Transcript solute - Life Science Academy

The Working Cell
Turning on the Lights to Be Invisible
 Take
place in cell organelles
 Light producing cells
 Enzymes embedded in membranes
of the organelle
 Control the reaction
Enzymes: How they Function
Membranes: Structure and Function
Transport: Through Membranes
Energy is the capacity to perform work 5.10
 All organisms require energy
 It is the CURRENCY of LIFE

 Cellular
Metabolism 5-12
◦ Sum of endo and exergonic
reactions carried out by every
working cell in every organism
 Endergonic reaction◦ Requires net input of energy
 Exergonic reaction◦ Chemical rxn that release energy
5.13 ATP shuttles chemical energy and drives
cellular work
 ATP- Adenosine Triphosphate
 ATP powers nearly all forms of cellular work
 The energy in an ATP molecule is in the bonds
between its phosphate groups
 ATP is the pocketbook!

Adenosine diphosphate
Adenosine Triphosphate
Phosphate
groups
H 2O
P
P
Adenine
P
Hydrolysis
P
Ribose
ATP
Figure 5.4A
ADP
P +
P +
Energy
◦ ATP drives reactions by phosphorylation
 Transferring a phosphate group to make molecules
more reactive
ATP
Mechanical work
Chemical work
P
+
Motor
protein
Transport work
Membrane
protein
Solute
P
Reactants
P
P
P
Product
Molecule formed
Protein moved
Figure 5.4B
ADP
+
P
P
Solute transported
◦ Cellular work can be sustained:
◦ “ATM Machine”
◦ ATP is a renewable resource that
cells regenerate
ATP
Energy from
exergonic
reactions
Figure 5.4C
Energy for
endergonic
reactions
ADP +
P

5.14 Enzymes speed up the cell’s chemical reactions by
lowering energy barriers
◦ Energy of Activation- Amount of Energy
reactants must absorb before a rxn can begin
◦ Reactants
Products
◦ Protiens, DNA, carbohydrates, phospholipids
are rich in “potential energy”

A protein catalyst called an enzyme decreases
the energy of activation needed to begin a
reaction

enzyme- a protein molecule that functions as
a biological catalyst, increasing the rate of a
reaction without itself being changed into a
different molecule
Enzyme
EA barrier
Reactants
1 Figure 5.5A
Products
2
EA without
enzyme
EA with
enzyme
Energy
Reactants
Net
change
in energy
Products
Figure 5.5B
Progress of the reaction

5.15 A specific enzyme catalyzes each
cellular reaction
◦ Enzymes have unique three-dimensional
shapes that determine which chemical
reactions occur in a cell
◦ Substrate- specific reactant that an
enzyme acts on
◦ Active site- region of enzyme that the
substrate fits into
◦ Induced fit- enzyme changes shape
slightly to fit the substrate best
◦ The catalytic cycle of an enzyme
1
Enzyme available
with empty active site
Substrate
(sucrose)
Active site
Substrate binds to
enzyme with induced fit
2
Glucose
Enzyme
(sucrase)
Fructose
H 2O
4
Products are
released
Figure 5.6
3
Substrate is
converted to products
5.16 Enzyme inhibitors block enzyme action
 Inhibitors interfere with an enzyme’s activity
◦ A competitive inhibitor
 Takes the place of a substrate in the active
site
◦ A noncompetitive inhibitor
 Alters an enzyme’s function by changing its
shape

•Feedback Inhibition
•Metabolic rxn is blocked by products
Substrate
Active site
Enzyme
Normal binding of substrate
Competitive
inhibitor
Figure 5.8
Noncompetitive
inhibitor
Enzyme inhibition

Membranes are composed of phospholipids and
proteins
–Membranes are commonly described as a
fluid mosaic
–This means that the surface appears mosaic
because of the proteins embedded in the
phospholipids and fluid because the proteins
can drift about in the phospholipids
Copyright © 2009 Pearson Education, Inc.
Carbohydrate of
glycoprotein
Glycoprotein
Glycolipid
Integrin
Phospholipid
fluid mosaic
Microfilaments
of cytoskeleton
Cholesterol
◦ The plasma membrane of the cell is selectively
permeable
 Controlling the flow of substances into or
out of the cell
TEM 200,000 
Outside
of cell
Cytoplasm
Figure 5.10
5.1 Membrane phospholipids form a bilayer
◦ Phospholipids:
◦ 1 phosphate group and 2 fatty acids
 Have a hydrophilic head
and two hydrophobic tails
 Are the main structural
components of membranes
◦ Phospholipids form a two-layer sheet
 phospholipid bilayer, with the heads
facing outward and the tails facing inward

