Chapter 01 Membranes

8/13/2019 Chapter 01 Membranes

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Membranes

Chapter 1


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Phospholipid Bilayer

Phospholipid

2 fatty-acid chainsGlycerol + Phosphate + nitrogenous compound

One end strongly non-polar

Other end strongly polar

Polar head Hydrophilic

Nonpolar tails Hydrophobic


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Cell Membrane Structure

Davson-Danielli Model(1935)

phopholipid bilayer sandwiched between 2 protein layers.

Singer-Nicolson, Fluid Mosaic Model(1972)Membrane proteins

embedded in phospholipid bilayer. Proteins free to move in the

lipid bilayer.

Cell membrane is selectively permeable


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Components of Cell Membrane

Eukaryotic cells have many membranes. All share similar structure

4 components:Phospholipid bilayer

All other components embedded in bilayer. Barrier to water-

soluble molecules

Transmembrane proteins

Span width of bilayer. Involved in transport. Can move within

bilayer

Interior protein network

Membranes supported by intracellular proteins. Other proteins

allow for movement of transmembrane proteins within bilayer.Cell surface markers

Sections of cell membrane have different types of glycolipids

and glycoproteins. Act as cell identity markers.


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Types of Membrane Proteins

Transporters-Involved in the movement of substances.

Enzymes-Allow chemical reactions on the interior of membrane

Cell surface receptors-Detect chemical messagesCell surface identity markers- different cell types have unique

markers

Cell adhesion proteins-cause cells to stick to one another

Attachments to cytoskeleton-proteins attach to cytoskeleton


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Membrane Protein Structure

Anchoring proteins to the bilayer-

Modified lipids link to membrane phospholipid and bond directly

to protein. Protein tethered to cell membrane

Transmembrane proteins-

nonpolar region of protein in bilayer

polar regions extend outward

Different types

Single-pass anchors-pass through bilayer only once

Ex hormone receptors Multiple-pass channels and carriers-multiple alpha helix

sections pass through membrane (move ions and water

soluble molecules)

Pores-beta sheet sections of protein form large opening that

allow water and other material to move through membrane


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Movement of materials across cell membrane

PassiveTransport Does NOT require energy

Diffusion

Facilitated Diffusion

Osmosis

ActiveTransportRequires the expenditure of energy

Sodium-Potassium Pump

Coupled Transport

OthermeansEndocytosisPhagocytosis and Pinocytosis

Receptor-mediated endocytosis

Exocytosis


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Molecules and Ions move about constantly and randomly

Diffusion

Net movement from areas of high concentration to areas

of low concentration.

Equilibrium

Passive Transport


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Cell Membrane Is Selectively Permeable

Many molecules needed by cells are polar

Polar molecules cannot cross non-polarPhospholipid barrier

Polar molecules diffuse through channel proteinsDifferent types of channels assist specific molecules

Ions diffuse through Ion Channels

Cations and Anionscannot move

through phospholipid layer

Interior of channel proteins is polar


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Facilitated Diffusion

Carrier Proteinstransport ions and other solutes (ex. glucose and

amino acids) across membrane down concentration gradient

Facilitate movement by physically binding moleculeson one side of

membrane then releasing them on the other (configuration change)

Characteristics of Facilitated diffusion

Specific-each carrier type

transports specific molecules

Saturates-if all carriers in use,Increase in gradient does not

Increase rate of transport


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OsmosisDiffusion of water across a selectively permeable membrane

Cytoplasm of a cell is an Aqueous Solutionlots of substances

(solute) dissolved in water (solvent).


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OsmosisCont.

Osmotic concentration- concentration of all solutes in an Aqueous

solution

Isosmotic

solute concentrations are equal

Hyperosmotic

solution with the higher solute

concentration

Hyposmotic

solution with the lower solute concentration


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Active Transport

Active transport requires energy(ATPs) to move a substance against

its concentration gradient.

Involves highly selective protein carriers within the membrane

Allows cells to maintain specific ions or molecules at cytoplasmic

concentration that are higher or lowerthan in the extra-cellular fluid.

Example of an active transport mechanism

Sodium-potassium pump

1/3 of all ATPs used by a cell fuels this pump


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Endocytosis- enveloping food phagocytosis- material taken in is in

particulate form

pinocytosis- material taken in is in liquidform

Exocytosis- discharge of material from

vesicles at the cell surface


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1. Apa perbedaan plasmolisis, krenasi

dan lisis?


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a. Lisis : hancurnya sel karena rusaknya atau

robeknya membran plasma.

b. Krenasi : sel berkeriput karena kekurangan air

c. Plasmolisis : peristiwa lepasnya membran plasma

dari dinding sel

d. Osmosis adalah perpindahan ion atau molekul air

(pelarut) dari kerapatan tinggi ke kerapatan rendah

dengan melewati suatu membran (disebut jugadifusi lewat membran)


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2. Mengapa peristiwa pompa Na+ dan K+termasuk transpor aktif? Jelaskan!


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Mekanisme pompa Na+ - K+

1. ATPase mengikat Na+ pada permukaan sitoplasmik

mengakibatkan ATPase menghidrolisa ATP ADP + P + E.

2. ATPase mengalami fosforilasi.

3. Terjadi perubahan konfigurasi dari ATPase Na+ ditranspor

keluar sel.

4. ATPase mengikat K+ pada permukaan ekstra seluler.

5. ATPase mengalami defosforilasi.

6. ATPase kembali pada posisi semula. K+ ditranspor ke dalam

sel.

2. Pompa Na+ dan K+ termasuk transpor aktif sebab:

- terjadi perpindahan zat dari konsentrasi rendah ke konsentrasi

tinggi

- perpindahan zat melawan gradien konsentrasi membuthkan

energi


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EXPERIMENTAL


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Diffusion, Osmosis, Plasmolisis, Crenation

Materials Sum

Allium cepa 2(bawang merah)

Solanum tuberosum 2

(kentang)

Pheretima sp. 2

(cacing tanah)

Rhoe discolor 1

(adam hawa)Ink (tinta) 1 bottle

Bottle 2

Sugar insufficient

Silet

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Chapter 01 Membranes