How cells use energy

Ch. 5 – How Cells Use Energy
The mitochondria are
the engines of our cells


ATP and cellular work
Enzymes
Burn sugar for fuel
Produce ATP for cellular
work
Mitochondria
Origin of mitochondria
Cellular power plants


Generate most of the cell’s
ATP
Surrounded by two membranes
with different properties


Outer membrane


Thought to have evolved from
small symbiotic prokaryotes
Have many features in common
with prokaryotes


Inner membrane


ATP synthesis
Proteins of the electron
transport chain

Important role in evolution

Most cells receive energy in a form they
can’t use directly


Energy from food
This energy has to be converted into a
usable form of energy


ATP (adenosine triphosphate)
NAD (nicotinamide adenine dinucleotide)
The ability of these bacteria to
conduct cell respiration was an
evolutionary advantage

The Structure of ATP
ATP powers cellular work

Single circular chromosome
Genes are closely related to
prokaryotic genes
Reproduce in a similar manner

freely permeable to small
molecules

A complex organic molecule

Adenosine plus a “tail” of 3 phosphate groups
containing a high-energy bond
The energy in ATP is used to
drive cellular work
Cells use ATP to build
macromolecules
The ATP Cycle
To transport molecules
across the membrane

ATP stores energy obtained from food and
releases it as needed at a later time
To move – by cilia or flagella
How do cells store energy?

ATP is a very
reactive molecule
Cell chemistry–catalyzed reactions

Cells use enzymes to
speed up chemical
reactions


As fat
and some glycogen
4 characteristics of enzymes


Proteins
Act as catalysts



speed up chemical reactions
Decrease the activation
energy
Recycled

enzymes can function over
and over again

Lower the activation energy
This process is called
catalysis
We say that enzymes are
catalysts
How enzymes work


Each enzyme is very
selective – it recognizes
its substrate
The substrate binds to a
special region of the
enzyme, the active site
How enzymes work
Enzymes in action


Stonewashed jeans are
no longer made using
stones
Using the enzyme
cellulase gives better
results

Cells can control enzymes

Enzyme inhibitors


Molecules in the cell
inhibit (slow down or
stop) enzymatic
reactions
Many bind to the
active site, as
substrate imposters.
It breaks down the
polysaccharide
cellulose, the main
component of cotton
Recap: Enzymes



Workhorse proteins
Speed up reactions
Orchestrate the majority of chemical reactions
needed for life
The energy in food comes
from the sun
How do we get energy
from food?
Cellular respiration
We use the energy that plants
capture from the sun
Organisms are Producers or
Consumers

Producers



Consumers

Producers
Consumers
Energy flow
Plants and algae convert solar energy to
chemical energy and make sugars and
other organic molecules
Autotrophs or “self-feeders”

Obtain their food by eating plants or
animals that have eaten plants.
Heterotrophs or “other-feeders”
Overview of photosynthesis

Occurs in

Photosynthesis

(plants)

Leaves of plants
Algae cells
Some protists and bacteria
Cellular respiration
(plants & animals)
Autotrophs!
Plants:
solar-powered chemical factories


Is it possible to make
food from sunshine,
water and air?
Plants do it everyday


The leaf is the primary site of
photosynthesis
Capture solar energy and
use it to build
carbohydrates from CO2
and water
Produce food for
themselves and all other
organisms
Overview of Photosynthesis

Photosynthesis feeds
nearly all life on earth



Light energy, CO2 and
water
sugars
Releases oxygen
Without plants we
would have no food to
eat or oxygen to breath
Photosynthesis

How plants capture solar energy


How do plants capture
solar energy?
Plant cells contain
chloroplasts that
actually carry out
photosynthesis
Role of chloroplast & chlorophyll (pigment)
How solar energy is converted to chemical
energy and used to build carbohydrates

Light reactions

Calvin cycle


produce high-energy molecules (ATP, NADPH)
‘fixes’ CO 2 as carbohydrates
Inside the chloroplast



The Overall Equation for
Photosynthesis
Chloroplasts convert solar
energy into chemical
energy
Process = photosynthesis
The chloroplast contains

Stacks of membranes called
thylakoids
substrates
A Photosynthesis Road Map

Photosynthesis is
composed of two
processes:
 The light reactions
convert solar energy to
chemical energy.


How plants capture energy from
sunlight


ATP and NADPH
The Calvin cycle uses
this energy to make
sugar from carbon
dioxide and water.
products

Photosynthesis starts with
the photosystem
It is a network of pigments
in the membrane of the
thylakoid
The primary pigment is
chlorophyll

Pigments are molecules that
capture solar energy
A photosystem
Why are leaves green?

Chloroplasts absorb certain
wavelengths of light that drive
photosynthesis
Main pigment is chlorophyll

Accessory pigments




A cluster of chlorophyll molecules.
Acts as a light-gathering antenna that focuses
energy onto the reaction center.


absorbs mainly blue and red light,
and transmits green light
Carotenoids absorb other light
wavelengths
Give color to flowers, fruits and
vegetables
How Photosystems Harvest
Light Energy

Chlorophyll molecules
absorb photons.


How the light reactions
generate ATP and NADPH

The absorption of a
photon cause electrons
in the pigment gain
energy
Photons captured by
chlorophyll are
converted to a “current”
of electrons
The energized
electrons pass thru a
series of proteins in
membrane of
chloroplast


electron transport
chain
Energy is used to
make ATP and
NADPH
Tony’s movie
The Calvin cycle:
making sugar from CO2
CO2


The ATP and NADPH of
the light-dependent
reactions are used to
build sugars in the Calvin
cycle
Photosynthesis is a way
of making sugars from
sunlight, H2 O and CO2
A review of photosynthesis

1.
Photosynthesis uses solar
energy, water and carbon
dioxide to make sugars
Light Reactions

2.
Use solar energy to make
high-energy molecules
(ATP and NADPH)
Calvin cycle

Uses these high-energy
molecules to capture CO2
and make sugars
Plants: photosynthesis (Britannica) 3:05
http://www.youtube.com/watch?v=yBfx3OcXS6A&feature=fvw