Regents Biology

Human Physiology: Unit-1

Source: Collected from various sources on the internet and modified by Dr Boominathan Ph.D.

BYBYDR BOOMINATHAN Ph.D. DR BOOMINATHAN Ph.D.

M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA)M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA)

PONDICHERRY UNIVERSITYPONDICHERRY UNIVERSITYIV LectureIV Lecture

9/August/20129/August/2012

Cell Membranes transport across cell and membrane

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Cell Membranes&

Movement Across Them

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Cell (plasma) membrane Cells need an inside & an outside…

separate cell from its environment cell membrane is the boundary

INfood- sugars- proteins- Lipids

-salts -O2

-H2O

OUTwaste- ammonia- salts- CO2

- H2O products- proteins

cell needs materials in & products or waste out

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Building a membrane How do you build a barrier that keeps

the watery contents of the cell separate from the watery environment?

What substance do you know that doesn’t mix with water?

LIPIDS

Remember: oil & water don’t mix!!

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Lipids of cell membrane Membrane is made of special kind of lipid

phospholipids

Membrane is a double layer phospholipid bilayer

inside cell

outside cell

lipid

“repelled by water”

“attracted to water”

phosphate

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Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all

— to pass through the membrane semi-permeable

only some material can get in or out

aa H2Osugar lipids salt waste

So what needs to get across the membrane?

O2

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Crossing the cell membrane What molecules can get through the cell

membrane directly? fats and oils can pass directly through

inside cell

outside cell

lipid

salt

aa H2Osugar

waste

but…what about other stuff?

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Cell membrane channels Need to make “doors” through membrane

protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc.

inside cell

outside cell

sugaraaH2O

saltwaste

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How do you build a semi-permeable cell membrane? Channels are made of proteins

proteins both “like” water & “like” lipids

bi-lipidmembrane

protein channelsin bi-lipid membrane

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Protein channels Proteins act as doors in the membrane

channels to move specific molecules through cell membrane

HIGH

LOW

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Movement through the channel Why do molecules move through

membrane if you give them a channel?

?

?

HIGH

LOW

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Molecules move from high to low Diffusion

move from HIGH to LOW concentration

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Diffusion Move from HIGH to LOW concentration

passive transport no energy needed

diffusion osmosis

diffusion of water

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Diffusion (without energy-simple) Move from HIGH to LOW

inside cell

outside cell

Which way will Lipid substances move?

LOW

HIGH

Lipid

Lipid

Lipid

Lipid

Lipid

LipidLipidLipid

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Facilitated Diffusion Move from HIGH to LOW through a channel

inside cell

outside cell

sugar

sugar

sugar

sugar

sugarsugar

sugar sugar

sugarsugarsugar

Which way will sugar move?

sugarsugar

LOW

HIGH

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Diffusion Move from HIGH to LOW concentration

directly through membrane simple diffusion no energy needed

help through a protein channel facilitated diffusion (with help) no energy needed HIGH

LOW

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Simple vs. facilitated diffusion

inside cell

outside cell

lipidinside cell

outside cell

H2O

simple diffusion facilitated diffusion

H2O

protein channel

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Active transport Cells may need molecules to move

against concentration “hill” need to pump “uphill”

from LOW to HIGH using energy protein pump requires energy

ATP

ATP

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Transport summary

simplediffusion

facilitateddiffusion

activetransport

ATP

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OsmosisMovement of Water Across Cell Membrane

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Osmosis Water is very important, so we talk about

water separately Osmosis

diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane

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Keeping water balance Cell survival depends on balancing

water uptake & water loss

freshwater balanced saltwater

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Keeping right amount of water in cell Freshwater

a cell in fresh water high concentration of water

around cell cell gains water

example: Paramecium problem: cells gain water,

swell & can burst water continually enters

Paramecium cell

solution: contractile vacuole transports water out of cell

freshwater

No problem,here

Burst

1

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Keeping right amount of water in cell Saltwater

a cell in salt water low concentration of water

around cell cell loses water

example: shellfish problem: cell loses water

in plants: plasmolysis in animals: shrinking cell

solution: take up water

saltwater

I willsurvive!

I’m shrinking,I’m shrinking!

