Sample questions
1) Those cells which have a nucleus are
classified as?
a) prokaryotes b) eukaryotes
2) Name two organelles, other than a
nucleus?
3) Where in a plant cell would you be
able to find DNA?
4) The ER has what structures
associated with it?
5) Is the plasma membrane composed
only of lipids (fats)?
6) Which microscope has the greater
resolution, light or electron?
7) Eukaryotic cells fall into 4 kingdoms.
Finish the list
 A) Animal
 B) Protists
 C) Plants
 D)
?
8) Which organelle do animal cells get
most of their energy?
9) Are viruses considered to be living?
10) Is glucose a protein, fat , or sugar?
11) DNA is made of a protein, fat , sugar,
or nucleic acids?
12) Proteins are made of what?
13) Give an example of something with a
high pH and another with a low pH.
State which is which.
14) Name at least two types of atomic
bond?
How Cells Work
Chapter 5
Part 1 of 2
What you will learn.
About energy and work
Order and disorder
What Is Energy?
Ability to do work
Forms of energy
 Potential energy
 Kinetic energy
 Chemical energy
What Can Cells Do
with Energy?
 Energy is used to
 make things, or
 move things, or
 break things
 Cells use energy for:
 Chemical work - making new stuff
 Mechanical work - moving around
 Electrochemical work - nerve impulses
One-Way Flow of Energy
 The sun is life’s primary energy source
 Food producers trap energy from the sun and
convert it into chemical bond energy
 Plants and some types of bacteria
 All organisms use the energy stored in the
bonds of organic compounds to do work
 All life forms including plants and photosynthetic
bacteria
Endergonic Reactions
 Overall energy input
required
glucose, a
high energy
product
 Energy is stored
+
6O2
inside the final
molecule
ENERGY IN
6
low energy
starting
substances
6
6
6
Exergonic Reactions
 Overall energy is
released
 Products have less
energy than starting
substance
 This energy is used
to power the cells
glucose, a high
energy starting
substance
+ 6O2
ENERGY OUT
low energy products
6
6
The Role of ATP
 Cells “earn” ATP in energy releasing reactions
 Cells “spend” ATP in energy requiring reactions
base
three
phosphate
groups
sugar
Basic Chemistry
In the next few slide we need to recall
our basic chemistry.
WHY?
 Because it is important in our
understanding of life...
Redox Reactions
‘OIL RIG’
Involves the movement of
ELECTRONS
OIL = Oxidation Is Loss
RIG = Reduction Is Gain
Electron Transfer Chains
Pass electrons from molecule to
molecule
In the process energy is made as ATP
Uncontrolled vs. Controlled
Energy Release
H2
1/2 O2
H2
2H+
Explosive
release of
energy as
heat that
cannot be
harnessed
for cellular
work
H2O
2e-
Energy input
splits hydrogen
Into protons (H+)
and electrons
1/2 O2
Some
released
energy is
harnessed
for cellular
work (e.g.,
making ATP)
Electrons
transferred
through electron
transfer chain
2e2H+
Spent electrons
and free oxygen
form water.
1/2 O2
H2O
Metabolic Pathways
Defined as enzymemediated sequences
of reactions in cells
 Biosynthetic
 Degradative
ENERGY IN
ENERGY IN
photosynthesis
organic
compounds,
oxygen
carbon
dioxide,
water
aerobic
respiration
ENERGY OUT
Enzyme Structure
and Function
 Enzymes are catalytic molecules
 They speed the rate of chemical reactions (in
some cases they speed them up billions of
times)
What do I need to know about…
ENZYMES
Four Features of Enzymes
1) Enzymes do not make anything happen that
could not happen on its own.
- They just make it happen much faster.
2) The enzyme is the same after the reaction as
it was before the reaction
- it comes out unchanged
Four Features of Enzymes
3) The same enzyme usually works for both the forward
and reverse reactions.
- forwards and backwards
4) Each type of enzyme is specific - it recognizes and
binds to only certain substrates.
