soluble/ charged molecules

Down a conc gradient

via a protein channel/carrier protein

Why can’t charged ions and polar molecules diffuse easily across the plasma membrane

• the hydrophobic nature of the fatty acid tails

• The movement of these molecules made easier

• By facilitated diffusion

Is facilitated diffusion passive or active

Passive

Is facilitated diffusion down or against a conc gradient

Down

But occurs at specific points on the plasma membrane

What two proteins are involved in facilitated diffusion

• protien carriers

• Protein channels

Wha are protien channels and what do they allow to diffuse thro the cell membrane

Water filled pores

Allow charged ions

why don’t protein channels diffuse ions freely

• channels are manly gated

• Part of the channel on the inside of the membrane

• Can move to close + open the pore

• Channel can control the exchange of ions

Can protein channels switch between two shapes?

No

Only carrier proteins can

How do carrier proteins function

• the binding site of the protien to be open on one side of the membrane

• Then open to the other side when the protein changes shape

• Each protein binds to specific type of molecule

• Down a conc gradient

What does osmosis mean

The net movement of water

from a region of high water potential

To a region of low water potential

Across a partially permeable membrane

Is osmosis passive or active

Passive

What is water potential and what is it represented by and its unit

• water conc

• Psi (trident)

• kPa (kilo pascal)

What is the water potential of pure water

• 0

What does hypertonic solution mean

Low water potential

Isotonic solution meaning

Same water potential compared to other solution

Hypertonic solution meaning

High water potential

Explain what happens if you put a red blood cell in a

• hypotonic solution

• Isotonic solution

• Hypertonic solution

• HYPERTONIC —> water leaves cell so shrinks

  —> RBC has higher water potential than solution

• HYPOTONIC —> water enter cell so cells burst and swell

—> RBC has lower water potential than solution

• ISOTONIC —> no net CHNAGE

  —> water potential is equal

Explain what happens when you put a plant cell in a

• hypotonic solution

• Isotonic solution

• Hypertonic solution

HYPERTONIC

—> water leaves plant cell thro osmosis

—> protoplast shrinks

—> pulls away from cell wall

—> plasmolysis

ISOTONIC

—> net movement equal

HYPOTONIC

—> water enters cell

—> vacuole expands

—> cell = turgid

—> cell wall prevent burst

Why do you blot the potatoe/beetroot cylinders dry

To remove excess moisture

Not to affect mass

Define active transport

The movement of molecules

From a region of low conc

To a region of high conc

Using energy from respiration

What two processes require a carrier protein

Active transport

Facilitated diffusion

Explain the process of active transport

1. Molecule binds to a complementary binding site on a carrier protein

2. On the inside of the cell - ATP binds to the carrier protein

3. ATP = hydrolysed to ADP and Pi by enzyme ATP hydrolase ands releases energy

4. Causes a conformational change in the protein

5. Allows the molecule to be transported to the other side of the membrane where it’s released

6. Pi molecule is released from protein

7. Pi recombines with ADP to form ATP in a condensation reaction catalysed by ATP synthase

8. Cause protein to return to original shape

NEED TO DO COTRANSPORT