chapter 1-part ii (student version)

8/7/2019 Chapter 1-part II (student version)

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Chapter 1

Transport of cell


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Importance of transport of cell

Supply raw material to cell for anabolism

Regulate pH and solute concentration for

maintaning a stable internal environment Excrete toxic waste substances

Secrete useful substances for cell

activities


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Permeability of membrane to

substances Structure of membrane

Size and charge of the molecule

concerned


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Different molecule move through different component of plasma membrane

Characteristic of

substance

Example Component of plasma

membrane

Method of

transport

Very small,

uncharged, non-polar,hydrophobic

Oxygen, carbon

dioxide, steroid

Phospholipid bilayer Simple

diffusion

Small, hydrophilic

ions,

Sodium ions,

bicarbonate ionsPore protein or carrier

protein

Facilitated

diffusion

Small, charged ions Potassium,sodium, calcium,

chloride,

bicarbonate ions,

Hydrophilic channelprotein

Facilitateddiffusion

Water molecules -- Aquaporins (water

channel protein)

Osmosis

Large, charged ions Sodium ions,

glucoseCarrier protein

(expenditure of energy)

Active

transport,

cytosis

Large, charged ions Amino acid,

glucose, nucleic

acid, glycerol

Carrier protein (does

not nee the

expenditure of energy)

Facilitated

diffusion


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Movement of substances across membrane

Consume cellular energy Does not Consume cellular

energy

Active

transport

Simple

diffusion OsmosisFacilitated

diffusion

Cytosis

EndocytosisExocytosis

Pinocytosis


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Diffusion


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Diffusion


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Diffusion:

Based on: (1) the concentration gradient

(2) surface area

(3) distance over which diffusion

takes place(4) size and nature of the diffusing

molecule

(5) surrounding temperature

Principle: from higher solute area to lower

solute area until equilibrium is

established


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concentration

Distance from dye region to water region

Concentration gradient ofwater molecule

Concentration gradient of

dye molecule

Concentration gradient of water molecule = o

Concentration gradient of dye molecule = o

Concentration

of dye molecule

Concentration ofwater molecule


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Facilitate

diffusion


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Facilitated

diffusion of

glucose into

cell


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Osmosis

P

rinciple: the passive movement of water(solvent molecule) from a region

of higher concentration of water

molecule to a region of lowerconcentration of water molecule

across a semi permeable

membrane


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Water potential:

the difference between the chemical

potential of the water in a biological

system and the pure water at the same

temperature and pressure.

water molecules have free kineticenergy which causes them to move

rapidly and randomly in a system. The

total kinetic energy of water moleculesin that system is termed as water potential

which is expressed on pressure.


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Direction of

water

diffusion

Water potential values

Pure water Higher

Lower

Zero 0

Less

negative

-500Pa

Other

solution

More

negative

-1000Pa


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Solute potential s

The force of attraction on water molecules

by solute molecules of the dissolved

substances in a solution

The attraction between solute molecule

and water molecule reduces the random

movement of water molecule. The addition

of more solute molecules lower the waterpotential of a solution.


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Pressure potential P

Is the pressure exerted on a fluid by itssurrounding. If pressure is applied to a solution,it tends to force the water molecule to move fromone place to another.

When water enters a plant cell by osmosis, the

vacuole expands and exert a pressure on thecell wall making the cell turgid. The cell walldevelops an opposing pressure or pressurepotential to resist the influx of water.

Pressure potential is usually positive and isexpressed in kPa. In a plant cell, the value ispositive when the cell is turgid and 0kPa when itis flaccid.


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= S + PWater solute pressure

potential of potential potential

cell

(Net tendency of plant osmotic pressure or called

cell to take up water in animal cell turgor pressure

by osmosis)


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Solution Water

potential

Solute

potential

S

Pressure

potential

P

Isotonic Same same same

Hypotonic high Low (less

negative)

low

hypertonic low High (more

negative)

high


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Exercise

1. Study the diagram shown in which twosolutions are separated by a partiallypermeable membrane.

(a) Which solution has a higher waterpotential?

(b) In which direction will osmosis occur?

Why?(c) What is the relationship between s and

of a solution?


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2. Which of the following two solutions with

values shown below is hypertonic to

the other and why?

(a) solution K = -2000kPa

(b) solution L = -1000kPa


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3. For question 3 -5,

(a) Calculate for cell A and cell B.

(b) State the direction of water movement.Cell A Cell B

3 s= -1400kPa

P

= 400kPa

s= -1800kPa

P

= 600kPa

4 s= -800kPa

P

= 400kPa

s= -800kPa

P

= 400kPa

5 s= -800kPa

P

= 500kPa

s= -600kPa

P

= 600kPa


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6. Explain briefly what is the outcome of

immersing an onion cell is a solution ofconcentrated sucrose solution,

(a) For 5 minutes and then placing the cell in

distilled water(b) For 20 minutes and then placing the cell

in distilled water


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Exercise

7. What type of drink should a heavily perspiring

athlete take, a hypertonic, hypotonic or

isotonic. Give the reason.

8. Plant cell X has a solute potential of -450kPaand a pressure potential of 150kPa. Adjacent

to it, is plant cell Y which has a solute potential

-350kPa and a pressure potential of 250kPa.

Use the water potential equation to predict thedirection of net movement of water in between

the two cell


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Condition of cells in different concentrations of solution


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Red blood cell feature in different concentration of

solution


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Incipient plasmolysis

the condition of the protoplast at thevery initial stage of plasmolysis.

this cause the plasma membrane of the

plant cell to just touch the cell wall


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Active transport Transport of substances across plasma membrane against

concentration gradient by using cellular energy and carrierprotein.

