Key Concepts
- All Cells Use Energy
Energy Conversions
- Reactions Absorb or Release Energy
Endergonic, Exergonic
- ATP is Cellular Energy
ATP Cycle
- Enzymes Speed Up Reactions
Enzyme Function, Factors
Affecting Enzyme Activity
- Membrane Transport
Passive and Active Transport,
Endocytosis, Exocytosis
A female firefly eating a male of
another species
1!
Cellular respiration
I. Membrane Structure
and Function
III. How Enzymes Function
II. Energy and the Cell
The Big Ideas
2!
Chemical Reactions Release/Store Energy
 Chemical
rxns either
– Release
energy (exergonic)
• Cellular respiration
– Require
energy input and store energy (endergonic)
• Photosynthesis
 Cells
manage energy w/ energy coupling
- Use energy from exergonic rxns to drive endergonic rxns
3!
Potential energy of molecules
Reactants
Amount of
energy
released
Energy released
Products
Exergonic reaction, energy released
4!
Potential energy of molecules
Products
Energy required
Amount of
energy
required
Reactants
Endergonic reaction, energy required
5!
Cellular Respiration Happens in the
Mitochondria
 Chemical
breakdown of glucose using
O2 releases CO2, water and energy
 That
energy is captured to make ATP!
6!
Fuel
Energy conversion
Waste products
Heat
energy
Glucose
+
Oxygen
Cellular respiration
Carbon dioxide
ATP
ATP
Energy for cellular work
+
Water
Energy conversion in a cell
7!
ATP is Cellular Energy Currency
 Adenosine triphosphate (ATP) is a nucleotide that
temporarily stores energy
 ATP has high energy phosphate bonds
Figure 4.6
8!
Removing the endmost phosphate group (by
hydrolysis) releases the energy stored in ATP.
The cell uses this energy to do work!
9!
The ATP Cycle
 ATP
Hydrolysis
Energy from
exergonic rxns
Phosphorylation
ATP
ADP +
P
Energy for
endergonic rxns
is a “renewable” energy source for cells
– When
energy is released in exergonic rxns, it can be
used to make more ATP
10!
Enzymes Speed Up the Cell’s Chemical Rxns
 Enzymes
are proteins that speed up cellular
metabolism (biological catalysts)
− They are not used up in the process
11!
The Catalytic Cycle of an Enzyme
1 Enzyme available
with empty active
site
Active site
Substrate
(sucrose)
2 Substrate binds to
enzyme with induced fit
Glucose
Enzyme
(sucrase)
Fructose
H 2O
4 Products are
released
3 Substrate is
converted to
products
12!
Specific Enzymes Catalyze Specific Rxns
 Enzymes
3-D shape determines its specificity
– The
specific reactant(s) that it acts on is
substrate
– The
substrate fits into the enzymes’ active
site
– Enzymes
are specific b/c the shape of the
active site must fit the shape the substrate
13!
Temperature affects enzyme activity
Most enzymes have an optimal temperature, at which
their activity is greatest
Figure 4.12
14!
 For
optimum activity, enzymes require specific
conditions
– Temperature
- human enzymes work best at
35-40ºC, ~ body temp.
• High temps denature enzymes
• Cold temps slow their activity
– pH
- optimum enzyme activity is near neutral
• Stomach enzymes work best at low pH
15!
Question
According to the graph, at what temperature
do you predict the bacterial enzyme becomes
denatured?
A. 55°C
B. 66°C
C. 73°C
D. 78°C
16!
How Do You Tell An Enzyme to STOP Making
Product?
 TWO
ways:
Enzyme Inhibitors You May Know
1. Roundup- Inhibits an
enzyme in weed (plant)
cells.
2. Aspirin- Blocks an
enzyme that cells use to
produce pain-related
molecules.
Mastering Concepts
What functions do
enzymes perform in
living cells?
Membranes – A Fluid Mosaic
 Membranes
are composed of
A phospholipid bilayer
– Embedded and attached proteins
– Commonly described as a fluid mosaic
– The plasma membrane of an animal cell
20!
CYTOPLASM
Enzymatic activity
Fibers of
extracellular
matrix (ECM)
Phospholipid
Cholesterol
Cell-cell
recognition
Receptor
Signaling
molecule
Transport
Attachment to the cytoskeleton
and extracellular matrix (ECM)
Signal
transduction
ATP
Intercellular
junctions
Glycoprotein
Microfilaments
of cytoskeleton
Some functions of membrane proteins
CYTOPLASM
21!
 Membranes
are selectively permeable
– Not all molecules can cross the cell membrane
– Small non-polar molecules (CO2 and O2) diffuse
freely
– Polar molecules (H2O, glucose and other sugars),
ions, and large molecules can not diffuse across
membrane
 Transport
proteins allow molecules that can
not diffuse to enter and leave a cell
22!
Passive Transport = Diffusion Across a
Membrane (no energy added)
✶ Diffusion - tendency of particles to spread out
evenly in an available space
 Particles move from high to low concentration
 They move down their concentration gradient
 Eventually, particles evenly disperse (equilibrium)
High concentration areas
Figure 4.13
Solute evenly dispersed
23!
Osmosis – the Diffusion of Water
Figure 4.14
Red Blood Cells are Affected by Tonicity
Figure 4.15
Transport Proteins Facilitate Diffusion
Across Membranes
 Polar
or charged substances do not cross
membranes easily
 – They require the help of specific transport proteins
– Process called facilitated diffusion, a type of passive
transport that does not require energy
Rapid diffusion of water into/out of cells made possible by
– Protein channel called an aquaporin
26!
Solute
molecule
Transport
protein
Transport protein providing a channel for diffusion of a
specific solute across a membrane
27!
Cells Expend Energy in Active Transport
 Cells
have a mechanism for moving a solute
against its concentration gradient
– Requires use of energy from ATP
– Shape of the membrane protein altered by
phosphorylation using ATP
28!
Active Transport
29!
Mastering Concepts
Distinguish between simple
diffusion, facilitated diffusion,
and active transport.
Endocytosis and Exocytosis Transport
Large Molecules Across Membranes
 Exocytosis
is used to export lg. molecules, such
as proteins or polysaccharides
 Endocytosis
is used to import substances useful
to cell’s life
– In both cases, material to be transported is packaged
within a vesicle that fuses with the membrane
31!
Exocytosis and Endocytosis
32!