- glucose to fructose can only be performed by
one type of enzyme
Energy use inside cells
Activation Energy
 For a reaction to
occur, an energy
barrier must be
surmounted
 Enzymes make the
energy barrier smaller
by bending the
molecules to the
optimal shape to react
activation energy
without enzyme
starting
substance
activation energy
with enzyme
energy
released
by the
reaction
products
Things which Influencing
Enzyme Activity
Temperature of the cell
pH of the cell
Salt concentration in the cell
Effect of Temperature
 Small increase in
temperature increases
the speed of reactions
 High temperatures
eventually destroy the
protein - egg whites
Effect of pH - depends on where
the enzyme is located!
Feedback Inhibition
enzyme 2
enzyme
1
SUBSTRATE
enzyme 3
enzyme 4
enzyme 5
A cellular change, caused by a
specific activity, shuts down the
activity that brought it about
END
PRODUCT
(tryptophan)
Lecture 7
Starts here!
Cell Membranes Show Selective
Permeability
oxygen, carbon
dioxide, and other
small, nonpolar
molecules; some
water molecules
glucose and other large,
polar, water-soluble
molecules; ions (e.g.,
H+, Na+, K+, Ca++,
Cl–); water molecules
Concentration Gradient
Means the number of molecules in one
region is different than the number in
another region
A smell moves from an area of high
concentration to one of low
concentration
Diffusion - spreading out evenly
The spreading of
molecules evenly to fill a
space
Factors Affecting
Diffusion Rate
 Steepness of concentration gradient
 Steeper gradient, faster diffusion
 Molecular size
 Smaller molecules, faster diffusion
 Temperature
 Higher temperature, faster diffusion
Membrane Crossing Mechanisms
- how to get into and out of a cell!
1) Diffusion across lipid bilayer
2) Passive transport
3) Active transport
4) Endocytosis - swallowing
5) Exocytosis - spitting
Membrane Crossing: Overview I
High
Concentration
gradient across
cell membrane
ATP
Low
Diffusion of
lipid-soluble
Substances
across bilayer
Passive transport of watersoluble substances
through channel protein;
no energy input needed
Active transport
through ATPase;
requires energy
input from ATP
Membrane Crossing: Overview II
Endocytosis (vesicles in)
Exocytosis (vesicles out)
Transport Proteins
Span the lipid bilayer
Interior is able to open to both sides
Change shape when they interact with
solute
Play roles in active and passive
transport
Passive (without using energy) Transport
Holes in the middle of the protein allow
the molecules to pass through in either
direction
Does not require any energy to be spent
Passive Transport
EXTRACELLULAR FLUID
glucose, more
concentrated
outside cell
than inside
passive
transport
protein
glucose
transporter
LIPID BILAYER
CYTOPLASM
d When the glucose binding
site is again vacant, the protein
resumes its original shape.
c Glucose becomes exposed to
fluid on other side of the membrane.
It detaches from the binding site and
diffuses out of the channel.
a Glucose binds to a vacant
site inside the channel through
the transport protein.
b Bound glucose makes the protein
change shape. Part of the channel
closes behind the solute. Another
part opens in front of it.
Active (I must use energy) Transport
 Push material into or out of the cell
 Transport protein must be activated
 Energy is required to push and pull
Osmosis
 Diffusion of water molecules across a
selectively permeable membrane
• Direction of net flow is
determined by which
side has the most
water
• Side with the most
solute molecules has
the lowest water
concentration
water molecules
semipermeable membrane
between two compartments
protein molecules
Tonicity
Refers to relative solute concentration of
a fluid
Hypertonic - having more solutes
Isotonic - having same amount
Hypotonic - having fewer solutes
Tonicity and Osmosis
2%
sucrose
water
10% sucrose
2% sucrose
Endocytosis and Exocytosis
 Exocytosis: A cytoplasmic vesicle fuses with
the plasma membrane and contents are
released outside the cell
 Endocytosis: A small patch of plasma
membrane sinks inward and seals back on
itself, forming a vesicle inside the cytoplasm –
membrane receptors often mediate this
process
Endocytosis and Exocytosis
endocytosis
a
exocytosis
a Molecules get concentrated inside
coated pits of plasma membrane.
b Endocytic vesicles form from
the pits.
coated pit
b
c Enclosed molecules are sorted
and often released from receptors.
d
e
c
f
d Many sorted molecules are cycled
back to the plasma membrane.
e,f Many other sorted molecules are
delivered to lysosomes and
stay there or are degraded. Still
others are routed to spaces in the
nuclear envelope and inside ER
membranes, and others to Golgi
bodies.