Fosfolipid bersifat amphipathic hidrofilik dan hidrofobik.

Artifisial membran ditunjukkan dalam bentuk lapisan dalam air:

Mengapa membran dibentuk bilayer?

Ada dua “watery” area yang berinteraksi dengan membran, diluar sel dan didalam sel.

Difusi. Apa yang menyebabkan difusi? Mengapa

hal tersebut terjadi secara spontan? Gradien konsentrasi mewakili energi

potensial. Perpindahan secara langsung menurunkan

energi bebas sistem tersebut. Hal tersebut terjadi secara spontan.

Apakah partikel akan berhenti berpindah pada

waktu keadaan kesetimbangan tercapai?

Gradien konsentrasi. Ingat gradien konsentrasi mewakili

potensial energi.

Apa yang disebut osmosis? Difusi dari air melewati membran semi-

permiabel.

Apa yang dimaksud difusi dengan fasilitas?

Difusi dari larutan dengan bantuan transpor protein.

Apakah merupakan proses pasif atau aktif?

Pasif. Mengapa larutan membutuhkan protein

untuk memfasilitasi difusi? Karena larutan terlalu polar untuk

melewati lipid bilayer.

Apa yang dimaksud dengan transpor aktif?

Memompa molekul lewat membran karena adanya konsentrasi gradien.

Membutuhkan energi, dalam bentuk ATP

Digunakan untuk membantu ionik gradien melewati membran

?

?

?

?

Endositosis – Pagositosis – endositosis terhadap

substansi-substansi partikulat besar Pinocytosis – endositosis cairan dan zat

yang tidak terlarut Reseptor termediasi

Eksositosis -

www.soulcare.org Sid Galloway

AS Biology, Cell membranes and Transport

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1. The steepness of the concentration gradient. The bigger the difference between the two sides of the membrane the quicker the rate of diffusion.

2. Temperature. Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster.

3. The surface area. The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment.

4. The type of molecule or ion diffusing. Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.

AS Biology, Cell membranes and Transport

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1. Oxygen – Non-polar so diffuses very quickly.

1. Carbon dioxide – Polar but very small so diffuses quickly.

2. Water – Polar but also very small so diffuses quickly.

AS Biology, Cell membranes and Transport

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Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na+ or Cl- cannot pass.

These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION.

Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.

secobarbital thiopentalbarbital

Assume weak acid drug (HA) w/ pKa=6.0 Assume [HA]=1.0 Stomach pH=1.0

1.0-6.0=log [A-]/[HA] 1.0x10-5=[A-]

Little ionized drug Blood pH=7.0

10=[A-] Much ionized drug

Expect stomach-to-plasma traverse BUT not plasma-to-stomach