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Cell Membranes. Structure and Function. W O R K T O G E T H E R. As a review, fill in the blanks: Molecules are made up of ___. Sugars link together to make ___. Amino acids link together to make ___. Fatty acids are components of ____. Quick review:. Atoms.

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cell membranes
Cell Membranes
  • Structure and Function
slide2

W

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  • As a review, fill in the blanks:
    • Molecules are made up of ___.
    • Sugars link together to make ___.
    • Amino acids link together to make ___.
    • Fatty acids are components of ____.
slide3

Quick review:

Atoms

bind together to make

molecules.

slide4

Complex carbohydrates are composed of simple sugars.

Lipids are composed of fatty acids plus a polar head.

slide5

Proteins are long chains of amino acids bound together.

Nucleic acids are composed of chains of nucleotides.

building cell parts
Building cell parts
  • The biological molecules are the basic building blocks of all cell parts.
  • Cell membranes are composed of proteins, lipids, and some complex carbohydrates.
slide7

In our model of scale, that the cruise ship represented the cell. We’re now going to assemble large chain molecules into the parts of a cell.

slide8

The Fluid Mosaic Model of the cell membrane

Which classes of biomolecules are represented here?

carbohydrate

extracellular fluid (outside)

receptor

protein

glycoprotein

protein

phospholipid

bilayer

recognition protein

binding

site

transport

protein

cholesterol

phospholipid

pore

protein filaments

cytosol (inside)

slide9

Membrane components: Lipid bilayer

extracellular fluid

(watery environment)

hydrophilic

heads

phospholipid

hydrophobic

tails

bilayer

hydrophilic

heads

cytosol

(watery environment)

why do the fatty acid tails of phospholipids point toward each other in the membrane
Why do the fatty acid tails of phospholipids point toward each other in the membrane?
  • They are non-polar, so they are hydrophilic.
  • They are non-polar, so they are hydrophobic.
  • They are polar, so they are hydrophilic.
  • They are polar, so they are hydrophobic.
slide11

Membrane components: proteins

The final shape of the protein determines its function.

What conditions can denature proteins?

slide12

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  • Make some predictions:
    • What are some characteristics of molecules that can diffuse directly through the lipid layer of the cell membrane?
    • What are some characteristics of molecules that will need the assistance of carrier proteins to move through the membrane?
transport of materials
Transport of Materials
  • Passive transport:
    • Simple diffusion
    • Facilitated diffusion
    • Osmosis
  • Energy-consuming transport:
    • Active transport
    • Exo/Endocytosis
slide14

Diffusion

1 A drop of dye is

placed in water.

2 Dye molecules

diffuse into the

water; water

molecules diffuse

into the dye.

3 Both dye molecules

and water molecules

Are evenly dispersed.

drop of

dye

water

molecule

The movement of molecules in solution from a high concentration of that molecule in the direction of a low concentration of that molecule until equilibrium is reached.

slide15

Diffusion across a membrane

(extracellular fluid)

lipid-soluble molecules

and O2, CO2

O2

(cytosol)

slide16
Why does passive diffusion through the lipid layer only occur with gases and small, lipid-soluble molecules?
  • These substances are non-polar, and so is the lipid layer.
  • These substances are polar, and so is the lipid layer.
  • These substances are non-polar, the lipid layer is polar.
  • These substances are polar, the lipid layer is non-polar.
slide17

Facilitated diffusion

H2O,

ions

Proteins form a

hydrophilic channel.

Cl–

Cl–

Cl–

Cl–

channel

protein

Cl–

(cytosol)

Why are channel proteins necessary to move hydrophilic ions through the membrane?

why are channel proteins necessary to move hydrophilic ions through the cell membrane
Why are channel proteins necessary to move hydrophilic ions through the cell membrane?
  • Ions are charged; they cannot go through a non-polar lipid layer.
  • Ions are not charged; they cannot move through a non-polar lipid layer.
slide19

Passive transport by facilitated diffusion

carrier

protein

amino acids,

sugars, small

proteins

(extracellular fluid)

(cytosol)

1 Carrier protein

has binding site

for a specific molecule.

2 Molecule

enters binding

site.

3 Carrier protein

changes shape,

transporting

molecule across

membrane.

4 Carrier protein

resumes original

shape.

slide20

Osmosis

The diffusion

of water

through a semi-permeable membrane.

Water moves from its own high concentration to its own low concentration.

Which direction will water move here?

slide21

Tonicity

If the contents of a cell and the fluid around the cell have the same concentration of dissolved solutes...

...the fluid is isotonic compared with the cell. Water moves in and out in equal amounts.

slide22

Tonicity

If the the fluid around the cell contains less dissolved solute than the fluid in the cell...

...the fluid is hypotonic compared with the cell. More water enters the cell than leaves. The cell may swell to the point of bursting.

slide23

Tonicity

If the fluid around the cell contains more dissolved solute than the fluid inside the cell...

...the fluid is hypertonic compared with the cell. More water leaves the cell than enters. The cell shrinks.

slide24

What is the tonicity of the solutions that these red blood cells have been dropped into?

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(a) Isotonic

solution

(b) Hypertonic

solution

(c) Hypotonic

solution

Net water

movement

out of cells.

Equal movement

of water into and

out of cells.

Net water

movement

into cells.

slide25

Tonicity and plant cells

cytosol

central

vacuole

When water is plentiful, it fills the central vacuole, pushes the cytosol against the cell wall, and helps maintain the cell's shape.

slide26

Tonicity and plant cells

cell wall

plasma

membrane

Plants wilt when water is scarce. They also wilt if salt is added to the soil. Why?

When water is scarce, the central vacuole shrinks and the cell wall is unsupported.

slide27

Active Transport

1 The transport protein

binds both ATP and Ca2+.

2 Energy from ATP

Changes the shape of

the transport protein

and moves the ion

across the membrane.

3 The protein releases

the ion and the remnants

of ATP (ADP and P) and

closes.

(extracellular fluid)

ATP

ADP

ATP

Ca2+

(cytosol)

P

recognition

site

ATP

binding

site

slide28

Endocytosis

Phagocytosis is one example of endocytosis.

(extracellular fluid)

food particle

pseudopods

food vacuole

(cytosol)

slide29

Exocytosis

secreted

material

plasma

membrane

(extracellular fluid)

vesicle

(cytosol)

Material is enclosed in a vesicle that

fuses with the plasma membrane,

allowing its contents to diffuse out.

0.2 micrometer

if a plant cell needs to concentrate sugar in a cell what kind of transport will it use
If a plant cell needs to concentrate sugar in a cell, what kind of transport will it use?
  • Simple diffusion.
  • Facilitated diffusion.
  • Active transport.
  • Osmosis.
slide31

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  • Osmosis is a kind of diffusion. Summarize what makes osmosis a special type of diffusion.
recap
Recap
  • Cell parts, such as cell membranes, are made up of biological molecules.
  • The form and properties of the molecules determine their functions.
  • Cell membranes actively and passively control what materials enter and leave the cell.