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Chapter 3Movement of substances across the plasma membrane

- Plasma membrane- outstanding features cell- Its control all the substances which is

moving in/ out of the cell

1)What cause of the substances to move in/out? And how does the plasma membrane control it?

2)Why the water molecule can enter to the cell and why doesn’t the same thing occurs when its comes to starch/ protein molecule which is larger?

- In the early of 70s , S.Singer and G.Nicholson did research on plasma membrane and called it as ‘Fluid Mosaic Model’.

- Plasma membrane consist of phospholipid bilayer, glycoprotein, protein, carbohydrates chain, cholesterol molecules , lots of carrier and pore proteins.

1) Fluid Mosaic ModelFluid- refer to not rigid/ static but form a dynamic and flexible structure

Mosaic- Protein molecules are found embedded/ attached partially to the surfaces.- these proteins float about freely on the bilayer to

form a ever changing pattern.

As a conclusion plasma membrane has a fluid characteristics which allow cell to be more flexible.

a) Does a cell looks like watermelon or 50 cents coins?

-fluid structure can be move freely and not being rigid.

b) What is rigid?

c) If the cell membrane can move so fluidly, what if too fluid then can’t support the mass of the cell and eventually it will burst, right? How the plasma maintain their structure?

- Researchers found out that, protein structure which are attached to it, they make stability for plasma membrane.

- Therefore fluid inside the plasma membrane is control by the protein & other structure that are embedded.

2) Structure of plasma membrane- Consists of bilayer phosphates (2 layer of lipid) embedded/ attached into them.a) What are the other things which are attached?- Proteins (3 different important protein)- Eg. Glucose molecules comes and attached to the

carrier protein, which will open up and allows the glucose molecule to pass thru the plasma membrane.

- Pore protein- has very thin pore in between/ smaller version of pore or hole. This little pores allows ions to move in/ out of the pore protein.

- Phospholipid bilayer separates both sides of the membrane and cholesterol attached to the plasma membrane.

- this links fatty acids of the phospholipids, stabilize and strengthens the cells.

- Cholesterol makes plasma membrane mr flexible and less permeable to other water soluble substances. Therefore its creating a semi permeable/ selective permeable. (characteristic of plasma membrane)

- Glycoprotein act as a part of identity to the cell. Recognize each other based on protein/ glycoprotein which are attached.

Protein- pore protein [transport small, polar substances such as ions K+(potassium), Na+(sodium) and Cl- (cloride ions) ]

- carrier protein (transport large, non polar substances such as amino acids/ glucose)

What is polar?-known as charged molecules- In biology, used the term ‘polarity/ polar’

3) Special characterictics of plasma membrane• selective permeability (Some substances can move across

but other can’t gain entry in to the cells)• Factor affecting permeability- Size of molecule- Polarity of the molecule

Eg. Bacteria trying to attack us, the moment the bacteria gets into our body, WBC will determine that it’s pathogen and WBC would identify these would not belong to us based on its protein found in the plasma membrane. WBC doesn’t attack our own cells.

4) Phospholipid bilayer- Consists of head and tail, between the 2 phospholipid molecules had to be a little gap which is small and allowing a very small molecules to squeeze to them.- Consists of reagent known as lipid (fats),

therefore only the same class as lipid could penetrate thru.

- Special molecules (H2O)can pass thru the plasma membrane.

So water, small lipid molecules (VIP of the cell) that pass thru without any obstruction.

Why we have 2 layers of phospholipids?Head - consists of phosphate ions

- hydrophilic - can dissolve in water- polar

Tail - consists of lipids- hydrophobic- can’t dissolve in water- non- polar

Que 1. What are characteristics of phospholipid molecules?Que 2. Why its called as hydrophilic/ hydrophobic characteristics?

- 2 phospholipids molecules will clear and push the water away, so that the tails faced on inside. In that case, the liquid inside/ outside was separated by the phospholipid molecules.

ASSESSMENT

1. The current structure of the plasma membrane is best describe by using the

A. Phospholipid bilayer modelB. Fluid mosaic modelC. S.Singer & G.Nicholson modelD. Plasma membrane of plant cell

2. The main component that make up the plasma membrane of cell areE. Protein & carbohydratesF. Protein & phospholipidsG. Phospholipids & carbohydratesH. Protein, phospholipids and carbohydrates

3. Which substances can move freely across the phospholipids of the plasma membrane?A. GlucoseB. GlyserolsC. Amino acidsD. Ions

4. When only specific substances can move across the plasma membrane, it is said to beE. Semi permeableF. ImpermeableG. PorousH. Selective diffusion

5. Why is the model used to describe the plasma membrane is called a ‘Fluid Mosaic Model’?- The protein molecule and phosphate float laterally

and freely- The various protein found in the phospholipid

bilayer that form the Mosaic pattern are always changing patterns

6. What are the factors that determine the permeability of a substances?- Size and polarity of the molecules

7. Why is the phospholipid bilayer of the plasma membrane arranged opposing each other?- The characteristic of the phospholipids where head is hydrophilic and tail to be hydrophobic made to be arranged opposing each other.

8.The tail of the phospholipid is hydrophobic and its prevent polar molecules from passing through. Why is water, being a polar molecule able to pass through the plasma membrane easily?- Water could pass through the plasma membrane easily because water molecule is very small.