Transcript Cell Communications & Intro to energetics

Cell-Cell Communication
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Signals sent to other cells
Three levels
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Direct contact
Local
Paracrine
 Synaptic
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Long distance
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Endocrine
Fig. 11-4
Plasma membranes
Gap junctions
between animal cells
(a) Cell junctions
(b) Cell-cell recognition
Plasmodesmata
between plant cells
Fig. 11-5
Long-distance signaling
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid
(a) Paracrine signaling
Endocrine cell
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Target cell
is stimulated
Blood
vessel
Hormone travels
in bloodstream
to target cells
Target
cell
(b) Synaptic signaling
(c) Hormonal signaling
The Three Stages of Cell
Signaling: A Preview
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Earl W. Sutherland discovered how the hormone
epinephrine acts on cells
Sutherland suggested that cells receiving signals
went through three processes:
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Reception
Transduction
Response
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 11.2: Reception: A signal molecule binds
to a receptor protein, causing it to change shape
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The binding between a signal molecule (ligand) and
receptor is highly specific
A shape change in a receptor is often the initial
transduction of the signal
Most signal receptors are plasma membrane
proteins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 11.3: Transduction: Cascades of
molecular interactions relay signals from
receptors to target molecules in the cell
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Signal transduction usually involves multiple steps
Multistep pathways can amplify a signal: A few
molecules can produce a large cellular response
Multistep pathways provide more opportunities for
coordination and regulation of the cellular response
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Nuclear and Cytoplasmic Responses
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Ultimately, a signal transduction pathway leads to
regulation of one or more cellular activities
The response may occur in the cytoplasm or may involve
action in the nucleus
Many signaling pathways regulate the synthesis of enzymes
or other proteins, usually by turning genes on or off in the
nucleus
The final activated molecule may function as a transcription
factor
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 11-7b
Plasma
membrane
G protein-coupled
receptor
Activated
receptor
Signaling molecule
GDP
CYTOPLASM
GDP
Enzyme
G protein
(inactive)
GTP
2
1
Activated
enzyme
GTP
GDP
Pi
Cellular response
3
4
Inactive
enzyme
Fig. 11-8-5
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
mRNA
NUCLEUS
CYTOPLASM
New protein
Biological Energetics
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How cells obtain and energy needed for
survival
Two types of organisms
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Autotrophs
Heterotrophs
Net loss of energy as it is transferred through
organisms
Autotrophs
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Are able to synthesize macromolecules by using
small molecules from environment
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Vast majority are photosynthetic
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Do not consume other organisms to obtain
molecules
Use energy from sunlight to power anabolic
reactions
All biological energy originates with autotrophs
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Life is solar powered
Heterotrophs
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Consume other organisms and utilize energy
obtained from catabolic degradation of
macromolecules
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Rely on the presence of autotrophs as original
energy source
Loss of energy in transfer means that the balance
between heterotrophs and autotrophs is crucial
Can consume autotrophs or other heterotrophs
Saprophytes-consume dead organisms
“decomposers”
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Bacteria, fungi, scavengers
Photosynthesis and
respiration
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Photosynthesis is the use of solar energy to
power anabolic reactions-autotrophs
Respiration is the process in which
macromolecules are degraded to obtain cellular
power-heterotrophs
They are complementary processes
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One relies on the products of the other and they
are linked biologically
Photosynthesis
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Takes place in the chloroplasts of plants and in the
cytoplasm of photosynthetic bacteria
Requires CO2 and a source of Hydrogen
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Usually water but can be H2S
Ultimately results in Glucose and Oxygen production
(water also)
CO2 +6H2O +Light energy--->C6H12O6 + 6O2
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Oxygen production by plants is essential for other life to
exist
Photosynthesis 2
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Actually two stages in Photosynthesis
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Light cycle-Sunlight is used to synthesize ATP
and other energy storing molecules
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Made up of Photosystems I and II
Calvin Cycle or Dark Cycle-Energy from ATP and
other molecules is used to synthesize sugars
Chloroplasts
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Light reactions happen in Thylakoids of Granum
Calvin cycle happens in Stroma
Chlorphyll is the molecule that catches solar energy in
chloroplasts
 Other chromoplasts exist that contain different molecules for
catching solar energy
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Why are chlorplasts green?
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Absorbs Red and Blue
light
Green light is transmitted
or reflected making plants
appear green