Two type of active transport:

(a) direct active transport

e.g. sodium potassium pump

ATP is hydrolysed and the binding ofphosphate group to the protein pump changes theprotein conformation

it actively transport 3 sodium ions out of the cell for every2 potassium ions pumped against concentration gradient

into the cell

this generates a difference in ionic charge on the twosides of membrane which is important for the transmission

of nerve impulses


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Active transport


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(b) indirect active transport (secondary active transport)

example is the couples uptake of glucose into

cell lining the ileum in mammals. This processalso known as contransport

ATP is used by sodium ions protein pump topump sodium ions out of the cell. This create a sodiumions concentration gradient

the sodium ions and glucose molecule bind to the sametransmembrane protein called contransport protein (orcoupled transport protein). They are then moved by theprotein inside the cell

sodium ions move down its concentration gradient whileglucose moves up its concentration gradient


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Only occur in living system

factor affecting active tranport:(a) temperature

(b) oxygen concentration

(c) presence of inhibitor which inhibit enzyme of

ATP formation such as cyanide(d) number of carrier protein

Cell carrying active transport are characterised

by(a) the presence of numerous mitochondria

(b) high concentration of ATP

(c) high respiratory rate


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Carrier protein for active transport:

(a) known as pump

(b) have specific binding site to particularsubstances

(c) are globular protein than span the phospholipd

bilayer

(d) pick up substances and transport them toanother side of the membrane

(e) need phosphate group from ATP molecule

to alter it shape when transporting substances

Substances transport by active transport are polar

and have diameter more than 1nm


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Type of carrier protein:

(a) uniport carrierwhich carry a single

ions or molecule in a single direction

(b) symport carriers (cotransport) which

carry two substances in the samedirection

(c) antiport carriers which carry two

substances in opposite


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After a substances is taken into cell through

active transport, it is not able to come out from

the cell even the presence of concentrationgradient. It is act as a one-way valve to make

the cell membrane exhibit it selective

permeability

Active transport occur in:

(a) the gut where absorption occur

(b) uptake of ions by root cell

(c) formation of urine in kidney tubule(d) transmission of nerve impulse in nerve fiber

(e) muscle contraction


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Cytosis Cytosis is a type of active transport involving

invagination and evagination of a small portion

of plasma membrane

A bulk transport of materials across plasmamembrane through the formation of vesicle and

vacuole

Type: (a) endocytosis (phagocytosis and

pinocytosis)

(b) exocytosis


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Phagocytosis :

cellular eating where solid substances or even wholeorgansim are taken into cell by invagination of

plasmam membrane

Pinocytosis:

cellular drinking where liquid is taken into cell byforming a fine pinocytic channel by microvilli on thesurface of plasma membrane

Exocytosis:

Vesicle or vacuole move to the plasma membrane,fuse with it and spill their bulky content out of the cell

Example: beta cell of pancreas manufacture insulin

and secrete it into blood stream by exocytosis


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Endocytosis and exocytosis provide a

mechanism for rejuvenating and

remodeling the plasma membrane.

The addition of membrane by exocytosis

offset the loss of membrane by

endocytosis


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Techniques of analysis

Paper chromatography

Electrophoresis

X-ray diffraction analysis


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Principle of paper chromatography:

(a) sample mixture dissolve in suitablesolvent or mobile phase, is allowed topass over a stationary phase, a porouschromatography paper which restrictsthe movement of macromolecule

(b) differences in molecular size, solubilityand adhesion of the macromolecules tothe chromatography paper causes the

component molecules to move throughthe pores of the paper at differentspeeds


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(c) components with higher affinity towardsthe solvent will move further up the

paper. In this way, all the componentmolecules in the mixture will becomeseparated.

(d) for the component that is colourless

and non-fluorescent, chromatogramneed to be coloured with chemicals.

(i) such as amino acid, can use

ninhydrin to produce a purplecolouration.


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(ii) position and intensity of the

coloured spot indicate the type and

the quantity of each constituent

(e) molecules in mixture can be identified

by their Rf(retardation factor)


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For example, if one component of a mixture

travelled 9.6 cm from the base line while the

solvent had travelled 12.0 cm, then the Rfvalue for that component is:


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RF of compound is constant for the same

solvent.

(f) two way chromatography: to separate the complex

mixture by rotating the paper chromatogram 90degrees and using the same or different solvent.


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Two way chromatography


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electrophoresis

Used to separate a mixture of charged molecules suchas amino acids and protein using an electric field

Principle: isoelectric point (pH of mobilephase)

if pH of solution is above themixture isoelectric point, the

amino acid or protein willnegative charged

if pH of solution is below the

mixture isoelectric point, theamino acid or protein willpositive charged


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X- ray diffraction analysis

X-ray crystallography used to study the

three dimensional structures of

macromolecules such as protein and

nucleic acid

Best used for crystallized molecules with

definite geometrical structures and not for

amorphous substances Carried out using spectrometer


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Atom in a crystal are regularly spaced andarranged to form a specific lattice

The regular small spacing of atoms in crystal issuitable to be used as a natural diffraction

grating for X-ray whose wave lengths are veryshort

When a beam of x-ray is directed into a crystal,they are scattered by interaction with electronsin the atoms to form a characteristic diffractionpattern that can be photographed

The pattern obtained gives information on thegeometrical spacing of the atoms


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chapter 1-part ii (student version)

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