Cell Membrane Structure and Function. What is the importance of having a cell membrane?

Transcription

1 Cell Membrane Structure and Function What is the importance of having a cell membrane?

2 I. Membrane Structure a. Membranes contain proteins, lipids, and carbohydrates (which are all types of macromolecules) b. The lipids in the cell membrane are phospholipids. c. The current model of the cell membrane is called the fluid mosaic model.

3 II. Evolution of Cell Membrane Theories a the cell membrane was thought to be made of lipids since substances that dissolved in lipids entered the cells faster than insoluble substances. b first artificial membrane formed from phospholipids. c idea that the membrane was a phospholipid bilayer. d the Sandwich model proposed a phospholipids bilayer between two layers of globular proteins. e phospholipid bilayer with membrane proteins dispersed throughout the cell membrane (CURRENT AND ACCEPTED MODEL)

4 Evolution of Cell Membrane Theories Sandwich model Phospholipid Bilayer

5 f. Fluidity of Membranes i. Lipids move freely in a membrane, but flipflopping is rare.

6 f. Fluidity of Membranes ii. Unsaturated hydrocarbons have kinks that keep the molecules from packing together and enhancing membrane fluidity.

7 f. Fluidity of Membranes iii. Cholesterol reduces membrane fluidity (at moderate temps). At low temps it hinders solidification by disrupting the packing of the phospholipids.

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10 Mosaic Structure of the Cell Membrane g. The Mosaic Structure of the Cell Membrane i. Mosaic many different parts make up the cell membrane, complicated structure How does the structure of the cell membrane support its function?

11 ii. Types of proteins in the membrane 1. Integral proteins proteins that span the entire plasma membrane. *What do you think the function of these proteins may be? 2. Peripheral proteins proteins that are not embedded in the plasma membrane. *What do you think the function of these proteins may be?

12 iii. Functions of Cell Proteins Transport Intercellular joining

13 iii. Functions of Cell Proteins Enzymatic activity Cell-Cell recognition

14 iii. Functions of Cell Proteins Signal Transduction Attachment to the cytoskeleton and ECM

15 iv. Cell membranes have distinct inside and outside faces. Carbohydrates are found on the outer side of the membrane. 1. The carbohydrates on the surface of the cell membrane function to distinguish one cell from another.

16 h. THE CELL MEMBRANE IS selectively permeable!!! So, what does that mean?

17 III. Traffic Across Membranes a. Permeability of the lipid bilayer i. Hydrophobic molecules can dissolve across the lipid bilayer 1. ex: hydrocarbons, CO 2, O 2, lipids ii. Ions and polar molecules can not dissolve across the membrane 2. ex: Water, glucose, Na +

18 III. Traffic Across Membranes iii. Transport proteins helps substances across the plasma membrane, type of integral protein 1. Channel proteins hydrophilic channel, tunnel 2. Pump proteins physically move substance across membrane 3. The proteins are substrate specific They will only allow specific molecules to pass through.

19 What do you see happening?

20 III. Traffic Across Membranes b. Passive Transport across the membrane i. Diffusion movement from an area of high concentration to an area of low concentration, reaches equilibrium

21 III. Traffic Across Membranes ii. Concentration gradient change in the density of a substance iii. Passive Transport does not require input of ATP (energy)

22 III. Traffic Across Membranes c. Osmosis the diffusion of water across a selectively permeable membrane *Osmosis is a special case of diffusion*

23 SIDEBAR: Prefixes What do the following prefixes mean? a. Hyper b. Hypo c. Iso

24 III. Traffic Across Membranes i. Hypertonic higher concentration of solutes ii. Hypotonic lower concentration of solutes iii. Isotonic equal concentration of solutes

25 Examples of solutions

26 III. Traffic Across Membranes d. Why is water balance important? i. The control of water balance is osmoregulation (animal cells). ii. Ex: Fish in salt water

27 III. Traffic Across Membranes iii. Plant cells can be turgid (normal state), flaccid (limp), or plasmolyzed (lethal state).

28 III. Traffic Across Membranes e. Facilitated Diffusion i. Facilitated diffusion requires the help of a transport protein to move molecules or ions.

29 III. Traffic Across Membranes f. Active Transport i. Active transport requires the use of ATP Energy is required because molecules are usually going against their concentration gradient. ii. Ex: Sodium-potassium pump

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32 III. Traffic Across Membranes

33 III. Traffic Across Membranes g. Some ion pumps generate voltage across membranes i. Ex: nerve cells (Sodium Potassium pump) ii. An unequal distribution of charged ions across a membrane will cause a membrane potential.

34 III. Traffic Across Membranes iii. A transport protein that generates voltage across a membrane is a Electrogenic pump. iv. Most common example of a electrogenic pump is the proton pump.

35 III. Traffic Across Membranes h. Cotransport i. Some molecules are transported across the membrane at the same time, this is cotransport. ii. Ex: H + ions are transported out of a cell, and both the H + ions and sucrose molecules are transported into the same cell.

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37 III. Traffic Across Membranes i. Exocytosis and Endocytosis i. When the cell secretes macromolecules by the fusion of vesicles with the plasma membrane, this is exocytosis (think exit) ii. When the cell takes in macromolecules and matter by forming new vesicles from the plasma membrane this is endocytosis (think enter)

38 III. Traffic Across Membranes **Examples of Endocytosis** 1. phagocytosis taking in of large molecules 2. pinocytosis taking in of water 3. receptor-mediated endocytosis specific substances are taken in such as hormones, neurotransmitter

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