Figure 5.11A
Hydrophilic head
Phosphate
group
CH3
+
N
CH2
CH3
CH3
CH2
O
O–
P
O
O
CH
CH2
O
C
CH2
O
O
C
O
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH
CH2
CH2
CH2
CH2
CH2
Symbol
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
CH3
Hydrophobic tails
Hydrophilic
heads
Water
Hydrophobic
tails
Hydrophilic
heads
Figure 5.11B
Water
Phospholipid
bilayer
Hydrophobic regions
of protein
Hydrophilic
regions of protein
1. Support (integrins) by attaching to the exoskeleton of
a cell
2. Cell-cell recognition (for sorting)
3. Intercellular junctions (where cells connect)
4. Enzymes
5. Signal transduction
6. Transport

Phospholipids, the key component of biological
membranes, naturally assemble into simple membranes
– Formation of a membrane that encloses collections of molecules
necessary for life was a critical step in evolution
– Can be demonstrated in vitro
– Allows cells to regulate chemical exchanges with the
environment
– Basic requirement for life
Copyright © 2009 Pearson Education, Inc.
Water-filled
bubble made of
phospholipids

5.3 Passive transport is diffusion across a membrane

Diffusion- the tendency for particles of any kind to
spread out evenly in an available space, moving from
where they are more concentrated to regions where they
are less concentrated
Concentration Gradient:
High Concentration
Low Concentration
Travel down concentration gradient until equilibrium is
obtained
Multiple substances diffuse independently




Molecules of dye
Membrane
Equilibrium
Equilibrium
◦ In passive transport- substances diffuse
through membranes without work by the cell
◦ Ex) O2 and Co2 move in and out of our red
blood cells in our lung
◦ Small, nonpolar molecules such as O2 and CO2
diffuse easily across the phospholipid bilayer
◦ What about large molecules, ions or polar
molecules?
Still passive transport- no energy required:
1. Transport protein provides a pore for
solute to pass
2. Transport protein binds to solute,
changes shape and releases it on the
other side
 Solute examples:
 Sugars, amino acids, ions and water

Transport proteins may facilitate diffusion
across membranes
◦ Many kinds of molecules do not diffuse freely
across membranes
◦ Charge, size, polarity
◦ transport proteins
 Provide passage across membranes through a
process called facilitated diffusion
 Still passive transport- no energy required
 transport protein provides a pore for solute to
pass
Figure 5.15
Solute Molecule
Transport Protein
 5.4
Osmosis is the diffusion of water
across a membrane
◦ In osmosis
 Water travels from a solution of lower
solute concentration to one of higher solute
concentration
 Water is used to “balance out” different
solute concentrations to equilibrium
 “waters down” the side with “too much”
solute
Lower
concentration
of solute
Higher
concentration
of solute
Equal
concentration
of solute
Solute
molecule
H2O
Selectively
permeable
membrane
Water
molecule
Solute molecule with
cluster of water molecules
Net flow of water
 5.5
Water balance

osmoregulation- the control of water balance

Isotonic- solution = in solute concentration to the cell

Hypotonic - solution with solute concentration lower
than the cell

Hypertonic- solution with solute concentration greater
than the cell

Osmosis causes cells to:
 shrink in hypertonic solutions
 swell in hypotonic solutions
Isotonic solution
H2O
Hypotonic solution
Hypertonic solution
H2O
H2O
H2O
Animal
cell
(1) Normal
H2O
H2O
(2) Lysed
H2O
(3) Shriveled
Plasma
membrane
H2O
Plant
cell
(4) Flaccid
(5) Turgid
(6) Shriveled
(plasmolyzed)

5.8 Cells expend energy for active transport
◦ Transport proteins can move solutes against a
concentration gradient
◦ To the side with the most solute
◦ Through active transport, which requires ATP
◦ Cell work is not ALWAYS about balance
◦ Ex) The cell needs more K+ and less Na+ than
its’ external environment (Na+/K+ PUMP) to
generate nerve signals
Transport
protein
P
ATP
Solute
1
Solute binding
P
ADP
2
Phosphorylation
Protein
changes shape
Phosphate
detaches
3
4
Transport
P
Protein reversion

5.9 Exocytosis and endocytosis transport large
molecules
◦ To move large molecules or particles through a
membrane
◦ Exocytosis
◦ A vesicle may fuse with the membrane and expel its
contents
◦ Endocytosis
◦ Membranes may fold inward enclosing material from
the outside
Vesicle
Protein
Vesicle forming
Figure 5.19B