2

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Keeping right amount of water in cell Balanced conditions

no difference in concentration of water between cell & environment cell in equilibrium example: blood problem: none

water flows across membrane equally, in both directions

volume of cell doesn’t change

balanced

I couldbe better…

That’sbetter!

3

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CELLS

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Chemical compositions of extracellular and intracellular fluids

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Na-K Channel: How it Works• A type of active transport. • 3 sodium ions move out of cell• 2 potassium ions move into cell.• ATP is needed as each of these ions are

moving against their conc. gradient.• Mostly used in cardiac muscle and nervous

tissue. Maintains Na+K gradient concentration.

• Huge amount of ATP goes into this NaK channel.

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Sodium –Potassium Channel

Figure 3.11

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Sodium-Potassium Channel

A molecule of ATP is used with each “swap of Na/K ions

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Endocytosis (phagocytosis-Cell Eating)

This is Vessicle transport during which the entire plasma membrane folds inward allowing large particles into the cell.

Ex; the cell is ingesting microbes , perhaps?

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Transport33

Cell Membrane - Function - Endocytosis The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins this process is known as endocytosis. In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this animation an ameba engulfs a

food particle.

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Exocytosis The opposite

of ENDOcytosis. Large particles are leaving the cell. (digested microbes for example).

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Receptor-mediated Endocytosis

This actually uses specifi c proteins to identif y the substance to be taken into the cell. This is how

your body gets rid of excess LDL (cholesterol)f rom your blood.

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Receptor- Mediated Endocytosis

Viruses are species –specific , and receptor specific,

transmitted via receptor-mediated endocytosis.

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Transport

38

Vesicle-mediated transport Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the term applied when transport is out of the cell.

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Cell Membrane (Transport) NotesCell Membrane and Cell Wall:• ALL cells have a cell membrane made of proteins and lipids

Cell Membrane

lipid bilayer

protein channel

protein pump

Layer 1

Layer 2

•SOME cells have cell membranes and cell walls – ex: plants, fungi and bacteria

Cell Membrane

Cell Wall

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• Plant cells have a cell wall made of cellulose – that cellulose is fiber in our diet

• Bacteria and fungi also have cell walls, but they do not contain cellulose

• Cell membranes and cell walls are porous allowing water, carbon dioxide, oxygen and nutrients to pass through easily

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Function of the Cell Membrane:•Cell membrane separates the components of a cell from its environment—surrounds the cell•“Gatekeeper” of the cell—regulates the flow of materials into and out of cell—selectively permeable•Cell membrane helps cells maintain homeostasis—stable internal balance

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Passive TransportA process that does not require energy to move molecules from a HIGH to LOW concentration

Diffusion

Facilitated Diffusion

Osmosis

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• Diffusion is the movement of small particles across a selectively permeable membrane like the cell membrane until equilibrium is reached.

These particles move from an area of high concentration to an area of low concentration.

outside of cell

inside of cell

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• Osmosis is the diffusion of water through a selectively permeable membrane like the cell membrane

Water diffuses across a membrane from an area of high concentration to an area of low concentration.

Semi-permeable membrane is

permeable to water, but not to sugar

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• Facilitated Diffusion is the movement of larger molecules like glucose through the cell membrane – larger molecules must be “helped”

Proteins in the cell membrane form channels for large molecules to pass through

Proteins that form channels (pores) are called protein channels

outside of cell

inside of cell

Glucose molecules

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Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.

Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.

Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.

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Active TransportActive transport is the movement of molecules from LOW to HIGH concentration.

Energy is required as molecules must be pumped against the concentration gradient.

Proteins that work as pumps are called protein pumps.

Ex: Body cells must pump carbon dioxide out into the surrounding blood vessels to be carried to the lungs for exhale. Blood vessels are high in carbon dioxide compared to the cells, so energy is required to move the carbon dioxide across the cell membrane from LOW to HIGH concentration.

outside of cell

inside of cell

Carbon Dioxide molecules

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NO ENERGY NEEDED: Diffusion Osmosis Facilitated Diffusion

ENERGY NEEDED: Active Transport

ANALOGY:

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Food is moved into the cell by Endocytosis

Wastes are moved out of the cell by Exocytosis

• Endocytosis and Exocytosis is the mechanism by which very large molecules (such as food and wastes) get into and out of the cell

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Ex: White Blood Cells, which are part of the immune system, surround and engulf bacteria by endocytosis.